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GEOLOGICAL OBSERVATIONS 



ON THE VOLCANIC ISLANDS AND PARTS OF SOUTH AMERICA 
VISITED DURING THE VOYAGE OF H M S 'BEAGLE' 



BY 

CHARLES DARWIN, M. A., F. R. S., ETC. 

AUTHOR OF 'THE STRUCTURE AND DISTRIBUTION 01- CORAL REEFS/ 
* I HE ORIGIN OF SPECIES/ tJC, 




THIRD EDITION 

WITH MAPS AND ILLUSTRATIONS 



NEW YORK 

D. AP PL ETON AND COMPANY 
1896 



Authorized Edition. 



PBEFAOE 

TO 

THE SECOND EDITION. 



THE FIRST EDITION of my < Geological Observations on 
the Volcanic Islands,' visited daring the voyage of 
H M.S. c Beagle/ under the command of Capt. Fitz- 
Roy, B.N., was published, with the approval of the 
Lords Commissioners of Her Majesty's Treasury, in the 
year 1844 ; and my 4 Observations on South America/ 
in 1846. As both these works are now out of print, and 
as I believe that they still contain matter of scientific 
value, it has appeared to me advisable that they should 
be republished. They relate to parts of the world 
which have been so rarely visited by men of science, 
that I am not aware tfeat much could be corrected or 
added from observations subsequently made. 

Owing to the great progress which Geology has 
made within recent times, my views on some few points 
may be somewhat antiquated ; but I have thought it 
best to leave them as they originally appeared. In 
order to complete my account of the Geological Obscr- 



vi Preface to the Second Edition, 

vations made during the voyage of the 'Beagle/ I will 
here give references to four papers which were separately 
published. First, c On the Connection of certain Vol- 
canic Phenomena in South America,' read in 1888, and 
published in Volume V, of the fc Transactions of the 
Geological Society.' Secondly, ' On the Distribution 
of the Erratic Boulders and on the contemporaneous 
Stratified Deposits of South America,' read in 1841, and 
published in Volume VI. of the ' Transactions ' of the 
same Society. Thirdly, c An Account of the Fine Dust 
which often falls on Vessels in the Atlantic Ocean : ? 
1 Proceedings of the Geological Society,' June 4, 1815. 
Fourthly, on March 25, 1816, in the same Journal, 
' On the Geology of the Falkland Islands/ 



CONTENTS. 



PART L 



CHAPTER I. 

ST. JAGO, IN THE CAPE DE VEKDE ARCHIPELAGO. 

Kocks of the lowest series A calcareous sedimentary deposit, witls 
recent shells, altered by the contact of superincumbent lava, its 
honzontality and extent Subsequent volcanic eruptions, asso- 
ciated with calcareous matter in an earthy and fibrous form, and 
often enclosed within the separate cells of the scoritB Ancient 
and obliterated orifices of eruption of small size Difficulty of 
tracing over a bare plain recent streams of lava Inland hills of 
more ancient volcanic rock Decomposed oil vine in large masses 
Feldspathic rocks beneath the upper crystalline basaltic strata 
Uniform structure and form of the more ancient volcanic 
hills Form of the valleys near the coast Conglomerate now 
forming on the sea beach ...... PAGE 3 

CHAPTER II. 

FEKNANDO NOKONHA ; TEECEIBA ; TAHITI, ETC. 

FERNANDO NOBONHA Precipitous hill of phonolite. TERCET R A 
Trachytic rocks ; their singular decomposition by steam of hieh 
temperature. TAHITI Passage from wacke into trap ; singular 
volcanic rock with the vesicles half filled with mesotype MACT- 
BITITJS Proofs of its lecent elevation Structure of its more 
ancient mountains ; similarity vsith St. Jago. ST. PAUL'S 
ItoCKS Not of volcanic origin their singular mmeralogical 
composition . ... 27 



viii Contents. 



CHAPTER IIL 

ASCENSION. 

Basaltic lavas Numerous craters truncated on the same side 
Singular structure of volcanic bombs Aeriform explosions 
Ejected granitic fragments Trachytic rocks Singular veins 
Jasper, its manner of formation Concretions in puiniceous tuff 
Calcareous deposits and frondescent incrustations on the coa^t 
Kemarkable laminated beds, alternating with, and passing 
into obsidian Origin of obsidian Lamination of volcanic 
rocks . PAGE 40 

CHAPTER IV. 

ST. HELENA. 

Lavas of the feldspathic, basaltic, and submarine series Section of 
Flagstaff Hill and of the Barn -Bikes Turk's Cap and Pros- 
perous Bays Basaltic ring -Central cratenform ridge, with an 
internal ledge and a parapetCones of phonolite Supeificial 
beds of calcareous sandstone Extinct land-shells Beds of 
detritus Elevation of the land Denudation Ciateis of 
elevation 83 

CHAPTER V. 

GALAPAGOS ARCHIPELAGO. 

Chatham Island Craters composed of a peculiar kind of tuff 
Small basaltic craters, with hollows at their bases Albemarle 
Island ; fluid lavas, their composition Craters of tuff j inclina- 
tion of their exterior diverging strata, and structure of their 
interior converging strata James Island, segment of a small 
basaltic crater j fluidity and composition of its lava streams, and 
of its ejected fragments Concluding remarks on the craters 
of tuff, and on the breached condition of their southern sides 
Mmeralogical composition of the rocks of the archipelago 
Elevation of the land Direction of the fissures of erup- 
tion ,.*..*, 3 10 



Contents* Ix 



CHAPTER VI. 

TEACHYTE AND BASALT. DISTRIBUTION OF VOLCANIC ISLES 

The sinking of crystals in fluid lava Specific gravity of the consti- 
tuent paits of trachyte and of basalt, and their consequent 
- separation Obsidian Apparent non-separation of the elements 
of plntonic rocks Origin of trap-dikes in the plutonic series 
Distribution of volcanic islands ; their prevalence in the great 
oceans They are generally arranged in lines The cential 
volcanos of Yon Buch doubtful Volcanic islands bordering con- 
tinents Antiquity of volcanic islands, and their elevation in 
mass Eruptions on parallel lines of fissure within the same 
geological period PAGE 132 

CHAPTER VII. 

AUSTRALIA; NEW ZEALAND; CAPE OF GOOD HOPE. 

New South Wales Sandstone formation Embedded pseudo-frag- 
ments of shale Stratification Cur rent- cleavage Great valleys 
Van Diem en's Laod Pal 8202010 formation Newer formation 
with volcanic rocks Ti aver tin with leaves of extinct plants 
Elevation of the land New Zealand King George's Sound 
Superficial ferruginous beds Superficial calcareous deposits, 
with casts of branches; its origin fiom drifted particles of shells 
and corals their extent Cape of Good Hope Junction of the 
gianite and clay-slate Sandstone formation , . 146 

APPENDIX TO PAET I. 

DESCRIPTION OP POSSIL SHELLS, BY G. B. SOWEUBY, ESQ , F.L.S, 

From a Tertiary deposit at St. Jago, in fche Cape de Vcrcle 

Archipelago 171 

Extinct land-shells from St. Helena 1 73 

Shells from the Palaeozoic formation of Van Diemen's Land . 170 
Description of Fossil Corals from the Palaeozoic formation of 

Van Diemen's Land, by W. Lonsdale, Esq , F.G.S. . .178 



x Contents. 



PART IL 



CHAPTER VIIL 

ON THE ELEVATION OF THE EASTERN COAST OF SOUTH AMERICA* 

Upiaised Shells of La Plata Bahia Blanca, Sand-dunes and 
Pumice-pebbles Step-formed Plains of Patagonia, with upraised 
shells Terrace-bounded Valley of Santa Cruz, formerly a Sea- 
strait Upraised shells of Tierra del Fuego Length and breadth 
of the elevated area Equability of the movements, as shown by 
the similai heights of the plains Slowness of the elevatory pro- 
cess Mode of formation of the step-foimed plains Summaiy 
Great Shingle Formation of Patagonia; its extent, origin, and 
distribution Formation of sea-cliffs . . . PAO-E 189 

CHAPTER IX. 

ON THE ELEVATION OJF THE WESTERN COAST OF SOUTH AMERICA. 

Chonos Archipelago Chiloe, recent and gradual elevation of, tradi- 
tions of the inhabitants on this subject Concepcion, earthquake 
and elevation of. YALPAKAISO, great elevation of, upraised 
shells, earth of marine origin, gradual rise of the land within the 
historical period COQUIMBO, elevation of, in recent times; 
tei races of marine ongm, their inclination, their escarpments 
not horizontal Guasco, gravel terraces of Copiapo, PERU 
Upraised shells of Cobija, Iquique, and Arica Lima, shell-beds 
and sea-beach on San Lorenzo Human remains, fossil earthen- 
ware, earthquake debacle, recent subsidence On the decay of 
upraised sheila General summary . , . SJ&J 

CHAPTER X. 

ON THE PLAINS AND VALLEYS OP CHILE : SA.LIFEBOUS SUPER- 
FICIAL DEPOSITS. 

Basin-like plains of Chile ; their drainage, their marine origin 
Marks of sea-action on the eastern flanks of the Cordillera 
Sloping-terrace-like fringes of stratified shingle within the "valleys 
of the Cordillera ; their marine origin Boulders in the valley of 
the Cachapual Horizontal elevation of the Cordillera Forma- 



Contents. xl 



tion of valleys Boulders moved by earthquake- waves Saline 
superficial deposits Bed of nitrate of soda at Iquique Saline 
incrustations Salt-lakes of La Plata and Patagonia ; purity of 
the salt ; its origin PAG-E 283 

CHAPTER XT. 

ON THE FORMATIONS OF THE PAMPAS, 

Mineralogical constitution Microscopical structure Buenos Ayres, 
shells embedded in tosca-rock Buenos Ayres to the Colorado 
S. Ventana Bahia Blanca; M. Hermoso, bones and infusoria of; 
P. Alta, shells, bones, and infusoria of ; co-existence of the recent 
shells and extinct mammifeis Buenos Ayres to St. Fe 
Skeletons of Mastodon Infusoria Inferior marine tertiary 
strata, their age Horse's tooth. BANDA ORIENTAL Superficial 
Pampean formation Inferior tertiary strata, variation of, con- 
nected with volcanic action; Macruchenia Patachonica at S. 
Julian in Patagonia, age of, subsequent to living mollusca and to 
the erratic block period. SUMMABY Area ot Panapean forma- 
tion Theoiies of origin Source of sediment Estuary origin 
Contemporaneous with existing mollusca [Relations to under- 
lying tertiaiy strata Ancient deposit of estuary origin Eleva- 
tion and successive deposition of the Pampean formation 
Number and state of the remains of mammifers ; their habitation, 
food, extinction, and range Conclusion -Supplement on the 
thickness of the Pampean Formation Localities in Pampas at 
which mammiferous" jemams have been found . . 313 

CHAPTER XII. 

ON THE OLDER TERTIARY FORMATIONS Otf PATAGONIA AND CHILE 

Rio Negro - S Josef Port Desire, white pumiceous mudstone with 
intusoria Port S. Julian Santa Cruz, basaltic lava of P. 
Gallegos Eastern, Tiena del Fuego ; leaves of extinct beech 
tiees Summary on the Patagoman tertiary formations Tertiary 
lormations of the Western Coast Chonos and Chiloe groups, 
volcanic rocks of Concepcion Navidad Coquimbo Summary 
Age of the tertiary formations Lines of elevation Sihcified 
wood Comparative ranges of the extinct and living Mollusca on 
the West Coast of S. America Climate of the tertiary period 
On the caubes of the absence of recent conchiferous deposits on 
the coasts of S. America On the contemporaneous deposition 
and preservation of sedimentary formations . . 370 



xii Contents. 



CHAPTER XIII. 

PLUTONIC AND METAMOEPHIO EOCKS : CLEAVAGE AND FOLIATION". 

Brazil, Bahia, gneiss with disjointed metamorphosed dikes Strike 
of foliation Eio de Janeiro, gneiss-granite, embedded fragment 
in, decomposition of La Plata, metamorphic and old volcanic 
rocks of S. Ventana Claystone porphyiy formation, of Pata- 
gonia; singular metamorphic rocks ; pseudo-dikes Falkland 
Islands, palseozoic fossils of Tierra del Fuego, clay -slate foi mo- 
tion, cretaceous fossils of ; cleavage and foliation ; form of land 
Chonos Archipelago, mica schists, foliation disturbed by granitic 
axis ; dikes Chiloe Concepcion, dikes, successive formation of 
Central and Northern Chile Concluding remarks on cleavage 
and foliation Their close analogy and similar origin Strati- 
fication of metamorphic schists Foliation of intrusive rocks 
Relation of cleavage and foliation to the lines of tension timing 
metamorphosis ....... PAGE 422 

CHAPTER XIV. 

CENTRAL CHILE : STEUCTUEE OF THE COEDILLB3EA. 

Central Chile Basal formations of the Cordillera Origin of the 
porphyritic claystone conglomerate Andesite Volcanic rocks 
Section ot the Cordillera by the Peuqnenes or Portillo Pass- 
Great gypseous formation Peuquenes line; thickness of strata, 
fossils of Portillo line conglomeiate, oithitic granite, mica* 
schist, volcanic rocks of Concluding remarks on the denudation 
and elevation of the Poitillo line Section by the Curnbre, or 
Uspallata Pass Porphyiies- Gypseous strata Section near the 
Puente del Inca; fossils of Gieat subsidence Jntnisive por- 
phyriesPlain of Uspallata Section of the Uspallata chain 
Structure and nature of the strata -Silicified vertical trees- 
Great subsidence Granitic rocks of axis Concluding remarks 
on the Uspallata range ; origin subsequent to that of the main 
Cordillera; two periods of subsidence; comparison with the 
Portillo chain 470 

CHAPTER XV. 

NORTHERN CHILE. CONCLUSION. 

Section from Illapel to Combarbala; Gypseous formation with 
Silicified wood Panuncillo Coquimbo; mines of Arqueros; 
section up Talley ; fossils Guasco, fossils of Copiapo section 



Contents - xiil 



up valley ; Las Amolanas, silicified wood conglomerates, nature 
of former land, fossils, thickness of strata, great subsidence 
Valley of Despoblado, tufaceous fossils, deposit, complicated 
dislocations of Relations between ancient orifices of eruption 
and subsequent axes of injection Iquique, Peru, fossils of, salt- 
deposits Metalliferous veins Summary on the Porpliyritic 
conglomerate and Gypseous formations Great subsidence with 
partial elevations duiing the Ore taceo -oolitic period On the 
elevation and stiucture of the Cordillera Eecapitulation on the 
tertiary series Relations between movements of subsidence and 
volcanic action Pampean formation Recent elevatory move- 
ments Long-continued volcanic action in the Cordillera, Con- 
clusion . . PAGE 535 



APPENDIX TO PART IL 

Descriptions of Tertiary Fossil Shells from South America, 

by G. B. Sowerby, Esq., F.L S , &c 605 

Descriptions of Secondary Fossil Shells from South America, 

by Professor E. Forbes, F R S , &c, . . . . . 624 

INDEX 629 



PAET I. 

VOLCANIC ISLANDS 

&C, 



CHAPTER L 

ST. JAGO, IN THE CAPE DE VERDE AKCHIPELAGO. 

Moc?ts of the lowest series. A calcareous sedimentary deposit, with 
recent shells, altered "by the contact of supermen mbent lava, its Jiori- 
zontality and extent Subsequent volcanic eruptions, associated with 
calcareous matter in an earthy and fibrous form, and often enclosed 
within the separate cells of the scoria? Ancient and obliterated 
orifices of erwjptwn of small size Difficulty of tracing over a bare 
plain recent streams of lava Inland Mils of more ancient volcanic 
rocJi, decomposed ohmne in large masses PeldspatJwc rocks beneath 
tJie upper crystalline basaltic strata Umjorm structure and form of 
the more ancient volcanic hills Form of the valleys near the coast 
Conglomerate nom forming on- the sea beach. 

THE island of St. Jago extends in a NNW. and SSB. 
direction, thirty miles in length by about twelve In 
breadth. My observations, made during two visits, were 
confined to the southern portion within the distance of 
a few leagues from Porto Praya. The country, viewed 
from the sea, presents a varied outline : smooth conical 
hills of a reddish colour (like Red Hill In the accompany- 
ing woodcut), 1 and others less regular, flat-topped, and 
of a blackish colour (like A 5 B, 0,) rise from successive, 
step-formed plains of lava. At a distance, a chain, of 
mountains, many thousand feet in height, traverses the 
Interior of the island. There Is no active volcano in 
St. Jago, and only one in the group, namely at Fogo. 

1 The outline of the coast, the position of the villages, streamlets, 
and of most of the hills in this woodcut, are copied from the chart 
made on board H.M.S. * Leven. 1 The square-topped hills(A,B 0,&c,) 
are put in merely by eye, to illustrate my desciiption. 

2 



Si. 



the sea, measured from the upper line of junction with 
the superincumbent basaltic lava, is about sixty feet ; 
and its thickness, although varying much from the 
Inequalities of the underlying formation, may be esti- 
mated at about twenty feet. It consists of quite white 
calcareous matter, partly composed of organic debris, 
and partly of a substance which may be aptly compared 
In appearance with mortar. Fragments of rock and 
pebbles are scattered throughout this bed, often forming, 
specially in the lower part, a conglomerate. Many 
of the fragments of rock are whitewashed with a thin 
coating of calcareous matter. At Quail Island, the 
calcareous deposit is replaced In its lowest part by a 
soft, brown, earthy tuff, full of Turritellse ; this is 
covered by a bed of pebbles, passing into sandstone, and 
mixed with fragments of echini, claws of crabs, and 
shells ; the oyster shells still adhering to the rock on 
which they grew. Numerous white balls appearing like 
pisolitic concretions, from the size of a walnut to that of 
an apple, are embedded In this deposit ; they usually 
have a small pebble in their centres. Although so like 
concretions, a close examination convinced me that they 
were Nulliporee, retaining their proper forms, but with 
their surfaces slightly abraded : these bodies (plants as 
they are now generally considered to be) exhibit under a 
microscope of ordinary power, no traces of organisation 
in their internal structure. Mr. George "R. Sowerby 
has been so good as to examine the shells which I col- 
lected : there are fourteen species in a sufficiently perfect 
condition for their characters to be made out with some 
degree of certainty, and four which can be referred only 
to their genera. Of 'the fourteen shells, of which a list 
is given in the Appendix, eleven are recent species; one, 
though undescribed, is perhaps identical with a species 
which I found living in the harbour of Porto Praya; 



CHAP, i. Calcareous Deposit altered by Heat. 7 

the two remaining species are unknown, and have been 
described by Mr. Sowerby. Until the shells of this 
Archipelago and of the neighbouring coasts are better 
known, it would be rash to assert that even these two 
latter shells are extinct. The number of species which 
certainly belong to existing kinds, although few in 
number, are sufficient to show that the deposit belongs 
to a late tertiary period. From its mineralogical char- 
acter, from the number and size of the embedded 
fragments, and from the abundance of Patellae, and 
other littoral shells, it is evident that the whole was 
accumulated in a shallow sea, near an ancient coast-line, 
Effects produced ly the flowing of the superincum- 
"bent basaltic lava over the calcareous deposit. These 
effects are very curious. The calcareous matter is altered 
to the depth of about a foot beneath the line of junction 
and a most perfect gradation can be'traced, from loosely 
aggregated, small, particles of shells, corallines, and 
Nulliporae, into a rock, in which not a trace of mechani- 
cal origin can be discovered, even with a microscope. 
Where the metamorphic change has been greatest, two 
varieties occur. The first is a hard, compact, white, 
fine grained rock, striped with a few parallel lines of 
black volcanic particles, and resembling a sandstone, 
but which, upon close examination, is seen to be crystal- 
lised throughout, with the cleavages so perfect that they 
can be readily measured by the reflecting goniometer. 
In specimens, where the change has been less complete, 
when moistened and examined under a strong lens, the 
most interesting gradation can be traced, some of the 
rounded particles retaining their proper forms, and others 
insensibly melting into the granule-crystalline paste. 
The weathered surface of this stone, as is so frequently 
the case with ordinary limestones, assumes a brick-red 
jcolour. 



8 ^7^ ***** 

The second metamorphosed variety is likewise a hard 
rock, but without any crystalline structure. It consists 
of a white, opaque, compact, calcareous stone, thickly 
mottled with rounded, though regular, spots of a soft, 
earthy, ochraceous substance. This earthy matter is of 
ft pale yellowish-brown colour, and appears to be a mix- 
ture of carbonate of lime with iron 5 it effervesces with 
acids, Is infusible, but blackens under the blowpipe, and 
becomes magnetic. The rounded form of the minute 
patches of earthy substance, and the steps in the progress 
of their perfect formation, which can be followed in a 
suit of specimens, clearly show that they are due either 
to some power of aggregation in the earthy particles 
amongst themselves, or more probably to a strong at- 
traction between the atoms of the carbonate of lime, 
and consequently to the segregation of the earthy ex- 
traneous matter. I was much interested by this fact, 
because I have often seen quartz rocks (for instance, in 
the Falkland Islands, and in the lower Silurian strata of 
the Stiper-stones in Shropshire), mottled in a precisely 
analogous manner, with little spots of a white, earthy 
substance (earthy feldspar ?) j and these rocks, there 
was good reason to suppose, had undergone the action of 
heat, a view which thus receives confirmation. This 
spotted structure may possibly afford some indication in 
distinguishing those formations of quartz, which owe 
their present structure to igneous action, from those pro- 
duced by the agency of water alone : a source of doubt, 
which I should think from my own experience, that 
most geologists, when examining arenaceo-quartzose dis- 
tricts, must have experienced. 

The lowest and most scoriaceous part of the lava, in 
rolling over the sedimentary deposit at the bottom of 
the sea, has caught up large quantities of calcareous 
matter, which now forms a snow-white, highly crystalline. 



i. Calcareous Deposit altered by Heat. 9 

basis to a "breccia, including small pieces of black, glossy 
scorise. A little above this, where the lime is less abun- 
dant, and the lava more compact, numerous little balls, 
composed of spicula of calcareous spar, radiating from 
common centres, occupy the interstices. In one part of 
Quail Island, the lime has thus been crystallised by the 
heat of the superincumbent lava, where it is only 
thirteen feet in thickness ; nor had the lava been origi- 
nally thicker, and since reduced by degradation, as could 
be told from the degree of cellularity of its surface. I 
have already observed that the sea must have been 
shallow in which the calcareous deposit was accumulated. 
In this case, therefore, the carbonic acid gas has been 
retained under a pressure, insignificant compared with 
that (a column of water, 1708 feet in height) originally 
supposed by Sir James Hall to be requisite for this 
end: but since his experiments, it has been discovered 
that pressure has less to do with the retention of carbonic 
acid gas, than the nature of the circumjacent atmo- 
sphere ; and hence, as is stated to be the case by Mr. 
Faraday, 1 masses of limestone are sometimes fused and 
crystallised even in common lime-kilns. Carbonate of 
lime can be heated to almost any degree, according to 
Faraday, in an atmosphere of carbonic acid gas, without 
being decomposed; and Gay-Lussac found that frag- 
ments of limestone, placed in a tube and heated to a 
degree, not sufficient by itself to cause their decomposi- 
tion, yet immediately evolved their carbonic acid, when 
a stream of common air or steam was passed over them : 
Gay-Lussac attributes this to the mechanical displace- 
ment of the nascent carbonic acid gas. The calcareous 

1 I am much indebted to Mr. B. W. Bray ley in having given me 
the following references to papeis on this subject : Faraday, in the 

Edinburgh New Philosophical Journal,' vol. xv p. 398 ; G-ay-Lussac, 
in * Annales de Chem et Phys ,' torn Ixiii. p. 219, translated in the 

* London and Edinburgh Philosophical Magazine,' vol. x. p. 496. > 



io St. J ago, 



matter beneath tlie lava, and especially that forming th 
crystalline spicula between the interstices of the scoriae, 
although heated in an atmosphere probably composed 
chiefly of steam, could not have been subjected to the 
effects of a passing stream ; and hence it is, perhaps, 
that they have retained their carbonic acid, under a 
small amount of pressure. 

The fragments of scorise, embedded in the crystalline 
calcareous basis, are of a jet black colour, with a glossy 
fracture like pitchstone. Their surfaces, however, are 
coated with a layer of a reddish-orange, translucent 
substance, which can easily be scratched with a knife ; 
hence they appear as if overlaid by a thin layer of rosin* 
Some of the smaller fragments are partially changed 
throughout into this substance: a change which appears 
quite different from ordinary decomposition. At the 
Galapagos Archipelago (as will be described in a future 
chapter), great beds are formed of volcanic ashes and 
particles of scoriae, which have undergone a closely 
similar change. 

The extent and JiorizontaJily of the calcareous stratum* 
The upper line of surface of the calcareous stratum^ 
which is so conspicuous from being quite white and so 
nearly horizontal, ranges for miles along the coast, at 
the height of about sixty feet above the sea. The sheet 
of basalt, by which it is capped, is on an average eighty 
feet in thickness. "Westward of Porto Praya beyond 
Red Hill, the white stratum with the superincumbent 
basalt is covered up by more recent streams. North- 
ward of Signal Post Hill, i could follow it with my 
eye, trending away for several miles along the sea cliffs, 
The distance thus observed is about seven miles ; but 
I cannot doubt from its regularity that it extends much 
farther. In some ravines at right angles to the coast, 
it is seen gently dipping towards the sea, probably with 



CHAP. i. Calcareous Horizontal Deposit, 1 1 

the same Inclination as when deposited round the 
ancient shores of the island. I found only one inland 
section, namely, at the base of the hill marked A, where, 
at the height of some hundred feet, this bed was ex- 
posed ; it here rested on the usual compact angitic rock 
associated with wacke, and was covered by the wide- 
spread sheet of modern basaltic lava. Some exceptions 
occur to the horizontality of the white stratum : at 
Quail Island, Its upper surface Is only forty feet above 
the level of the sea ; here also the capping of lava is 
only between twelve and fifteen feet in thickness ; on 
the other hand, at the NE. side of Porto Praya 
harbour, the calcareous stratum, as well as the rock on 
which it rests, attain a height above the average level s 
the inequality of level in these two cases is not, as I 
believe, owing to unequal elevation, but to original 
irregularities at the bottom of the sea. Of this fact, at 
Quail Island, there was clear evidence in the calcareous 
deposit being in one part of much greater than the 
average thickness, and in another part being entirely 
absent; in this latter case, the modern basaltic lavas 
rested directly on those of more ancient origin. 

Under Signal Post Hill, the white stratum dips 
into the sea in a remarkable manner. This hill is 
conical, 450 feet in height, and retains some traces of 
having had a crateriform structure ; it is composed 
chiefly of matter erupted posteriorly to the elevation of 
the great basaltic plain, but partly of lava of apparently 
submarine origin and of considerable antiquity. The 
surrounding plain, as well as the eastern flank of this 
hill, have been worn into steep precipices, overhanging 
the sea. In these precipices, the white calcareous 
stratum may be seen, at the height of about 70 feet 
above the beach, running for some miles both north- 
ward and southward of the Mil, in a line appearing to 



12 St. J ago, 



be perfectly Horizontal ; but for a space of a quarter of 

a mile directly under the hill, it dips into the sea and 
disappears. On the south side the dip is gradual, on 
the north side it is more abrupt, as Is shown in the 
woodcut. As neither the calcareous stratum, nor the 
No. 2. 




SIGNAL POST HILL. 

A Ancient volcanic rocks. B Calcareous stratum. 

Upper basaltic lava. 

superincumbent basaltic lava (as far as the latter can 
be distinguished from the more modern ejections), 
appear to thicken as they dip, I infer that these strata 
were not originally accumulated in a trough, the 
centre of which afterwards became a point of eruption ; 
but that they have subsequently been disturbed and 
bent. We may suppose either that Signal Post Hill 
subsided after its elevation with the surrounding country, 
or that it never was uplifted to the same height with it. 
This latter seems to me the most probable alternative, 
for during the slow and equable elevation of this portion 
of the island, the subterranean motive power, from ex- 
pending part of its force in repeatedly erupting volcanic 
matter from beneath this point, wouldj it is likely, have 
less force to uplift it. Something of the same kind 
seems to have occurred near Eed Hill, for when tracing 
upwards the naked streams of lava from near Porto 
Praya towards the interior of the island, I was strongly 
induced to suspect, that since the lava had flowed, the 
slope of the land had been slightly modified, either by a 
small subsidence near Eed Hill, or by that portion of 
the plain having been uplifted to a less height during 
the elevation of the whole area. 



. i. Calcareous Deposit. 13 

The basaltic Itvua, superincumbent on the calcareous 
deposit, This lava is of a pale gray colour, fusing 
into a black enamel; its fracture Is rather earthy 
and concretionary ; it contains olivine in small grains, 
The central parts of the mass are compact, or at most 
crenulated with a few minute cavities, and are often 
columnar. At Quail Island this structure was assumed 
in a striking manner; the lava in one part being 
divided into horizontal laminaa, which became in another 
part split by vertical fissures into five-sided plates ; and 
these again, being piled on each other, insensibly 
became soldered together, forming fine symmetrical 
columns. The lower surface of the lava is vesicular, 
but sometimes only to the thickness of a few inches ; 
the upper surface, which is likewise vesicular, is divided 
into balls, frequently as much as three feet in diameter, 
made up of concentric layers. The mass is composed of 
more than one stream ; its total thickness being, on an 
average, about eighty feet : the lower portion has cer- 
tainly flowed beneath the sea, and probably likewise the 
upper portion. The chief part of this lava has flowed 
from the central districts, between the hills marked 
A, B, C, &c. in the woodcut-map. The surface of the 
country, near the coast, is level and barren ; towards 
the interior, the land rises by successive terraces, of 
which four, when viewed from a distance, could be 
distinctly counted. 

Volcanic eruptions subsequent to the elevation of 
the coastland; the ejected matter associated with earthy 
lime. These recent lavas nave proceeded from those 
scattered, conical, reddish-coloured kills, which rise 
abruptly from the plain-country near the coast. I 
ascended some of them, but will describe only one, 
namely, Red Hill, which, may serve as a type of its class, 
and is remarkable in some especial respects. Its height 



14 St. J ago. AET x, 

is about 600 feet ; It is composed of bright red, highly 
scoriaceous rock of a basaltic nature ; on one side of its 
summit there is a hollow, probably the last remnant of 
a crater. Several of the other hills of this class, judging 
from their external forms, are surmounted by much 
more perfect craters. When sailing along the coast, it 
was evident that a considerable body of lava had flowed 
from Red Hill, over a line of cliff about 120 feet in 
height, into the sea : this line of cliff is continuous 
with that forming the coast, and bounding the plain on 
both sides of this hill ; these streams, therefore, were 
erupted, after the formation of the coast-cliffs, from 
Red Hill, when it must have stood, as it now does, 
above the level of the sea. This conclusion accords 
with the highly scoriaceous condition of all the rock on 
it, appearing to be of subaerial formation ; and this is 
important, as there are some beds of calcareous matter 
near its summit, which might, at a hasty glance, have 
been mistaken for a submarine deposit. These beds 
consist of white, earthy, carbonate of lime, extremely 
friable so as to be crushed with the least pressure ; the 
most compact specimens not resisting the strength of 
the fingers. Some of the masses are as white as quick- 
lime, and appear absolutely pure ; but on examining 
them with a lens, minute particles of scorise can always 
be seen, and I could find none which, when dissolved in 
acids, did not leave a residue of this nature. It is, 
moreover, difficult to find a particle of the lime which 
does not change colour under the blowpipe, most of 
them even becoming glazed. The scoriaceous frag- 
ments and the calcareous matter are associated in the 
most irregular manner, sometimes in obscure beds, but 
more generally as a confused breccia, the lime in some 
parts and the scoriae in others being most abundant. 
Sir H. D la Beche has been so kind as to have some of 



CHAP, I 



Calcareous Matter entangled in L ava* 1 5 



the purest specimens analysed, with a view to discover, 
considering their volcanic originj whether they con- 
tained much magnesia ; but only a small portion was 
found, such as is present in most limestones. 

Fragments of the scoriae embedded in the calcareous 
mass, when broken, exhibit many of their cells lined 
and partly filled with a white, delicate, excessively 
fragile, moss-like, or rather conferva-like, reticulation 
of carbonate of lime. These fibres, examined under a 
lens of one-tenth of an inch focal distance, appear 
cylindrical ; they are rather above the -nfW of an inch 
In diameter ; they are either simply branched, or more 
commonly united into an irregular mass of net-work, 
with the meshes of very unequal sizes and of unequal 
numbers of sides. Some of the fibres are thickly 
covered with extremely minute spicula, occasionally 
aggregated into little tufts ; and hence they have a 
hairy appearance. These spicula are of the same dia- 
meter throughout their length ; they are easily detached, 
so that the object-glass of the microscope soon becomes 
scattered over with "them. Within the cells of many 
fragments of the scoriae, the lime exhibits this fibrous 
structure, but generally in a less perfect degree. These 
cells do not appear to be connected with one another, 
There can be no doubt, as will presently be shown, that 
the lime was erupted, mingled with the lava in its fluid 
state ; and therefore I have thought it worth while to 
describe minutely this curious fibrous structure, of which 
I know nothing analogous. From the earthy condition 
of the fibres, this structure does not appear to be related 
to crystallisation. 

Other fragments of the scoriaceous rock from this 
hill, when broken, are often seen marked with short and 
irregular white streaks, which are owing to a row of 
separate cells being partly, or quite, filled with white 



PABT I. 



16 St. J ago. 

calcareous powder. This structure immediately re- 
minded me of the appearance in badly kneaded dough, 
of balls and drawn-out streaks of flour, which have re- 
mained unmixed with the paste ; and I cannot doubt 
that small masses of the lime, in the same manner re- 
maining unmixed with the fluid lava, have been drawn 
out when the whole was in motion. I carefully ex- 
amined, by trituration and solution in acids, pieces of 
the scoriae, taken from within, half-an-inch of those cells 
which were filled with the calcareous powder, and they 
did not contain an atom of free lime. It is obvious 
that the lava and lime have on a large scale been very 
imperfectly mingled ; and where small portions of the 
lime have been entangled within a piece of the viscid 
lava, the cause of their now occupying, in the form of 
a powder or of a fibrous reticulation, the vesicular 
cavities, is, I think, evidently due to the confined gases 
having most readily expanded at the points where the 
incoherent lime rendered the lava less adhesive. 

A mile eastward of the town of Praya, there is 
a steep-sided gorge, about 150 yards in width, cutting 
through the basaltic plain and underlying beds, but 
since filled up by a stream of more modern lava. This 
lava is dark gray, and in most parts compact and rudely 
columnar; but at a little distance from the coast, it 
includes in an irregular manner a brecciated mass of 
red scorise mingled with a considerable quantity of 
white, friable, and in some parts, nearly pure earthy 
lime, like that on the summit of Eed Hill. This lava, 
with its entangled lime, has certainly flowed in the 
form of a regular stream ; and, judging from the shape 
of the gorge, towards which the drainage of the country 
(feeble though it now be) still is directed, and from the 
appearance of the bed of loose water-worn blocks with 
their interstices unfilled, like those in the bed of a 



CHAP. i. Calcareous Matter entangled in Lava, i 7 

torrent, on which the lava rests, we may conclude that 
the stream was of subaerial origin. I was unable to 
trace it to its source, but, from its direction, it seemed 
to have come from Signal Post Hill, distant one mile 
and a quarter, which, like Bed Hill, has been a point 
of eruption subsequently to the elevation of the great 
basaltic plain. It accords with this view, that I found 
on Signal Post Hill, a mass of earthy, calcareous matter 
of the same nature, mingled with scoriae. I may here 
observe that part of the calcareous matter forming the 
horizontal sedimentary bed, especially the finer matter 
with which the embedded fragments of rock are white- 
washed, has probably been derived from similar volcanic 
eruptions, as well as from triturated organic remains : 
the underlying, ancient, crystalline rocks, also, are as- 
sociated with much carbonate of lime, filling aniygda- 
loidal cavities, and forming irregular masses, the nature 
of which latter I was unable to understand. 

Considering the abundance of earthy lime near the 
summit of Red Hill, a volcanic cone 600 feet in height, 
of subae'rial growth, considering the intimate manner 
in which minute particles and large masses of scoriae 
are embedded in the masses of nearly pure lime, and 
on the other hand, the manner in which small kernels 
and streaks of the calcareous powder are included in 
solid pieces of the scoriae, considering, also, the similar 
occurrence of lime and scorise within a stream of Iava 5 
also supposed, with good reason, to have been of modern 
subaerial origin, and to have flowed from a hill, where 
earthy lime also occurs: I think, considering these 
facts, there can be no doubt that the lime has been 
erupted, mingled with the molten lava. I am not 
aware that any similar case has been described: it 
appears to me an interesting one, inasmuch as most 
geologists must have speculated on the probable 



1 8 St. J "ago* PAST i. 

effects of a volcanic focus, bursting through deep-seated 
beds of different mineralogical composition. The great 
abundance of free silex in the trachytes of some coun- 
tries (as described by Beudant in Hungary, and by 
P. Scrope in the Panza Islands), perhaps solves the en- 
quiry with respect to deep-seated beds of quartz ; and 
we probably here see it answered, where the volcanic 
action has invaded subjacent masses of limestone. One 
is naturally led to conjecture in what state the now 
earthy carbonate of lime existed, when ejected with the 
intensely heated lava : from the extreme cellularity of 
the scorise on Ked Hill, the pressure cannot have been 
great, and as most volcanic eruptions are accompanied 
by the emission of large quantities of steam and other 
gases, we here have the most favourable conditions, 
according to the views at present entertained by 
chemists, for the expulsion of the carbonic acid. 1 Has 
the slow re-absorption of this gas, it may be asked, 
given to the lime in the cells of the lava, that peculiar 
fibrous structure, like that of an efflorescing salt ? 
Finally, i may remark on the great contrast in appear- 
ance between this earthy lime, which must have been 
heated in a free atmosphere of steam and other gases, 
with the white, crystalline, calcareous spar, produced by 
a single thin sheet of lava (as at Quail Island) rolling 
over similar earthy lime and the debris of organic 
remains, at the bottom of a shallow sea. 

Signal Post Hill. This hill has already been 

1 Whilst deep beneath the surface, the carbonate of lime was, I 
presume, in a fluid state. Hutton, it is known, thought that all 
amj gdaloids were produced by drops of molten limestone floating 
in the trap, like oil in water : this no doubt is erroneous, but if the 
matter forming the summit of Bed Hill had been cooled under the 
piessure of a moderately deep sea, or within the walls of a dike, 
we should, in all probability, have had a trap rock associated wilh 
large masses of compact, crystalline, calcareous spar, which, accord- 
ing to the views entertained by many geologists, would have been 
wrongly attributed to subsequent infiltration. 



CHA.P. i. Small Orifices of Eritption* 19 

several times mentioned, especially with reference to 
the remarkable manner in which the white calcareous 
stratum, in other parts so horizontal (Woodcut No. 2), 
dips under it into the sea. It is a broad summit, with 
obscure traces of a crateriform structure, and is com- 
posed of basaltic rocks, 1 some compact, others highly 
cellular, with inclined beds of loose scoriae, of which 
some are associated with earthy lime. Like Red Hill, 
it has been the source of eruptions, subsequently to the 
elevation of the surrounding basaltic plain ; but unlike 
that hill, it has undergone considerable denudation, 
and has been the seat of volcanic action at a remote 
period, when beneath the sea. I judg*e of this latter 
circumstance from finding on its inland flank the last 
remnants of three small points of eruption. These 
points are composed of glossy scoriae, cemented by 
crystalline calcareous spar, exactly like the great sub- 
marine calcareous deposit, where the heated lava has 
rolled over it : their demolished state can, I think, be 
explained only by the denuding action of the waves of 
the sea. I was guided to the first orifice by observing 
a sheet of lava, about 200 yards square, with steepish 
sides, superimposed on the basaltic plain, with no adjoin- 
ing hillock, whence it could have been erupted ; and 
the only trace of a crater which I was able to discover, 
consisted of some inclined beds of sconge at one of its 
corners. At the distance of fifty yards from a second 
level-topped patch of lava, but of much smaller size, I 

1 Of these, one common variety is remarkable for being full of 
small fragments of a dark jasper-ied earthy mineral, which, when 
examined carefully, shows an indistinct cleavage ; the little frag- 
ments are elongated in form, are soft, are magnetic before and after 
being heated, and fuse with difficulty into a dull enan el This 
lameial is evidently closely related to the oxides of iron, but I 
cannot ascertain what it exactly is. The rock containing this 
mineral is crenulated with small angular cavities, which aie lined 
and filled with yellowish crystals of carbonate of lime. 



2Q St. J agO. PARTI. 

found an irregular circular group of masses of cemented, 
sconaceous breccia, about six feet in height, which 
doubtless had once formed the point of eruption. The 
third orifice is now marked only by an irregular circle 
of cemented scoriae, about four yards m diameter, arid 
rising in its highest point scarcely three feet above the 
level of the plain, the surface of which, close all round, 
exhibits its usual appearance : here we have a hori- 
zontal basal section of a volcanic spiracle, which, to- 
gether with all its ejected matter, has been almost 
totally obliterated. 

The stream of lava, which fills the narrow gorge l 
eastward of the town of Praya, judging from its course, 
seems, as before remarked, to liave come from Signal 
Post Hill, and to have flowed over the plain, after its 
elevation : the same observation, applies to a stream 
(possibly part of the same one) capping the sea cliUs, a 
little eastward of the gorge. When I endeavoured to 
follow these streams over the stony level plain, which is 
almost destitute of soil and vegetation, i was much 
surprised to find, that although composed of hard 
basaltic matter, and not having been exposed to marine 
denudation, all distinct traces of them soon become 
utterly lost. But 1 have since observed at tlu* Gala- 
pagos Archipelago, that it is often impossible to follow 
even great deluges of quite recent lava across* older 
streams, except by the size of the bushes growing on 
them, or by the comparative states ofglossincsH of their 
surfaces, characters which a short lapse of time would 
be sufficient quite to obscure. I may remark, that in a 
country, with a dry climate, and with the wind blowing 

1 The sides of this goige, where the tipper bfjwiltic Hfnifuni IH 
intersected, are almost peipenclicnlar. The lava, wiuoh luus since 
jailed it up, is attached to these sides, almost as fiimi} us a dike fa to 
its walls In most cases, where a stream of lava hah (lowed down a 
valley, it is bounded on each side b} r loose sconaccous xua k se&. 



, i. 



Ancient Volcanic Hills. 21 



always In one direction (as at the Cape de Verde Archi- 
pelago), the effects of atmospheric degradation are pro- 
bably much greater than would at first be expected ; 
for soil in this case accumulates only in a few protected 
hollows, and being blown in one direction, it is always 
travelling towards the sea in the form of the finest dust, 
leaving the surface of the rocks bare, and exposed to 
the full effects of renewed meteoric action. 

Inland hills of more ancient volcanic rocks. These 
hills are laid down by eye, and marked as A, B, C, &c., 
in the woodcut-map. They are related in mineralogical 
composition, and are probably directly continuous with 
the lowest rocks exposed on the coast. These hills, 
viewed from a distance, appear as if they had once 
formed part of an irregular table-land, and from their 
corresponding structure and composition this probably 
has been the case. They have fiat, slightly inclined 
summits, and are, on an average, about 600 feet in 
height ; they present their steepest slope towards the 
interior of the island, from which point they radiate 
outwards, and are separated from, each other by broad 
and deep valleys, through which the great streams of 
lava, forming the coast-plains, have descended. Their 
inner and steeper escarpments are ranged in an ir- 
regular curve, which rudely follows the line of the shore, 
two or three miles inland from it. I ascended a few of 
these hills, and from others, which I was able to examine 
with a telescope, I obtained specimens, through the 
kindness of Mr. Kent, the assistant-surgeon of the 
' Beagle 7 ; although by these means I am acquainted with 
only apart of the range, five or six miles in length, yet 
I scarcely hesitate, from their uniform structure, to 
affirm that they are parts of one great formation, stretch* 
ing round much of the circumference of the island. 

The upper and lower strata of these hills differ 



22 St. J LgO. 



greatly in composition. The upper are basaltic, gener- 
ally compact, but sometimes sconaceous and amygrla- 
loidal, with associated masses of wacke : where the basalt 
is compact, it is either fine-grained or very coarsely 
crystallised ; in the latter case it passes into an augitio 
rock, containing much olivine ; the olivine is either 
colourless, or of the usual yellow and dull reddish 
shades. On some of the hills, beds of calcareous matter, 
both in an earthy and in a crystalline form, including 
fragments of glossy scoriae, are associated with the 
basaltic strata. These strata differ from the streams of 
basaltic lava forming the coast-plains, only in being 
more compact, and in the crystals of augite, and in the 
grains of olivine being of much greater size ; characters 
which, together with the appearance of the associated 
calcareous beds, induce me to believe that they are of 
submarine formation. 

Some considerable masses of wacke, which are 
associated with these basaltic strata, and which likewi.se 
occur in the basal series on the coast, especially at 
Quail Island, are curious. They consist of a pule 
yellowish-green argillaceous substance, of a crumbling 
texture when dry, but unctuous when moist : in its 
purest form, it is of a beautiful green tint, with 
translucent edges, and occasionally with, obscure traces 
of an original cleavage. Under the blowpipe it fuses 
very readily into a dark gray, and sometimes even black 
bead, which is slightly magnetic. From these char- 
acters, I naturally thought that it was one of the pale 
species, decomposed, of the genus augite ; a conclusion 
supported by the unaltered rock being full of large 
separate crystals of black augite, and of balls and 
irregular streaks of dark gray augitic rock. As the 
basalt ordinarily consists of augite, and of olivine off-en 
tarnished and of a dull red colour 3 I was led to examine 



CHAP. i. Ancient Volcanic Hills. 23 

the stages of decomposition of this latter mineral, and 
I found, to my surprise, that I could trace a nearly 
perfect gradation from unaltered olivine to the green 
waeke. Part of the same gram under the blowpipe 
would in some instances behave like olivine, its colour 
being only slightly changed, and part would give a 
black magnetic bead. Hence I can have no doubt that 
the greenish wacke originally existed as olivine ; but 
great chemical changes must have been effected during 
the act of decomposition thus to have altered a very 
hard, transparent, infusible mineral, into a soft, unctu- 
ous, easily melted, argillaceous substance. 1 

The basal strata of these hills, as well as some 
neighbouring, separate, bare, rounded hillocks, consist 
of compact, fine-grained, non-crystalline (or so slightly 
as scarcely to be perceptible,) ferruginous feldspathio 
rocks, and generally in a state of semi-decomposition. 
Their fracture is exceedingly irregular, and splintery ; 
yet small fragments are often very tough. They 
contain much ferruginous matter, either in the form of 
minute grains with a metallic lustre, or of brown hair- 
like threads : the rock in this latter case assuming a 
pseudo-brecciated structure. These rocks sometimes 
contain mica and veins of agate. Their rusty brown or 
yellowish colour is partly due to the oxides of iron, but 

1 D'Aubuisbon, 'Traite de Ge'ognosie* (torn li. p 569), mentions, 
on the authoiity of M Marcel de Series, masses of green earth near 
Montpelher, which are supposed to be due to the decomposition of 
olivine. I do not, however, find, that the action of this mineial 
under the blowpipe being entirely altered, as it, becomes decom- 
posed, has been noticed ; and the knowledge of this fact is im- 
portant, as at first it appears highly improbable that a haid, 
transpaient, refractory mineral should be changed into a soft, 
easily- 1 used, clay, like this of St. Jago. I shall hereafter descube 
a green substance, forming threads within the cells of s r rue vesicular 
basaltic rocks in Van Diemen's Land, which behave tinder the blow- 
pipe like the green wacke of St Jago ; but its occurrence m 
cylindrical threads, shows it cannot have resulted fiora the decom- 
position of olrvine, a mineral always existing in the form of grains 
or crystals. 



24 St. 



chiefly to innumerable, microscopically minute, black 
specks, which, when a fragment is heated, are easily 
fused, and evidently are either hornblende or augite. 
These rocks, therefore, although at first appearing like 
baked clay or some altered sedimentary deposit, contain 
all the essential ingredients of trachyte ; from which 
they differ only in not being harsh, and in not con- 
taining crystals of glassy feldspar. As is so often 
the case with trachytic formation, no stratification is 
here apparent. A person would not readily believe that 
these rocks conld have flowed as lava; yet at St. Helena 
there are well characterised streams (as will be described 
in an ensuing chapter) of nearly similar composition. 
Amidst the hillocks composed of these rocks, I found in 
three places, smooth conical hills of phonolite, abound- 
ing with fine crystals of glassy feldspar, and with needles 
of hornblende. These cones of phonolite, I believe, 
bear the same relation to the surrounding feldspatlue 
strata which some masses of coarsely crystallised augitic 
rock, in another part of the island, bear to the surround- 
ing basalt, namely, that both have been injected. The 
rocks of a feldspathic nature being anterior in origin to 
the basaltic strata, which cap them, as well as to the 
basaltic streams of the coast-plains, accords with the 
usual order of succession of these two grand divisions of 
the volcanic series, 

The strata of most of these hills in the upper part, 
where alone the planes of division are distinguishable, 
are inclined at a small angle from the interior of the 
island towards the sea-coast. The inclination is not f ho 
same in each hill ; in that marked A it is less than 
in B, D, or E \ in C the strata are scarcely deflected 
from a horizontal plane, and in P (as for as 1 could 
judge without ascending it) they are slightly inclined 
in a reverse direction, that is ? inwards and towards the 



CHAP. i. Valleys near the Coast. 2 5 

centre of the Island. Notwithstanding these differences 
of inclination, their correspondence in external form, 
and in the composition both of their upper and lower 
parts, their relative position in one curved line, with 
their steepest sides turned inwards, all seem to show 
that they originally formed parts of one platform ; 
which platform, as before remarked, probably extended 
round a considerable portion of the circumference of 
the island. The upper strata certainly flowed as lava, 
and probably beneath the sea, as perhaps did the lower 
feldspathic masses : how then come these strata to 
hold their present position, and whence were they 
erupted ? 

In the centre of the island * there are lofty moun- 
tains, but they are separated from the steep inland 
flanks of these hills by a wide space of lower country : 
the interior mountains, moreover, seem to have been 
the source of those great sti earns of basaltic lava which, 
contracting as they pass between the bases of the hills 
in question, expand into the coast-plains. Round the 
shores of St. Helena there is a rudely-formed ring of 
basaltic rocks, and at Mauritius there are remnants of 
another such a ring round part, if not round the whole, 
of the island ; here again the same question immediately 
occurs, how come these masses to hold their present 
position, and whence were they erupted? The same 
answer, whatever it may be, probably applies In these 
three cases ; and in a future chapter we shall recur to 
this subject. 

Valleys newr the coast. These are broad, very flat, 

1 I saw very little of the inland paits of the island Near the 
Tillage of St. Domingo, there are magnificent oliils of lather coarsely 
crystallised basaltic lava. Following the little stream in this 
valley, about a mile above the village, the base of the great cliff 
was ioimed of a compact fine-grained basalt, conformably covered 
by a bed of pebbles Near Fuentes, I met with pap- formed bills of 
the compact feldspa'hic series of rocks. 



PART I. 



26 6V. Jggo- 

and generally bounded by low cliff-formed sides. Por- 
tions of the basaltic plain are sometimes nearly or quite 
isolated by them ; of which fact, the place on which 
the town of Praya stands offers an instance. The great 
valley west of the town has its bottom filled up to a 
depth of more than twenty feet by well-rounded pebbles, 
which in some parts are firmly cemented together by 
white calcareous matter. There can be no "doubt, from. 
the form of these valleys, that they were scooped out by 
the waves of the sea, during that equable elevation of 
the land, of which the horizontal calcareous deposit, 
with its existing species of marine remains, gives evi- 
dence. Considering how well shells have been preserved 
in this stratum, it is singular that I could not find even a 
single small fragment of shell in the conglomera f o at 
the bottom of the valleys. The bed of pebbles in the 
valley west of the town is intersected by a second valley 
joining it as a tributary, but even this valley appears 
much too wide and flat-bottomed to have been formed 
by the small quantity of water, which falls only dining 
one short wet season ; for at other times of the year 
these valleys are absolutely dry, 

Recent conglomerate. On the shores of Quail 
Island, I found fragments of brick, bolts of iron, 
pebbles, and large fragments of basalt, united by a 
scanty "base of impure calcareous matter into a firm, 
conglomerate. To show how exceedingly firm this recent 
conglomerate is, I may mention, that I endeavoured 
with a heavy geological hammer to knock out a thick 
bolt of iron, which was embedded a little above low- 
water mark,- but was quite unable to succeed. 



CHAPTER IL 

FERNANDO NOEONHA Precipitous hill of phonolite. TBKCEIRA 
Trachi/He roclts ; their singular decomposition by steatu f>f "high ttm- 
perature. TAHITI Passage from tvacJte into trap ; si-nqidar vol- 
canic rock nlth the vesieles half filled with mvsotype. MAUBITIUS 
Proofs of its recent elevation Structure of its more ancient 
mountains ; similarity with St. Jaffa ST. PAUL'S BOOKS Not of 
volcanic origin their singular mincralogical composition 

Fernando NoronJia During our short visit at tins 
and tlie four following islands, I observed very little 
worthy of description. Fernando Noronha is situated 
in the Atlantic Ocean, in lat. 3 50' 8., and 230 miles 
distant from the coast of South America. It consists 
of several islets, together nine miles in length by three 
in breadth. The whole seems to be of volcanic origin ; 
although there is no appearance of any crater, or of any- 
one central eminence. The most remarkable feature 
is a hill 1,000 feet nigh, of which the upper 400 feet 
consist of a precipitous, singularly shaped pinnacle, 
formed of columnar phonolite, containing numerous 
crystals of glassy feldspar, and a few needles of horn- 
blende. From the highest accessible point of this hill, 
I could distinguish in different parts of the group 
several other conical hills, apparently of the same nature. 
At St. Helena there are similar, great, conical, protu- 
berant masses of phonolite, nearly 1,000 feet in height, 
which ha.ve been formed by the injection *of fluid felcl- 
spathic lava into yielding strata. If this hill has bad, 



28 Terceira. 



PART I. 



as is probable, a similar origin, denudation has been 
here effected on an enormous scale. Near the base of 
this hill, I observed beds of white tuff, intersected 
by numerous dikes, some of amygdaloidal basalt and 
others of trachyte ; and beds of slaty phonolite wit h 
the planes of cleavage directed NW. and SE. Parts 
of this rock, where the crystals were scanty, closely re- 
sembled common clay-slate, altered by the contact of a 
trap-dike. The lamination of rocks, which undoubtedly 
have once been fluid, appears to me a subject well deserv- 
ing attention On the beach there were numerous frag- 
ments of compact basalt, of which rock a distant fayade 
of columns seemed to be formed. 

Tercftira in the Azores. The central parts of this 
island consist of irregularly rounded mountains of no 
great elevation, composed of trachyte, which closely 
resembles in general character the trachyte of Ascension, 
presently to be described. This formation is in many 
parts overlaid, in the usual order of superposition, by 
streams of basaltic lava, which near the coast compose 
nearly the whole surface. The course which these 
streams have followed from their craters, can often be 
followed by the eye. The town of Angra is overlooked 
by a cratenform hill (Mount Brazil), entirely built of 
thin strata of fine-grained, harsh, brown-coloured tuff, 
The upper beds are seen to overlap the basaltic streams 
on which the town stands. This hill is almost iden- 
tical in structure and composition with numerous crater- 
formed hills in the Galapagos Archipelago 

Effects of steam on the tr achy tic rocfo. In the 
central part of the island there is a spot, where steam 
is constantly issuing in jets from the bottom of a small 
ravine-like hollow, which has no exit, and which abuts 
against a range of trachytic mountains. The steam is 
emitted from several irregular fissures : it is scentless, 



CHAP. II. 



Terceira. 29 



soon blackens iron, and is of much too high temperature 
to be endured by the hand. The manner in which the 
solid trachyte is changed on the borders of these orifices 
is curious : first, the base becomes earthy, with red 
freckles evidently due to the oxidation of particles of 
iron ; then it becomes soft ; and lastly, even the crystals 
of glassy feldspar yield to the dissolving agent. After 
the mass is converted into clay, the oxide of iron seems 
to be entirely removed from some parts, which are left 
perfectly white, whilst in other neighbouring parts, 
which are of the brightest red colour, it seems to be 
deposited in greater quantity ; some other masses are 
marbled with the two distinct colours. Portions of the 
white clay, now that they are dry, cannot be distinguished 
by the eye from the finest prepared chalk ; and when 
placed between the teeth they feel equally soft-grained ; 
the inhabitants use this substance for white- washing 
their houses. The cause of the iron being dissolved in 
one part, and close by being again deposited, is obscure; 
but the fact has been observed in several other places. 1 
In some half-decayed specimens, I found small, globular, 
aggregations of yellow hyalite, resembling gum-arabic, 
which no doubt had been deposited by the steam. 

As there is no escape for the rain-water, which 
trickles down the sidefc of the ravine-like hollow, whence 
the steam issues, it must all percolate downwards 
through the fissures at its bottom. Some of the in- 
habitants informed me that it was on record that 
flames (some luminous appearance?) had originally 
proceeded from these cracks, and that the flames had 

1 Spallanzani, Dolomieu and Hoffman have described similar 
cases in the Italian volcanic islands. Dolomieu says the iron at the 
Panza Islands is redeposited in the form of veins (p 86, * Memoire 
surles Isles Ponces'). These authors likewise believe that the steam 
deposits silica* it is now experimentally knowu that vapour of a 
high temperature is able to dissolve silica. 



30 Tahiti. PAET L 

been succeeded by the steam ; but 1 was not able to 
ascertain how long this was ago, or anything certain on 
the subject. When viewing the spot, I imagined that 
the injection of a large mass of rock, like the cone of 
phouolite at Fernando Noronha, in a semi-fluid state, by 
arching the surface might have caused a wedge-shaped 
hollow with cracks at the bottom, and that the rain- 
water percolating to the neighbourhood of the heated 
mass, would during many succeeding years be driven 
back in the form, of steam. 

Tahiti (Otaheite). I visited only a part of the 
north-western side of this island, and this part is en- 
tirely composed of volcanic rocks. Near the coast there 
are several varieties of basalt, some abounding with 
large crystals of augite and tarnished olivine, others 
compact and earthy, some slightly vesicular, and 
others occasionally amygdaloidaL These rocks are 
generally much decomposed, and to my surprise, I found 
in several sections that it was impossible to distinguish, 
even approximately, the line of separation between the 
decayed lava and the alternating beds of tuff. Since 
the specimens have become dry, it is rather more easy 
to distinguish the decomposed igneous rocks from the 
sedimentary tuffs. This gradation in character be- 
tween rocks having such widely different origins, may I 
think be explained by the yielding under pressure of 
the softened sides of the vesicular cavities, which in 
many volcanic rocks occupy a large proportion of their 
bulk. As the vesicles generally increase in size and 
number in the upper parts of a stream of lava, so would 
the effects of their compression increase; the yielding, 
moreover, of each lower vesicle must tend to disturb all 
the softened matter above it. Hence we might expect 
to trace a perfect gradation from an unaltered crystal- 
line rock to one in which all the particles (although 



CHAP. n. Tahiti. 3 1 

originally forming part of the same solid mass) had 
undergone mechanical displacement ; and such particles 
could hardly be distinguished from others of similar 
composition, which had been deposited as sediment. 
As lavas are sometimes laminated in their upper parts, 
even horizontal lines, appearing like those of aqueous 
deposition, could not in all cases be relied on as a 
criterion of sedimentary origin. Prom these considera- 
tions it is not surprising that formerly many geologists 
believed in real transitions from aqueous deposits, 
through wacke, into igneous traps. 

In the valley of Tia-auru, the commonest rocks are 
basalts with much olivine, and in some cases almost 
composed of large crystals of augite. I picked up some 
specimens, with much glassy feldspar, approaching in 
character to trachyte. There were also many large 
blocks of vesicular basalt, with the cavities beautifully 
lined with chabasie (?), and radiating bundles of meso- 
type. Some of these specimens presented a curious 
appearance, owing to a number of the vesicles being 
half filled np with a white, soft, earthy mesotypic 
mineral, which intumesced under the blowpipe in 
a remarkable manner. As the upper surfaces in all 
the half-filled cells are exactly parallel, it is evident 
that this substance has sunk to the bottom of each cell 
from its weight. Sometimes, however, it entirely fills 
the cells. Other cells are either quite filled, or lined, 
with small crystals, apparently of chabasie ; these 
crystals, also, frequently line the upper half of the cells 
partly filled with the earthy mineral, as well as the 
upper surface of this substance itself, in which case the 
two minerals appear to blend into each other. I have 
never seen any other amygdaloid l with the cells half 

1 MacCulloch, however, has described and given a plate of 
* 0eolog. Trans.,' 1st Series, vol. iv. p. 225) a trap rock, with cavities 



32 Tahiti. I>AKT i. 

filled in the manner here described ; and it is difficult 
to imagine the causes which determined the earthy 
mineral to sink from its gravity to the bottom of the 
cells, and the crystalline mineral to adhere in a coating 
of equal thickness round the sides of the cells. 

The basaltic strata on the sides of the valley are 
gently inclined seaward, and I nowhere observed any 
sign of disturbance \ the strata are separated from each 
other by thick, compact beds of conglomerate, m which 
the fragments are lai^ge, some being rounded, but most 
angular. From the character of these beds, from the 
compact and crystalline condition of most of the lavas, 
and from the nature of the infiltrated minerals, 1 was 
led to conjecture that they had originally flowed beneath 
the sea. This conclusion agrees with the fact that the 
Eev. W. Ellis found marine remains at a considerable 
height, which he believes were interstratified with 
volcanic matter ; as is likewise described to be the case 
by Messrs. Tyerman and Bennett at Huaheine, an island 
in this same archipelago. Mr. Stutchbury also dis- 
covered near the summit of one of the loftiest moun- 
tains of Tahiti, at the height of several thousand feet, 
a stratum of semi-fossil coral. None of these remains 
have been, specifically examined. On the coast, where 
masses of coral rock would have afforded the clearest evi- 
dence, I looked in vain for any signs of recent elevation. 
For references to the above authorities, and for more 
detailed reasons for not believing that Tahiti has been 
recently elevated, I must refer to my volume on the 
c Structure and Distribution of Coral Reefs ' (p. 138 of 
the 1st edit., or p. 182 of the 2nd. edit.). 

filled up horizontally with quartz and chalcedony. The upper 
halves of these cavities are often filled by layers, which follow each 
irregularity of the surface, and by little depending stalactites of the 
same siliceous substances. 



CHAP, ii. Mauritius. 33 

Mauritius. Approaching this island on the 
northern or north-western side, a curved chain of bold 
mountains, surmounted by rugged pinnacles, is seen to 
rise from a smooth border of cultivated land, which 
gently slopes down to the coast. At the first glance, 
one is tempted to believe that the sea lately reached 
the base of these mountains, and upon examination, 
this view, at least with respect to the inferior parts of 
the border, is found to be perfectly correct. Several 
authors 1 have described masses of upraised coral rock 
round the greater part of the circumference of the 
island. Between Tamarin Bay and the Great Black 
River I observed, in company with Capt. Lloyd, two 
hillocks of coral rock 3 formed in their lower part of 
hard calcareous sandstone, and in their upper of great 
blocks, slightly aggregated, of Astraea and Madrepora, 
and of fragments of basalt ; they were divided into beds 
dipping seaward, in one case at an angle of 8, and in 
the other at 18; they had a water- worn appearance, 
and they rose abruptly from a smooth surface, strewed 
with rolled debris of organic remains, to a height of 
about twenty feet. The Officier du Eoi, in his most 
interesting tour in 1768 round the island, has described 
masses of upraised coral rocks, still retaining that moat- 
like structure (see { Coral Reefs/ 2nd edit. p. 69) 
which is characteristic of the living reefs. On the. 
coast northward of Port Louis, I found the lava con- 
cealed for a considerable space inland by a conglo- 
merate of corals and shells, like those on the beach, 
but in parts consolidated by red ferruginous matter. 

1 Captain Carmiohael, in Hooker's Bot. Misc' vol ii. p. 301 
Captain Lloyd has lately, in Ibe ' Proceedings of the Geological 
Society ' (vol in. p. 317), described carefully some of these masses. 
In ihe 'Voyage & 1'Iale de France, par un Officier du Eoi,' many 
interesting facts are given on this subject Consult also * Voyage 
aux Quatre Isles d'Afrique, par M. Bory St. Vincent.' 



34 Mauritius. PAET i. 

M. Bory St Vincent has described similar calcareous beds 
over nearly the whole of the plain of Parnplemou&ses. 
Near Port Louis, when turning over some large stones, 
which lay in the bed of a stream at the head of a pro- 
tected creek, and at the height of some yards above the 
level of spring tides, I found several shells of serpula 
still adhering to their under sides. 

The jagged mountains near Port Louis rise to a 
height of between 2,000 and 8 5 000 feet ; they consist 
of strata of basalt, obscurely separated from each other 
by firmly aggregated beds of fragmentary matter ; and 
they are intersected by a few vertical dikes. The 
basalt in some parts abounds with large crystals of 
augite and olivine, and is generally compact. The 
interior of the island forms a plain, raised probably 
about a thousand feet above the level of the sea, and 
composed of streams of lava which have flowed round 
and between the rugged basaltic mountains. These 
more recent lavas are also basaltic, but less compact, 
and some of them abound with feldspar, so that they 
even fuse into a pale coloured glass. On the banks of 
the Great River, a section is exposed nearly 500 feet 
deep, worn through numerous thin sheets of the lava of 
this series, which are separated from each other by beds 
of scorise. They seem to havo been of siibuorial forma- 
tion, and to have flowed from several points of eruption 
on the central platform, of which the Piton du Milieu 
is said to be the principal one. There are also several 
volcanic cones, apparently of this modern poriod, round 
the circumference of the island, especially at the 
northern end, where they form separate islets. 

The mountains composed of the more compact and 
crystalline basalt, form the main skeleton of the island. 
M. Bailly l states that they all ' se d6veloppeut autour 
i Voyage aux Terres Australes,' torn. i. p, 54 



CHAP. n. J/f#^re/Z2^ 35 

d'elle comme une celnture d'immenses remparts, toutes 
affectant une pente plus ou moins inclinee vers le rivage 
de la mer ; tandis, au contraire, que vers le centre de 
File elles presentent nne coupe abrupte, et souvent 
taillee a pic. Toutes ces raontagnes sont form6es de 
couches parallSles inclinees du centre de File vers la 
mer.' These statements have been disputed, though 
not in detail, by M. Quoy, in the voyage of Freycinet. 
As far as my limited means of observation went, I 
found them perfectly correct. 1 The mountains on the 
NW. side of the island, which I examined, namely, La 
Pouce, Peter Botts, Corps de Garde, Les Mamelles, 
and apparently another farther southward, have pre- 
cisely the external shape and stratification described by 
M Bailly. They form about a quarter of his girdle of 
ramparts. Although these mountains now stand quite 
detached, being separated from each other by breaches, 
even several miles in width, through which deluges of 
lava have flowed from the interior of the island ; never- 
theless, seeing their close general similaiity, one must 
feel convinced that they originally formed parts of one 
continuous mass. Judging from the beautiful map of 
the Mauritius, published by the Admiralty from a 
French MS., there is a range of mountains (M. Bamboo) 
on the opposite side of the island, which correspond in 
height, relative position, and external form, with those 
just described. Whether the girdle was ever complete 
may well be doubted ; but from M. Bailly's statements, 
and my own observations, it may be safely concluded that 
mountains with precipitous inland flanks, and composed 
of strata dipping outwards, once extended round a con- 
siderable portion of the circumference of the island. 
The ring appears to have been oval and of vast size ; its 

1 M. Lesso % in his account of the island, m the Towage of tlie 
1 Coqiulle,' seems to follow M. Railly's vie\\s. 
4 



36 Mauritius. 



shorter axis, measured across from the inner sides of 
the mountains near Port Louis and those near Grand 
Port, being no less than thirteen geographical miles in 
length. M. Bailly boldly supposes that this enormous 
gulf, which has since been filled up to a great extent 
by streams of modern lava, was formed by the sinking 
in of the whole upper part of one great volcano. 

It is singular in how many respects those portions 
of St, Jago and of Mauritius which I visited agree in 
their geological history. At both islands, mountains 
of similar external form, stratification, and (at least in 
their upper beds) composition, follow in a curved chain 
the coast-line. These mountains in each case appear 
originally to have formed parts of one continuous muss. 
The basaltic strata of which they are composed, from 
their compact and crystalline structure, seem, when 
contrasted with the neighbouring basaltic streams of 
subaerial formation, to have flowed beneath the pressure 
of the sea, and to have been subsequently elevated 
We may suppose that the wide breaches between the 
mountains were in both cases worn by the \\aves, 
during their gradual elevation of which process, within 
recent times, there is abundant evidence on the coast - 
land of both islands. At both, vast streams of more 
recent basaltic lavas have flowed from the interior of 
the island, round and between the ancient basaltic hills; 
at both, moreover, recent cones of eruption are scattered 
around the circumference of the island; but at neither 
have eruptions taken place within the period of history. 
As remarked in the last chapter, it is probable that 
these ancient basaltic mountains, which resemble (at 
least in many respects) the basal and disturbed remnants 
of two gigantic volcanos, owe their present form, struc- 
ture, and position, to the action of mrmlar causes. 

St. PitnVs lloclis." This small island is situated in 



CHAP. n. St. Paul's Rocks. 37 

the Atlantic Ocean, nearly one degree north of the 
equator, and 540 miles distant from South America, in 
29 15' west longitude. Its highest point is scarcely 
fifty feot above the level of the sea; its outline is 
irregular, and its entire circumference barely three- 
quarters of a mile. This little point of rock rises 
abruptly out of the ocean ; and, except on its western 
side, soundings were not obtained, even at the short 
distance of a quarter of a mile from its shore. It is 
not of volcanic origin ; and this circumstance, which is 
the most remarkable point in its history (as will here- 
after be referred to), properly ought to exclude it from 
the present volume. It is composed of rocks, unlike 
any which I have met with, and which I cannot charac- 
terise by any name, and must therefore describe. 

The simplest, and one of the most abundant kinds, 
is a very compact, heavy, greenish-black rock, having 
an angular, irregular fracture, with some points just 
hard enough to scratch glass, and infusible. This 
variety passes into others of paler green tints, less hard, 
but with a more crystalline fracture, and translucent on 
their edges ; and these are fusible into a green enamel. 
Several other varieties are chiefly characterised by 
containing innumerable threads of dark-green serpen- 
tine, and by having calcareous matter in their inter- 
stices. These rocks have an obscure, concretionary 
structure, and are full of variously-coloured angular 
pseudo fragments. These angular psendo fragments 
consist of the first-described dark green rock, of a brown 
softer kind, of serpentine, and of a yellowish harsh stone, 
which, perhaps, is related to serpentine rock. There 
are other vesicular, calcareo-ferruginous, soft stones. 
There is no distinct stratification, but parts are imper- 
fectly laminated ; and the whole abounds with innu- 
merable veins, and vein-like masses, both small and 



38 St. PanFs Rocks. PART i. 

large. Of these vein-like masses, some calcareous ones, 
which contain minute fragments of shells, are clearly 
of subsequent origin to the others. 

A glossy incrustation. Extensive portions of these 
rocks are coated by a layer of a glossy polished sub- 
stance, with a pearly lustre and of a grayish white 
colour; it follows all the inequalities of the surface, to 
which it is fiimly attached. When examined with a 
lens, it is found to consist of numerous exceedingly thin 
layers, their aggregate thickness being about the tenth 
of an inch. It is considerably harder than calcareous 
spar, but can be scratched with a knife ; under the 
blowpipe it scales off, decrepitates, slightly blackens, 
emits a fetid odour, and becomes strongly alkaline : ife 
does not effervesce in acids. 1 1 presume this substance 
has been deposited by water draining from the birds' 
dung, with which the rocks are covered. At Ascension, 
near a cavity in the rocks which was filled with a 
laminated mass of infiltrated birds' dung, I found some 
irregularly-formed, stalactitical masses of apparently 
the same nature. These masses, when broken, had an 
earthy texture ; but on their outsides, and especially at 
their extremities, they were formed of a pearly sub- 
stance, generally in little globules,' like the enamel of 
teeth, but more translucent, and so hard as just to 
scratch plate-glass. This substance slightly blackens 
under the blowpipe, emits a bad smell, then becomes 
quite white, swelling a little, and fuses into a dull white 
enamel; it does not become alkaline; nor docs it 
effervesce in acids. The whole mass had a collapsed 
appearance, as if in the formation of the hard glossy 
crust the whole had shrunk much. At the Abrolhos 
Islands on the coast of Brazil, where also there is much 

1 In my Journal I have described tins si bs ance ; I then belie\c*<3 
that it \\as an impure phosphate of lime. 



CHAP. ii. ,$/. Paul's Rocks. 39 

birds' dung, I found a great quantity of a brown ? 
arborescent substance adhering to some trap-rook* In 
Its arborescent form, this substance singularly resembles 
some of the branched species of Nullipora. Under the 
blowpipe, it behaves like the specimens from Ascension ; 
but it is less hard and glossy, and the surface has not 
the shrunk appearanca 



4O Ascension, PIBT i. 



CHAPTER IIL 

ASCENSION. 

Basaltic lavas Numerous craters truncated on tlie same side 
Singular structure ofwleanio bombs Aeriform explosionsEjected 
granitic fragments TrarJnjtio rooks Singular r&n* Jaajjer, it* 
manner of formation Concretion* in pwmct'om titffCalttaretntt 
deposits and frondcscent merit stations on the coast Remarltabfo 
laminated leds^ alternating with, and passing into 
Or^ff^/l qfoltndian Lamination oj wlcanto 



THIS island is situated in the Atlantic Ocean, in lat. 8 
S , long. 14 W. It lias the form of an irregular triangle 
(see accompanying Map), each side being about six 
miles in length. Its highest point is 2,870 feet 1 above 
the level of the sea. The whole is volcanic, and, from 
the absence of proofs to the contrary, I believe of sub- 
aerial orgin. The fundamental rock is everywhere of 
a pale colour, generally compact, and of a fHdspathie 
nature. In the SE. portion of the island, whore tho 
highest land is situated, well characterised trachyte, 
and other congenerous rocks of that varying fainilv, 
occur. Nearly the entire circumference is covered up 
by black and rugged streams of basaltic lava, with lion) 
and there a hill or single point of rock (one of which 
near the sea-coast, north of the Port, is only two or 
three yards across) of the trachyte still remaining 
exposed. 

Basaltic rocks. The overlying basaltic lava is in 

1 * Geographical Journal,* vol v. p, 213. 



CHAP, in. Basaltic Rocks. 41 

some parts extremely vesicular, in others little so ; it is 
of a black colour, but sometimes contains crystals of 
glassy feldspar, and seldom much olivine. These 
streams appear to have possessed singularly little 
fluidity; their side walls and lower ends being very 
steep, and even as much as between twenty or thirty 
feet in height. Their surface is extraordinarily rugged, 
and from a short distance appears as if sfcudded with 
small craters. These projections consist of broad, 
irregularly conical, hillocks, traversed by fissures, and 
composed of the same unequally scoriaceous basalt with 
the surrounding streams, but having an obscure ten- 
dency to a columnar structure ; they rise to a height 
between ten and thirty feet above the general surface, 
and have been formed, as I presume, by the heaping up 
of the viscid lava at points of greater resistance. At 
the base of several of these hillocks, and occasionally 
likewise on more level parts, solid ribs, composed of 
angulo-globular masses of basalt, resembling in size 
and outline arched sewers or gutters of brickwork, but 
not being hollow, project between two or three feet 
above the surface of the streams; what their origin 
may have been, I do not know. Many of the super- 
ficial fragments from these basaltic streams present 
singularly convoluted forms ; and some specimens could 
hardly be distinguished from logs of dark- coloured wood 
without their bark. 

Many of the basaltic streams can be traced, either 
to points of eruption at the base of the great central 
mass of trachyte, or to separate, conical, red-coloured 
hills, which are scattered over the northern and western 
borders of the island. Standing on the central eminence, 
I counted between twenty and thirty of these cones of 
eruption. The greater number of them had their trun- 
cated summits cut off obliquely, and they all sloped 



Ascension. 



PAET I. 



towards the SE , whence the trade-wind blows. 1 This 
structure no doubt has been caused by the ejected 
fragments and ashes being always blown, during erup- 
tions, in greater quantity towards one side than towards 
the other M. Moreau de Jonnes has made a similar 
observation with respect to the volcanic orifices in the 
West Indian Islands. 

Volcanic bombs. These occur in great numbers 
strewed on the ground, and some of them lie at con- 
siderable distances from any points of eruption. They 
vary in size from that of an apple to that of a man's 

No 3 




Fragment; of a spherical volcanic bomb, -with the interior parts cwa*!y 
coaled by a concentric layer of compact lava, and this again bj a cnust o 
cellular rock. 

body ; they are either spherical or pear-shape^ or wltli 
the hinder part (corresponding to the tail of a comet) 

1 M. Lesson, in the c Zoology of the "Voyage of the ** Coqiille wt 
(p 490), has observed this fact, Mr Hennah ( Geolog, Proceedings,' 
1835, p. 189) further remarks that the most estensiTe feetls of 
at Ascension invariably occur on the leeward side of the island. 



CHAP. m. Volcanic Bombs. 43 

irregular 3 studded with, projecting points, and even 
concave. Tlieir surfaces are rough, and fissured with 
branching cracks ; their internal structure is either 
irregularly scoriaceous and compact, or it presents a 
symmetrical and very curious appearance. An irregular 
segment of a bomb of this latter kind, of which I 
found several, is accurately represented in the accom- 
panying woodcut. Its size was about that of a man's 
head. The whole interior is coarsely cellular ; the cells 
averaging in diameter about the tenth of an inch , but 
nearer the outside they gradually decrease in size. This 
part Is succeeded by a well-defined shell of compact 
lava, having a nearly uniform thickness of about the 
third of an inch ; and the shell is overlaid by a some- 
what thicker coating of finely cellular lava (the cells 
varying from the fiftieth to the hundredth of an inch in 
diameter), which forms the external surface : the line 
separating the shell of compact lava from the outer 
scoriaceous crust is distinctly defined. This structure 
is very simply explained, if we suppose a mass of viscid, 
scoriaceous matter, to be projected with a rapid, rota- 
tory motion through the air ; for whilst the external 
crust, from cooling, became solidified (in the state we 
now see it), the centrifugal force, by relieving the 
pressure in the interior parts of the bomb, would allow 
the heated vapours to expand their cells ; but these 
being driven by the same force against the already- 
hardened crust, would become, the nearer they were to 
this part, smaller and smaller or less expanded, until 
they became packed into a solid, concentric shell. As 
we know that chips from a grindstone * can be flirted 
off, when made to revolve with sufficient velocity, we 
need not doubt that the centrifugal force would have 
power to modify the structure of a softened bomb, in 

1 Kichol's 'Architecture of the Heavens.* 



44 Ascension. PUIT i, 

the manner here supposed. Geologists have remarked, 
that the external form of a bomb at once bespeaks the 
history of its aerial course, and we now see that the 
internal structure can speak, with almost equal plainness, 
of its rotatory movement. 

M Bory St. Vincent 1 has described some balls of 
lava from the Isle of Bourbon, which have a closely 
similar structure ; his explanation, however (if I under- 
stand it rightly), is very different from that which I 
have given ; for he supposes that they have rolled, like 
snow-balls, down the sides of the crater. M. Beudant, 2 
also, has described some singular little balks of obsidian T 
never more than six or eight inches m diameter, which 
he found strewed on the surface of the ground : their 
form is always oval ; sometimes they are much swollen 
in the middle, and even spindle-shaped : their surface 
is regularly marked with concentric ridges and furrows^ 
all of which on the same ball are at right angles to one 
axis : their interior is compact and glassy, M. Beudant 
supposes that masses of lava, 
when soft, were shot into the air, 
with a rotatory movement round 
the same axis, and that the form 
and superficial ridges of the 
bombs were thus produced, Kir 
Thomas Mitchell has given rate 
what at first appears to be tlw 
half of a much flattened oval ball 
of obsidian ; it has a singular 
artificial-like appearance, winch 
volcanic bomb of obsidian from is well represented (of the natural 
size) in the accompanying wood- 





* side TOW of the same ob- ^ j t wag found 

1 * Voyage aux Quatre Isles d'Afrique/ torn, i, |> 222, 

2 * Voyage en Hongrie,' torn, li, p. 214, 



CHAP. in. Aeriform Explosions. 45 

sent state, on a great sandy plain between the rivers 
Darling and Murray, in Austialia, and at the distance 
of several hundred miles from any known volcanic 
region. It seems to have been embedded in some 
reddish tufaceous matter; and may have been trans- 
ported either by the aborigines or by natural means. 
The external saucer consists of compact obsidian, of a 
botfcle-green colour, and is filled with finely-cellular 
black lava, much less transparent and glassy than the 
obsidian. The external surface is marked with four 
or five not quite perfect ridges, which are represented 
rather too distinctly in the woodcut. Here then we 
have the external structure described by M. Beudant, 
and the internal cellular condition of the bombs from 
Ascension. The lip of the saucer is slightly concave, 
exactly like the margin of a soup-plate, and its inner 
edge overlaps a little the central cellular lava. This 
structure is so symmetrical round the entire circum- 
ference, that one is forced to suppose that the bomb 
burst during its rotatory course, before being quite 
solidified, and that the lip and edges were thus slightly 
modified and turned inwards. It may be remarked that 
the superficial ridges are in planes, at right angles to an 
axis, transverse to the longer axis of the flattened oval : 
to explain this circumstance, we may suppose that when 
the bomb burst, the axis of rotation changed. 

Aeriform explosions. The flanks of Green Moun- 
tain and the surrounding country are covered by a 
great mass, some hundred feet in thickness, of loose 
fragments. The lower beds generally consist of fine- 
grained, slightly consolidated tuffs, 1 and the upper beds 
of great loose fragments, with alternating finer beds. 2 

1 Some of this peperino, or tuff, is sufficiently hard not to be 
broken by the greatest force of the fingers. 

2 On the northern side of the Green Mountain, a thin seam, about 
an inch in thickness, of compact oxide of iron, extends over a con- 



46 Ascension. PABT L 

One white ribbon-like layer of decomposed, puniiceous 
breccia, was curiously bent into deep unbroken curves, 
beneath each of the larger fragments in the superin- 
cumbent stratum. Prom the relative position of these 
beds, I presume that a narrow-mouthed crater, standing 
nearly in the position of Green Mountain, like a great 
air-gun, shot forth, before its final extinction^ this vast 
accumulation of loose matter. Subsequently to this 
event, considerable dislocations have taken place, and 
an oval circus has been formed by subsidence. This 
sunken space lies at the north-eastern foot of Green 
Mountain, and is well represented in the accompanying 
map. Its longer axis, which is connected with a NE. 
and SW. line of fissure, is three-fifths of a nautical mile 
in length ; its sides are nearly perpendicular, except in 
one spot, and about 400 feet in height ; they consist, ia 
the lower part, of a pale basalt with feldspar, and in the 
upper part, of the tuff and loose ejected fragments ; 
the bottom is smooth and level, and under almost any 
other climate a deep lake would have been formed 
here. Prom the thickness of the bed of loose fragments, 
with which the surrounding country is covered, the 
amount of aeriform matter necessary for their projection 
must have been enormous; hence we may suppose it 
probable that after the explosions vast subterranean 
caverns were left, and that the falling in of the roof of 
one of these produced the hollow here described. At 
the Galapagos Archipelago, pits of a similar character, 



siderable area ; it lies conformably in the lower part of the 
mass of ashes and fragments. This substance is of a reddish 'brovtri 
colour, with an almost metallic lustre ; it is not magnet- c, btit bo- 
comes so after having been heated under the blowpipe, by which it 
is blackened and partly fused. This seam of compact sccme, by 
intercepting the little rain-water which falls on the island, gives rise 
to a small dripping spring, first discovered by Dampier. It is the 
only fresh-water on the island, so that the possibility of its being in- 
habited has entirely depended on the occurrence of this f errugirioui 
layer. 



CHAP. m. Ejected Granitic Fragments. 47 

but of a much smaller size, frequently occur at the bases 
of small cones of eruption, 

Ejected granitic fragments. In the neighbour- 
hood of Green Mountain, fragments of extraneous rock 
are not unfrequently found embedded in the midst of 
masses of scoriae Lieut, Evans, to whose kindness 1 
am indebted for much information, gave me several 
specimens, and I found others myself. They nearly all 
have a granitic structure, are brittle, harsh to the touch, 
and apparently of altered colours. First, a white syenite, 
streaked and mottled with red } it consists of well 
crystallised feldspar, numerous grains of quartz, and 
brilliant, though small, crystals of hornblende. The 
feldspar and hornblende in this and the succeeding 
cases have been determined by the reflecting gonio- 
meter, and the quartz by its action under the blowpipe. 
The feldspar in these ejected fragments, like the glassy 
kind in the trachyte, is from its cleavage a potash- 
feldspar. Secondly, a brick-red mass of feldspar, quartz, 
and small dark patches of a decayed mineral; one 
minute particle of which I was able to ascertain, by its 
cleavage, to be hornblende. Thirdly, a mass of con- 
fusedly crystallised white feldspar, with little nests of a 
dark coloured mineral, often carious, externally rounded, 
having a glossy fracture, but no distinct cleavage ; from 
comparison with the second specimen, I have no doubt 
that it is fused hornblende. Fourthly, a rock, which 
at first appears a simple aggregation of distinct and 
large-sized crystals of dusky-coloured Labrador feldspar ; l 

1 Professor Miller has been so kind as to examine tins mineral. 
He obtained two good cleavages of 86 80' and 8(> GO'. The mean 
of several, which I made was8G 30' Prof. Miller states that these 
crystals, when reduced to a line powder, are soluble in hydrochloric 
acid, leaving some uodissolved silex behind ; the addition of oxalate 
of ammonia gives a copious precipitate ot lime. He further re- 
imrks, that according to Von Kobell, anrthite(a mineral occurring- 
In the ejected fragments at Mount h-cinna) is always white and 



48 Ascension. PART i. 

but in their interstices there is some vdiite granular 
feldspar, abundant scales of mica, a little altered horn- 
blende, and, as I believe, no quartz. I have described 
these fragments in detail, because it is rare 1 to find 
granitic rocks ejected from volcanos with their minerals 
unchanged, as is the case with the first specimen, and 
partially with the second. One other large fragment, 
found in another spot, is deserving of notice ; it is a 
conglomerate, containing small fragments of granitic, 
cellular, and jaspery rocks, and of hornstone porphyries, 
embedded in a base of wacke, threaded by numerous 
thin layers of a concretionary pitchstone passing into 
obsidian. These layers are parallel, slightly tortuous, 
and short; they thin out at their ends, and resemble in 
form the layers of quartz in gneiss. It is probable 
that these small embedded fragments were not separately 
ejected, but were entangled in a fluid volcanic rock, 
allied to obsidian ; and we shall presently see that 
several varieties of this latter series of rock assume a 
laminated structure. 

Tr achy tic series of rocks Those occupy the more 
elevated and' central, and likewise the south-eastern, 
parts of the island. The trachyte is generally of a pah*. 
brown colour, stained with small darker patches; it 
contains broken and bent crystals of glassy feldspar, 

transparent, so that if this be the case, these crystals from Ascension 
mast be considered as Labrador feldspar. Prof. Miller adds, that 
he has seen an account, m Erdmann's * Journal fur teehmsehe 
Chetme/ of a mineral ejected from a volcano, which had the external 
characters of Labrador feldspar, but differed in the analysis fiorn 
that given by mmeralogibtb of this mineral ; the author attributed 
this difference to an error m the analysis of Labrador teldpar 
which is very old 

1 Dauberry, in his work on Yolcanos (p, 3B9), remarks that this 
is the case; and Humboldt, in Ins * Personal Nanative* (vol. 1 
p. 2 i 6), says, * In general, the masses of known primitive rock,% I 
mean those which perfectly resemble our granites, gneihs, and mica- 
slate, are very rare in lavas the substances we generally denote by 
the name of granite, thrown out by Yebuvius, are mixtures* of 
nephelme, mica, and pyroxene.' 



CHAP. in. Trachytic Rocks. 49 

grains of specular iron, and black microscopical points, 
which latter, from being easily fused, and then becom- 
ing magnetic, I presume are hornblende. The greater 
number of the hills, however, are composed of a quite 
white, friable stone, appearing like a trachytic tuff 
Obsidian, hornstone, and several kinds of laminated 
feldspathic rocks, are associated with the trachyte. 
There is no distinct stratification ; nor could I distin- 
guish a crateriform structure in any of the hills of this 
series. Considerable dislocations have taken place; 
and many fissures in these rocks are yet left open, or 
are only partially filled with loose fragments. Withm 
the space, 1 mainly formed of trachyte, some basaltic 
streams have burst forth; and not far from the summit 
of Green Mountain, there is one stream of quite black, 
vesicular basalt, containing minute crystals of glassy 
feldspar, which have a rounded appearance. 

The soft white stone above mentioned is remarkable 
from its singular resemblance, when viewed in mass, to 
a sedimentary tuff: it was long before I could persuade 
myself that such was not its origin ; and other geologists 
have been perplexed by closely similar formations in 
trachytic regions. In two cases, this white earthy stone 
formed isolated hills ; in a third, it was associated with 
columnar and laminated trachyte ; but I was unable to 
trace an actual junction. It contains numerous crystals 
of glassy feldspar and black microscopical specks, and 
is marked with small darker patches, exactly as in the 
surrounding trachyte. Its basis, however, when viewed 
under the microscope, is generally quite earthy; but 
sometimes it exhibits a decidedly crystalline structure. 
On the hill marked c Crater of an old volcano,' it passes 

1 This space is nearly included by a line sleeping round Green 
Mountain, and joining the hills, called the Weather Fort Signal, 
lUlytiead, and that denominated (improperly in a geological sense) 
* the Orai er of an old volcano.' 



5<D Ascension. PAKT i, 

Into a pale greenish-gray variety, differing only in its 
colour, and in not being so earthy ; the passage was in 
one case effected insensibly ; in another, it was formed 
by numerous, rounded and angular, masses of the green- 
ish variety, being embedded in the white variety ; in 
this latter case, the appearance was very much like that 
of a sedimentary deposit, torn up and abraded during 
the deposition, of a subsequent stratum. Both these 
varieties are traversed by innumerable tortuous veins 
(presently to be described), which are totally unlike 
injected dikes, or indeed any other veins which I have 
ever seen. Both varieties include a few scattered frag- 
ments, large and small, of dark-coloured scoriaceons 
rocks, the cells of some of which are partially filled with 
the white earthy stone ; they likewise include some 
huge blocks of a cellular porphyry. 1 These fragments 
project from the weathered surface, and perfectly re- 
semble fragments embedded iu a true sedimentary tuff. 
But as it is known that extraneous fragments of cellu- 
lar rock are sometimes included in columnar trachyte, 
in phonolite, 2 and in other compact lavas, this circum- 
stance is not any real argument for the sedimentary 
origin of the white earthy stone. 3 The insensible 
passage of the greenish variety into the white ont% 
and likewise the more abrupt passage by fragments of 
the former being embedded in the latter, might result 

1 The porphyry is dark coloured ; it contains numerous, often 
fractured, crystals of white opaque feldspar, also decomposing 
crystals of oxide of iron ; its vesicles include masses of delicatu* 
hau -like, crystals, apparently of analcime. 

2 D'Aubuisson, * Traitg de Q-eognosie,' torn. ii. p. 648, 

3 Dr. Daubeny (on Volcanos, p. 180) seems to have "fcren led to 
believe that certain tr.tchy tic f 01 mations of Iscuia and of the Puy 
de D6me, which closely resemble these of Ascension, were of sedi- 
mentary origin, chiefly from the frequent presence in them *of 
sconf orm portions, different in. colour from t he matrix/ Dr. Dauben v 
adds, that on the other hand, Brocchi, and other eminent geologists, 
have considered these beds as earthy varieties of trachyte ; ho con- 
siders the subject deseiung of further attention. 



CHAP. in. Veins. 51 

from slight differences in the composition ,of the same 
mass of molten stone, and from the abrading action of 
one such part still fluid on another part already solidi- 
fied. The curiously formed veins have, I believe, been 
formed by siliceous matter being subsequently segre- 
gated. But my chief reason for believing that these 
soft earthy stones, with their extraneous fragments, are 
not of sedimentary origin, is the extreme improbability 
of crystals of feldspar, black microscopical specks, and 
small stains of a darker colour occurring in the same 
proportional numbers in an aqueous deposit, and in 
masses of solid trachyte. Moreover, as I have remarked, 
the microscope occasionally reveals a crystalline struc- 
ture in the apparently earthy basis, On the other 
hand, the partial decomposition of such great masses of 
trachyte, forming whole mountains, is undoubtedly a 
circumstance of not easy explanation. 

Veins in tlw ea/rtliy tracliytic masses. These veins 
are extraordinarily numerous, intersecting in the most 
complicated manner both coloured varieties of the 
earthy trachyte : they are best seen on the flanks of 
the ' Crater of the old volcano/ They contain crystals 
of glassy feldspar, black microscopical specks and little 
dark stains, precisely as in the surrounding rock ; but 
the basis is very different, being exceedingly hard, 
compact, somewhat brittle, and of rather less easy 
fusibility. The veins vary much, and suddenly, from 
the tenth of an inch to one inch in thickness ; they 
often thin out, not only on their edges, but in their 
central parts, thus leaving round, irregular apertures ; 
their surfaces are rugged., They are inclined at every> 
possible angle with the horizon, or are horizontal ; they^ 
'are generally curvilinear, and often ityterbranch onef * 
with another. From their hardness they withstand? 
weathering, and projecting two or three feet jabovQ thel 
5 



52 Ascension. 



ground, they occasionally extend some yards in length ; 
these plate-like veins, when struck, emit a sound, almost 
like that of a drum, and they may be distinctly seen to 
vibrate; their fragments, which are strewed on the 
ground, clatter like pieces of iron when knocked against 
each other. They often assume the most singular 
forms ; I saw a pedestal of the earthy trachyte, covered 
by a hemispherical portion of a vein, like a great 
umbrella, sufficiently large to shelter two persons. 1 
have never met with, or seen described, any veins like 
these ; but in form they resemble the ferruginous seams, 
due to some process of segregation, occurring not un- 
commonly in sandstones, for instance, in the New Red 
sandstone of England. Numerous veins of jasper and 
of siliceous sinter, occurring on the summit of this 
same hill, show that there has been some abundant 
source of silica, and as these plate-like veins differ from 
the trachyte only in their greater hardness, brittleness, 
and less easy fusibility, it appears probable that their 
origin is due to the segregation or infiltration of silice- 
ous matter, in the same manner as happens with the 
oxides of iron in many sedimentary rocks. 

SiUoecnis sinter and jasper. The siliceous sinter 
is either quite white, of little specific gravity, and with 
a somewhat pearly fracture, passing into pinkish pearly 
quartz ; or it is yellowish white, with a harsh fracture, 
and it then contains an earthy powder in small cavities. 
Both varieties occur, either in large irregular masses 
in the altered trachyte, or in seams included in broad, 
vertical, tortuous, irregular veins of a compact, harsh, 
stone of a dull red colour, appearing like a sandstone, 
This stone, however, is only altered trachyte; and a 
nearly similar variety, but often honeycombed, some- 
times adheres to the projecting plate-like veins, de- 
scribed in the last paragraph. The* jasper is of an oehre 



CHAP. m. Siliceous Sinter and Jasper* 53 

yellow or red colour ; it occurs in large irregular masses, 
and sometimes in veins, both in the altered trachyte 
and in an associated mass of scoriaceous basalt. , The 
cells of the scoriaceous basalt are lined or filled with 
fine, concentric layers of chalcedony, coated and studded 
with bright-red oxide of iron. In this rock, especially 
in the rather more compact parts, irregular angular 
patches of the red jasper are included, the edges of 
which insensibly blend into the surrounding mass; 
other patches occur having an intermediate character 
between perfect jasper and the ferruginous, decomposed, 
basaltic base. In these patches, and likewise in the 
large vein-like masses of jasper, there occur little 
rounded cavities, of exactly the same size and form 
with the air-cells, which in the scoriaceous basalt are 
filled and lined with layers of chalcedony. Small frag- 
ments of the jasper, examined under the microscope, 
seem to resemble the chalcedony with its colouring 
matter not separated into layers, but mingled in the 
siliceous paste, together with some impurities. I can 
understand these facts, namely, the blending of the 
jasper into the semi-decomposed basalt, its occurrence 
in angular patches, which clearly do not occupy pre- 
existing hollows in the rock, and its containing little 
vesicles filled with chalcedony, like those in the scori- 
aceous lava, only on the supposition that a fluid, 
probably the same fluid which deposited the chalcedony 
in the air-cells, removed in those parts where there 
were no cavities, the ingredients of the basaltic rock, 
and left in their place silica and iron, and thus pro- 
duced the jasper. In some specimens of silicified wood, 
I have observed, that in the same manner as in the 
basalt, the solid parts were converted into a dark- 
coloured homogeneous stone, whereas the cavities 
formed by the larger sap- vessels (which may be com- 



FAET L 



54 Ascension. 

pared with the air-Tesicles In the basaltic lava) and 
other it-regular hollows, apparently produced by decay, 
were filled with concentric layers of chalcedony ; in this 
case, there can be little doubt that the same fluid 
deposited the homogeneous base and the chalcedonic 
layers. After the ( se considerations, I cannot donbt but 
that the jasper of Ascension may be viewed as a volcanic 
rock silicified, in precisely the same sense as this terra 
is applied to wood, when silicified; we are equally 
ignorant of the means by which every atom of wood, 
whilst in a perfect state, is removed and replaced by 
atoms of silica, as we are of the means by which the 
constituent parts of a volcanic rock could be thus acted 
on. 1 I was led to the careful examination of these rocks, 
and to the conclusion here given, from having heard 
the Rev. Professor Henslow express a similar opinion, 
regarding the origin in trap-rocks of many chalcedonies 
and agates. Siliceous deposits seem to be very general, 
if not of universal occurrence, in partially decomposed 
trachytic tuffs ; 2 and as these hills, according to the 
view above given, consist of trachyte softened and 
altered in situ, the presence of free silica in this case 
may be added as one more instance to the list. 

Concretions in pwniceoiis tuff. The hill, marked 

' * Betidant ('Voyage en Hongrie,' torn, ili. pp. 602, 504) describes 
kidney-shaped masses of jasper-opal, which either blend into the 
surrounding trachytic conglomerate, or axe embedded in it like chalk- 
flints ;' and he comjpares them with the fragments of opalised wood, 
which are abundant in this same formation. Bettdant, however, 
appears to have viewed the process of their formation rather as one 
of simple infiltration than of molecular exchange ; but the prmmee 
of a concretion, wholly different from the surrounding matter, if not 
formed in a pre-existing hollow, clearly seems to me to require, either 
a molecular or mechanical displacement of the atoms, which ocou* 
pied the space afterwards filled by it. The jasper-opal of Hungary 
passes into chalcedony, and therefore in this case, as in that of Ascen- 
sion, jasper seems to be intimately related in origin with chalce40By+ 
2 Beudant ( Voyage Min/ 1pm. iii p. 507) enumerates in 

Hungary, Germany, Central Fiance, Italy, Greece, and Mexico* 



CHAP, in. Concretions in Pumice otts Tuff. 55 

In the map Crater of an old volcano/ has no claims to 
this appellation, which I could discover, except in being 
surmounted by a circular, very shallow^ saucer-like 
summit, nearly half a mile In diameter. This hollow 
has been nearly filled up with many successive sheets of 
ashes and scorige, of different colours, and slightly con- 
solidated. Each successive saucer-shaped layer crops 
out all round the margin, forming so many rings of 
various colours, and giving to the hill a fantastic 
appearance. The outer ring Is broad, and of a white 
colour ; hence it resembles a course round which horses 
have been exercised, and has received the name of the 
Devil's Eiding School, by which it is most generally 
known. These successive layers of ashes must have 
fallen over the whole surrounding country, but they 
have all been blown away except in this one hollow, 
in which probably moisture accumulated, either during 
an extraordinary year when rain fell, or during the 
storms often accompanying volcanic eruptions. One of 
the layers of a pinkish colour^ 'and chiefly derived 
from small, decomposed fragments of pumice, is remark- 
able, from containing numerous concretions. These 
are generally spherical, from half-an-inch to three 
inches in diameter ; but they are occasionally cjlis^ 
drical, like those of iron-pyrites in the chalk of Europe. 
They consist of a very tough, compact, pale-brown 
stone, with a smooth and even fracture. They are 
divided into concentric layers by thin white partitions, 
resembling the external superficies; six -or eight of 
such layers are distinctly defined near the outside j but 
those towards the inside generally become indistinct, 
and blend into a homogeneous mass. - 4 I presume that 
these concentric layers were formed by the shrinking of 
the concretion, as it became compact. The interior 
part is generally fissured by minute cracks or septaria 



56 Ascension, 



PABT 



which are lined, both by black, metallic, and by other 
white and crystalline specks, the nature of which I was 
unable to ascertain. Some of the larger concretions 
consist of a mere spherical shell, filled with slightly 
consolidated ashes. The concretions contain a small 
proportion of carbonate of lime: a fragment placed 
under the blowpipe decrepitates, then whitens and 
fuses into a blebby enamel, but does not become caustic, 
The surrounding ashes do not contain any carbonate of 
lime ; hence the concretions have probably been formed, 
as is so often the case, by the aggregation of this sub- 
stance. I have not met with any account of similar 
concretions ; and considering their great toughness and 
compactness, their occurrence in a bed, which probably 
has been subjected only to atmospheric moisture, is 
remarkable. 

Formation of calcareous rocks (m the sea-coast. 
On several of the sea-beaches, there are immense accu- 
mulations of small, well-rounded particles of shells and 
corals, of white, yellowish, and pink colours, inter- 
spersed with a few volcanic particles. At the depth of 
a few feet, these are found cemented together into 
stone, of which the softer varieties are used for build- 
ing; there are other varieties, both coarse and fine- 
grained, too hard for this purpose : and I saw one 
mass divided into even layers half-an-inch itx thickness, 
which were so compact that when struck with a hammer 
they rang like flint. It is believed by the inhabitants, 
that the particles become united in the course of a 
single year. The union is effected by calcareous 
matter ; and in the most compact varieties, each 
rounded particle of shell and volcanic rock can be dis-* 
tinctly seen to be enveloped in a husk of pellucid 
carbonate of lime. Extremely few perfect shells ara 
embedded in these agglutinated masses ; and I have 



CHAP. in. Recent Calcareous Formation. 57 

examined even a large fragment under a microscope s 
without being able to discover the last vestige of stri83 
or other marks of external form : this shows how long 
each particle must have been rolled about, before its 
turn canie to be embedded and cemented, 1 One of the 
most compact varieties, when placed in acid, was en- 
tirely dissolved, with the exception of some flocculent 
animal matter; Its specific gravity was 2'63. The 
specific gravity of ordinary limestone varies from 2*6 to 
275 ; pure Carrara marble was found by Sir H. De la 
Beche 2 to be 2'7. It is remarkable that these rocks of 
Ascension, formed close to the surface, should be nearly 
as compact as marble, which has undergone the action 
of heat and pressure in the plutonic regions. 

The great accumulation of loose calcareous particles, 
lying on the beach near the Settlement, commences in 
the month of October, moving towards the SW., which, 
as I was informed by Lieut. Evans, is caused by a change 
In the prevailing direction of the currents. At this period 
the tidal rocks, at the SW. end of the beach, where the 
calcareous sand is accumulating, and round which the 
currents sweep, become gradually coated with a calcare- 
ous incrustation, half-an-inch in thickness. It is quite 
white, compact, with some parts slightly spathose, and 
Is firmly attached to the rock. After a short time it 
gradually disappears, being either redissolved, when 
the water is less charged with lime, or more probably is 
mechanically abraded. Lieut. Evans has observed these 
facts, during the six years he has resided at Ascension. 
The incrustation varies in thickness in different years : 
in 1831 it was unusually thick. When I was there in 

1 The eggs of the turtle being burled by the parent, sometimes 
become enclosed in the solid rock. Mr. Lyell has given a figure 
( Principles of Geology/ book iii. ch. 17) of some eggs, containing 
the bones of young turtles, found thus entombed. 

2 * Besearches in Theoretical Geology/ p. 12. 



58 Ascension. 



PAET 



July, there was no remnant of the incrustation ; but on 
a point of basalt, from which the quarrymen had lately 
removed a mass of the calcareous freestone, the incrusta- 
tion, was perfectly preserved. Considering the position 
of the tidal rocks, and the period at which they become 
coated, there can be no doubt that the movement and dis- 
turbance of the vast &ccomulation of calcareous particles, 
many of them being partially agglutinated together^ 
cause the waves of the sea to be so highly charged 
with carbonate of lime, that they deposit it on the first 
objects against which they impinge. I have been in- 
formed by Lieut. Holland, E.N., that this incrastar 
tion is formed on many parts of the coast, on most of 
which, I believe, there are likewise great masses of 
comminuted shells. 

A frondescent calcareous incrustation.-^!*! many 
respects this is a singular deposit ; it coats through- 
out the year the tidal volcanic rocks, that project from 

No. 5. 






.An incrustation of calcareous and animal matter, coating the tidal roote at 
Ascension. 

the beaches composed of broken shells. Its general 
appearance is well represented in the accompanying 
woodcut j but the fronds or disks, of which it is com- 



CHAJP. in. Calcareous Incrustation, 59 

posed, are generally so closely crowded together as to 
touch. These fronds have their <sinuous edges finely 
crenulated, and they project over their pedestals or 
supports ; their upper surfaces are either slightly con- 
cave, or slightly convex ; they are highly polished, and 
of a dark gray or jet black colour ; their form is irre- 
gular, generally circular, and from the tenth of an inch 
to one inch and a-half in diameter ; their thickness, or 
amount of their projection from the rock on which they 
stand, varies much, about a quarter of an inch being per- 
haps most usual. The fronds occasionally become more 
and more convex, until they pass into botryoidal massea 
with their summits fissured ; when in this state, they are 
glossy and of an intense black, so as to resemble some 
fused metallic substance. I h ave shown the incrustation, 
both in this latter and in its ordinary state to several 
geologists, but not one could conjecture its origin, except 
that perhaps it was of volcanic nature ! 

The substance forming the fronds has a very com- 
pact and often almost crystalline fracture; the edges 
being translucent, and hard enough easily to scratch 
calcareous spar. Under the blowpipe it immediately be- 
comes white, and emits a strong animal odour, like that 
from fresh shells. It is chiefly composed of carbonate 
of lime ; when placed in muriatic acid it froths much, 
leaving a residue of sulphate of lime, and of an oxide of 
iron, together with a black powder, which is not soluble 
in heated acids. This latter substance seems to be car- 
bonaceous, and is evidently the colouring matter. The 
sulphate of lime is extraneous, and occurs in distinct, 
excessively minute, lamellar plates, studded on the sur- 
faces of the fronds, and embedded between the fine 
layers of which they are composed ; when a fragment is 
heated in the blowpipe, these lamellae are immediately 
rendered visible* The original outline of the fronds 



60 Ascension. BABT x. 

may often be traced, either to a minute particle of shell 
fixed in a crevice of the rock, or to several cemented 
together; these first become deeply corroded, by the 
dissolving power of the waves, into sharp ridges, and 
then are coated with successive layers of the glossy, 
gray, calcareous incrustation. The inequalities of the 
primary support affect the outline of every successive 
layer, in the same manner as may often be seen in 
bezoar-stones, when an object like a nail forms the 
centre of aggregation. The crenulated edges, how- 
ever, of the frond appear to be due to the corroding 
power of the surf on its own deposit, alternating with 
fresh depositions. On some smooth basaltic rocks on 
the coast of St. Jago, I found an exceedingly thin layer 
of brown calcareous matter, which under a lens pre- 
sented a miniature likeness of the crenulated and 
polished fronds of Ascension ; in this case a basis was 
not afforded by any projecting extraneous particles. 
Although the incrustation at Ascension is persistent 
throughout the year ; yet from the abraded appearance 
of some parts, and from the fresh appearance of other 
parts, the whole seems to undergo a round of decay 
and renovation, due probably to changes in the form 
of the shifting beach, and consequently in the action 
of the breakers : hence probably it is, that the incrusta- 
tion never acquires a great thickness. Considering the 
position of the incrusted rocks in the midst of the cal- 
careous beach, together with its composition, I think: 
there can be no doubt that its origin is due to the dis- 
solution and subsequent deposition of the matter com- 
posing the rounded particles of shells aud corals. 1 

1 The selenite, as I have remarked, is extraneous, and must have 
been derived from the sea-water. It is an interesting circam*tano6 
thus to find the waves of the ocean, sufficiently charged with sul- 
phate of lime, to deposit it on the rocks, agamst winch they 
every tide. Dr. Webster has described ('Voyage of the 



CHAP. m. Calcareous Incrustation. 6 1 

From this source it derives its animal matter, which 
is evidently the colouring principle. The nature of 
the deposit, in its incipient stage, can often be well 
seen upon a fragment of white shell, when jammed be- 
tween two of the fronds ; it then appears exactly like 
the thinnest wash of a pale gray varnish. Its darkness 
varies a little, but the jet blackness of some of the 
fronds and of the botryoidal masses seems due to the 
translucency of the successive gray layers. There iSj 
however, this singular circumstance, that when de- 
posited on the under side of ledges of rock or in fissures, 
it appears always to be of a pale, pearly gray colour, 
6ven when of considerable thickness : hence one is led 
to suppose, that an abundance of light is necessary to 
the development of the dark colour, in the same 
manner as seems to be the case with the upper and ex- 
posed surfaces of the shells of living mollusca, which 
are always dark, compared with their under surfaces 
and with the parts habitually covered by the 'mantle of 
the animal. In this circumstance, in the immediate 
loss of colour and in the odour emitted under the blow- 
pipe, in the degree of hardness and translucency of 
the edges, and in the beautiful polish of the surface, 1 
rivalling when in a fresh state that of the finest Oliva, 
there is a striking analogy between this inorganic in- 



cleer," ' vol. ii. p. 319) beds of gypsum and salt, as much as two feet 
in thickness, left by the evaporation of the spray on the rocks on 
the windward coast. Beautiful stalactites of selenite, resembling 
in form those of carbonate of lime, are formed near these beds. 
Amorphous masses of gypsum, also, occur in caverns in the interior 
of the island ; and at Cross HiU (an old crater) I saw a considerable 
quantity of salt oozing from a pile of scoriae In these latter cases, 
the salt and gypsum appear to be volcanic products. 

1 From the fact described in my * Journal of ^Researches' (p. 12), 
of a coating of oxide of iron, deposited by a streamlet on the rocks 
in its bed (like a nearly similar coating at the great cataracts of the 
Orinooco and Nile), becoming finely polished where the surf acts, I 
presume that the surf in this instance, also, is the polishing agent. 



62 Ascension, 



PART L 



crastation and the shells of living molluscous animals. 1 
This appears to me to b an interesting physiological 
fact. 2 

Singula/r laminated beds alternating with and 
passing into obsidian. These beds occur within the 
trachytic district, at the western base of Green Mountain, 
under which they dip at a high inclination. They are 
only partially exposed, being covered up by modern 
ejections; from this cause, I was unable to trace their 
junction with the trachyte, or to discover whether they 
had flowed as a stream of lava, or had been injected 
amidst the overlying strata. There are three principal 
beds of obsidian, of which the thickest forms the base 
of the section. The alternating stony layers appear to 
me eminently curious, and shall be first described, and 
afterwards their passage into the obsidian. They have 
an extremely diversified appearance ; five principal 
varieties may be noticed, but these insensibly blend 
into each other by endless gradations. 

First, A pale gray, irregularly and coarsely lami- 
nated, 3 harsh- feeling rock, resembling clay-slate which, 

1 In tlie section descriptive of St. Paul's Bocks, I have describe*! 
a glossy, pearly substance, which coats the rocks, and an allied 
stalactitical ID crustation from Ascension, the crust of which re- 
sembles the enamel of teeth, but is hard enough to scratch plate 
glass, Both these substances contain animal matter, and seem to 
have been derived from water infiltering through birds* dung, 

2 Mr. Horner and Sir David Bre water have described (* Philo- 
sophical Transactions,' 1884, p. 66) a singular * artificial suManco, 
resembling shell.' It is deposited in fine, transparent, highly- 
polished, brown-coloured laminae, possessing peculiar optical pro- 
perties, on the inside of a vessel, in which cloth, first prepared with 
glue and then with lime, is made to revolve rapidly in water. It is 
much softer, more transparent, and contains more animal matter, 
than the natural incrustation at Ascension; but wo here again gid 
the strong tendency which carbonate of lime and animal matter 
evince to form a solid substance allied to shell* 

8 This term is open to some misinterpretation* as it may be applied 
both to rocks divided into laminae of exactly the same composition, 
and to layers firmly attached to each other, with DO fisnile tendency, 
but composed of different minerals, or of different shades of ooloar* 



, ni. Obsidian Formation* 63 

has been In .contact with a trap-dike, and with a frac- 
ture of about the same degree of crystalline structure. 
This rock, as well as the following varieties, easily fuse 
into a pale glass. The greater part is honey-combed 
with irregular, angular, cavities, so that the whole has 
a curious appearance, and some fragments resemble in 
a remarkable manner silicified logs of decayed wood. 
This variety, especially where more compact, is often 
marked with thin whitish streaks, which are either 
straight or wrap round, one behind the other, the elon- 
gated carious hollows. 

Secondly, A bluish gray or pale brown, compact, 
heavy, homogeneous stone, with an 'angular, uneven, 
earthy fracture ; viewed, however, tinder a lens of high 
power, the fracture is seen to be distinctly crystalline, 
and even separate minerals can be distinguished. 

Thirdly, A stone of the same kind with the last, 
but streaked with numerous, parallel, slightly tortuous, 
white lines of the thickness of hairs. These white lines 
are more crystalline than the parts between them ; and 
the stone splits along them : they frequently expand 
into exceedingly thin cavities, which are often only 
just perceptible with a lens* -The mate- forming the 
white lines becomes better crystallised in theee cavities, 
and Prof. Miller was fortunate enough, after Several 
trials, to ascertain that the white crystals, which are the 
largest, were of quartz, 1 and that the minute green trans- 
parent needles were augite, or, as they would more 
generally be called, diopsicle : besides these crystals, 
there are some minute, dark specks without a trace of 

The term * laminated,' in this chapter, is applied in these latter 
senses ; where a homogeneous rook splits, as in the former sense, in 
a given direction, like clay-slate, I have used the term * fissile.' 

1 Professor Miller informs me that the crystals which he measured 
had the faces P, 2, m of the figure (14:7) given by Haidtnger in his 
Translation of Mohs : and he adds, that it is remarkable, that none of 
them had the slightest trace of faces r of the regular six-sided prism. 



64 Ascension. PART L 

crystallisation, and some fine, white, granular, crystal- 
line matter which is probably feldspar. Minute frag- 
ments of this rock are easily fusible. 

Fourthly, A compact crystalline rock, banded in 
straight lines with innumerable layers of white and 
gray shades of colour, varying in width from the ^-th 
to the g-f-frth of an inch ; these layers seem to be com- 
posed chiefly of feldspar, and they contain numerous 
perfect crystals of glassy feldspar, which are placed 
lengthways ; they are also thickly studded with micro- 
scopically minute, amorphous, black specks, which are 
placed in rows, either standing separately, or more 
frequently united, two or three or several together, into 
black lines, thinner than a hair, When a small frag- 
ment is heated in the blowpipe, the black specks are 
easily fused into black brilliant beads, which become 
magnetic, characters that apply to no common mineral 
except hornblende or augite. With the black specks 
there are mingled some others of a red colour, which are 
magnetic before being heated, and no doubt are oxide 
of iron. Round two little cavities, in a specimen of 
this variety, I found the black specks aggregated into 
minute crystals, appearing like those of augite or horn- 
blende, but too dull and small to be measured by the 
goniometer ; in this specimen, also, I could distinguish 
amidst the crystalline feldspar, grains, which had the 
aspect of quartz. By trying with a parallel ruler, I 
found that the thin gray layers and the black hair-like 
lines were absolutely straight and parallel to each 
other. It is impossible to trace the gradation from th 
homogeneous gray rocks to these striped varieties, or 
indeed the character of the different layers in the same 
specimen, without feeling convinced that the more or 
less perfect whiteness of th crystalline feld&pathic 
matter depends on the more or less perfect aggregation 



CHAP. m. Obsidian Formation. 65 

of diffused matter. Into tlie black and red specks of 
hornblende and oxide of iron. 

Fifthly, A compact heavy rock, not laminated, 
with an irregular, angular, highly crystalline, fracture ; 
it abounds with distinct crystals of glassy feldspar, and 
the crystalline feldspathic base is mottled with a black 
mineral, which on the weathered surface is seen to be 
aggregated into small crystals, some perfect, but the 
greater number imperfect. I showed this specimen to 
an experienced geologist, and asked him what it was, 
he answered, as I think every one else would have done, 
that it was a primitive greenstone. The weathered 
surface, also, of the foregoing (So. 4) banded variety, 
strikingly resembles a worn fragment of finely laminated 
gneiss. 

These five varieties, with many intermediate ones, 
pass and repass into each other. As the compact 
varieties are quite subordinate to the others, the whole 
may be considered as laminated or striped. The laminae, 
to sum np their characteristics, are either quite straight, 
or slightly tortuous, or convoluted ; they are all parallel 
to each other, and to the intercalating strata of obsidian; 
they are generally of extreme thinness; they consist 
either of an apparently homogeneous, compact rock, 
striped with different shades of gray and brown colours, 
or of crystalline feldspathic layers in a more or less 
perfect state of purity, and of different thicknesses, with 
distinct crystals of glassy feldspar placed lengthways, or 
of Tery thin layers chiefly composed of minute crystals 
of quartz and augite, or composed of black and red 
specks of an augitic mineral and of an oxide of iron, 
either not crystallised or imperfectly so. After having 
fully described the obsidian, I shall return to the subject 
of the lamination of rocks of the trachytic series. 

The passage of the foregoing beds into the strata of 



66 Ascension. PABT i, 

glassy obsidian is effected in several ways : first, angulo 
nodular masses of obsidian, both large and small, 
abruptly appear disseminated in a slaty, or in an amor- 
phous, pale-coloured feldspathic rock, with a somewhat 
pearly fracture. Secondly, small irregular nodules of 
the obsidian, either standing separately, or united into 
thin layers, seldom more than the tenth of an inch 
in thickness, alternate repeatedly with very thin layers 
of a feldspathic rock, which is striped with the finest 
parallel zones of colour, like an agate, and which some- 
times passes into the nature of pitclistone ; the interstices 
between the nodules of obsidian are generally filled by 
soft white matter, resembling pumiceous ashes. Thirdly, 
the whole substance of the bounding rock suddenly 
passes into an angulo-concretionary mass of obsidian. 
Such masses (as well, as the small nodules) of obsidian 
are of a pale green colour, and are generally streaked 
with different shades of i colour, parallel to the laminae 
of the surrounding rock ; they likewise generally con- 
tain minute white sphserulites, of which half is some- 
times embedded in a zone of one shade of colour, and 
half in a zone of another shade. The obsidian assumes 
its jet black colour and perfectly conchoidal fracture, 
only when in large masses ; but even in these, on careful 
examination and -on holding the specimens ia different 
lights, I could generally distinguish parallel streaks of 
different shades of darkness. 

On of the commonest transitional rocks deserves in 
several respects a further description. It is of a very 
complicated nature, and consists of numerous thin, 
slightly tortuous, layers of a , pale-coloured feldspathic 
stone, often passing into an imperfect pitchstone, alter- 
nating with layers formed of numberless little globules 
of two Tarieties of obsidian, and of two kinds of sphas- 
rulites, embedded in a- soft or in a hard pearly base. 



CHAP, in. Obsidian Formation. 67 

The sphseruhtes are either wMte and translucent, or 
dark brown and opaque ; the former are quite spherical, 
of {small size, and distinctly radiated from their centre. 
The dark brown sphgerulites are less perfectly round, 
and vary in diameter from the -^-th to -g-^-th of an inch ; 
when broken they exhibit towards their centres, which 
are whitish, an obscure radiating structure ; two of 
them when united, sometimes have only one central 
point of radiation ; there is occasionally a trace of a 
hollow or crevice in their centres. They stand either 
separately, or are united two or three or many together 
into irregular groups, or more commonly into layers, 
parallel to the stratification of the mass. This union 
in many cases is so perfect, that the two sides of the 
layer thus formed, are quite even ; and these layers, as 
they become less brown and opaque, cannot be distin- 
guished from the alternating layers of the pale-coloured 
feldspathic stone. The sphseruhtes, when not united, 
are generally compressed in the plane of the lamination 
of the mass ; and in this same plane, they are often 
marked internally, by zones of different shades of 

No 6. 




Opaque brown sphserulites, drawn on an enlarged scale. The upper ones are ex- 
ternally marked with parallel ridges The internal radiating structure of the 
lower ones, is much too plainly represented. 

colour, and externally by small ridges and furrows. In 
the upper part of the accompanying woodcut, the 



68 Ascension. 



PAET I. 



sphserulites with, the parallel ridges and furrows are 
represented on an enlarged scale, but they are not well 
executed ; and in the lower part, their usual manner of 
grouping is shown. In another specimen, a thin layer 
formed of the brown spheerulites closely united together, 
intersects, as represented in the woodcut, No. 7 a layer 

No. 7 




A layer formed by the union of mmute brown sphaerulites, intersecting two other 
similar layers the whole represented of nearly the natural size 

of similar composition ; and after running for a short 
space in a slightly curved line, again intersects it, and 
likewise a second layer lying a little way beneath that 
first intersected. The small nodules also of obsidian are 
sometimes externally marked with ridges and furrows, 
parallel to the lamination of the mass, but always less 
plainly than the sphserulites. These obsidian nodules 
are generally angular, with their edges blunted : they 
are often impressed with the form of the adjoining 
sphaerulites, than which, they are always larger; the 
separate nodules seldom appear to nave drawn each other 
out by exerting a mutual attractive force. Had I not 
found in some cases, a distinct centre of attraction in 
these nodules of obsidian, I should have been led to 
have considered them as residuary matter, left during 
the formation of the pearlstone, in which they are 
embedded, and of the sphserulitic globules. 

The sphferulites and the little nodules of obsidian 
in these rocks so closely resemble, in general form and 



CHAP. in. Obsidian Formation* 69 

structure, concretions in sedimentary deposits, that one 
is at once tempted to attribute to them an analogous 
origin. They resemble ordinary concretions in the 
following respects : in their external form, in the union 
of two or three, or of several, into an irregular mass, or 
into an even-sided layer, in the occasional intersection 
of one such layer by another, as in the case of chalk- 
flints, in the presence of two or three kinds of nodules, 
often close together, in the same basis, in their fibrous, 
radiating structure, with occasional hollows in their 
centres, in the co-existence of a laminary, concretionary, 
and radiating structure, as is so well developed in the 
concretions of magnesian limestone, described by Pro- 
fessor Sedgwick. 1 Concretions in sedimentary deposits, 
it is known, are due to the separation from the sur- 
rounding mass of the whole or part of some mineral 
substance, and its aggregation round certain points of 
attraction. Guided by this fact, I have endeavoured 
to discover whether obsidian and the sphasrulites (to 
which ID ay be added marekanite and pearlstone, both 
of them occurring in nodular concretions in the trachytic 
series) differ in their constituent parts, from the minerals 
generally composing trachytic rocks. It appears from 
three analyses, that obsidian contains on an average 76 
per cent, of silica ; from one analysis, that sphserulites 
contain 79*12 ; from two, that marekanite contains 
79*25 ; and from two other analyses, that pearlstone 
contains 75'62 of silica. 2 Now, the constituent parts 
of trachyte, as far as they can be distinguished, consist 
of feldspar, containing 65*21 of silica ; or of albite, con- 
taining 69*09 ; of hornblende, containing 55*27, 3 and of 

1 ' Geological Transactions,' vol. iii part i. p 37. 

2 The foregoing analyses aie taken from Beudant, ' Trait e" de 
Mne*ralogie,' torn li p. 113 ; and one analysis of ob:idian, from 
Phillips *s * Mineralogy/ 

8 These analyses are taken from Von Kobell's * Grundziige der 
Mineralogie,' 1838. 



7O Ascension. PAET i. 

oxide of iron: so that the foregoing glassy concre- 
tionary substances all contain a larger proportion of 
silica than that occurring in ordinary feldspathic or 
trachytic rocks. D'Aubuisson, 1 also, has "remarked on 
the large proportion of silica compared with alumina, 
in sis analyses of obsidian and pearlstone given in 
Brongniart's l Mineralogy/ Hence I conclude, that the 
foregoing coiici'etions have been formed by a process of 
aggregation, strictly analogous to that which takes 
place in aqueous deposits, acting chiefly on the silica, 
but likewise on some of the other elements of the sur- 
rounding mass, and thus producing the different con- 
cretionary varieties. Prom the well-known effects of 
rapid cooling 2 in giving glassiness of texture, it is 
probably necessary that the entire mass, in cases like 
that of Ascension, should have cooled at a certain rate; 
but considering the repeated and complicated alterna- 
tions of nodules and thin layers of a glassy texture 
with other layers quite stony or crystalline, all within 
the space of a few feet or even inches, it is hardly 
possible that they could have cooled at different rates, 
and thus have acquired their different textures. 

The natural sphserulites in these rocks 3 very closely 

1 * Trait6 de G6ogn ' torn li. p. 535. 

2 This is seen in the manufacture of common glass, and in 
Gregory Watts's experiments on molten trap; also on the natural 
surfaces of lava-streams, and on the side-walls of dikes. 

3 I do not knowwhether it is generally known, that bodies having 
exactly the same appearance as sphaerulites, sometimes occm in 
agates. Mr. Kobert Brown showed me in an agate, formed withm 
a cavity in a piece of silicified wood, some little specks, which were 
only just visible to the naked eye : these specks, when placed by 
Mm under a lens of high power, piesented a beautiful appearance : 
they were perfectly circular, and consisted of the finest fibres of a 
brown colour, radiating with great exactness from a common centre. 
These little radiating stars are occa ion ally intersected, and portions 
are quite cut off by the fine, ribbon-like zones of colour in the agate. 
In the obsidian of Ascension, the halves of a sphasruhfce often lie in 
different zones of colour, but they are not cut off by them, as in the 
agate. 



CHAP. m. Obsidian Formation. 7 1 

resemble those produced In glass, when slowly cooled. 
In some fine specimens of partially de vitrified glass, 
in tlie possession of Mr. Stokes, the sphgerulites are 
united into straight layers with even sides, parallel to 
each other, and to one of the outer surfaces, exactly as 
in the obsidian. These layers sometimes interbranch 
and form loops ; but I did not see any case of actual 
intersection. They form the passage from the perfectly 
glassy portions, to those nearly homogeneous and stony, 
with only an obscure concretionary structure. In the 
same specimen, also, sphaerulites differing slightly in 
colour and in structure, occur embedded close together. 
Considering these facts, it is some confirmation of the 
view above given of the concretionary origin of the 
obsidian and natural spheerulites, to find that M. Dar- 
tigues, 1 in his curious paper on this subject, attributes 
the production of sphserulites in glass, to the different 
ingredients obeying their own laws of attraction and 
becoming aggregated. He is led to believe that this 
takes place, from the difficulty in renielting sphaerulitic 
glass, without the whole be first thoroughly pounded 
and mixed together; and likewise from the fact, that 
the change takes place most readily in glass composed 
of many ingredients. In confirmation of M. Dartigues' 
view, I may remark, that M. Fleurian de Bellevue 2 
found that the sphserulitic portions of devitrified glass 
were acted on both by nitric acid and under the blow- 
pipe, in a different manner from the compact paste in 
which they were embedded. 

Comparison of the olsidian "beds and alternating 
strata of Ascension, with those of other countries. 
I have been struck with much surprise, how closely the 
excellent description of the obsidian rocks of Hungary, 

1 * Journal de Physique,' ton. 59 (1804), pp. 10, 12. 
8 Idem, torn. 60 (1805), p. 418. 



7 2 Ascension. PART x. 

given by Beudant, 1 and that by Hianboldt, of the same 
formation in Mexico and Peru, 2 and likewise the descrip- 
tions given by several authors 3 of the trachytic regions 
in the Italian islands, agree with my observations at 
Ascension. Many passages might have been transferred 
without alteration from the works of the above authors, 
and would have been applicable to this island. They 
all agree in the laminated and stratified character of 
the whole series ; and Humboldt speaks of some of the 
beds of obsidian being ribboned like jasper. 4 They all 
a^ree in the nodular or concretionary character of the 
obsidian, and of the passage of these nodules into layers. 
They all refer to the repeated alternations, often in un- 
dulat ory planes, of glassy, pearly, stony, and crystalline 
layers : the crystalline layers, however, seem to be much 
more perfectly developed at Ascension, than in the 
above-named countries. Humboldt compares some of 
the stony beds, when viewed from .a distance, to strata 
of a schistose sandstone. Sphserulites are described as 
occurring abundantly in all cases ; and they everywhere 

1 * Voyage en Hongrie,' torn, i p. 330 ; torn. ii. pp. 221 and 315 ; 
torn. iii. pp 36S>, 371, 377, 381 

2 'Essai Geognostique,' pp 176, 326, 328. 

3 P. Scrope, in * Geological Transactions,' vol. ii. (second series) 
p 195. Consult, alto, Dohmieu's * Voyage aux Isles Lipari,' and 
D'Aubuisson, *Trait6 de Geogn.' torn. n. p. 534. 

4 In Mr. Stokes' fine collection of obsidians from Mexico, I 
observe that the sphaerulites are generally much larger than those of 
Ascension; they are generally white, opaque, and are united into 
distinct layers- there are many singular varieties, different from 
any at Ascension. The obsidians are finely zoned* in quite straight 
or curved lines, with exceedingly slight differences of tint, of 
cellular ity, and of more or less perfect degrees of glassme'ss. Tracing- 
some of the less perfectly glassy zones, they are seen to become 
studded with minute white sphseruhtes, which become more and 
more numerous, until at last they unite and form a distinct layer : 
on the other hand, at Ascension, only the brown sphasralitos unite 
and form layers; the white ones always being irregularly dis- 
seminated. Some specimens at the Geological Society, said to 
belong to an obsidian foiniation from Mexico, have an earthy frac- 
ture, and are divided in the finest parallel larninse, by specks of a 
black mineral, like the augitic or hoinblendic specks in the rocks at 
Ascension. 



CHAP. in. Obsidian Formation. 73 

seem to mark the passage, from the perfectly glassy to 
the stony and crystalline beds. * Beudant's account * of 
his * perlite lithoide globnlaire ' in every, even the 
most trifling particular, might have been written for 
the little brown sphaerulitic globules of the rocks of 
Ascension. 

From the close similarity in so many respects, be- 
tween the obsidian formations of Hungary, Mexico, 
Peru, and of some of the Italian islands, with that of 
Ascension, I can hardly doubt that in all these cates, 
the obsidian and the sphserulites owe their origin to a 
concretionary aggregation of the silica, and of some of 
the other constituent elements, taking place whilst the 
liquefied mass cooled at a Certain required rate. It is, 
however, well known, that in several places, obsidian 
has flowed in streams like lava ; for instance, at Teneriffe, 
at the Lipari Islands, and at Iceland. 2 In these cases, 
the superficial parts are the most perfectly glassy, the 
obsidian passing at the depth of a few feet into an opaque 
stone. In an analysis by Yauquelin of a specimen of 
obsidian from Hecla, which probably flowed as lava, the 
pioportion of silica is nearly the same as in the nodular 
or concretionary obsidian from Mexico. It would be 
interesting to ascertain, whether the opaque interior 
portions and the superficial glassy coating contained 
the same proportional constituent parts : we know from 
M. Dufrenoy 3 that the exterior and interior parts of 
the same stream of lava sometimes differ considerably 
in their composition. Even should the whole body ol 
the stream of obsidian turn out to be similarly com- 

1 Beudant's * Voyage,' torn, iii p. 373 

2 For Teneriffe, see Von Buch, * Descript des Isles Canaries,' pp. 
184 and 190 , for the Lipari Islands, see Dolimieu's ' Voyage,' p. 34 j 
for Iceland, see Mackenzie's * Travels,' p. 369. 

9 * M&noires pour servir & une Descript. Ge"olog. dc la France," 
fcom. iv p. 371. 



74 Ascension. PAET i. 

posed with nodular obsidian, it would only be necessary, 
in accordance with the foregoing facts, to suppose that 
lava in these instances had been erupted with its ingre- 
dients mixed in the same proportion, as in the concre- 
tionary obsidian. 

Lamination of volcanic rocks of fke trachytic series. 

We have seen that, in several and widely distant 
countries, the strata alternating with beds of obsidian, 
are highly laminated. The nodules, also, both large 
and small, of the obsidian, are zoned with different 
shades of colour; and I have seen a specimen from 
Mexico in Mr. Stokes' collection, with its external 
surface weathered l into ridges and furrows, correspond- 
ing with the zones of different degrees of glassiness : 
Humboldt, 2 moreover, found on the Peak of Teneriffe, 
a stream of obsidian divided by very thin, alternating, 
layers of pumice. Many other lavas of the feldspathic 
series are laminated ; thus, masses of common trachyte 
at Ascension are divided by fiae earthy lines, along 
which the rock splits, separating thin layers of slightly 
different shades of colour ; the greater number, also, of 
the embedded crystals of glassy feldspar are placed 
lengthways in the same direction. Mr. P. Scrope 3 has 
described a remarkable columnar trachyte in the 
Panza Islands, which seems to have been injected into 
an overlying mass of trachytic conglomerate: it is 
striped with zones, often of extreme tenuity, of dif- 
ferent textures and colours; the harder and darker 

1 MacCulloch states ( Classification of Books/ p. 5S1), that the 
exposed surfaces of the pitchstone dikes in Arran are furrowed, 
'with undulating lines, resembling certain varieties of marbled 
paper, and which evidently result from some corresponding diifeience 
of laminar structure.' 

2 * Personal Narrative/ vol. i. p. 222. 

* ' Geological Transactions/ vol. u (second series) p. 195. 



CHAP. in. Lamination of Trachytic Rocks. 75 

zones appearing to contain a larger proportion of silica. 
In another part of the island, there are layers of pearl- 
stone and pitchstone, which in many respects resemble 
those of Ascension. The zones in the columnar trachyte 
are generally contorted; they extend uninterruptedly 
for a great length in a vertical direction, and apparently 
parallel to the walls of the dike-like mass. Von Buch 1 
has described at Teneriffe, a stream of lava containing 
innumerable, thin, plate-like crystals of feldspar, which 
are arranged like white threads, one behind the other,, 
and which mostly follow the same direction. Dolimieu 2 
also states, that the gray lavas of the modern cone of 
Vulcano, which have a vitreous texture, are streaked 
with parallel white lines : he further describes a solid 
pumice-stone which possesses a fissile structure, like 
that of certain micaceous schists. Phonolite, which I 
may observe is often, if not always, an injected rock, 
also, often has a fissile structure ; this is generally due 
to the parallel position of the embedded crystals of 
feldspar, but sometimes, as at Fernando Noron ha, seems 
to be nearly independent of their presence, 3 From 
these facts we see, that various rocks of feldspathic 
series have either a laminated or fissile structure, and 
that it occurs both in masses, which have been injected 
into overlying strata, and in others which have flowed 
as streams of lava. 

The laminae of the beds, alternating with the obsi- 
dian at Ascension, dip at a high angle under the moun- 

1 * Description des lies Canaries,' p 184. 

" * Yoyage aux Isles de Lipari,' pp. 35 and 85. 

8 In this case, and in that of the fissile pumice-stone, the struc- 
ture is very different from that in the foregoing cases, where the 
laminae consist of alternate layers of different composition or texture. 
In some sedimentary formations, however, which apparently are 
homogeneous and fissile, as in glossy clay-slate, theie is reason TO 
believe, according to D'Aubuisson, that the laminae are really due to 
excessively thin, alternating, layers of mica. 



76 Lamination of Volcanic Rocks PART i, 

tain, at the base of which they are situated ; and they 
do not appear as if they had been inclined by violence. 
A high inclination is common to these beds in Mexico, 
Peru, and in some of the Italian islands : J on the other 
hand, in Hungary, the layers are horizontal ; the 
laminse, also, of some of the lava-streams above referred 
to, as far as I can understand the descriptions given 
of them, appear to be highly inclined or vertical. I 
doubt whether in any of these cases, the laminse have 
been tilted into their present position; and in some 
instances, as in that of the trachyte described by Mr. 
Scrope, it is almost certain that they have been origin- 
ally formed with a high inclination. In many of these 
cases, there is evidence that the mass of liquefied rock 
has moved in the direction of the laminae. At Ascen- 
sion, many of the air-cells have a drawn-out appearance, 
and are crossed by coarse semi-glassy fibres, in the 
direction of the laminae ; and some of the layers, sepa- 
rating the sphserulitic globules, have a scored appear- 
ance, as if produced by the grating of the globules. I 
have seen a specimen of zoned obsidian from Mexico, 
in Mr. Stokes 3 collection, with the surfaces of the best- 
defined layers streaked or furrowed with parallel lines ; 
and these lines or streaks precisely resembled those, 
produced on the surface of a mass of artificial glass by 
its having been poured out of a vessel. Humbolcltj 
also, has described little cavities, which he compares to 
the tails of comets, behind spkaerulites in laminated obsi- 
dian rocks from Mexico, and Mr. Scrope has described 
other cavities behind fragments embedded in Ms lami- 
nated trachyte, and which, he supposes to have been 

1 See PMlhps's * Mineralogy/ for the Italian Islands, p. 13ft. 
For Mexico and Peru, see Humboldt's ' Essai Ge'ognostique,' Mr. 
Edwards, also, describes the high lochnation of the obsidian rooks 
of the Qerro del Navaja in Mexico, in the ' Proc. of the Gfeolog. Soc. 1 
for June, 1838. 



CHAP, m. of the Tr achy tic Series. 77 

produced during the movement of the mass. 1 Prom 
such facts, most authors have attributed the lamination 
of these volcanic rocks to their movement whilst lique- 
fied. Although it is easy to perceive, why each separate 
air-cell, or each fibre in pumice-stone, 2 should be drawn 
out in the direction of the moving mass ; it is by no 
means at first obvious why such air-cells and fibres 
should be arranged by the movement, in the same 
planes, in laminae absolutely straight and parallel to 
each other, and often of extreme tenuity ; and still less 
obvious is it, why such layers should come to be of 
slightly different composition and of different textures. 
In endeavouring to make out the cause of the 
lamination of the igneous feldspathic rocks, let us 
return to the facts so minutely described at Ascension, 
We there see, that some of the thinnest layers are 
chiefly formed by numerous, exceedingly minute, though 
perfect, crystals of different minerals ; that other layers 
are formed by the union of different kinds of concre- 
tionary globules, and that the layers thus formed, often 
cannot be distinguished from the ordinary feldspathic 
and pitchstone layers, composing a large portion of the 
entire mass. The fibrous radiating structure of the 
sphasrulites seems, judging from many analogous cases, 
to connect the concretionary and crystalline forces : the 
separate crystals, also, of feldspar all lie in the same 

1 * Geological Transactions,' vol. ii (second series) p. 200, &c. 
These embedded fragments, in some instances, consist of the lami- 
nated trachyte broken off and * enveloped in those parts, which still 
remained liquid/ Beudant, also, frequently refers, in his great work 
on ' Hungary ' (torn. m. p 386), to trachytic rocks, irregularly spotted 
with fragments of the same varieties, which in other parts form the 
parallel ribbons. In these cases, we must suppose, that afte*- part 
of the molten mass had assumed a laminated structure, a fresh 
irruption of lava broke up the mass, and involved fragments, and 
that subsequently the whole became relaminated. 

2 Doiimieu's * Voj age,' p 64. 



78 Lamination of Volcanic Rocks 

parallel planes. 1 These allied forces, therefore, have 
played an important part In the lamination of the mass, 
but they cannot be considered the primary force ; for 
the several kinds of nodules, both the smallest and the 
largest, are internally zoned with excessively fine shades 
of colour, parallel to the lamination of the whole ; and 
many of them are, also, externally marked in the same 
direction with parallel ridges and furrows, which have 
not been produced by weathering. 

Some of the finest streaks of colour in the stony 
layers, alternating with the obsidian, can be distinctly 
seea to be due to an incipient crystallisation of the 
constituent minerals. The extent to which the minerals 
have crystallised can, also, be distinctly seen to be 
connected with the greater or less size, and with the 
number, of the minute, flattened, crenulated air-cavities 
or fissures. Numerous facts, as in the case of geodes, 
and of cavities in silicified wood, in primary rocks, and 
in veins, show that crystallisation is much favoured 
by space. Hence, I conclude, that, if in a mass of 
cooling volcanic rock, any cause produced in parallel 
planes a number of minute fissures or zones of less 
tension, (which from the pent-up vapours would often 
be expanded into crenulated air-cavities), the crystal- 
lisation of the constituent paits, and probably the for- 
mation oi concretions, would be superinduced or much 
favoured in such planes ; and thus, a laminated struc- 
ture of the kind we are here considering would be 
generated. 

That some cause does produce parallel zones of less 

1 The formation, indeed, of a large crystal of any mineral in a 
rock of mixed composition implies an aggregation of the requisite 
atoms, allied to concretionary action. The cause of the crystals of 
feldspar in these rocks of Ascension, being all placed lengthways, is 
probably the same with that which elongates and flattens all the 
brown sphaerulitic globules (which behave like feldspar under the 
blowpipe) in this same direction. 



CHAP. in. of the Tr achy tic Series. 79 

tension in volcanic rocks, during their consolidation, we 
must admit in the case of the thin alternate layers of 
obsidian and pumice described by Humboldt, and of 
the small, flattened, crenulated air-cells in the lami- 
nated rocks of Ascension ; for on no other principle can 
we conceive why the confined vapours should through 
their expansion form air-cells or fibres in separate, 
parallel planes, instead of irregularly throughout the 
mass. In Mr. Stokes' collection, I have seen a 
beautiful example of this structure, in a specimen of 
obsidian from Mexico, which is shaded and zoned, like 
the finest agate, with numerous, straight parallel layers, 
more or less opaque and white, or almost perfectly 
glassy ; the degree of opacity and glassiness depending 
on the number of microscopically minute, flattened 
air-cells ; in this case, it is scarcely possible to doubt 
but that the mass, to which the fragment belonged, 
must have been subjected to some, probably prolonged, 
action, causing the tension slightly to vary in the suc- 
cessive planes. 

Several causes appear capable of producing zones of 
different tension, in masses semi-liquefied by heat. In 
a fragment of devitrified glass, I have observed layers 
of sphaeruhtes which appearedj from the manner in 
which they were abruptly bent, to have been produced 
by the simple contraction of the mass in the vessel, in 
which it cooled. In certain dikes on mount Etna, de- 
scribed by M. Elie de Beaumont, 1 as bordered by alter- 
nating bands of scoriaceous and compact rock, one is 
led to suppose that the stretching movement of the 
surrounding strata, which originally produced the 
fissures, continued whilst the injected rock remained 
fluid. Guided, however, by Professor Forbes' 2 clear 

1 * M6m potir servir,' &c , torn. iv. p. 131. 

8 'Edinburgh New Phil, Journal,' 1842, p. 350. 



8o Lamination of Volcanic Rocks PAET i. 

description of the zoned structure of glacier-ice, far the 
most probable explanation of the laminated structure 
of these feldspathic rocks appears to be, that they have 
been stretched whilst slowly flowing onwards in a pasty 
condition, 1 in precisely the same manner as Professor 
Forbes believes, that the ice of moving glaciers is 
stretched and fissured. In both cases, the zones may 
be compared to those in the finest agates; in both, 
they extend in the direction in which the mass has 
flowed, and those exposed on the surface are generally 
vertical : in the ice, the porous laminse are rendered 
distinct by the subsequent congelation of infiltrated 
water, in the stony feldspathic lavas, by subsequent 
crystalline and concretionary action. The fragment of 
glassy obsidian in Mr. Stokes* collection, which is zoned 
with minute air-cells, must strikingly resemble, judging 
from Professor Forbes 3 descriptions, a fragment of the 
zoned ice ; and if the rate of cooling and nature of the 
mass had been favourable to its crystallisation or to 
concretionary action, we should here have, had the finest 
parallel zones of different composition and texture. 
In glaciers, the lines of porous ice and of minute 
crevices seem to be due to an incipient stretching, 
caused by the central, parts of the frozen stream moving 
faster than the sides and bottom, which are retarded by 
friction : hence in glaciers of certain forms and towards 
the lower end of most glaciers, the zones become hori- 
zontal. May we venture to suppose that in the feld- 
spathic lavas with horizontal laminae, we see an analo- 
gous case ? All geologists, who have examined trachytic 
regions, have come to the conclusion, that the lavas of 

1 I presume that tip s is nearly the same explanation which Mr. 
Scrope had in his mmd, when he speaks (' Geolog. Tiansact.* vol ii. 
second series, p. 228) of the ribboned structure of his trachytic rocks, 
having arisen, from * a linear extension of the mass, while in a state 
of imperfect liquidity, coupled with a concretionary process.' 



CHAP. in. of the Tr achy tic Series. 81 

this series have possessed an exceedingly imperfect 
fluidity; and as it is evident that only matter thus 
characterised would be subject to become fissured and 
to be formed into zones of different tensions, in the 
manner here supposed, we probably see the reason why 
augitic lavas, which appear generally to have possessed 
a high degree of fluidity, are not, 1 like the feldspathic 
lavas, divided into lammae of different composition and 
texture. Moreover, in the augitic series, there never 
appears to be any tendency to concretionary action, 
which we have seen plays an important part in the 
lamination of rocks of the trachytic series, or at least in 
rendering that structure apparent. 

Whatever may be thought of the explanation here 
advanced of the laminated structure of the rocks of the 
trachytic series, I venture to call the attention of geolo- 
gists to the simple fact, that in a body of rock at 
Ascension, undoubtedly of volcanic origin, lasers often 
of extreme tenuity, quite straight, and parallel to each 
other, have been produced ; some composed of distinct 
crystals of quartz and diopside, mingled with amorphous 
augitic specks and granular feldspar, others entirely 
composed of these black augitic specks, with granules 
of oxide of iron, and lastly, others formed of crystal- 
line feldspar, in a more or less perfect state of purity, 
together with numerous crystals of feldspar, placed 
lengthways. At this island, there is reason to believe, 
and in some analogous cases, it is certainly known, that 
the laminae have originally been formed with their pre- 



1 Basaltic lavas, and many other rocks, are not unfrequently 
divided into thick lammse or plates, of the same composition, which 
are either straight or curved j these being crossed by vertical lines 
of fissure, sometimes become united into columns. This structure 
seems related, in its origin, to that by which many rocks, both 
igneous and sedimentary, become traversed by parallel systems of 
fissures. 



82 Lamination of Tr achy tic Rocks. PAET i. 

sent high inclination. Pacts of this nature are mani- 
festly of importance, with relation to the structural 
origin of that grand series of plutonic rocks, which like 
the volcanic have undergone the action of heat, and 
which consist of alternate layers of quartz, feldspar f 
mica, and other materials. 



CHAPTEE IV. 

ST. HELENA. 

Lavas oftliefeldspatMe, basaltic, and submarine series Section Flag" 
staff Hill and of the Ba/rn. Dikes Tw> *?s Cap and Prosperous 
Says Basaltic ring Central orateriform ridge, with an internal 
ledge and a parapet Cones of pkonohte Superficial beds of cal- 
careous sandstone Extinct land-shells Beds of detritus JEleva- 
tion of the land Denudation Craters of eleiatwn. 

THE whole island Is of volcanic origin ; its circumference, 
according to Beatson, 1 is about twenty-eight miles. 
The central and largest part consists of rocks of a f eld- 
spathic nature, generally decomposed to an extraordi- 
nary degree ; and when in this state, presenting a singu- 
lar assemblage of alternating, red, purple, brown, yellow, 
and white, soft, argillaceous beds. From the shortness 
of our visit. I did not examine these beds with care ; 
some of them, especially those of the white, yellow, 
and brown shades, originally existed as streams of lava, 
but the greater number were probably ejected in the 
form of scoriae and ashes : other beds of a purple tint, 
porphyritic with crystal- shaped patches of a white, soft 
substance, which are now unctuous, and yield, like 
wax, a polished streak to the nail, seem once to have 
existed as solid claystone-porphyries : the red argil- 
laceous beds generally have a brecciated structure, and 
no doubt have been formed by the decomposition of 

1 Governor Beatson's ' Account of St. Helena/ 

r 



PAET I. 



84 Sf. Helena. 

gcorise. Several extensive streams, however, belonging 
to this series, retain their stony character; these are 
either of a blackish-green colour, with minute acicular 
crystals of feldspar, or of a very pale tint, and almost 
composed of minute, often scaly, crystals of feldspar, 
abounding with microscopical black specks; they are 
generally compact and laminated ; others, however, of 
similar composition, are cellular and somewhat decom- 
posed. None of these rocks contain large crystals of 
feldspar, or have the harsh fracture peculiar to trachyte. 
These feldspathic lavas and tuffs are the uppermost or 
those last erupted ; innumerable dikes, however, and 
great masses of molten rock, have subsequently been 
injected into them. They converge, as they rise, 
towards the central curved ridge, of which one point 
attains the elevation of 2,700 feet. This ridge is the 
highest land in the island ; and it once formed the 
northern rim of a great crater, whence the lavas of this 
series flowed : from its ruined condition, from the 
southern half ha\ing been removed, and from the 
violent dislocation which the whole island has under- 
gone, its structure is rendered very obscure. 

Basaltic series. The margin of this island is 
formed by a rude circle of great, black, stratified, rani- 
parts of basalt, dipping seaward, and worn into cliffs, 
which are often nearly perpendicular, and vary in. 
height from a few hundred feet to two thousand. 
This circle, or rather horse-shoe shaped ring, is open to 
the south, and is breached by several other wide spaces. 
Its rim or summit generally projects little above the 
level of the adjoining inland country; and the more 
recent feldspathic lavas, sloping down from the central 
heights, generally abut against and overlap its inner 
margin ; on the north-western side of the island, how- 
ever, they appear (judging from a distance) to have 



CHAP. IT. Basaltic Series. 85 

flowed over and concealed portions of It. In some 
parts, where the basaltic ring had been breached, and 
the black ramparts stand detached, the feldspathic 
lavas have passed between them, and now overhang 
the sea-coast in lofty cliffs. The basaltic rocks are of a 
black colour and thinly stratified ; they are generally 
highly vesicular, but occasionally compact ; some ol 
them contain numerous crystals of glassy feldspar and 
octahedrons of titaniferous iron ; others abound with 
crystals of augite and grains of olivine. TLe vesicles 
are frequently lined with minute crystals (of chabasie ?) 
and even become amygdaloidal with them. The 
streams are separated from each other by cindery 
matter, or by a bright red, friable, saliferous tuff, which 
is marked by successive lines like those of aqueous 
deposition ; and sometimes it has an obscure, concre- 
tionary structure. The rocks of this basaltic series 
occur nowhere except near the coast In most volcanic 
districts the trachytic lavas are of anterior origin to the 
basaltic ; but here we see, that a great pile/ of rock, 
closely related in composition to the trachytic family, 
has been erupted subsequently to the basaltic strata : 
the number, however, of dikes, abounding with large 
crystals of augite, with which the feldspathic lavas have 
been injected, shows perhaps, some tendency to a re- 
turn to the more usual order of superposition. 

Basal submarine lavas. The lavas of this basal 
series lie immediately beneath both the basaltic and 
feldspathic rocks. According to Mr. Seale, 1 they may 
be seen at intervals on the sea beach round the entire 
island. In the sections which I examined, their nature 
varied much ; some of the strata abound with crystals of 

1 Geognosy of the Island of Rt Helena ' Mr. Seale has con- 
structed a gigantic model of St Helena, well worth visiting, winch 
is now deposited at Addiscombe College, in Suney. 



86 .5V. Helena. PART i. 

augite ; others are of a brown colour, either lami- 
nated or in a rubbly condition ; and many parts are 
highly amygdaloidal with calcareous matter. The 
successive sheets are either closely united together, or 
are separated from each other by beds of scoriaceous 
rock and of laminated tuff, frequently containing well- 
rounded fragments. The interstices of these beds are 
filled with gypsum and salt ; the gypsum also sometimes 
occurring in thin layers. From the large quantity of 
these two substances, from the presence of rounded 
pebbles in the tuffs, and from the abundant amygdaloids, 
I cannot doubt that these basal volcanic strata flowed be- 
neath the sea. This remark ought perhaps to be extended 
to a part of the superincumbent basaltic rocks ; but on 
this point, I was not able to obtain clear evidence. The 
ntrata of the basal series, whenever I examined them, 
were intersected by an extraordinary number of dikes. 

flagstaff Hill and the Bam. I will now describe 
some of the more remarkable sections, and will com- 
mence with these two hills, which form the principal 
external feature on the north-eastern side of the island. 
The square, angular outline, and black colour of the 
Barn, at once show that it belongs to the basaltic 

No. 8. 




Flagstaff HiU. The Barn. 

2,272 feet high. 2,015 feet high, 

The double lines represent the basaltic strata , the single, the baal submarine strata ; 
the dotted, the upper feldspathic strata , the dikes are shaded transversely. 

series ; whilst the smooth, conical figure, and the 
varied bright tints of Flagstaff Hill, render it equally 
clear, that it is composed of the softened, feldspathic 



CHAP. IT. 



Flagstaff Hill and the Barn. 8 7 



rocks. These two lofty hills are connected (as is shown 
in the accompanying woodcut) by a sharp ridge, 
which is composed of the rubbly lavas of the basal 
series. The strata of this ridge dip westward, the in- 
clination becoming less and less towards the Flagstaff; 
and the upper feldspathic strata of this hill can be seen, 
though with some difficulty, to dip conformably to the 
WSW. Close to the Barn, the strata of the ridge are 
nearly vertical, but are much obscured by innumerable 
dikes ; under this hill, they probably change from being 
vertical into being inclined into an opposite direction ; 
for the upper or basaltic strata, which are about 800 
or 1,000 feet in thickness, are inclined north-eastward, 
at an angle between thirty and forty degrees. 

This ridge, and likewise the Barn and Flagstaff Hills, 
are interlaced by dikes, many of which preserve a re- 
markable parallelism in a NNW. and SSE. direction 
The dikes chiefly consist of a rock, porphyntic with 
large crystals of augite ; others are formed of a fine- 
grained and brown-coloured trap. Most of these dikes 
are coated by a glossy layer, 1 from one to two-tenths of 
an inch in thickness, which, unlike true pitchstone, 
fuses into a black enamel ; this layer is evidently ana- 
logous to the glossy superficial coating of many lava 
streams. The dikes can often be followed for great 
lengths both horizontally and vertically, and they seem 
bo preserve a nearly uniform thickness : 2 Mr. Seale 

1 This circumstance has "been observed (Lyell, 'Principles of: 
Geology/ vol iv chap. x. p. 9) in the dikes of the Atrio del Cavallo, 
but apparently it is not of very common occurrence. Sir G. Mac- 
kenzie, however, states (* Travels in Iceland/ p. 372) that all the 
veins in Iceland have a ' black vitreous coating on their sides ' Capt. 
Carrnichael, speaking of the dikes in Tristan D'Acttnha, a volcanic 
island in the southern Atlantic, says (' Linnsean Transactions/ vol. 
xii. p. 485) that their sides, ' where they come in contact with the 
rocks, are invariably in a semi- vitrified state ' 

a * Geognosy of the Island of St. Helena/ plate 5. 



88 St. Helena. PART i* 

states, that one near the Barn, in a height of 1,260 feet, 
decreases in width only four inches, from nine feet at 
the bottom, to eight feet and eight inches, at the top. 
On the ridge, the dikes appear to have been guided in 
their course, to a considerable degree, by the alterna- 
ting soft and hard strata : they are often firmly united 
to the harder strata, and they preserve their paral- 
lelism for such great lengths, that in very many in- 
stances it was impossible to conjecture, which of the 
beds were dikes, tjid which streams of lava. The dikes, 
though so numerous on this ridge, are even more 
numerous in the valleys a little south of it, and to a 
degree I never saw equalled anywhere else : in these 
valleys they extend in less regular lines, covering the 
ground with a network, like a spider's web, and with 
some parts of the surface even appearing to consist 
wholly of dikes, interlaced by other dikes. 

From the complexity produced by the dikes, from 
the high inclination and anticlinal dip of the strata of 
the basal series, which are overlaid, at the opposite 
ends of the short ridge, by two great masses of different 
ages and of different composition, I am not surprised 
that this singular section has been misunderstood. It 
has even been supposed to form part of a crater ; but 
so far is this from having been the case, that the summit 
of Flagstaff Hill once formed the lower extremity of a 
sheet of lava and ashes, which were erupted from the 
central, crateriform ridge. Judging from the slope of 
the contemporaneous streams in an adjoining and un- 
disturbed part of the island, the strata of the Flagstaff 
Hill must have been upturned at least twelve hundred 
feet, and probably much more, for the great truncated 
dikes on its summit show that it has been largely 
denuded. The summit of this hill now nearly equals 
in height the crateriform ridge; and before having 



CHAP. rv. Flagstaff Hill and the Barn. 89 

been denuded, it was probably higher than this ridge, 
from which it is separated by a broad and much lower 
tract of country; we here, therefore, see that the lower 
extremity of a set of lava-streams have been tilted up 
to as great a height as, or perhaps greater height than, 
the crater, down the flanks of which they originally 
flowed. I believe that dislocations on so grand a scale 
are extremely rare * in volcanic districts. The forma- 
tion of such numbers of dikes in this part of the island 
shows that the surface must here have been stretched to a 
quite extraordinary degree : this stretching, on the ridg^ 
between Flagstaff and Barn Hills, probably took place 
subsequently (though perhaps immediately so) to the 
strata being tilted ; for had the strata at that time 
extended horizontally, they would in all probability 
have been fissured and injected transversely, instead of 
in the planes of their stratification. Although the 
space between the Barn and Flagstaff Hill presents a 
distinct anticlinal line extending north and south, and 
though most of the dikes range with much regularity 
in the same line, nevertheless, at only a mile due south 
of the ridge the strata lie undisturbed. Hence the 
disturbing force seems to have acted under a point, 
rather than along a line. The manner in which it has 
acted, is probably explained by the structure of Little 
Stony-top, a mountain 2,000 feet high, situated a few 
miles southward of the Barn ; we there see, even from 
a distance, a dark-coloured, sharp, wedge of compact 
columnar rock, with the bright-coloured felrlspathic 
strata, sloping away on each side from its uncovered 
apex. This wedge, from which it derives its name of 
Stony-top, consists of a body of rock, which has been 

1 M. Constant Prevost (<Me"m. de la Soc. Golog,' torn, ii) 
observes, that *les produits Yolcaniques n'ont que local ement et 
rarement m^rne d6rang6 le sol, & travers lequel ils se sont fait jour/ 



St. Helena. PAET i, 



injected whilst liquefied into the overlying strata ; and 
if we may suppose that a similar body of rock lies in- 
jected, beneath, the ridge connecting the Barn and Flag- 
staff, the structure there exhibited would be explained. 
TurKis Gap and Prosperous Says. Prosperous 
Hill is a great, black, precipitous mountain, situated 
two miles and a half south of the Barn, and composed, 
like it, of basaltic strata. These rest, in one part, on 
the brown-coloured, porphyritic beds of the basal series, 
and in another part, on a fissured mass of highly scori- 
aceous and amygdaloidal rock, which seems to have 
formed a small point of eruption beneath the sea, con- 
temporaneously with the basal series. Prosperous Hill, 
like the Barn, is traversed by many dikes, of which the 
greater number range north and south, and its strata 
dip, at an angle of about 20, rather obliquely from the 
island towards the sea. The space between Prosperous 
Hill and the Barn, as represented in this woodcut, con- 
sists of lofty cliffs, composed of the lavas of th upper 



Flagstaff Hill 




Prosperous Hill. The Barn. 

The double lines represent the basaltic strata , the single, the basal submarine strata 
the dotted, the upper feldspatliic strata. 

or feldspathic series, which rest, though unconform- 
ably, on the basal submarine strata, as we have seen 
that they do at Flagstaff Hill. But differently from 
what occurs in that hill, these upper strata are nearly 
horizontal, gently rising towards the interior of the 
island,^ they are also composed of greenish-black, or 
more commonly, pale brown, compact lavas, instead of 
softened and highly coloured matter These brown- 
coloured, compact lavas, consist almost entirely of small 



CHAP. IT. Turk's Cap and Prosperous Bays. 9 1 

glimmering scales, or of minute acicular crystals, of 
feldspar, placed close by the side of each other, and 
abounding with minute black specks, apparently of 
hornblende. The basaltic strata of Prosperous Hill 
project only a little above the level of the gently-sloping, 
feldspathic streams, which wind round and abut against 
their upturned edges. The inclination of the basaltic 
strata seems to be too great, to have been caused by 
their having flowed down a slope, and they must have 
been tilted into their present position before the erup- 
tion of the feldspathic streams. 

Basaltic ring. Proceeding round the island, the 
lavas of the upper series, southward of Prosperous Hill, 
overhang the sea in lofty precipices. Further on, the 
headland, called Great Stony-top, is composed, as I 
believe, of basalt; as is Long "Range Point, on the 
inland side of which, the coloured beds abut. On the 
southern side of the island, we see the basaltic strata of 
the South Barn, dipping obliquely seaward at a con- 
siderable angle ; this headland, also, stands a little 
above the level of the more modern, feldspathic lavas. 
Further on, a large space of coast, on each side of Sandy 
Bay, has been much denuded, and there seems to be 
left only the basal wreck of the great, central crater. - 
The basaltic strata reappear, with their seaward dip, at 
the foot of the hill called Man-and -Horse; and thence 
they are continued along the whole north-western coast 
to Sugar-Loaf Hill, situated near to the Flagstaff; and 
they everywhere have the same seaward inclination, 
and rest, in some parts at least, on the lavas of the basal 
series. We thus see that the circumference of the 
island is formed by a much-broken ring, or rather a 
horse-shoe, of basalt, open to the south, and interrupted 
on the eastern side by many wide breaches. The 
breadth of this marginal* fringe on. the north-western 



94 Si. Helena. PAET i. 

not unfrequently within volcanic craters, and their 
formation seems to be due to the sinking down of a 
level sheet of hardened lava, the edges of which re- 
main (like the ice round a pool, from which the water 
has been drained) adhering to the sides. 1 

In some parts, the ridge is surmounted by a wall 
or parapet, perpendicular on both sides. Near Diana's 
Peak this wall is extremely narrow. At the Galapagos 
Archipelago I observed parapets, having a quite similar 
structure and appearance, surmounting several of the 
craters ; one, which I more particularly examined, 
was composed of glossy, red scorise firmly connected 
together; being externally perpendicular, and extend- 
ing round nearly the whole circumference of the crater, 
it rendered it almost inaccessible. The Peak of Tene- 
riffe and Cotopaxi, according to Humboldt, are similarly 
constructed ; he states 2 that ' at their summits a cir- 
cular wall surrounds the crater, which wall, at a 
distance, has the appearance of a small cylinder placed 
on a truncated cone. On Cotopaxi 3 this peculiar 
structure is visible to the* naked eye at more than 
2,000 toises' distance 5 and no person has ever reached 
its crater. On the Peak of Teneriffe, the parapet is so 
high, that it would be impossible to reach the colder a, 
if on the eastern side there did not exist a breach/ 
The origin of these circular parapets is probably due 
^o the heat or vapours from the crater, penetrating 
and hardening the sides to a nearly equal depth, and 
afterwards to the mountain being slowly acted on by 
the weather, which would leave the hardened part, 

1 A most remarkable instance of this structure is described in 
Ellis's ' Polynesian Besearches ' (second edit ), where an admirable 
drawing is given of the successive ledges or terraces, on the borders 
of the immense crater at Hawaii, in the Sandwich Islands, 

2 * Personal Narrative,' vol. i. p 171. 

8 Humboldt's 'Picturesque Atlas,' folio, pi. 10. 



CHAP, IT. 



Central Curved Ridge. 95 



projecting in the form of a cylinder or circular 
parapet. 

From the points of structure in the central ridge, 
now enumerated, namely, from the convergence to- 
wards it of the beds of the upper series, from the 
lavas there becoming highly cellular, from the flat 
ledge, extending along its inner and precipitous side, 
like that within some still active craters, from the 
parapet-like wall on its summit, and lastly, from its 
peculiar curvature, unlike that of any common line of 
elevation, I cannot doubt that this curved ridge 
forms the last remnant of a great crater. In endeavour- 
ing, however, to trace its former outline, one is soon 
baffled ; its western extremity gradually slopes down, 
and, branching into other ridges, extends to the sea- 
coast ; the eastern end is more curved, but it is only 
a little better defined. Some appearances lead me to 
suppose that the southern wall of the crater joined the 
present ridge near Nest Lodge ; in this case the crater 
must have been nearly three miles long, and about a 
mile and a half in breadth. Had the denudation of 
the ridge and the decomposition of its constituent 
rocks proceeded a few steps farther, and had this ridge, 
like several other parts of the island, been broken up 
by great dikes and masses of injected matter, we should 
in vain have endeavoured to discover its true nature. 
Even now we have seen that at Flagstaff Hill the 
lower extremity and most distant portion of one sheet 
of the erupted matter has been upheaved to as great a 
height as the crater down which it flowed, and pro- 
bably even to a greater height. It is interesting thus 
to trace the steps by which the structure of a volcanic 
district becomes obscured, and finally obliterated : so 
near to this last stage is St. Helena, that I believe no 
one has hitherto suspected that the central ridge or 



96 Si. Helena. 



JPABI I 



axis of the island, is the last wreck of the crater, 
whence the most modern volcanic streams were poured 
forth. 

The great hollow space or valley southward of the 
central carved ridge, across which the half of the crater 
must once have extended, is formed of bare, water- 
worn hillocks and ridges of red, yellow, and brown 
rocks, mingled together in chaos-like confusion, inter- 
laced by dikes, and without any regular stratification. 
The chief part consists of red decomposing scoria* 
associated with various kinds of tuff and yellow argil- 
laceous beds, full of broken crystals, those of angite 
being particularly large Here and there masses of 
highly cellular and amygdaloidal lavas pi otrude. From 
one of the ridges in the midst of the valley, a conical 
precipitous hill, called Lot, boldly stands tip, and forms 
a most singular and conspicuous object. It is com- 
posed of phonolite, divided in one part into great 
curved lammge, in another, into angular concretionary 
balls, and in a third part into outwardly radiating 
columns. At its base the strata of lava, tuff, and 
scorias, dip away on all sides : 1 the uncovered portion 
is 197 2 feet in height, and its horizontal section gives 
an oval figure. The phonolite is of a greenish -gray 
colour, and is full of minute aciculnr crystals of 
feldspar; in most parts it has a couchoidal fracture, 
and is sonorous, yet it is crenulated with minute air- 
cavities. In a SW. direction from Lot, there are 
some other remarkable columnar pinnacles, but of a 

1 Abich, in Ms 'Views of Vesuvius' (plate vl), has shown the 
manner in which beds, under neaily similar circumstances, are tilted 
up. The upper beds are more turned up than the lower; and ha 
accounts for this, by showing- that the lava insinuates itself hori- 
zontally between the lower becls 

4 This height is given by Mr. Seale,inhis Geognosy of the island, 
The height of the summit above the level of th sea, its, said bo b& 
1 444: feet. 



CHAP. rv. Hills of Phonolite. 97 

less regular shape, namely, Lot's Wife, and the Asses 
Ears, composed of allied kinds of rock. From their 
flattened shape, and their relative position to each 
other, they are evidently connected on the same line of 
fissure. It is, moreover, remarkable that this same 
NE, and SW. line, joining Lot and Lot's Wife, if 
prolonged, would intersect Flagstaff Hill, which, as 
before stated, is crossed by numerous dikes running 
in this direction, and which has a disturbed structure, 
rendering it probable that a great body of once fluid 
rock lies injected beneath it. 

In this same great valley there are several other 
conical masses of injected rock (one, I observed, was 
composed of compact greenstone), some of which are 
not connected, as far as is apparent, with any line of 
dike ; whilst others are obviously thus connected. Of 
these dikes, three or four great lines stretch across the 
valley in a NE. and SW. direction, parallel to that 
one connecting the Asses' Ears, Lot's Wife, and pro- 
bably Lot. The number of these masses of injected 
rock is a remarkable feature in the geology of St. 
Helena. Besides those just mentioned, and the hypo- 
thetical one beneath Flagstaff Hill, there is Little 
Stony-top and others, as I have reason to believe, at 
the Man-and-Horse, and at High Hill. Most of these 
masses, if not all of them, have been injected subse- 
quently to the last volcanic eruptions from the central 
crater. The formation of conical bosses of rock on 
lines of fissure, the walls of which are in most cases 
parallel, may probably be attributed to inequalities in 
the tension, causing small transverse fissures ; and at 
these points of intersection the edges of the strata 
would naturally yield, and be easily turned upwards* 
Finally, I may remark, that hills of phonolite every- 



98 St. Helena. 



PART I. 



where are apt l to assume singular and even grotesque 
shapes, like that of Lot : the peak at Fernando Noronha 
offers an instance; at St. Jago, however, the cones 
of phonolite, though tapering, have a regular form. 
Supposing, as seems probable, that all such hillocks 
or obelisks nave originally been injected, whilst 
liquefied, into a mould formed by yielding strata, as 
certainly has been the case with Lot, how are we to 
account for the frequent abruptness and singularity of 
their outlines, compared with similarly injected masses 
of greenstone and basalt? Can it be due to a less 
perfect degree of fluidity, which is generally supposed 
to be characteristic of the allied trachytic lavas ? 

Superficial deposit?. Soft calcareous sandstone 
occurs in extensive, though thin, superficial beds, both 
on the northern and southern shores of the island. 
It consists of very minute, equal-sized, rounded particles 
of shells, and other organic bodies, which partially 
retain their yellow, brown, and pink colours, and oc- 
casionally, though very rarely, present an obscure trace 
of their original external forms. I in vain endeavoured 
to find a single unrolled fragment of a shell. The 
colour of the particles is the most obvious character 
by which their origin can be recognised, the tints 
being affected (and an odour produced) by a moderate 
heat, in the same manner as in fresh shells. The par- 
ticles are cemented together, and are mingled with 
some earthy matter : the purest masses, according to 
Beatson, contain 70 per cent, of carbonate of lime. 
The beds, varying in thickness from two or three feot 
to fifteen feet, coat the surface of the ground ; they 
generally lie on that side of the valley which is pro- 
tected from the wind, and they occur at the "height 

1 D'Anbuisson, in his * Trait3 de G6ognosie' (torn, ii. p. 540) 
particularly remarks that this is the case. 



CHAP. IT. Superficial Calcareous Beds. 99 

of several hundred feet above the level of the sea. 
Their position is the same, which sand, if now drifted 
by the trade-wind, would occupy; and no doubt they 
thus originated, which explains the equal size and 
minuteness of the particles, and likewise the entire 
absence of whole shells, or even of moderately-sized 
fragments. It is remarkable that at the present day 
there are no shelly beaches on any part of the coast, 
whence calcareous dust could be drifted and winnowed ; 
we must, therefore, look back to a former period when 
before the land was worn into the present great 
precipices, a shelving coast, like that of Ascension, 
was favourable to the accumulation of shelly detritus. 
Some of the beds of this limestone are between 600 
and 700 feet above the sea ; but part of this height 
may possibly be due to an elevation of the land, sub- 
sequent to the accumulation of the calcareous sand. 

The percolation of rain-water has consolidated parts 
of these beds into a solid rock, and has formed masses 
of dark brown, stalagmitic limestone. At the Sugar- 
Loaf quarry, fragments of rock on the adjoining slopes, 1 
have been thickly coated by successive fine layers of 
calcareous matter. It is singular, that many of these 
pebbles have their entire surfaces coated, without any 
point of contact having been left uncovered; hence-, 
these pebbles must have been lifted up by the slow 
deposition between them of the successive films of car- 
bonate of lime. Masses of white, finely oolitic rock are 
attached to the outside of some of these coated pebbles. 



1 In the earthy detritus on several parts of this hill, irregular 
masses of very impmc, crystallised sulphate of lime occur As this 
substance is now being abundantly deposited hy the surf at Ascen- 
sion, it is possible that these masses may thus have originated; but 
if so, it must have been at a penod when the land stood at a much 
lower level This earthy selenite is now found at a s height of 
between 600 and 700 feet. 



1OO St. Helena, PAET i, 

Von Buch has described a compact limestone at 
Lanzarote, which seems perfectly to resemble the sta- 
lagmitic deposition just mentioned : it coats pebbles, 
and in parts is finely oolitic : it forms a far-extended 
layer, from one inch to two or three feet in thickness, 
ml it occurs at the height of 800 feet above the sea, 
but only on that side of the island exposed to the violent 
north-western winds. Von Buch remarks, 1 that it is 
not found in hollows, but only on the unbroken and 
inclined surfaces of the mountain. He believes, that 
it has been, deposited by the spray which is borne over 
the whole island by these violent winds. It appears, 
however, to me much more probable that it has been 
formed, as at St. Helena, by the percolation of water 
through finely comminuted shells : for when sand is 
blown on a much exposed coast, it always tends to accu- 
mulate on broad, even surfaces, which offer a uniform 
resistance to the winds. At the neighbouring island, 
moreover, of Fuerteventura, 2 there is an earthy lime- 
stone, which, according to Von Buch, is quite similar 
to specimens which he has seen from St. Helena, and 
which he believes to have been formed by the drifting 
of shelly detritus. 

The upper beds of the limestone, at the above- 
mentioned quarry on the Sugar-Loaf Hill, are softer, 
finer-grained and less pure, than the lower beds. They 
abound with fragments of land-shells, and with some 
perfect ones ; they contain, also, the bones of birds, and 
the large eggs, 3 apparently of water-fowl. It is pro- 
bable that these upper beds remained long in an uncon- 

1 * Description des Isles Canaries/ p. 293. 

2 Idem, pp. 314 and 374. 

9 Colonel Wilkes, in a catalogue presented with some specimens 
to the Geological Society, states that as many as ten eggs were found 
by one person. Dr. Buckland has remarked (' Geolog. Trans.' vol. v, 
p. 474) on these eggs. 



CHAP. iv. Extinct Land Shells. 101 

solidated form, during which time, these terrestrial 
productions were embedded, Mr. G. R. Sowerby has 
kindly examined three species of land-shells, which I 
procured from this bed, and his descriptions are given 
in the Appendix, One of them Is a Succinea, identical 
with a species now living abundantly on the island : 
the two others, namely, OocJdogena fossilis and Helix 
biplicata, are not known in a recent state : the latter 
species was also found in another and different locality, 
associated with a species of Cochlogena which is un- 
doubtedly extinct. 

Beds of extinct land-shells. Land-shells, all of 
which appear to be species now extinct, occur embedded 
in earth, in several parts of the island. The greater 
number have been found at a considerable height on 
Flagstaff Hill. On the NW. side of this hill, a rain- 
channel exposes a section of about twenty feet in thick- 
ness, of which the upper part consists of black vegetable 
mould, evidently washed down from the heights above, 
and the lower part of less black earth, abounding with 
young and old shells, and with their fragments : part 
of this earth is slightly consolidated by calcareous 
matter, apparently due to the partial decomposition of 
some of the shells. Mr. Seale, an intelligent resident, 
who first called attention to these shells, gave me a 
large collection from another locality, where the shells 
appear to have been embedded in very black earth. 
Mr. G. R. Sowerby has examined these shells, and has 
described them in the Appendix. There are seven 
species, namely, one Cochlogena, two species of the 
genus Cochlicopa, and four of Helix : none of these are 
known, in a recent state, or have been found in any 
other country. The smaller species were picked out of 
the inside of the large shells of the OoMogena auris- 
vulpina. This last-mentioned species is in many 



IO2 



Si. Helena. PAET 



respects a very singular one ; it was classed, even by 
Lamarck, in a marine genus, and having thus been 
mistaken for a sea-shell, and the smaller accompanying 
species having been overlooked, the exact localities 
where it was found have been measured, and the eleva- 
tion of this island thus deduced ! It is very remarkable 
that all the shells of this species found by me in one 
spot, form a distinct variety, as described by Mr. 
Sowerby, from those procured from another locality by 
Mr. Seale. As this Cochlogena is a large and con- 
spicuous shell, I particularly enquired from several 
intelligent countrymen whether they had ever seen it 
alive ; they all assured me that they had not, and they 
would not even believe that it was a land animal : Mr. 
Seale, moreover, who was a collector of shells all his 
life at St< Helena, never met with it alive. Possibly 
some of the smaller species may turn out to be yet 
living kinds ; but, on the other hand, the two land-shells 
which are now living on the island in great numbers, 
do not occur embedded, as far as it is yet known, with 
the extinct species. I have shown in my Journal, 1 that 
the extinction of these land-shells possibly may not be 
an ancient event ; as a great change took place in the 
state of the island about 120 years ago, when the old 
trees died, and were not replaced by young ones, these 
being destroyed by the goats and hogs, which had run 
wild in numbers, from the year 1502. Mr. Seale states, 
that on Flagstaff" Hill, where we have seen, that the 
embedded land-shells are especially numerous, traces 
are everywhere discoverable, which plainly indicate 
that it was once thickly clothed with trees ; at present 
not even a bush grows there. The thick bed of black 
vegetable mould which covers the shell-bed, on the 

1 * Journal of Researches,' 1845, p. 489. 



CHAP. iv. Elevation of the Land. 103 

flanks of this Mil, was probably washed down from the 
upper part, as soon as the trees perished, and the shelter 
afforded by them was lost. 

Elevation of the land. Seeing that the lavas of 
the basal series, which are of submarine origin, are 
raised above the level of the sea, and at some places to 
the height of many hundred feet, I looked out for 
superficial signs of the elevation of the land. The 
bottoms of some of the gorges, which descend to the 
coast, are filled up to the depth of about a hundred 
feet, by rudely divided layers of sand, muddy clay, and 
fragmentary masses ; in these beds, Mr. Seale has found 
the bones of the tropic-bird and of the albatross ; the 
former now rarely, and the latter never visiting the 
island. From the difference between these layers, and 
the sloping piles of detritus which rest on them, I 
suspect that they were deposited, when the gorges stood 
beneath the sea. Mr. Seale, moreover, has shown that 
some of the fissure-like gorges, 1 become, with a concave 
outline, gradually rather wider at the bottom than at 
the top; and this peculiar structure was probably 
caused by the wearing action of the sea, when it entered 
the lower part of these gorges. At greater heights, 
the evidence of the rise of the land is even less clear : 
nevertheless, in a bay-like depression on the table-land 
behind Prosperous Bay, at the height of about 1,000 
feet, there are flat-topped masses of rock, which it is 
scarcely conceivable, could have been insulated from 
the surrounding and similar strata, by any other agency 
than the denuding action of a sea-beach. Much denu- 
dation, indeed, has been effected at great elevations, 
which it would not be easy to explain by any other 
means: thus, the flat summit of the Barn, wliicli is 

* A fissure-like gorge, near Stony-top, Is said by Mr. Seale to "be 
840 feet deep, and only 115 feet in width. 



IO4 $* Helena. PART i. 

2,000 feet high, presents, according to Mr. Seale, a 
perfect network of truncated dikes; on tills like the 
Flagstaff, formed of soft rock, we might suppose that 
the dikes had been worn down and cut off by meteoric 
agency, but we can hardly suppose this possible with 
the hard, basaltic strata of the Barn. 

Coast denudation. The enormous cliffs, in many 
parts between 1,000 and 2,000 feet in height, with 
which this prison-like island is surrounded, with the 
exception of only a few places, where narrow valleys 
descend to the coast, is the most striking feature in its 
scenery. We have seen that portions of the basaltic 
ring, two or three miles in length by one or two miles 
in breadth, and from one to two thousand feet in height, 
have been wholly removed. There are, also, ledges and 
banks of rock, rising out of profoundly deep water, and 
distant from the present coast between three and four 
miles, which, according to Mr. Seale, can be traced to 
the shore, and are found to be the continuations of 
certain well-known great dikes. The swell of the 
Atlantic Ocean has obviously been the active power in 
forming these cliffs; and it is interesting to observe 
that the lesser, though still great, height of the cliffs 
on the leeward and partially protected side of the 
island, (extending from the Sugar-Loaf Hill to South 
West Point,) corresponds with the lesser degree of 
exposure. When reflecting on the comparatively low 
coasts of many volcanic islands, which also stand ex- 
posed m the open ocean, and are apparently of consider- 
able antiquity, the mind recoils from an attempt to 
grasp the number of centuries of exposure, necessary to 
have ground into mud and to have dispersed the enor- 
mous cubic mass of hard rock which has been pared off 
the circumference of this island. The contrast in the 
superficial state of St. Helena, compared with the 



CHAP. IT. Craters of Elevation. 105 

nearest island, namely, Ascension, is very striking. At 
Ascension, the surfaces of the lav a- streams are glossy, as 
if just poured forth, their boundaries are well defined, 
and they can often be traced to perfect craters, whence 
they were erupted ; in the course of many long walks, 
I did not observe a single dike ; and the coast round 
nearly the entire circumference is low, and has been 
eaten back (though too much stress must not be placed 
on this fact, as the island may have been subsiding) 
into a little wall only from ten to thirty feet high. Yet 
during the 340 years, since Ascension has been known, 
not even the feeblest signs of volcanic action have been 
recorded. 1 On the other hand, at St. Helena, the course 
of no one stream of lava can be traced, either by the 
state of its boundaries or of its superficies ; the mere 
wreck of one great crater is left ; not the valleys only, 
but the surface of some of the highest hills, are inter- 
laced by worn-down dikes, and, in many places, the 
denuded summits of great cones of injected rock stand 
exposed and naked ; lastly, as we have seen, the entire 
circuit of the island has been deeply worn back into the 
grandest precipices. 

Craters of Elevation. 

There Is much resemblance in structure and in 
geological history between St. Helena, St. Jago, and 
Mauritius. All three islands are bounded (at least in 

1 In the ' Nautical Magazine' for 1835, p. 642, and for 1838, p. 
361, and in the * Comptes Bendus,' April, 1838, accounts aie given of 
a series of volcanic phenomena earthquakes troubled water 
floating scoriae and columns ot smoke which have been observed at 
intervals since the middle of the last century, in a space of open sea 
between longitudes 20 and 22 west, about half a degree south of 
the equator. These facts seem to show, that an island or an archi- 
pelago is in process of formation in the middle of the Atlantic : a 
line joining St. Helena and Ascension, prolonged, intei sects this 
slowly nascent focus of volcanic action. 



loS St. Helena. PART i. 

the parts which I was able to examine) by a ring of 
basaltic mountains, now much broken, but evidently 
once continuous. These mountains have, or apparently 
once had, their escarpements steep towards the interior 
of the island, and their strata dip outwards. I was 
able to ascertain, only in a few cases, the inclination of 
the beds ; nor was this easy, for the stratification was 
generally obscure, except when viewed from a distance. 
I feel, however, little doubt that, according to the re- 
searches of M. Elie de Beaumont, their average in- 
clination is greater than that which they could have 
acquired, considering their thickness and compactness, 
by flowing down a sloping surface. At St. Helena, 
and at St. Jago, the basaltic strata rest on older and 
probably submarine beds of different composition At 
all three islands, deluges of more recent lavas have 
flowed from the centre of the island, towards and be- 
tween the basaltic mountains ; and at St. Helena the 
central platform has been filled up by them. All 
three islands have been raised in mass. At Mauritius 
the sea, within a late geological period, must have 
reached to the foot of the basaltic mountains, as it now 
does at St. Helena ; and at St. Jago it is cutting back 
the intermediate plain towards them. In these three 
islands, but especially at St. Jago and at Mauritius, 
when, standing on the summit of one of the old basaltic 
mountains, one looks in vain towards the centre of the 
island, the point towards which the strata beneath 
one's feet, and of the mountains on each side, rudely 
converge, for a source whence these strata could have 
been erupted ; but one sees only a vast hollow platform 
stretched beneath, or piles of matter of more recent 
origin. 

These basaltic mountains come, I presume, into 
the class of Craters of elevation: it is immaterial 



CHAP. IT. Craters of Elevation. 107 

whether the rings were ever completely formed, for the 
portions which now exist have so uniform a structure, 
that, if they do not form fragments of true craters, 
they cannot be classed with ordinary lines of elevation. 
With respect to their origin, after having read the 
works of Mr. Lyell, 1 and of MM. 0. Prevost and Virlet, 
I cannot believe that the great central hollows have 
been formed by a simple dome-shaped elevation, and 
the consequent arching of the strata. On the other 
hand, I have very great difficulty in admitting that 
these basaltic mountains are merely the basal fragments 
of great volcanos, of which the summits have either 
been blown off, or more probably swallowed up by 
subsidence. These rings are, in some instances, so 
immense, as at St. Jago and at Mauritius, and their 
occurrence is so frequent, that I can hardly persuade 
myself to adopt this explanation. Moreover, I suspect 
that the following circumstances, from their frequent 
concurrence, are someway connected together, a con- 
nection not implied in either of the above views : 
namely, first, the broken state of the ring, showing 
that the now detached portions have been exposed to 
great denudation, and in some cases, perhaps, rendering 
it probable that the ring never was entire; secondly, 
the great amount of matter erupted from the central 
area after or during the formation of the ring; and 
thirdly, the elevation of the district in mass. As far 
as relates to the inclination of the strata being greater 
than that which the basal fragments of ordinary vol- 
canos would naturally possess, I can readily believe 
that this inclination might have been slowly acquired 
by that amount of elevation, of which, according to 
M. Elie de Beaumont, the numerous upfilled fissures or 

1 'Principles of Geology' (fifth edit.), vol. ii. p. 171. 



io8 - St. Helena. 



PAKE 



dikes are the evidence and the measure, a view 
equally novel and important, which we owe to the re- 
searches of that geologist on Mount Etna. 

A conjecture, including the above circumstances, 
occurred to me, when, with my mind fully convinced, 
from the phenomena of 1835 in South America, 1 that 
the forces which eject matter from volcanic orifices and 
raise continents in mass are identical, I viewed that 
part of the coast of St. Jago, where the horizontally 
upraised, calcareous stratum dips into the sea, directly 
beneath a cone of subsequently erupted lava. The 
conjecture is that, during the slow elevation of a vol- 
canic district or island, in the centre of which one or 
more orifices continue open, and thus relieve the sub- 
terranean forces, the borders are elevated more than 
the central area; and that the portions thus upraised 
do not slope gently into the central, less elevated area, 
as does the calcareous stratum under the cone at St. 
Jago, and as does a large part of the circumference of 
Iceland,' 2 but that they are separated from it by curved 

1 I have given a detailed account of these phenomena, in a paper 
read before the Geological Society in March, 1838. At the instant 
of time, when an immense area was convulsed and a large tract 
elevated, the districts immediately surrounding seveial of ttie great 
vents in the Cordillera remained quiescent ; the subtenanean forces 
being apparently relieved by the eruptions, which then recommenced 
with great violence An event of somewhat the same kind, but on 
an infinitely smaller scale, appears to have taken place, according 
to Abich (' Views of Vesuvius,' plates i. and ix.), within the great 
crater of Vesuvius, where a platform on one side of a fissure was 
raised in mass twenty feet, whilst on the other side, a tiain of small 
volcanos burst forth in eruption 

2 It appears, from information communicated to me in the most 
obliging manner by M B Bobert, that the circumferential p^rts of 
Iceland, which are composed of ancient basaltic s rata alternating 
with tuff, dip inland, thus forming a gigantic saucer M. Robert 
found that this was the case, with a few and quite local exceptions, 
for a space of coast several hundred miles in length. I fiod this 
statement coiroborated, as far as regards one place, by Mackenzie, 
in his 'Travels ' (p. 377), and m another place by some MS. notes 
kindly lent me by Dr. Holland. The coast is deeply indented by 
creeks, at the head of which the land is generally low, M Boberfc 



CHAP. IT. Craters of Elevation* 109 

faults. We might expect, from what we see along 
ordinary faults, that the strata on the upraised side, 
already dipping outwards from their oiiginal formation 
as lava-streams, would be tilted from the line of fault, 
and thus have their inclination increased. According 
fco this hypothesis, which I am tempted to extend only 
fco some few cases, it is not probable that the ring 
would ever be formed quite perfect; and from the 
elevation being slow, the upraised portions would 
generally be exposed to much denudation, and hence 
the ring become broken ; we might also expect to find 
occasional inequalities in the dip of the upraised 
masses, as is the case at St. Jago. By this hypothesis 
the elevation of the districts in mass, and the flowing 
of deluges of lava from the central platforms, are like- 
wise connected together. On this view the marginal 
basaltic mountains of the three foregoing islands might 
fctill be considered as forming < Craters of elevation ; ' 
the kind of elevation implied having been slow, and 
the central hollow or platform having been formed, not 
by the arching of the surface, but simply by that part 
having been upraised to a less height. 

informs me, that the inwardly dipping strata appear to extend <ts 
far as this line, and that their inclination usually corresponds with 
the slope of the surface, from the high coast- mountains to the low 
land at the head of these creeks In the section descnbed by Sir 
G-. Mackenzie, the dip is 12. The interior parts of the island chiefly 
consist, as f c \r as is known, of recently eiupted matter. The great 
size, however, of Iceland, equalling the bulkiest part of England, 
ought perhaps to exclude it from the class of islands we have boen 
considering ; but I cannot avoid suspecting that if the coast-moun- 
tains, instead of gently Doping into the less elevated central area, 
IT ad been separated from, it by irregularly curved faults the strata 
would have been tilted seaward, and a ' Crater of elevation/ like 
that of St. Jago or that of Mauritius, but of much vaster dimensions, 
would have been formed I will only further remark, that the 
frequent occurrence of extensive lakes at the foot of large volcanos, 
and the frequent association of volcanic and fresh-water strata, 
seem to indicate that the areas abound volcanos are apt to be 
depressed beneath the general level of the adjoining country, eithei 
from having been less elevated, or from the effects of subsidence. 



no Galapagos Archipelago. PAET 



CHAPTER, V, 

GALAPAGOS ARCHIPELAGO. 

Chatham Island Craters composed of a peculiar kind of tuff Small 
basaltic craters, with hollows at their bases Albemarle Island, fluid 
lai,as, their composition -Craters of tuff, inclination of their ex- 
terior diverging strata* and &tr*cture of their interior comecging 
strata James Island, segment of a small 'basaltic crater ; fluidity 
and composition of its lava streams* and of its ejected fragments 
Concluding remarlts on the craters of tuff, and on the breached con- 
dition of their southern &de$~Mvneralogical composition of the 
vochs of the arc hipelago Elevation of the land Direction of the 
fissures of eruption. 

THIS archipelago is situated tracbr the Equator, at a 
distance of between five and six hundred miles from 
the west coast of South America. It consists of five 
principal islands, and of several small ones, which 
together are equal in area, 1 but not in extent of land, 
to Sicily, conjointly with the Ionian Islands. They are 
all volcanic : on two, craters have been seen in erup- 
tion, and on several of the other islands, streams of 
lava have a recent appearance. The larger islands are 
chiefly composed of solid rock, and they rise with a 
tame outline to a height of between one and four 
thousand feet. They are sometimes, but not generally, 
surmounted by one principal orifice. The craters vary 

1 I exclude from this measurement, the small volcanic islands 
of Culpepper and Wenman, lying seventy miles northward of the 
group Craters were visible on all the islands of the group, except 
on Towers Island, which is one of the lowest ; this island is, however, 
formed of volcanic locks 



CHAP. V. 



Altered Tuff. 



in 



in size from mere spiracles to huge caldrons several 
miles in circumference ; they are extraordinarily 
numerous, so that I should think, if enumerated, they 
would be found to exceed two thousand ; they are 
formed either of scorias and lava, or of a brown coloured 
tuff; and these latter craters are in several respects 

No. 11. 



Wenman /. 



Abingdon L 



Narborougk I. 



Albemarle /, 




Tower I 



Tnfafatigable L 



BamngtonL 



Chatham 2, 



Hoods I 



GALAPAGOS ABCHIPXLAQO. 



remarkable. The whole group was surveyed by the 
officers of the Beagle. I visited myself four of the 
principal islands, and received specimens from all the 
others. Under the head of the different islands I will 
describe only that which appears to me deserving of 
attention. 

CHATHAM ISLAND. Craters composed of a singular 
Und of tuff. Towards the eastern end of this island 



112 Galapagos Archipelago. PAET i. 

there occur two craters composed of two kinds of tuff; 
one kind being friable, like slightly consolidated ashes ; 
and the other compact, and of a different nature from 
anything which I have met with described. This 
latter substance, where it is best characterised, is of a 
yellowish-brown colour, translucent, and with a lustre 
somewhat resembling resin ; it is brittle, with art 
angular, rough, and very irregular fracture, sometimes, 
however, being slightly granular, and even obscurely 
crystalline : it can readily be scratched with a knife, 
yet some points are hard enough just to mark common 
glass ; it fuses with ease into a blackish-green glass. 
The mass contains* numerous broken crystals of olivine 
and augite, and small particles of black and brown 
scoriae : it is often traversed by thin seams of calcareous 
matter. It generally affects a nodular or concretionary 
structure. In a hand specimen this substance would 
certainly be mistaken for a pale and peculiar variety of 
pitchstone ; but when seen in mass its stratification, 
and the numerous layers of fragments of basalt, both 
angular and rounded, at once render its subaqueous 
origin evident. An examination of a series of speci- 
mens shows that this resm-hke substance results from a 
chemical change on small particles of pale and dark- 
coloured sconaceous rocks; and this change could be 
distinctly traced in different stages round the edges of 
even the same particle. The position near the coast 
of all the craters composed of this kind of tuff or 
peperino, and their breached condition, renders it 
probable that they were all formed when standing im- 
mersed in the sea ; considering this circumstance, 
together with the remarkable absence of large beds of 
ashes in the whole archipelago, I think it highly 
probable that much the greater part of the tuff has 
originated from the trituration of fragments of the 



CHAP. T. Altered Tuff. 113 

gray, basaltic lavas in the mouths of craters standing in 
the sea. It may be asked whether the heated water 
within these craters has produced this singular change 
in the small scoriaceous particles, and given to them 
their translucent, resin-like fracture? Or has the 
associated lime played any part in this change ? I ask 
these questions from having found at St. Jago, in the 
Cape de Vercle Islands, that where a great stream of 
molten lava has flowed over a calcareous bottom into 
the sea, the outermost film, which in other parts re- 
sembles pitchstone, is changed, apparently by its 
contact with the carbonate of lime, into a resin-like 
substance, precisely like the best characterised speci- 
mens of the tuff from this archipelago. 1 

To return to the two craters : one of them stands at 
the distance of a league from the coast, the intervening 
tract consisting of a calcareous tuff, apparently of sub- 
marine origin. This crater consists of a circle of hills, 
some of which stand quite detached, but all have a very 
regular, qua-qu4 versal dip, at an inclination of between 
thirty and forty degrees. The lower beds, to the thick- 
ness of several hundred feet, consist of the resin-like 
stone, with embedded fragments of lava. The upper 
beds, which are between thirty and forty feet in thick- 
ness, are composed of a thinly stratified, fine-grained, 
harsh, friable, brown-coloured tuff, or pepermo. 2 A 
central mass without any stratification, which must 



1 The concretions containing lime, which I have described at 
Ascension, as formed in a bed of ashes, present some degree of re- 
semblance to this substance, but they have not a resinous fracture 
At at Helena, also, I found veins of a somewhat similar, compact, but 
non-resinous substance, occurring m a bed of pumiceous ashes, appa- 
rently free from calcareous matter : in neither of these cases could 
heat have acted 

* Those geologists who restr ct the term of * tuff to ashes of a 
white colour, resulting from the attrition of feldspatlnc lavas, would 
call these brown-coloured strata ' pepermo/ 



114 Galapagos Archipelago. PAKT i. 

formerly have occupied the hollow of the crater, but is 
now attached only to a few of the circumferential hills, 
consists of a tuff, intermediate in character between 
that with a resm-hke, and that with an earthy fracture. 
This mass contains white calcareous matter in small 
patches. The second crater (520 feet in height) must 
have existed until the eruption of a recent, great stream 
of lava, as a separate islet \ a fine section, worn by the 
sea, shows a grand funnel-shaped mass of basalt, sur- 
rounded by steep, sloping flanks of tuff, having in parts 
an earthy, and in others, a semi-resinous fracture. The 
tuff is traversed by several broad, vertical dikes, with 
smooth and parallel sides, which I did not doubt were 
formed of basalt, until I actually broke off fragments. 
These dikes, however, consist of tuff like that of the 
surrounding strata, but more compact, and with a 
smoother fracture; hence we must conclude, that 

No. 12. 




The Kicker Rock. 400 feet high. 

fissures were formed and filled up with the finer nrnd 
or tuff from the crater, before its interior was occupied, 
as it now is, by a solidified pool of basalt. Other 
fissures have been subsequently formed, parallel to 
these singular dikes, and are merely filled with loose 
rubbish. The change from ordinary scoriaceous parti- 
cles to the substance with a semi-resinous fracture, 



CHAP, v. Small Basaltic Craters. 115 

could be clearly followed in portions of the compact 
tuff of these dikes, 

At the distance of a few miles from these two 
craters, stands the Kicker Rock, or islet, remarkable 
from its singular form. It is unstratified, and is com- 
posed of compact tuff, in parts having the resin-like 
fracture. It is probable that this amorphous mass, 
like that similar mass in the case first described, once 
filled up the central hollow of a crater, and that its 
flanks, or sloping walls, have since been worn quite 
away by the sea, in which it stands exposed. 

Small basaltic craters. A bare, undulating tract, 
at the eastern end of Chatham Island, is remarkable 
from the number, proximity, and form of the small 
basaltic craters with which it is studded. They consist, 
either of a mere conical pile, or, but less commonly, of 
a circle, of black and red, glossy scoriae, partially ce- 
mented together. They vary in diameter from 30 to 
150 yards, and rise from about 50 to 100 feet above 
the level of the surrounding plain. From one small 
eminence, I counted sixty of these craters, all of which 
were within " a third of a mile from each other, and 
many were much closer. I measured the distance 
between two very small craters, and found that it was 
only thirty yards from the summit-rim of one to the 
rim of the other. Small streams of black, basaltic lava, 
containing olivine and much glassy feldspar, have flowed 
from many, but not from all of these craters. The 
surfaces of the more recent streams were exceedingly 
rugged, and were crossed by great fissures ; the older 
streams were only a little less rugged ; and they were 
all blended and mingled together in complete confusion. 
The different growth, however, of the trees on the 
streams, often plainly marked their different ages. 
Had it not been for this latter character, the streams 



1 16 Galapagos Arckipelag0* PART i. 

could in few cases have been distinguished ; and, con- 
sequently, this wide undulatory tract might have, (as 
probably many tracts have,) been erroneously considered 
as formed of one great deluge of lava, instead of by a 
multitude of small streams, erupted from many small 
orifices. 

In several parts of this tract, and especially at the 
base of the small craters, there are circular pits, with 
perpendicular sides, from twenty to forty feet deep. At 
the foot of one small crater, there were three of these 
pits. They have probably been formed, by the falling 
in of the roofs of small caverns. 1 In other parts, there 
are mammiform hillocks, which resemble great bubbles 
of lava, with their summits fissured by irregular cracks, 
which appeared, upon entering them, to be very deep; 
lava has not flowed from these hillocks. There are, 
also, other very regular, mammiform hillocks, composed 
of stratified lava, and surmounted by circular, steep- 
sided hollows, which, I suppose have been formed by a 
body of gas, first, arching the strata into one of the 
bubble-like hillocks, and then, blowing off its summit. 
These several kinds of hillocks and pits, as well as the 
numerous, small, scoriaceous craters, all show that this 
tract has been penetrated, almost like a sieve, by the 
passage of heated vapours. The more regular hillocks 
could only have been heaved up, whilst the lava was in 
a softened state. 2 

1 M Elie de Beaumont has described (* Me"m pour servir/ &c. 
torn iv. p I IB) many ' petits cirques d'e'bouleinent ' on Etna, of some 
of which the origin is historically known. 

2 Sir G- Mackenzie ('Travels in Iceland/ pp 889 to 392) has de- 
scribed a plain of lava at the foot of Hecla, everywhere heaved up into 
great bubbles or blisters. Sir George states that this cavernous lava 
composes the uppermost stratum ; and the same fact is affirmed by 
Von Buch ('Descript cles Isles Canaries/ p. 1 59), with respect to the 
bkb/altic stream near "Rialejo, in Teneriffe. It appears singular that 
it should be the upper streams that are chiefly cavernous, for one 
sees no reason why the upper and lower should not have been equally 



CHAP. Y. Fluidity of different Lavas. 117 

ALBEMAKLE ISLAND. This island consists of five 5 
great, flat-topped craters, which, together with the one 
on the adjoining island of Narborough, singularly re- 
semble each other, in form and height. The southern 
one is 4,700 feet high, two others are 3,720 feet, a third 
only 50 feet higher, and the remaining ones apparently 
of nearly the same height. Three of these are situated 
on one line, and their craters appear elongated in nearly 
the same direction. The northern crater, which is not 
the largest, was found by the triangulation to measure, 
externally, no less than three miles and one-eighth of a 
mile in diameter. Over the lips of these great, broad 
caldrons, and from little orifices near their summits, 
deluges of black lava have flowed down their naked sides. 

Fluidity of different lavas. Near Tagus or Banks' 
Cove, I examined one of these great streams of lava, 
which is remarkable from the evidence of its former 
high degree of fluidity, especially when its composition 
is considered. Near the sea-coast this stream is several 
miles in width. It consists of a black, compact base, 
easily fusible into a black bead, with angular and not 
very numerous air-cells, and thickly studded with large, 
fractured crystals of glassy albite, 1 varying from the 

affected at different times; have the inferior streams flowed "beneath 
the pressure of the sea, and thus been flattened, after the passage 
through them, of bodies of gas 1 

1 In the Cordillera of Chile, I ha\ e seen lava very closely resem- 
bling this variety at tV e Galapagos Archipelago. It contained, how- 
e\er, besides the albite, well-formed crystals of augite,and the base 
(perhaps in consequence of the aggregation of the augitic particles) 
was a shade lighter in colour. I may here remaik, that in all these 
cases, I call the feldspathic crystals, albite^ from their cleavage- 
planes (as measured by the reflecting goniometer) corresponding 
with those of that mineral. As, however, other species of this genus 
have lately been discovered to cleave in neaily the same planes with 
albite, this determination must be considered as only piovisional. I 
examined the crystals in the lavas of many different parts of the 
G-alapagos group, and I found that none of them, with the exception 
of some crystals from one part of James Island, cleaved in the 
direction of orthite or potash-feldspar. 



1 1 8 Galapagos Archipelago. BAET L 

tenth of an inch to half~an-inch, in diameter. This 
lava, although at first sight appearing eminently por- 
phyritic, cannot properly be considered so, for the 
crystals have evidently been enveloped, rounded, and 
penetrated by the lava, like fragments of foreign rock 
in a trap- dike. This was very clear in some specimens 
of a similar lava, from Abingdon Island, in which the 
only difference was, that the vesicles were spherical and 
more numerous. The albite in these lavas is in a 
similar condition with the leucite of Vesuvius, and with 
the olivine, described by Von Buch, 1 as projecting in 
great balls from the basalt of Lanzarote. Besides the 
albite, this lava contains scattered grains of a green 
mineral, with no distinct cleavage, and closely resem- 
bling olivine ; 2 but as it fuses easily into a green glass, 
it belongs probably to the augitic family: at James 
Island, however, a similar lava contained true olivine. 
I obtained specimens from the actual surface, and from 
a depth of four feet, but they differed in no respect. 
The high degree of fluidity of this lava-stream was at 
once evident, from its smooth and gently sloping sur- 
face, from the manner in which the main stream was 
divided by small inequalities into little nils, and es- 
pecially from the manner in which its edges, far below 
its source, and where it must have been in some degree 
cooled, thinned out to almost nothing ; the actual 
margin consisting of loose fragments, few of which were 
larger than a man's head. The contrast between this 
margin, and the steep walls, above twenty feet high, 
bounding many of the basaltic streams at Ascension, is 
very remarkable. It has generally been supposed that 
lavas abounding with large crystals, and including 

1 ' Description des Isles Canaries/ p 295. 
* Humboldt mentions that he mistook a green augitic mineral, 
occurring in the volcanic rocks of the Cordillera of Quito, for olivine. 



CHAP. v. Fluidity of different Lavas. 119 

angular vesicles, 1 have possessed little fluidity ; but we 
see that the case has been very different at Albemarle 
Island. The degree of fluidity in different lavas, does 
not seem to correspond with any apparent corresponding 
amount of difference in their composition : at Chatham 
Island, some streams, containing much glassy albite 
and some olivine, are so rugged, that they may be com- 
pared to a sea frozen during a storm ; whilst the great 
stream at Albemarle Island is almost as smooth as a 
lake when ruffled by a breeze. At James Island, black 
basaltic lava, abounding with small grains of olivine, 
presents an intermediate degree of roughness ; its sur- 
face being glossy, and the detached fragments resem- 
bling in a very singular manner, folds of drapery, cables, 
and pieces of th,e bark of trees. 2 

Graters of tuff. About a mile southward of Banks 5 
Cove, there is a fine elliptic crater, about 500 feet in 
depth, and three quarters of a mile in diameter. Its 
bottom is occupied by a lake of brine, out of which 
some little crateriform hills of tuff rise. The lower 
beds are formed of compact tuff, appearing like a 

1 The irregular and angular form of the vesicles is probably 
caused by the unequal yielding of a mass composed, in almost equal 
proportion, of solid crystals and of a viscid base It certainly seems 
a general circumstance, as might have been expected, that in lava, 
which has possessed a high degree of fluidity, as well as an even- 
sized grain, the vesicles are internally smooth and spherical 

2 A specimen of basaltic lava, with a few small broken crystals 
of albite, given me by one of the officers, is perhaps worthy of de- 
scription. It consists of cylindrical ramifications, some of which are 
only the twentieth of an inch in diameter, and are drawn out into 
the sharpest points. The mass has not been formed like a stalactite, 
for the points terminate both upwards and downwards. Globules, 
only the fortieth of an inch in diameter, have dropped from some of 
the points, and adhere to the adjoining branches The lava is vesi- 
cular, but the vesicles never reach the suiface of the branches, 
which are smooth and glossy. As it is generally supposed that vesi- 
cles are always elongated in the direction of the movement of the 
fluid mass, I may observe, that in these cylindrical branches, which 
vary from a quarter to only the twentieth of an inch in, diameter, 
every air-cell is spherical. 



I2O Galapagos Archipelago, PAST i, 

subaqueous deposit ; whilst the upper beds, round the 
entire circumference, consist of a harsh, friable tuff, 
of little specific gravity, but often containing fragments 
of rock in layers. This upper tuff contains numerous 
pisolitic balls, about the size of small bullets, which 
differ from the surrounding matter, only in being 
slightly harder and finer grained. The beds dip away 
very regularly on all sides, at angles varying, as I 
found by measurement, from 25 to 80 degrees. The 
external surface of the crater slopes at a nearly similar 
inclination ; and is formed by slightly convex ribs, 
like those on the shell of a pecten or scallop, which 
become broader as they extend from the mouth of the 
crater to its base. These ribs are generally from eight 
to twenty feet in breadth, but sometimes they are as 
much as forty feet broad ; and they resemble old, 
plastered, much flattened vaults, with the plaster 
scaling off in plates: they are separated from each 
other by gullies, deepened by alluvial action. At their 
upper and narrow ends, near the mouth of the crater, 
these ribs often consist of real hollow passages, like, 
but rather smaller than, those often formed by the 
cooling of the crust of a lava-stream, whilst the inner 
parts have flowed onward \ of which structure I saw 
many examples at Chatham Island. There can be no 
doubt but that these hollow ribs or vaults have been 
formed in a similar manner, namely, by the setting 
or hardening of a supeificial crust on streams of mud, 
which have flowed down from the upper part of the 
crater. In another part of this same crater, I saw 
open concave gutters between one and two feet wide, 
which appear to have been formed by the hardening 
of the lower surface of a mud-stream, instead of, 
as in the former case, of the upper surface. From 
these facts I think it is certain that the tuff must have 



CHAP. y. Craters of Tuff. 121 

flowed as mud. 1 This mud may have been formed 
either within the crater, or from ashes deposited on 
its upper parts, and afterwards washed down by torrents 
of rain. The former method, in most of the cases, 
appears the more probable one; at James Island, how- 
ever, some beds of the friable kind of tuff extend so 
continuously over an uneven surface,, that probably 
they were formed by the falling of showers of ashes. 

Within this same crater, strata of coarse tuff 3 chiefly 
composed of fragments of lava, abut, like a consoli- 
dated talus, against the inside walls. They rise to a 
height of between 100 and 150 feet above the surface 
of the internal brine-lake; they dip inwards, and are 
inclined at an angle varying from SO to 36 degrees. 
They appear to have been formed beneath water, pro- 
bably at a period when the sea occupied the hollow of 
the crater. I was surprise to observe that beds having 
this great inclination did not, as far as they could be 
followed, thicken towards their lower extremities. 

Banks' Cove. This harbour occupies part of the 
interior of a shattered crater of tuff larger than that 
last described. All the tuff is compact, and includes 
numerous fragments of lava ; it appears like a sub- 
aqueous deposit. The most remarkable feature in 
this crater is the great development of strata con- 
verging inwards ? as in the last case, at a considerable 
inclination, and often deposited in irregular curved 

1 This conclusion is of some interest, because M Dufrenoy 
(' Mem. pour servir,' torn iv, p 274) has argued from strata of tuff, 
apparently of similar composition with that here described, being 
inclined at angles hetween 18 and 20, that Monte Nuevo and some 
other craters of Southern Italy have been formed by upheaval. 
From the facts given above, of the vaulted character of the separate 
rills, and from the tuff not extending in horizontal sheets round 
these cratenf orm hills, no one will suppose that the strata have here 
been produced by elevation ; and yet we see that their inclination is 
above 20, and often as much as 80. The consolidated strata, also, 
of the internal talus, as will be immediately been, dips at an angle 
of above 30, 



122 Galapagos Archipelago. PART i. 

layers. These interior converging beds, as well as the 

proper, diverging, crateriform strata, are represented 

No, 13. 




A sectional sketch of the headlands forming Banks' Cove, showing the divciRing 
crateriform strata, and the converging stiatified talus The highest pumt of 
these hills is 817 feet above the sea 

in the accompanying rude, sectional sketch of the head- 
lands, forming this Cove. The internal and external 
strata differ little in composition, and the former have 
evidently resulted from the wear and tear, and re- 
deposition of the matter forming the external crateriform 
strata. From the great development of these inner 
beds, a person walking round the rim of this crater 
might fancy himself on a circular anti-clmal ridge 
of stratified sandstone and conglomerate. The sea is 
wearing away the inner and outer strata, and especially 
the latter ; so that the inwardly converging strata will, 
perhaps, in some future age, be left standing alone a 
case which might at first perplex a geologist. 1 

JAMES ISLAND Two craters of tuff on this island 
are the only remaining ones which require any notice. 

1 I believe that this case actually occurs m the Azores, where 
Dr Webster (< Description,' p 185) has described a basin-formed, 
little island, composed of strata of tuff, dipping inwards and 
bounded externally by steep sea-worn cliffs Dr, Daubeny supposes 
(on Volcanos, p 266), that this cavity must have been formed by a 
circular subsidence It appeais to me far more probable, that we 
here have strata which were originally deposited within the hollow 
of a crater, of which the exterior walls have since been removed by 
the sea. 



CHAP. T. James Island. 123 

One of them lies a mile and a-half inland from Puerto 
Grande : it is circular, about the third of a mile in 
diameter, and 400 feet in depth. It differs from all 
the other tuff-craters which I examined, in having the 
lower part of its cavity, to the height of between 100 
and 150 feet, formed by a precipitous wall of basalt, 
giving to the crater the appearance of having burst 
through a solid sheet of rock. The upper part of this 
crater consists of strata of the altered tuff, with a 
semi-res mo us fracture. Its bottom is occupied by a 
shallow lake of brine, covering layers of salt, which 
rest on deep black mud. The other crater lies at the 
distance of a few miles, and is only remarkable from 
its size and perfect condition. Its summit is 1,200 
feet above the level of the sea, and the interior hollow 
is 600 feet deep. Its external sloping surface presented 
a curious appearance from the smoothness of the wide 
layers of tuff, which resembled a vast plastered floor. 
Brattle Island is, I believe, the largest crater in the 
Archipelago composed of tuff; its interior diameter 
is nearly a nautical mile. At present it is in a ruined 
condition, consisting of little more than half a circle 
open to the south ; its great size is probably due, in 
part, to internal degradation, from the action of the sea. 
Segment of a small "basaltic crater. One side of 
Fresh-water Bay, in James Island, is bounded by a 
promontory, which forms the last wreck of a great 
crater, On the head of this promontory, a quadrant- 
shaped segment of a small subordinate point of 
eruption stands exposed. It consists of nine separate 
little streams of lava piled upon each other ; and 
of an irregular pinnacle, about fifteen feet high, of 
reddish -brown, vesicular basalt, abounding with large 
crystals of glassy albite, and with fused augite. 
This pinnacle, and some adjoining paps of rock on 



124 



Galapagos Archipelago. 



PART I. 



the beach, represents the axis of the crater. The 
streams of lava can be followed up a litttle ravine, at 
right angles to the coast, for between ten and fifteen, 
yards, where they are hidden by detritus: along the 
beach they are visible for nearly eighty yards, and I 
do not believe that they extend much farther. The 
three lower streams are united to the pinnacle ; and at 
the point of junction (as is shown in the accompanying 
rude sketch made on the spot), they are slightly arched, 

No. 14. 




Segment of a very small orifice of eruption, on the beach of Freshwater Bay 

as if in the act of flowing over the lip of the crater. 
The six upper streams no doubt were originally united 
to this same column before it was worn down by the 
sea. The lava of these streams is of similar com- 
position with that of the pinnacle, excepting that the 
crystals of albite appear to be more comminuted, and 
the grains of fused augite are absent. Each stream 
is separated from the one above it by a few inches, or 
at most by one or two feet in thickness, of loose frag- 
mentary scorias, apparently derived from the abrasion 
of the streams in passing over each other. All these 
streams are very remarkable from their thinness. I 
carefully measured several of them ; one was eight inches 
thick, but was firmly coated with three inches above. 



CHAP. v. Segment of a small Crater. 125 

and three inches below, of red scoriaceons rock (which 
is the case with all the streams), making altogether a 
thickness of fourteen inches: this thickness was pre- 
served quite uniformly along the entire length of the 
section. A second stream was only eight inches thick, 
including both the upper and lower scoriaceous surfaces. 
Until examining this section, I had not thought it 
possible that lava could have flowed in such uniformly 
thin sheets over a surface far from smooth. These 
little streams closely resemble in composition that 
great deluge of lava at Albemarle Island, which like- 
wise must have possessed a high degree of fluidity. 

Pseudo-extraneous^ ejected fragments. In the 
lava and in the scorise of this little crater, I found 
several fragments, which, from their angular form, 
their granular structure, their freedom from air-cells, 
their brittle and burnt condition, closely resembled 
those fragments of primary rocks which are occasionally 
ejected, as at Ascension, from volcanos. These frag- 
ments consist of glassy albite, much mackled, and with 
very imperfect cleavages, mingled with semi-rounded 
grains, having tarnished, glossy surfaces, of a steel-blue 
mineral. The crystals of albite are coated by a red 
oxide of iron, appearing like a residual substance ; and 
their cleavage-planes also are sometimes separated by 
excessively fine layers of this oxide, giving to the 
crystals the appearance of being ruled like a glass 
micrometer. There was no quartz. The steel-blue 
mineral, which is abundant in the pinnacle, but which 
disappears in the streams derived from the pinnacle, 
has a fused appearance, and rarely presents even a 
trace of cleavage ; I obtained, however, one measure- 
ment, which proved that it was augite; and in one 
other fragment, which differed from the others, in 
being slightly cellular, and in gradually blending into 



126 Galapagos Archipelago. PAET i 

the surrounding matrix the small grains of this mineral 
were tolerably well crystallised. Although there is so 
wide a difference in appearance between the lava of 
the little streams, and especially of their red scoriaceous 
crusts, and one of these angular ejected fragments, 
which at first sight might readily be mistaken for 
syenite, yet I believe that the lava has originated from 
the melting and movement of a mass of rock of abso- 
lutely similar composition with the fragments. Besides 
the specimen above alluded to, in which we see a 
fragment becoming slightly cellular, and blending into 
the surrounding matrix, some of the grains of the steel- 
blue augite also have their surfaces becoming very 
finely vesicular, and passing into the nature of ihe 
surrounding paste ; other grains are throughout, in an 
intermediate condition. The paste seems to consist 
of the augite more perfectly fused,, or, more probably, 
merely disturbed in its softened state by the movement 
of the mass, and mingled with the oxide of iron and 
with finely comminuted, glassy albite. Hence pro- 
bably it is that the fused albite, which is abundant 
in the pinnacle, disappears in the streams. The albite 
is in exactly the same state, with the exception of 
most of the crystals being smaller in the lava and in 
the embedded fragments ; but in the fragments they 
appear to be less abundant: this, however, would 
naturally happen from the intumescence of the augitic 
base, and its consequent apparent increase in bulk. It 
is interesting thus to trace the steps by which a com- 
pact granular rock becomes converted into a vesicular, 
pseudo-porphyritic lava, and finally into red scoriae. 
The structure and composition of the embedded frag- 
ments show that they are parts either of a mass of 
primary rock which has undergone considerable change 
from volcanic action, or more probably of the crust of 



CHAP. v. Ejected Fragments. 127 

a body cf cooled and crystallised lava, which has after- 
wards been broken up and re-liquefied ; the crust being 
less acted on by the renewed heat and movement. 

Concluding remarks on the tuff-craters. These 
craters, from the peculiarity of the resin-like substance 
which enters largely into their composition, from their 
structure, their size and number, present the most strik- 
ing feature in the geology of this Archipelago. The 
majority of them form either separate islets, or promon- 
tories attached to the larger islands; and those which 
now stand at some little distance from the coast are 
worn and breached, as if by the action of the sea, 
From this general circumstance of their position, and 
from the small quantity of ejected ashes in any part 
of the Archipelago, I am led to conclude, that the tuff 
has been chiefly produced, by the grinding together of 
fragments of lava within active craters, communicating 
with the sea. In the origin and composition of the 
tuff, and in the frequent presence of a central lake of 
brine and of layers of salt, these craters resemble, though 
on a gigantic scale, the ' salses/ or hillocks of mud, which 
are common in some parts of Italy and in other countries. 1 
Their closer connection, however, in this Archipelago, 
with ordinary volcanic action^ is shown by the pools of 
solidified basalt, with which they are sometimes filled up, 

It at first appears very singular, that all the craters 
formed of tuff have their southern sides, either quite 
broken down and wholly removed, or much lower than 
the other sides. I saw and received accounts of twenty- 
eight of these craters ; of these, twelve form separate 

1 D'Aubuisson's 'TrailS de GSognosie,' torn. i. p. 189 I may 
remark. tha,t I saw at Terceira, in the Azores, a crater of tuff or 
pepenno, very similar to these of the Galapagos Archipelago. From 
the description given in Frey chiefs * Voyage,' similar ones occur at 
the Sandwich Islands ; and probably they are present in many othet 
places. 



128 Galapagos Archipelago. PAET i. 

islets, 1 and now exist as mere crescents quite open to 
the south, with occasionally a few points of rock mark- 
ing their former circumference ; of the remaining six- 
teen, some form promontories, and others stand at a 
little distance inland from the shore ; but all, have 
their southern sides either the lowest, or quite broken 
down. Two, however, of the sixteen had their northern 
sides also low, whilst their eastern and western sides 
were perfect. I did not see, or hear of, a single ex- 
ception to the rule, of these craters being broken down 
or low on the side, which faces a point of the horizon 
between SE. and SW. This rule does not apply to 
craters composed of lava and scoriae. The explanation 
is simple : at this Archipelago, the waves from the 
trade-wind, and the swell propagated from the distant 
parts of the open ocean, coincide in direction, (which 
is not the case in many parts of the Pacific,) and with 
their united forces attack the southern sides of all the 
islands ; and consequently the southern slope, even 
when entirely formed of hard basaltic rock, is invariably 
steeper than the northern slope. As the tuff-craters 
are composed of a soft material, and as probably all, or 
nearly all, have at some period stood immersed in the 
sea, we need not wonder that they should invariably 
exhibit on their exposed sides the effects of this great- 
denuding power. Judging from the worn condition of 
many of these craters, it is probable that some have 
been entirely washed away. As there is no reason to 
suppose, that the craters formed of scorias and lava 



1 These consist of tlie three Grossman Islets, the largest of which 
is 600 feet m height : Enchanted Island , Gardner Island (760 feet 
high) : Champion Island (381 feet high) ; Enderby Island ; Brattle 
Island ; two islets near Indefatigable Island ; and one near James 
Island. A second crater near James Island (with a salt lake in its 
centre) has its southern side only about twenty feet high, whilst the 
other parts of the circumference are about 300 feet in height. 



CHAP. T. Breached Craters. 129 

were erupted whilst standing In the sea, we can see 
why the rule does not apply to them. At Ascension, it 
was shown that the mouths of the craters, which are 
there all of terrestrial origin, have been affected by the 
trade wind ; and this same power might here, also, aid 
in making the windward and exposed sides* of some of 
the craters originally the lowest. 

Mineralogical composition of the rocks. In the 
northern islands, the basaltic lavas seem generally to con- 
tain more albite than they do in the southern half of the 
Archipelago ; but almost all the streams contain some. 
The albite is not unfrequently associated with olivine. 
I did not observe in any specimen distinguishable 
crystals of hornblende or augite; I except the fused 
grains in the ejected fragments, and in the pinnacle of 
the little crater, above described. I did not meet with 
a single specimen of true trachyte ; though some of the 
paler lavas, when abounding with large crystals of the 
harsh and glassy albite, resemble in some degree this 
rock ; but in every case the basis fuses into a black 
enamel. Beds of ashes and far-ejected scoriae, as pre- 
viously stated, are almost absent ; nor did I see a frag- 
ment of obsidian or of pumice. Von Buch 1 believes 
that the absence of pumice on Mount Etna is conse- 
quent on the feldspar being of the Labrador variety ; 
if the presence of pumice depends on the constitution 
of the feldspar, it is remarkable, that it should be ab- 
sent in this archipelago, and abundant in the Cordillera 
of South America, in both of which regions the feld- 
spar is of the albitic variety. Owing to the absence of 
ashes, and the general indecomposable character of the 
lava in this Archipelago, the islands are slowly clothed 
with a poor vegetation, and the scenery has a desolate 
and frightful aspect. 

1 Description des Isles Canaries,' p. 328, 



130 Galapagos Archipelago. PARTI. 

'Elevation of ilw land. Proofs of tlie rising of the 
land are scanty and Imperfect. At Chatham Island, I 
noticed some great "blocks of lava, cemented by cal- 
careous matter, containing recent shells; but they 
occurred at the height of only a few feet above high- 
water mark. One of the officers gave me some frag- 
ments of shells, which he found embedded several 
hundred feet above the sea, in. the tuff of two craters, 
distant from each other. It is possible, that these 
fragments may have been carried up to their present 
height in an eruption of mud ; but as, in one instance, 
they were associated with broken oyster-shells, almost 
forming a layer, it is more probable that the tuff was 
uplifted with the shells in mass. The specimens are 
so imperfect that they can be recognised only as be- 
longing to recent marine genera. On Charles Island, 
I observed a line of great rounded blocks, piled on the 
summit of a vertical cliff, at the height of fifteen feet 
above the line, where the sea now acts during the 
heaviest gales. This appeared, at first, good evidence 
In favour of the elevation of the land but it was 
quite deceptive, for I afterwards saw on an adjoining 
part of this same coast, and heard from eye-witnesses, 
that wherever a recent stream of lava forms a smooth 
inclined plane, entering the sea, the waves during gales 
have the power of rolling up rounded blocks to a great 
height, above the line of their ordinary action. As the 
little cliff in the foregoing case is formed by a stream 
of lava, which, before being worn back, roast have en- 
tered the sea with a gently sloping surface, it is possible 
or rather it is probable, that the rounded boulders ? 
now lying on its summit, are merely the remnant of 
those which had been rolled up during storms to their 
present height. 

Direction of the fissures of eruption. The volcanic 



CHAP. v. Fissures of Eruption. 131 

orifices In this group cannot be 3 considered as Indis- 
criminately scattered. Tliree great craters on Albemarle 
Island form a well marked line, extending NW. by N. 
and SE. by S. Narborough Island, and the great crater 
on the rectangular projection of Albemarle Island, 
form a second parallel line. To the east. Hood's 
Island, and the islands and rocks between it and James 
Island, form another nearly parallel line, which, when 
prolonged, includes Culpepper and Wenmaii Islands, 
lying seventy miles to the north. The other Islands 
lying farther eastward, form a less regular fourth line. 
Several of these islands, and the vents on Albemarle 
Island, are so placed, that they likewise fall on a set 
of rudely parallel lines, intersecting the former lines at 
right angles ; so that the principal craters appear to 
lie on the points where two sets of fissures cross each 
other. The Islands themselves, with the exception of 
Albemarle Island, are not elongated in the same direc- 
tion with the lines on which they stand. The direction 
of these islands is nearly the same with that which 
prevails In so remarkable a manner in the numerous 
archipelagos of the great Pacific Ocean. Finally, I may 
remark, that amongst the Galapagos Islands there is no 
one dominant vent much higher than all the others, 
as may be observed in many volcanic archipelagos : the 
highest Is the great mound on the south-western ex- 
tremity of Albemarle Island, which exceeds by barely 
a thousand feet several other neighbouring craters. 



1 32 Trachyte and Basalt* PAET i. 



OHAPTEE VI. 

TRACHYTE AND BASALT. DISTRIBUTION OF VOLCANIC 
ISLES. 

The Uniting of crystals in fluid fava Specific gravity of the consti- 
tuent parts of trachyte and of basalt 9 and tlmr consequent separa- 
tion Obsidian Apparent non-separation of the element qfplutomc 
rocks Origin of trap-dikes in the plutonie series Ihst'ribution of 
volcanic islands; their preialence in fhe great oeeans TJiey are 
generally arranged in lines The central volcanos of Von Such 
&o\ibtfiil Volcanic islands "bordering continents Antiquity of 
volcanic idands, and their elevation in mass JUrujjtions on 
parallel lines ofjissure mthin the same geological period. 

On the separation of the constituent minerals of lava, 
according to their specific gravities. One side of 
Fresh-water Bay, in James Island, is formed by the 
wreck of a large crater, mentioned in the last chapter, 
of which the interior has been filled up by a pool of 
basalt, about 200 feet in thickness. This basalt is of a 
gray colour, and contains many crystals of glassy albite, 
which become much more numerous in the lower 
scoriaceous part. This is contrary to what might have 
been expected, for if the crystals had been originally 
disseminated in equal numbers, the greater intumescence 
of this lower scoriaceous part would have made them 
appear fewer in number. Von Buch * has described a 
stream of obsidian on the peak of Teneriffe, in which 
1 * Description des Isles Canaries/ pp. 190 and 191. 



YI, Trachyte and Basalt. 133 

the crystals of feldspar become more and more numerous, 
as the depth or thickness increases, so that near the 
lower surface of the stream the lava even resembles a 
primary rock. Von Buch further states, that M. Dree, 
in his experiments in melting lava, found that the 
crystals of feldspar always tended to precipitate them- 
selves to the bottom of the crucible. IB these cases, I 
presume there can be no doubt 1 that the crystals sink 
from their weight. The specific gravity of feldspar 
varies 2 from 2*4 to 2*58 3 whilst obsidian seems com- 
monly to be from 23 to 24; and in a fluidified state 
its specific gravity would probably be less, which would 
facilitate the sinking of the crystals of feldspar. At 
James Island, the crystals of albite, although no duubt 
of less weight than the gray basalt, in the parts where 
compact, might easily be of greater specific gravity 
than the scoriaceous mass, formed of melted lava and 
bubbles of heated gas. 

The sinking of crystals through a viscid substance 
like molten rock, as is unequivocally shown to have 
been, the case in the experiments of M. Dree, is worthy 
of further; consideration, as throwing light on the sepa- 
ration of the trachytic and basaltic series of lavas. 
Mr. P. Scrope has speculated on this subject ; but he 

1 In a mass of molten iron, it is found (' Edinburgh New Philoso- 
phical Journal,' vol xxiv p, 66) that the substances, which have a 
closer affinity for oxygen than iron has, rise from the interior of 
the mass to the surface But a similar cause can hardly apply to 
The separation of the crystal*, of these lava streams. The cooling of 
the surface of lava seems, in some cases, to have affected its compo- 
sition; for Dufrenoy (' Mem. pourservir,' torn, iv p, 271) found that 
the interior parts of a stieam near Naples contained two-thuds of a 
mineral which was acted on by acids, whilst the surface consisted 
chiefly of a mineral unattackable by acids. 

2 I have taken the specific gravities of the simple minerals from 
Yon Kobell, one of the latest and best authorities, and of the rocks 
from various authorities Obsidian, according to Phillips, is 2*35 ; 
and Jameson says it never exceeds 2-4 ; but a specimen from 
Ascension, weighed by myself, was 2*42, 



134 Trachyte and Basalt. PAET i, 

does not seem to have been aware of any positive facts 3 
such as those above given ; and he has overlooked one 
very necessary element, as it appears to me, in the 
phenomenon namely, the existence of either the 
hghter or heavier mineral in globules or in crystals. 
In a substance of imperfect fluidity, like molten rock, 
it is hardly credible, that the separate, infinitely small 
atoms, whether of feldspar, augite, or of any other 
mineral, would have power from their slightly different 
gravities to overcome the friction caused by their 
movement | but if the atoms of any one of these 
minerals became, whilst the others remained fluid, 
united into crystals or granules, it is easy to perceive that 
from the lessened friction, their sinking or floating power 
would be greatly increased. On the other hand, if all 
the minerals became granulated at the same time, it is 
scarcely possible, from their mutual resistance, that any 
separation could take place. A valuable, practical dis- 
covery, illustrating the effect of the granulation of one 
element in a fluid mass, in aiding its separation, has 
lately been made : when lead containing a small pro- 
portion of silver, is constantly stirred whilst cooling, it 
becomes granulated, and the grains or imperfect crystals 
of nearly pure lead sink to the bottom, leaving' a 
residue of melted metal much richer in silver ; whereas 
if the mixture be left undisturbed, although kept fluid 
for a length of time, the two metals show no signs of 
separating. 1 The sole use of the stirring seems to be, 



1 A full and interesting account of this discovery, by Mr. 
Pattinson, was read before the British Association in September, 
1838 In some alloys, according to Turner (' Chemistry,' p 210), 
the heaviest metal sinks, and it appears that this takes place whilst 
both metals are fluid. Where theie is a considerable diUerence in 
gravity, as between iron and the slag formed during the fusion of 
the ore, we need not be surprised at the atoms separating, without 
either substance being granulated, 



CIIA.P. vi. Trachyte and Basalt. 135 

tlie formation of detached granules. The specific 
gravity of silver is 10*4 3 and of lead 11-35 : the granu- 
lated lead, which sinks, is never absolutely pure, and 
the residual fluid metal contains, when richest, only 
i-fe part of silver. As the difference in specific gravity, 
caused by the different proportions of the two metals, 
is so exceedingly small, the separation is probably aided 
in a great degree by the difference in gravity between 
the lead, when granular though still hot, and when 
fluid. 

In a body of liquefied volcanic rock, left for some 
time without any violent disturbance, we might expect, 
in accordance with the above facts, that if one of the 
constituent minerals became aggregated into crystals 
or granules, or had been enveloped in this state from 
some previously existing mass, such crystals or granules 
would rise or sink, according to their specific gravity. 
Now we have plain evidence of crystals being embedded 
in many lavas, whilst the paste or basis has continued 
fluid. I need only refer, as instances, to the several, 
great, pseudo-porphyritic streams at the Galapagos 
Islands, and to the trachytic streams in many parts of 
the world, in which we find crystals of feldspar bent 
and broken by the movement of the surrounding, semi- 
fluid matter. Lavas are chiefly composed of three 
varieties of feldspar, varying in specific gravity from 
2*4 to 2 74 : of hornblende and augite, varying from 3 
to 3'4 1 of olivine, varying from 3*3 to 8*4; and lastly, 
of oxides of iron, with specific gravities from 4*8 to 5"2. 
Hence crystals of feldspar, enveloped in a ma r s of 
liquefied, but not highly vesicular lava, would tend to 
rise to the upper parts ; and crystals or granules of the 
other minerals, thus enveloped, would tend to sink. 
We ought not, however, to expect any perfect degree 
of separation in such viscid materials, Trachyte, 



1 36 Trachyte and Basalt. *ABT r. 

which consists chiefly of feldspar, with some hornblende 
and oxide of iron, has a specific gravity of about 2 45 ; l 
whilst basalt composed chiefly of augite and feldspar, 
often with much iron and olivine, has a gravity of about 
3-0. Accordingly we find, that where both trachytic 
and basaltic streams have proceeded from the same 
orifice, the tracnytic streams have generally been first 
erupted, owing, as we must suppose, to the molten lava of 
this series having accumulated in the upper parts of 
the volcanic focus. This order of eruption has been 
observed by Beudant, Scrope, and by other authors; 
three instances, also, have been given in this volume. 
As the later eruptions, however, from most volcanic 
mountains, burst through their basal parts, owing to 
the increased height and weight of the internal column 
of molten rock, we see why, in most cases, only the 
lower flanks of the central, trachytic masses, are en- 
veloped by basaltic streams.^ The separation of the 
ingredients of a mass of lava would, perhaps, sometimes 
take pla.ce within the body of a volcanic mountain, if 
lofty and of great dimensions, instead of within the 
underground focus; in which case, trachytic streams 
might be poured forth, almost contemporaneously, or 
at short recurrent intervals, from its summit, and 
basaltic streams from its base this seems to have taken 
place at Teneriffe. 2 I need only further remark, that 
from violent disturbances the separation of the two 
series, even tinder otherwise favourable conditions, 
would naturally often be prevented, and likewise their 

1 Trachj te from Java, was found by Von Buch to be 2 47; from 
Auvergne, by De la Beche, it was 2-42; from Ascension, by myself, 
it was 2*42. Jameson and other authors give to basalt a specific 
gravity of 3-0 , but specimens from Auvergne were found, by De la 
Beche, to be only 2-78 ; and from the Giant's Causeway, to be 2'9L 

2 Consult Von Buch's well-known and admirable Description 
Physigue of this island, which might serve as a model of descriptive 
geology 



CHAP. TI Trachyte and Basalt. 137 

usual order of eruption be inverted. From the high 
degree of fluidity of most basaltic lavas, these perhaps, 
alone, would in many cases reach the surface. 

As we have seen that crystals of feldspar, in the 
instance described by Von Buch, sink in obsidian, in 
accordance with their known greater specific gravity, 
we might expect to find in every trachytic district, 
where obsidian has flowed as lava, that it had proceeded 
from the upper or highest orifices. This, according to 
Von Buch, holds good in a remarkable manner both at 
the Lipari Islands and on the Peak of Teneriffe; at 
this latter place obsidian has never flowed from a less 
height than 9,200 feet. Obsidian, also, appears to have 
been erupted from the loftiest peaks of the Peruvian 
Cordillera. I will only further observe, that the specific 
gravity of quartz varies from 2-6 to 2*8 ; and therefore, 
that when present in a volcanic focus, it would not tend 
to sink with the basaltic bases ; and this, perhaps, 
explains the frequent presence, and the abundance of 
this mineral, in the lavas of the trachytic series, as 
observed in previous parts of this volume. 

An objection to the foregoing theory, will, perhaps, 
be drawn, from the plutonic rocks not being separated 
into two evidently distinct series, of different specific 
gravities ; although, like the volcanic, they have been 
liquefied. In answer, it may first be remarked, that 
we have no evidence of the atoms of any one of the 
constituent minerals in the plutonic series having been 
aggregated, whilst the others remained fluid, which we 
have endeavoured to show is an almost necessary con- 
dition of their separation ; on the contrary, the crystals 
have generally impressed each other with their forms. 1 

1 The crystalline paste of phonolite is frequently penetrated by 
long needles of hornblende ; from which it appears, that the horn- 
blende, though the more fusible mineral, has crystallised before, or 



138 Trachyte and Basalt* PART T, 

In the second place, the perfect tranquillity, under 
which it is probable that the plutonic masses, buried at 
profound depths, have cooled, would, most likely, be 
highly unfavourable to the separation of their consti- 
tuent minerals ; for, if the attractive force, which during 
the progressive cooling draws together the molecules of 
the different minerals, has power sufficient to keep 
them together, the friction between such half-formed 
crystals or pasty globules would effectually prevent the 
heavier ones from sinking, or the lighter ones from 
rising. On the other hand, a small amount of disturb- 
ance, which would probably occur in most volcanic 
foci, and which we have seen does not prevent the 
separation of granules of lead from a mixture of molten 
lead and silver, or crystals of feldspar from streams of 
lava, "by breaking and dissolving the less perfectly 
formed globules, would permit the more perfect and 
therefore unbroken crystals, to sink or rise, according 
to their specific gravity. 

Although in plutonic rocks two distinct species, 
corresponding to the trachytic and basaltic series, do 
not exist, I much suspect, that a certain amount of 
separation of their constituent parts has often taken 
place. I suspect this from having observed how fre- 
quently dikes of greenstone and basalt intersect widely 

at the same time with a more refractory substance. Phonolite, as far 
as my observations serve, in every instance appears to be an injected 
rock, like those of the plutonic series ; hence probably, like these 
latter, it has generally been cooled without repeated and violent dis- 
turbances. Those geologists who have doubted whether granite 
could have been formed by igneous liquefaction, because minerals 
of different degrees of fusibility impress each other with their forms, 
could not have been aware of the fact of crystallised hornblende 
penetrating phonolite, a rock undoubtedly of igneous origin. The 
viscidity, which it Is now known, that both feldspar and quartz retain 
at a temperature much below thair points of fusion, easily explains 
their mutual impressment. Consult on this subject Mr. Homer's 
paper on Bonn, * G-eolog. Transact.' vol. iv. p. 439 ; and ' I/Institut* 
with respect to quartz, 1839, p 161. 



CHAP. TI. Trachyte and Basalt. 139 

extended formations of granite and the allied meta- 
m orphic rocks. I have never examined a district in 
an extensive granitic region without discovering dikes j 
I may instance the numerous trap-dikes, in several 
districts of Brazil, Chile, and Australia, and at the Cape 
of Good Hope : many dikes likewise occur in the great 
granitic tracts of India, in the north of Europe, and in. 
other countries. Whence, then, has the greenstone 
and basalt, forming these dykes, come ? Are we to 
suppose, like some of the elder geologists, that a zone 
of trap is uniformly spread out beneath the granitic 
series, which composes, as far as we know, the founda- 
tions of the earth's crust ? Is it not more probable, that 
these dikes have been formed by fissures penetrating 
into partially cooled rocks of the granitic and meta- 
morphic series, and by their more fluid parts, consisting 
chiefly of hornblende, oozing out, and being sucked 
into such fissures ? At Bahia, in Brazil, in a district 
composed of gneiss and primitive greenstone, I saw 
many dikes, of a dark augitic (for one crystal certainly 
was of this mineral) or hornblendic rock, which, as 
several appearances clearly proved, either had been 
formed before the surrounding mass had become solid, 
or had together with it been afterwards thoroughly 
softened. 1 On both sides of one of these dikes, the 
gneiss was penetrated, to the distance of several yards, 
by numerous, curvilinear threads or streaks of dark 
matter, which resembled in form clouds of the class 
called cirrhi-comae 5 some few of these threads could be 
traced to their junction with the dike. When examin- 

1 Portions of these dikes have been broken off, and are now sur- 
rounded "by the primary rocks, with their laminse conformably wind- 
ing round them. Dr. Hubbard, also (* Silliman's Journal,' vol. xxxiv. 
p. 119), has described an interlacement of trap-veins in the granite 
of the White Mountains, which he thinks must have been formed 
when both rocks were soft. 



140 The Distribution of PAST j. 

ing them, I doubted whether such, hair-like and curvili- 
near veins could have been injected s and I now snspect ? 
that instead of having been injected from the dike, 
they were its feeders. If the foregoing view of the 
origin of trap-dikes in widely extended granitic regions 
far from rocks of any other formation, be admitted as 
probable, we may further admit 3 in the case of a great 
body of plutonic rock, being impelled by repeated 
movements into the axis of a mountain-chain, that its 
more liquid constituent parts might drain into deep 
and unseen abysses ; afterwards, perhaps, to be brought 
to the surface under the form, either of injected masses 
of greenstone and augitic porphyry, 1 or of basaltic 
eruptions. Much of the difficulty which geologists 
have experienced, when they have compared the com- 
position of volcanic with plutonic formations, will, I 
think, be removed, if we may believe, that most plutonic 
masses have been, to a certain extent, drained of those 
comparatively weighty and easily liquefied elements, 
which compose the trappean and basaltic series of 
rocks. 

On the distribution of volcanio islands, During 
my investigations on coral-reefs, I had occasion to 
consult the works of many voyagers, and I was invari- 
ably struck with the fact, that with rare exceptions, the 
innumerable islands scattered throughout the Pacific, 
Indian, and Atlantic Oceans, were composed either of 

1 Mr. Phillips ('Lardner's Cyclopaedia,' vol ii,p 115) quotes Von 
Buch's statement, that augitic poiphyry ranges parallel to, and is 
found constantly at the base of, great chains of mountains. 
Humboldt, also, has remarked the frequent occurrence of trap-rock, 
in a similar position ; of which fact I have observed many examples 
at the foot of the Chilian Cordillera. The existence of granite in 
the axes of great mountain chains is always probable, and I am 
tempted to suppose, that the laterally in-jectect masses of augitic 
porphyry and of trap, bear nearly the same relation to the granitic 
axes which basaltic lavas bear to the central trachytic masses, round 
the flanks of which they have so frequently been erupted. 



CHAP. YI. Volcanic Islands. 141 

volcanic, or of modern coral rocks. It would be tedious 
to give a long catalogue of all the volcanic islands ; but 
the exceptions which I have found are easily enumer~ 
ated: in the Atlantic, we have St. Paul's Eock, de- 
scribed in this volume, and the Falkland Islands, 
composed of quartz and clayslate; but these latter 
islands are of considerable size, and lie not very far 
from the South American coast : l in the Indian Ocean, 
the Seychelles (situated in a line prolonged from Mada- 
gascar) consist of granite and quartz: in the Pacific 
Ocean, New Caledonia, an island of large size, belongs 
(as far as is known) to the primary class. New Zealand, 
which contains much volcanic rock and some active 
volcanos, from its size cannot be classed with the small 
islands, which we are now considering. The presence 
of a small quantity of non- volcanic rock, as of clay-slate 
on three of the Azores, 2 or of tertiary limestone at 
Madeira, or of clay-slate at Chatham Island in the 
Pacific, or of lignite at Kerguelen Land, ought not to 
exclude such islands or archipelagos, if formed chiefly 
of erupted matter, from the volcanic class. 

The composition of the numerous islands scattered 
through the great oceans being with such rare excep- 
tions volcanic, is evidently an extension of that law, 
and the effect of those same causes, whether chemical 
or mechanical, from which it results, that a vast majority 
of the volcanos now in action stand either as islands 

1 Judging from Forster's imperfect observation, perhaps Georgia 
is not volcanic Dr. Allan is my informant with regard to the 
Seychelles. I do not know of what formation Kodriguez, in the 
Indian Ocean, is composed. 

2 This is stated on the authority of Count Y. de Bederaar, with 
respect to Flores and Graciosa (Charlsworth ' Magazine of Nat. Hist.' 
vol. i. p. 557). St Maria has no volcanic rock, according to Captain 
Boyd (Von Buoh's * Descnpt.' p. 365). Chatham Island has been 
described by Dr Diefenbachm the ' Geographical Journal,' 1841, p. 
201. As yet we have received only imperfect notices on Kerguelen 
Land, from the Antarctic Expedition, 



142 The Distribution of PAET i* 

in the sea, or near Its shores. This fact of the ocean- 
islands being so generally volcanic is also interesting 
in relation to the nature of the mountain-chains on 
our continents, which are comparatively seldom vol- 
canic; and yet we are led to suppose that where our 
continents now stand an ocean once extended. Do 
volcanic eruptions, we may ask, reach the surface more 
readily through fissures formed during the first stages 
of the conversion of the bed of the ocean into a tract 
of land ? 

Looking at the charts of the numerous volcanic 
archipelagos, we see that the islands are generally 
arranged either in single, double, or triple rows, in 
lines which are frequently curved in a slight degree. 1 
Bach separate island is either rounded, or more gene- 
rally elongated in the same direction with the group 
in which it stands, but sometimes transversely to it. 
Some of the groups which are not much elongated 
present little symmetry in their forms ; M. Virlet 2 
states that this is the case with the Grecian Archi- 
pelago : in such groups I suspect (for I am aware how 
easy it is to deceive oneself on these points), that the 
vents are generally arranged on one line, or on a set 
of short parallel lines, intersecting at nearly right 
angles another line, or set of lines. The Galapagos 
Archipelago offers an example of this structure, for 
most of the islands and the chief orifices on the largest 
island are so grouped as to fall on a set of lines ranging 
about NW. by E"., and on another set ranging about 
WSW. : in the Canary Archipelago we have a simpler 
structure of the same kind: in the Cape de Verde 

1 Professors William and Henry Darwin Rogers have lately in- 
sisted much, in a memoir read before the American Association, on 
the regularly curved lines of elevation in parts of the Appalachian 
range. 

2 Bulletin de la Soc. Ge*olog. torn. ill. p. 110. 



CHAP. YI. Volcanic Islands. ' 143 

group, which appears to be the least symmetrical of 
any oceanic volcanic archipelago, a NW. and SE. 
line formed by several islands, if prolonged, would 
intersect at right angles a carved line, on which the 
remaining islands are placed. 

Von Bach 1 has classed all volcanos ander two heads, 
namely, central volcanos, round which numerous erup- 
tions have taken place on all sides, in a manner almost 
regular, and volcanic chains. In the examples given 
of the first class, as far as position is concerned, I can 
see no grounds for their being called < central ; ' and 
the evidence of any difference in mineral ogical nature 
between central volcanos and volcanic chains appears 
slight. No doubt some one island in most small 
volcanic archipelagos is apt to be considerably higher 
than the others ; in a similar manner, whatever the 
cause may be, that on the same island one vent is 
generally higher than all the others. Von Buch does 
not include in his class of volcanic chains small archi- 
pelagos, in which the islands are admitted by him, as 
at the Azores, to be arranged in lines ; but when 
viewing on a map of the world how perfect a series 
exists from a few volcanic islands placed in a row to 
a train of linear archipelagos following each other in 
a straight line, and so on to a great wall like the 
Cordillera of America, it is difficult to believe that 
there exists any essential difference between short and 
long volcanic chains. Von Buch 2 states that his 
volcanic chains surmount, or are closely connected 
with, mountain-ranges of primary formation: but if 
trains of linear archipelagos are, in the course of time, 
by the long-continued action of the elevatory and 
volcanic forces, converted into mountain-ranges, it 

1 ' Description des Isles Canaries/ p. 324. 
a Idem, p. 393. 



144 The Distribution of 

would naturally result that the inferior primary rocks 
would often Tbe uplifted and brought into view. 

Some authors have remarked that volcanic islands 
occur scattered, though at very unequal distances, along 
the shores of the great continents, as if in some measure 
connected with them. In the case of Juan Fernandez, 
situated 330 miles from the coast of Chile, there was 
undoubtedly a connection between the volcanic forces 
acting under this island and under the continent, as 
was shown during the earthquake of 1835. The 
islands, moreover, of some of the small volcanic groups 
which thus border continents, are placed in lines, re- 
lated to those along which the adjoining shores of 
the continents trend; I may instance the lines of 
intersection at the Galapagos, and at the Cape de 
Yerde Archipelagos, and the best marked line of the 
Canary Islands. If these facts be not merely accidental, 
we see that many scattered volcanic islands and small 
groups are related not only by proximity, but in the 
direction of the fissures of eruption to the neighbouring 
continents a relation, which Von Buch considers, cha- 
racteristic of his great volcanic chains. 

In volcanic archipelagos, the orifices are seldom in 
activity on more than one island at a time ; and the 
greater eruptions usually recur only after long intervals. 
Observing the number of craters, that are usually found 
on each island of a group, and the vast amount of 
matter which has been erupted from them, one is led 
to attribute a high antiquity even to those groups, which 
appear, like the Galapagos, to be of comparatively recent 
origin. This conclusion accords with the prodigious 
amount of degradation, by the slow action of the sea, 
which their originally sloping coasts must have suffered, 
when they are worn back, as is so often the case, into 
grand precipices. "We ought not, however to suppose^ 



CHAP. 7i. Volcanic Islands, 145 

in hardly any Instance, that the whole body of matter, 
forming a volcanic island, has been erupted at the 
level, on which it now stands : the number of dikes, 
which seem invariably to intersect the interior parts of 
every volcano, show, on the principles explained by 
M. Elie de Beaumont, that the whole mass has been 
uplifted and fissured. A connection, moreover, between 
volcanic eruptions and contemporaneous elevations in 
mass * has, I think, been shown to exist, in my work on 
Coral Eeefs, both from the frequent presence of upraised 
organic remains, and from the structure of the accom- 
panying coral-reefs. Finally, I may remark, that in 
the same Archipelago, eruptions have taken place within 
the historical period on more than one of the parallel 
lines of fissure : thus, at the Galapagos Archipelago, 
eruptions have taken place from a vent on Narborough 
Island, and from one on Albemarle Island, which vents 
do not fall on the same line ; at the Canary Islands, 
eruptions have taken place in Teneriffe and Lanzarote ; 
and at the Azores, on the three parallel lines of Pico, 
St. Jorge, and Terceira. Believing that a mountain- 
axis differs essentially from a volcano, only in plutonic 
rocks having been injected, instead of volcanic matter 
having been ejected, this appears to me an interesting 
circumstance ; for we may infer from it as probable, 
that in the elevation of a mountain-chain, two or more 
of the parallel lines forming it may be upraised and 
injected within the same geological period. 

1 A similar conclusion is forced on us. by the phenomena, which 
accompanied the earthquake of 1835, at Conception, and which are 
detailed in my paper (vol. v. & 601) in the ' Geological Transactions-' 



146 New Soiith Wales. TAEX i. 



CHAPTER VIL 

N$w SoutJi Wales Sandstone formation JUnibedded pseudo-frag- 
ments of sfiale Stratification Currait-clcai age Great ? alleys 
Van Diemerfs Land Palaeozoic formation Newer formation, 
with volcanic rocks Travertin with leaves of eztinct giants 
Elevation of the land New Zealand King Greorgtfb Sound 
Superficial ferruginous beds Superficial calcareous deposit^ mtJi 
casts of branches Thewwigm ftom drifted ^articles of shells and 
corals Thevr exten 1 ' Cajie of Good Hojja Junction of the granite 
and clay -slate Sandstone f w mation. 

THE Beagle, in her homeward voyage, touched at New 
Zealand, Australia, Van Diemen's Land, and the Cape 
of Good Hope. In order to confine the Second Part of 
these Geological Observations to South America, I will 
here briefly describe all that I observed at these places 
worthy of the attention of geologists. 

New South Wales. My opportunities of observa- 
tion consisted of a ride of ninety geographical miles to 
Bathurst, in a "WTSTW. direction from Sydney. The 
first thirty miles from the coast passes over a sandstone 
country, broken up in many places by trap-rocks, and 
separated by a bold escarpment overhanging the river 
ISTepean, from the great sandstone platform of the Blue 
Mountains. This tipper platform is 1,000 feet high at 
the edge of the escarpment, and rises in a distance of 
twenty-five miles to between 8,000 and 4,000 feet above 
the level of the sea* At this distance the road descends 
to a country rather less elevated, and composed in chief 
part of primary rocks. There is much granite, in one 
part passing into a red porphyry with octagonal 



CHIP. TO. Sandstone Platforms* 147 

crystals of quarfcz, and Intersected in some places by 
trap-dikes. Near the Downs of Bathurst I passed over 
much pale-brown, glossy clay-slate, with the shattered 
laminse running north and south : I mention this fact, 
because Captain King informs me that, in the country 
a hundred miles southward, near Lake George, the 
mica-slate ranges so invariably north and south that 
the inhabitants take advantage of it in finding their 
way through the forests. 

The sandstone of the Blue Mountains is at least 
1,200 feet thick, and in some parts is apparently of 
greater thickness \ it consists of small grains of quartz, 
cemented by white earthy matter, and it abounds with 
ferruginous veins. The lower beds sometimes alternate 
with shales and coal : at Wolgan I found in carbona- 
ceous shale leaves of the Glosbopteris Brownii^ a fern 
which so frequently accompanies the coal of Australia. 
The sandstone contains pebbles of quartz; and these 
generally increase in number and size (seldom, however, 
exceeding an inch or two in diameter) in the upper 
beds : I observed a similar circumstance in the grand 
sandstone formation at the Cape of Good Hope, On 
the South American coast, where tertiary aud supra- 
tertiary beds have been extensively elevated, I re- 
peatedly noticed that the uppermost beds were formed 
of coarser materials than the lower : this appears to 
indicate that, as the sea became shallower, the force of 
the waves or currents increased. On the lower plat- 
form, however, between the Blue Mountains and the 
coast, I observed that the upper beds of the sandstone 
frequently passed into argillaceous shale, the effect, 
probably, of this lower space having been protected 
from strong currents during its elevation. The sand- 
stone of the Blue Mountains evidently having heen of 
mechanical origin, and not having suffered any meta- 
13 



1 4.8 ^ w South Wales, PAET i, 

morpMc action, I was surprised at observing that. In 
some specimens, nearly all the grains of quartz were so 
perfectly crystallised with brilliant facets that they 
evidently had not in their present form been aggregated 
in any previously existing rock. 1 It is difficult to 
imagine how these crystals could have been formed; 
one can hardly believe that they were separately pre- 
cipitated in their present crystallised state. Is it 
possible that rounded grains of quartz may have been 
acted on by a fluid corroding their surfaces, and de- 
positing on them fresh silica ? I may remark that, in 
the sandstone formation of the Cape of Good Hope, it 
is evident that silica has been profusely deposited from 
aqueous solution. 

In several parts of the sandstone I noticed patches 
of shale which might at the first glance have been 
mistaken for extraneous fragments; their horizontal 
lammse, however, being parallel with those of the 
sandstone, showed that they were the remnants of thin, 
continuous beds. One such fragment (probably the 
section of a long narrow strip) seen in the face of a cliff, 
was of greater vertical thickness tban breadth, which 
proves that this bed of shale must have been in some 
slight degree consolidated, after having been deposited, 
and before being worn away by the currents. Each 
patch of the shale shows, also, how slowly many of the 
successive layers of sandstone were deposited. These 
pseudo-fragments of shale will perhaps explain, in some 
cases, the origin of apparently extraneous fragments in 

1 I have lately seen, in a paper "by Smith (the father of English 
geologists), in the * Magazine of Natural History/ that the^grains of 
quartz in the millstone grit of England are of cen crystallised. Sir 
David Bre^ster, in a paper read before the British Association, 1840, 
states, that in old decomposed glass, the silex and metals separate 
into concentric rings, and that the silex regains its crystalline struc- 
ture, as is shown by its action oo light. 



CHAP. TO. Sandstone Platforms. 149 

crystalline metamorphic rocks. I mention this, because 
I found near Bio de Janeiro a well-defined angular 
fragment, seven yards long by two yards in breadth, of 
gneiss containing garnets and mica in layers, enclosed 
in the ordinary, stratified, porphyritic gneiss of the 
country. The laminae of the fragment and of the sur- 
rounding matrix ran in exactly the same direction, but 
they dipped at different angles. 1 do not wish to 
affirm that this singular fragment (a solitary case, as 
far as I know) was originally deposited in a layer, like 
the shale in the Blue Mountains, between the strata of 
the porphyritic gneiss, before they were metamorphosed; 
but there is sufficient analogy between the two cases to 
render such an explanation possible. 

Stratification of the escarpment. The strata of 
the Blue Mountains appear to the eye horizontal ; but 
they probably have a similar inclination with the sur- 
face of the platform, which slopes from the west to- 
wards the escarpment over the Nepean, at an angle of 
one degree, or of one hundred feet in a mile. 1 The 
strata of the escarpment dip almost conformably with 
its steeply inclined face, and with so much regularity, 
that they appear as if thrown into their present position j 
but on a more careful examination, they are seen to 
thicken and to thin out, and in the upper part to be 
succeeded and almost capped by horizontal beds. These 
appearances render it probable, that we here see an 
original escarpment, not formed by the sea having 
eaten back into the strata, but by the strata having 
originally extended only thus far. Those who have 
been in the habit of examining accurate charts of sea- 
coasts, where sediment is accumulating, will be aware, 
that the surfaces of the banks thus formed, generally 

1 This is stated on the authority of Sir T, Mitchell, in Ms 
4 Travels,' vol. ii. p. 357. 



1 50 New Sovtstfa Wales. PART i. 

slope from the coast very gently towards a certain line 
In the offing, beyond which the depth in most cases sud- 
denly becomes great. I may Instance the great banks 
of sediment within the West Indian Archipelago, 1 
which terminate in submarine slopes, inclined at angles 
of between 30 and 40 degrees, and sometimes even at 
more than 40 degrees : every one knows how steep such 
a slope would appear on the land. Banks of this nature, 
if uplifted, would probably have nearly the same ex- 
ternal form as the platform of the Blue Mountains, 
where it abruptly terminates over the Nepean. 

Current cleavage. The strata of sandstone in the 
low coast country, and likewise on the Blue Mountains, 
are often divided by cross or current laminae, which 
dip in different directions, and frequently at an angle 
of forty-five degrees. Most authors have attributed 
these cross layers to successive small accumulations on 
an inclined surface ; but from a careful examination in 
some parts of the New Red sandstone of England, I 
believe that such layers generally form parts of a series 
of curves, like gigantic tidal ripples, the tops of which 
have since been cut off, either by nearly horizontal 
layers, or by another set of great ripples, the folds of 
which do not exactly coincide with those below them. 
It is well known to surveyors that mud and sand are dis- 
turbed during storms at considerable depths, at least from 
800 to 450 feet, 2 so that the nature of the bottom even 
becomes temporarily changed; the bottom, also, at a 

1 I have described these very curious banks in the Appendix 
(2nd edit p 255) to my volume on the structure of Coral Reefs I 
have ascertained the inclination of the edges of the banks, from, 
information given me by Captain B. Allen, one of the surveyors, and 
by carefully measuring the honzontal distances between the la&t 
sounding on the bank and the first in the deep water. Wic3ely ex- 
tended banks in all parts of the West Indies have the same general 
form of surface. 

2 See Martin White, OB * Soundings in the British Channel,' pp, i 
and 166. 



CHAP. TXT. Great Valleys. 151 

depth between 60 and 70 feet, Las been observed 1 to be 
broadly rippled. One may, therefore, be allowed to 
suspect, from the appearances just mentioned in the 
New Eed sandstone, that at greater depths, the bed of 
the ocean is heaped up during gales into great ripple- 
like furrows and depressions, which are afterwards cut 
off by the currents during more tranquil weather, and 
again furrowed during gales. 

Valleys in the sandstone platforms. The grand 
valleys, by which the Blue Mountains and the other 
sandstone platforms of this part of Australia are pene- 
trated, and which long offered an insuperable obstacle 
to the attempts of the most enterprising colonist to 
reach the interior country, form the most striking 
feature in the geology of New South Wales. They are 
of grand dimensions, and are bordered by continuous 
lines of lofty cliffs. It is not easy to conceive a more 
magnificent spectacle, than is presented to a person 
walking on the summit-plains, when without any notice 
he arrives at the brink of one of these cliffs, which are 
so perpendicular, that he can strike with a stone (as I 
have tried) the trees growing, at the depth of between 
1,000 and 1,500 feet below him ; on both hands he sees 
headland beyond headland of the receding line of cliff, 
and on the opposite side of the valley, often at the 
distance of several miles, he beholds another line rising 
up to the same height with that on which he stands, 
and formed of the same horizontal strata of pale sand- 
stone. The bottoms of these valleys are moderately level, 
and the fall of the rivers flowing in them, according to 
Sir T. Mitchell, is gentle. The main valleys often send 
into the platform great bay-like arms, which expand at 
their upper ends ; and on the other hand, the platform 

1 M. Siau on the ' Action of Waves : * * Edin. New Phil. Journ. 
vol xxxi p 245. 



152 New South Wales* ?AET t 

often sends promontories into the valley, and even 
leaves in them great, almost insulated, masses- So 
continuous are the bounding lines of cliff, that to 
descend into some of these valleys, it is necessary to go 
round twenty miles ; and into others, the surveyors 
have only lately penetrated, and the colonists have not 
yet been able to drive in their cattle. But the most 
remarkable point of structure in these valleys, is, that 
although several miles wide in their upper parts, they 
generally contract towards their mouths to such a degree 
as to become impassable. The Surveyor-General, Sir 
T. Mitchell, 1 in vain endeavoured, first on foot and then 
by crawling between the great fallen fragments of sand- 
stone, to ascend through the gorge by which the river 
Grose joins the Nepean ; yet the valley of the Grose in 
its upper part, as I saw, forms a magnificent basin some 
miles in width, and is on all sides surrounded by cliffs, 
the summits of which are believed to be nowhere less 
than 3,000 feet above the level of the sea. When cattle 
are driven into the valley of the Wolgan by a path 
(which I descended) partly cut by the colonists, they 
cannot escape ; for this valley is in every other part 
surrounded by perpendicular cliffs, and eight miles 
lower down, it contracts, from an average width of half 
a mile, to a mere chasm impassable to man or beast. 
Sir T. Mitchell 2 states, that the great valley of the Cox 
river with all its branches contracts, where it unites 
with the Nepean, into a gorge 2,200 yards wide, and 
about 1,000 feet in depth. Other similar cases might 
have been added. 

The first impression, from seeing the correspondence 

1 * Travels in Australia/ vol. i. p 154. I must express my obliga- 
tion to Sir T Mitchell, for several interesting personal communica- 
tions on the subject of these great valleys of New South Wales. 

* Idem/ vol. ii, p. 358. 



CHAP. TO. Great Valleys. 153 

of the horizontal strata 3 on each side of these valleys 
and great amphitheatre-like depressions, is that they 
have been in chief part hollowed out, like other 
valleys, by aqueous erosion ; but when one reflects on 
the enormous amount of stone, which on this view 
must have been removed, in most of the above cases 
through mere gorges or chasms, one is led to ask 
whether these spaces may not have subsided. But con- 
sidering the form of the irregularly branching valleys, 
and of the narrow promontories, projecting into them 
from the platforms, we are compelled to abandon this 
notion. To attribute these hollows to alluvial action, 
would be preposterous ; nor does the drainage from 
the summit-level always fall, as I. remarked near 
the Weatherboard, into the head of these valleys, but 
into one side of their bay-like recesses. Some of the 
inhabitants remarked to me, that they never viewed 
one of these bay-like- recesses, with the headlands re- 
ceding on both hands, without being struck with their 
resemblance to a bold sea-coast. This is certainly the 
case ; moreover, the numerous fine harbours, with theii 
widely branching arms, on the present coast of Ne 1 ^ 
South Wales, which are generally connected with the 
sea by a narrow mouth, from one mile to a quarter of a* 
mile in width, passing through the sandstone coast-cliffs, 
present a likeness, though on a miniature scale, to the 
great valleys of the interior. But then immediately 
occurs the startling difficulty, why has the sea worn out 
these great, though circumscribed, depressions on a 
wide platform, and left merfe gorges, through which 
the whole vast amount of triturated matter must have 
been carried away? The only light I can throw on 
this enigma, is by showing that banks appear to be 
forming in some seas of the most irregular forms, and 
fchat the sides of such banks are so steep (as before 



1 54 New South Wales. PAET t 

stated) that a comparatively small amount of subse- 
quent erosion would form them into cliffs: that the 
waves have power to form high and precipitous cliffs, 
even in land-locked harbours, I have observed in many 
parts of South America. In the Eed Sea, banks with 
an extremely irregular outline and composed of sedi- 
ment, are penetrated by the most singularly shaped 
creeks with narrow mouths : this is likewise the case, 
though on a larger scale, with the Bahama Banks. 
Such banks, I have been led to" suppose, 1 have been 
formed by currents heaping sediment on an irregular 
bottom. That in some cases, the sea, instead of spread- 
ing out sediment in a uniform sheet, heaps it round 
submarine rocks and islands, it is hardly possible to 
doubt, after having examined the charts of the West 
Indies. To apply these ideas to the sandstone plat- 
forms of New South Wales, I imagine that the strata 
might have been heaped on an irregular bottom by the 
action of strong currents, and of the undulations of an 
open sea ; and that the valley-like spaces thus left un-% 
filled might, during a slow elevation of the land, have 
had their steeply sloping flanks worn into cliffs; the 
worn-down sandstone being removed, either at the time 
when the narrow gorges were cut by the retreating sea, 
or subsequently by alluvial action. 



Van Biemen's Land. 

The southern part of this island is mainly formed of 
mountains of greenstone, which often assumes a syenitic 

1 See the < Appendix* (2nd edit. pp. 251 and 255) to the * Part 
on Coral Beefs.' The fact of the sea heaping up mud round a sub- 
marine nucleus, is worthy of the notice of geologists : for outlayers 
of the same composition with the coast-banks are t hus formed ; and 
these, if upheaved and worn into cliffs, would naturally be thought 



CHAP. TH. Volcanic Rocks. 155 

character, and contains much, hypersthene. These moun- 
tains, in their lower half, are generally encased by strata 
containing numerous small corals and some shells. 
These shells have been examined by Mr. G. B. Sowerby, 
and are described in the Appendix : they consist of two 
species of Producta, and of six of Spirifera \ two of 
these, namely, P. rugata .and S. rotundata, resemble, 
as far as their imperfect condition allows of comparison, 
British mountain-limestone shells. Mr. Lonsdale has 
had the kindness to examine the corals ; they consist 
of six undescribed species, belonging to three genera. 
Species of these genera occur in the Silurian, Devonian, 
and Carboniferous strata of Europe. Mr. Lonsdale 
remarks, that all these fossils have undoubtedly a 
Palaeozoic character, and that probably they correspond 
in age to a division of the system above the Silurian 
formations. 

The strata containing these remains are singular 
from the extreme variability of their mineralogical 
composition. Every intermediate form is present, 
between flinty-slate, clay-slate passing into gray-wacke, 
pure limestone, sandstone, and porcellanic rock 5 and 
some of the beds can only be described as composed 
of a siliceo-calcareo-clayslate. The formation, as far 
as I could judge, is at least a thousand feet in thick- 
ness : the upper few hundred feet usually consist of a 
siliceous sandstone, containing pebbles and no organic 
remains ; the inferior strata, of which a pale flinty slate 
is perhaps the most abundant, are the most variable ; 
and these chiefly abound with the remains. Between 
two beds of hard crystalline limestone, near Newtown, 
a layer of white soft calcareous matter is quarried, and 
is used for whitewashing houses. From information 
given to me by Mr. JPrankland, the Surveyor-General, 
it appears that this Palaeozoic formation is found in 



156 Van Dieniens Land* PAET * 

different parts of the whole island; from the same 
authority, I may add, that on the north-eastern coast and 
in Bass' Straits primary roots extensively occur. 

The shores of Storm Bay are skirted, to the height 
of a few hundred feet, by strata of sandstone, contain- 
ing pebbles of the formation just described, with, its 
characteristic fossils, and therefore belonging to a sub- 
sequent age. These strata of sandstone often pass into 
shale, and alternate with layers of impure coal; they 
have in many places been violently disturbed. Near 
Hobart Town, I observed one dike, nearly a hundred 
yards in width, on one side of which the strata were 
tilted at an angle of 60, and on the other they were 
in some parts vertical, and had been altered by the 
effects of the heat. On the west side of Storm Bay, I 
found these strata capped by streams of basaltic lava 
with olivine ; and close by there was a mass of brecci- 
ated scoriae, containing pebbles of lava, which probably 
marks the place of an ancient submarine crater. Two 
of these streams of basalt were separated from each 
other by a layer of argillaceous wacke, which could be 
traced passing into partially altered scoriae. The 
wacke contained numerous rounded grains of a soft, 
grass-green mineral, with a waxy lustre, and translu- 
cent/ on its edges : under the blowpipe it instantly 
blackened, and the points fused into a strongly magnetic, 
black enamel. In these characters, it resembles those 
masses of decomposed olivine, described at St. Jago in 
the Cape de Verde group ; and I should have thought 
that it had thus originated, had I not found a similar 
substance, in cylindrical threads, within the cells of the 
vesicular basalt, a state under which olivine never 
appears ; this substance, 1 J. believe, would be classed as 
bole by mineralogists. 

1 Chlorophaeite, described by Dr. MacOulloch (* Western Islands/ 



OHAJP. VII. 



Travertin, with Extinct Plants. 157 



Travertin with extinct plants. Behind Hobarfc 
Town there is a small quarry of a hard travertin, the 
lower strata of which abound with distinct impressions 
of leaves. Mr. Robert Brown had the kindness to 
look at my specimens, and he informed me that there 
are four or five kinds, none of which le recognises as 
belonging to existing species. The most remarkable 
leaf is palmate, like that of a fan-palni, and no plant 
having leaves of this structure has hitherto been dis- 
covered in Van Diemen's Land. The other leaves do 
not resemble the most usual form of the Eucalyptus, 
(of which tribe the existing forests are chiefly com- 
posed,) nor do they resemble that class of exceptions to 
the common form of the leaves of the Eucalyptus, which 
occur in this island. The travertin containing this 
remnant of a lost vegetation, is of a pale yellow colour, 
hard, and in parts even crystalline ; but not compact, 
and is everywhere penetrated by minute, tortuous, 
cylindrical pores. It contains a very few pebbles of 
quartz, and occasionally layers of chalcedonic nodules, 
like those of chert in our Greensand. From the pure- 
ness of this calcareous rock, it has been searched for in 
other places, but has never been found. From this 
circumstance, and from the character of the deposit, it 
was probably formed by a calcareous spring entering a 
small pool or narrow creek. The strata have subse- 
quently been tilted and fissured ; and the surface has 
been covered by a singular mass, with which, also, a 
large fissure has been filled up, formed of balls of trap 
embedded in a mixture of wacke and a white, earthy, 
alurmno-calcareous substance. Hence it would appear, 

vol i p 504) as occurring in a basaltic amygdaloid, differs from this 
substance, in remaining unchanged before the blowpipe, and in 
blackening from exposure to the air. May we suppose that olivine, 
in undergoing the remarkable change described at St Jago, passes 
through several states 1 



158 Van Diemens Land, 

as if a volcanic eruption had taken place on the "borders 
of the pool, in which the calcareous matter was deposit- 
ing, and had broken it up and drained It. 

Elevation of the land, Both the eastern and 
western shores of the bay, in the neighbourhood of 
Hobarfc Town, are in most parts covered to the height 
of thirty feet above the level of high-water mark, with 
broken shells, mingled with pebbles. The colonists 
attribute these shells to the aborigines having carried 
them up for food : undoubtedly, there are many large 
mounds, as was pointed out to me by Mr. Frankland, 
which have been thus formed; but I think from the 
numbers of the shells, from their frequent small size, 
from the manner in which they are thinly scattered, 
and from some appearances in the form of the land, 
that we must attribute the presence of the greater 
number to a small elevation of the land. On the shore 
of Ealph Bay (opening into Storm Bay) I observed a 
continuous beach about fifteen feet above high-water 
mark, clothed with vegetation, and by digging into it, 
pebbles encrusted with Serpulge were found : along the 
banks, also, of the river Derwent, T found a bed oi 
broken sea shells above the surface of the river, and at 
a point where the water is now much too fresh for sea- 
shells to live ; but in both these cases, it is just possible, 
that before certain spits of sand and banks of mud in 
Storm Bay were accumulated, the tides might have 
risen to the height where we now find the shells. 1 

1 It would appear that some changes are now in progress in Ralpli 
Bay, for I was assured by an in'elhgent farmer, that oysters were 
formerly abundant in it, but that about the year 1834: they had, with- 
out any apparent cause, disappeared In the * Transactions of the 
Maryland Academy* (vol i parti p 28), there is an account by Mr. 
Dacatel, of vast beds of oysters and clams having been destroyed by 
the gradual filling up of the shallow lagoons and channels, on the shores 
of the southern United States. At Chiloe, in South America, I heard 
of a similar loss, sustained by the inhabitants, in the disappearance 
fiom one part of the coast of an edible species of Ascidia. 



CHAP. TO. Elevation of the Land. 159 

Evidence more or lesB distinct of a change of level 
between the land and water, has been detected on 
almost all the land on this side of the globe. Oapt. 
Grey, and other travellers, have found in southern 
Australia upraised shells, belonging either to the recent, 
or to a late tertiary period. The French naturalists 
in Bauclin's expedition, found shells similarly circum- 
stanced on the S. W. coast of Australia. The Eev. W. B. 
Clarke ! finds proofs of the elevation of the land, to the 
amount of 400 feet, at the Cape of Good Hope. In the 
neighbourhood .of the Bay of Islands in New Zealand, 2 
I observed that the shores were scattered to some height, 
as at Van Diemen's Land, with sea-shells, which the 
colonists attribute to the natives. Whatever may have 
been the origin of these shells, I cannot doubt, after 
having seen a section of the valley of the Thames Eiver 
(37 S.), drawn by the Eev. W. Williams, that the land 
has been there elevated : on the opposite sides of this 
great valley, three step-like terraces, composed of an 
enormous accumulation of rounded pebbles, exactly 
correspond with each other : the escarpment of each 
terrace is about fifty feet in height. No one after 
having examined the terraces in the valleys on the 

1 e Proceedings of the Geological Society,' vol iii. p. 420, 

2 I will here give a catalogue of the rocks which I met with near 
the Bay of Islands, in New Zealand * 1st, Much basaltic lava, and 
sconform rocks, forming distinct craters, 1 2nd, A castellated hill of 
horizontal strata of flesh-coloured limestone, showing when fractured 
distinct crystalline facets : the rain has acted on this rock in a 
remarkable manner, corroding its surface into a miniature model of 
an Alpine country : I observed here layers of chert and clay iron- 
stone ; and in the bed of a stream, pebbles of clay-slate; 3rd, The 
shores of the Bay of Islands are formed of a feldspathic rock, of a 
bluish-gray colour, often much decomposed, with an angular frac- 
ture, and crossed by numerous ferruginous seams, but without any 
distinct stratification or cleavage. Some varieties are highly 
crystalline, and would at once be pronounced to be trap ; others 
strikingly resembled clay-slate, slightly altered by heat : I was un 
able to form any decided opinion on this formation. 



j 60 King Georges Sound. * ART i. 

western shores of South America, which are strewed 
with sea-shells, and have been formed during intervals 
of rest in the slow elevation of the land, could doubt 
that the New Zealand terraces have been similarly 
formed. I may add, that Dr. Dieffenbacli, in his de- 
scription of the Chatham Islands, 1 (S.W. of New Zealand) 
states that; It is manifest that the sea has left many 
places bare which were once covered by its waters/ 



King George's Sound. 

This settlement is situated at the south-western 
angle of the Australian continent : the whole country 
is granitic, with the constituent minerals sometimes 
obscurely arranged in straight or curved lamina). In 
these cases, the rock would be called by Humboldt> 
gneiss-granite, and it is remarkable that the form of 
the bare conical hills, appearing to be composed of 
great folding layers, strikingly resembles, on a small 
scale, those composed of gneiss-granite at Bio de Janeiro, 
and those described by Humboldt at Venezuela. These 
piutonic rocks are, in many places, intersected by trap- 
pean-dikes ; in one place, I found ten parallel dikes 
ranging In an E. and W. line ; and not far off another 
set of eight dikes, composed of a different variety of 
trap, ranging at right angles to the former ones. I 
have observed in several primary districts, the occur- 
rence of systems of dikes parallel and close to each other* 

Superficial ferruginous beds, -The lower parts of 
the country are everywhere covered by a bed, following 
the inequalities of the surface, of a honeycombed sand- 
stone, abounding with oxides of iron. Beds of nearly 
similar composition are common.,, I belie ve 5 along the 
whole western coast of Australia, and on many of the 

1 * Geographical Journal/ vol. xi. pp. 202, 205, 



CHAP. vn. S^lperjicial Calcareous Deposit* 161 

East Indian islands. At the Cape of Good Hope, at 
the base of the mountains formed of granite and capped 
with sandstone, the ground is everywhere coated either 
by a fine-grained, rubbly, ochraceous mass, like that at 
King George's Sound, or by a coarser sandstone with 
fragments of quartz, and rendered hard and heavy by 
an abundance of the hydrate of iron, which presents, 
when freshly broken, a metallic lustre. Both these 
varieties have a very irregular texture, including spaces 
either rounded or angular, full of loose sand; from 
this cause the surface is always honey-combed. The 
oxide of iron is most abundant on the edges of the 
cavities, where alone it affords a metallic fracture. In 
these formations, as well as in many true sedimentary 
deposits, it is evident that iron tends to become aggre- 
gated, either in the form of a shell, or of a netwcrk. 
The origin of these superficial beds, though sufficiently 
obscure, seems to be due to alluvial action on detritus 
abounding with iron. 

Superficial calcareous deposit. A calcareous de- 
posit on the summit of Bald Head, containing branched 
bodies, supposed by some authors to have been corals, has 
been celebrated by the descriptions of many distinguished 
voyagers. 1 It folds round and conceals irregular hum- 
mocks of granite, at the height of 600 feet above the 
level of the sea. It varies much in thickness ; where 
stratified, the beds are often inclined at high angles, 
even as much as at 30 degrees, and they dip in all 
directions. These beds are sometimes crossed by 
oblique and even-sided laminse. The deposit consists 
either of a fine, white, calcareous powder, in which not 
a trace of structure can be discovered, or of exceedingly 
minute, rounded grains, of brown, yellowish, and pur- 

I visited this hill, in company with Captain FitzRoy, and we 
came to a similar conclusion regarding these branching bodies. 



1 62 King Georges Sound, PAKE 



rc & 



plish colours; botli varieties being generally, but not 
always, mixed with small particles of quartz, and being 
cemented into a more or less perfect) stone. The rounded 
calcareous grains, when heated in a slight degree, in- 
stantly lose their colours; in this and in every other 
respect, closely resembling those minute, equal-sized 
particles of shells and corals, which at St. Helena have 
been drifted up the sides of the mountains, and have 
thus been winnowed of all coarser fragments. I cannot 
doubt, that the coloured calcareous particles here have 
had a similar origin. The impalpable powder has 
probably been derived from the decay of the rounded 
particles; this certainly is possible, for on the coast of 
Peru, I have traced large imbrolten shells gradually 
falling into a substance as fine as powdered chalk. 
Both of the above-mentioned varieties of calcareous 
sandstone frequently alternate with, and blend into, 
thin layers of a hard substalagmitic * rock, which, even 

1 I adopt this term from Lieut. Kelson's excellent paper on the 
Bermuda Islands ( Geolog. Trans.* vol. v. p IOC), for the bard, com- 
pact, cream- or brown-coloured stone, without any crystalline struc- 
ture, which so of ten accompanies superficial calcai eous accumulations. 
I have obseived such superficial beds, coated with substala#mitic 
rock, at the Cape of Good Hope, in several pails of Chile, and over 
wide spaces in La Plata and Patagonia. Some of these beds have 
been lormed from decayed shells, but the oiigm of the Boater 
number is sufficiently obscure. The causes which determine water 
to dissolve lime, and then soon to icdepo&it it, aie not, I think, known. 
The surface of the substalagrmtic layeis appeals always to be 
corroded by the rain-water As all the above-mentioned countries 
have a long dry season, compared with the rainy one, I should have 
thought that the piesence of the substalagmite was connected with 
the climate, had not Lieut. Nelson found this substance forming 
under sea- water. Disintegrated shell seems to be extremely soluble ; 
of which I found good evidence, in a curious rock at. Coquimbo In 
Chile, which consis ed of small, pellucid, empty husks, cemented 
together. A series of specimens clearly showed that those hunks 
had originally contained small rounded particles of shells, which had 
been enveloped and cemented together by calcai ecus matter (as 
of ten. happens on sea- beaches), and which subsequently had decayed, 
and been dissolved by water, that must have penetrated through the 
calcareous husks, without corroding them 9 oi which processes, every 
stage could be seen. 



CHAP. vii. Superficial Calcareous Deposit. 163 

when, the stone on each side contains particles of quartz, 
is entirely free from them : hence we must suppose that 
these layers, as well as certain vein-like masses, have 
been formed by rain dissolving the calcareous matter 
and re-precipitating it, as has happened at St. Helena. 
Each layer probably marks a fresh surface, when the, 
now firmly cemented, particles existed as loose sand. 
These layers are sometimes brecciated and re-cemented, 
as if they had been broken by the slipping of the sand 
when soft. I did not find a single fragment of a sea- 
shell ; but bleached shells of the Helix melo* an existing 
land species, abound in all the strata ; and I likewise 
found another Helix, and the case of an Oniscus. 

The branches are absolutely undistinguishable in 
shape from the broken and upright stumps of a thicket ; 
their roots are often uncovered, and are seen to diverge 
on all sides 5 here and there a branch lies prostrate. 
The branches generally consist of the sandstone, rather 
firmer than the surrounding matter, with the centra 
parts filled, either with friable calcareous matter, or 
with a substalagmitic variety ; this central part is also 
frequently penetrated by linear crevices, sometimes, 
though rarely, containing a trace of woody matter. 
These calcareous, branching bodies, appear to have 
been formed by fine calcareous matter being washed 
into the casts or cavities, left by the decay of branches 
and roots of thickets, buried under drifted sand. The 
whole surface of the hill is now undergoing disintegra- 
tion, and hence the casts, which are compact and hard, 
are left projecting. In calcareous sand at the Cape of 
Good Hope, I found the casts, described by Abel, quite 
similar to these at Bald Head; but their centres are 
often filled with black carbonaceous matter, not yet 
removed. It is not surprising, that the woody matter 
should have been almost entirely removed from the 
12 



164 King George's Sound. 



PAET I, 



casts on Bald Head ; for it is certain, that many cen- 
turies must have elapsed since the thickets were buried ; 
at present, owing to the form and height of the narrow 
promontory, no sand is drifted up, and the whole sur- 
face, as I have remarked, is wearing away, We must, 
therefore, look back to a period when the land stood 
lower, of which the French naturalists l found evidence 
in upraised shells of recent species, for the drifting on 
Bald Head of the calcareous and quartzose sand, and 
the consequent embedment of the vegetable remains. 
There was only one appearance which at first made me 
doubt concerning the origin of the cast, namely, that 
the finer roots from different stems sometimes became 
united together into upright plates or veins ; but when 
the manner is borne in mind in which fine roots often 
fill up cracks in hard earth, and that these roots would 
decay and leave hollows, as well as the stems, there is 
no real difficulty in this case. Besides the calcareous 
branches from the Cape of Good Hope, I have seen 
casts, of exactly the same forms, from Madeira 2 and 

1 See M Pe'ron's ' Voyage,' torn. i. p. 204 

2 Dr. J Macaulay has fully described (' Edinb New Phil, Journ.' 
vol. xxix p 850) the casts from Madeira. He considers (differently 
from Mr. Smith of Jordan Hill) these bodies to be coralb, and the cal- 
careous deposit to be of subaqueous origin. His arguments chiefly 
rest (for his remarks on their structure are vagae) on the great 
quantity of the calcareous matter, and on the casts containing animal 
matter, as shown by their evolving ammonia. Had Dr. Macaulay 
seen the enormous masses of rolled particles of shells and corals on. 
the beach of Ascension, and especially on coral-reefs ; and had he 
reflected on the effects of long -continued, gentle winds, in drifting 
up the finer particles, he would hardly have advanced the argument 
of quantity, which is seldom trustworthy in geology. If the calca- 
reous matter has originated from disintegrated shells and coials, the 
presence of animal matter is what might have been expected. Mr, 
Anderson analyzed for Dr. Macaulay part of a cast, and he found it 
composed of 

Carbonate of lime 7315 

Silica 11-90 

Phosphate of lime .. 8"S1 
Animal matter ...,,,. 4-25 
Sulphate of lime .. a trace 

__ 



CHAP. TO. Superficial Calcareous Deposit. 165 

from Bermuda ; at this latter place, the surrounding 
calcareous rocks, judging from the specimens collected 
by Lieut. Nelson, are likewise similar, as is their sub- 
aerial formation. Eeflecting on the stratification of 
the deposit on Bald Head, on the irregularly alter- 
nating layers of substalagmitic rock, on the uniformly 
sized, and rounded particles, apparently of sea shells 
and corals, on the abundance of land-shells throughout 
the mass, and finally, on the absolute resemblance of 
the calcareous casts, to the stumps, roots, and branches 
of that kind of vegetation, which would grow on sand- 
hillocks, I think there can be no reasonable doubt, 
notwithstanding the different opinion of some authors, 
that a true view of their origin has been here given. 

Calcareous deposits, like these of King George's 
Sound, are of vast extent on the Australian shores. 
Dr. Fitton remarks, that c recent calcareous breccia (by 
which term all these deposits are included) was found 
during Baudm's voyage, over a space of no less than 
25 degrees of latitude and an equal extent of longitude, 
on the southern, western, and north-western coasts. ?1 
It appears also from M. Peron, with whose observations 
and opinions on the origin of the calcareous matter and 
branching casts mine entirely accord, that the deposit 
is generally much more continuous than near King 
George's Sound. At Swan River, Archdeacon Scott 2 
states that in one part it extends ten miles inland. 
Captain Wickham, moreover, informs me that during 
Ms late survey of the western coast, the bottom of the 

1 For ample details on tins formation, consult Dr Fitton's 
'Appendix to Capt King's Voyage' Dr Fitton is inclined to 
attribute a concrei ionary origin to the branching bodies : I may 
remark, that I have seen in beds of sand in La Plata cylindrical 
stems which no doubt thus originated ; but they differed much in 
appearance from these at Bald Head, and the other places above 
specified. 

2 * Proceedings of Geolog. Soc.' vol. i. p 320. 



1 66 Cape of Good Hope. PAST i. 

sea, wherever the vessel anchored, was ascertained by 
crow-bars being let down, to consist of white calcareous 
matter. Hence it seems that along this coast, as at 
Bermuda and at Keeling Atoll, submarine and sub- 
aerial deposits are contemporaneously in process of 
formation, from the disintegration of marine organic 
bodies. The extent of these deposits, considering their 
origin, is very striking ; and they can be compared in 
this respect only with the great coral-reefs of the Indian 
and Pacific Oceans. In other parts of the world, 
for instance in South America, there are superficial 
calcareous deposits of great extent, in which not a trace 
of organic structure is discoverable ; these observations 
would lead to the enquiry, whether such deposits may 
not, also, have been formed from disintegrated shells 
and corals. 

Cape of Good Hope. 

After the accounts given by Barrow, Carmichael, 
Basil Hall, and W. B. Clarke of the geology of this 
district, I shall confine myself to a few observations on 
the junction of the three principal formations. The 
fundamental rock is granite, 1 overlaid by clay-slate : 
the latter is generally hard, and glossy from containing 
minute scales of mica ; it alternates with, and passes 
into, beds of slightly crystalline, feldspathic, slaty rock. 
This clay-slate is remarkable from being in some places 
(as on the Lion's Rump) decomposed, even to the depth 
of twenty feet, into a pale-coloured, sandstone-like rock, 
which has been mistaken, I believe, by some observers, 

1 In several places I observed in the granite, small dark-coloured 
balls, composed of minute scales of black mica in a tough basis In 
another place, I found crystals of black schorl radiating from a 
common centre Dr Andrew Smith found, in the interior paits of 
the country, some beautiful specimens of granite, with silvery mica 
radiating or rather branching, like moss, from central points At 
the Geological Society, there are specimens of granite withcrystallised 
feldspar branching and radiating in like manner. 



. TO. Junction of Granite and Clay Slate. 167 

for a separate formation. I was guided by Dr. Andrew 
Smith to a fine junction at Green Point between the 
granite and clay-slate : the latter at the distance of a 
quarter of a mile from the spot, where the granite 
appears on the beach (though, probably, the granite is 
much nearer underground), becomes slightly more com- 
pact and crystalline. At a less distance, some of the 
beds of clay- slate are of a homogeneous texture, and 
obscurely striped with different zones of colour, whilst 
others are obscurely spotted. Within a hundred yards 
of the first vein of granite, the clay-slate consists of 
several varieties ; some compact with a tmge of purple, 
others glistening with numerous minnte scales of mica 
and imperfectly crystallised feldspar; some obscurely 
granular, others porphyritic with small, elongated spots of 
a soft white mineral, which being easily corroded, gives 
to this variety a vesicular appearance. Close to the 
granite, the clay- slate is changed into a dark-coloured, 
laminated rock, having a granular fracture, which is 
due to imperfect crystals of feldspar, coated by minute, 
brilliant, scales of mica. 

The actual junction between the granitic and clay- 
slate districts extends over a width of about 200 yards, 
and consists of irregular masses and of numerous dikes 
of granite, entangled and surrounded by the clay- slate : 
most of the dikes range in a NW. and SE. line, 
parallel to the cleavage of the slate. As we leave the 
junction, thin beds, and lastly, mere films of the altered 
clay-slate are seen, quite isolated, as if floating, in the 
coarsely-crystallised granite; but although completely 
detached, they all retain traces of the uniform NW. 
and SE. cleavage. This fact has been observed in 
other similar cases, and has been advanced by some 
eminent geologists, 1 as a great difficulty on the ordinary 

1 See M. Keilhau's * Theory on Granite,' tianslated in the ' Ediu 
burgh New Philosophical Journal,' voL xxiv. p, 402. 



1 6 8 Cape of Good Hope. I?AKT i, 

theory, of granite having been injected whilst liquefied; 
but if we reflect on the probable state of the lower 
surface of a laminated mass, like clay-slate, after having 
been violently arched by a body of molten granite, we 
may conclude that it would be full of fissures parallel 
to the planes of cleavage; and that these would be 
filled with granite, so that wherever the fissures were 
close to each other, mere parting layers or wedges of 
the slate would depend into the granite. Should, 
therefore, the whole body of rock afterwards become 
worn down and denuded, the lower ends of these de- 
pendent masses or wedges of slate would be left quite 
isolated in the granite; yet they would retain their 
proper lines of cleavage, from 1 having been united, 
whilst the granite was fluid, with a continuous covering 
of clay-slate. 

Following, in company with Dr. A, Smith, the line 
of junction between the granite and the slate, as it 
stretched inland, in a SE. direction, we came to a 
place, where the slate was converted into a fine-grained, 
perfectly characterised gneiss, composed of yellowish- 
brown granular feldspar, of abundant black brilliant 
mica, and of few and thin lammas of quartz. Prom 
the abundance of the mica in this gneiss, compared 
with the small quantity and excessively minute scales, 
in which it exists in the glossy clay-slate, we must 
conclude, that it has been here formed by the meta- 
morphic action a circumstance doubted, under nearly 
similar circumstances, by some authors. The laminae 
of the clay-slate are straight ; and it was interesting to 
observe, that as they assumed the character of gneiss, 
they became undulatory with some of the smaller 
flexures angular, like the laminse of many true meta- 
morphic schists. 

Sandstone formation. ---This formation makes the 



CHAP. vii. Sandstone Formation. 169 

most imposing feature in the geology of Southern 
Africa, The strata are in many parts horizontal, and 
attain a thickness of about 2,000 feet. The sandstone 
varies in character ; it contains little earthy matter, 
but is often stained with iron ; some of the beds are 
very fine-grained and quite white ; others are as com- 
pact and homogeneous as quartz rock. In some places 
I observed a breccia of quartz, with the fragments 
almost dissolved in a siliceous paste Broad veins of 
quartz, often including large and perfect crystals, are 
very numerous; and it is evident in nearly all the 
strata, that silica has been deposited from solution in 
remarkable quantity. Many of the varieties of quartzite 
appeared quite like metamorphic rocks ; but from the 
upper strata being as siliceous as the lower, and from the 
undisturbed junctions with the granite, which in many 
places can be examined, I can hardly believe that these 
sandstone-strata have been exposed to heat. 1 On the 
lines of junction between these two great formations, I 
found in several places the granite decayed to the 
depth of a few inches, and succeeded, either by a thin 
layer of ferruginous shale, or by four or five inches in 
thickness of the re-cemented crystals of the granite, on 
which the great pile of sandstone immediately rested. 

Mr. Schomburgk has described 2 a great sandstone 
formation in northern Brazil, resting on granite, and 
resembling to a remarkable degree, in composition and 
in the external form of the land, this formation of the 
Cape of Good Hope. The sandstones of the great plat- 
forms of Eastern Australia, which also rest on granite, 
differ in containing more earthy and less siliceous 

1 The Rev. W. B. Clarke, however, states, to my surprise 
(< Geolog Proceedirgs/ vol ui p. 422), that the sandstone in some 
parts is penetrated by granitic dikes : such dikes must belong to an 
epoch altogether subsequent to that when the molten granite acted 
on the clay-slate. 

2 ' GeographioalJoiunal,' vol x. p 246. 



1 70 Cape of Good Hope. PAET i. 

matter. No fossil remains have been discovered in 
these three vast deposits. Finally, I may add that I 
did not see any boulders of far-transported rocks at 
the Cape of Good Hope, or on the eastern and western 
shores of Australia, or at Van Diemen's Land. In the 
northern island of New Zealand, I noticed some large 
blocks of greenstone, but whether their parent rock was 
far distant, I had no opportunity of determining. 



APPENDIX TO PAET I 



DESCRIPTION OF FOSSIL SHELLS. 
BY Gr. B. SOWEKBY, ESQ., F.L S. 



SHELLS from a Tertiary deposit, beneath a great basaltic 
stream, at St. Jago in the Cape de Verde Archipelago, 
referred to at p. 6 of this volume. 

1. LIITOEINA PLANAXIS. Gr. Sowerby. 

Testd subovatd, crassd, Icevigatd, anfractibus guatuor, spiralit&r 
striatis; apertufd subovatd ; labio columellari infimdque parte 
anfractus ultimi planatis : long. 6, lot. O45, poll 

In stature and nearly in form this resembles a small periwinkle ; 
it difiers, however, very materially in having 1 the lower part of the 
last volution, and the columellarlip as it were cut off and flattened, 
as in the Pui purse. A mong the recent shells from the same locality, 
is one which greatly resembles this, and which may be identical, but 
which is a very young shell, and cannot therefoie be strictly com- 
pared. 

2 CERITHTUM ^MTTLTIM:. G. Sowerby. 

Testd oblongo-turritd, subventricostf, apice subulato, anfractibus 
decem lemter spirahilr striatts, primis sei'ie umcd tuberculorum 
insti uctis, intei mechis irregulantdr obsolete tufierculzferis, ultimo 
lonye inajori absque tukerculis, sulcis duobus fere basalibus in-" 
structo ; labii f>,&temi margine vnt&)*no intus crenulato : long. 1'8, 
lat. Q 7, poll. 

This species resembles so nearly one qf the shells brought to- 
gether by Lamarck, under the name of Cerithium Vertagus, that at 



172 Appendix to Part L 

first sight I thought it might be identical with it j it may be easily 
distinguished, however, by its being destitute of the fold in the 
centre of the eolumella so conspicuous m those shells. There is 
only one specimen, which has unfortunately lost the lower part of 
the outer ip, so that it is impossible to describe the form of the 
aperture. 

3. VE^TJS SIMULANTS. O. Sowerby. 

Testa rotundatd, ventiicosd, Iczviusculd, crassd; costis obfusis, 
fatmscults, concentricis, anHce posticeque tuberculatim solutis ; 
area cardinali potf.icd alter valvte latmsculd; impiessione 
mbumbonah posticd circulan: long. 1-8, alt. 1'8 3 tot. 15, 
poll 

A shell which is intermediate in its characters, taking its 
place between the Venus verrucosa of the British Channel and the 
F. rosalma of Rang of the western coast of Africa, but sufficiently 
distinguished fiom both by its broad, obtuse, concentric ribs, which 
are divided into tubercles both before and behind. It is also of a 
more circular foi m than either of those species. 

The following Shells, from the same bed, as far as they can 
be distinguished, are known to be recent species ; 

4. PtJEPUEA Ftrous. 

6. AMPHIDESMA ATJSTEALE. Sowerby. 

6. CONTJS YENTJLATTJS. Lam. 

7. FlSSUEELLA COAECTATA. Kiwg, 

8. PEKKA two odd valves, but in. such condition that it can- 
not "be identified. 

9. OSTREA COKNTTCOPIJE. Lam. 

10. AEG A OVATA. Lam. 

11. PATELLA NIGEITA. Budgm. 

12. TUEEITELLA BICiTOTJXATA ? Lam. 

13. STEOMBUS too much worn and mutilated to be identified. 

14. HIPPOISTX EADIATA. Gray. 

15. NATICA TTBEK. Valenciennes. 

16. PECTEN*, which in form resembles opercularis, but which is 
distinguishable by several characters. There is only a single valve, 
wherefore I cannot consider myself warranted to describe it. 

J7. PUPA STTBDIAPEANA. King. 
18. TEOOHUS indeterminable. 



Appendix to Part /. 173 



EXTINCT LAND-SHELLS PROM ST. HELENA. 

The following six species were found associated together, at 
the bottom of a thick bed of mould; the last two species 
namely, the Cochlogenafossilis and Helix biplicata were 
found, together with a species of Succinea now living on 
the Island, in a very modern calcareous sandstone. 
These Shells are referred to at p. 101 of this volume. 

1. COCHLOGBITA ATJKIS-VUXPINA. De Fer. 

This species is well described and figured in Martini and Chem- 
nitz's eleventh volume, Chemnitz expresses doubts as to what 
genus it might properly "be referj ed, and also a strong opinion un- 
favourable to the conclusion than it should be regarded as a land- 
shell. His specimens were bought at a public auction in Hamburg 1 , 
having been sent there by the late G Humphrey, who appeal s 
to have been very well acquainted with their real locality, and who 
sold them for land-shells Chemnitz, however, mentions one speci- 
men in Spengler's collection, in a fresher condition than his own, 
and which was said to be from China. The representation which he 
has given is taken from this individual, and appears to me to have 
been only a cleaned specimen of the St. Helena shell. It is easy to 
suppose that a shell from St. Helena might have been either acci- 
dentally or interestedly, after passing through two or three hands, 
sold as a Chinese shell, I think it is not possible that a shell of 
this species could have been really found in China ; and among the 
immense quantities of shells that come to this country from the 
Celestial Empire, I have never seen one. Chemnitz could not bring 
himself to establish a new genus for the reception of this remarkable 
shell, though he evidently could not collate it with any of the then 
known genera, and though he did not think it a land-shell, he has 
called it A.uris-vulpma. Lamarck has placed it as the second 
species of his genus Struthiolaria, under the name of crenulata. 
To this genus it does not however bear any affinity ; and there can 
be no doubt about the correctness of De Ferussac's views, who 
places it in the fourth division of his sub-genus CocMogena : and 
Lamarck would have been correct, according to his own principles, 
if he had placed it with his Auricula. A variety of this species 
occurs, which may be characterised as follows : 

COCHLOGEA ATTRlS-VTJLPINAj VOT* 

Testd subpyramidali, apetturd breviori, lablo tenuiori; long. 1'68, 
aperturcB O76, lat. 0-87, poll. 

OBS. The proportions of this differ from those of the usual 
variety, which are as follows: Length 1"65> of the aperture 1*, 



J 74 Appendix to Part L 

width 9C inch. It is worthy of observation, that all the shells 
of this variety came from a different part of the island, from the 
foregoing specimens. 4 

2. COCHLOGENA FOSSILIS. G. Soiverly. 

Testa oblongd, crassiusculd, spird subacumznafd, obtusd^ anfractibus 
seniS) subventncosis, leviter striatis, suturd profunde ^mpressd ; 
aperturd su^ovata ; pent remote continuo, subincrassato ; wribihco 
long. 8, lot. 37, poll. 



This species is of the stature of C. Guadaloupensis, but may 
easily he distinguished by the form of the volutions and the deeply- 
marked suture. The specimens vary a little in their proportions. 
This species was not obtained by Mr. Darwin, but is from the 
collection of the Geological Society. 

1. COCHLICOPA STTBPLICATA. G. Soiverby. 

Testd oblonf/d, subacumwato-pyraimdali, apice oUuso, anfractibus 
novem kevibus, postice subpheatis, suturd crenulatd ; aperturd 
ovatd, postice acutd, labio externo tenui; columelld obsolete sub- 
truncatd ; umbilico minima : long 0*93, lot. 28, poll. 

This and the following are placed with De Ferussac's sub-genus 
Oochlicopa, because they are most nearly related to his Cochlicopa 
follwulus. As species they are, however, both perfectly distinct, 
bein^r much larger, and not shining and smooth like C. folkculus, 
which is found in the south of Europe and at Madeira. Some very 
young shells and an egg were found, which I conjecture to belong 
to this species. 

2. COCHLICOPA TEEEBEILUM. G. Soiverby. 

Testd oblongdj cylindraceo-pyramidali, apice obtusiusculo, anfractibus 
septems, l&vibus; suturd postice crenulatd; aperturd ovali, 
postice acutd, labio externo tenui, antice dechm; columelld 
obsolete truncatd, umbilico minimo: long. 077, lot. 0'25 ; 
poll. 

This species differs from the last in being more cylindrical, and 
in being nearly free, when full grown, from the obtuse folds of th^ 
posterior volutions, as well as m the form of the aperture. The 
young shells of this species are longitudinally striated, and they 
have some very obsolete longitudinal folds. 

1. HELIX BILAMELLATA. G. Sowerby. 

Testd orbiculato-depressd, spird pland, anfractibus senis, ultimo 
subtus ventricoso, superne anyulari; umbilico parvo; aperturd 



Appendix to Part I. 175 

semilunari) superne extm angulatd, labio externo tenui: vnterno 
plias duabus spiralibus, posticd majori: long. O15, lot. 0*33. 
poll, 

The young- shells of this species have very different proportions 
from those marked above, their axis being nearly as great as their 
width. The largest specimen is white, with irregular ferruginous 
rays. This is very different from any known recent species, although 
there are several to which it appears to have some analogy, such as 
JSeliM epistyhum or Coohiana, and H. gularis : in both of these, 
however, the internal spiral plaits are placed within the outer wall 
of the shell, and not upon the inner lamina, as in Hehi bilamdlata. 
There is another recent species, which is somewhat analogous to 
this; it is as yet undescribed, and differs from this and from 
Cookiana, in the circumstance of its possessing four internal spiral 
plaits, two of Tvhich are placed within the outer, and two upon 
the inner wall of the shell ; it was brought from Tahiti, in the 
Bcayle. 

2. HELIX POLTODOK. O. Soiverby. 

Testa orbzculnto-subdepressd, anfractibus sex, rotundatis, striatis ; 
aperturd $< milunari, labio interno phcis tribus spiralibus, posticis 
gradatwi majonbus, e&tcrno wtus denftbus qmnqup instructo ; 
umbihco mediocn : long. 0*07, lai, \^,poll. 

This is somewhat ^related to Helix contorta of De Ferussac, 
<Moll. terr. et fluv.' Tab. 51 A, f. 2; but differs from it in several 
particulars. 

3. HELIX SPTJKCA. 6r. Sowerby. 

Testd suborbiculari, spird subconoided f obtusd ; anfractibus guatuor 
tumidiSj subsh wtis; aperturd mayna,pemtremate tenui; umbilico 
parvOj pro/undo : long. O'l, lot. ()'13,poZl. 

Easily distinguished from Helix polyodon, by its wide, toothless 
aperture. 

4. HELIX BIPLICATA. O. Sowerby. 

Tesfd orbiculato-depressd, anfractibus qmnque rotundcrfis, striatis ; 
aperturd sevnlimari, lobio interno plitis duabusspircdibuSj postud 
majori; umbilico mac/no : long (K)4, lat. O'l, poll. 

This must be regarded as perfectly distinct from Helix bilamellata. 
on account of its form ; its umbilicus is much larger, its spire is not 
flat, nor is the posterior edge of each volution angular. There are 
specimens, which must be referred to this species, found with the 
foregoing species, and with the Cochloffenafossilts, which latter is 
associated with a living Succmea, in the modern calcareous sand* 
stone. 



176 Appendix to Part L 

PALAEOZOIC SHELLS FROM VAN DIEMENS LAND, 

BEFEBUED TO AT P. 155 OF THIS VOLOTE. 
1. PEOEtrCTA ETJGATA. 

This is probably the same species with that named Producta 
ntgata by Phillips (' Geology of Yorkshire/ part n. plate vii. f 16) : 
it is, however, in too imperfect a condition to allow me to decide 
positively. 

2. PEODUCTA BEACEYTH^ETTS. G. Sowerby. 

Producta, Testa subtrnpeziformi, compressd, parte anticd latiori, wb~ 
bilobdj posticd angustiori, lined cat dinali brevi. 

The most remarkable characters of this species are the shortness 
of the hmsre-line, and the comparative width of the anterior part: 
its outside is ornamented with small, blunt tubercles, irregularly 
placed : it is in limestone, of the ordinary grey colour of mountain 
limestone. Another specimen which I suppose to be an impression 
of the inside of the fat valve, is in stone, of a light rusty-brown 
colour. There is a third specimen, which I believe to be* the im- 
pression of the inside of the deeper valve, in a nearly similar stone, 
accompanied by other shells. 

1, SPIEIFEEA STJBEADJATA. G. Soiverby. 

Spirifera, Tesrd I&utssimd, pa> te mtchand laid, radiis lateralibus 
latins pawns, inconspicuis 



The breadth of this shell is rather greater than its length. The 
rays of the lateral surfaces are very few and indistinct, and the 
medial lobe is uncommonly large and wide. 

2. SPJEIEEEA EOTUHBATA? Phillips' 8 { Geoloyy of Yorkshire} 
pi. ix. f. 17. 

Although this shell is not exactly like the figure above referred 
to, it would perhaps be impossible to find any good distinguishing 
character. Our specimen is much distorted j it is, moreover, an 
example of that sort of accidental variation that shows how little 
dependence, ou^ht, in some instances, to be placed upon particular 
characters ; for the radiating ribs of one side of one valve are much 
more numerous and closer than those on the other side of the same 
valve. 



Appendix to Part L 177 

3. SPIEIFEBA TRAPEZOIDALIS. G. Sowerly. 

Spirifera, Testd subteti agond, mediand parte profundd, radiis non- 
nullis, subinconspicms ; radiis lateralibus utriusquelaterisseptem 
ad octo distinctis : long. 1 5, lot. %', poll. 

There are two specimens of this, in a dark, rusty, gray limestone, 
probably bituminous. 

SPIKIEBRA TRAPEZOIDALIS, var. ? G. Sowerby. 
Spirifera, Testa radiis lateralibus tripartitim divisis, lineis incrementi 
antiquaiis, cater oquin omninb ad Spiriferam ti apesoidalem 
swmlhmd. 

At first I hesitated to unite this to Spirifera trapezoidahs, but 
observing that at the commencement the radiating ribs were simple, 
and knowing that thee are subject to variations, I have thought it 
best merely to distinguish this specimen as a variety. 



There are several other, probably distinct, species of Spiriferse, 
"bat as these are only casts, it is obviously impossible to give the 
external characters of the species. Since, however, they are very 
remarkable, I have thought it advisable to give a name, together 
with a short description of each. 

4. SPIRIFERA PATTCICOSTATA. G. Soiuerly. 

Length equal to about two-thirds of its breadth ; ribs few and 
"Variable. 

5. SPIEIFEEA VESPEKTILIO. G. Soiverby. 

Breadth more than double its length, radiating ribs rather large, 
distinct, and not numerous , posterior inner surface covered with 
distinct punctulations in both valves. 

6. SPIRIFEEA AVTCTJUA. G. Sowerby. 

The proportions of this species are very remarkable, inasmuch 
as it appears to have been nearly three times as wide as it is long; 
the radiating ribs are not very numerous, and the Internal posterior 
surface of one valve alone (the large valve) has been punctulated. 
In its proportions it resembles Phillips's Spinfera convoluta, but as 
our $p amcida is only a cast of the inside, its proportions are not 
so abnormal as those of Sp conwluta. 1 

A specimen, which is very much pressed out of its natural shape, 
but which still appears to differ somewhat in its proportions, shows 
not only the cast of the inside, but also the impression of the out- 
side ; its radiating ribs are very irregular, and numerous, but it 
must be regarded as doubtful whether some of them be not principal 
and others only interstitial : their irregularity renders it impossible 
to decide. 

1 ' Geology of Yorkshire,' part ii. plate ix f . 7. 



178 Appendix to Part L 



DESCBIPTION OP SIX SPECIES OF COBALS, 
FBOM THE PALAEOZOIC FORMATION OF 

YAH DIEMEN'S LAND. 

Bx W. LONSDALE, ESQ., F.G.S. 



1. STENOPOKA TASMANIENSIS, sp. n. 1 

Branched, tranches cylindrical, variously inclined or contorted; 
tubes more or less divergent; mouths oval, divisional ridges 
strongly tuberculatcd; indications of successive narrowing in 
each tube, I 2. 

THIS coral, In its general mode of growth, resembles Calamopora 
(Stenopoia?) tumida, (Mr. Phillips, 'Geol. of Yorkshire/ part n. 
pi. 1, fig 62), but in the form of the mouth and other structural 
details the differences are very great. Stenopora Tasmamensis 
attains considerable dimensions, one specimen being 4^ inches in 
length and half an inch in diameter 

The branches have individually great uniformity in their circum- 
ference, but they differ with respect to each other in the same speci- 
men, and there is no definite method of subdivision or direction 
of growth. The extiemities are occasionally hollow ; and one 
specimen, about 1 inch in length, and half an inch in breadth, is 
crushed completely flat. The tubes, in the best exposed cases, have 
considerable length, springing almost solely from the axis of the 
branch, and diverging very gently till they nearly reach the circum- 
ference, where they bend outwards In the body of the branch 
the tubes are angular from lateral interference ; but, on approaching 
the outer surface, they become oval in consequence of the inter- 
spaces prod uced by the greater divergence. Their diameter is ver y 
uniform throughout, with the exception of the narro wings near the 
terminations of the full-grown tubes. The walls in the interior of 

1 Though the characters of this genus are unpublished, it has been 
thought advisable not to give them fully in this notice, a very few 
species only having been examined. The coral is essentially com- 
posed of simple tabes, variously aggregated and radiating outwards. 
The month is round or oblong, and suirounded by projecting walls, 
having along the crest a row of tubercles. The mouth originally 
oval is gradually narrowed (crrev6s) by a band projecting from the 
inner wall of the tube, and is finally closed. [Shortly after the pub- 
lication of the first edition, Mr Lonsdale informed me that he 
believed this coral ought to have been included in the genus Tham- 
nopora of Steininger.] 



Appendix to Part L 1 79 

the branches were apparently very thin, but there is a relatively 
considerable thickness of matter at the circumference. No traces 
of transverse diaphragms have been noticed within the tubes. 

Oases illustrative of the changes to maturity and final oblitera- 
tion in the oval termination of the tubes are rare, but the following 
have been observed. Where the mouth becomes free and oval, the 
walls are thin and sharp, and perpendicular within the tube. In 
some cases they are in contact ; but, m others, they are separated 
by grooves of variable dimensions, 111 which very minute foramina 
or pores may be detected. As the mouth approaches towards 
maturity, the grooves are more or less filled up, and the walls 
thicken, a row of very minute tubercles being discoverable along 
the crest. At this stage the inner side of the tube ceases to be 
vertical, being lined by a very narrow inclined band. The mature 
mouths are separated by a bold ridge, generally simple, but not 
unfrequently divided by a groove j the double as well as the single 
ridge being surmounted by a row of prominent tubercles almost 
in contact with each other. Only one example of the filling np 
of the mouths has been observed, but it affords satisfactory evi- 
dence of a gradual expansion of the inner band, before alluded to, 
and a final meeting in the centre. In this extreme state, there is 
a general blending of details, but the tubercles are for the most 
part distinct. 

In this species, proofs of a narrowing- of the mouth previously 
to the formation of the perfect tube, and the final contraction, are 
not very prominently exhibited in the long cylindrical straight 
branches ; but near the point where the tubes bent outwards there 
is an annular indentation, which may be tiaced successively from 
cast to cast in a lineal direction, parallel to the surface ; and be- 
tween the prominent narrowing and the perfect surface, the walls 
of the tubes were slightly rugose. In another short branch, "be- 
lieved to belong to this species, but in which the tubes diverged 
outwards very rapidly, the narrowing is strongly marked, but nofc 
to an equal extent throughout the specimen 

The matrix, in which the fossil is imbedded, is a coarse calca- 
reous shale, or a gray limestone ; and in which occur also Fenestvlla 
internata, &c. 

2. STESTOPOBA OVATA, sp. n. 

Branched, branches oval; tubes relatively short, divergence great; 
mouths round; contractions or irregularities of growth ntt- 
meraus. 

The characters of this species have been very imperfectly ascer- 
tained. The branches are not uniformly oval, even in apparently 
the same fragment. The tubes diverged rapidly along the line of 
the major axis, and had but a very limited vertical growth. Their 
casts exhibit a rapid succession of irregularities of development. 
The mouths, as far as they can be determined, were round or 

13 



1 8o Appendix to Part I. 

slightly oval, and the dividing, tuberculated ridges sharp ; but in 
consequence of the outer surface not being exposed, their perfect 
characters, and the changes incidental upon growth, could not be 
ascertained. 

The coral is imbedded in a dark gray limestone. 

1. FE^ESTELLA AMPLA, sp. n. 

Cup-shaped; cellulifei ous surface internal ; branches dichotomous, 
broad, flat, thin ; meshes oval ; rows of cells numerous, rarely 
limited to two, alternate ; transvet se connecting processes some- 
times cellular ; inner layer of non-cellular surface very fibrous ; 
external layer very granular, non-fibrous; gemmuliferous vesicle f 
small. 

Some of the casts of this coral have a general resemblance to 
Fenestclla polyporata, as represented in Captain Portlock's ' Report 
on the Geology of Londonderry/ pi xxii. A. fig 1 a, 1 d , but 
there is no agreement between the Van Diemen's Land fossil and 
the structure of that species as given in PI xxii. fig. 3, of the 
same work, or in Mr, Phillips's original figures, ' Geology of York- 
shire/ part ii,, pi i figs. 19, 20. A general resemblance also exists 
between Fenestclla ampla and a coral obtained by Mr Murchison 
from the carboniferous limestone of Kossatchi Datchi, on the eastern 
flank of the Ural Mountains, but there is again a marked difference 
In structural details. 

Fenestella ampla attained considerable dimensions, fragments 
apparently of one specimen covering an area of 4J inches by 3 
inches; and it displays considerable massiveness of outline, the 
branches at the points where they dichotomise often exceeding the 
tenth of an inch in breadth. 

In the general aspect of the coral a considerable uniformity pre- 
vails, but the branches vary in breadth, swelling out gieatly near the 
"bifurcations ; nevertheless, there is no marked difference of character 
between the base and the upper part of the cup, even in the number 
of the rows of cells. 

In the best state of the cellular surface, which has been noticed, 
the mouths of the cells are relatively large, round or oval, and are 
defined by a slightly raised margin ; and an undulating, thread-like 
ridge winds between them, dividing the interspaces into lozenge- 
shaped areas. The rows of cells, immediately preceding the bifurca- 
tion, sometimes amount to ten, and after the separation generally 
exceed two. The mouths of the lateral rows project into the 
meshes; and the transverse connecting processes are sometimes 
cellular. The interspaces between the mouths, as well as the un- 
dulating ridges, are granular, or very minutely tuberculated. In- 
ternally, the cells exhibit the usual oblique arrangement, overlaying 
each other and terminating abruptly against the dorsal part of the 
branch The perfect cabta of the cellular surface give the reverse 



Appendix to Part /. 1 8 1 

of tlie chaiacters just noticed, but more generally the impressions 
display scarcely a trace of any other structure than longitudinal 
rows of circular mouths. 

On the inner layer of the non-cellular surface, twenty well- 
marked parallel fibres, with intermediate narrow grooves or corre- 
sponding casts, may sometimes be detected, and the number is 
always considerable. The mode of preservation did not permit the 
true nature of the fibres to be discovered, but m consequence of 
what has been noticed in other species, it is inferred that they are 
tubular. Their range is considerable, but in the specimen, which 
exhibits their structure most fully, they are frequently cut off by 
circular foramina. Their perfect, surface is minutely granular. 
The outer layer, or back of the branches, is composed of an uniform 
crust without any indications of fibres, but covered with numerous 
microscopic papillae, and corresponding pores penetrating the sub- 
stance of the layer. 

The only indications of gemmuliferous vesicles, are small circular 
pits occasionally situated over the mouth, and agreeing in position 
with the vesicles, which in other cellular genera, have been con- 
sidered as gemmuliferous. In the Russian specimen before alluded 
to, casts of similar pits are very uniformly distributed between the 
casts of the mouths. 

The youngest state of the coral has not been noticed, nor have 
any marked changes incident upon age, except the gradual thicken- 
ing of the non-cellular surface, by the coating over of the fibrous 
layer. 

The matrix of the specimens is a dark gray splintery or an earthy 
limestone. 

2. FENBSTELLA IKTERFATA, sp. n. 

Cup-shaped; celluhferous surface internal; bramche* dichotomous, 
compressed, breadth variable; meshes oblong \ narrow; rows of 
cells 2 5, divided by longitudinal ridges ; transverse connecting 
processes short without cells ; non-cellular surface, inner layer, 
sharply fibrous, outer layer, minutely yranular. 

By the delicacy of its structure, this species is easily distinguish- 
able from Fen. ampla ; and in the rows of cells varying from two 
to five, as well as in their mode of development, there are further 
well-marked differences. It appears to have attained considerable 
dimensions, fragments having been noticed an inch and a-half in 
length and an inch in breadth. 

The branches vary in width, swelling cut gradually towards the 
bifurcations, but without any alteration m the Jorm or size of the 
meshes ; and as far as the state of the specimens will permit an 
opinion to be formed, no marked changes occurred during the deve- 
lopment of the cup, except one about to be noticed. On the cellu- 
liferous surface of the branches, considerable, but uniform, altera- 
tions take place between the successive bifurcations. For a short 



1 82 Appendix to Part L 

distance above the point of separation, the "branch is narrow and 
angular, and traversed along the centre by a ridge, and there is only 
one row of cellular mouths on each side. As the branch grew, the 
ndge widened, and ultimately became celluhferous, a row of mouths 
springing from its place (internata). The three ranges of cellular 
openings are, in this state of the branch, separated by two ridges, 
and these, as the development advanced, again widened and became 
cellular, the five rows being divided by four ridges. This appears 
to be tt e extreme stage of growth, another bifurcation taking place 
immediately after. In the earliest foimed part of the cup only two 
or three rows of mouths prevail ; and where the number is greater, 
a certain amount of irregularity in the linear arrangement is percep- 
tible, resulting from the lateral expansion of the branch. 

In the best preserved specimens, the mouths are relatively large, 
round or oval, and the margin is slightly raised. In the middle 
rows they are parallel, or nearly parallel, and m the direction of the 
axis of the branch ; but in the side rows they are often obliquely 
placed , inclining towards the me&hes. In these nearly perfect speci- 
mens the dn iding- ridges are thread-like and slightly waved, but 
there is no trace of the lozenge-shaped compartments so distinctly 
exhibited in Fenestellu itrnpla. The mteispaces between the mouths 
are flat or slightly convex. In specimens less finely preserved, or 
deprived of the original surface, the mouths are not uniform in out- 
line, and have no projecting margin. The diverging ridges are also 
relatively broader ; and the whole surface, including the transverse 
connecting processes) is granular or minutely tuberculated. 

The inner layer of the non-cellular surface is sharply fibrous, and 
the same structure may be more or less clearly detected in the 
tiansverse, connecting processes. The number of fibres on the 
branches do not apparently exceed twelve, and they are in general 
less numerous. Their range is considerable, additional ones being 
interpolated as the branch widens ; and their surface is minutely 
tuberculated. JSTo separate, circular foiarmna were noticed. The 
outer layer is uniformly granular, where completed, but every inter- 
mediate state from the sharply nbrous may be traced on the same 
specimen. 

No distinct proofs of gemmuliferous vesicles have been observed, 
but in a specimen, which is believed to exhibit impressions of this 
species, there are occasionally to be detected, near the mouths, 
hemispherical casts, perfectly rounded on the surface, and evidently 
unconnected immediately with the interior of the cells, and which 
it is presumed may represent those vesicles. Fmcstella internata 
appears to be an abundant fos&il, one slab nearly eight inches long 
and six wide, being covered on both sides with fragments of it, 
and numerous smaller specimens occur in the collection. The 
matrix is chiefly a coarse gray calcareous shale, but it is sometimes 
a splintery limestone, or a hard feiruginous or light-coloured clay- 
stone. 



Appendix to Part I. 183 



3. FESTESTELLA FOSSTJLA, sp. n. 

Cup-shaped^ celluliferous surface internal; branches dichotomous, 
slender; ntesJies oval; rows of cells, tioo; transverse processes 
non-cellular , inner layer of non-celluhferous surface minutely 
Jibrous ? external layer smooth or gianular. 

In general aspect and structural details, this species bears a great 
resemblance to Fenestellaflustracea of the niag-nesian limestone of 
England (JRetepora jlustracea, ' G-eol. Trans,,' 2nd series, vol. in. 
pi. xii. f. 8), but it differs from it in the peculiar character ex- 
hibited in the cast of the celluliferous surface, the nature of which 
will be given in noticing that surface. 

The principal specimen is a neaily perfect cup 1 J inch in height, 
and about two inches across the widest, compressed part. There 
are no marked variations of character, but occasionally, irregu- 
larities of growth, due, apparently, to accidents during progressive 
development. 

The following details have been obtained from casts, no perfect 
surface having been noticed The branches had great uniformity of 
dimensions, swelling but very slightly at the distant points of bifur- 
cation, and their thickness was apparently nearly equal to their 
breadth. The cast of the cellulai surlace is traversed along the 
centre by a sharp narrow trench (fossula), with marly vertical 
sides, the distinguishing ehdiaeter between this species and Fen. 
flustracea. The cylindrical casts of the mouths, or the interior of 
the cells, are arranged in a single row on each side of the trench, 
and no increase of number is clearly perceptible at the bifurcations. 
Along the centre of the trench is a row of indentations or minute 
conical pits, a character noticeable in other species, particularly in 
Fen Jlustracea. They are plainly not casts of cellular openings, 
but of relatively large papillae. Traces of such projections have 
also been noticed in several other instances. 

The mouths of the cells, in the minute fragment which has been 
obtained exhibiting them, are large, round, slightly projecting, and 
not very distant, and in the same atom is an imperfect keel. The 
remains of the non-cellular surface exhibit no characters requiring 
notice, but indications of a striated and smooth layer have been 
observed. 

The two specimens which afforded these structural details have 
a matrix of dark-coloured, hard limestone. 

HEMITRYPA SEXAJTGTTLA, sp, n. 
Net-work Jine, hexagonal; meshes round in double rows. 

The coral to which the above inefficient characters are applied, 
is imbedded in the shaly surface of a dark, hard limestone. It is 



184 Appendix to Part L 



about an ineli in "breadth and half an inch in height, and consists of 
two layers of net- work, one presenting quadrangular meshes, aud 
the other hexagonal, with a round, inner area , and over a consider- 
able part of the specimen, the quadrangular net-work has been 
removed, whereby the connexion of the two structures is perfectly 
exposed* 

This fossil is believed to agree completely in its essential generic 
characters with those of Hetmtrypa (* Pal. Foss. Cornwall,' p 27), 
but its state of preservation, and some facilities afforded by it lor 
determining structural details, have led to an inference respecting 
its nature somewhat different from that given in the work just 
quoted. 

The inner surface of Hemitrypa oculata (loc. cit.) is described as 
' marked with radiating ridges,' having intervening ' oval depres- 
sions, which penetrate only half through the substance of the coral, 
and nowhere reach the outer surface,' The equivalent portion of 
the Van Uiemen's Land specimen agrees perfectly with this state- 
ment, except in the form of the meshes or depressions; it is, how- 
ever, not merely 'like some Fenestellse/ but it possesses all the 
essential characters of that genus, and is believed to be a fragment 
of Fen. fo^sula. This inference is drawn from a minute portion 
mechanically detached, and which exhibited a row of large, roand, 
projecting, cellular mouths. The external surface of Hem oculata 
is described as * wholly covered with numerous round pores or 
cells' 'associated in double rows, 1 and the corresponding portion 
of Hem sesangula has been ascertained to consist also of a similar 
surface of double rows of round meshes or 'pores,' but with hexa- 
gonal boundaries ; and they are shown, as exhibited by the speci- 
men in its imbedded state, to penetrate to the surface of the Fene- 
stella or quadi angular net-work. 

These details are conceived to be sufficient to establish a generic 
agreement between the Van Diemens Land coral and Ilevrwtrypa 
oculata ; and an examination of an Irish specimen of that genus 
has fully confirmed the structural details exhibited in the ' inner 
surface J of the specimen to which, provisionally, the name of JECemz- 
try pa sexangula is applied. 

Of the true nature of the * external 7 net-work no opinion is 
ventured. ^ It is formed almost entirely of dark gray, calcareous 
matter, filling apparently an originally cellular structure j but there 
are also a few small patches of the outer covering, consisting of an 
opaque white crust on the surface, which was originally in contact 
with the external net-work. That it was a parasite little doubt 
is entertained ; and the interesting agreement between the space 
occupied by the double row of meshes, and that of the parallel 
branches of the Fenestella, arises apparently from the latter having 
afforded suitable base lines for attachment. In the Van Diernen'a 
Land specimen, the agreement is marked by an increased breadth in 
the net-work, and by a row of projecting points. There is also a re- 
markable agreement between the arrangement of the mouths of the 



Appendix to Part /. 185 

Fenestella and the meshes of the * inner ? net-work. Similar con- 
formities are admirably shown in Mr. Phillrps's excellent figures 
(' Pal. Foss.' pi. xiii f. 38). 

The solid portions of the structure being- exceedingly fine, resem- 
bling the thread of the most delicate lace, attempts to discover satis- 
factorily internal characters proved unsuccessful, except in one place, 
where a true cellular arrangement was believed to be visible. 1 
Of the nature of the investing crust, nothing also has been deter- 
mined. 

Though the name Hemitrypa may be objectionable, as applied 
to the corals under consideration, it has been thought right to re- 
tain the word, until the full characters of the genus shall have 
been ascertained. 

FAI.MOITTH:, January 1844. 

1 A Codrington lens, half-an-inch in diameter, was invariably 
used in examining the corals described in this notice. 



PAKE H. 

SOUTH AMEEICA. 



CHAPTER VIIL 

ON THE ELEVATION OF THE EASTERN COAST OF SOUTH 
AMEEICA. 

Upraised SJiells of La Plata Bahia JBlanca, Sand-dunes and Pumice- 
pebbles Step-formed Plains of Patagoma> with upraised Shells 
Terraoe-hoimded Valley of Santa Cruz, formerly a Sea-strait Up- 
raised Shells of Ti>erra del Fuego Length and breadth of the 
elevated area Equability of the movement^ as shown ly the similar 
lieights of the plains Slowness of the elevatory process Mode of 
formation of the ste}) -formed ^7^/2/2$ Summary Great Slnngle 
* Formation of Patagonia; its extent* origin,, and distribution 
Formation of sea-chjfs. 

IN the following Part, which treats of the geology of 
South America, and almost exclusively of the parts 
i south ward of the Tropic of Capricorn, I have arranged 
the chapters according to the age of the deposits, occa- 
sionally departing from this order, for the sake of geo- 
graphical simplicity. 

The elevation of the land within the recent period, 
and the modifications of its surface through the action 
of the sea (to which subjects I paid particular attention) 
will be first discussed ; I will then pass on to the tertiary 
deposits, and afterwards to the older rocks. Only those 
districts and sections will be described in detail which 
appear to me to deserve some particular attention ; and 
I will, at the end of each chapter, give a summary of 
the results. We will commence with the proofs of the 
upheaval of the eastern coast of the continent, froiu 
the Eio Plata southward; and, in the next chapter, 



I go Elevation* of La Plata. PAET n. 

follow up the same subject along the shores of Chile and 
Peru. 

On the northern bank of the great estuary of the 
Rio Plata, near Maldonado, I found at the head of a 
lake, sometimes brackish, but generally containing fresh 
water, a bed of muddy clay, six feet in thickness, with 
numerous shells of species still existing in the Plata, 
namely, the Azara labiata, d'Orbig, fragments of 
Mytilus edulifrrmis, d'Orbig., Paludestrina Isabdtei, 
d'Orbig., and the Solen Oaribceus, Lam., which last was 
embedded vertically in the position in which it had 
lived. These shells lie at the height of only two feet 
above the lake, nor would they have been worth mention- 
ing, except in connection with analogous facts. 

At Monte Video, I noticed near the town, and along 
the base of the mount, beds of a living Mytilus, raised 
some feet above the surface of the Plata : in a similar 
bed, at a height from thirteen to sixteen feet, M. Isabelle 
collected eight species, which, according to M. d'Or- 
bigny, 1 now live at the mouth of the estuary. At 
Colonia del Sacramiento, further westward, I observed 
at the height of about fifteen feet above tihfe river, there 
of quite fresh water, a small bed of the same Mytilus, 
which lives in brackish water at Monte Video. Near the 
mouth of the Uruguay, and for at least thirty-five miles 
northward, there are at intervals large sandy tracts, 
extending several miles from the banks of the river, 
but not raised much above its level, abounding with 
small bivalves, which occur in such numbers that at 
the Agraciado they are sifted and burnt for lime. 
Those which I examined near the A. S. Juan were much 
worn : they consisted of Maetrra Isabellei y d'Orbig., 
mingled with few of Venus sinuosa., Lam., both in- 
1 'Voyage dans rAm&iqne M6rid Part. GSolog.'p. 21. 



CHAP. vni. Elevation of La Plata. 191 

habiting, as I am informed by M. cTOrbigny, brackish 
water at the mouth of the Plata, nearly or quite as salt 
as the open sea. The loose sand, in which these shells 
are packed, is heaped into low, straight, long lines of 
dunes, like those left by th,e sea at the head of many 
bays. M, d'Orbigny has described J an analogous phe- 
nomenon on a greater scale, near S f an Pedro on 1 the 
river Parana, where he found widely extended beds and 
hillocks of sand, with vast numbers of the Azara 
lability at the height of nearly 100 feet (English) 
above the surface of that river. The Azara inhabits 
brackish water, and is not known to be found nearer to 
San Pedro than Buenos Ayres, distant above 100 miles 
in a straight line. Nearer Buenos Ayres, on the road 
from that place to San Isidro, there are extensive beds, 
as I am informed by Sir Woodbine Parish, 2 of the Azara 
luliata, lying at about forty feet above the level of the 
river, and distant between two and three miles from it. 
These shells are always found on the highest banks in 
the district : they are embedded in a stratified earthy 
mass, precisely like that of the great Pampean deposit 
hereafter to be described. In one collection of these 
shells, there were some valves of the Venus sinuosa, 
Lam., the same species found with the Mactra on the 
banks of the Uruguay. South of Buenos Ayres, near 
Ensenada, there are other beds of the Azara, some of 
which seem to have been embedded in yellowish, cal- 
careous, semi-crystalline matter ; and Sir W. Parish 
has given me from the banks of the Arroyo del Tristan, 
situated in this same neighbourhood, at the distance of 
above a league from the Plata, a specimen of a pale- 
reddish, calcareo-argillaceous stone (precisely like parts 
of the Pampean deposit, the importance of which fact 

1 * Voyage dans I Am 6riqxie M&rid : Part. G-eolog'p 43. 
* Buenos Ayres,' &c., by Sir Woodbine Parish, p JR8. 



1 92 Elevation of La Plata. PART n 

will be referred to in a succeeding chapter), abounding 
with shells of an Azara, much worn, but which in 
general form and appearance closely resemble, and are 
probably identical with, the A. labiata. Besides these 
shells, cellular, highly crystalline rock, formed of the 
casts of small bivalves, is found near Ensenada ; and 
likewise beds of sea-shells, which from their appearance 
appear to have lam on the surface. Sir W. Parish has 
given me some of these shells, and M. d'Orbigny pro- 
nounces them to be, 



1. Buccmanops globulosum, 

d Orbig. 

2. Olivancillana auricularia, 

do. 



3. Yenus flexuosa, Lam. 

4. CKtherasa (imperfect) 

6. Mactia Labellei, d'Orbig. 
6. Ostrea pulchella, do. 



Besides these. Sir W. Parish procured * (as named 
by Mr. G. B. Sowerby) the following shells : 

7. Voluta colocynthis. I 9. Buccinum (not spec. ?). 

8. V. angnlata. ' 

All these species (with, perhaps, the exception of 
the last) are recent, and live on the South American 
coa^t. These shell-beds extend from one league to six 
leagues from the Plata, and must lie many feet above 
its level I heard, also, of beds of shells on the Som- 
borornbon, and on the Rio Salado, at which latter 
place, as M. d'Orbigny informs me, the Mactra Isabellei 
and Venus sinuosa are found. 

During the elevation of the Provinces of La Plata, 
the waters of the ancient estuary have but little affected 
(with the exception of the sand-hills on the banks of 
the Parana and Uruguay) the outline of the land. 
M. Parchappe, 2 however, has described groups of sand- 
dunes scattered over the wide extent of the Pampas 

1 Buenos Ayres,' &c , by Sir W. Parish, p. 168 
9 D'Orbigny's * Voyage &6olog ' p, 44. 



CHAP. TIH. Elevation of Bakia, Blanca. 193 

southward of Buenos Ayres, which M. d'Orbigny attri- 
butes with much probability to the action of the sea, 
before the plains were raised above its level. 1 

Soutliiua/rd of the Plata. The coast as far as Bahia 
Blanca (in lat. 39 S.) is formed either of a horizontal 
range of cliffs, or of immense accumulations of sand- 
dunes. "Within Bahia Blanca, a small piece of table- 
land, about twenty feet above high-water mark, called 
Punia Alta, is formed of strata of cemented gravel and 
of red earthy mud, abounding with shells (with others 
lying loose on the surface), and the bones of extinct 
mammifers. These shells, twenty in number, together 
with a Balanus and two corals, are all recent species, 
still inhabiting the neighbouring seas. They will be 
enumerated in the eleventh Chapter, when describing 
the Pampean formation; five of them are identical 
with the upraised ones from near Buenos Ayres. The 
northern shore of Bahia Blanca is, in main part, formed 

1 Before proceeding to the districts southward of La Plata, it may 
be worth while just to state, that there is some evidence that the 
coast of Brazil has participated in a small amount of elevation Mr. 
Burchell informs me, that he collected at Santos (lat. 24- S.) oyster- 
shells, apparently recent, some miles from the shore, and quite above 
the tidal action. Westward of Rio de Janeiro, Capt. Elliot is asserted 
(see Harlan, * Med. and Phys. Res / p. 35, and Dr. Meigs, in * Trans. 
Amer. Phil. Soc '), to have found human bones, encrusted with sea- 
shells, between fifteen and twenty feet above the level of the sea. 
Between Eio de Janeiro and Cape Frio I crossed sandy tracts 
abounding with sea-shells, at the distance of a league from the coast; 
but whether these tracts have been formed by upheaval, or through 
the mere accumulation of drift sand, I am not prepared to assert. 
At Bahia (lat 13 S ), in some parts near the coast, there are traces 
of sea-action at the height of about twenty feet above its present 
level ; there are also, in many parts, remnants of beds of sandstone 
and conglomerate with numerous recent shells, raised a little abo\e 
the sea-level. I may add, that at the head of Bahia bay there is a 
formation, about forty feet in thickness, containing tertiary shells 
apparently of fresh- water origin, now washed by the sea and en- 
crusted with Balani; this appears to indicate a small amount of 
subsidence subsequent to its deposition. At Pernambuco (lat 8 
S ), in the alluvial or tertiary cliffs, surrounding the low land on 
which the city stands, I looked in vain for organic remains, or other 
evidence of changes in level. 



194 Elevation of Bahia Blanca. PART n. 

of immense sand-dunes, resting on gravel with recent 
shells, and ranging in lines parallel to the shore. These 
ranges are separated from each other by flat spaces, 
composed of stiff impure red cby, in which, at the 
distance of ahout two miles from the coast, I found by 
digging, a few minute fragments of sea-shells. The 
sand-dunes extend several miles inland, and stand on a 
plain, which slopes up to a height of between one and 
two hundred feet. Numerous, small, well rounded 
pebbles of pumice lie scattered both on the plain and 
sand-hillocks : at Monte Hermoso, on the flat summit 
of a cliff, I found many of them at a height of 120 feet 
(angular measurement) above the level of the sea. 
These pumice pebbles, no doubt, were originally brought 
down from the Cordillera by the rivers which cross the 
continent, in the same way as the river Negro anciently 
brought down, and still brings down, pumice, and as 
the river Chupat brings down scorige : when once de- 
livered at the mouth of a river, they would naturally 
have travelled along the coasts, and been cast up, dur- 
ing the elevation of the land, at different heights. The 
origin of the argillaceous flats, which separate the 
parallel ranges of sand-dunes, seems due to the tides 
here having a tendency (as I believe they have on most 
shoal-protected coasts) to throw up a bar parallel to 
the shore, and at some distance from it ; this bar 
gradually becomes larger, affording a base for the 
accumulation of sand-dunes, and the shallow space 
within then becomes silted up with mud. The repe- 
tition of this process, without any elevation of the land, 
would form a level plain traversed by parallel lines of 
sand-hillocks ; during a slow elevation of the land, the 
hillocks would rest on a gently inclined surface, like 
that otx the northern shore of Bahia Blanca. I did not 
observe any shells in this neighbourhood at a greater 



CHAP. TUX. Elevation of Bakia Blanca. 195 

freight than twenty feet ; and therefore the age of the 
sea-drifted pebbles of pumice, now standing at the height 
of 120 feet, must remain uncertain. 

The main plain surrounding Bahia Blanca I esti- 
mated at from 200 to 300 feet; It insensibly rises 
towards the distant Sierra Ventana. There are in this 
neighbourhood some other and lower plains, but they 
do not abut one at the foot of the other, in the manner 
hereafter to be described, so characteristic of Patagonia. 
The plain on which the settlement stands is crossed by 
many low sand-dunes, abounding with the minute shells 
of the Paludestrina australis, d Orbig., which now lives 
in the bay. This low plain Is bounded to the south, 
at the Oabeza del Buey, by the cliff-formed margin 
of a wide plain of the Pampean formation, which I 
estimated at sixty-feet In height. On the summit of 
this cliff there is a range of high sand-dunes extending 
several miles in an east and west line. 

Southward of Bahia Blanca, the river Colorado 
flows between two plains, apparently from thirty to 
forty feet in height. Of these plains, the southern one 
slopes up to the foot of the great sandstone plateau of 
the Rio Negro ; and the northern one against an escarp- 
ment of the Pampean deposit; so that the 06lorad, 
flows in a valley fifty miles In width, between the upper 
escarpmerts. I state this, because on the low plain at 
the foot of the northern escarpment, I crossed an im- 
mense accumulation of high sand-dunes, estimated by 
the Gauchos at no less than eight miles in breadth. 
These dunes range westward from the coast, which is 
twenty miles distant, to far inland, in lines parallel to 
the valley ; they are separated from each other by 
argillaceous flats, precisely like those on the northern 
shore of Bahia Blanca. At present there is no source 
whence this immense accumulation of sand could pro- 
14 



196 Elevation of Patagonia. PART IL 

ceed ; but if, as I believe, the upper escarpments once 
formed the shores of an estuary, in that case the sand- 
stone formation of the river Negro would have afforded 
an inexhaustible supply of sand, which would naturally 
have accumulated on the northern shore, as on every 
part of the coast open to the south winds between Bahia 
Blanca and Buenos Ayres. 

At San Bias (40. 40' S.), a little south of the 
mouth of the Colorado, M. d'Orbigny * found fourteen 
species of existing shells (six of them identical with 
those from Bahia Blanca), embedded in their natural 
positions. From the zone of depth which these shells 
are known to inhabit, they must have been uplifted 
thirty-two feet. He also found, at from fifteen to 
twenty feet above this bed, the remains of an ancient 
beach. 

Ten miles southward, but 120 miles to the west, at 
Port S. Antonio j the Officers employed on the Survey 
assured me that they saw many old sea-shePs strewed 
on the surface of the ground, similar to those found on 
other parts of the coast of Patagonia. At San Josef, 
ninety miles south in nearly the same longitude, I found, 
above the gravel, which caps an old tertiary forma- 
tion, aft irregular bed and hillocks of sand, several feet 
in thickness, abounding with shells of Patella deaurita, 
Mytilus Magellanicus, the latter retaining much of its 
colour ; Fusus Magellanicus, (and a variety of the same) 
and a large Balanus (probably S. Tulipa), all now found 
on this coast : I estimated this bed at from eighty to 
one hundred feet above the level of the sea. To the 
westward of this bay, there is a plain estimated at be- 
tween 200 and 300 feet in height : this plain seems, 
from many measurements, t> be a continuation of the 
sandstone platform of the river Negro. The next 
1 * Voyage/ c. p 54. 



CHAP. nn. Elevation of Patagonia. 197 

place southward, where I landed, was at Port Desire, 
340 miles distant ; but from the intermediate districts 
I received, through the kindness of the Officers of the 
Survey, especially from Lieut. Stokes and Mr. King, 
many specimens and sketches, quite sufficient to show 
the general uniformity of the whole line of coast. I 
may here state, that the whole of Patagonia consists of 
a tertiary formation, resting on and sometimes sur- 
rounding hills of porphyry and quartz : the sunace is 
worn into many wide valleys and into level step-formed 
plains, rising one above another, all capped by irregular 
beds of gravel, chiefly composed of porphyritic rocks. 
This gravel formation will be separately described at 
the end of the chapter. 

My object in giving the following measurements 
of the plains, as taken by the Officers of the Survey, 
is, as will hereafter be seen, to show the remarkable 
equability of the recent elevatory movements. Eound 
the southern parts of ISTuevo Gulf, as far as the Eiver 
Ghupat, (seventy miles southward of San Josef) there 
appear to be several plains, of which the best defined 
are here represented. 

No 15. 

Section of Step-formed Plains South of Nuero Gulf 
350 ft An ML 200-220 An M. 80 Est 



West ! * East 

Lerel of sea Scale V of mcl1 * 10 feet vertical. 

N B An M always stands for angular or trigonometrical measurement 
Ba M barometrical measurement. 

Est estimation by the Officer of the Survey. 

The upper plain is here well defined (called Table 
Hills) ; its edge forms a cliff or line of escarpment 
many miles in length, projecting over a lower plain. 
The lowest plain corresponds with that at San Josef 
with the recent shells on its surface. Between this 



198 Elevation of Patagonia. PAET n, 

lowest and the uppermost plain, there is probably more 
than one step-formed terrace: several measurements 
show the existence of the intermediate one of the height 
given in the diagram. 

Near the north headland of the great Bay of St. 
George (100 miles south of the Chupat), two well 
marked plains of 250 and 330 feet were measured: 
these are said to sweep round a great part of the Bay. 
At its south headlandj 120 miles distant from the north 
headland, the 250 feet plain was again measured. In 
the middle of the bay, a higher plain was found at 
two neighbouring places (Tilli Roads and C. Marques) 
to be 580 feet in height. Above this plain, towards 
the interior, Mr. Stokes informs me that there were 
several other step formed plains, the highest of which 
was estimated at 1,200 feet, and was seen ranging at 
apparently the same height for 150 miles northward. 
All these plains have been worn into great valleys and 
much denuded. The following section is illustrative of 
the general structure of the great Bay of St. George. 

No 16 
Section of Plains in the Bay of St George, 

1,200 feet Est. Not measured, 

v.... 



\....^580An M 

"X 



\ ^ 580 An M 330 An M. 250 An. M 



Level of sea. Scale ^ of inch to 100 feet vertical. 

At the south headland of the Bay of St, George (near 
C. Three Points) the 250 plain is very extensive. At 
Port Desire (forty miles southward) I made several 
measurements with the barometer of a plain, which 
extends along the north side of the port and along the 
open coast, and which varies from 245 to 255 feet in 



CHAP. vm. Elevation of Patagonia. 199 

height : this plain abuts against the foot of a higher 
plain of 330 feet, which extends also, far northward 
along the -coast, and likewise into the interior. In the 
distance a higher inland platform was seen, of which 
do not know the height. In three separate places, I 
observed the cliff of the 245-255 feet plain, fringed by 
a terrace or narrow plain estimated at about 100 feet 
in height. These plains are represented in the fol- 
lowing section : 

No. 17. 
Section of Plains at Port Desire. 

Not Measured. 



v_ 


craft 


Ja <-< 2 
5385 


w* 3 1* 
eJwPQ 53 o 


1 


100 ft Safe. 










\ 



Level of sea. Scale -^ of inch to ICO feet vertical 

In many places, even at the distance of three and 
four miles from the coast, I found on the gravel-capped 
surface of the 245-255 feet, and of the 330 feet plain, 
shells of Mytilus MagellanicuSj M. edulis, Patella 
deaurita, and another Patella, too much worn to be 
identified, but apparently similar to one found abun- 
dantly adhering to the leaves of the kelp. These 
species are the commonest now living on this coast. 
The shells all appeared very old : the blue of the 
mussels was much faded ; and only traces of colour 
could be perceived in the Patellas, of which the outer 
surfaces were scaling off. They lay scattered on the 
smooth surface of the gravel, but abounded most in 
certain patches, especially at the heads of the smaller 
valleys : they generally contained sand in their insides ; 
and I presume that they have been washed by alluvial 
action out of thin sandy layers, traces of which may 
sometimes be seen covering the gravel. The several 



2OO Elevation of Patagonia. PART n. 

plains have very level surfaces ; but all are scooped out 
by numerous, broad, winding, flat-bottomed valleys, in 
which, judging from the bushes, streams never flow, 
These remarks on the state of the shells, and on the 
nature of the plains, apply to the following cases, so 
need not be repeated. 

Southward of Port Desire, the plains have been 
greatly denuded, with only small pieces of table-land 
marking their former extension. But opposite Bird Is- 
land, two considerable step-formed plains were measured, 
and found respectively to be 350 and 590 feet in heighb. 
This latter plain extends along the coast close to Port 
St. Julian (110 miles south of Port Desire) ; where we 
have the following section : 

No. 18. 

Section of Plains at Port St Julian. 
950 ft. An M. 



\ 



560 An. M. 

430 An. M. 



Level of sea. Scale -^ of inch to 100 feet vertical 

The lowest plain was estimated at ninety feet : it is 
remarkable from the usual gravel-bed being deeply 
worn into hollows, which are filled up with, as well as 
the general surface covered by, sandy and reddish earthy 
matter : in one of the hollows thus filled up, the skeleton 
of the MacrauGhenia Patachonica, as will hereafter be 
described, was embedded. On the surface and in the 
upper parts of this earthy mass, there were numerous 
shells of Mytilm Magellmicus and M. edulis, Patella 
deaurita^ and fragments of other species. This plain 
is tolerably level, but not extensive; it forms a pro- 
montory seven or eight miles long, and three or four 
wide. The upper plains in the above diagram were 



CHAP. vm. Elevation of Patagonia. 201 

measured by the Officers of the Survey; they were all 
capped by thick beds of gravel, and were all more or 
less denuded : the 950 plain consists merely of separate, 
truncated, gravel-capped hills, two of which, by measure- 
ment, were found to differ only three feet. The 430 
feet plain extends, apparently with hardly a break, to 
near the northern entrance of the Rio Santa Cruz (fifty 
miles to the south) ; but it was there found to be only 
330 feet in height. 

On the southern side of the mouth of the Santa Cruz 
we have the following section, which I am able to give 
with more detail than in the foregoing cases : 

No. 19. 
Section of Plains at the moutli of tne Rio Santa Cruz. 

An M 710 An M, ,. m i 



%* SB* 

TJ< d X ^ o 



Level ot sea Scale ^ of inch to 100 feet vertical. 

The plain marked 355 feet (as ascertained by the 
barometer and by angular measurement) is a continua- 
tion of the above-mentioned 330 feet plain : it extends 
in a NW. direction along the southern shores of the 
estuary. It is capped by gravel, which in most parts is 
covered by a thin bed of sandy earth, and is scooped out 
by many flat-bottomed valleys. It appears to the eye 
quite level, but in proceeding in a SSW. course, towards 
an escarpment distant about six miles, and likewise 
ranging across the country in a NW. line, it was found 
to rise at first insensibly, and then for the last half mile, 
sensibly, close up to the base of the escarpment: at 
this point it was 463 feet in height, showing a rise of 
108 feet in the six miles. On this 355 to 463 feet 
plain, I found several shells of Mytilus Mayellanicm 



2O2 Valley of Santa Cruz* PAET n. 

and of a Mytilus, which Mr. Sowerby informs me is yet 
unnamed, though well known as recent on this coast; 
Patella deaurita ; Fusus, I believe, Magelltmicus, but 
the specimen has been lost; and at the distance of four 
miles from the coast, at the height of about 400 feet, 
there were fragments of the same Patella and of a 
Voluta (apparently V. ancilla) partially embedded in 
the superficial sandy earth. All these shells had the 
same ancient appearance with those from the foregoing 
localities. As the tides along this part of the coast 
rise at the Syzygal period forty feet, and therefore form 
a well-marked beach-line, I particularly looked out for 
ridges in crossing this plain, which, as we have seen, 
rises 108 feet in about six miles, but I could not see 
any traces of such. The next highest plain is 710 feet 
above the sea; it is very narrow, but level, and is 
capped with gravel ; it abuts to the foot of the 840 
feet plain. This summit-plain extends as far as the 
eye can range, both inland along the southern side ot 
the valley of the Santa Cruz, and southward along the 
Atlantic. 

The Valley of the R. Santa Cruz. This valley runs 
in an east and west direction to the Cordillera, a dis- 
tance of about 160 miles. It cuts through the great 
Patagonian tertiary formation, including, in the upper 
half of the valley, immense streams of basaltic lava, 
which, as well as the softer beds, are capped by gravel ; 
and this gravel, high up the river, is associated with a 
vast boulder formation. 1 In ascending the valley, the 
plain which at the mouth on the southern side is 355 
feet high, is seen to trend towards the corresponding 
plain on the northern side, so that their escarpments 
appear like the shores of a former estuary, larger than 

1 I have described this formation in a paper in the ' Geological 
Transactions,' vol. vi. p. 415. 



CHAP. Tin. Valley of Santa Cruz. 203 

the existing one : the escarpments, also, of the 840 feefe 
summit-plain (with a corresponding northern one, 
which is met with some way up the valley), appear like 
the shores of a still larger estuary. Farther up the val- 
ley, the sides are bounded throughout its entire length 
by level, gravel-capped terraces, rising above each other 
in steps. The width between the upper escarpments is 
on an average between seven and ten miles ; in one 
spot, however, where cutting through the basaltic lava, 
it was only one mile and a half. Between the escarp- 
ments of the second highest terrace the average width 
is about four or five miles. The bottom of the valley, 
at the distance of 110 miles from its mouth, begins 
sensibly to expand, and soon forms a considerable plain, 
440 feet above the level of the sea, through which the 
river flows in a gut from twenty to forty feet in depth, 
1 here found, at a point of 140 miles from the Atlantic, 
and seventy miles from the nearest creek of the Pacific, 
at the height of 410 feet, a very old and worn shell of 
Patella deawita. Lower down the valley, 105 miles 
from the Atlantic (long. 71 W.), and at an elevation 
of about 300 feet, I also found, in the bed of the river, 
two much worn and broken shells of the Valuta ancilla-^ 
still retaining traces of their colours ; and one of the 
Patella deaurita. It appeared that these shells had 
bepn washed from the banks into the river ; considering 
the distance from the sea, the desert and absolutely 
unfrequented character of the country, and the very 
ancient appearance of the shells (exactly like those 
found on the plains nearer the coast), there is, I think, 
no cause to suspect that they could have been brought 
here by Indians. 

The plain at the head of the valley is tolerably 
level, but water-worn, and with many sand-dunes on it 
like those on a sea-coast. At the highest point to which 



204 Valley of Santa Cruz. PABT IT. 

we ascended. It was sixteen miles wide in a north and 
south line; and forty-five miles m length in an east 
and west line. It is bordered by the escarpments, one 
above the other, of two plains, which diverge as they 
approach the Cordillera, and consequently resemble, at 
two levels, the shores of great bays facing the moun- 
tains ; and these mountains are breached in front of the 
lower plain by a remarkable gap. The valley, therefore, 
of the Santa Cruz consists of a straight broad cut, 
about ninety miles in length, bordered by gravel-capped 
terraces and plains, the escarpments of which at both 
ends diverge or expand, one over the other, after the 
manner of the shores of great bays. Bearing in mind 
this peculiar form of the land the sand-dunes on the 
plain at the head of the valley the gap in the Cordil- 
lera, in front of it the presence in two places of very 
ancient shells of existing species and lastly, the cir- 
cumstance of the 355 to 453 feet plain, with the 
numerous marine remains on its surface, sweeping from 
the Atlantic coast, far up the valley, I think we must 
admit, that within the recent period, the course of the 
Santa Croz formed a sea-strait intersecting the con- 
tinent. At this period, the southern part of South 
America consisted of an archipelago of islands 360 
miles in a N. and 8. line. We shall presently see, that 
two other straits also, since closed, then cut through 
Tierra del Fuego ; I may add, that one of them must 
at that time iiave expanded at the foot of the Cordillera 
into a great bay (now Otway Water) like that which 
formerly covered the 440 feet plain, at the head of the 
Santa Cruz. 

I have said that the valley in its whole course is 
bordered by gravel-capped plains. The following sec- 
tion, supposed to be drawn in a JSL and S* line across 
the valley, can scarcely be considered as more than 



CHAP. TIII. Valley of Santa Cruz. 205 

illustrative; for during our hurried ascent it was im- 
possible to measure all the plains at any one place. 

No 20. 

North and South Section across the Terraces bounding the Valley of 
the Eiver Santa Cruz, high up its course. 

A south A north, 

V B s. B n. 




1,122ft 869ft. 639 tc Bed of 63Jfc wj it 1,122ft. 

river. 

The height of each terrace abore the level of the river, is shown by the number 
under it Vertical scale ^ of inch to a 100 feet ; but terrace E being oaly 
twenty feet above the river, has necessarily been raided. The horizontal dis- 
tances much contracted , the distance from the edge of A n. to A s being ou am 
average from seven to ten miles. 

At a point nearly midway between the Cordillera and 
the Atlantic, I found the plain (A north) 1,122 feet 
above the river ; all the lower plains on this side were 
here united into one great broken cliff: at a point 
sixteen miles lower down the stream, I found by 
measurement and estimation that B (n) was 869 above 
the river: very near to where A (n) was measured, 
(n) was 639 above the same level : the terrace D (n) 
was nowhere measured : the lowest E (n) was in many 
places about twenty feet above the river. These plains 
or terraces were best developed where the valley was 
widest; the whole five, like gigantic steps, occurred 
together only at a few points. The lower terraces are 
less continuous than the higher ones, and appear to be 
entirely lost in the upper third of the valley. Terrace 
(s) : however, was traced continuously for a great 
distance. The terrace B (%), at a point of fifty-five 
miles from the mouth of the river, was four miles in 
width; higher up the valley this terrace (or at least 
the second highest one, for I could not always trace it 
continuously) was about eight miles wide. This second 



206 Valley of Santa Cruz. PAET n. 

plain was generally wider than the lower ones as 
indeed follows from the valley from A (n) to A (s) 
being generally nearly double the width from B (n) 
to B (s). Low down the valley, the summit-plain A ($) 
is continuous with the 840 feet plain on the coast, but it 
is soon lost or unites with the escarpment of B (s). 
The corresponding plain A (?*/), on the north side of the 
valley, appears to range continuously from the Cordil- 
lera to the head of the present estuary of the S. Cruz, 
where it trends northward towards Port St. Julian. 
Near the Cordillera the summit-plain on both sides of 
the valley is between 3,200 and 3,300 feet in height ; 
at 100 miles from the Atlantic, it is 1,4 16 feet, and on 
the coast 840 feet, all above the sea-beach ; so that in 
a distance of 100 miles the plain rises 576 feet, and 
much more rapidly near to the Cordillera. The lower 
terraces B and C also appear to rise as they run up the 
valley ; thus D (T&), measured at two points twenty- 
four miles apart, was found to have risen 185 feet. 
From several reasons I suspect, that this gradual 
inclination of the plains up the valley, has been chiefly 
caused by the elevation of the continent in mass, 
having been the greater the nearer to the Cordillera. 

All the terraces are capped with well-rounded gravel, 
which rests either on the denuded and sometimes 
furrowed surface of the soft tertiary deposits, or on the 
basaltic lava. The difference in height between some 
of the lower steps or terraces seems to be entirely 
owing to a difference in the thickness of the capping 
gravel. Furrows and inequalities in the gravel, where 
such occur, are filled up and smoothed over with sandy 
earth. The pebbles, especially on the higher plains, 
are often whitewashed, and even cemented together by 
a white aluminous substance ; and I occasionally found 
this to be the case with the gravel on the terrace D. 



CHAP. YIII. Valley of Santa Cruz. 207 

I could not perceive any trace of a similar deposi- 
tion on the pebbles now thrown up by the river, and 
therefore I do not think that terrace D was river- 
formed. As the terrace E generally stands about 
twenty feet above the bed of the river, my first impres- 
sion was to doubt whether even this lowest one could 
have been so formed ; but it should always be borne in 
mind, that the horizontal upheaval of a district, by in- 
creasing the total descent of the streams, will always 
tend to increase, first near the sea-coast and then 
farther and farther up the valley, their corroding and 
deepening powers : so that an alluvial plain, formed 
almost on a level with a stream,, will, after an elevation 
of this kind, in time be cut through, and left standing 
at a height never again to be reached by the water, 
"With respect to the three upper terraces of the S. Cruz, 
I think there can be no doubt, that they were modelled 
by the sea, when the valley was occupied by a strait, in 
the same manner (hereafter to be discussed), as tbe 
greater, step-formed, shell-strewed plains along the 
coast of Patagonia. 

To return to the shores of the Atlantic the 840 
feet plain, at the mouth of the Santa Cruz,, is seen ex- 
tending horizontally far to the south ; and I am in- 
formed by the Officers of the Survey, that bending round 
the head of Coy Inlet (sixty-five miles southward), it 
trends inland. Outliers of apparently the same height 
are seen forty miles farther south, inland of the river 
Gallegos; and a plain comes down to Cape Gregory 
(thirty-five miles southward), in the Strait of Magellan, 
which was estimated at between 800 and 1,000 feet 
in height, and which, rising towards the interior, is 
capped by the boulder formation. South of the Strait 
of Magellan, there are large outlying masses of appa- 
rently the same great table-land, extending at interval? 



208 Concluding Remarks on the PAET n. 

along the eastern, coast of Tierra del Fuego : at two 
places here, 110 miles apart, this plain was found to be 
950 and 970 feet in height. 

From Coy Inlet, where the high summit-plain 
trends inland, a plain estimated at 350 feet in height, 
extends for forty miles to the river Gallegos. From 
this point to the Strait of Magellan, and on each side 
of that Strait, the country has been much denuded and 
is less level. It consists chiefly of the boulder forma- 
tion, which rises to a height of between 150 and 250 
feet, and is often capped by beds of gravel. At N.S. 
Gracia, on the north side of the Inner Narrows of the 
Strait of Magellan, I found on the summit of a cliff, 
160 feet in height, shells of existing Patellge and My till, 
scattered on the surface and partially embedded in 
earth. On the eastern coast, also, of Tierra del Fuego, 
in latitude 58 20' S., I found many Mytili on some 
level land, estimated at 200 feet in height. Anterior 
to the elevation attested by these shells, it is evident 
by the present form of the land, and by the distribution 
of the great erratic boulders s on the surface, that two 
sea-channels connected the Strait of Magellan both 
with Sebastian Bay and with Otway Water. 

Concluding remarks on the recent elevation of the 
south-eastern coasts of America., and on the action of 
the sea on the land, Upraised shells of species, still ex- 
isting as the commonest kinds in the adjoining sea, occur, 
as we have seen, at heights of between a few feet and 410 
feet, at intervals from latitude 33 40 f to 53 20' South. 
This is a distance of 1,180 geographical miles about 
equal from London to the North Cape of Sweden. As 
the boulder formation, extends with nearly the same 
height 150 miles south of 53 20', the most southern 
point where I landed and found upraised shells; and 

1 * Geolog. Transactions/ vol. vi. p, 419. 



CHAP. TJII. Area of Recent Elevation* 209 

as the level Pampas ranges many hundred miles north- 
ward of the point, where M. d'Orbigny found at the 
height of 100 feet beds of the Azara, the space in a 
north and south line, which has been uplifted within 
the recent period ? must have been much, above the 
1,180 miles. By the term c recent,' I refer only to that 
period within which the now living mollusca were 
called into existence ; for it will be seen in the eleventh 
Chapter, that both at Bahia Blanca and P. S. Julian, the 
mamniiferous quadrupeds which co-existed with these 
shells belong to extinct species. I have said that the 
upraised shells were found only at intervals on this line 
of coast, but this in all probability may be attributed 
to my not having landed at the intermediate points ; 
for wherever I did land, with the exception of the 
river Negro, shells were found : moreover, the shells 
are strewed on plains or terraces, which, as we shall 
immediately see, extend for great distances with ^a 
uniform height. I ascended the higher plains only in 
a few places, owing to the distance at which their 
escarpments generally range from the coast, so that I 
am far from knowing that 410 feet is the maximum of 
elevation of these upraised remains. The shells are 
those now most abundant in a living state in the 
adjoining sea. 1 All of them have an ancient appear- 
ance ; but some, especially the mussels, although lying 
fully exposed to the weather, retain to a considerable 
extent their colours : this circumstance appears at first 
surprising, but it is now known that the colouring 
principle of the Mytilus Is so enduring, that it is pre- 
served when the shell itself is completely disintegrated. 2 

1 Capt. King, * Voyages of Adventure and Beagle/ vol. i. pp. 6 
and 138, 

a See Mr Lyell's * Proofs of a Gradual Rising In Sweden/ in the 
* Philosoph Transact ' 1835, p. 1. See also Mr. Smith, of Joidan 
Hill, in the * Edm. New Phil. Journal/ vol. xxv. p. 393. 



210 Area of Recent Elevation. PART IF. 

Most of the shells are broken ; I nowhere found two 
valves united ; the fragments are not rounded, at least 
in none of the specimens which I brought home. 

With respect fco the breadth of the upraised area in 
an east and west line, we know from the shells found at 
the inner Narrows of the Strait of Magellan, that the 
entire width of the plain, although there very narrow, 
has been elevated. It is probable that in this southern- 
most part of the continent, the movement has extended 
tinder the sea far eastward ; for at the Falkland Islands, 
though I could not find any shells, the bones of whales 
have been noticed by several competent observers, lying 
on the land at a considerable distance from the sea, and 
at the height of some hundred feet above it. 1 More- 
over, we know that in Tierra del Fuego the boulder for- 
mation has been uplifted within the recent period, and a 
similar formation occurs 2 on the north-western shores 
(Byron Sound) of these islands. The distance from 
this point to the Cordillera of Tierra del Fuego, is 360 
miles, which we may take as the probable width of the 
recently upraised area. In the latitude of the E. Santa 
Cruz, we know from the shells found at the mouth and 
head, and in the middle of the valley, that the entire 
width (about 160 miles) of the surface eastward of the 
Cordillera has been upraised. From the slope of the 
plains, as shown by the course of the rivers, for several 
degrees northward of the S. Cruz, it is probable that the 
elevation attested by the shells on the coast has likewise 
extended to the Cordillera. When, however, we look as 
far northward as the provinces of La Plata, this conclusion. 

1 'Voyages of the Adventure and Beagle,' vol. ii. p. 227. And 
Bougainville's < Yoyage,' tome i p. 112. 

3 1 owe this fact to the kindness of Oapt. Sulivan, E.K., a highly 
competent observer. I mention it more especially, as in my Paper 
(p. 427) on the Boulder Formation, I have, after having examined 
the northern and middle part^ of the eastern island, said that the 
formation was here wholly absent. 



CHAP. Yin. Uniform Height of Terraces. 



211 



would be very hazardous ; not only is the distance from 
Maldonado (where I found upraised shells) to the 
Cordillera great, namely, 7GO miles, but at the head 
of the estuary of the Plata, a NNE. and SSW. range 
of tertiary volcanic rocks has been observed, 1 which 
may well indicate an axis of elevation quite distinct 
from that of the Andes. Moreover, in the centre of 
the Pampas in the chain of Cordova, severe earthquakes 
have been felt ; 3 whereas at Mendoza, at the eastern 
foot of the Cordillera, only gentle oscillations, trans- 
mitted from the shores of the Pacific, have ever been 
experienced. Hence the elevation of the Pampas may 
be due tt> several distinct axes of movement ; and we 
cannot judge, from the upraised shells round the estuary 
of the Plata, of the breadth of the area uplifted within 
the recent period. 

Not only has the above specified long range of coast 
been elevated within the recent period, but I think it 
may be safely inferred from the similarity in height of 
the gravel-capped plains at distant points, that there 
has been a remarkable degree of equability in the 
elevatory process. I may premise, that when I mea- 
sured the plains, it was simply to ascertain the heights 
at which shells occurred ; afterwards, comparing these 
measurements with some of those made during the 
Survey, I was struck with their uniformity, and accord- 

1 This volcanic formation will be described in Chapter XI It is 
not impiobable that the height of the upraised shells at the head 
of the estuary of the Plata, being- greater lhan at Bahia Blanca or 
at San Bias, may be owing to the upheaval of these latter places 
having been connected with the distant line of the Cordillera, whilst 
that of the provinces of La Plata was in connection with the adjoin- 
ing tertiary volcanic axis. 

2 See Sir W. Parish's work on * La Plata,' p 242 For a notice of 
an earthquake which drained a lake near Coidova, see also Temple's 
'Tiavels in Pern ' Sir W. Parish informs me, that a town between 
Salta and Tucuman (north of Cordova) was formerly utterly over- 
thrown by an earthquake. 



2 1 2 Uniform Height of Terraces. PABT n, 

ingly tabulated all those which, represented the sum- 
mit-edges of plains. The extension of the 330 to 355 
feet plain is very striking, being found over a space of 
500 geographical miles in a north and south line. A 
table of the measurements is here given. The angular 
measurements and all the estimations are by the Officers 
of the Survey; the barometrical ones by myself: 

Feet 
Galles-os River to Coy Inlet (partly angular meas gmd partly . 

estim ) : ... 350 

South Side of Santa Cruz (ang. and barom, meas.) , * . 355 

North Side of do. (an.m) 330 

Bird Island, plain opposite to (ang m ) 350 

Port Desire, plain extending far along coast (barom. m ) . . 330 
St George's Bay, north promontory (ang, m ) . . . . 330 
Table Land, south of New Bay (ang. m ) . . . : .350 

A plain, varying from 245 to 255 feet, seems to 
extend with much uniformity from Port Desire to the 
north of St. George's Bay, a distance of 170 miles; 
and some approximate measurements, also given in the 
following table, indicate the much greater extension of 
780 miles: 

Feet 

Coy Inlet, south of (partly ang m. and partly estim.) 200 to 300 

Port Desire (barom. m ) 245 to 255 

C Blanco (ang. m ) 250 

North Promontory of St George's Bay (ang m.) 250 

South of New Bay (ang m ) 200 to 220 

North of S Josef (ebtim.) ..,,. 200 to 300 

Plain of Bio Negro (ang. m.) 200 to 220 

Bahia Blanca (estim.) 200 to BOO 

The extension, moreover, of the 560 to 580, and of 
the 80 to 100 feet, plains is remarkable, though some- 
what less obvious than in the former cases. Bearing 
in mind that I have not picked these measurements 
out of a series, but have used all those which repre- 
sented the edges of plains, I think it scarcely possible 
that these coincidences in height should be accidental. 
We must therefore conclude that the action, whatever 
it may have been, by which these plains have been 



CHAP. VIIL Uniform Height of Terraces. 213 

modelled into their present foims, lias been singularly 
uniform. 

These plains or great terraces, of which three and 
four often rise like steps one behind the other, are 
formed by the denudation of the old Patagonian 
tertiary beds, and by the deposition on their surfaces of 
a mass of well-rounded gravel, varying, near the coast, 
from ten to thirty-five feet in thickness, but increasing 
in thickness towards the interior. The gravel is often 
capped by a thin irregular bed of sandy earth. The 
plains slope up, though seldom sensibly to the eye, 
from the summit-edge of one escarpment to the foot of 
the next highest one. Within a distance of 150 miles, 
between Santa Cruz to Port Desire, where the plains 
are particularly well developed, there are at least seven 
stages or steps, one above the other. On the three 
lower ones, namely, those of 100 feet, 250 feet, and 
350 feet in height, existing littoral shells are abundantly 
strewed, either on the surface, or partially embedded in 
the superficial sandy earth. By whatever action these 
three lower plains have been modelled, so undoubtedly 
have all the higher ones, up to a height of 950 feet at 
S. Julian, and of 1,200 feet (by estimation) along St. 
George's Bay. I think it will not be disputed, con- 
sidering the presence of the upraised marine shells, that 
the sea has been the active power during stages of some 
kind in the elevatory process. 

We will now briefly consider this subject: if we 
look at the existing coast-line, the evidence of the 
great denuding power of the sea is very distinct ; for, 
from Cape St. Diego, in lat. 54 30' to the mouth of 
the Rio Negro, in lat. 31 (a length of more than 800 
miles), the shore is formed, with singularly few excep- 
tions, of bold and naked cliffs : In many places the 
cliffs are high ; thus, south of the Santa Cruz, they are 



Nature of the Elevation, PAET n. 

between 800 and 900 feet in height, with their hori- 
zontal strata abruptly cut off, showing the immense 
mass of matter which has been removed. Nearly this 
whole line of coast consists of a series of greater or 
lesser curves, the horns of which, and likewise certain 
straight projecting portions, are formed of hard rocks ; 
hence the concave parts are evidently the effect and the 
measure of the denuding action on the softer strata. 
At the foot of all the cliffs, the sea shoals very gradually 
far outwards ; and the bottom, for a space of some 
miles, everywhere consists of gravel. I carefully ex- 
amined the bed of the sea off the Santa Cruz, and found 
that its inclination was exactly the same, both in 
amount and in its peculiar curvature, with that of the 
855 feet plain at the same place. If, therefore, the 
coast, with the bed of the adjoining sea, were now sud- 
denly elevated 100 or 200 feet, an inland line of cliffs, 
that is an escarpment, would be formed, with a gravel- 
capped plain at its foot gently sloping to the sea, and 
having an inclination like that of the existing 355 feet 
plain. From the denuding tendency of the sea, this 
newly formed plain would in time be eaten back into a 
cliff: and repetitions of this elevatory and denuding 
process would produce a series of gravel-capped, sloping 
terraces, rising one above another, like those fronting 
the shores of Patagonia. 

The chief difficulty (for there are other inconsider- 
able ones) on this view, is the fact, as far as I can 
trust two continuous lines of soundings carefully taken 
between Senta Cruz and the Falkland Islands, and 
several scattered observations on this and other coasts, 
that the pebbles at the bottom of the sea qidcldy and 
regularly decrease in size with the increasing depth 
and distance from the shore, whereas in the gravel on 
the sloping plains, no such decrease in size was per- 



CHAP. vm. Elevation Gradual* 215 

ceptible. The following table gives the average result 
of many soundings off the Santa Cruz : 

Under two m les from the shore, many of the pebbles were of 
lar^e size mingled with some small ones. 



Dist ince 
3 to 4 miles fiom the shore. 



6 to 7 mi'es do. 
10 to 11 miles do. 



12 miles do, 

22 to 150 miles do. 



Depth 
11 to 12 fathoms. 



17 to 19 do 
23 to 25 do. 



30 to 40 do 
45 to 63 do 



Size of Pebbles 
As large a= walnuts ; mingled 

in every case wibh some 

smallei ones 
As large as hazel nuts 
Fiora three to foui tenths oi 

an men in diameter 
Tuo-tenths of,<in m*h 
Ono-teiwli of an inch, to the 

finest sand. 



I particularly attended to the size of the pebbles on 
the 355 feet Santa Cruz plain, and I noticed that on 
the summit-edge of the present sea-cliffs many were 
as large as half of a man's head ; and in crossing from 
these cliffs to the foot of the next highest escarpment, 
a distance of six miles, I could not observe any increase 
in their size. We shall presently see that the theory 
of a slow and almost insensible rise of the land, will 
explain all the facts connected with the gravel-capped 
terraces, better than the theory of sudden elevations of 
from one to two hundred feek 

M d'Orbigny has argued, from the upraised shells 
at San Bias being embedded in the positions in which 
they lived, and from the valves of the Azara labiata 
high on the banks of the Parana being united and un- 
rolled, that the elevation of Northern Patagonia and of 
La Plata must have been sudden ; for he thinks, if it 
had "been gradual, these shells would all have been 
rolled on successive beach-lines. But in protected bays, 
such as in that of Bahia Blanca, wherever the sea is 
accumulating extensive mud-banks, or where the winds 
quietly heap up sand-dunes, beds of shells might assuredly 
be preserved buried in the positions in which they had 
lived, even whilst the land retained the same level ; any, 
the smallest, amount of elevation would directly aid in 



216 Elevation Gradual. PABT n. 



their preservation. I saw a multitude of spots in Bah la 
Blanca where this might have been effected; and at 
Maldonado it almost certainly has been effected. In 
speaking of the elevation of the land having been slow, 
I do not wish to exclude the small starts which accom- 
pany earthquakes, as on the coast of Chile ; and by such 
movements beds of shells might easily be uplifted, even 
in positions exposed to a heavy surf, without undergoing 
any attrition : for instance, in 1835, a rocky flat off the 
island of Santa Maria was at one blow upheaved abo\ e 
high-water mark, and was left covered with gaping and 
putrefying mussel-shells, still attached to the bed on 
which they had lived. If M. cTOrhigny had been aware 
of the many long parallel lines of sand-hillocks, with 
infinitely numerous shells of the Mactra and Venus, at 
a low level near the Uruguay ; if he had seen at Bahia 
Blanca the immense sand-dunes, with water-worn pebbles 
of pumice, ranging, in parallel lines, one behind the other 
up a height of at least 120 feet ; if he had seen the sand- 
dunes, with the countless Paludestrinas, on the low plain 
near the Fort at this place, and that long line on the edge 
of the cliff, sixty feet higher up ; if he had crossed that 
long and great belt of parallel sand-dunes, eight miles m 
width, standing at the height of from forty to fifty feet 
above the Colorado, where sand could not now collect, 
I cannot believe he would have thought that the eleva- 
tion of this great district had been sudden. Certainly the 
sand-dunes (especially when abounding with shells), 
which stand in ranges at so many different levels, must 
all have required long time for their accumulation ; and 
hence I do not doubfc that the last 100 feet of elevation 
of La Plata and Northern Patagonia has been exceed- 
ingly slow. 

If we extend this conclusion to Central and Southern 
Patagonia, the inclination of the successively rising 



CHAP. TOI. Elevation GradiiaL 217 

gravel-capped plains can be explained quite as well, as 
by the more obvious view already given of a few com- 
paratively great and sudden elevations; in either case 
we must admit long periods of rest, during which the 
sea ate deeply into the land. Let us suppose the 
present coast to rise at a nearly equable, slow rate, yet 
sufficiently quick to prevent the waves quite removing 
each part as soon as brought up; in this case every 
portion of the present bed of the sea will successively 
form a beach-line, and from being exposed to a like 
action will be similarly affected. It cannot matter to 
what height the tides rise, even if to forty feet as at 
Santa Cruz, for they will act with equal force and in 
like manner on each successive line. Hence there is 
no difficulty in the fact of the 355 feet plain ,at Santa 
Cruz sloping up 108 feet to the foot of the next highest 
escarpment, and yet having no marks of any one par- 
ticular beach-line on it ; for the whole surface on this 
view has been a beach. I cannot pretend to follow out 
the precise action of the tidal waves during a rise of 
the land, slow, yet sufficiently quick to prevent or check 
denudation : but if it be analogous to what takes place 
on protected parts of the present coast, where gravel is 
now accumulating in large quantities/ an inclined 
surface, thickly capped by well-rounded pebbles of 
about the same size, would be ultimately left. On the 
gravel now accumulating, the waves, aided by the win d, 
sometimes throw up a thin covering of sand, together 
with the common coast-shells. Shells thus cast up by 
gales, would, during an elevatory period, never again 
be touched by the sea. Hence, on this view of a slow 
and gradual rising of the land, interrupted by periods 

1 On the eastern side of Chiloe, which island we shall see in the 
next chapter is now rising, T observed that all the beaches and exten- 
sive tidal flats were formed of shingle, 



218 Summary of Results. I>AET BL 

of rest and denudation, we can understand the pebbles 
being of about the same size over the entire width of 
the step-like plains, the occasional thin covering of 
sandy earth, and the presence of broken, unrolled 
fragments of those shells, which now live exclusively 
near the coast. 

Summary of Results. It may be concluded that 
the coast on this side the continent, for a space of at 
least 1,180 miles, has been elevated to a height of 100 
feet in La Plata, and of 400 feet in Southern Patagonia, 
within the period of existing shells, but not of existing 
mammifers. That in La Plata the elevation has been 
very slowly effected : that in Patagonia the movement 
may have been by considerable starts, but much more 
probably slow and quiet. In either case, there have 
been long intervening periods of comparative rest, 1 
during which the sea corroded deeply, as it is still cor- 
roding, into the land. That the periods of denudation 
and elevation were contemporaneous and equable o?er 
great spaces of coast, as shown by the equable heights 
of the plains ; that there have been at least eight 
periods of denudation, and that the land, up to a height 
of from 950 to ] ,200 feet, has been similarly modelled 
and affected : that the area elevated, in the southern* 
most part of the continent, extended in breadth to 
the Cordillera, and probably seaward to the Falkland 
Islands ; that northward, in La Plata, the breadth is 
unknown, there having been probably more than one 
axis of elevation; and finally, that, anterior to the 
elevation attested by these upraised shells, the land was 
divided by a Strait where the river Santa Cruz now 

J I say comparative and not absolute rest, because the sea acts, 
as we have seen, with great denuding power on this whole line of 
coast; and therefore, during an elevation of the land, if excessively 
6<o.v(andof coarse during a subsidence of the land), it is quite 
possible that lines of cliff might be formed. 



CHIP. vm. Gravel Formation of Patagonia. 219 

flows, and that farther southward there were other sea- 
straits, since closed, I may add, that at Santa Cruz, 
in lat. 50 S., the plains have been uplifted at least 
1,400 feet, since the period when gigantic boulders 
were transported between sixty and seventy miles from 
their parent rock, on floating icebergs. 

Lastly, considering the great upward movements 
which this long line of coast has undergone, and the 
proximity of ils southern half to the volcanic axis of 
the Cordillera, it is highly remarkable that in the many 
fine sections exposed in the Pampean, Patagoman 
tertiary, and Boulder formations, I nowhere observed 
the smallest fault or abrupt curvature in the strata. 

Gravel Formation of Patagonia. 

I will here describe in more detail than has been as 
yet incidentally done, the nature, origin, and extent of 
the great shingle covering of Patagonia : but I do not 
mean to affirm that all of this shingle, especially that 
on the higher plains, belongs to the recent period. A 
thin bed of sandy earth, with small pebbles of various 
porphyries and of quartz, covering a low plain on the 
north side of the Bio Colorado, is the extreme northern 
limit of this formation. These little pebbles have 
probably been derived from the denudation of a more 
regular bed of gravel, capping the old tertiary sand- 
stone plateau of the Eio Negro. The gravel-bed near 
the Eio Negro is, on an average, about ten or twelve 
feet in thickness ; and the pebbles are larger than on 
the northern side of the Colorado, being from one to 
two inches in diameter, and composed chiefly of rather 
dark-tinted porphyries. Amongst them I here first 
noticed a variety often to be referred to, namely, a 
peculiar gallstone-yellow siliceous porphyry, frequently, 



220 Gravel Formation of Patagonia. PIET EL 

but not invariably, containing grains of quartz. The 
pebbles are embedded in a white gritty calcareous 
matrix: very like mortar, sometimes merely coating 
with a whitewash the separate stones, and sometimes 
forming the greater part of the mass. In one place I 
saw in the gravel concretionary nodules (not rounded) 
of crystallized gypsum, some as large as a man's head. 
I traced this bed for forty-five miles inland, and was 
assured that it extended far into the interior. As the 
surface of the calcareo-argillaceous plain of Pampean 
formation, on. the northern side of the wide valley of 
the Colorado, stands at about the same height with the 
mortar-like cemented gravel capping the sandstone on 
the southern side, it is probable, considering the appa- 
rent equability of the subterranean movements along 
this side of America, that this gravel of the Bio Negro 
and the upper beds of the Pampean formation north- 
ward of the Colorado, are of nearly contemporaneous 
origin, and that the calcareous matter has been derived 
from the same source. 

Southward of the Eio Negro, the cliffs along the 
great bay of S. Antonio are capped with gravel : at Saa 
Josef, I found that the pebbles closely resembled those 
on the plain of the Eio Negro, but that they were not 
cemented by calcareous matter. Between San Josef 
and Port Desire. I was assured by the Officers of the 
Survey that the whole face of the country is coated with 
gravel. At Port) Desire and over a space of twenty-five 
miles inland, on the three step-formed plains and in the 
valleys, I everywhere passed over gravel which, where 
thickest, was between thirty and forty feet. Here, as 
in other parts of Patagonia, the gravel, or its sandy 
covering, was, as we have seen, often strewed with re- 
cent marine shells. Th.e Bandy covering sometimes 
fills up furrows in the gravel, as does the gravel in the 



CHAP. Yin, Gravel Formation of Patagonia. 221 

underlying tertiary formations. The pebbles are fre- 
quently whitewashed and even cemented together by 
a peculiar, white, friable, aluminous, fusible, substance, 
which I believe is decomposed feldspar. A t Port Desire, 
the gravel rested sometimes on the basal formation of 
porphyry, and sometimes on the upper or the lower 
denuded tertiary strata. It is remarkable that most 
of the porphyritic pebbles differ from those varieties of 
porphyry which occur here abundantly in situ. The 
peculiar gallstone-yellow variety was common, but less 
numerous than at Port 8. Julian, where it formed 
nearly one-third of the mass of gravel ; the remaining 
part there consisting of pale gray and greenish por- 
phyries with many crystals of feldspar. At Port S. 
Julian, I ascended one of the flat-topped hills, the de- 
nuded remnant of the highest plain, and found it, at 
the height of 950 feet, capped with the usual bed of 
gravel. 

Near the mouth of the Santa Cruz, the bed of gravel 
on the 355 feet plain is from twenty to about thirty- 
five feet in thickness. The pebbles vary from minute 
ones to the size of a hen's egg, and even to that of half 
a man's head ; they consist of paler varieties of porphyry 
than those found farther northward, and there are fewer 
of the gallstone-yellow kind ; pebbles of compact black 
clay-slate were here first observed. The gravel, as we 
have seen, covers the step-formed plains at the mouth, 
head, and on the sides of the great valley of the Santa 
Cruz. At a distance of 110 miles from the coast, the 
plain has risen to the height of 1,416 feet above the 
sea ; and the gravel, with the associated great boulder 
formation, has attained a thickness of 212 feet. The 
plain, apparently with its usual gravel covering, slopes 
up to the foot of the Cordillera to the height of between 
3 3 200 and 3 3 300 feet. In ascending the valley, the 



222 Gravel Formation of Patagonia. PAET n e 

gravel gradually becomes entirely altered in character: 
high up, we have pebbles of crystalline feldspalhic rocks, 
compact clay-slate, quartzose schists and pale-coloured 
porphyries; these rocks, judging both from the gigantic 
boulders in the surface and from some small pebbles 
embedded beneath 700 feet in thickness of the old 
tertiary strata, are the prevailing kinds in this part of 
the Cordillera ; pebbles of basalt from the neighbouring 
streams of basaltic lava are also numerous ; there are 
few or none of the reddish or of the gallstone-yellow 
porphyries so common near the coast. Hence the 
pebbles on the 850 feet plain at the mouth of the Santa 
Cruz cannot have been derived (with the exception of 
those of compact clay-slate, which, however, may equally 
well have come from the south) from the Cordillera in 
this latitude $ but probably, in chief part, from farther 
north. 

Southward of the Santa Cruz, the gravel may be 
seen continuously capping the great 840 feet plain : at 
the Rio Gallegos, where this plain is succeeded by a 
lower one, there is, as I am informed by Captain Suli- 
van, an irregular covering of gravel from ten to twelve 
feet in thickness over the whole country. The district 
on each side of the Strait of Magellan is covered up 
either with gravel or the bo alder formation : it was 
interesting to observe the marked difference between 
the perfectly rounded state of the pebbles in the great 
shingle formation of Patagonia, and the more or less 
angular fragments in the boulder formation. The 
pebbles and fragments near the Strait of Magellan 
nearly all belong to rocks known to occur in Fucgia. 
I was therefore much surprised in dredging south of 
the Strait to find, in lat. 54 10' south, many pebbles 
of the gallstone-yellow siliceous porphyry; I procured 
others from a great depth off Staten Island^ aiid others 



CHAP, TIII. Gravel Formation of Patagonia. 223 

were brought me from the western extremity of the 
Falkland Islands. 1 The distribution of the pebbles of 
this peculiar porphyry, which I venture to affirm is not 
found in situ either in Fuegia, the Falkland Islands, 
or on the coast of Patagonia, is very remarkable, for 
they are found over a space of 840 miles in a north and 
south line, and at the Falklands, 300 miles eastward of 
the coast of Patagonia. Their occurrence in Fuegia 
and the Falklands may, however, perhaps be due to 
the same ice-agency by which the boulders have been 
there transported. 

We have seen that porphyritic pebbles of a small 
size are first met with on the northern side of the Rio 
Colorado, the bed becoming well developed near the 
Bio Negro : from this latter point I have every reason 
to "believe that the gravel extends uninterruptedly over 
the plains and valleys of Patagonia for at least 630 
nautical miles southward to the Eio Gallegos. From 
the slope of the plains, from the nature of the pebbles, 
from their extension at the Kio Negro far into the 
interior, and at the Santa Cruz close up to the Cor- 
dillera, I think it highly probable that the whole breadth 
of Patagonia is thus covered. If so, the average width 
of the bed must be about 200 miles. Near the coast 
the gravel is generally from ten to thirty feefc in thick- 
ness ; and as in the valley of Santa Cruz it attains, at 
some distance from the Cordillera, a thickness of 214 
feet, we may, I think, safely assume Its average thick- 

a At my request, Mr Kent collected for me a bag of pebbles from 
the beach of White Rock harbour, in the northern part of the sound, 
between the two Falkland Islands. Out of these well-rounded 
pebbles, varying in size from a walnut to a hen's egg 1 , with some 
larger, thirty-eight evidently belonged to the rocks of these islands; 
twenty-six were similar to the pebbles of porphyry found on the 
Patagonian plains, which rocks do not exist m situm the Falklands; 
one pebble belonged to the peculiar yellow siliceous porphyrj ; thirty 
were ot doubtful origin. 



224 Gravel Formation of Patagonia. PAST it 

ness over the whole area of 630 by 200 miles, at fifty 
feet! 

The transportal and origin of this vast bed of pebbles 
is an interesting problem. IVom the manner in which 
they cap the step-formed plains, worn by the sea within 
the period of existing shells, their deposition, at least 
on the plains up to a height of 400 feet, must have 
been a recent geological event. Prom the form of the 
continent, we may feel sure that they have come from 
the westward, probably, in chief part from the Cordillera, 
but, perhaps, partly from unknown rocky ridges in the 
central districts of Patagonia. That the pebbles have 
not been transported by rivers, from the interior towards 
the coast, we may conclude from the fewness and small- 
ness of the streams of Patagonia : moreover, in. the case 
of the one great and rapid river of Santa Cruz, we have 
good evidence that its transporting power is very trifling. 
This river is from 200 to 300 yards in width, about 
seventeen feet deep in its middle, and runs with a sin- 
gular degree of uniformity five knots an hour, with no 
lakes and scarcely any still reaches : nevertheless, to 
give one instance of its small transporting power, upon 
careful examination, pebbles of compact basalt could 
not be found tn the bed of the river at a greater distance 
than ten miles below the point where the stream rushes 
over the debris of the great basaltic cliffs forming its 
shore: fragments of the cellula/r varieties have been 
washed down twice or thrice as far. That the pebbles 
in Central and Northern Patagonia have not been trans- 
ported by ice-agency, as seems to have been the case to 
a considerable extent farther south, and likewise in the 
northern hemisphere, we may conclude, from the absence 
of all angular fragments in. the gravel, and from the 
complete contrast in many other respects between the 
shingle and neighbouring boulder formation. 



TOI. Distribution of GraveL 225 

Looking to the gravel on any one of the step-formed 
plains, I cannot doubt, from the several reasons assigned 
in this chapter, that it has been spread ont and levelled 
by the long-continued action of the sea, probably during 
the slow rise of the land. The smooth and perfectly 
rounded condition of the innumerable pebbles alone 
would prove long-continued action. But how the whole 
mass of shingle on the coast-plains has been transported 
from the mountains of the interior, Is another and more 
difficult question. The following considerations, how- 
ever, show that the sea by its ordinary action has con- 
siderable power in distributing pebbles. A table has 
already been given, showing how very uniformly and 
gradually l the pebbles decrease in size with the gradu- 
ally seaward increasing depth and distance. A series 
of this kind irresistibly leads to the conclusion, that 
the sea has the power of sifting and distributing the 
loose matter on its bottom. According to Martin 
White, 2 the bed of the British Channel is disturbed 
during gales at depths of sixty-three and sixty-seven 
fathoms, and at thirty fathoms, shingle and fragments 
of shells are often deposited, afterwards to be carried 
away again. Ground-swells, which are believed to be 

1 I may mention, that at the distance of 150 miles from the 
Patagonian shore I carefully examined the minute-rounded particles 
in the sand, and found them to be fusible like the porphyries of the 
grear shingle bed. I could even distinguish particles of the gall- 
stone yellow porphyry. It was interesting to notice how gradually 
the particles of white quartz increased, as we approached the Falk- 
land Islands, which are thus constituted. In the whole line of 
soundings between these islands and the coast of Patagonia dead or 
living organic remains were most rare. On the relations between 
the depth of water and the nature of the bottom, see Martin White 
on 4 Soundings in the Channel, 7 pp 4, 6, 175 ; also Captain Beechey's 
* Voyage to the Pacific,' chap xvni. 

2 * Soundings in the Channel,' pp. 4, 166. M. Siau states 
('Edin. New Phil Jour 'vol. xxxi. p 246), that he found the sedi- 
ment, at a depth of 188 metres, arranged in ripples of different 
degrees of fineness. There are some excellent discussions on this 
and allied subjects in Sir BL De la Beche's ' Theoretical Researches. 9 



226 Distribution of Gravel. PAET u. 

caused Iby distant gales, seem especially to affect the 
bottom : at such times 3 according to Sir R. Scliom- 
burgk, 1 the sea to a great distance round the West 
Indian Islands, at depths from five to fifteen fathoms, 
becomes discoloured, and even the anchors of vessels 
have been moved. There are, however, some difficulties 
in understanding how the sea can transport pebbles 
lying at the bottom, for, from experiments instituted 
on the power of running water, it would appear that 
the currents of the sea have not sufficient velocity to 
more stones of even moderate size : moreover, I have 
repeatedly found in the most exposed situations that 
the pebbles which lie at the bottom are encrusted with 
fall-grown living corallines, furnished with the most 
delicate, yet unbroken spines : for instance, in ten 
fathoms water off the mouth of the Santa Cruz, many 
pebbles, under balf an Inch in diameter, were thus 
coated with Plnstracean zoophytes. 2 Hence we must 
conclude that these pebbles are not often violently dis- 
turbed : it should, however, be borne in mind that the 
growth of corallines is rapid The view, propounded 
by Prof Playfair, will, I believe, explain this apparent 
difficulty, namely, that from the undulations of the 
sea tending to lift up and down pebbles or other loose 
bodies at the bottom, such are liable, when thus quite 
or partially raised, to be moved even by a very small 

1 * Journal of Koyal Geograph Soc'vol v. p 25. It appears from 
Mr Scott Russell's investigations (see Mr. MurcMsou's 'Anmver. 
Addiess Geolog Soc ' 18-13, p. 40), that m waves of translation the 
motion of the paiticles of water Is nearly as great at the bottom as 
at the top. 

2 A pebble, one and a half inch square and half an Inch thick, was 
given me, dredged up from twenty-seven fathoms depth off the west- 
ern, end of the Falkland Islands, where the sea is remaikably stormy, 
and subject to violent tides. This pebble v^as encrusted on all sides 
by a delicate living coralline I have seen many pebbles from depths 
between forty and seventy fathoms thus enciusted ; one from the 
latter depth of Cape Horn. 



CHAP, vm. Distribiition of Gravel* 227 

force, a little onwards. We can thus understand how 
oceanic or tidal currents of no great strength, or that 
recoil movement of the bottom-water near the land, 
called by sailors the c undertow ' (which I presume must 
extend out seaward as far as the breaJdny waves impel 
the surface-water towards the beach), may gain the 
power during storms of sifting and distributing pebbles 
even of considerable size, and yet without so violently 
disturbing them as to injure the encrusting corallines. 1 
The sea acts in another and distinct manner in 
the distribution of pebbles, namely by the waves on the 
beach. Mr. Palmer, 2 in his excellent memoir on this 
subject, has shown that vast masses of shingle travel 
with surprising quickness along lines of coast, according 
to the direction with which the waves break on the 
beach, and that this is determined by the prevailing 
direction of the winds. This agency must be powerful 
in mingling together and disseminating pebbles derived 
from different sources : we may, perhaps, thus under- 
stand the wide distribution of the gallstone-yellow 
porphyry and likewise, perhaps, the great difference in 
the nature of the pebbles at the mouth of the Santa 

1 1 may take this opportunity of remaiking on a singular but 
very common character in the rorm of the bottom, in the creeks 
which deeply penetrate the western shores otTierradel Fuego; namely, 
that they are almost invariably much shallower close to the openhea 
at their mouths ihan inland. Thus, Cook, in entering Christmas 
Sound, first had soundings in thirty-seven fathoms, thenm fifty, then 
in sixty, and a little farther in no bottom, with 170 fathoms. The 
sealers are so familiar with this fact, that they always look out for 
anchorage near the entrances of the creeks. See, also, on this subject, 
the ' Voyage of the Adventuie and Beagle,* vol. i p. 375, and * Appen- 
dix,' p 313. This shoalness of the sea-channels near their entrances 
probably results from the quantity ofc sediment formed by the wear 
and tear of the outer rocks exposed to the full force of the open sea. 
I have no doubt that many Jakes, for instance in Scotland, which are 
very deep within, and are separated from the sea apparently only by 
a tract of detritus, weie originally sea-channels with banks of this 
nature near their mouths, which have since been upheaved. 

2 ' Philosophical Transactions,' 1834, p 576. 

16 



228 Formation of Sea- Cliffs. PART IT, 

Cruz from those in the same latitude at the head of the 
valley, 

I will not pretend to assign to these several and 
complicated agencies their shares in the distribution of 
the Patagonian shingle ; but from the several considera- 
tions given in this chapter, and I may add, from the 
frequency of a capping of gravel on tertiary deposits in 
all parts of the world, as I have myself observed and 
seen stated in the works-of various authors, I cannot doubt 
that the power of widely dispersing gravel is an ordinary 
contingent on the action of the sea ; and that even in 
the case of the great Patagonian shingle-bed we have 
no occasion to call in the aid of debacles. I at one 
time imagined that perhaps an immense accumulation 
of shingle had originally been collected at the foot of 
the Cordillera; and that this accumulation, when up- 
raised above the level of the sea, had been eaten into 
and partially spread out (ad off the present line of coast) ; 
and that the newly-spread out bed had in its turn been 
upraised, eaten into, and re-spread out ; and so onwards, 
until the shingle, which was first accumulated in great 
thickness at the foot of the Cordillera, had reached in 
thinner beds its present extension. By whatever means 
the gravel formation of Patagonia may have been dis- 
tributed, the vastness of its area, its thickness, its 
superficial position, its recent origin, and the great 
degree of similarity in the nature of its pebbles, all 
appear to me well deserving the attention of geologists, 
in relation to the origin of the widely-spread beds of 
conglomerate belonging to past epochs. 

Formation of Cliffs. When viewing the sea- worn 
cliffs of Patagonia, in some parts between 800 and 900 
feet in height, and formed of horizontal tertiary strata, 
which must once have extended far seaward or again, 
when viewing the lofty cliffs round many volcanic 



CHAP vin Formation of Sea-Cliffs. 



229 



islands, in which the gentle inclination of the lava- 
streams indicates the former extension of the land, a 
difficulty often occurred to me, namely, how the strata 
could possibly have been removed by the action of the 
sea at a considerable depth beneath its surface. The 
following section, which represents the general form of 
the land on the northern and leeward side of St. Helena 
(taken from Mr. Seal's large model and various measure- 
ments), and of the bottom of the adjoining sea (taken 
chiefly from Captain Austin's survey and some old 
charts), will show the nature of this difficulty : 

No 21 
Section of Coast Cliffs and Bottom of Sea, off the Island of St Helena 




SOfath. 



100 fa 250 fa- 



Level of sea. 



Bottom rocky 
only to a depth of 
five or six fathoms 



Mud and sand. 



Vertical and horizontal scale, two inches to a nautical mile. The point marked 
1,600 feet is at the foot ot High Knoll , point marked 510 feet is on the edge of 
Ladder HilL The strata consist ot basaltic streams 

If, as seems probable, the basaltic streams were 
originally prolonged with nearly their present inclina- 
tion, they must, as shown by the dotted line in the 
section, once have extended at least to a point, now 
covered by the sea to a depth of nearly thirty fathoms : 
but I have every reason to believe they extended con-: 
siderably farther, for the inclination of the streams is 
less near the const than farther inland. It should also 
be observed, that other sections on the coast of this 
island would have given far more striking results, but 
I had not the exact measurements ; thus, on the wind- 
ward side, the cliffs are about 2,000 feet in height and 



030 Formation of Sea-Cliffs. PAET n. 

the cnt-off lava streams very gently inclined, and the 
bottom of the sea has nearly a similar slope all round 
the island. How, then, has all the hard basaltic rock, 
which once extended beneath the surface of the sea, 
been worn away ? According to Captain Austin, the 
bottom is uneven and rocky only to that very small 
distance from the beach within which the depth is from 
five to six fathoms; outside this line, to a depth of 
about 100 fathoms, the bottom is smooth, gently in- 
clined, and formed of mud and sand; outside the 100 
fathoms, it plunges suddenly into unfathomable depths, 
as is so very commonly the case on all coasts where 
sediment is accumulating. At greater depths than the 
five or six fathoms, it seems impossible, under existing 
circumstances, that the sea can both have worn away 
hard rock, in parts to a thickness of at least 150 feet, 
and have deposited a smooth bed of fine sediment. 
Now, if we had any reason to suppose that St. Helena 
had, during a long period, gone on slowly subsiding, 
every difficulty would be removed : for looking at the 
diagram, and imagining a fresh amount of subsidence, 
we can see that the waves would then act on the coast- 
cliffs with fresh and unimpaired vigour, whilst the 
rocky ledge near the beach would be carried down to 
that depth, at which sand and mud would be deposited 
on its bare and uneven surface : after the formation 
near the shore of a new rocky shoal, fresh subsidence 
would carry it down and allow it to be smoothly 
covered up. But in the case of the many cliff-bounded 
islands, for instance in some of the Canary Islands and 
of Madeira, round which the inclination of the strata 
shows that the land once extended far into the depths 
of the sea, where there is no apparent means of hard 
rock being worn away are we to suppose that all these 
islands have slowly subsided ? Madeira, I may remark, 



CHAP. TIH. formation of Sea-Cliffs, 231 

lias, according to Mr. Smith of Jordan-hill, subsided. 
Are we to extend this conclusion to the high, cliff- 
bound, horizontally-stratified shores of Patagonia, oS 
which, though the water is not deep even at the dis- 
tance of several miles, yet the smooth bottom of pebbles 
gradually decreasing in size with the increasing depth, 
and derived from a foreign source, seem to declare that 
the sea is now a depositing and not a corroding agent ? 
I am much inclined to suspect, that we shall hereafter 
find in all such cases, that the land with the adjoining 
bed of the sea has in truth subsided : the time will, I 
believe, come, when geologists will consider it as im- 
probable, that the land should have retained the same 
level during a whole geological period, as that the 
atmosphere should have remained absolutely calm 
during an entire season. 



232 Elevation of Chiloe. PABT n. 



CHAPTER IX. 

ON THE ELEVATION OF THE WESTERN COAST OF SOUTH 
AMERICA. 

Chonos Archipelago Cliiloe, recent and gradual elevation of) tradi- 
tions of the inhabitants on this subject Conception, earthquake and 
el&i atlon of. VALPARAISO, great elevation of, iqwaised shells, eartJt 
of mar inn origin, gradual rise of tlie land within the historical 
period COQUIMB'O, deration of, in recent time*, terraces of marine 
origin, their inclination, tlwir escarpments not horizontal Giiasco, 
graiel terraces of Copiapo, PERU Upraised sliells of Cobija, 
Iqu igiie, and A rit a Lima, <thel^oed<t and sea-beach on San Lorenzo, 
Hwnian remains, fossil earthenware, earthquake deltaole^ recent sub- 
sidence 0)i the decay of tyiraised shelh General summary, 

COMMENCING at the south and proceeding northward, 
the first place at which I landed, was at Cape Tres 
Montes, in lat. 46 35'. Here, on the shores of Christ- 
mas Cove, I observed in several places a beach of 
pebbles with recent shells, about twenty feet above 
high-water mark. Southward of Tres Montes (between 
lat. 47 and 48), Byron * remarks, ' we thought it very 
strange, that upon the summits of the highest hills 
were found beds of shells, a foot or two thick.' In the 
Chonos Archipelago, the island of Lemus (lat. 44 3CK) 
was, according to M. Coste, 2 suddenly elevated eight 
feet, during the earthquake of 1839 : he adds, * dos 
roches jadis toujours couvertes par la mer, restant 
aujourd'hui constarnment decouvertes/ In other parts 

1 ' Narrative of the Loss, of the Wager.' 
* ' Couiptes Rendus/ October 1838, p. 706. 



CHAP. ix. Elevation of Ckiloe. 233 

of this archipelago, I observed two terraces of gravel, 
abutting to the foot of each other : at Lowe's Harbour 
(43 48'), under a great mass of the boulder formation, 
about 300 feet in thickness, I found a layer of sand, 
with numerous comminuted fragments of sea-shells, 
having a fresh aspect, but too small to be identified. 

The Island of Ohiloe. The evidence of recent 
elevation is here more satisfactory. The bay of San 
Carlos is in most parts bounded by precipitous cliffs 
from about ten to forty feet in height, their bases 
being separated from the present line of ticlal action 
by a talus, a few feet in height, covered with vegetation. 
In one sheltered creek (west of P. Arena) instead of a 
loose talus, there was a bare sloping bank of tertiary 
mudstone, perforated, above the line of the highest 
tides, by numerous shells of a Pholas now common in 
the harbour. The upper extremities of these shells, 
standing upright m their holes with grass growing out 
of them, were abraded about a quarter of an inch, to 
the same level with the surrounding worn strata. In 
other parts, I observed (as at Pudeto) a great beach, 
formed of comminuted shells, twenty feet above the 
present shore. In other parts, again, there were small 
caves worn into the foot of the low cliffs, and protected 
from the waves by the talus with its vegetation : one 
such cave which I examined, had its mouth about 
twenty feet, and its bottom, which was filled with sand 
containing fragments of shells and legs of crabs, from 
eight to ten feet above high-water mark. From these 
several facts, and from the appearance of the upraised 
shells, I inferred that the elevation had been quite 
recent ; and on inquiring from Mr. Williams, the Port- 
master, he told me he was convinced that the land had 
risen, or the sea fallen, four feeb within the last four 
years. Daring this period, there had been one severe 



234 Elevation of Ckiloe. FABT H, 

earthquake, but no particular change of level was then 
observed ; from the habits of the people who all keep 
boats in the protected creeks, it is absolutely impossible 
that a rise of four feet could have taken place suddenly 
and been unperceived. Mr. Williams believes that the 
change has been quite gradual. Without the elevatory 
movement continues at a quick rate, there can be no 
doubt that the sea will soon destroy the talus of earth 
at the foot of the cliffs round the bay, and will then 
reach its former lateral extension, but not of course its 
former level : some of the inhabitants assured me, that 
one such talus, with a footpath on it, was even already 
sensibly decreasing in width. 

I received several accounts of beds of shells, existing 
at considerable heights in the inland parts of Chiloe; 
and to one of these, near Catiman, I was guided by a 
countryman. Here, on the south side of the peninsula 
of Lacuy, there was an immense bed of the Venus 
costellata and of an oyster, lying on the summit-edge 
of a piece of table land, 350 feet (by the barometer) 
above the level of the sea. The shells were closely 
packed together, embedded in and covered by, a very 
black, damp peaty mould, two or three feet in thick- 
ness, out of which a forest of great trees was growing. 
Considering the nature and dampness of this peaty soil, 
it is surprising, that the fine ridges on the outside of 
the Venus are perfectly preserved, though all the 
shells have a blackened appearance. I did not doubt 
that the black soil, which, when dry, cakes hard, was 
entirely of terrestrial origin, but on examining it under 
the microscope, I found many very minute rounded 
fragments of shells, amongst which I could distinguish 
bits of serpulae and mussels. . The Venus costettata, 
and the ostrea (0. edulis, according to Captain. King) 
are now the commonest shells in the adjoining ba^ & . 



CHAP. ix. Elevation of Chiloe* 235 

In a bed of shells, a few feet below the 350 feet bed, I 
found a horn of the little Gervus humilis, which now 
inhabits Ohiloe. 

The eastern or inland side of Chiloe, with its many 
adjaceut islets, consists of tertiary and boulder deposits, 
worn into irregular plains capped by gravel. Near 
Castro, and for ten miles southward, and on the islet of 
Leniuy, I found the surface of the ground to a height 
of between twenty and thirty feet above high-water 
mark, and in several places apparently up to fifty feet, 
thickly coated by much comminuted shells, chiefly of 
the Venus costellata and Mytilus Ohiloensis-, the 
species now most abundant on this line of coast. As 
the inhabitants carry immense numbers of these shells 
inland, the continuity of the bed at the same height 
was often the only means of recognising its natural 
origin. Near Castro, on each side of the creek and 
rivulet of the Gamboa, three distinct terraces are seen : 
the lowest was estimated at about 150 feet in height, 
and the highest at about 500 feet, with the country 
irregularly rising behind it; obscure traces, also, of 
these same terraces could be seen along other parts of 
the coast. There can be no doubt that their three 
escarpments record pauses in the elevation of the 
island. I may remark that several promontories have 
the word Huapi, which signifies in the Indian tongue, 
island, appended to them, such as Huapilinao, Huapi- 
lacuy, Caucahuapi, etc. ; and these, according to Indian 
traditions, once existed as islands. In the same manner 
the term Pulo in Sumatra is appended l to the names 
of promontories, traditionally said to have been islands ; 
in Sumatra, as in Chiloe, there are upraised recent 
shells. The Bay of Oarelmapu, on the mainland nortli 

1 Marsden's * Sumatra,' p. 31. 



236 Elevation of Conception. FAET u, 

of Chlloe, according to Agiierros, 1 was in 1643 a good 
harbour; it is now quite useless, except for boats. 

Valdivia.! did not observe here any distinct proofs 
of recent elevation ; but in a bed of very soft sandstone, 
forming a fringe-like plain, about sixty feet in height, 
round the hills of mica-slate, there are shells of Mytilus, 
Grepidula, Solen, Novaculina, and Cytheraaa, too im- 
perfect to be specifically recognised. At Imperial, 
seventy miles north of Valdivia, Aguerros 2 states that 
there are large beds of shells, at a considerable distance 
from the coast, which are burnt for lime. The island 
of Mocha, lying a little north of Imperial, was uplifted 
two feet, 3 during the earthquake of 1835. 

Conception. I cannot add anything to the excellent 
account by Captain FitzRoy 4 of the elevation of the 
land at this place, which accompanied the earthquake 
of 1835. I will only recall to the recollection of 
geologists, that the southern end of the island of St. 
Mary was uplifted eight feet, the central part nine, and 
the northern end ten feet and the whole island more 
than the surrounding districts. Great beds of mussels, 
patellae, and chitons still adhering to the rocks were 
upraised above high-water mark ; and some acres of a 
rocky flat, which was formerly always covered by the 
sea, was left standing dry, and exhaled an offensive 
smell, from the many attached and putrefying shells. 

1 ' Descnpcion Hist de la Provincia de ChiloeY p. 78. From the 
account given by the old Spanish writers, it would appear that several 
other harbours, between this point and Concepcion, were formerly 
much deeper than they now are. 

2 ' Descnpc. Hist ' p. 25 

3 ' Voyages of Adventure and Beagle/ vol. ii. p. 415. 

4 Ibid, vol ii. p. 412 et se% In vol. v. (p. 601) of the ' Geolo- 
gical Transactions,' I have given an, account of the remarkable vol- 
canic phenomena, which accompanied this earthquake These 
phenomena appear to me to prove that the action, by which large 
tracts of land are uplifted, and by which volcanic eruptions ara 
produced, is in every respect identical. 



CHAP. is. Elevation of Conception. 237 

It appears from the researches of Capt. FitzKoy that 
both the island of St. Mary and Concepcion (which was 
uplifted only four or five feet) in the course of some 
weeks subsided, and lost part of their first elevation. 
I will only add as a lesson of caution, that round the 
sandy shores of the great Bay of Concepcion, it was 
most difficult, owing to the obliterating effects of the 
great accompanying wave, to recognise any distinct 
evidence of this considerable upheaval; one spot must 
be excepted, where there was a detached rock whicli 
before the earthquake had always been covered by the 
sea, but afterwards was left uncovered. 

On the island of Quinquina (in the Bay of Concep- 
cion), I found, at an estimated height of 400 feet, 
extensive layers of shells, mostly comminuted, but some 
perfectly preserved and closely packed in black vege- 
table mould ; they consisted of Concholepas, Fissurella, 
Mytilus, Trochus, and Balanus. Some of these layers 
of shells rested on a thick bed of bright-red, dry, friable 
earth, capping the surface of the tertiary sandstone, 
and extending, as I observed whilst sailing along the 
coast, for 150 miles southward: at Valparaiso, we shall 
presently see that a similar red earthy mass, though 
quite like terrestrial mould, is really ID chief part of 
recent marine origin. On the flanks of this Island of 
Quiriquina, at a less height than the 400 feet, there 
were spaces several feet square, thickly strewed with 
fragments of similar shells. During a subsequent visifc 
of the 'Beagle to Concepcion, Mr. Kent, the assistant- 
surgeon, was so kind as to make for me some measure- 
ments with the barometer: he found many marine 
remains along the shores of the whole bay, at a height 
of about twenty feet ; and from the hill of Sentinella 
behind Talcahuano, at the height of 160 feet, he col~ 
lected numerous shells, packed together close 



238 Elevation of Conception. 

the surface in black earth, consisting of two species 
of Mytilus, two of Crepidula, one of Concholepas, of 
Kssurella, Venus, Mactra, Turbo, Monoceros, and the 
Balanus psittacnts. These shells were bleached, and 
within some of the Balani other Balani were growing, 
showing that they must have long lain dead in the sea. 
The above species I compared with living ones from 
the bay, and found them Identical; but having since 
lost the specimens, I cannot give their names: this is 
of little importance, as Mr. Broderip has examined a 
similar collection, made during Capt. Beechey's expedi- 
tion, and ascertained that they consisted of ten recent 
species, associated with fragments of Echini, crabs, and 
Flustrae; some of these remains were estimated by 
Lieut. Belcher to lie at the height of nearly a 1,000 feet 
above the level of the sea. 1 In some places round the 
bay, Mr. Kent observed that there were beds formed 
exclusively of the Mytilus Ghiloensis : this species now 
lives in parts never uncovered by the tides. At con- 
siderable heights, Mr. Kent found only a few shells; 
but from the summit of one hill, 625 feet high, he 
brought me specimens of the Concholepas, Mytilus 
Chiloensis, and a Turbo. These shells were softer and 
more brittle than those from the height of 164 feet; 
and these latter had obviously a much more ancient 
appearance than the same species from the height of 
only twenty feet. 

Coast north of Conception. The first point exa- 
mined was at the mouth of the Eapel (160 miles N.o f 
Concepcion and sixty miles 8. of Valparaiso), where I 
observed a few shells at the height of 100 feet, and 
some barnacles adhering to the rocks three or four feet 
above the highest tides: M. Gay 2 found here recent 

1 * Zoology of Capt Beechey's Voyage/ p. 162* 
* l Annales des Scienc, Nat/ Ami 1833. 



CHAP, ix. Elevation of Valparaiso. 239 

shells at the distance of two leagues from the shore. 
Inland there are some wide, gravel-capped plains, inter- 
sected by many broad, flat-bottomed valleys (now carry- 
ing insignificant streamlets) with their sides cut into 
successive wall-like escarpments, rising one above 
another, and in many places, according to M. Gay, 
worn into caves. The one cave (0. del Obispo) which 
I examined, resembled those formed on many sea-coasts, 
with its bottom filled with shingle. These inland 
plains, instead of sloping towards the coast, are inclined 
in an opposite direction towards the Cordillera, like the 
successively rising terraces on the inland or eastern side 
of Ohiloe : some points of granite, which project through 
the plains near the coast, no doubt once formed a chain 
of outlying islands, on the inland shores of which 
the plains were accumulated. At Bucalemu, a few 
miles northward of the Rapel, I observed at the foot 
and on the summit-edge of a plain, ten miles from the 
coast, many recent shells, mostly comminuted, but 
some perfect. There were, also, many at the bottom of 
the great valley of the Maypu. At San Antonio, shells 
are said to be collected and burnt for lime. At the 
bottom of a great ravine (Quebrada Onda, on the road 
to Oasa Blanca), at the distance of several miles from 
the coast, I noticed a considerable bed, composed ex- 
clusively of Mesodesma donadforme, Desh., lying on a 
bed of muddy sand: this shell now lives associated 
together in great numbers, on tidal flats on the coast of 
Chile. 

Valparaiso. 

During two successive years I carefully examined, 
part of the time in company with Mr. Alison, into all 
the facts connected with the recent elevation of this 
neighbourhood. In very many parts a beach of broken 



240 Elevation of Valparaiso. PIET XL 

shells, about fourteen or fifteen feet above high-water 
mark, may be observed; and at this level the coast- 
rocks, where precipitous, are corroded in a band. At 
one spot, Mr. Alison, by removing some birds' dung, 
found at this same level barnacles adhering to the rocks. 
For several miles southward of the bay, almost every 
flat little headland, between the heights of 60 and 230 
feet (measured by the barometer), is smoothly coated 
by a thick mass of comminuted shells, of the same 
species, and apparently in the same proportional num- 
bers with those existing in the adjoining sea. The 
Concholepas is much the most abundant, and the best 
preserved shell; but I extracted perfectly preserved 
specimens of the Fissurella liradiata, a Trochus and 
Balanus (both well known, but according to Mr. Sowerby 
yet unnamed) and parts of the MytiliAS Ghiloewsis. 
Most of these shells, as well as an encrusting Nullipora, 
partially retain, their colour ; but they are brittle, and 
often stained red from the underlying brecciated mass 
of primary rocks ; some are packed together, either in 
black or reddish mould; some lie loose on the bare 
rocky surfaces. The total number of these shells is 
immense ; they are less numerous, though still far from 
rare, up a height of 1,000 feet above the sea. On the 
summit of a hill, measured 557 feet, there was a small 
horizontal band of comminuted shells, of which many 
consisted (and likewise from lesser heights) of very 
young and small specimens of the still living Con- 
cholepas, Trochus, Patellse, Crepidulae, and of Mytilus 
Magellanicus (?) : ! several of these shells were under 
a quarter of an inch in their greatest diameter. My* 

1 Mr Cuming" informs me that he does not think this species 
identical with, though closely resembling, the true M. Magellanicus 
of the southern and eastern coast of South America; it lives abun- 
dantly on the coast of Chile. 



CHAP. rx. Elevation of Valparaiso. 241 

attention was called to this circumstance by a native 
fisherman, whom I took to look at these shell-beds; 
and he ridiculed the notion of such small shells having 
been brought up for food ; nor could some of the species 
have adhered when alive to other larger shells On 
another hill, some miles distant, and 648 feet high, I 
found shells of the Ooncholepas and Trochus, perfect, 
though very old, with fragments of Mytilits GTiiloensis^ 
all embedded in reddish-brown mould: I also found 
these same species, with fragments of an Echinus and 
of Balanus psittacits, on a hill 1 ,000 feet high. Above 
this height, shells became very rare, though on a hill 
1,300 feet high, 1 I collected the Ooncholepas, Trochus, 
Fissurella, and a Patella. At these greater heights the 
shells are almost invariably embedded in mould, and 
sometimes are exposed only by tearing up bushes. 
These shells obviously had a very much more ancient 
appearance than those from the lesser heights; the 
apices of the Trochi were often worn down; the little 
holes made by burrowing animals were greatly en- 
larged ; and the Concholepas was often perforated quite 
through, owing to the inner plates of shell having 
scaled off. 

Many of these shells, as I have said, were packed in, 
and were quite filled with, blackish or reddish-brown 
earth, resting on the granitic detritus. I did not doubt 
until lately that this mould was of purely terrestrial 
origin, when with a microscope examining some of it 
from the inside of a Ooncholepas from the height of 
about 100 feet, I found that it was in considerable part 
composed of minute fragments of the spines, mouth- 
bones and shells of Echini, and of minute fragments, 

1 Measured by the barometer . the highest point in the ran:e 
behind Valparaiso I found to be 1,G2G feet above the level of the 
sea. 



242 Elevation of Valparaiso. TAUT it 

oF chiefly very young Patellae, Mytili, and other species, 
I found similar microscopical fragments in earth filling 
up the central orifices of some large Fissurellse. This 
earth when crushed emits a sickly smell, precisely like 
that from gai den-mould mixed with guano. The earth 
accidentally preserved within the shells, from the greater 
heights, has "the same general appearance, but it is a 
little redder ; it emits the same smell when rubbed, but 
I was unable to detect with certainty any marine remains 
in it. This earth resembles in general appearance, as 
before remarked, that capping the rocks of Quinquina 
in the Bay of Concepciou, on which beds of sea-shells 
lay. I have, also, shown that the black, peaty soil, in 
which the shells at the height of S50 feet at Ohiloe 
were packed, contained many minute fragments of 
marine animals. These facts appear to me interesting, 
as they show that soils, which would naturally be con- 
sidered of purely terrestrial nature, may owe their origin 
in chief part to the sea. 

Being well aware from what I have seen at Chiloe 
and in Tierra del Fnego, that vast quantities of shells 
are carried, during successive ages, far inland, where the 
inhabitants chiefly subsist on these productions, I am 
bound to state that at greater heights than 557 feet, 
where the number of very young and small shells proved 
that they had not been carried up for food, the only 
evidence of the shells having been naturally left by the 
sea, consists in their invariable and uniform appearance 
of extreme antiquity in the distance of some of the 
places from the coast, in others being inaccessible from 
the nearest part of the beach, and in the absence of 
fresh water for men to drink in the shells not lying 
in Aeops, and, lastly, in the close similarity of the 
soil in which they are embedded, to that which lower 



CHAP. ix. Elevation of Valparaiso. 243 

down can be unequivocally shown to be in great part 
formed from the debris of the sea animals. 1 

With respect to the position in which the shells lie, 
I was repeatedly struck here, at Ooncepcion, and at 
other places, with the frequency of their occurrence on 
the summits and edges either of separate hills, or of 
little flat headlands often terminating precipitously 
over the sea. The several above-enumerated species of 
Mollusca, which are found strewed on the surface of 
the land from a few feet above the level of the sea up 
to the height of 1,300 feet, all now live either on the 
beach, or at only a few fathoms' depth : Mr. Edmonston, 
in a letter to Prof. E Forbes, states that in dredging 
in the Bay of A r alparaiso, he found the common species 
of Concholepas, Fissurella," Trochus, Monoceros, Chi- 
tons, &c living in abundance from the beach to a depth 
of seven fathoms ; and dead shells occurred only a few 
fathoms deeper. The common Ttirritellct, cingidata, 
was dredged up living at even from ten to fifteen 
fathoms ; but this is a species which I did not find here 
amongst the upraised shells. Considering this fact of 
the species being all lifctoral or sub-littoral, considering 
their occurrence at various heights, their vast numbers, 
and their generally comminuted state, there can be 
little doubt that they were left on successive beach-lines 

1 In the * Proceedings of the Geolog. Soc ' vol. ii. p. 446, 1 have 
given a brief account of the upraised shells on the coast of Chile, 
and have there stated that the proofs of elevation are not satisfactory 
above the height of 230 feet, I had at that time unfortunately over- 
looked a separate page written dm ing my second vLsit to Valparaiso, 
describing the shells now in my possession from the 5o7 feet bill ; I 
had not then unpacked my collections, and had not reconsidered 
the obvious appearance of greater antiquity of the shells from the 
greater heights, nor had I at that time discovered the maiine origin of 
the earth in which many of the shells are packed. Consideung these 
facts, I do not now feel a shadow of doubt that the shells, at the 
height of 1,300 feet, have been upraised by natuial causes in o their 
present position. 

ir 



244 Elevation of Valparaiso PAET n, 

during a gradual elevation of the land. The presence, 
however, of so many whole and perfectly preserved 
shells appears at first a difficulty on this view, consider- 
ing that the coast is exposed to the full force of an 
open ocean : but we may suppose, either that these 
shells were thrown during gales on flat ledges of rock 
just above the level of high-water mark, and that 
during the elevation of the land they were never again 
touched by the waves, or, that during earthquakes, such 
as those of 1822, 1835, and 1837, rocky reefs covered 
with marine-animals were at one blow uplifted above 
the future reach of the sea. This latter explanation is, 
perhaps, the most probable one with respect to the beds 
at Concepcion entirely composed of the Mytilus Chi- 
loensis, a species which lives below the lowest tides; 
and likewise with respect to the great beds, occurring 
both north and south of Valparaiso, of the Mesodesma 
donaciforme, a shell which, as I am informed by Mr. 
Cuming, inhabits sand-banks at the level of the lowest 
tides. But even in the case of shells having the habits 
of this Mytilus and Mesodesma, beds of them, wherever 
the sea gently throws up sand or mud, and thus protects 
its own accumulations, might be upraised by the ^lowest 
movement, and yet remain undisturbed by the waves of 
each new beach-line. 

It is worthy of remark, that nowhere near Valparaiso 
above the height of twenty feet, or rarely of fifty feet, 
I saw any lines of erosion on the solid rocks, or any 
beds of pebbles ; this, I believe, may be accounted for 
by the disintegrating tendency of most of the rocks in 
this neighbourhood. Nor is the land here modelled 
into terraces: Mr. Alison, however, informs me, that 
on both sides of one narrow ravine, at the height of 
300 feet above the sea, he found a succession of rather 
indistinct step-formed beaches ? composed of broken 



CHAP. ix. within the Historical Period. 245 

shells, which together covered a space of about eighty 
feet vertical. 

I can add nothing to the accounts already published 
of the elevation of the land at Valparaiso/ which ac- 
companied the earthquake of 1822 : but I heard it 
confidently asserted, that a sentinel on duty, immedi- 
ately after the shock, saw a part of a fort, which pre- 
viously was not within the line of his vision, and this 
would indicate that the uplifting was not horizontal: 
it would even appear from some facts collected by Mr. 
Alison, that only the eastern half of the bay was then 
elevated. Through the kindness of this same gentle- 
man, I am able to give an interesting account of the 
changes of level, which have supervened here within 
historical periods: about the year 1680 a long sea-wall 
(or PreSl) was built, of which onl} T a few fragments 
now remain 5 up to the year 1817, the sea often broke 
over it, and washed the houses on the opposite side of 
the road (where the prison now stands) ; and even in 
1819, Mr, J. Martin remembers walking at the foot of 
this wall, and being often obliged to climb over it to 
escape the waves. There now stands (1884) on the 
seaward side of this wall, and between it and the beach, 
in one part a single row of houses, and in another part 
two rows with a street between them. This great 
extension of the beach in so short a time cannot be 
attributed simply to the accumulation of detritus ; for 
a resident engineer measured for me the height between 
the lowest part of the wall visible, and the present 
beach-line at spring-tides, and the difference was eleven 
feet six inches. The church of S. Augustin is believed 
to have been built in 1614, arid there is a tradition that 

1 Dr. Meyen ( Reise urn Erde,' Th. I. S. 221) found in 1831 sea- 
weed and other bodies still adhering to some rocks which during the 
shock of 1822 were lit ted above the sea 



246 Elevation of Coquimbo* PART n, 

the sea formerly flowed very near it ; "by levelling, its 
foundations were found to stand nineteen feet six inches 
above the highest beach-line ; so that we see in a period 
of 220 years, the elevation cannot have been as much 
as nineteen feet six iDches. From the facts given with 
respect to the sea-wall, and from the testimony of the 
elder inhabitants, it appears certain that the change in 
level began to be manifest about the year 1817. The 
only sudden elevation of which there is any record 
occurred in 1822, and this seems to have been less than 
three feet. Since that year, I was assured by several 
competent observers, that part of an old wreck, which 
is firmly embedded near the beach, has sensibly 
emerged; hence here, as at Chiloe, a slow rise of the 
land appears to be now in progress. It seems highly 
probable that the rocks which are corroded in a band 
at the height of fourteen feet above the sea were acted 
on during the period, when by tradition the base of 
S. Augustin church, now nineteen feet six inches above 
the highest water-mark, was occasionally washed by 
the waves. 

Valparaiso to Ooqidmbo. For the first seventy- 
five miles north of Valparaiso I followed the coast-road, 
and throughout this space I observed innumerable 
masses of upraised shells. About Quintero there are 
immense accumulations (worked for lime) of the Meso- 
desma donaciforme^ packed in sandy earth, they abound 
chiefly about fifteen feet above high- water, but shells 
are here found, according to Mr. Mieis, 1 to a height of 
500 feet, and at a distance of three leagues from the 
coast : I here noticed barnacles adhering to the rocks 
three or four feet above the highest tides. In the 

1 * Travels in Chile,' vol i pp. 458, 395. I received several similar 
accounts from the inhabitants, and was assured that there are many 
shells an the plain of Casa Blanca, hetween Valparaiso and Santiago, 
at the height of 800 feet. 



CHAP. ix. Elevation of Coqiiimbo. 247 

neighbourhood of Plazilla and Catapilco, at heights of 
between 200 and 800 feet, the number of comminuted 
shells, with some perfect ones, especially of the Meso- 
desma, packed in layers, was truly immense : the land 
at Plazilla had evidently existed as a bay, with abrupt 
rocky masses rising out of it, precisely like the islets in 
the broken bays now indenting this coast. On both 
sides of the rivers Ligua, Longotomo, Gruachen, and 
Qmlimari, there are plains of gravel about 200 feet in 
height, in many parts absolutely covered with shells. 
Close to Conch alee, a gravel-plain is fronted by a lower 
and similar plain about sixty feet in height, and this 
again is separated from the beach by a wide tract of 
low land : the surfaces of all three plains or terraces 
were strewed with vast numbers of the Concholepas, 
Mesodesma, an existing Venus, and other still existing 
littoral shells. The two upper terraces closely resemble 
in miniature the plains of Patagonia ; and like them 
are furrowed by dry, flat-bottomed, winding valleys. 
Northward of this place I turned inward ; and therefore 
found no more shells : but the valleys of Chuapa, Illapel, 
and Limari, are bounded by gravel- capped plains, often 
including a lower terrace within. These plains send 
bay-like arms between and into the surrounding hills; 
and they are continuously united with other extensive 
gravel-capped plains, separating the coast mountain- 
ranges from the Cordillera. 

Goqidmho. 

A. narrow fringe-like plain, gently inclined towards 
the sea, here extends for eleven miles along the coast, 
with arms stretching up between the coast-mountains, 
and likewise up the valley of Coquimbo : at its southern 
extremity it is directly connected with the plain of 



248 Elevation of Coquimbo. *AET n. 

Limari, out of which hills abruptly rise like islets, and 
other hills project like headlands on a coast. The 
surface of the fringe-like plain appears level, but differs 
insensibly in height, and greatly in composition, in 
different parts. 

At the mouth of the valley of Coquimbo, the surface 
consists wholly of gravel, and stands from 300 to 350 
feet above the level of the sea, being about 100 feet 
higher than in other parts. In these other and lower 
parts, the superficial beds consist of calcareous matter, 
and rest on ancient tertiary deposits hereafter to be 
described. The uppermost calcareous layer is cream- 
coloured, compact, smooth-fractured, sub-stalactiform, 
and contains some sand, earthy matter, and recent shells. 
It lies on, and sends wedge-like veins into, 1 a much 
more friable, calcareous, tuff-like variety; and both 
rest on a mass about twenty feet in thickness, formed 
of fragments of recent shells, with a few whole ones, 
and with small pebbles firmly cemented together. This 
latter rock is called by the inhabitants losa, and is used 
for building; in many parts it is divided into strata, 
which dip at an angle of ten degrees seaward, and ap- 
pear as if they had originally been heaped in successive 
layers (as may be seen on coral-reefs) on a steep beach. 
This stone is remarkable from being in parts entirely 
formed of empty, pellucid capsules or cells of calcareous 
matter, of the size of small seeds : a series of specimens 
unequivocally showed that all these capsules once con- 
tained minute rounded fragments of shells which have 

1 In many respects this upper hard, and the underlying more 
friable varieties, resemble the great superficial beds at King George's 
Sound in Australia, which I have described in Chapter VII. p 161 
There could be little doubt that the tipper layers there have been 
hardened by the action of rain on the friable calcareous matter, and 
that the whole mass has originated in the decay of minutely commi- 
nuted sea^-shells and corals. 



CHAP. ts. Elevation of Coquimbo. 249 

since been gradually dissolved by water percolating 
through the mass. 1 

The shells embedded in the calcareons beds forming 
the surface of this fringe-like plain, at the height of 
from 200 to 250 feet above the sea, consist of. 



1. "V enns opaca. 

2. Mulima Byronensis. 

3. Pecten purpuratus. 

4. Me&odesma donaciforme. 

5. Turritella cingulata 



6. Monoceros costatum. 

7. Concholepas Peruviana. 

8. Trochus (common Valpa- 

raiso species), 

9. Calyptrsea B} ronensis. 



Although these species are all recent, and are all 
found in the neighbouring sea, yet I was particularly 
struck with the difference in the proportional numbers 
of the several species, and of those now cast up on the 
present beach. I found only one specimen of the Con- 
cholepas, and the Pecten was very rare, though both 
these shells are now the commonest kinds, with the 
exception, perhaps, of the Calyptrcea radians, of which 
1 did not find one in the calcareous beds. I will not 
pretend to determine how far this difference in the 
proportional numbers depends on the age of the deposit, 
and how far on the difference in nature between the 
present sandy beaches and the calcareous bottom, on 
which the embedded shells must have lived. 

On the bare surface of the calcareous plain, or in a 
thin covering of sand, there were lying at a height from 
200 to 252 feet, many recent shells, which had a much 
fresher appearance than the embedded ones : fragments 
of the Concholepas, and of the common Mytilus, still 
retaining a tinge of its colour, were numerous, and 
altogether there was manifestly a closer approach in 
proportional numbers to those now lying on the beach. 
In a mass of stratified, slightly agglutinated sand, which 
in some places covers up the lower half of the seaward 

1 I have already had occasion to describe this rock in Chapter VII 



250 Elevation of Coquimbo. PAET IL 

escarpment of the plain, the included, shells appeared to 
be in exactly the same proportional numbers with those 
on the beach. On one side of a steep-sided ravine, 
cutting through the plain behind Herradura Bay, 1 
observed a narrow strip of stratified sand, containing 
similar shells m similar proportional numbers: a section 
of the ravine is represented in the following diagram, 
which serves also to show the general composition of the 
plain. I mention this case of the ravine chiefly because 
without the evidence of the marine shells in the sand, 
any one would have supposed that it had been hollowed 
out by simple alluvial action. 

No. 22. 

Section of Plain of Coquimbo, 
B Surface of plain 252 feet above sea 










JU.vt.1 of tea, 

A Stratified sand, with recent shells in same proportions as on the beach, half filling 

up a rarme. 

B Surface of plain with scattered shells m nearly same proportions as on the beach 

C Upper calcareous bed, ) with recent shells, but not in same propor- 

D Lower calcareous sandy bed (Losa), j tions as on the beach 

E Upper ferrugino-sandy old tertiary stratum, ) 'with all, or nearly all, extinct 

F Lower old tertiary stratum, I shells 

The escarpment of the fringe-like plain, which 
stretches for*eleven miles along the coast, is in some 
parts fronted by two or three narrow, step-formed ter- 
races, one of which at Herradura Bay expands into a 
small plain. Its surface was there formed of gravel, 
cemented together by calcareous matter ; and out of it 
I extracted the following recent shells, which are in 
a more perfect condition than those from the upper 
plain : 



CHAP. ix. Elevation of Coquimbo. 



251 



1. Calyptrsea radians 

2, Tmritellci cingulata* 
3 Oliva Peruviana 

4. Mm ex labio&us, var. 

5. Nassa (identical with a living 
species), 

6. ISolen Dornbeiana. 

7. Pecten purpuratus, 

8. Venus Chilensis. 



9. Ampbiclesma rugulosuru. The 
small 11 regular wi inkles of the 
posterior part of this shell aie 
rather fationger than m the 
recent specimens of this species 
from Goquimbo. (G-. B 
Sowerby ) 

10, Balanus (identical with liv- 
ing species) 



On the syenitic ridge, whicli forms the southern 
boundary of Herradura Bay and Plain, I found the 
Conch olepas and Turrit etta cing'iilata (mostly in frag- 
ments) 5 at the height of 242 feet above the sea. I could 
not have told that these shells had not formerly been 
brought up by man, if J had not found one very small 
mass of them cemented together in a friable calcareous 
tuff. I mention this fact more particularly, because I 
carefully looked, in many apparently favourable spots 
at lesser heights on the side of this ridge, and could not 
find even the smallest fragment of a shell. This is only 
one instance out of many, proving that the absence of 
sea-shells on the surface, though in many respects inex- 
plicable, is an argument of very little weight in opposi- 
tion to other evidence on the recent elevation of the 
laud. The highest point in this neighbourhood at which 
I found upraised shells of existing species was on an 
inland calcareous plain, at the height of 252 feet above 
the sea. 

It would appear from Mr. Caldcleugh's researches, 1 
that a rise has taken place here within the last century 
and a half; and as no sudden change of level has been 
observed during the not very severe earthquakes, which 
have occasionally occurred here, the rising has probably 
been slow, like that now, or quite lately, in progress at 
Chiloe and at Valparaiso : there are three well-known 
rocks, called the Pelicans, which in 1710, according to 

1 f Proceedings of the G-eological Society,' vol ii p. 446. 



252 Elevation of Coquimbo. PAET n. 

Feuillee, were d fleur d'eau, but now are said to stand 
twelve feet above low- water mark : the spring-tides rise 
here only five feet. There is another rock ; now nine 
feet above high-water mark, which in the time of Prezier 
and of Feuillee rose only five or six feet out of water. 
Mr. Caldcleugh, I may add, also shows (and I received 
similar accounts) that there has been a considerable 
decrease in the soundings during the last twelve years 
in the Bays of Coquimbo, Ooncepcion, Valparaiso, and 
Guasco; but as in these cases it is nearly impossible to 
distinguish between the accumulation of sediment and 
the upheavement of the bottom, I have not entered into 
any details. 

Valley of Ooqitimbo. The narrow coast-plain sends, 
as before stated, an arm, or more correctly a fringe on 
both sides, but chiefly on the southern side, several 
miles up the valley. These fringes are worn into steps 
or terraces, which present a most remarkable appear- 
ance, and have been compared (though not very cor- 
rectly) by Oapt. Basil Hall, to the parallel roads of Glen 
Roy in Scotland : their origin has been ably discussed 
by Mr. Lyell. 1 The first section which I will give, is 
not drawn across the valley, but in an east and west 

No. 2S. 

East and "West Sectum through the Tenaces at Coquimbo, where they debouch 
from the Valley, and front the Sea. 




Level of sea. To\\ n of Coquimbo. 

Vertical scale ^th of inch to 100 feet : horizontal scale much contracted. 

line at its mouth, where the step-formed terraces de- 
bouch and present their very gently inclined surfaces 
towards the Pacific. 

1 * Principles of Geology ' (1st edit.), vol. iii. p. 131. 



CHAP. ix. Gravel-Terraces of Coquimbo. 253 

The bottom plain (A) is about a mile in width, and 
rises quite insensibly from the beach to a height of 
twenty-five feet at the foot of the next plain : it is sandy, 
and abundantly strewed with shells. 

Plain or terrace (B) is of small extent, and is almost 
concealed by the houses of the town, as is likewise the 
escarpment of terrace (0). On both sides of a ravine, ' 
two miles south of the town, there are two little ter- 
races, oue above the other, evidently corresponding with 
(B) and (0) ; and on them marine remains of the species 
already enumerated were plentiful. Terrace (E) is very 
narrow, but quite distinct and level ; a little southward 
of the town there were traces of a terrace (D) inter- 
mediate between (E) and (0). Terrace (F) is pait of 
the fringe-like plain, which stretches for the eleven 
miles along 'the coast ; it is here composed of shingle, 
and is 100 feet higher than where composed of calca- 
reous matter. This greater height is obviously clue to 
the quantity of shingle, which at some former period 
has been bi ought down the great valley of Coquimbo. 

Considering the many shells strewed over the ter- 
races (A) (B) and (0), and a few miles southward on 
the calcareous plain, which is continuously united with 
the upper step-like plain (F), there can not, I apprehend, 
be any doubt, that these six terraces have been formed 
by the action of the sea ; and that their five escarp- 
ments mark so many periods of comparative rest in the 
elevatory movement, during which the sea wore into 
the land. The elevation between these periods may 
have been sudden and on an average not more than 
seventy-two feet each time, or it may have been gradual 
and insensibly slow. From the shells on the three 
lower terraces, and on the upper one, and I may add OB 
the three gravel-capped terraces at Conchalee, being all 
littoral and sub-littoral species, and from the analogical 



254 Gravel-Terraces of Coquimbo PAET IL 

facts given at Valparaiso, and lastly from the evidence 
of a slow rising lately or still in progress here, it appears 
to me far more probable, that the movement has been 
slow. The existence of these successive escarpments, 
or old cliff-lines, is in another respect highly instructive, 
for they show periods of comparative rest in the eleva- 
tory movement, and of denudation, which would never 
even have been suspected from a close examination of 
many miles of coast southward of Coquimbo. 

We come now to the terraces on the opposite sides 
of the east and west valley of Coquimbo : the following 
section is taken in a north and south line across the 
valley at a point about three miles from the sea. The 
valley measured from the edges of the escarpments of 
the upper plain (P) (Fj is about a mile in width ; but 
from the bases of the bounding mountains it is from 
three to four miles wide. The terraces marked with 
an interrogative do not exist on that side of the valley, 
but are introduced merely to render the diagram more 
intelligible. 

No. 24. 



North and South Section acioss the Valley of Coquimbo. 




Level of sea. 



Vertical scale T \th of inch to 100 feet horizontal scale much contracted terraces < 
marked with (?) do not occur on that side of the valley, and are introduced only 
to make the diagram inoic intelligible A river and bottom-plain of v.Uley C, E, 
and F, on the south side of valley, are respectively, 197, 377, and 420 feet above 
the level of the sea. 

A A The bottom of the valley, believed to be 100 feet above the sea : it is continu- 
ously united \vith the kmes-t plain (A) of the former section 

B This terrace higher up the valley expands considerably , seaward it is soon lost, 
its escarpment being united with that of (0) it is not developed at all ou the 
south side of the valley. 

This terrace like the last, is considerably expanded higher up the valley These 
two terraces appaieiitly correspond \vibh (B) and (0) ot the formei section 

B is not well developed m the line ot thib section , but seaward it expands into & 
plain * it is not present on the south side of the valley , but it is met with, aa 
stated under the former section, a little south of the town. ' 



CHAP. is. not Horizontal, 255 

E is well developed on the south, side, but absent on the north side of the valley % 
though not continuously united with (E) of the former section, it apparently 
corresponds with it 

F This is the surface-plain, and is continuously united with that which stretches 
like a fringe along the coast In ascending the valley it gradually becomes 
nariower, and is at last, at the distance of about ten miles from the sea, reduced 
to a row of flat-topped patches on the sides of the mountains. None of the lower 
tei races extend so far up the valley, 

These five terraces are formed of shingle and sand ; 
three of them, as marked by Capt. Basil Hall (namely, 
B, C, and F), are much more conspicuous than the others. 
From the marine remains copiously strewed at the 
mouth of the valley on the lower terraces, and south- 
ward of the town on the upper one, they are, as before 
remarked, undoubtedly of marine origin ; but within 
the valley, and this fact well deserves notice, at a dis- 
tance of from only a mile and a half to three or four 
miles from the sea, I could not find even a fragment of 
a shell. 

On the inclination of the terraces of Coqiiimbo, 
and on the upper and lasal edges of their escarpments 
not leing horizontal. The surfaces of these terraces 
slope in a slight degree, as shown by the last two sections 
taken conjointly, both towards the centre of the valley, 
and seawards towards its mouth. This double or 
diagonal inclination, which is not the same in the 
several terraces, is, as we shall immediately see, of 
simple explanation. There are, however, some other 
points which at first appear by no means obvious, 
namely, first, that each terrace, taken in its whole 
breadth from the summit-edge of one escarpment to 
the base of that above it, and followed up the valley, is 
not horizontal ; nor have the several terraces, when 
followed up the valley, all the same inclination; thus 
1 found the terraces 0, E, and F, measured at a point 
about two miles from the mouth of the valley, stood 
severally between fifty-six to seventy-seven feet higher 
than at the mouth. Again, if we look to any one line 



256 Gravel-Terraces of Coquimbo PAKT n. 

of cliff or escarpment, neither its summit-edge nor its 
base is horizontal. On the theory of the terraces having 
been formed during a slow and equable rise of the land, 
with as many intervals of rest as there are escarpments, 
it appears at first very surprising that horizontal lines 
of some kind should not have been left on the land. 

The direction of the diagonal inclination in the 
different terraces being different, in some being direc- 
ted more towards the middle of the valley, in others 
more towards its mouth, naturally follows on the 
view of each terrace, being an accumulation of successive 
beach-lines round bays, which must have been of dif- 
ferent forms and sizes when the land stood at different 
levels : for if we look to the actual beach of a narrow 
creek, its slope is directly towards the middle ; whereas, 
In an open bay, or slight concavity on a coast, the slope 
is towards the mouth, that is, almost directly seaward ; 
hence as a bay alters in form and size, so will the direc- 
tion of the inclination of its successive beaches become 
changed. 

If it were possible to trace any one of the many 
beach-lines, composing each sloping terrace, it would 
of course be horizontal ; but the only lines of demarca- 
tion are the summit and basal edges of the escarpments. 
Now the summit-edge of one of these escarpments 
marks the furthest line or point to which the sea has 
cut into a mass of gravel sloping seaward ; and as the 
sea will generally have greater power at the mouth than 
at the protected head of a bay, so will the escarpment 
at the mouth be cut deeper into the land, and its 
summit-edge be higher; consequently it will not be 
horizontal. With respect to the basal or lower edges 
of the escarpments, from picturing in one's mind ancient 
bays entirely surrounded at successive periods by cliff- 
formed shores, one's first impression is that they at least 



CHAP. ix. not Horizontal* 257 

necessarily must be horizontal, if the elevation has been 
horizontal. But here is a fallacy : for after the sea has, 
during a cessation of the elevation, worn cliffs all round 
the shores of a bay, when the movement recommences, 
and especially If it recommences slowly, it might well 
happen that, at the exposed mouth of the bay, the 
waves might continue for some time wearing infco the 
land, whilst in the protected and upper parts successive 
beach- lines might be accumulating in a sloping surface 
or terrace at the foot of the cliffs which had been lately 
reached : henije, supposing the whole line of escarpment 
to be finally uplifted above the reach of the sea, its 
basal line or foot near the mouth will run at a lower 
level than in the upper and protected parts of the bay ; 
consequently this basal line will not be horizontal. And 
it has already been shown that the summit-edges of 
each escarpment will generally be higher near the 
mouth (from the seaward sloping land being there most 
exposed and cut into) than near the head of the bay ; 
therefore the total height of the escarpments will be 
greatest near the mouth ; and further up the old bay 
or valley they will on both sides generally thin out and 
die away; I have observed this thinning out of the 
successive escarpment at other places besides Coquimbo ; 
and for a long time I was quite unable to understand 
its meaning. The following rude diagram will perhaps 
render what I mean more intelligible ; it represents a 
bay in a district which has begun slowly rising. Before 
the movement commenced, it is supposed that the 
waves had been enabled to eat into the land and form 
cliffs, as far up, but with gradually diminishing power, 
as the points A A : after the movement had commenced 
and gone on for a little time, the sea is supposed still to 
have retained the power, at the exposed mouth of the 
bay, of cutting down and into the land as it slowly 



258 Gravel- Terraces of Coqnimbo PAET n. 

emerged; but in the upper parts of the bay it is 

supposed soon to have lost this power, owing to the more 

No. 




protected situation and to the quantity of detritus 
brought down by the river ; consequently low land was 
there accumulated. As this low land was formed during 
a slow elevatory movement, its surface will gently slope 
upwards from the beach on all sides. Now, let us 
imagine the bay, not to make the diagram more com- 
plicated, suddenly converted into a valley: the basal 
line of the cliffs will of course be horizontal, as far as 
the beach is now seen extending in the diagram ; but 
in the upper part of the valley, this line will be higher, 
the level of the district having been raised whilst the 
low land was accumulating at the foot of the inland 
cliffs. If, instead of the bay in the diagram being 
suddenly converted into a valley, we suppose with much 
more probability it to be upraised slowly, then the 
waves in the upper parts of the bay will continue very 
gradually to fail to reach the cliffs, which are now in 
the diagram represented as washed by the sea, and 



ix. not Horizontal. 259 

which, consequently, will be left standing higher and 
higher above its level ; whilst at the still exposed mouth, 
it might well happen that the waves might be enabled 
to cut deeper and deeper, both down and into the cliffs, 
as the land slowly rose. 

The greater or lesser destroying rower of the waves 
at the mouths of successive bays, comparatively with 
this same power in their upper and protected parts, will 
vary as the bays become changed in form and size, and 
therefore at different levels, at their mouths and heads, 
more or less of the surfaces between the escarpments, 
(iiiat is, the accumulated beach-lines or terraces) will 
be left undestroyed : from what has gone before we can 
see that, according as the elevatory movements after 
each cessation recommence more or less slowly, according 
to the amount of detritus delivered by the river at the 
heads of the successive bays, and according to the degree 
of protection afforded by their altered forms, so will a 
greater or less extent of terrace be accumulated in the 
upper part, to which there will be no surface at a cor- 
respooding level at the mouth : hence we can perceive 
why no one terrace, taken in its whole breadth and 
followed up the valley, is horizontal, though each 
separate beach-line must have been so; and why the 
inclination of the several terraces, both transversely, 
and longitudinally up the valley, is not alike. 

I have entered into this case in some detail, for I 
was long perplexed (and others have felt the same 
difficulty) in understanding how, on the idea of an 
equable elevation with the sea at intervals eating into 
the land, it came that neither the terraces nor the upper 
nor lower edges of the escarpments were horizontal. 
Along lines of coast, even of great lengths, such as that 
of Patagonia, if they are nearly uniformly exposed, the 
corroding power of the waves will be checked and 

18 



260 Gravel- Terraces of Coquimbo PABT n, 

conquered by the elevatory movement, as often as it 
recommences, at about the same period \ and hence the 
terraces, or accumulated beach-lines, will commence 
being formed at nearly the same levels : at each suc- 
ceeding period of rest, they will, also, be eaten into at 
nearly the same rate, and consequently there will be a 
much closer coincidence in their levels and inclinations, 
than in the terraces and escarpments formed round 
bays with their different parts very differently exposed 
to the action of the sea It is only where the waves 
are enabled, after a long lapse of time, slowly to corrode 
hard rocks, or to throw up, owing to the supply of 
sediment being small and to the surface being steeply 
inclined, a narrow beach or mound, that we can expect, 
as at Grlen Roy in Scotland, 1 a distinct line marking an 
old sea-level, and which will be strictly horizontal, if 
the subsequent elevatory movements have been so : for 
in these cases no discernible effects will be produced, 
except during the long intervening periods of rest; 
whereas in the case of step-formed coasts, such as those 
described in this and the preceding chapter, the terraces 
themselves are accumulated during the slow elevatory 
process, the accumulation commencing sooner in pro- 
tected than in exposed situations, and sooner where 
there is copious supply of detritus than where there is 
little ; on the other hand, the steps or escarpments are 
formed during the stationary periods, and are more 
deeply cut down and into the coast-land, in exposed 
than in protected situations ; the cutting action, more- 
over, being prolonged In the most exposed parts, both 
during the beginning and ending, if slow, of the upward 
movement. 

Although in the foregoing discussion I have assumed 
the elevation to have been horizontal, it may be sus* 
1 ' Philosophical Transactions,* 1839, p. 39. 



CHAP. ix. not Horizontal. 26 1 



pec ted, from the considerable seaward slope of the 
terraces, both up the valley of S. Cruz and up that of 
Coquimbo, that the rising has been greater inland than 
nearer the coast. There is reason to believe., 1 from the 
effects produced on the water-coarse of a mill during 
the earthquake of 1822 in Chile, that the upheaval one 
mile inland was nearly double, namely, between five 
and seven feet, to what it was on the Pacific. We know, 
also, from the admirable researches of M. Bravais, 2 that 
in Scandinavia the ancient sea-beaches gently slope 
from the interior mountain-ranges towards the coast, 
and that they are not parallel one to the other, showing 
that the proportional difference in the amount of eleva- 
tion on the coast and in the interior, varied at different 
periods. 

Goquimbo to Guasco. In this distance of ninety 
miles, I found in almost every part marine shells up to 
a height of apparently from 200 to 300 feet. The 
desert plain near Chores is thus covered ; it is bounded 
by the escarpment of a- higher plain, consisting of pale- 
coloured, earthy, calcareous stone, like that of Coquimbo, 
with the same recent shells embedded in it. In the 
valley of Chaneral, a similar bed occurs in which, dif- 
ferently from that of Coquimbo, I observed many shells 
Of the Concholepas : near Guasco the same calcareous 
bed is likewise met with. 

In the valley of Guasco. the step-formed terraces of 
gravel are displayed in a more striking manner than at 
any other point. I followed the valley for thirty-seven 
miJes (as reckoned by the inhabitants) from the coast 
to Ballenar : in nearly the whole of this distance, five 



1 Mr. Place, in the * Quarterly Journal of Science,' 1824, vol. xvii. 

P 42 

2 ' Voyages de la Comm du Nord,' c. : also, * Comptes Rendus, 1 

Occ, 1842. 



262 Gravel- Terraces of Guasco. PABT n. 

grand terraces, running at corresponding heights on 
both sides of the broad valley, are more conspicuous 
than the three best developed ones at Coquimbo. They 
give to the landscape the most singular and formal 
aspect; and when the clouds hung low, hiding the 
neighbouring mountains, the valley resembled in the 
most striking manner that of Santa Cruz. The whole 
thickness of these terraces or plains seems composed of 
gravel, rather firmly aggregated together, with occasional 
parting seams of clay : the pebbles on the upper plain 
are often white-washed with an albuminous substance, 
as in Patagonia. Near the coast I observed many sea- 
shells on the lower plains. At Freyrma (twelve miles 
up the valley), there are six terraces beside the bottom- 
surface of the valley : the two lower ones are here only 
from 200 to cSOO yards in width, but higher up the 
valley they expand into plains : the third terrace is 
generally narrow : the fourth I saw only m one place, 
but there it was distinct for the length of a mile : the 
fifth is very broad : the sixth is the summit-plain, 
which expands inland into a great basin Not 
having a barometer with me, I did not ascertain the 
height of these plains, but they appeared consider- 
ably higher than those at Coquimbo. Their width 
varies much, sometimes being very broad, and some- 
times contracting into mere fringes of separate flat- 
topped projections, and then quite disappearing: at 
the one spot, where the fourth terrace was visible, the 
whole six terraces were cut off for a short space by one 
single bold escarpment, Near Ballenar (thirty-seven 
miles from the mouth of the river), the valley between 
the summit-edges of the highest escarpment is several 
miles in width, and the five terraces on both sides are 
broadly developed : the highest cannot be less than 
600 feet above the bed of the river, which itself must/, 



CHAP. ix. Gravel-Terraces of Copiapo* 263 

I conceive, be some hundred feet above the sea. A 
north and south section across the valley in this part is 
here represented. 

No 26 

North and South. Section across the Valley of Guasco, and of a pi am north of it 
North South. 



Biver of G-uasco. 




Town of Ballenar 

On the northern side of the valley the summit-plain 
of gravel (A) has two escarpments, one facing the valley, 
and the other a great basin-like plain (B), which 
stretches for several leagues northward. This narrow 
plain (A) with the double escarpment, evidently once 
formed a spit or promontory of gravel, projecting into 
and dividing two great bays, and subsequently was 
worn on both sides into steep cliffs. Whether the 
several escarpments in this valley were formed during 
the same stationary periods with those of Coquimbo 
I will not pretend to conjecture ; but if so, the inter- 
vening and subsequent elevatory movements must have 
been here much more energetic, for these plains cer- 
tainly stand at a much higher level than do those of 
Coquimbo. 

Gopiapo. From Guasco to Copiapo, I followed the 
road near the foot of the Cordillera, and therefore saw 
no upraised remains. At the mouthj however, of the 
valley of Copiapo there is a plain, estimated by Meyen 1 
between fifty and seventy feet in height, of which the 
upper part consists chiefly of gravel, abounding with 
recent shells, chiefly of the Conch olepas, Venus Dombeyi, 
and Caliiptrcea trochiformis. A little inland, on a 
plain estimated by myself at nearly 300 feet, the upper 
* Eeise urn die Erde ' Th. 1 s. 372, et seq 



264 Gravel- Terraces of Copiapo. PART n. 

stratum was formed of broken shells and sand cemented 
by white calcareous matter, and abounding with em- 
bedded recent shells, of which the Mulinia Byronensis 
and Pecten purpw atus were the most numerous. The 
lower plain stretches for some miles southward, and for 
an unknown distance northward, but not far up the 
valley; its seaward face, according to Meyen, is worn 
into caves above the level of the present beach. The 
valley of Copiapo is much less steeply inclined and less 
direct in its course than any other valley which I saw 
in Chile ; and its bottom does not generally consist of 
gravel : there are no step-formed terraces in it, except at 
one spot near the mouth of the great lateral valley of 
the Despoblado where there are only two, one above the 
other : lower down the valley, in one place I observed 
that the solid rock had been cut into the shape of a 
"beach and was smoothed over with shingle. 

Northward of Copiapo, in lat. 26 S , the old voyager 
Wafer 1 found immense numbers of sea-shells some 
miles from the coast. At Oobija (lat. 22 34'), M. 
d'Orbigny observed beds of gravel and broken shells, 
containing ten species of recent shells ; he also found, 
on projecting points of porphyry, at a height of 800 
feet, shells of Concholepas, Chiton, Calyptrsea, Pissurella, 
and Patella, still attached to the spots on which they 
had lived. M. d'Orbigny argues from this fact, that 
the elevation must have been great and sudden : 2 to 

1 Burnett's * Collection of Voyages/ vol. iv. p. 1 93. 

2 'Voyage. Part G6olog ' p. 94. M. d'Orbigny (p 98 in sum- 
ming up, says, < S'll est certain (as he believes) que tons les terrains 
en pente, compris entre la mer et les montagnes sont 1'ancien nvage 
de la mer, on doit supposer, pour Pensemble, un exhaussement qui ne 
serait pas moindre de deux cent metres ; il faudi ait supposer encore 
que ce soulevement n'a point e" t6 graduel ; . . . mais qu'il r^sulterait 
d'une senle et m&ne cause fortmte,' &c. Now, on this view, when 
the sea was forming the beach at the foot of the mountains, many 
shells of Concholepas, Chiton, Calyptraea, Fissurella, and Patella 
(which are known to live close to the beach), were attached to rocks 



is. Elevation of the Coast of Pern. 265 

me it appears far more probable that tlie movement; 
was gradual, with small starts as during the earth- 
quakes of 1822 and 1885, by which whole beds of shells 
attached to the rocks were lifted above the subsequent 
reach of the waves. M. d'Orbigny also found rolled 
pebbles, extending up the mountain to a height of at 
least 600 feet. At Iquique (lat. 20 12' S.), m a great 
accumulation of sand, at a height estimated between 150 
and 200 feet, I observed many large sea-shells which I 
thought could not have been blown up by the wind to 
that height. Mr. J. H. Blake has lately * described 
these shells : he states that c inland toward the moun- 
tains they form a compact uniform bed, scarcely a trace 
of the original shells being discernible ; but as we 
approach the shore, the forms become gradually more 
distinct till we meet with the living shells on the coast. 5 
This interesting observation, showing by the gradual 
decay of the shells how slowly and gradually the coast 
must have been uplifted, we shall presently see fully 
confirmed at Lima. At Arica (lat. 18 28'), M. 
d'Orbigny 2 found a great range of sand-dunes, four- 
teen leagues in length, stretching towards Tacna, in- 
cluding recent shells and bones of Oetacea ; and reach- 
ing up to a height of 300 feet above the sea. Lieut. 
Freyer has given some more precise facts : he states 3 
that the Morro of Arica is about 400 feet high ; it is 
worn into obsc ure terraces, on the bare rock of which 
he found Balini and Milleporse adhering. At the 

at a depth of 300 feet, and at a depth of fiOO feet several of these 
same shells were accumulating in great numbeis in honzontal beds. 
From what I have m> self seen in dredging, I believe this to be 
improbable in the highest degree, if not impossible; and I think 
every one who has read Prof E. Forbes's excellent researches ontha 
sub]ect, will without hesitation agree in this conclusion. 

1 Silhman's * Amer. Jour, of Science/ vol. xhv. p. 2. 

2 *Vo\age,'&c p. 101. 

8 In a letter to Mr Lyell, 'Geolog Proc.* vol. ii p. 1T9. 



266 Elevation of Lima. PABT n. 

height of between twenty and thirty feet the shells 
and corals were in a quite fresh state, but at .fifty feet 
they were much abraded ; there were, however, traces 
of organic remains at greater heights. On. the road 
from Tacna to Arequipa, between Loquimbo and 
iloquegua, Mr. M. Hamilton 1 found numerous recent 
sea-shells in sand, at a considerable distance from the 
sea, 

Lima. 

Northward of Arica, I know nothing of the coast 
for about a space of five degrees of latitude ; but near 
Callao, the port of Lima, there is abundant and 
very curious evidence of the elevation, of the land. 
The island of San. Lorenzo is upwards of 1,000 feet 
high ; the basset edges of the strata composing the 
lower part are worn into three obscure, narrow, sloping 
steps or ledges, which can be seen, only when standing 
on them : they probably resemble those described by 
Lieut. Freyer at Arica. The surface of the lower ledge, 
which extends from a low cliff overhanging the sea to 
the foot of the next upper escarpment, is covered by an. 
enormous accumulation of recent shells. 2 The bed is 
level, and in some parts more than two feet in thick- 
ness ; I traced it over a space of one mile in length, 
and heard of it in other places : the uppermost part is 
eighty-five feet by the barometer above high-water 
mark. The shells are packed together, but not strati- 
fied ; they are mingled with earth a.nd stones, and are 
generally covered by a few inches of detritus; they 
rest on a mass of nearly angular fragments of the 
underlying sandstone, sometimes cemented together by 

1 Edin. New Phil Jour * vol. xxx. p 155. 

2 M. Chevalier, in the * Voyage of the Bomte,' observed these 
shells; but his specimens were lost. L'lnstitut, 1 1838, p. 151. 



CHAP. IX. 



Elevation of Lima. 



267 



common salt. I collected eighteen species of shells of 
all ages and sizes. Several of the univalves had evi- 
dently long lain dead at the bottom of the sea, for 
their insides were incrusted with Balani and Serpulas. 
All, according to Mr. Gr. B. Sowerby, are recent species : 
they consist of 



1. MytilnsMagrellanicns: sameas 

that found at Valparaiso, and 
there stated to be probably 
distinct from the true M. 
Magellanwus of the east 
coast 

2. Venus costellata, Sowb *Zool. 

Proc' 

3. Pecten purpuratus, Lam. 

4. Chama, probably echinulata, 

Biod 

5. Calyptrsea "Hyronensis. Gray. 
6. radians (Trochus, 

Lam.), 



7. Fissurella affinis, Gray. 

8. biradiata, Trembly, 

9 Purpura chocolatta, Duclos. 
Pemviana, Gray. 

- labiata, Gray 

- buxea(Murex, Brod ). 



10 

11. 

13 



Goncholepas Peruvian a 

14 Nassa, lelated to reticulaia 

15 'luton rudis, Brod 

16. Tiochtis, not yet desciibed, 
but well known and veiy 
common. 

17 and 18 Balanus, two species, 
both common on the coast. 



These upraised shells appear to be nearly in the 
same proportional numbers witli the exception of 
the Orepidulse being more numerous with those on 
the existing beach. The state of preservation of the 
different species differed much ; but most of them were 
much corroded, brittle, and bleached: the upper and 
lower surfaces of the Concholepas had generally quite 
scaled off: some of the Trochi and Fissurellge still 
partially retain their colours. It is remarkable that 
these shells, taken all together, have fully as ancient an 
appearance, although the extremely arid climate appears 
highly favourable ior their preservation, as those from 
1,300 feet at Valparaiso, and certainly a more ancient ap- 
pearance than those from 500 to 600 feet from Valparaiso 
and Concepcion : at which places I have seen grass and 
other vegetables actually growing out of the shells. 
Many of the univalves here at San Lorenzo were filled 
and united together by pure salt, probably left by the 



268 Fossil Remains of Human Art. PABT n. 

evaporation of the sea-spray, as the land slowly emerged. 1 
On the highest parts of the ledge, small fragments of 
the shells were mingled with, and evidently in process 
of reduction into, a yellowish-white, soft, calcareous 
powder, tasting strongly of salt, and in some places as 
fine as prepared medicinal chalk. 

Fossil Remains of Human Art. In the midst of 
these shells on San Lorenzo, I found light corallines, 
the horny ovule-cases of Mollusca, roots of sea-weed, 2 
hones of birds, the heads of Indian corn and other 
vegetable matter, a piece of woven rushes, and another 
of nearly decayed cotton string. I extracted these re- 
mains by digging a hole, on a level spot ; and they had 
all indisputably been embedded with the shells. I 
compared the plaited rush, the cotton string, and Indian 
corn, at the house of an antiquary, with similar object?, 
taken from the Huacas or burial-grounds of the ancient 
Peruvians, and they were undistinguishable ; it should 
be observed that the Peruvians used string only ot 
cotton. The small quantity of sand or gravel with the 
shellsj the absence of large stones, the width and thick- 
ness of the bed, and the time requisite for a ledge to 

1 The underlying sandstone contains true layeis of salt; so that 
the salt may possibly Lave come from the beds in the higher paits 
of the island , but 1 think moie piobably fiom the &ea-spiay. It is 
generally asserted that lam never falls on the coast of Peru ; but thus 
is not quite accurate ; for, on several da> s, during our visit, the so- 
called Peiuvian dew fell in sufficient quantity to make the stieets 
muddy, and It would certainly have washed so deliquescent a sub- 
stance as salt into the soil X state this because M. d'Orbigny, m 
discussing an analogous subject, supposes that 1 had forgotten that 
it never rams on this whole line of coast. See Ulloa's * Voyage ' (\ol. 
11. 'Eng. Trans ' p. 67) for an account of the muddy stieets of Lima, 
and on the continuance of the mists during the whole winter. Earn, 
also, falls at rare intervals even in the driest districts, as, for in- 
stance, during foity days, in 1726, at Chocope (7 46'); this rain 
entirely lumed ('Ulloa,'&c. p. 18) the mud-houses of the inhabi- 
tants. 

2 Mr. Smith of Jordanhill found pieces of sea- weed in an upraised 
pleistocene deposit in Scotland, fcjee his admirable Paper in the 
* Bdm. New. Phil Journal/ vol. xxv p 384 



CHAP. TX. Fossil Remains of Human Art. 269 

be cut into the sandstone, all snow that these remains 
were not thrown high up by an earthquake-wave : on 
the other hand, these facts, together with the number 
of dead shells, and of floating objects, both marine and 
terrestrial, both natural and human, render it almost 
certain that they were accumulated on a true beach, 
since upraised eighty-five feet, and upraised this much 
since Indian man inhabited Peru. The elevation 
may have been, either by several small sudden starts, 
or quite giadual ; in this latter case the unrolled shells 
having been thrown up during gales beyond the reach 
of the waves which afterwards broke on the slowly 
emerging land. I have made these remarks, chiefly 
because I was at first surprised at the complete differ- 
ence in nature, between this broad, smooth, upraised 
bed of shells, and the present shingle-beach at the foot 
of the low sandstone-cliffs ; but a beach formed, when 
the sea is cutting into the land, as is shown now to be 
the case by the low bare sandstone-cliffs, ought not to 
be compared with a beach accumulated on a gently in- 
clined rocky surface, at a period when the sea (probably 
owing to the elevatory movement in process) was not 
able to eat into the land. With respect to the mass of 
nearly angular, salt-cemented fragments of sandstone, 
which lie under the shells, and which are so unlike the 
materials of an ordinary sea-beach ; I think it probable 
after having seen the remarkable effects * of the earth- 
quake of 1835, in absolutely shattering as if by gan- 
powder the surface of the primary rocks near Concepcion, 
that a smooth bare surface of stone was left by the sea 
covered by the shelly mass, and that afterwards when 
upraised, it was superficially shattered by the severe 
shocks so often experienced here. 

1 I have described these effects in my * Journal of Researches, 'p* 
80S, 2nd edit, 1845. 



270 Fossil Earthenware near Lima. PAET n, 

The very low land surrounding the town of Callao, 
is to the south joined by an obscure escarpment to a 
higher plain (south of Bella Vista), which stretches 
along the coast for a length of about eight miles. This 
plain appears to the eye quite level ; but the sea-cliffs 
show that its height varies (as far as I could estimate) 
from 70 to 120 feet. It is composed of thin, sometimes 
waving, beds of clay, often of bright red and yellow 
colours, of layers of impure sand, and in one part with 
a great stratified mass of granitic pebbles. These beds 
are capped by a remarkable mass, varying from two to 
six feet in thickness, of reddish loam or mud, containing 
many scattered and broken fragments of recent marine 
shells, sometimes though rarely single large round 
pebbles, more frequently short irregular layers of fine 
gravel, and very many pieces of red coarse earthenware, 
which from their curvatures must once have formed 
parts of large vessels. The earthenware is of Indian 
manufacture ; and 1 found exactly similar pieces acci- 
dentally included within the bricks, of which the neigh- 
bouring ancient Peruvian burial-mounds are built. 
These fragments abounded in such numbers in certain 
spots, that it appeared as if waggon-loads of earthen- 
ware had been smashed to pieces. The broken sea- 
shells and pottery are strewed both on the surface, and 
throughout the whole thickness of this upper loamy 
mass. I found them wherever I examined the cliffs, 
for a space of between two and three miles, and for 
half a mile inland ; and there can be little doubt that 
this same bed extends with a smooth surface several 
miles further over the entire plain. Besides the little 
included irregular layers of small pebbles, there are 
occasionally very obscure traces of stratification. 

At one of the highest parts of the cliff, estimated 
120 feet above the sea } where a little ravine came down, 



CHAP. ix. Fossil Earthenware near Lima. 271 

there were two sections, at right angles to each other, 
of the floor of a shed or building. In both sections or 
faces, two rows, one over the other, of large round stones 
could be distinctly seen; they were packed close to- 
gether on an artificial layer of sand two inches thick, 
which had been placed on the natural clay-beds; the 
round stones were covered by three feet in thickness of 
the loam with broken sea-shells and pottery. Hence, 
before this widely spread- out bed of loam was deposited, 
it is certain that the plain was inhabited ; and it is 
probable, from the broken vessels being so much more 
abundant in certain spots than in others, and from the 
underlying clay being fitted for their manufacture, that 
the kilns stood here. 

The smoothness' and wide extent of the plain, the 
bulk of matter deposited, and the obscure traces of 
stratification seem to indicate that the loam was de- 
posited under water ; on the other hand, the presence 
of sea-shells, their broken state, the pebbles of various 
sizes, and the artificial floor of round stones, almost 
prove that it must have originated in a rush of water 
from the sea over the land. The height of the plain, 
namely, 120 feet, renders it improbable that an earth- 
quake-wave, vast as some have here been, could have 
broken over the surface at its present level ; but when 
the land stood eighty-five feet lower, at the period when 
the shells were thrown up on the ledge at S. Lorenzo, 
and when as we know man inhabited this district, such 
an event might well have occurred ; and if we may fur- 
ther suppose, that the plain was at that time converted 
into a temporary lake, as actually occurred, during the 
earthquakes of 1713 and 1746, in the case of the low 
land round Callao owing to its being encircled by a 
high shingle- beach, all the appearances above described 
will be perfectly explained, I must add, that at a 



2J2 Recent Subsidence near Lima. 



PART n. 



lower level near the point where the present low land 
round Callao joins the higher plain, there are appear- 
ances of two distinct deposits both apparently formed 
by debacles: in the upper one, a horse's tooth and a 
dog's jaw were embedded ; so that both must have been 
formed after the settlement of the Spaniards: accord- 
ing to Acosta, the earthquake-wave of 1586 rose eighty- 
four feet. 

The inhabitants of Callao do not believe, as far as I 
could ascertain, that any change in level is now in pro- 
gress. The great fragments of brickwork, which it is 
asserted can be seen at the bottom of the sea, and which 
have been adduced as a proof of a late subsidence, are, 
as I am informed by Mr. Gill, a resident engineer, 
loose fragments; this is probable, for 1 found on the 
beach, and not near the remains of any building, masses 
of brickwork, three and four feet square, which had 
been washed into their present places, and smoothed 
over with shingle during the earthquake of 1746. The 
spit of land, on which the ruins of Old Callao stand, is 
so extremely low and narrow, that it is improbable in 
the highest degree that a town should have been founded 
on it in its present state ; and I have lately heard 1 that 
M. Tschudi has come to the conclusion, from a com- 
parison of old with modern charts, that the coast both 
south and north of Callao has subsided. I have shown 
that the island of San Lorenzo has been upraised eighty- 
five feet since the Peruvians inhabited this country; 
and whatever may have been the amount of recent sub- 
sidence, by so rnuch more must the elevation have ex- 
ceeded the eighty-five feet. In several places 2 in this 

1 I am indebted for this fact to Dr E DievFenbach. I may add 
that there is a tradition, that the Islands of 8an Lorenzo and Fronton 
were once joined, and that the channel between. S. Lorenzo and the 
mainland, now above two miles in width, was so narrow that cattle 
used to swim over. 

' Observaciones sobre el Chma del Lima,' par Dr. H. Unantie, 



CHAP, ix. Decay of Upraised Sea-S hells* 273 

neighbourhood, marks of sea-action have been observed : 
Ulloa gives a detailed account of such appearances at a 
point five leagues northward of Callao : Mr. Omk&hank 
found near Lima successive lines of sea-cliffs, with 
rounded blocks at their bases, at a height of 700 feet 
above the present level of the sea. 

On the Decay of upraised Sea-Shells. I have 
stated that many of the shells on the lower inclined 
ledge or terrace of San. Lorenzo are corroded in a pecu- 
liar manner, and that they have a much more ancient 
appearance than the same species at considerably greater 
heights on the coast of Chile. I have, also, stated that 
these shells in the upper part of the ledge, at the height 
of eighty-five feet above the sea, are falling, and in 
some parts are quite changed into a fine, soft, saline, cal- 
careous powder. The finest part of this powder has been 
analysed for me, at the request of Sir H. De la Beche, 
by the kindness of Mr, Trenhani Reeks of the Museum 
of Economic Geology , it consists of carbonate of lime 
in abundance, of sulphate and muriate of lime, and of 
muriate and sulphate of soda. The carbonate of lime 
is obviously derived from the shells; and common salt 
is so abundant m parts of the bed, that, as before 
remarked, the univalves are often filled with it. The 
sulphate of lime may have been derived, as has probably 
the common salt, from the evaporation of the sea-spray, 
during the emergence of the land ; for sulphate of lime 
is now copiously deposited from the spray on the shores 
of Ascension. 1 The other saline bodies may perhaps 
have been partially thus derived, but chiefly, as 1 con- 
clude from the following facts, through a different 
means. 

p. 4 Ulloa's * Yojage,' vol ii. * Eng. Trans.' p. 07. For Mr. Crnik- 
shank's observations, see Mr. Lyell's ' Principles of Geology' (Ibt 
edit ), vol. in. p 130. 

1 See my discussion on a calcareous incrustation in Ohap f er IIL 



274 Decay of Upraised Sea-Shells. PAET n. 

On most parts of the second ledge or old sea-beach, 
at a height of 170 feet, there is a layer of white powder 
of variable thickness, as much in some parts as two 
inches, lying on the angular, salt-cemented fragments 
of sandstone and under about four inches of earth, which 
powder, from its close resemblance in nature to th 
upper and most decayed parts of the shelly mass, I can 
hardly doubt originally existed as a bed of shells, now 
much collapsed and quite disintegrated. I could not 
discover with the microscope a trace of organic structure 
in it ; but its chemical constituents, according to Mr. 
Reeks, are the same as in the powder extracted from 
amongst the decaying shells on the lower ledge, with 
the marked exception that the carbonate of lime is 
present m only very small quantity. On the third and 
highest ledge, I observed some of this powder m a 
similar position, and likewise occasionally in small 
patches at considerably greater heights near the summit 
of the island. At Iquique, where the whole face of the 
country is covered by a highly sahferous alluvium, and 
where the climate is extremely dry, we have seen that, 
according to Mr. Blake, the shells which are perfect 
near the beach become, in ascending, gradually less 
and less perfect, until scarcely a trace of their original 
structure can be discovered. It is known that car- 
bonate of lime and common salt left in a mass together, 1 
and slightly moistened, partially decompose each other : 
now we have at San Lorenzo and at Iquique, in the 
shells and salt packed together, and occasionally mois- 

1 I am informed by Dr. Kane, through Mr. Keeks, that a manu- 
factory was established on this principle in France, but failed from 
the small quantity of carbonate of soda produced. Sprecgel 
(* Gardeners' Chron.' 18-45, p. 157) states, that salt and carbonate of 
lime are liable to mutual decomposition in the soil. Sir H, De la 
Beche informs me, that calcaieous rocks, washed by the spray of the 
sea, are often corroded in a peculiar manner j see also on this latter 
subject ' Gardeners' Chron.' p. 675, 



CHAP. ix. Recent Elevafory Movements. 275 

tened by the so-called Peruvian dew, the proper elements 
for this action. We can thus understand the peculiar 
corroded appearance of the shells on San Lorenzo, and 
the great decrease of quantity in the carbonate of lime 
in the powder on the upper ledge. There is, however, 
a great difficulty on this view, for the resultant salts 
should be carbonate of soda and muriate of lime ; the 
latter is present, but not the carbonate of soda. Hence 
I am led to the perhaps unauthorised conjecture (which 
I shall hereafter have to refer to) that the carbonate of 
soda, by some unexplained means, becomes converted 
into a sulphate. 

If the above remarks be just, we are led to the very 
unexpected conclusion, that a dry climate, by leaving 
the salt from the sea-spray unclissolved, is much less 
favourable to the preservation of upraised shells than 
a humid climate. However this may be, it is interest- 
ing to know the manner in which masses of shells, 
gradually upraised above the sea-level, decay and finally 
disappear. 

Summary on the recent Elevation of the West 
Coast of South America. We have seen that upraised 
marine remains occur at intervals, and in some parts 
almost continuously, from lat. 45 35 / to 12 S., along 
the shores of the I 3 acific. This is a distance, in a north 
and south line, of 2,075 geographical miles. From 
Byron's observations, the elevation has no doubt extended 
sixty miles farther south; and from the similarity in 
the form of the country near Lima, it has probably 
extended many leagues farther north. 1 Along this 
great line of coast, besides the organic remains, there 
are in very many parts, marks of erosion, caves, ancient 

1 I may take this opportunity of stating that in a MS in the 
Geological Boc by Me Weaver, it is stated that beds of oysters and 
other recent shells aie found thuty feet above the level of the sea, 
in many parts of Tampico, in the G-ulf of Mexico. 

19 



276 Recent Elevafory Movements, IPAET m 

Leaches, sand-dunes, and successive terraces of gravel, 
all above the present level of the sea. From the steep- 
ness of the land on this side of the continent, shells 
have rarely been found at greater distances inland than 
from two to three leagues ; but the marks of sea-action 
are evident farther from the coast ; for instance, in the 
valley of Guasco, at a distance of between thirty and 
forty miles. Judging from the upraised shells alone, 
the elevation in Chiloe has been 350 feet, ( at Concepcion 
ceitamly 625 feet, and by estimation 1,000 feet; at 
Valparaiso 1,300 feet; at Coquimbo 252 feet; north- 
ward of this place, sea-shells have not, I believe, been 
found above 300 feet; and at Lima they were falling 
into decay (hastened probably by the salt) at eighty-five 
feet. Not only has this amount of elevation taken 
place within the period of existing Mollusca and Gir- 
ripedes ; but their proportional numbers in the neigh- 
bouring sea have in most cases remained the same. 
Near Lima, however, a small change in this respect 
between the living arid the upraised was observed : at 
Coquimbo this was more evident, all the shells being 
existing species, but with those embedded in the upper- 
most calcareous plain not approximating so closely in 
proportional numbers, as do those that lie loose on its 
surface at the height of 252 feet, and still less closely 
than those which are strewed on the lower plains, which 
latter are identical in proportional numbers with those 
now cast up on the beach. From this circumstance, 
and from not finding, upon careful examination, near 
Coquimbo any shells at a greater height than 252 feet, 
I believe that the recent elevation there ha^ been much 
less than at Valparaiso, where it has been 1,300 feet, 
and I may add, than at Concepcion. This considerable 
inequality in the amount of elevation at Coquimbo and 
Valparaiso, places only 200 miles apart, is not im- 



CHAP. ix. and Action of Sea on the Laud. 277 

probable, considering, first, the difference in the force 
and number of the shocks now yearly affecting different 
parts of this coast ; and, secondly, the fact of single 
areas, such as that of the province of Concepcion, having 
been uplifted very unequally during the same earth- 
quake. It would, in most cases, be very hazardous to 
infer an inequality of elevation, from shells being found 
on the surface or in superficial beds at different heights ; 
for we do not know on what their rate of decay depends ; 
and at Ooquimbo one instance out of many has been 
given, of a promontory, which, from the occurrence of 
one very small collection of lime-cemented shells, has 
indisputably been elevated 242 feet, and yet on which, 
not even a fragment of shell could be found on careful 
examination between this height and the beach, although 
many sites appeared very favourable for the preservation 
of organic remains : the absence, also, of shells on the 
gravel-terraces a short distance up the valley of Co- 
quimbo, though abundant on the corresponding terraces 
at its mouth, should be borne in mind. 

There are other epochs, besides that of the existence 
of recent Mollusca, by which to judge of the changes 
of level on this coast. At Lima, as we have just seen, 
the elevation has been at least eighty-five feet, within 
the Indo-human period; and since the arrival of the 
Spaniards in 1530, there has apparently been a sinking 
of the surface. At Valparaiso, in the course of 220 
\ears, the rise must have been less than nineteen feet; 
but it has been as much as from ten to eleven feet in 
the seventeen years subsequently to 1817, and of this 
rise only a part can be attributed to the earthquake 
of 1822, the remainder having been insensible and 
apparently still, in 1884, in progress. At Ohiloe the 
elevation has been gradual, and about four feet during 
four years. At Ooquimbo 3 also, it has been gradual, 



278 Recent Elevatory Movements, PAET n. 

and in the course of 150 years has amounted to several 
feet. The sudden small upheavals, accompanied by 
earthquakes, as in 1822 at Valparaiso, in 1835 at Con- 
cepcion, and -in 1837 in the Ohonos Archipelago, are 
familiar to most geologists, but the gradual rising of 
the coast of Chile has been hardly noticed ; it is, how- 
ever, very important, as connecting together these two 
orders of events. 

The rise of Lima, having been eighty-five feet within 
the period of man, is the more surprising if we refer to 
the eastern coast of the continent, for at Port S. Julian, 
in Patagonia, there is good evidence (as we shall here- 
after see) that when the land stood ninety feet lower, 
the Jlacrauchenia, a mammiferous beast, was alive ; 
and at Bahia Blanca, when it stood only a few feet 
lower than it now does, many gigantic quadrupeds 
ranged over the adjoining country. But the coast of 
Patagonia is some way distant from the Cordillera,, and 
the movement at Bahia Blanca is perhaps no ways 
connected with this great range, but rather with the 
tertiary volcanic rocks of Banda Oriental, and therefore 
the elevation at these places may have been infinitely 
slower than on the coast of Peru. All such speculations, 
however, must be vague, for as we know with certainty 
that the elevation of the whole coast of Patagonia has 
been interrupted by many and long pauses, who will 
pretend to say that, in such cases, many and long periods 
of subsidence may not also have been intercalated ? 

In many parts of the coast of Chile and Peru there 
are marks of the action of the sea at successive heights 
on the land, showing that the elevation has been inter- 
rupted by periods of comparative rest in the upward 
movement, and of denudation in the action of the sea. 
These are plainest at Chiloe, where, in a height of about 
500 feet, there are three escarpments, at Coquimbo, 



CHAP, ix, and Action of Sea on the Land. 279 

where, in a height of 364 feet 5 there are five, at Gruasco, 
where there are six, of which five may perhaps cor- 
respond with those at Coqtnmbo, but if so, the subse- 
quent and intervening elevatory movements have been 
here much more energetic, at Lima, where, in a height 
of about 250 feet, there are three terraces, and others, 
as it is asserted, at considerably greater heights. The 
almost entire absence of ancient marks of sea-action at 
defined levels along considerable spaces of coast, as near 
Valparaiso and Concepcion, is highly instructive, for as 
it is improbable that the elevation at these places alone 
should have been continuous, we must attribute the 
absence of such marks to the nature and form of the 
coast-rocks. Seeing over how many hundred miles of 
the coast of Patagonia, and on how many places on the 
shores of the Pacific, the elevatory process has been 
interrupted by periods of comparative rest, we may 
conclude, conjointly with the evidence drawn from 
other quarters of the world, that the elevation of the 
land is generally an intermittent action. Prom the 
quantity of matter removed in the formation of the 
escarpments, especially of these of Patagonia, it appears 
that the periods of rest in the movement, and of denu- 
dation of the land, have generally been very long. In 
Patagonia, we have seen that the elevation has been 
equable, and the periods of denudation synchronous 
over very wide spaces of coast ; on the shores of the 
Pacific, owing to the terraces chiefly occurring in the 
valleys, we have not equal means of judging on this 
point ; and the very different heights of the upraised 
shells at Coquimbo, Valparaiso, and Concepcion seem 
directly opposed to such a conclusion. 

Whether on this side of the continent the elevation, 
between the periods of comparative rest when the 
.escarpments were formed, has been by small sudden 



2 So Recent Eletatory Movements, PAST IL 

starts, such a& those accompanying recent earthquakes, 
or, as is most probable, by such starts conjointly with a 
gradual upward movement, or by great and sudden 
upheavals, I have no direct evidence. But as on the 
eastern coast, I was led to think, from the analogy of 
the last hundred feet of elevation in La Plata, and from 
the nearly equal size of the pebbles over the entire 
width of the terraces, and from the upraised shells 
being all littoral species, that the elevation had been 
gradual ; so do I on this western coast, from the analogy 
of the movements now in progress, and from the vast 
numbers of shells now living exclusively on or close to 
the beach, which are strewed over the whole surface of 
the land up to very considerable heights, conclude, that 
the movement here also has been slow and gradual, 
aided probably by small occasional starts. We know 
at least that *t Coquimbo, where five escarpments occur 
in a height of 364 feet, that the successive elevations, 
if they have been sudden, cannot have been, very great. 
It has, I think, been shown that the occasional preserva- 
tion of shells, unrolled and unbroken, is not improbable 
even during a quite gradual rising of the land ; and 
their preservation, if the movement has been aided by 
small starts, is quite conformable with what actually 
takes place during recent earthquakes. 

Judging from the present action of the sea, along 
the shores of the Pacific, on the deposits of its own 
accumulation, the present time seems in most places to 
be one of comparative rest in the elevatory movement, 
and of denudation of the land. Undoubtedly this is 
the case along the whole great length of Patagonia. 
At Ohiloe, however, we have seen that a narrow sloping 
fringe, covered with vegetation, separates the present 
sea-beach from a line of low cliffs, which the waves 
lately reached ; here, then, the land is gaining io 



CHAP. ix. and Action of Sea on the Land. 281 

breadth and height, and the present period is not one 
of rest in the elevation and of contingent denudation ; 
but if the rising be not prolonged at a quick rate, there 
is every probability that the sea will soon regain its 
former horizontal limits. I observed similar low slop- 
ing fringes on, several parts of the coast, both northward 
of Valparaiso and near Ooquimbo ; but at this latter 
place, from the change in form which the coast has 
undergone since the old escaipments were worn, it may 
be doubted whether the sea, acting for any length of 
time at its present level, would eat into the land ; for 
it now rather tends to throw up great masses of sand, 
It is from facts such as these that I have generally used 
the teim comparative rest, as applied to the elevation 
of the land; the rest or cessation in the movement 
being comparative both with what has preceded it and 
followed it, and with the sea's power of corrosion at 
each spot and at each level. Near Lima, the cliff- 
formed shores of San Lorenzo, and on the mainland 
south of Oallao, show that the sea is gaining on the 
land ; and as we have here some evidence that its 
surface has lately subsided or is still sinking, the periods 
of comparative rest in the elevation and of contingent 
denudation, may probably in many cases include periods 
of subsidence. It is only, as was shown in detail when 
discussing the terraces of Ooquimbo, when the sea with 
difficulty and after a long lapse of time has either 
corroded a narrow ledge into solid rock, or has heaped 
up on a steep surface a narrow mound of detritus, that 
we can confidently assert that the land at that level and 
at that period long remained absolutely stationary. In 
the case of terraces formed of gravel or sand, although 
the elevation may have been strictly horizontal, it may 
well happen that no one level beach- line may be trace- 
able, and that neither the terraces themselves nor the 



282 Recent Elevatory Movements. PAST n, 

summit nor basal edges of tlieir escarpments may be 
"horizontal. 

Finally, comparing the extent of the elevated area, 
as deduced from the upraised recent organic remains, 
on the two sides of the continent, we have seen that on 
the Atlantic, shells have been found at intervals from 
eastern Tierra del Fuego for 1,180 miles northward, 
and on the Pacific for a space of 2,075 miles. For a 
length of 775 miles, they occur in the same latitudes 
on both sides of the continent. Without taking this 
circumstance into consideration, it is probable from 
the reasons assigned in the last chapter, that the entire 
breadth of the continent in Central Patagonia has been 
uplifted in mass ; but from other reasons there given, it 
would be hazardous to extend this conclusion to La 
Plata. From the continent being narrow in the south- 
ernmost parts of Patagonia, and from the shells found 
at the Inner Narrows of the Strait of Magellan, and 
likewise far up the valley of the S. Cruz, it is probable 
that the southern part of the western coast, which was 
not visited by me, has been elevated within the period 
of recent Mollusca : if so, the shores of the Pacific 
bave been continuously, recently, and in a geological 
sense synchronously upraised, from Lima for a height of 
2,480 nautical miles southward, a distance equal to that 
from the Red Sea to the North Cape of Scandinavia ! 



283 



CHAPTER X. 

ON THE PLAINS AND VALLEYS OF CHILE : SALIFEROUS 
SCJPERFICIAL DEPOSITS. 

Jtasin-hke plains of Chile ; their drainage, their marine origin 
Marks of sea-action on the eastern flanks of the Cordillera Sloping 
terrace-lilte fringes of stratified shingle nithin the valleys of the 
Cordillera-, their marine origin-- Jboiddeis in the valley of the 
Caohapual Horizontal elci atwn of the Cordillera Formation <>f 
valleys Boulders moved % earth Qitahe-mai'ex Saline siijjeiftcial 
deposits Bed of nitrate of soda at Iquiqite Saline incrustations 
Salt lakes of La Plata and Patagonia purity of the salt ; its owyin. 

THE space between the Cordillera and the coast of Chile is 
on a rude average from eighty to above one hundred 
miles in width ; it is formed, either of an almost 
continuous mass of mountains, or more commonly of 
several nearly parallel ranges, separated by plains; in 
the more southern parts of this province the mountains 
are quite subordinate to the plains; in the northern 
part the mountains predominate. 

The basin-like plains at the foot of the Cordillera 
are in several respects remarkable ; that on which the 
capital of Chile stands is fifteen miles in width, in an 
east and west line, and of much greater length in a 
north and south line ; it stands 1,750 feet above the sea; 
its surface appears smooth, but really falls and rises 
in wide gentle undulations, the hollows corresponding 
with the main valleys of the Cordillera : the striking 
manner in which it abruptly comes up to the foot of 



284 Basin- like Plains of Chile. PART IL 

this great range has been remarked by every author ] 
since the time of Molina. Near the Cordillera it is 
composed of a stratified mass of pebbles of all sizes, 
occasionally including rounded boulders: near its 
western boundary, it consists of redcfish sandy clay, 
containing some pebbles and numerous fragments of 
pumice, and sometimes passes into pure sand or into 
volcanic ashes. At Podaguel, on this western side of 
the plain, beds of sand are capped by a calcareous 
tuff, the uppermost layers being generally hard and 
substalagmitic, and the lower ones white and friable, 
both together precisely resembling the beds at Co- 
quimbo, which contain recent marine shells. Abrupt, 
but rounded, hummocks of rock rise out of this plain : 
those of Sta. Lucia and S. Cristoval are formed of 
greenstone-porphyry almost entirely denuded of its 
original covering of porphyritic claystone breccia; on 
their summits, many fragments of rock (some of them 
kinds not found in situ) are coated and united together 
by a white, friable, calcareous tuff, like that found at 
Podaguel. When this matter was deposited on the 
summit of S. Cristoval, the water must have stood 
946 feet 2 above the surface of the surrounding plain. 

To the south this basin-like plain contracts, and 
rising scarcely perceptibly with a smooth surface, 

1 This plain is partially separated into two basins by a range ot 
hills, the southern half, according to Meyen (' Beise um Eide,' Th i 
8 274), falls in height, by an abrupt step, of between nf t een and twenty 
feet 

2 Or 2,690 feet above the sea, as measured barometrically by Mr. 
Eck This tuff appears to the eye nearly pure ; but when placed in 
acid it leaves a considerable residue of sand and broken crystals, 
apparently of feldspar Dr Meyen ( s Reise,' Th. i s 269) says, he 
iound a similar substance on the neighbouring hill of Dommico (and 
I found it also on the Cerro Blanco), and he attributes it to the 
weathering of the stone. In some places which J examined, its bulk 
put this view of its origin quite out of question ; and I should much 
doubt whether the decomposition of a porphyry would, in any case, 
leave a crust chiefly composed of carbonate of lime The white 
crust, which is commonly seen on weathered feldspathic rocks, 
does not appeal to contain any free carbonate of lime. 



CHAP, x. Basin- like Plains of Chile. 285 

passes through a remarkable level gap in the moun- 
tains, forming a true land-strait, and called the~A ngostura. 
It then immediately expands into a second basin-formed 
plain : this again to the south, contracts into another 
land-strait, and expands into a third basin, which, how- 
ever, falls suddenly in level about forty feet. This third 
basin, to the south, likewise contracts into a strait, and 
then again opens into the great plain of S. Fernando,, 
stretching so far south that the snowy peaks of the dis- 
tant Cordillera are seen rising above its horizon as above 
the sea. These plains, near the Cordillera, are generally 
formed of a thick stratified mass of shingle ; * in other 
parts, of a red sandy clay, often with an admixture of pu- 
miceous matter. Although these basins are connected to- 
gether like a necklace, in a north and south line, by smooth 
land-straits, the streams which drain them do not all flow 
north and south, but mostly westward, through breaches 
worn in the bounding mountains ; and in the case of 
the second basin, or that of Rancagua, there are two 
distinct breaches. Each basin, moreover, is not drained 
singly : thus, to give the most striking instance, but 
not the only one, in proceeding southward over the 
plain of Kancagua, we first find the water flowing 
northward to and through the northern land-strait; 
then, without crossing any marked ridge or water-shed, 
we see it flowing south-westward towards the northern 
one of the two breaches in the western mountainous 
boundary ; and lastly, again without any ridge, it flows 
towards the southern breach in these same mountains, 
Hence the surface of this one basin-like plain, appear- 
ing to the eye so level, has been modelled with great 
nicety, so that the drainage, without any conspicuous 

1 The plain of S. Fernando has, according to MM Meyen and 
Gay (' Reise,' &c. Th i. ss. 295 and 298), near the Cordillera, an 
upper step-formed plain of clay, on the Miiface of which they found 
numerous blocks of locks, fiom two or thiee feet long, either lying 
single or piled in heaps, but all arranged m nearly straight lines 



286 Basin-like Plains of Chile. PART n, 

watersheds, is directed towards three openings in the 
encircling mountains. 1 The streams flowing from the 
three southern basin-like plains, after passing through 
the breaches to the west, unite and form the river 
Rapel, which enters the Pacific near Navidad. I 
followed the southernmost branch of this river, and 
found that the basin or plain of S. Fernando is con- 
tinuously and smoothly united with those plains, 
which were described in the ninth chapter, as being 
worn near the coast into successive cave-eaten escarp- 
ments, and still nearer to the coast, as being strewed with 
upraised recent marine remains. 

I might have given descriptions of numerous other 
plains of the same general form, some at the foot of 
the Cordillera, some near the coast, and some half-way 
between these points. I will allude only to one other, 
namely, the plain of Uspallata, lying on the eastern 
or opposite side of the Cordillera, between, that great 
range and the parallel lower range of Uspallata. 
According to Miers, its surface is 6,000 feet above the 
level of the sea : it is from ten to fifteen miles in 
width, and is said to extend with an unbroken surface 
for 180 miles northwards: it is drained by two rivers 
passing through breaches in the mountains to the east. 
On the banks of the R. Mendoza it is* seen to be 
composed of a great accumulation of stratified shingle, 
estimated at 400 feet in thickness. In general appear- 
ance, and in numerous points of structure, this plain 
closely resembles those of Chile. 

The origin and manner of formation of the thick 
beds of gravel, sandy clay, volcanic detritus, and cal- 
careous tuff, composing these basin-like plains, is very 

1 It appears from Capt. Herbeit's account of the Diluvium of the 
Himalaya ('Gleanings of Science,' Calcutta, vol. ii. p. 164), that 
precisely similar remarks apply to the drainage of the plains oi 
valleys between those great mountains. 



CHAP. x. Basin-like Plains of Chile. 287 

important ; because, as we shall presently show, they 
send arms or fringes far np the main valleys of the 
Cordillera. Many of the inhabitants believe that these 
plains were once occupied by lakes, suddenly drained ; 
bnt I conceive that the number of the separate breaches 
at nearly the same level in the mountains surrounding 
them, quite precludes this idea. Had not such distin- 
guished naturalists as MM. Meyen and Gay stated 
their belief that these deposits were left by great 
debacles rushing down from the Cordillera, I should 
not have noticed a view, which appears to me from 
many reasons improbable in the highest degree 
namely, from the vast accumulation of ^v ell-rounded 
peWUs their frequent stratification with layers of 
saB( j the overlying beds of calcareous tuff this same 
substance coating and uniting the fragments of rock 
on the hummocks in the plain of Santiago and lastly 
even from the worn, rounded, and much denuded state 
of these hummocks, and of the headlands which pro- 
ject from the surrounding mountains. On the other 
hand, these several circumstances, as well as the con- 
tinuous union of the basins at the foot of the Cor- 
dillera, with the great plain of the Eio Rapel which 
still retains the marks of sea-action at various levels, 
and their general similarity in form and composition 
with the many plains near the coast, which are either 
similarly marked or are strewed with upraised marine 
remains, fully convince me that the mountains bound- 
ing these basin-plains were breached, their islet-like 
projecting rocks worn, and the loose stratified detritus 
forming their now level surfaces deposited, by the sea, 
as the land slowly emerged. It is hardly possible to 
state too strongly the perfect resemblance in outline be- 
tween these basin-like, long, and narrow plains of Chile, 
(especially when in the early morning the mists hang- 



288 Basin- like Plains of Chile. FAET n. 

ing low represented water,) and the creeks and fiords 
now intersecting the southern and western shores of 
the continent. We can on this view of the sea, when 
the land stood lower, having long and tranquilly 
occupied the spaces between the mountain-ranges,, un- 
derstand how the boundaries of the separate basins 
were breached in more than one place ; for we see that 
this is the general character of the inland bays and 
channels of Tierra del Fuego ; we there, also, see in 
the sawing action of the tides, which flow with great 
force in the cross channels, a power sufficient to keep 
the breaches open as the land emerged. We can 
further see that the waves would naturally leave the 
smooth bottom of each great bay or channel as it be- 
came slowly converted into land, gently inclined to as 
tnany points as there were mouths, thi^ough which the 
sea finally retreated, thus forming so many water-sheds, 
without any marked ridges, on a nearly level surface. 
The absence of marine remains in these high inland 
plains cannot be properly adduced as an objection to 
their marine origin : for we may conclude, from shells not 
being found in the great shingle beds of Patagonia, 
though copiously strewed on their surfaces, and from 
many other analogous facts, that such deposits are 
eminently unfavourable for the embedment of such 
remains ; and with respect to shells not being found 
strewed on the surface of these basin-plains, it was 
shown in the last chapter that remains thus exposed in 
time decay and disappear. 

1 observed some appearances on the plains at the 
eastern and opposite foot of the Cordillera which are 
worth notice, as showing that the sea there long acted 
at nearly the same level as on the basin-plains of Chile. 
The mountains on this eastern side are exceedingly 
abrupt; they rise out of a smooth, talus-like, very 



CHAP x. Sea-action at Eastern Foot of Andes. 289 

gentle, slope, from five to ten miles in width (as repre- 
sented m the following diagram), entirely composed of 

No. 27 
Section of the Plain at the Eastern Foot of the Chilian Cordillera. 




Oordilleia, Talus-plain Level surface, Gravel 

2,700 feet above sea teiraces. 

perfectly rounded pebbles, often white-washed with an 
aluminous substance like decomposed feldspar. This 
sloping plain or tains blends into a perfectly flat space 
a few miles in width, composed of reddish impure clay, 
with small calcareous concretions as in the Pampean 
deposit, of fine white sand with small pebbles in 
layers, and of the above-mentioned white aluminous 
earth, all mterstratified together This flat space runs 
as far as Mendoza, thirty miles northward, and stands 
probably at about the same height, namely, 2,700 feet 
(Pentland and Miers) above the sea. To the east it 
is bounded by an escarpment, eighty feet in height, 
running for many miles north and south, and composed 
of perfectly round pebbles, and loose, white-washed, or 
embedded in the aluminous earth : behind this escarp- 
ment there is a second and similar one of gravel 
Northward of Mendoza, these escarpments become 
broken and quite obliterated; and it does not appear that 
they ever enclosed a lake-like area : I conclude, there- 
fore, that they were formed by the sea, when it reached 
the foot of the Cordillera, like the similar escarpments 
occurring at so many points on the coasts of Chile and 
Patagonia. 

The talus-like plain slopes up with a smooth 
surface into the great dry valleys of the Cordillera On 
each hand of the Portillo valley, the mountains are 



290 Sloping Terraces of Gravel PART n. 

formed of red granite, mica-slate, and basalt, which all 
have suffered a truly astonishing amount of denudation; 
the gravel in the valley, as well as on the talus-like 
plain in front of it, is composed of these rocks ; but at 
the mouth of the valley, in the middle (height proba- 
bly about 3,500 feet above the sea), a few small isolated 
hillocks of several varieties of porphyry project, round 
which, on all sides, smooth and often white-washed 
pebbles of these same porphyries, to the exclusion of 
all others, extend to a circumscribed distance. Now, 
it is difficult to conceive any other agency, except the 
quiet and long- continued action of the sea on these 
hillocks, which could have rounded and white-washed 
the fragments of porphyry, and caused them to radiate 
from such small and quite insignificant centres, in the 
midst of that vast stream of stones which has descended 
from the main Cordillera. 

Sloping To/race* of Gravel in the Valleys of the 
Cordillera. All the main valleys on both flanks of the 
Chilian Cordillera have formerly had, or still have, their 
bottoms filled up to a considerable thickness by a mass 
of rudely stratified shingle. In central Chile, the 
greater part of this mass has been removed by the 
torrents ; cliff-bounded fringes, more or less continuous, 
being left at corresponding heights on both sides of 
the valleys. These fringes, or as they may be called 
terraces, have a smooth surface, and as the valleys rise, 
they gently rise with them : hence they are easily irri- 
gated, and afford great facilities for the construction of 
the roads. From their uniformity, they give a re- 
markable character to the scenery of these grand, wild, 
broken valleys. In width, the fringes vary much, 
sometimes being only broad enough for the roads, and 
sometimes expanding into narrow plains. Their sur- 
faces, besides gently rising up the valley, are slightly 



CHAP. X. 



in the Valleys of the Cordillera. 291 



inclined towards its centre in such a manner as to 
show that the whole bottom must once have been filled 
up with a smooth and slightly concave mass, as still are 
the dry unfurrowed valleys of northern Chile. Where 
two valleys unite into one, these terraces are particu- 
larly well exhibited, as is represented in the following 
diagram. The thickness of the gravel forming these 

No. 28. 




Ground-plan of a bifurcating valley in the Cordillera, bordered by smooth, sloping 
gravel-fringes (A A A.), worn along the course of the nver into cliffs 

fringes, on a rude average, may be said to vary from 
thirty to sixty or eighty feet ; but near the mouths of 
the valleys it was in several places from 200 to 300 
feet. The amount of matter removed by the torrents 
has been immense; yet in the lower parts of the 
valleys the terraces have seldom been entirely worn 
away on either side, nor has the solid underlying rock 
been reached : higher up the valleys, the terraces have 
frequently been removed on one or the other side, and 
sometimes on both sides ; but in this latter case they 
re-appear after a short interval on the line, which they 
would have held had they been unbroken. Where the 
20 



Sloping Terraces of Gravel PART n. 



solid rock has "been reached, it has been cut into deep 
and narrow gorges. Still higher np the valleys, the 
terraces gradually become more and more broken, 
narrower, and less thick, until, at a height of from 
7,000 to 9,000 feet, they become lost, and blended with 
the piles of fallen detritus. 

I carefully examined in many places the state of the 
gravel, and almost everywhere found the pebbles equally 
and perfectly rounded, occasionally with great blocks 
of rock, and generally distinctly stratified, often with 
parting seams of sand. The pebbles were sometimes 
coated with a white aluminous, and less frequently with 
a calcareous, crust. At great heights up the valleys, 
the pebbles become less rounded; and as the terraces 
become obliterated, the whole mass passes into the 
nature of ordinary detritus. I was repeatedly struck 
with the great difference between this detritus high up 
the valleys, and the gravel of the terraces low down, 
namely, in the greater number of the quite angular 
fragments in the detritus, in the unequal degree to 
which the other fragments have been rounded, in the 
quantity of associated earth, in the absence of stratifi- 
cation, and in the irregularity of the upper surfaces. 
This difference was likewise well shown at points low 
down the valleys, where precipitous ravines, cutting 
through mountains of highly coloured rock, have thrown 
down wide, fan-shaped accumulations of detritus on the 
terraces : in such cases, the line of separation between 
the detritus and the terrace could be pointed out to 
within an inch or two ; the detritus consisting entirely 
of angular and only partially rounded fragments of the 
adjoining coloured rocks; the stratified shingle (as I 
ascertained by close inspection, especially in one case, 
in the valley of the B Mendoza) containing only a 



. in the Valleys of the Cordillera. 293 

small proportion of these fragments, and those few well 
rounded. 

I particularly attended to the appearance of the 
terraces where the valleys made abrupt and considerable 
bends, but I could perceive no difference in their struc- 
ture ; they followed the bends with their usual nearly 
equable inclination. I observed, also, in several 
valleys, that wherever large blocks of any rock became 
numerous, either on the surface of the terrace or em- 
bedded in it, this rock soon appeared higher up in situ : 
thus I have noticed blocks of porphyry, of andesitic 
syenite, of porphyry and of syenite, alternately becoming 
numerous, and in each case succeeded by mountains 
thus constituted. There is, however, one remarkable 
exception to this rule; for along the valley of the 
Cachapual, M. Gay found numerous large blocks of 
white granite, which does not occur in the neighbour- 
hood : I observed these blocks, as well as others of 
andesitic syenite (not occurring here in situ^ near the 
baths of Cauquenes at a height of between 200 and 300 
feet above the river, and therefore quite above the 
terrace or fringe which borders that river ; some miles 
higher up the valleys there were other blocks at about 
the same height : I also noticed, at a less height, just 
above the terrace, blocks of porphyries (apparently not 
found in the immediately impending mountains), 
arranged in rude lines, as on a sea-beach. All these 
blocks were rounded, and though large, not gigantic, 
like the true erratic boulders of Patagonia and Fuegia 
M. Gay * states that granite does not occur in situ 
within a distance of twenty leagues; I suspect, for 
several reasons, that it will ultimately be found at a 

1 * Annales des Scieiic. Nat.' (I. seiies torn. 28). M. Gay, as I 
was informed, penetrated the Cordillera by the great oblique valley 
of Los Cupressos, and not by the most direct line. 



294 Sloping Terraces of Gravel: PABT it. 

much less distance, though certainly not in the imme- 
diate neighbourhood. The boulders found by MM. 
Meyen and Gay on the upper plain of S. Fernando 
(mentioned in a previous note) probably belong to this 
same class of phenomena. 

These fringes of stratified gravel occur along all the 
great valleys of the Cordillera, as well as along their 
main branches; they are strikingly developed in the 
valleys of the Maypu, Mendoza, Aconcagua, Cachapual, 
and according to Meyen, 1 in the Tinguirica. In the 
valleys, however, of northern Chile, and in some on the 
eastern flank of the Cordillera, as in the Portillo 
Valley, where streams have never flowed, or are quite 
insignificant in volume, the presence of a mass of 
stratified gravel can be inferred only from the smooth 
slightly concave form of the bottom. One naturally 
seeks for some explanation of so general and striking a 
phenomenon; that the matter forming the fringes 
along the valleys, or still filling up their entire beds, 
has not fallen from the adjoining mountains like 
common detritus, is evident from the complete con- 
trast in every respect between the gravel and the piles 
of detritus, whether seen high up the valleys on their 
sides, or low down in front of the more precipitous 
ravines; that the matter has not been deposited by 
debacles, even if we could believe in debacles having 
rushed down every valley, and all their branches, east- 
ward and westward from the central pinnacles of the 
Cordillera, we must admit from the following reasons, 
from the distinct stratification of the mass, its 
smooth upper surface, the well-rounded and some- 
times encrusted state of the pebbles, so different from 
the loose d6bris on the mountains, and especially from 
the terraces preserving their uniform inclination round 
1 Eeise/ &c. Th. I. s. 302. 



CHAP. x. their Marine Origin. 295 

the most abrupt bends. To suppose that as the land 
now stands, the rivers deposited the shingle along the 
course of every valley, and all their main branches, 
appears to me preposterous, seeing that these same 
rivers not only are now removing and have removed 
much of this deposit, but are everywhere tending to cut 
deep and narrow gorges in the hard underlying rocks. 

I have stated that these fringes of gravel, the origin 
of which is inexplicable on the notion of debacles or 
of ordinary alluvial action, are directly continuous with 
the similarly-composed basin-like plains at the foot of 
the Cordillera, which, from the several reasons before 
assigned, I cannot doubt were modelled by the agency 
of the sea. Now if we suppose that the sea formerly 
occupied the valleys of the Chilian Cordillera, in pre- 
cisely the same manner as it now does in the more 
southern parts of the continent, where deep winding 
creeks penetrate into the very heart of, and in the case 
of Obstruction Sound quite through, this great range ; 
and if we suppose that the mountains were upraised in 
the same slow manner as the eastern and western coasts 
have been upraised within the recent period, then the 
origin and formation of these sloping, terrace-like fringes 
of gravel can be simply explained. For every part of 
the bottom of each valley will, on this view, have long 
stood at the head of a sea-creek, into which the then 
existing torrents will have delivered fragments of rocks, 
where, by the action of the tides, they will have been 
rolled, sometimes encrusted, rudely stratified, and the 
whole surface levelled by the blending together of the 
successive beach lines. 1 As the land rose, the torrents 

1 Sloping terraces of precisely similar structure have been de- 
scribed by me (' Philosoph. Transactions,' 1839, p. 58) in the valleys 
of Lochaber in Scotland, where, at higher levels, the parallel roads 
of Glen Roy show the marks of the long and quiet residence of a 
glacial lake. I have no doubt that sloping terraces would have been 



296 Sloping Terraces of Gravel: PAET n, 

in every valley will have tended to have removed the 
matter which just before had been arrested on, or near, 
the beach-lines; the torrents, also, having continued 
to gain in force by the continued elevation increasing 
their total descent from their sources to the sea. This 
slow rising of the Cordillera, which explains so well the 
otherwise inexplicable origin and structure of the ter- 
races, judging from all known analogies, will probably 
have been interrupted by many periods of rest ; but we 
ought not to expect to find any evidence of these periods 
in the structure of the gravel-terraces : for, as the waves 
at the heads of deep creeks have little erosive power, so 
the only effect of the sea having long remained at the 
same level will be that the upper parts of the creeks 
will have become filled up at such periods to the level 
of the water with gravel and sand ; and that afterwards 
the rivers will have thrown down on the filled-np parts 
a talus of similar matter, of which the inclination (as 
at the head of a partially filled-up lake) will have been 
determined by the supply of detritus, and the force of 
the stream. 1 Hence, after the final conversion of the 
erf eks into valleys, almost the only difference in the 
terraces at those points at which the sea stood long, will 
be a somewhat more gentle inclination, with river-worn 
instead of sea- worn detritus on the surface. 

I know of only one difficulty on the foregoing view, 
namely, the far-transported blocks of rock high on the 
sides of the valley of the Oachapual : I will not attempt 
any explanation of this phenomenon, but I may state 

present in the valleys of most of the European ranges, had not 
every trace of them, and all wrecks of sea-action, been swept away 
by the glaciers which have since occupied them. I have shown that 
this is the case with the mountains ('London and Edin. Phil,, 
Journal,' vol. xxi p. 187) of North Wales. 

1 I have attempted to explain this process in a more detailed 
manner, in a letter to Mr. Maclaren, published In the * Edinburgh 
New Phil. Journal,' voL xxxv. p. 288. 



CHAP. x. their Marine Origin. 297 

my belief that a mountain ridge near the Baths of Cau- 
quenes has been upraised long subsequently to all the 
other ranges in the neighbourhood, and that when this 
was effected the whole face of the country must have 
been greatly altered. In the course of ages, moreover, 
in tliis and other valleys, events may have occurred like. 
But even on a grander scale than, that described by 
Molina, 1 when a slip during the earthquake of 1762 
banked up for ten days the great river Lontue, which 
then bursting its barrier 4 inundated the whole country/ 
and doubtless transported many great fragments of rock. 
Finally, notwithstanding this one case of difficulty, I 
cannot entertain any doubt, that these terrace-like 
fringes, which are continuously united with the basin- 
shaped plains at the foot of the Cordillera, have been 
formed by the arrestment of river-borne detritus at 

1 ' Oompendio de la Hist.' &c. &c 1. 1. p 30. M Brongniart, ia 
his report on 11 Gay's labours ('Annales des Sciences/ 1833) con- 
siders that the boulders in the Cachapual belong to the same class 
with the erratic boulders of Europe. As the blocks which I saw are 
not gigantic, and especially as they are not angular, and as they 
have not been Transported fairly across low spaces or wide valleys, 
I am unwilling to clats them with those, which, both in the northern 
and southern hemisphere (' Geolog Transact vol. vi. p. 415), have 
been transported by ice. It is to be hoped, that when M. Gay's long- 
continued and admirable labours in Chile are published, more light 
will be thrown on this subject. However, the boulders may have 
been primarily tiansported ; the final position of those of porphyry, 
which have been described as arranged at the foot of the mountain 
in rude lines, 1 cannot doubt, has been due to the action of waves 
on a beach. The valley of the Cachapual, in the part where the 
boulders occur, bursts through the high ridge of Cauquenes, which 
runs parallel to, but at some distance from, the Cordilleia. This 
ridge has been subjected to excessive violence ; trachytic lava has 
burst from it, and hot springs yet flow at its base. Seeing the 
enormous amount of Denudation of solid rock in the upper and much 
broader paits of this valley where it enters the Coidillera, and see- 
ing to what extent the ridge of Gauquenes now protects the great 
range, I could not help believing (as alluded to in the text) that 
this ridge with its trachytic eruptions had been thrown up at a much 
later period than the Cordillera. If this has been the case, the 
boulders, after having been transported to a low level by the 
torrents (which exhibit in every valley proofs of their power of 
moving great fragments), may have been raised up to their present 
height, with the land on which they rested. 



298 Formation of Valleys. PART a. 

successive levels , in the same manner as we see now 
taking place at the heads of all those many, deep ? 
winding fiords intersecting the southern coasts. To my 
mind, this has been one of the most important con- 
clusions to which my observations on the geology of 
South America have led me ; for we thus learn that one 
of the grandest and most symmetrical mountain-chains 
in the world, with its several parallel lines/ have been 
together uplifted in mass between 7,000 and 9,000 
feet, in the same gradual manner as have the eastern 
and western coasts within the recent period. 

Formation of Valleys. 

The bulk of solid rock which has been removed in 
the lower parts of the valleys of the Cordillera has been 
enormous; it is only by reflecting on such cases as that 
of the gravel beds of Patagonia, covering so many thou- 
sand square leagues of surface, and which if heaped into 
a ridge, would form a mountain-range, almost equal to 
the Cordillera, that the amount of denudation becomes 
credible. The valleys within this range, often follow 

1 I do not wish to affirm that all the lines have been uplifted 
quite equally; slight differences in the elevation would leave no 
perceptible eiiect on the tenaces. It may, however, be inferred, 
perhaps with one exception, that since the period when the sea 
occupied these valleys, the several ranges have not been dislocated 
by great and cubruyt faults or upheavals j for if such had occurred, 
the terraces of gravel at these points would not have been conti- 
nuous. The one exception is at the lower end of a plain in the Valle 
del Teso (a branch of the Maypu), where, at a great height, the 
terraces and valley appear to have been broken through by a line of 
upheaval, of which the evidence is plain in the adjoining mountains ; 
this dislocation, perhaps, occurred ajt&r the elevatwn of this part of 
the valley above the level of the sea. The valley here is almost 
blocked up by a pile above 1,000 feet in thickness, formed, as far as 
I could judge, from three sides, entirely, or at least in chief part, of 
gravel and detritus. On the south side, the river has cut quite 
through this mass ,* on the northern side, and on the very summit 
deep ravines, parallel to the line of the valley, are worn, as if the 
drainage from the valley above had passed by the^e two lines before 
following its present course. 



. x. Formation of Valleys. 299 

anticlinal but rarely synclinal lines ; that is, the strata 
on the two sides more often dip from the line of valley 
than towards it. On the flanks of the range ? the valleys 
most frequently run neither along anticlinal nor syn- 
clinal axes, but along lines of flex are or faults ; that is, 
the strata on both sides dip in the same direction, but 
with different, though often only slightly different, 
inclinations. As most of the nearly parallel ridges 
which together form the Cordillera run approximately 
north and south, the east and west valleys cross them 
in zig-zag Iines 3 bursting through the points where the 
strata have been least inclined. No doubt the greater 
part of the denudation was affected at the periods when 
tidal creeks occupied the valleys, and when the outer 
flanks of the mountains were exposed to the full force 
of an open ocean. I have already alluded to the power 
of the ticlal action in the channels connecting great 
bays ; and I may here mention that one of the surveying 
vessels in a channel of this kind, though under sail, 
was whirled round and round by the force of the current. 
We shall hereafter see, that of the two main ridges 
forming the Chilian Cordillera, the eastern and loftiest 
one, owes the greater part of its angular upheaval to a 
period subsequent to the elevation of the western ridge ; 
and it is likewise probable that many of the other 
parallel ridges have been angularly upheaved at different 
periods ; consequently many parts of the surfaces of 
these mountains must formerly have been exposed to 
the full force of the waves, which, if the Cordillera 
were now sunk into the sea, would be protected by 
parallel chains of islands. The torrents in the valleys 
certainly have great power in wearing the* rocks ; as 
could be told by the dull rattling sound of the many 
fragments night and day hurrying downwatf s ; and as 
was attested by the vast size of certain fragments 3 which 



300 Formation of Valleys. BAEX n 

1 was assured had been carried onwards during floods ; 
yet we have seen in the lower parts of the valleys, that 
the torrents have seldom removed all the sea-checked 
shingle forming the terraces, and have had time since 
the last elevation in mass only to cat in the under- 
lying rocks, gorges, deep and narrow, but quite insigni- 
ficant in dimensions compared with the entire width 
and depth of the valleys. 

Along the shores of the Pacific, I never ceased 
during my many and long excursions to feel astonished 
at seeing every valley, ravine, and even little inequality 
of surface, both in the hard granitic and soft tertiary 
districts, retaining the exact outline, which they had 
when the sea left their surfaces coated with organic 
remains, "When these remains shall have decayed, 
there will be scarcely any difference in appearance be- 
tween this line of coast-land and most other countries, 
which we are accustomed to believe have assumed their 
present features chiefly through the agency of the 
weather and fresh-water streams. In the old granitic 
districts, no doubt it would be rash to attribute all the 
modifications of outline exclusively to the sea-action; 
for who can say how often, this lately submerged coast 
may not previously have existed as land, worn by run- 
ning streams and washed by rain ? This source of doubt, 
however, does not apply to the districts superficially 
formed of the modern tertiary deposits. The valleys 
worn by the sea, through the softer formations, both on 
the Atlantic and Pacific sides of the continent, are 
generally broad, winding, and flat-bottomed : the only 
district of this nature now penetrated by arms of the 
sea, is the Island of Chiloe. 

Finally, the conclusion at which I have arrived, 
with respect to the relative powers of rain and sea water 
on the land, is ; that the latter is far tlae most efficient 



CHAP. X. 



Formation of Valleys. 301 



agent, and that its chief tendency is to widen the 
valleys; whilst torrents and rivers tend to deepen them, 
and to remove the wreck of the sea's destroying action. 
As the waves have more power, the more open and ex- 
posed the space may be, so will they always tend to 
widen more and more the mouths of valleys compared 
with their upper parts : hence, doubtless, it is, that 
most valleys expand at their mouths, that part, at 
which the rivers flowing in them, generally have the 
least wearing power. 

When reflecting on the action of the sea on the 
land at former levels, the effect of the great waves, 
which generally accompany earthquakes, must not be 
overlooked : few years pass without a severe earthquake 
occurring on some part of the west coast of South. 
America ; and the waves thus caused have great power. 
At Concepcion, after the shock of 1835, I saw large 
slabs of sandstone, one of which was six feet long, three 
in breadth, and two in thickness, thrown high up on 
the beach ; and from the nature of the marine animals 
still adhering to it, it must have been torn up from a 
considerable (Jepth. On the other hand, at Callao, the 
recoil- wave of the earthquake of 1746 carried great 
masses of brickwork, between three and four feet square, 
some way out seaward. During the course of ages, the 
effect thus produced at each successive level, cannot 
have been small ; and in some of the tertiary deposits 
on this line of coast, I observed great boulders of 
granite and other neighbouring rocks, embedded in 
fine sedimentary layers, the transportal of which, except 
by the means of earthquake-waves, always appeared to 
me inexplicable. 



JO2 Superficial Saline Deposits. PAET n. 



Sziperficial Saline Deposits. 

This subject may be here conveniently treated of: 
I will begin with the most interesting case, namely, 
the superficial saline beds near Iquiqne in Peru. The 
porphyritic mountains on the coast rise abruptly to a 
height of between 1,900 and 8,000 feet: between their 
summits and an inland plain, on which the celebrated 
deposit of nitrate of soda lies, there is a high undulatory 
district, covered by a remarkable superficial saliferous 
crust, chiefly composed of common salt, either in white, 
hard, opaque nodules, or mingled with sand, in this 
latter case forming a compact sandstone. This sali- 
ferous superficial crust extends from the edge of the 
coast-escarpment, over the whole face of the country ; 
bat never attains, as I am assured by Mr. Bollaert 
(long resident here) any great thickness. Although a 
very slight shower falls only at internals of many years, 
yet small funnel-shaped cavities show that the salt has 
been in some parts dissolved. 1 In several places I saw 
large patches of sand, quite moist, owing to the quan- 
tity of muriate of lime (as ascertained by Mr. T. Reeks) 
contained in them. From the compact salt-cemented 
sand being either red, purplish, or yellow, according 
to the colour of the rocky strata on which it rested, 
I imagined that this substance had probably been 
derived through common alluvial action from the layers 
of salt which occur interstratified in the surrounding 
mountains : but from the interesting details given by 

1 It is singular how slowly, according to the observations of M. 
Cordier on the salt-mountain of Cardona in Spain ('Ann. des Mines 
Transl. of Geolog. Mem.* by De la Beche, p 60), salt is dissolved 
where the amount of rain is supposed to be as much as 31*4 of an 
inch in the year. It is calculated that only five feet in thickness is 
dissolved in the course of a century. 



CHAP. 



Saline Beds at Iquique. 303 



M. d'Orbigny, and from finding on a fresh, examination 
of this agglomerated sand, that it is not irregularly 
cemented, but consists of thin layers of sand of different 
tints of colour, alternating with excessively fine paral- 
lel layers of salt, I conclude that it is not of alluvial 
origin. M. d'Orbigny * observed analogous saline beds 
extending from Cobija for five degrees of latitude 
northward, and at heights varying from 600 to 900 
feet: from finding recent sea-shells strewed on these 
saliferous beds, and under them, great, well-rounded 
blocks, exactly like those on the existing beach, he 
believes that the salt, which is invariably superficial, 
has been left by the evaporation of the sea-water. This 
same conclusion must, I now believe, be extended to 
the superficial saliferous beds of Iquique, though they 
stand about 3,000 feet above the level of the sea. 

Associated with the salt in the superficial beds, 
there are numerous, thin, horizontal layers of impure, 
dirty- white, friable, gypseous and calcareous tuffs. The 
gypseous beds are very remarkable, from abounding 
with, so as sometimes to be almost composed of, irregu- 
lar concretions, from the size of an egg to that of a 
man's head, of very hard, compact, heavy gypsum, in 
the form of anhydrite. This gypsum contains some 
foreign particles of stone ; it is stained, judging from 
its action with borax, with iron, and it exhales a strong 
aluminous odour. The surfaces of the concretions are 

1 'Toy age/ &c. p. 102 M. d'Orbigny found this deposit inter- 
sected, in many places, by deep ravines, in which there was no salt. 
Streams must once, though historically unknown, have flowed in 
them ; and M. d' Orbigny argues from, the presence of undissolved 
salt over the whole surrounding country, that the streams must have 
arisen from rain or snow having fallen, not in the adjoining country, 
but on the now arid Cordillera I may remark, that from having 
observed ruins of Indian buildings in absolutely sterile parts of the 
Chilian Cordillera (* Journal,' 2nd edit. p. 357), I am led to believe 
that the climate, at a time when Indian man inhabited this part of 
the continent, was in some slight degree more humid than it is at 
present. 



304 Nitrate of Soda. PAET it 

marked by sharp, radiating, or bifurcating ridges, as if 
they had been (but not really) corroded : internally 
they are penetrated by branching veins (like those of 
calcareous spar In the septaria of the London clay) of 
pure white anhydrite. These veins might naturally 
have been thought to have been formed by subsequent 
infiltration, had not each little embedded fragment of 
rock been likewise edged in a very remarkable manner 
by a narrow border of the same white anhydrite : this 
shows that the veins must have been formed by a pro- 
cess of segregation, and not of infiltration. Some of 
the little included and cracked fragments of foreign 
rock are penetrated by the anhydrite, and portions have 
evidently been thus mechanically displaced: at St. 
Helena^ I observed that calcareous matter, deposited by 
rain-water, also had the power to separate small frag- 
ments of rock from the larger masses. I believe the 
superficial gypseous deposit is widely extended : I re- 
ceived specimens of it from Pisagua, forty miles north 
of Iquique, and likewise from Arica, where it coats a 
layer of pure salt. M. d'Orbigny l found at Oobija a 
bed of clay, lying above a mass of upraised recent shells, 
which was saturated with sulphate of soda, and included 
thin layers of fibrous gypsum. These widely extended, 
superficial, beds of salt and gypsum, appear to me an 
interesting geological phenomenon, which could be pre- 
sented only under a very dry climate. 

The plain or basin, on the borders of which the 
famous bed of nitrate of soda lies, is situated at a 
distance of about thirty miles from the sea, being sepa- 
rated from it by the saliferous district just described. 
It stands at a height of 3,300 feet ; its surface is level, 
and some leagues in width; it extends forty miles 
northward, and has a total length (as I was informed 
1 * Voyage Go!og.' &c. p. 95. 



CHAP, x. Nitrate of Soda. 305 

by Mr, Belford Wilson, the Consul-General at Lima) 
of 420 miles. In a well near tlie works, thirty-six 
yards in depth, sand, earth, and a little gravel were 
found : in another well, near Almonte, fifty yards deep, 
the whole consisted, according to Mr. Blake, 1 of clay, 
including a layer of sand two feet thick, which rested 
on fine gravel, and this on coarse gravel, with large 
rounded fragments of rock. In many parts of this now 
utterly desert plain, rushes and large prostrate trees in 
a hardened state, apparently Mimosas, are found buried, 
at a depth from three to six feet,* according to Mr. 
Blake, they have all fallen to the south-west. The bed 
of nitrate of soda is said to extend for forty or fifty 
leagues along the western margin of the plain, but is 
not found in its central parts : it is from two to three 
feet in thickness, and is so hard that it is generally 
blasted with gunpowder ; it slopes gently upwards from 
the edge of the plain to between ten and thirty feet 
above its level. It rests on sand in which, it Is said, 
vegetable remains and broken shells have been found; 
shells have also been found, according to Mr. Blake, 
both on and in the nitrate of soda. It is covered by 
a superficial mass of sand, containing nodules of common 
salt, and, as I was assured by a miner, much soft gyp- 
seous matter, precisely like that in the superficial crust 
already described : certainly this crust, with its charac- 
teristic concretions of anhydrite, comes close down to 
the edge of the plain. 

The nitrate of soda varies In purity in different 
parts, and often contains nodules of common salt. 
According to Mr. Blake, the proportion of nitrate of 
silver varies from twenty to seventy-five per cent. An " 

1 See an admirable paper, 'G-eolog. and Miscell. Notices of 
Tarapaca/ in Silliman's * American Journal/ vol. xliv. p. i. 



Saline Incrustations. PAET n. 



analysis by Mr. A. Hayes, of an average specimen, 
gave 

Nitrate of Soda ...... 64-98 

Sulphate of Soda ...... 300 

Chloride of Soda ...... 2869 

lodic Salts ....... 0-63 

Shells and Marl ...... 260 

9990 

The 'mother water' at some of the refineries is very 
rich in iodic salts, and is supposed ! to contain much 
muriate of lime. In an unrefined specimen brought 
home by myself, Mr. T. Reeks has ascertained that the 
muriate of lime is very abundant. With respect to the 
origin of this saline mass, from the manner in which 
the gently inclined, compact bed follows for so many 
miles the sinuous margin of the plain, there can be no 
doubt that it was deposited from a sheet of water : from 
the fragments of embedded shells, from the abundant 
iodic salts, from the superficial saliferous crust occur- 
ring at a higher level and being probably of marine 
origin, and from the plain resembling in form those of 
Chile and that of Uspallata, there can be little doubt 
that this sheet of water was, at least originally, con- 
nected with the sea. 2 

Thin, superficial, saline Incrustations. These 
saline incrustations are common in many parts of 
America, : Humboldt met with them on the table-land 



Literary Gazette,' 1841, p. 475. 

2 From an official document, shown me by Mr. Belford Wilson, 
it appears that the first export of nitrate of soda to Europe was in 
July 1830, on French account, in a British ship: 

Quintals. 

In 1830, the entire export was 17,300 



1831, 
1832, 
1833, 
18S4, 



40,885 
61,400 
91,335 
149,538 



> The Spanish quintal nearly equals 100 English pounds. 



CHAP. x. Saline Incrustations, 307 

of Mexico, and the Jesuit Falkner and other authors s 
state that they occur at intervals over the vast plains 
extending from the mouth of the Plata to Eioja and 
Catamarca. Hence it is that during droughts, most of 
the streams in the Pampas are saline. I nowhere met 
with these incrustations so abundantly as near Bania 
Blanca : square miles of the mud-flats, which near that 
place are raised only a few feet above the sea, just; 
enough to protect them from being overflowed, appear, 
after dry weather, whiter than the ground after the 
thickest hoar-frost. After rain the salts disappear, and 
every puddle of water becomes highly saline ; as the 
surface dries, the capillary action draws the moisture up 
pieces of broken earth, dead sticks, and tufts of grass, 
where the salt effloresces. The incrustation, where 
thickest, does not exceed a quarter of an inch. M. 
Parch appe 2 has analysed it ; and finds that the speci- 
mens collected at the extreme head of the low plain, 
near the R. Manuelo, consist of ninety-three per cent, 
of sulphate of soda, and seven of common salt ; whilst 
the specimens taken close to the coast contain only 
sixty-three per cent, of the sulphate and thirty-seven 
of the muriate of soda. This remarkable fact, together 
with our knowledge that the whole of this low muddy 
plain has been covered by the sea within the recent 
period, must lead to the suspicion that the common 
salt, by some unknown process, becomes in time 
changed into the sulphate. Friable calcareous matter 
is here abundant, and the case of the apparent double 
decomposition of the shells and salt on S. Lorenzo, 
should not be forgotten. 

The saline incrustations, near Bahia Blanca, are not 

3 Azara (' Travels/ vol. i. p. 55) considers that the Parana is the 
eastern boundary of the salif erous region j but I heard of * salitrales ' 
in the Province of Bntre Rios. 

2 M. d Orbigny's < Voyage,' &c. Part. Hist, torn, 1 p 664. 



308 Salt Lakes *ABT it, 

confined to, though, most abundant on, the low muddy 
flats ; for I noticed some oil a calcareous plain between 
thirty and forty feet above the sea, and even a little 
occurs in still higher valleys. Low alluvial tracts in 
the valleys of the rivers Negro and Colorado are also 
encrusted, and in the latter valley such spaces appeared 
to be occasionally overflowed by the river. I observed 
saline incrustations in some of the valleys of southern 
Patagonia. At Port Desire a low, flat, muddy valley 
was thickly incrusfced by salts, which on analysis by 
Mr. T. Beeks, are found to consist of a mixture of sul- 
phate and muriate of soda, with carbonate of lime and 
earthy matter. On the western side of the continent, 
the southern coasts are much too humid for this phe- 
nomenon; but in northern Chile I again met with 
similar incrustations. Oa the hardened raud, in parts 
of the broad, flat-bottomed valley of Copiapo, the saline 
matter incrusts the ground to the thickness of some 
inches : specimens, sent by Mr. Bingley to Apothe- 
caries 7 Hall for analysis, were said to consist of car- 
bonate and sulphate of soda. Much sulphate of soda is 
found in the desert of Atacama* In all parts of S. 
America, the saline incrustations occur most frequently 
on low damp surfaces of mud, where the climate is 
rather dry; and these low surfaces have, in almost 
every case, been upraised above the level of the sea 5 
within the recent period. 

Salt-lakes of Patagonia and La Plata. Salinas, 
or natural salt-lakes, occur in various formations on the 
eastern side of the continent, in .the argillaceo-calca- 
reous deposit of the Pampas, in the sandstone of the 
Bio Negro, where they are very numerous, in the pumi- 
ceous and other beds of the Patagonian tertiary forma- 
tion, arid ia small primary districts in the midst of this 
latter formation. Port S. Julian is the most southerly 



CHAP. x. of La Plata and Patagonia. 309 

point (lat. 49 to 50), at which salinas are known to 
occur, 1 The depressions, in which these salt-lakes lie, 
are from a few feet to sixty metres, as asserted by 
M. d'Orbigny, 2 below the surface of the surrounding 
plains; and, according to this same author, near the 
liio Negro they all trend, either in the KTB. and SW. 
or in E. and W. lines, coincident with the general slope 
of the plain. These depressions in the plain generally 
have one side lower than the others, but there are no 
outlets for drainage. Under a less dry climate, an 
outlet would soon have been formed, and the salt 
washed away. The salinas occur at different elevations 
above the sea; they are often several leagues in dia- 
meter ; they are generally very shallow, but there is a 
deep one in a quartz-rock formation near 0. Blanco. In 
the wet season, the whole, or a part, of the salt is dis- 
solved, being redeposited during the succeeding dry 
season. At this period the appearance of the snow- 
white expanse of salt crystallised in great cubes, is very 
striking. In a large salina, northward of the Rio Negro, 
the salt at the bottom, during the whole year, is between 
two and three feet in thickness. 

The salt rests almost always on a thick bed of black 
muddy sand, which is fetid, probably from the decay 
of the burrowing worms inhabiting it. 3 In a salina, 
situated about fifteen miles above the town of El Oar- 
men on the Bio Negro, and three or four miles from 
the banks of that river, I observed that this black mud 
rested on gravel with a calcareous matrix, similar to 
that spread over the whole surrounding plains: at Port 

1 According to Azara (* Travels,* vol. i. p 56) there are salt lakes 
as far north as Ohaco (lat. 25), on the banks of the Verrnejo. The 
salt lakes of Siberia appear (Pallas's * Tiavels,* English Trans vol i. 
p. 284) to occur in very similar depressions to those of Patagonia. 

2 * Voyage Ge"olog.' p. 63. 

s Prof Ehrenberg examined some of this muddy sand, but was 
anable to find in it any infusoria. 



3io 



Salt Lakes PAET 



St. Julian the mud, also, rested on the gravel: lience 
the depressions must have been formed anteriorly to, 
or contemporaneously with, the spreading out of the 
gravel. I was informed that one small salma occurs in 
an alluvial plain within the valley of the Rio Negro, 
and therefore its origin must be subsequent to the exca- 
vation of that valley. When I visited the salma, fifteen 
miles above the to\vn, the salt was beginning to crystal- 
lise, and on the muddy bottom there were lying many 
crystals, generally placed cross-ways of sulphate of soda 
(as ascertained by Mr. Reeks), and embedded in the mud, 
numerous crystals of sulphate of lime, from one to three 
inches in length: M. d'Orbigny 1 states that some of 
these crystals are acicular and more than even nine 
inches in length ; others are macled and of great purity: 
those I found all contained some sand in their centres. 
As the black and fetid sand overlies the gravel, and 
that overlies the regular tertiary strata, I think there 
can be no doubt that these remarkable crystals of sul- 
phate of lime have been deposited from the waters of 
the lake. The inhabitants call the crystals of selenifce, 
the padre dd sal, and those of the sulphate of soda, 
the mctclre del sal ; they assured me that both are found 
under the same circumstances in several of the neigh- 
bouring salinas ; and that the sulphate of soda is an- 
nually dissolved, and is always crystallised before the 
common salt on the muddy bottom. 2 The association 
of gypsum and salt in this case, as well as in the super- 
ficial deposits of Iquique, appears to me interesting, 
considering how generally these substances are associated 
in the older stratified formations. 

* Voyage G6olog.' p. 64. 

2 This is what might have been expected ; for M. Ballard asserts 
(*Acad des Sciences,' Oct. 7, 3844) that sulphate of soda is precipi- 
tated from, solution more readily from, water containing muriate 
of soda in excess, than from pure water. 



CHAP. x. of La Plata and Patagonia. 311 

Mr. Reeks lias analysed for me some of the salt 
from the salina near the Eio Negro, lie finds It com- 
posed entirely of chloride of sodium, with the exception 
of -2 6 of sulphate of lime and of 0*22 of earthy matter : 
there are no traces of iodic salts. Some salts from the 
salina Ohiquitos in the Pampean formation, is equally 
pure. It is a singular fact, that the salt from these 
salmas does not serve well for preserving meat, as 
sea-salt from the Gape de Verde Islands ; and a mer- 
chant at Buenos Ayres told me that he considered it as 
fifty per cent, less valuable. The purity of the Pata- 
gonian salt, or absence from it of those other saline 
bodies found in all sea-water, is the only assignable 
cause for this inferiority; a conclusion which is sup- 
ported by the fact lately ascertained, 1 that those salts 
answer best for preserving cheese which contain most of 
the deliquescent chlorides. 2 

With respect to the origin of the salt in the salinas, 
the foregoing analysis seems opposed to the view enter- 
tained by M. d'Orbigny and others, and which seems 
so probable considering the recent elevation of this line 
of coast, namely, that it is due to the evaporation of 
sea-water and to the drainage from the surrounding 
strata impregnated with sea-salt. I was informed (1 
know not whether accurately) that on the northern side 
of the salina on the Eio Negro, there is a small brine 
spring which flows at all times of the year : if this be 
so, the salt in this case at least, probably is of subter- 
ranean origin. It at first appears very singular that 

* * Hort. and Agncult Gazette,' 1845, p. 93. 

2 It would probably well answer for the merchants of Buenos 
Ayres (considering the great consumption there of salt for preserving 
meat) to import the deliquescent chlorides to mix with the salt from 
the salinas. I may call attention to the fact, that at Iquique, a large 
quantity of muriate of lime, left in the moth&r-nat&r during the 
refinement of the nitrate of soda, is annually thrown away. 



3 1 2 Salt Lakes. PAET n. 

fresh-water can often be proem ed in wells, 1 and is some- 
times found in small lakes, quite close to these salinas. 
I am not aware that this fact bears particularly on the 
origin of the salt ; but perhaps it is rather opposed to 
the view of the salt having been washed out of the 
surrounding superficial strata, but not to its having 
been the residue of sea-water, left in depressions as the 
land was slowly elevated. 

1 Sir W. Parish states (' Buenos Ayres,' &o pp. 122 and 170) that 
this is the case near the great Salinas westwaid of the S. Ventana. 
I have seen similar statements in an ancient MS Journal lately 
published by S. Angelis At Iquique, where the surface is so thickly 
encrusted with saline matter, I tasted watei only slightly brackish, 
procured in a well thirty-six yaids deep, hut here one feels less sur- 
puse at its presence, as pure water might percolate underground 
from the not very dibtant Cordilleia. 



3*3 



CHAPTER XL 

ON THE FORMATIONS OF THE PAMPAS. 

Mineralogical constitution Microscopical structure Buenos Ayres, 
shells embedded in tosca-rock Buenos Ayrcs to the Colorado 8. 
"Ventana, Bahia Blanca ; M Hermow^ bones and infusoria of; P. 
Alta, shells, bones and injusonaof; co-existence of the recent shells 
and extinct mammifers Buenos Ayres to St M Skeletons of 
Mastodon Infusoria Inferior marine tertiary strata, their age 
Horses tooth BAND A OBIENTAL Superficial Patnpean forma- 
tion, Inferior tertiary strata, variation of, connected nitk wlcatiio 
action , Macrauchenia Patachomea at S. Julian in Patagonia, age 
of, subsequent to liiing mollusca and to the erratic "block penod. 
SUMMARY Area of Pampean formation Theories of origin 
Source of sediment Estuary origin Contemporaneous with exist- 
ing mollusca Relations to underlying tertiary strata Ancient 
deposit of estuary origin Elevation and successive deposition of 
the Pampean formation Number and state of the remains of 
mammifers ; their halitatwn t food, extinction, and range Con- 
elusion Localities in Pampas at which mammif&rom remains 
have leen found. 

THE Pampean formation is highly interesting from its 
vast extent, its disputed origin, and from the number 
of extinct gigantic mammifers embedded in it. It has 
upon the whole a very uniform character: consisting of 
a more or less dull reddish, slightly indurated } argil- 
laceous earth or mud, often, but not always, including 
in horizontal lines concretions of marl, and frequently 
passing into a compact marly rock. The mud, wher- 
ever I examined it, even close to the concretions, did 
not contain any carbonate of lime. The concretions are 
generally nodular, sometimes rough externally, some- 



Pampean Formation. JART it, 

times stalactiformed ; they are of a compact structure, 
but often penetrated (as well as the mud) by hair-like 
serpentine cavities, and occasionally with irregular 
fissures in their centres, lined with minute crystals of 
carbonate of lime ; they are of white, brown, or pale 
pinkish tints, often marked by black dendritic man- 
ganese or iron ; they are either darker or lighter tinted 
than the surrounding mass; they contain much car- 
bonate of lime, but exhale a strong alumimous odour^ 
and leave, when dissolved in acids, a large but varying 
residue, of which the greater part consists of sand. 
These concretions often unite into irregular strata ; and 
over very large tracts of country, the entire mass consists 
of a hard, but generally cavernous marly rock : some 
of the varieties might be called calcareous tuffs. 

Dr. Carpenter has kindly examined under the mi- 
croscope, sliced and polished specimens of these concre- 
tions, and of the solid marl-rock, collected in various 
places between the Colorado and St. Fe Bajada. In 
the greater number, Dr. Carpenter finds that the whole 
substance presents a tolerably uniform amorphous cha- 
racter, but with traces of incipient crystalline meta- 
morphosis ; in other specimens he finds microscopically 
minute rounded concretions of an amorphous substance 
(resembling in size those in oolitic rocks, but not having 
a concentric structure), united by a cement which is 
often crystalline. In some, Dr. Carpenter can perceive 
distinct traces of shells, corals, Polythalamia, and rarely 
of spongoid bodies. For the sake of comparison, I sent 
Dr. Carpenter specimens of the calcareous rock, formed 
chiefly of fragments of recent shells, from Coquimbo in 
Chile : in one of these specimens, Dr. Carpenter finds, 
besides the larger fragments, microscopical particles of 
shells, and a varying quantity of opaque amorphous 
mattery ia another specimen from the same bed 3 he 



CHAP. xi. Pampean Formation. 315 

finds the whole composed of the amorphous matter, 
with layers showing indications of an incipient crystal- 
line metamorphosis : hence these latter specimens, both 
in external appearance and m microscopical structure, 
closely resemble those of the Pampas. Di. Carpenter 
informs me that it is ^well known that chemical preci- 
pitation throws down carbonate of lime in the opaque 
amorphous state ; and he is inclined to believe that the 
long-continued attrition of a calcareous body in a state 
of crystalline or semi-crystalline aggregation (as, for 
instance, in the ordinary shells of Mollusca, which, 
when sliced, are transparent) may yield the same result. 
From the intimate relation between all the Coquimbo 
specimens, I can hardly doubt that the amorphous 
carbonate of lime in them has resulted from the attri- 
tion and decay of the larger fragments of shell : whether 
the amorphous matter in the marly rocks of the Pampas 
has likewise thus originated, it would be hazardous to 
conjecture. 

For convenience sake, I will call the marly rock by 
the name given to it by the inhabitants, namely, Tosca 
rock; and the reddish argillaceous earth, Pampean 
mud. This latter substance, I may mention, has been 
examined for me by Professor Ehrenberg, and the 
result of his examination will be given under the proper 
localities. 

I will commence my descriptions at a central spot, 
namely, at Buenos Ayres, and thence proceed first south- 
ward to the extreme limit of the deposit, and afterwards 
northward. The plain on which Buenos Ayres stands 
is from thirty to forty feet in height. The Pampean 
mud is here of a rather pale colour, and includes small 
nearly white nodules, and other irregular strata of an 
unusually arenaceous variety of tosca-rock. in a well at 
the depth of seventy feet, according to Ignatio Nunez, 



3 1 6 Pampean Formation. IPAET n. 

much tosca-roek was met with, and at several points, 
at 100 feet deep, beds of sand have been found. I have 
already given a list of the recent marine and estuary 
shells found in many parts on the surface near Buenos 
Avres, as far as three and four leagues from the Plata, 
Specimens from near Ensenada, given me by Sir W. 
Parish, where the rock is quarried just beneath the 
surface of the plain, consist of broken bivalves, cemented 
by and converted into, white crystalline carbonate oi 
lime. I have already alluded, in the first chapter, to 
a specimen (also given me by Sir W. Parish) from the 
A. del Tristan, in which shells, resembling in every 
respect the Azara, labiata, d'Orbig ? as far as their 
worn condition permits of comparison, are embedded in 
a reddish, sottish, somewhat arenaceous marly rock: 
after careful comparison, with the aid of a microscope 
and acids, I can perceive no difference between the 
basis of this rock and the specimens collected by me 
In many parts of the Pampas. I have also stated, on 
the authority of Sir W. Parish, that northward of 
Buenos Ayres, on the highest parts of the plain, about 
forty feet above the Plata, and two or three miles from 
it, numerous shells of the Azara labiata (and I believe 
of Venus sinuosa) occur embedded in a stratified 
earthy mass, including small marly concretions and said 
to be precisely like the great Pampean deposit. Hence 
we may conclude that the mud of the Pampas continued 
to be deposited to within the period of this existing 
estuary shell. Although this formation is of such 
immense extent, I know of no other instance of the 
presence of shells in it. 

Buenos Ayres to the Rio Colorado. With the 
exception of a few metamorphic ridges, the country 
between these two points, a distance of 400 geographical 
miles j belongs to the Pampean formation, and in the 



CHAP. si. Sierra Ventana. 3 1 7 

southern part is generally formed of the harder and 
more calcareous varieties. I will briefly describe my 
route : about twenty-five miles SSW. of the capital, 
in a well forty yards in depth, the upper part, and, as I 
was assured, the entire thickness, was formed of dark 
red Pampean mud without concretions. North of the 
R. Salado, there are many lakes ; and on the banks of 
one (near the Guardia) there was a little cliff similarly 
composed, but including many nodular and stalactiform 
concretions : I found here a large piece of tesselated 
armour, like that of the Glyptodon, and many fragments 
of bones. The cliffs on the Salado consist of pale- 
coloured Pampean mud, including and passing into 
great masses of tosca-rock : here a skeleton of the 
Megatherium and the bones of other extinct quadrupeds 
(see the list at the end of this chapter) weie found. 
Large quantities of crystallized gypsum (of which 
specimens were given me) occur in the cliffs of this 
river ; and likewise (as I was assured by Mr. Lurnb) in 
the Pampean mud on the R. Chuelo, seven leagues 
from Buenos Ayres : I mention this because M. d'Or- 
bigny lays some stress on the supposed absence of this 
mineral in the Pampean formation. 

Southward of the Salado the country is low and 
swampy, with tosca-rock appearing at long intervals at 
the surface. On the banks, however, of the Tapalguen 
(sixty miles south of the Salado) there is a large extent 
of tosca-rock, some highly compact and even semi- 
crystalline 3 overlying pale Pampean mud with the usual 
concretions. Thirty miles further south, the small 
quartz-ridge of Tapalguen is fringed on its northern 
and southern flank, by little, narrow, flat-topped hills 
of tosca-rock, which stand higher than the surrounding 
plain. Between this ridge and the Sierra of Guitru- 
gueyu, a distance of sixty miles, the country is swampy, 



318 Pantpean Formation. PART n 

with the tosca-rock appearing only in four or five spots : 
this sierra, precisely like fchat of Tapalguen, is bordered 
by horizontal, often cliff-bounded, little hills of tosca- 
rock, higher than the surrounding plain. Here, also, 
a new appearance was presented in some extensive and 
level banks of alluvium or detritus of the neighbouring 
metamorphic rocks ; but I neglected to observe whether 
it was stratified or not. Between Guitru-gueyu and 
the Sierra Yentana, I crossed a dry plain of tosca-rock 
higher than the country hitherto passed over 3 and with 
small pieces of denuded table-land of the same forma- 
tion, standing still higher. 

The marly or calcareous beds not only come up 
nearly horizontally to the northern and southern foot 
of the great quartzose mountains of the Sierra Ventana, 
but interfold between the parallel ranges. The super- 
ficial beds (for I nowhere obtained sections more than 
twenty feet deep) retain, even close to the mountains, 
their usual character : the uppermost layer, however } 
in one place included pebbles of quartz, and rested on 
a mass of detritus of the same rock. At the very foot 
of the mountains, there were some few piles of quartz 
and tosca-rock detritus, including land-shells ; but at 
the distance of only half a mile from these lofty, jagged, 
and battered mountains, I could not, to my great sur- 
prise, find on the boundless surface of the calcareous 
plain even a single pebble. Quartz-pebbles, however, 
of considerable size have at "some period been trans- 
ported to a distance of between forty and fifty miles to 
the shores of Bahia Blanca. 1 

The highest peak of the S. Ventaua is, by Captain 
FitzEoy's measurement, 8,340 feet, and the calcareous 
plain at its foot (from observations taken, by some 

1 Schraidtmeyer (* Travels in Chile/ p. 150) states that he first 
potioed on the Pampas, very small bits of red granite, when fifty 
miles distant from the southern extremity of the mountains of 
Cordova, which project on the plain, like a reef into the sea. 



CHAP. xi. Sierra Ventana. 319 

Spanish officers ! ) 840 feet above the sea-level. On the 
flanks of the mountains, at a height of 300 or 400 feet 
above the plain, there were a few small patches of con- 
glomerate and breccia, firmly cemented by ferruginous 
matter to the abrupt and battered face of the quartz 
traces being thus exhibited of ancient sea-action. The 
high plain round this range sinks quite insensibly to 
the eye on all sides, except to the north, where its 
surface Is broken into low cliffs. Bound the Sierras 
Tapalguen, Guitru-gueyu, and between the latter 
and the Ventana we have seen (and shall hereafter 
see round some hills in Banda Oriental), that the 
tosca-rock forms low, flat-topped, cliff-bounded hills, 
higher than the surrounding plains of similar compo- 
sition. Prom the horizontal stratification and from 
the appearance of the broken cliffs, the greater height 
of the Pampean formation round these primary hills 
ought not to be altogether or in chief part attributed 
to these several points having been uplifted more ener- 
getically than the surrounding country, but to the 
argillaceo-calcareous mud having collected round them, 
when they existed as islets or submarine rocks, at a 
greater height, than at the bottom of the adjoining 
open sea ; the cliffs having been subsequently worn 
during the elevation of the whole country in mass. 

Southward of the Ventana, the plain extends farther 
than the eye can range; its surface is not very level, 
having slight depressions with no drainage exits ; it is 
generally covered by a few feet in thickness of sandy 
earth ; and in some places, according to M. Parchappe, 2 
by beds of clay two yards thick. On the banks of the 
Sauce, four leagues SE. of the Ventana, there is an im- 
perfect section about 200 feet in height, displaying in 
the tipper part tosca-rock and in the lower part red 

1 l La Plata,' &c. by Sir W. Parish, p. 146. 

2 M d'Orbigny. Voyage, Part. Gteolog.' pp. 47, 48. 



22O Pampean Formation. PART n. 

Paiiipean mud. At the settlement of BaHa Blanca, 
the uppermost plain is composed of very compact, 
stratified tosca-rock, containing rounded grains of 
quartz distinguishable by the naked eye: the lower 
plain, on which the Fortress stands, is described by 
M. Parchappe 1 as composed of solid tosca-rock , but the 
sections which I examined appeared more like a re- 
deposited mass of this rock, with small pebbles and frag- 
ments of quarfcz. I shall immediately return to the 
important sections on the shores of Bahia Blanca. 
Twenty miles southward of this place, there is a re- 
markable ridge extending W. by N. and E. by S., 
formed of small, separate, flat-topped, steep-sided hills, 
rising between 100 and 200 feet above the Pampean 
plain at its southern base, which plain is a little lower 
than that to the north. The uppermost stratum in 
this ridge consists of pale, highly calcareous, compact 
tosca-rock, resting (as seen in one place) on reddish 
Pampean mud, and this again on a paler kind : at the 
foot of the ridge, there is a well in reddish clay or 
mud. I have seen no other instance of a chain of hills 
belonging to the Pampean formation ; and as the 
strata shows no signs of disturbance, and as the direc- 
tion of the ridge is the same with that common to all 
the metam orphic lines in this whole area, I suspect 
that the Pampean sediment has in this instance been 
accumulated on and over a ridge of hard rocks, instead 
of. as in the case of the above-mentioned Sierras, round 
their submarine flanks. South of this little chain of 
tosca-rock, a plain of Pampean mud declines towards 
the banks of the Colorado : in the middle a well has been 
dug in red Pampean mud, covered by two feet of white 
softish, highly calcareous tosca-rock, over which lies sand 
with small pebbles three feet in thickness the first 
appearance of that vast shingle formation described in 
1 M. d'Orbigny, Voyage, Part GSolog.' pp. 47, 48. 



CHAP. xi. Bahia Blanca* 3 2 1 

the eighth chapter. In the first section after crossing 
the Colorado, an old tertiary formation, namely, the Eiu 
Negro sandstone (to be described in the next chapter), is 
met with : but from the accounts given me by the Gau- 
chos, I believe that at the mouth of the Colorado the 
Pampean formation extends a little farther southwards. 
Bahia Blanca, To return to the shores of this 
bay. At Monte Hermoso there is a good section, 
about 100 feet in height, of four distinct strata, appear- 
ing to the eye horizontal, but thickening a little 
towards the NW. The uppermost bed, about twenty 
feet in thickness, consists of obliquely laminated, soft 
sandstone, including many pebbles of quartz, and fall- 
ing at the surface into loose sand. The second bed, only 
six inches thick, is a hard, dark-coloured sandstone. 
The third bed is pale-coloured Pampean mud; and 
the fourth is of the same nature, but darker coloured, 
including in its lower part horizontal layers and lines 
of concretions of not very compact pinkish tosca-rock. 
The bottom of the sea, I may remark, to a distance of 
several miles from the shore, and to a depth of between 
sixty and one hundred feet, was found by the anchors 
to be composed of tosca-rock and reddish Pampean 
mud. Professor Ehrenberg has examined for me speci- 
mens of the two lower beds, and finds in them three 
Polygastrica and six Phytolitharia. 1 Of these, only 
one (jSpongolithis Fustis ? ) is a marine form ; five of 
them are identical with microscopical structures, of 

1 The following list is given in the Monatsberichten der konig. 
Akad zu Berlin/ April 1845 : 

POLYGASTEICA. 

Fragilaria rhabdosoma. | Pinnularia ? 

G-ailionella distans. | 

PHYTOLITHAEIA. 



lathodontium Bursa. 

furcatum. 

Lithostylidium exesum. 



Lithostylidium rude. 

Serra. 

SpongolitMs Fustis 1 



322 Pampean Formation. PAET n. 

brackish-water origin, hereafter to be mentioned, from 
a central point in the Pampean formation. In these 
two beds, especially in the lower one, bones of extinct 
mammifers, some embedded in their proper relative 
positions and others single, are very numerous in a small 
extent of the cliffs. These remains consist of, first, 
the head of Gtenomys antiquus, allied to the living 
0. Brasiliensis ; secondly, a fragment of the remains 
of a rodent ; thirdly, molar teeth and other bones of a 
large rodent, closely allied to, but distinct from, the 
existing species of Eydrochoerus, and therefore probably 
an inhabitant of fresh water ; fourth and fifthly, portions 
of vertebras, limbs, ribs, and other bones of two rodents; 
sixthly, bones of the extremities of some great mega- 
theroid quadruped. 1 The number of the remains of 
rodents gives to this collection a peculiar character, 
compared with those found in any other locality. All 
these bones are compact and heavy ; many of them are 
stained red, with their surfaces polished ; some of the 
smaller ones are as black as jet. 

Monte Hermoso is between fifty and sixty miles 
distant in a SE. line from the Ventana, with the inter- 
mediate country gently rising towards it, and all con- 
sisting of the Pampean formation. What relation, 
then, do these beds, at the level of the sea and under 
it, bear to those on the flanks of the Ventana, at the 
height of 840 feet, and on the flanks of the other 
neighbouring sierras, which, from the reasons already 
assigned, do not appear to owe their greater height to 
unequal elevation ? When the tosca-rock was accumu~ 
lafcing round the Ventana, and when, with the exception 
of a few small ragged primary islands, the whole wide 

1 See * Fossil Mammalia,' (p. 109), by Professor Owen, in the 
Zoology of the Vojage of the Beagle ; ' and Catalogue (p 36) of 
* Jfossil Remains in Museum of Royal College of Surgeons. 3 



CHAP. si. Bahia, Blanca. 323 

surrounding plains must have been under water, were 
the strata at Monte Hertnoso depositing at the bottom 
of a great open sea, between 800 and 1,000 feet in 
depth ? I much doubt this ; for if so, the almost per- 
fect carcasses of the several small rodents, the remains 
of which are so ver}' numerous in so limited a space, 
musfc have been drifted to this spot from the distance 
of many hundred miles. It appears to me far more 
probable, that during the Pampean period this whole 
area had commenced slowly rising (and in the cliffs, at 
several different heights, we have proofs of the land 
having been exposed to sea-action at several levels), and 
that tracts of land had thus been formed of Pampean 
sediment round the Ventana and the other primary 
ranges, on which the several rodents and other quadru- 
peds lived, and that a stream (in which perhaps the 
extinct aquatic Hydrochoerus lived) drifted their bodies 
into the adjoining sea, into which the Pampean mud 
continued to be poured from the north. As the land 
continued to rise, it appears that this source of sediment 
was cut off; and in its place sand and pebbles were 
borne down by stronger currents, and conformably de- 
posited over the Pampean strata. 

Punta Alta is situated about thirty miles higher up 
on the northern side of this same bay : it consists of 
a small plain, between twenty and thirty feet in height, 
cut off on the shore by a line of low cliffs about a mile 
in length, represented in the diagram, with its vertical 
scale necessarily exaggerated. The lower bed (A) is 
more extensive than the upper ones ; it consists of 
stratified gravel or conglomerate, cemented by calcareo- 
arenaceous matter, and is divided by curvilinear layers 
of pinkish marl, of which some are precisely like tosca- 
rock, and some more sandy. The beds are curvilinear, 
owing to the action of currents^ and dip iu different 
22 



324 Pampean Formation. PABT u. 

directions; they include an extraordinary number of 
bones of gigantic mamnaifers and many shells. The 
pebbles are of considerable size, and are of hard sand- 
stone, and of quartz, like that of the Ventana : there 
are also a few well-rounded masses of tosca-rock. 
No 29. 

Section of Bed*, with Becent Shells and Extinct Mammifers, at Puuta Alta in 
Batua Blauca. 




The second bed (B) is about fifteen feet in thickness,, 
but towards both extremities of the cliff (not included 
in the diagram) it either thins out and dies away, or 
passes insensibly into an cverlying bed of gravel. It 
consists of red, tough clayey mud, with minute linear 
cavities; it is marked with faint horizontal shades of 
colour ; it includes a few pebbles, and rarely a minute 
particle of shell : in one spot, the dermal armour and a 
few bones of a Dasypoid quadruped were embedded in 
it : it fills up furrows in the underlying gravel. With 
the exception of the few pebbles and particles of shells, 
this bed resembles the true Pampean mnd ; but it still 
more closely resembles the clayey flats (mentioned in 
the eighth chapter) separating the successively rising 
parallel ranges of sand-dunes. 

The bed (0) is of stratified gravel, like the lowest 
one; it fills up furrows in the underlying red mud, and 
is sometimes interstratified with it, and sometimes in- 
sensibly passes into it ; as the red mud thins out, this 
upper gravel thickens. Shells are more numerous in 
it than in the lower gravel; but the bones, though 
some are still present, are less numerous. In one part, 
however 3 where this gravel and the red mud passed into 



CHAP. 



Bahia Blanca. 



325 



each other, I found several bones and a tolerably per- 
fect head of the Megatherium. Some of the large 
Volutas, though embedded In the gravel-bed (C), were 
filled with the red mud, including great numbers of the 
little recent Paludestrina australis. These three lower 
beds are covered by an unconformable mantle (D) of 
stratified sandy earth, including many pebbles of quartz, 
pumice and phonolite, land and sea-shells. 

M. d'Orbigny has been so obliging as to name for 
me the twenty species of Mollusca embedded in the two 
gravel beds ; they consist of 

1. Volutella angulata, d'Orblg. 12 

' Voyage' Mollu&q. and Pal. 13 

2. Yoluta Brasihana, Sol. 14. 

3. Ohcancilleria Brasiliensis, 

[d'Oibig 

auriculana, do 

Ohvma puelchana, do 
Buccinanops cochlidmm, do. 
globulosum, do. 
Colombella sertulariamm, do. 
9 Trochus Patagonicus, and var. 
of ditto, d'Orbig. 

10. Paludestrina australis, 

[d Orbig. 

11. Fissurella Patagomca^^ do. 



Ciepidulamurlcata, Lam. 
Venus pnrpurata, do. 

rostrata, Phillippi. 



15 Mytilus Darwiuianus, 

[d'Orbig 

16 Nucula semiornata, do. 
17. Cardita Patagooica, do. 

18 Corbula (?) do. 

19 Pecten tethuelchus, do. 

20. Ostrea puelonana, do. 

21. A living species of Balanus. 

22. and 23 An Astoa and en- 

crusting Flustra, apparently 
identical with species now 
living in the Bay. 

All these shells now live on this coast, and most of them 
in this same bay. I was also struck with the fact, that 
the proportional numbeis of the different kinds appeared 
to be the same with those now cast up on the beach : 
in both cases specimens of Voluta, Crepidula, Venus, 
and Trochus are the most abundant. Four or five of 
the species are the same with the upraised shells on 
the Pampas near Buenos Ayres, All the specimens 
have a very ancient and bleached appearance, 1 and do 
not emit, when heated, an animal odour; some of them 

1 A Bu linns, mentioned in the Introduction to the * Fossil Mam- 
malia in the Zoology of the 03 age of the Beagle/ has so much 
fiesher an appearance, than the marine species, that I suspect it 
must have fallen amongst the others, and "been collected by mistake. 



326 Pampean Formation. PAET ir. 

are changed throughout into a white, soft, fibrous sub- 
stance; others have the space between the external 
walls, either hollow, or filled up with crystalline car- 
bonate of lime. 

The remains of the extinct mammiferous animals, 
from the two gravel beds have been described by Pro- 
fessor Owen in the ' Zoology of the Voyage of the Beagle : 5 
they consist of 1st, one nearly perfect head and three 
fragments of heads of the Megatherium Cuvierii ; 2nd, 
a lower jaw of Megalonyx Jeffersonii ; 3rd, lower jaw 
of Mylodon Dtwwinii', 4th, fragments of a head of 
some gigantic Edental quadruped ; 5th, an almost entire 
skeleton of the great Scelidotherium leptncephalum, 
with most of the bones, including the head, vertebrse, 
ribs, some of the extremities to the claw-bone, and even, 
as remarked by Professor Owen, the knee-cap, all nearly 
in their proper relative positions; 6th, fragments of 
the jaw and a separate tooth of a Toxodon, belonging 
either to T. Platensis, or to a second species lately dis- 
covered near Buenos Ayres ; 7th, a tooth of Hlquus 
curvidens ; 8th, tooth of a Pachyderm, closely allied to 
Pal^potheriuni, of which parts of the head have been 
lately sent from Buenos Ayres to the British Museum ; 
in all probability this pachyderm is identical with the 
Ma&raiwlienia Patachonica from Port S. Julian, here- 
after to be referred to. Lastly, and 9thly, in a cliff of 
the red clayey bed (B), there was a double piece, about 
three feet long and two wide, of the bony armour of a 
large Dasypoid quadruped, with the two sides pressed 
nearly close together : as the cliff is now rapidly wash- 
ing away, this fossil probably was lately much more 
perfect ; from between its doubled-up sides, I extracted 
the middle and ungueal phalanges, united together, of 
one of the feet, and likewise a separate phalang : hence 
one or more of the limbs must have been attached to 



CHIP, xi, Bahid Blanca. 327 

the dermal case, when It was embedded. Besides these 
several remains in a distinguishable condition, there 
were very many single bones : the greater number were 
embedded in a space 200 yards square. The prepon- 
derance of the Edental quadrupeds is remarkable ; as 
is, in contrast with the beds of Monte Hermoso, the 
absence of Rodents. Most of the bones are now in a 
soft and friable condition, and, like the shells, do not 
emit when burnt an animal odour. The decayed state 
of the bones may be partly owing to their late exposure 
to the air and tidal waves. Barnacles, Serpulas and 
corallines are attached to many of the bones, but I 
neglected to observe 1 whether these might not have 
grown on them since being exposed to the present tidal 
action ; but I believe that some of the barnacles must 
have grown on the Scelidotherium, soon after being 
deposited, and before being wholly covered up by the 
gravel. Besides the remains in the condition here 
described, I found one single fragment of bone very 
much rolled, and as black as jet, so as perfectly to re- 
semble some of the remains from Monte Herrnoso, 

Very many of the bones had been broken, abraded, 
and rolled, before being embedded. Others, even some 
of those included in the coarsest parts of the now hard, 
conglomerate, still retain all their minutest promi- 
nences perfectly preserved 5 so that I conclude that 
they probably were protected by skin ; flesh, or ligaments, 
whilst being covered up. In the case of the Scelido- 
therium, it is quite certain that the whole skeleton 
was held together by its ligaments, when deposited in 
the gravel in which I found it. Some cervical vertebras 
and a humerus of corresponding size lay so close to- 

1 After having packed up my specimens at Baliia Blanca, this 
point occurred to me, and I noted it ; but forgot it on my return, 
until the remains had been cleaned and oiled : my attention was 
afterwards recalled to the subject by some remarks by M d'0rbigny< 



328 Pampean Formation. IPART n. 

gather, as did some ribs and the bones of a leg, that I 
thought that they must originally have belonged to two 
skeletons, and not have been washed in single ; but as 
remains were here very numerous, I will not lay much 
stress on these two cases. We have just seen that the 
armour of the Dasypoid quadruped was certainly em- 
bedded together with some of the bones of the feet- 
Professor Ehrenberg l has examined for me speci- 
mens of the finer matter from in contact with these 
mammiferous remains : he finds In them two Polygas- 
trica, decidedly marine forms ; and six Phytolitharia, 
of which one is probably marine, and the others either 
of fresh- water or terrestrial origin. Only one of these 
eight microscopical bodies is common to the nine from 
Monte Hermoso : but five of them are in common with 
those from the Pampeaa mud on the banks of the 
Parana. The presence of any fresh-water Infusoria, 
considering the aridity of the surrounding country, is 
here remarkable : the most probable explanation appears 
to be, that these microscopical organisms were washed 
out of the adjoining great Pampean formation during 
Its denudation, and afterwards redeposited, 

We will now see what conclusions may be drawn 
from the facts above detailed. It is certain that the 
gravel-beds and intermediate red mud were deposited 
within the period, when existing species of Mollusca 
held to each other nearly the same relative proportions 

1 * Mpnatsberichten der konig. Akad. zu Berlin,' April, 1845 The 
list consists of, 

POLYGASTBICA. 

Gallionella sulcata, | Stauroptera aspera 1 f ragnx 

PHYTQLITHARIA. 

LithasteriscnstuTberctilatus. I Spongolithis ackmlaris 

Lithostyhditun Clepsammidmnx, 
qnadratura. 

rude, 

n untdentatum.. 



CHAP. xi. Bahia Blanc. 329 

as they do on the present coast. These beds, from the 
number of littoral species, must have been accumulated 
in shallow water ; but not, judging from the stratifica- 
tion of the gravel and the layers of marl, on a beach. 
From the manner in which the red clay fills up furrows 
in the underlying gravel, and is in some parts itself 
furrowed by the overlying gravel, whilst in other parts 
it either insensibly passes into, or alternates with, this 
upper gravel, we may infer several local changes in the 
currents, perhaps caused by slight changes, up or down, 
in the level of the land. By the elevation of these 
beds, to which period the alluvial mantle with pumice- 
pebbles, land and sea-shells belongs, the plain of Punta 
Alta, from twenty to thirty feet in height, was formed. 
In this neighbourhood there are other and higher sea- 
formed plains and lines of cliffs in the Pampean forma- 
tion worn by the denuding action of the waves at 
different levels. Hence we can easily understand the 
presence of rounded masses of tosca-rock in this lowest 
plain; and likewise, as the cliffs at Monte Hermoso 
with their mammiferous remains stand at a higher level, 
the presence of the one much-rolled fragment of bone 
which was as black as jet : possibly some few of the 
other much-rolled bones may have been similarly de- 
rived, though I saw only the one fragment, in the same 
condition with those from Monte Hermoso. M. d'Or- 
bigny has suggested l that all these mammiferous 
remains may have been washed out of the Patnpean 
formation, and afterwards redeposited together with 
the recent shells. Undoubtedly it is a marvellous fact 
that these numerous gigantic quadrupeds, belonging, 
with the exception of the jEquus curvidens, to seven 
extinct genera, and one, namely, the Toxodon, not 
falling into any existing family, should have co-existed 
1 * Voyage, Part. GSolog/ p. 49, 



Pantpean Formation. *ABX n, 

with Mollnsca, all of which are still living species; bufc 
analogous facts have been observed in N. America and 
in Europe. In the first place, it should not be over- 
looked, that most of the co-embedded shells have a 
more ancient and altered appearance than the bones. 
In the second place, is it probable that numerous bones 
not hardened by silex or any other mineral, could have 
retained their delicate prominences and surfaces perfect 
if they had been washed out of one deposit, and re- 
embedded in another ; this later deposit being formed 
of large, hard pebbles, arranged by the action of currents 
or breakers in shallow water into variously curved and 
inclined layers ? The bones which are now in so perfect 
a state of preservation, must, I conceive, have been 
fresh and sound when embedded, and probably were 
protected by skin, flesh, or ligaments. The skeleton of 
the Scelidotherium indisputably was deposited entire : 
shall we say that when held together by its matrix it 
was washed oat of an old gravel -bed (totally unlike in 
character to the Pampean formation), and re-embedded 
in another gravel-bed, composed (I speak after careful 
comparison) of exactly the same kind of pebbles, in 
the same kind of cement ? I will lay no stress on the 
two cases of several ribs and bones of the extremities 
having apparently been embedded in their proper 
relative position : but will anyone be so bold as to affirm 
that it is possible, that a piece of the thin tesselated 
armour of a Dasypoid quadruped, at least three feet 
long and two in width, and now so tender that I was 
unable with the utmost care to extract a fragment more 
than two or three inches square, could have been washed 
out of one bed, and re-embedded in another, together 
with some of the small bones of the feet, without having 
been dashed into atoms ? We must then wholly reject 



CHAP. xi. Buenos Ay res to St. Ft Bajada. 331 

M. d'Orbigny's supposition, and admit as certain, that 
the Scelidotherium and the large Dasypoid quadruped, 
and as highly probable, that the Toxodon, Megatherium, 
&c., some of the bones of which are perfectly preserved, 
were embedded for the first time, and in a fresh condi- 
tion, in the strata in which they were found entombed. 
These gigantic quadrupeds, therefore, though belonging 
to extinct genera and families, co-existed with the 
twenty above-enumerated Mollusca, the barnacle and 
two corals, still living on this coast. From the rolled 
fragment of black bone, and from the plain of Punta 
Alta being lower than that of Monte Hermoso, I con- 
clude that the coarse sub-littoral deposits of Punta Alta, 
are of subsequent origin to the Pampean mud of Monte 
Hermoso ; and the beds at this latter place, as we have 
seen, are probably of subsequent origin to the high 
tosca-plain round the Sierra Ventana : we shall, how- 
ever, return, at the end of this chapter, to the considera- 
tion of these several stages in the great Pampean 
formation. 

Buenos Ayres to St. F6 Bajada in Untre Bios, 
For some distance northward of Buenos Ayres, the 
escarpment of the Pampean formation does not approach 
very near to the Plata, and it is concealed by vegeta- 
tion : but in sections on the banks of the Kios Luxan, 
Areco, and Arrecifes, 1 observed both pale and dark 
reddish Pampean mud, with small, whitish concretions 
of tosca ; at all these places mammiferous remains have 
been found. In the cliffs on the Parana, at San Nicolas, 
the Pampean mud contains but little tosca; here M. 
d'Orbigny found the remains of two rodents (Ctenomys 
Bonariensis and Kerodon antiques) and the jaw of a 
Cards : when on the river I could clearly distinguish in 
this fine line of cliffs, < horizontal lines of variation 



332 Pampean Formation, PAKT it. 

both In tint and compactness.' 1 The plain northward of 
tins point is very level, but with some depressions and 
lakes; I estimated its height at from forty to sixty feet 
above the Parana. At the A. Meclio the bright red 
Pampean mud contains scarcely any tosca-rock ; whilst 
at a short distance the stream of the Pabon forms a 
cascade, about twenty feet in height, over a cavernous 
mass of two varieties of tosca-rock ; of which one is 
very compact and semi-crystalline, with seams of crys- 
tallised carbonate of lime : similar compact varieties 
are met with on the Sahdillo and Seco. The absolute 
identity (I speak after a comparison of my specimens) 
between some of these varieties, and those from Tapal- 
guen., and from the ridge south of Bahia Blanca, a dis- 
tance of 400 miles of latitude, is very striking. 

At Eosario there is but little tosca-rock : near this 
place I first noticed at the edge of the river traces of 
an underlying formation, which, twenty-five miles 
higher up in the estancia of Gorodona, consists of a 
pale yellowish clay, abounding with concretionary 
cylinders of a ferruginous sandstone. This bed, which 
is probably the equivalent of the older tertiary marine 
strata, immediately to be described in Entre Rios, only 
just rises above the level of the Parana when low. The 
rest of the cliff at Gorodona, is formed of red Pampean 
mud, with, in the lower part, many concretions of 
tosca, some stalactiformed, and with only a few in the 
upper part : at the height of six feet above the river, 
two gigantic skeletons of the Mastodon Andium were 
here embedded; their bones were scattered a few feet 
apart, but many of them still held their proper relative 
positions: they were much decayed and as soft as cheese, 

1 I quote these words from my note-book, as written down on 
the spot, on account of the general absence of stratification in the 
Painpean formation having been insisted on by M. d'Orbigny as a 
proof of the diluvial origin of this great deposit. 



CHAP. xi. - St. F Bajada, 333 

so that even one of the great molar teeth fell into 
pieces in my hand. We here see that the Pampean 
deposits contains rnammiferous remains close to its base. 
On the banks of the Carcarana, a few miles distant, the 
lowest bed visible was pale Pampean mud, with masses 
of tosca-rock, in one of which I found a much decayed 
tooth of the Mastodon: above this bed, there was a 
thin layer almost composed of small concretions of 
white tosca, out of which I extracted a well preserved, 
but slightly broken tooth of Toxodon Platensis : above 
this there was an unusual bed of very soft impure sand- 
stone. In this neighbourhood I noticed many single 
embedded bones, and I heard of others having been 
found in so perfect a state that they were long used as 
gate-posts : the Jesuit Falkner found here the dermal 
armour of some gigantic Edental quadruped. 

In some of the red mud scraped from a tooth of 
one of the mastodons at Gorodona, Professor Ehrenberg 
finds seven Polygastrica and thirteen Phytolitharia, 1 all 
of them, I believe, with two exceptions, already known 
species. Of these twenty, the preponderating number 
are of fresh-water origin ; only two species of Coscino- 
discus and a Spongolithis show the direct influence of 

1 ' Monatsberichten der konlg Akad. zu Berlin/ April, 1845. The 
list consists of : 

POLYGASTRICA. 



Cfimpylodiscus clypeus. 
Coscinodiscns subtilis. 



al. sp. 



Grallionella gratmlata. 
Himantidium giacile. 
Pinnularia borealis. 



Eunotia. 

PHYTOLITHAKTA. 



Lithasteriscus tuberculatus. 
Lithodontium bursa. 

furcatum. 

rostral urn. 

Lithostylidmm Amphiodon. 



sammidium. 



Clep- 



Lithostylidiura Hamtis, 
polyedrum. 
quadratom. 



rude. 

Serra. 

uniden- 



tafram. 



SpongolitMs Fustis. 



334 Pampean Formation. PAET n, 

the sea; therefore Professor Ehrenberg arrives at the 
Important conclusion that the deposit must have been 
of brackish-water origin. Of the thirteen Phy tolitharia, 
nine are met with in the two deposits in Bahia Blanca, 
where there is evidence from two other species of 
Polygastrica that the beds were accumulated in brackish 
water. The traces of corals, sponges, and Polythalamia, 
found by Dr. Carpenter in the tosca-rock (of which I 
must observe the greater number of specimens were 
from the upper beds in the southern parts of the 
formation), apparently show a more purely marine 
origin, 

At St. F& Bajada, in Entre Rios, the cliffs, esti- 
mated at between sixty and seventy feet in height, 
expose a.n interesting section : the lower half consists 
of tertiary strata with marine shells, and the upper half 
of the Pampean formation. The lowest bed is an 
obliquely laminated, blackish, indurated mud, with 
distinct traces of vegetable remains. 1 Above this there 
is a thick bed of yellowish sandy clay, with much crys- 
tallised gypsum and many shells of Ostrese, Pectens, 
and Arcaa : above this there generally comes an arena- 
ceous crystalline limestone, but there is sometimes 
interposed a bed, about twelve feet thick, of dark green, 
soapy clay, weathering into small angular fragments. 
The limestone, where purest, is white, highly crystalline, 
and full of cavities : it includes small pebbles of quartz, 
broken shells, teeth of sharks, and sometimes, as I was 
informed, large boues : it often contains so much sand 
as to pass into a calcareous sandstone, and in such 

1 M. d'Orbigny has given (* Voyage, Part G-golog * p. 37) a 
detailed description of this section, "but as he d es not mention this 
lowest bed, it may have been concealed when he was there by the 
river. There Is a considerable discrepancy between his description 
and mine, which I can only account for by the beds themselves 
varying- considerably in short distances. 



CHAP, xi, St. F Bajada. 335 

parts the great Ostrea Patagonica 1 chiefly abounds. 
In the upper part, the limestone alternates with layers 
of fine white sand. The shells included in these beds 
have been named for me by M. d'Orbigny; they consist 
of- 

1. Ostrea Patagonica, d'Orbig. 



4 Voyage,' Part. Pal. 

2. Alvarezii, do. 

3. Pecten Paranensis, do (and 

PI IV of this work, fig HO), 

4. JDarvviniamis, do and PI 

IV of this work, figs 28, 29. 



5 Venus Munsterii, d'Orbig. 

* Voyage/ Pal 
6. Area Bonplandiana, do. 

7 Cardium Platen^e, do. 

8 Tellina, probably nov spec., 

but too imperfect for de- 
scription. 



These species are all extinct : the six first were 
found by M. d'Orbigny and myself in the formations of 
the Rio Negro, 8. Josef, and other parts of Patagonia ; 
and therefore, as first observed by M. d'Orbigny, these 
beds certainly belong to the great Patagonian forma- 
tion, which will be described in the ensuing chapter, 
and which we shall see must be considered as a very 
ancient tertiary one. North of the Bajada, M. d'Orbigny 
found, in beds which he considers as lying beneath the 
strata here described, remains of a Toxodon, which he 
has named as a distinct species from the T. Platensis 
of the Pampean formation. Much silicified wood is 
found on the banks of the Parana (and likewise on the 
Uruguay), and I was informed that they come out of 
these lower beds; four specimens collected by myself 
are dicotyledonous. 

The upper half of the cliff, to a thickness of about 
thirty feet, consists of Pampean mud, of 'which the 
lower part is pale coloured, and the upper part of a 
brighter red, with some irregular layers of an arenaceous 
variety of tosca, and a few small concretions of the 
ordinary kind Close above the marine limestone, 

1 Oapt Sulivan E N , has given me a specimen of this shel! 9 
which he found in the cliffs at Point Cerrito, between twenty and 
thirty miles above the Bajada. 



336 Pampean Formation, PART n, 

there Is a thin stratum with, a concretionary outline of 
white hard tosca-rock or marl, which may be considered 
either as the uppermost bed of the inferior deposits, 
or the lowest of the Pampean formation ; at one time 
I considered this bed as marking a passage between 
the two formations; but I have since become convinced 
that I was deceived on this point. In the section on 
the Parana, I did not find any mammiferous remains ; 
but at two miles distance on the A. Tapas (a tributary 
of the Conchitas), they were extremely numerous in a 
low cliff of red Pampean mud with small concretions, 
precisely like the upper bed on the Parana. Most of 
the bones were solitary and much decayed ; but I saw 
the dermal armour of a gigantic Edental quadruped, 
forming a cauldron-like hollow, four or five feet in 
diameter, out of which, as I was informed, the almost 
entire skeleton had been lately removed. I found single 
teeth of the Mastodon Andium, Toxodon Platensis, 
and Hlquus eurvidens, near to each other. As this 
latter tooth approaches closely to that of the common 
horse, I paid particular attention to its true embedment, 
for I did not at that time know that there was a similar 
tooth hidden in the matrix with the other mammiferous 
remains from Punta Alta, It is an interesting circum- 
stance, that Prof. Owen finds that the teeth of this 
horse approach more closely in their peculiar curvature 
to a fossil specimen brought by Mr. Lyell 1 from North 
America, than to those of any other species of Equns. 

The underlying marine tertiary strata extend over a 
wide area: I was assured that they can be traced in 
ravines in an east and west line across Entre Rios to 
the Uruguay, a distance of about 135 miles. In a SE, 
direction I heard of their existence at the head of the 

1 Lyell's * Travels in North America,* vol. i. p. 164, and * Proc. oi 
Geolog. Soc.' vol. iv. p. 39. 



CHAP. XL Banda Oriental. 337 

E. Nankay ; and at P. Gorda in Banda Oriental, a 
distance of 170 miles, I found the same limestone, 
containing the same fossil shells, lying at about the 
same level above the river as at St. F6. In a southerly 
direction, these beds sink in height, for at another P. 
Gorda in Entre Bios, the limestone is seen at a much 
less height; and there can be lit Lie doubt that the 
yellowish sandy clay, on a level with the river, between 
the Carcarana and S. Nicolas, belongs to this same 
formation ; as perhaps do the beds of sand at Buenos 
Ayres, which lie at the bottom of the Pampean forma- 
tion, about sixty feet beneath the surface of the Plata. 
The southerly declination of these beds may perhaps be 
due, not to unequal elevation, but to the original form 
of the bottom of the sea, sloping from land situated to 
the north ; for that land existed at no great distance, 
we have evidence in the vegetable remains in the lowest 
bed at St. Fe ; and in the silicified wood and in the 
bones of Toxodon Pamnensis^ found (according to 
M. d'Orbigny) in still lower strata. 

Banda Oriental. This province lies on the north- 
ern side of the Plata, and eastward of the Uruguay : it 
has a gently undulatory surface, with a .sis of primary 
rocks 5 and is in most parts covered up with an un- 
stratified mass, of no great thickness, of reddish 
Pampean mud. In the eastern half, near Maldonado, 
this deposit is more arenaceous than in the Pampas ; it 
contains many though small concretions of marl or 
tosca-rock, and others of highly ferruginous sandstone ; 
in one section, only a few yards in depth, it rested on 
stratified sand. Near Monte Video this deposit in some 
spots appears to be of greater thickness ; and the re- 
mains of the Glyptodon and other extinct mammifers 
have been found in it. In the long line of cliffs, between 
fifty and sixty feet in height, called the Barrancas da 



338 Pampean Formation. FAET n. 

S Gregovio, which extend westward of the Bio S. Lucia ? 
the lower half is formed of coarse sand of quartz and 
feldspar without mica, like that now cast up on the 
beach near Maldonado ; and the upper half of Pampean 
mud, varying in colour and containing honey-combed 
veins of soft calcareous matter and small concretions of 
tosca-rock arranged in lines, and likewise a few pebbles 
of quartz. This deposit fills up hollows and furrows in 
the underlying sand ; appearing as if water charged 
with mud had invaded a sandy beach. These cliffs 
extend far westward, and at a distance of sixty miles, 
near Colonia del Sacramiento, I found the Pampean 
deposit resting in some places on this sand, and in 
others on the primary rocks : between the sand and the 
reddish mud, there appeared to be interposed, but the 
section was not a very good one, a thin bed of shells of 
an existing Mytilus, still partially retaining their colour. 
The Pampean formation in Banda Oriental might readily 
be mistaken for an alluvial deposit : compared with 
that of the Pampas, it is often more sandy, and con- 
tains small fragments of quartz; the concretions are 
much smaller, and there are no extensive masses of 
tosca-rock. 

In the extreme western parts of this province, be- 
tween the Uruguay and a line drawn from Colonia to 
the R. Perdido (a tributary of the E. Negro), the 
formations are far more complicated. Besides primary 
rocks, we meet with extensive tracts and many flat- 
topped, horizontally stratified, cliff-bounded, isolated 
hills of tertiary strata, varying extraordinarily in 
mineralogical nature, some identical with the old 
marine beds of St. T6 Bajada, and some with those of 
the much more recent Pampean formation. There are, 
also, extensive low tracts of country covered with a 
deposit containing mammiferous remains, precisely like 



CHAP, xi. Banda Oriental. 339 

that jnst described in the more eastern parts of the 
province. Although from the smooth and unbroken 
state of the country, I never obtained a section of this 
latter deposit close to the foot of the higher tertiary 
hilh, yet I have not the least doubt that it is of quite 
subsequent origin ; having been deposited after the sea 
had worn the tertiary strata into the cliff-bounded hills. 
This later formation, which is certainly the equivalent 
of that of the Pampas, is well seen in the valleys in the 
estancia of Berquelo, near Mercedes ; it here consists of 
reddish earth, full of rounded grains of quartz, and 
with some small concretions of tosca-rock arranged in 
horizontal lines, so as perfectly to resemble, except in 
containing a little calcareous matter, the formation in 
the eastern parts of Banda Oriental, in Entre Bios, and 
at other places : in this estancia the skeleton of a great 
Edental quadruped was found. In the valley of the 
Sarandis, at the distance of only a few miles, this de- 
posit has a somewhat different character, being whiter, 
softer, finer-grained, and full of little cavities, and con- 
sequently of little specific gravity ; nor does it contain 
any concretions or calcareous matter : I here procured 
a head, which when first discovered must have been 
quite perfect, of the Toxodon Platensis, another of a 
Mylodon, 1 perhaps M. Darwinii^ and a large piece of 
dermal armour, differing from that of the Olyptodon 
clavipes. These bones are remarkable from their ex- 
traordinarily fresh appearance ; when held over a lamp 
of spirits of wine, they give out a strong odour and 
burn with a small flame ; Mr. T. Reeks has been so kind 
as to analyse some of the fragments, and he finds that 



1 This head was at first considered by Professor Owen (in the 
1 Zoology of the Beagle's Voyage ') as belonging to a distinct genus, 
namely, Glossotheriiim. 



34 Pampean Formation. PAET n, 

they contain about seven per cent, of animal matter, 
and eight per cent of water, 1 

The older tertiary strata, forming the higher isolated 
hills and extensive tracts of country, vary, as I have 
said, extraordinarily in composition: within the dis- 
tance of a few miles, I sometimes passed over crystalline 
limestone with agate, calcareous tuffs, and marly rocks, 
all passing into each other, red and pale mud with 
concretions of tosca-rock, quite like the Pampean for- 
mation, calcareous conglomerates and sandstones, 
bright red sandstones passing either into red con- 
glomerate, or into white sandstone, hard siliceous 
sandstones, jaspery and chalcedonic rocks, and numerous 
other subordinate varieties. I was unable to make out 
the relations of all these strata, and will describe only 
a few distinct sections : in the cliffs between P, Gorda 
on the Uruguay and the A. de Vivoras, the upper bed 
is crystalline cellular limestone often passing into cal- 
careous sandstone, with impressions of some of the same 
shells as at St. Fe Bajada ; at P. Gorda, 2 this limestone 
is interstiatified with, and rests on, white sand, which 
covers a bed about thirty feet thick of pale-coloured 
clay, with many shells of the great Ostrea Patagonica : 
beneath this, in the vertical cliff, nearly on a level with 
the river, there is a bed of red mud absolutely like the 
Pampean deposit, with numerous often large concre- 
tions of perfectly characterised white, compact tosca- 
rock. At the mouth of the Vivoras, the river flows 
over a pale cavernous tosca-rock, quite like that in the 

1 Liebig (' Chemistry of Agriculture/ p. 194) states that fresh 
dry bones contain from thirty- two to thirty-three per cent, of dry 
gelatine. See also Dr. Daubeny in ' Edin. New Phil. Journ.' vol. 
xxxvii.p 29 

2 In rx*y 'Journal' (p. 171, 1st edit ) I have hastily and inaccu- 
rately stated that the Pampean mud, which is found over the eastern 
part of B. Oriental, lies orer the limestone at P. Oorda ; I should 
have said that there was reason to infer that it was a subsequent of 
superior deposit. 



CHAP. xi. Banda Oriental* 341 

Pampas, and tliis appeared to underlie the crystalline 
limestone; but the section was not unequivocal like 
that at P. Gorda. These beds now form only a narrow 
and much denuded strip of land ; but they must once 
have extended much farther ; for on the next stream, 
south of the S. Juan, Captain Sulivan, R.N., found a 
little cliff, only just above the surface of the river, with 
numerous shells of the Venus Munsterii, d'Orbig., 
one of the species occurring at St. Fo, and of which 
there are casts at P. Gorda: the line of cliffs of the 
subsequently deposited true Pampean mud, extend 
from. Colonia to within half a mile of this spot, and no 
doubt once covered up this denuded marine stratum. 
Again at Colonia, a Frenchman found, in digging the 
foundations of a house, a great mass of the Ostrea Pata- 
gonica (of which I saw many fragments), packed to- 
gether just beneath the surface, and directly superim- 
posed on t^ie gneiss. These sections are important: 
M. d'Orbigny is unwilling to believe that beds of the 
same nature with the Pampean formation ever underlie 
the ancient marine tertiary strata j and I was as much 
surprised at it as he could have been ; but the vertical 
cliff at P. Gorda allowed of no mistake, and I must be 
permitted to affirm, that after having examined the 
country from the Colorado to St. F6 Bajada, I could not 
be deceived in the mineralogical character of the Pam- 
pean deposit. 

Moreover, in a precipitous part of the ravine of 
Las Bocas, a red sandstone is distinctly seen to overlie 
a thick bed of pale mud, also quite like the Pampean 
formation, abounding with concretions of true tosca- 
ro:k. This sandstone extends over many miles of 
country : it is as red as the brightest volcanic scoriaa ; 
it sometimes passes into a coarse red conglomerate 
composed of the underlying primary rocks ; and often 



34^ Pampean Formation. PAET n 

passes into a soft wliite sandstone with, red streaks. 
At the Calera de los Huerfanos, only a quarter of a 
mile south of where I first met with the red sand- 
stone, the crystalline white limestone is quarried: as 
this bt d is the uppermost, and as it often passes into 
calcareous sandstone, interstratified with pure sand ; 
and as the red sandstone likewise passes into soft white 
sandstone, and is also the uppermost bed, I believe 
that these two beds, though so different, are equiva- 
lents. A few leagues southward of these two places, 
on each side of the low primary range of S. Juan, 
there are some flat-topped, cliff- bounded, separate 
little hills, very similar to those fringing the primary 
ranges in the great plain south of Buenos Ayres : they 
are composed 1st, of calcareous tuff with many par- 
ticles of quartz, sometimes passing into a coarse con- 
glomerate ; 2nd, of a stone undistinguishable on the 
closest inspection from the compacter varieties of 
tosca-rock ; and 3rd, of semi- crystalline limestone, 
including nodules of agate : these three varieties pass 
insensibly into each other, and as they form the upper- 
most stratum in this district, T believe that they, also, 
are the equivalents of the pure crystalline limestone, 
and of the red and white sandstones and conglomerates. 
Between these points and Mercedes on the Rio 
Negro, there are scarcely any good sections, the road 
passing over limestone, tosca-rock, calcareous and 
bright red sandstones, and near the source of the S. Sal- 
vador over a wide extent of jaspery rocks, with much 
milky agate, like that in the limestone near S. Juan. 
In the estancia of Berquelo, the separate, flat-topped, 
cliff-bounded hills are rather higher than in other parts 
of the country ; they range in a NE. and SW. direc- 
tion ; their uppermost beds consist of the same bright 
red sandstone, passing sometimes into a conglomerate, 



CHAP. xi. Ban da Orient aL 343 

and in the lower part Into soft wLite sandstone, and 
even into loose sand: beneath this sandstone, I saw 
In two places layers of calcareous and marly rocks, and 
In one place red Pampean-like earth ; at the base of 
these sections, there was a hard, stratified, white sand- 
stone, with chalcedonic layers. Near Mercedes, beds 
of the same nature and apparently of the same age, are 
associated with compact, white, crystalline limestone, 
including much botryoidal agate, and singular masses, 
like porcelain, but really composed of a calcareo-sili- 
ceous paste. In sinking wells in this district the 
chalcedonic strata seem to be the lowest. Beds, such 
as here described, occur over the whole of this neigh- 
bourhood ; but twenty miles further up the R. Negro, 
in the cliffs of Perika, which are about fifty feet in 
height, the upper bed is a prettily variegated chalce- 
dony, mingled with a pure white tallowy limestone; 
beneath this there is a conglomerate of quartz and 
granite ; beneath this many sandstones, some highly 
calcareous ; and the whole lower two-thirds of the cliff 
consist of earthy calcareous beds of various degrees of 
purity, with one layer of reddish Pampean-like mud. 

When examining the agates, the chalcedonic and 
jaspery rocks, some of the limestones, and even the 
bright red sandstones, I was forcibly struck with 
their resemblance to deposits formed in the neigh- 
bourhood of volcanic action. I now find that M. 
Isabella, in his ' Voyage & Buenos Ayres,' has described 
closely similar beds on Itaquy and Ibicuy (which, enter 
the Uruguay some way north of the R. Negro) and these 
beds include fragments of red decomposed true scoriae 
hardened by zeolite, and of black retinite: we have 
then here good evidence of volcanic action during our 
tertiary period. Still farther north, near S. Anna/ 
1 M. d'Orbigny, * Voyage, Part. Golog / p. 29. 



n. 



344 P amp can Formation. 

where the Parana makes a remarkable bend, M. 
Bonpland found some singular amygdaloidal rocks, 
which perhaps may belong to this same epoch, 1 may 
remark that, judging from, the size and well-rounded 
condition of the blocks of rock in the above- described 
conglomerates, masses of primary formation probably 
existed at this tertiary period above water : there is, 
also, according to M. Isabella, much conglomerate 
farther north, at Salto. 

From whatever source and through whatever means 
the great Pampean formation originated, we here have, 
I must repeat, unequivocal evidence of a similar 
action at a period before that of the deposition of the 
marine tertiary strata with extinct shells, at St. Fe and 
P. Gorda. During also the deposition of these strata, 
we have in the intercalated layers of red Pampean-like 
mud and tosea-rock, and in the passage near S. Juan of 
the semi-crystalline limestones with agate into tosca 
undistinguishable from that of the Pampas, evidence 
of the same action, though continued only at intervals 
and in a feeble manner. We have further seen that in 
this district, at a period not only subsequent to the de- 
position of the tertiary strata, but to their upheavement 
and most extensive denudation, true Pampean mud 
with its usual characters and including niaramiferous 
remains, were deposited round and between the hills 
or islets formed of thebe tertiary strata, and over the 
whole eastern and low primary districts of Ban da 
Oriental. 

Ucvrthy mass, with extinct mammiferous remains, 
ov&r the porphyritio gravel at 8. Julian, lat. 49 14 ; 
8. in Patagonia. This case, though not coming 
strictly under the Pampean formation, may be con- 
veniently given here. On the south side of the 
harbour^ there is a nearly level plain (mentioned in 



CHAP. xi. Mammiferoiis Remains at S. Julian. 345 

the eighth chapter) about seven miles long, and three or 
four miles wide, estimated at ninety feet in height, and 
bordered by perpendicular cliffs, ot which a section Is 
here represented. 

No so. 

Section of the Lowest Plain at Port S Julian* 

A A A 



A A. Superficial bed ot reddish earth, with the remains of the Macrauchenia, and 

with recent sea-shells on the surface. 
B. Gravel of porphyntic rocks 

G and D Punnc^ous mudstone 1 Ancient tertiarv frwrnition. 

B and F. Sandbtoue and aigillaceous beds J ^^nt tertiary toimation. 

The lower old tertiary strata (to be described in the 
next chapter) are covered by the usual gravel bed; 
and this by an Irregular earthy, sometimes sandy mass, 
seldom more than two or three feet in thickness, except 
where it fills up furrows or gullies worn not only 
through the underlying gravel, but even through the 
upper tertiary beds. This earthy mass is of a pale 
reddish colour, like the less pure varieties of Pampean 
mud in Banda Oriental ; it includes small calcareous 
concretions, like those of tosca-rock but more arena- 
ceous, and other concretions of a greenish, indurated 
argillaceous substance : a few pebbles, also, from the 
underlying gravel-bed are also included in it, and these 
being occasionally arranged in horizontal lines, show 
that the mass is of sub-aqueous origin. On the sur- 
face and embedded in the superficial parts, there are 
numerous shells, partially retaining their colours, of 
three or four of the now commonest littoral species. 
Near the bottom of one deep furrow (represented in 
the diagram), filled up with this earthy deposit, I 
found a large part of the skeleton of the Macrauckenia 



346 Pampcan Formation. BART n. 

Patadwnica a gigantic and most extraordinary 
pachyderm , allied, according to Professor Owen, to 
the PaltBotheriiiffl, "but with afBnities to the Ruminants, 
especially to the American, division of the Oamelidas. 
Several of the vertebras in a chain, and nearly all the 
bones of one of the limbs, even to the smallest bones of 
the foot, were embedded in their proper relative posi- 
tions : hence the skeleton was certainly united by its 
flesh or ligaments, when enveloped in the mad. This 
earthy mass, with its concretions and mammiferous 
remains, filling up furrows in the underlying gravel, 
certainly presents a very striking resemblance to some 
of the sections (for instance, at P. Alta in B. Blanca ? 
or at the Barrancas de S. Gregorio) in the Pampean 
formation ; but I must believe that this resemblance is 
only accidental. I suspect that the mud which at the 
present day is accumulating in deep and narrow gullies 
afc the head of the harbour, would, after elevation, pre- 
sent a very similar appearance. The southernmost 
part of the true Pampean formation, namely, on the 
Colorado, lies 5GO miles of latitude north of this 
point. 1 

With respect to the age of the Macrauchenia, the 
shells on the surface prove that the mass in which the 
skeleton was enveloped has been elevated above the 
sea within the recent period : I did not see any of the 
shells embedded at a sufficient depth to assure me 
(though it be highly probable) that the whole thick- 
ness of the mass was contemporaneous wit! these indi- 
vidual specimens. That the Macrauchenia lived sub- 
sequently to the spreading out of the gravel on this 

1 In the succeeding chapter I shall have to refer to a great 
deposit of extinct mammiferous remains, lately discovered by (''apt. 
Sulivan, B.N , at a point still farther south, namely at the B, 
Gallegos ; their age must at present remain doubtful. 



CH4P, xi. Mammif er oits Remains at S.J^i>l^an. 347 

plain Is certain ; and tiiat tins gravel, at the height of 
ninety feet, was spread out long after the existence of 
recent shells, is scarcely less certain. For, it was 
shown in the eighth chapter ? that this line of coast has 
been upheaved with remarkable equability, and that 
over a vast space both north and south of S. Julian, 
recent species of shells are strewed on (or embedded in) 
the surface of the 250 feet plain, and of the 850 feet 
plain up to a height of 400 feet. These wide step- 
formed plains have been formed by the denuding action 
of the coast-waves on the old tertiary strata; and 
therefore, when the surface of the 350 feet plain, with 
the shells on it, first rose above the level of the sea, 
the 250 feet plain did not exist, and its formation, as 
well as the spreading out of the gravel on Its summit, 
must have taken place subsequently. So also the 
denudation and the gravel-covering of the ninety feet 
plain must have taken place subsequently to the eleva- 
tion of the 250 feet plain, on which recent shells are 
also strewed. Hence there cannot be any doubt that 
the Macrauchenia, which certainly was entombed In a 
fresh state, and which must have been alive after the 
spreading out of the gravel on the ninety feet plain, 
existed, not only subsequently to the upraised shells on 
the surface of the 250 feet plain, but also to those on 
the 350 to 400 feet plain : these shells, eight in number 
(namely, three species of Mytilus, two of Patella, one 
FusuSj Voluta, and Balanus), are undoubtedly recent 
species, and are the commonest kinds now living on 
this coast. At Punta Alta in B. Blanca, I remarked 
how marvellous it was, that the Toxodon, a mammifer 
so nnhke to all known genera, should have co-existed 
with twenty-three still living marine animals ; and now 
we find that the Macrauchenia, a quadruped only a 
little less anomalous than the Toxodon, also co-existed 



Pampean Formation : ?AET 11. 

\\itb eight oilier sbill existing Mollusca : It should, 
moreover, be borne in mind, that a tooth of a pachy- 
dermatous animal was found with the other remains at 
Punta Alia, \\hich Professor Owen thinks almost cer- 
tainly belonged to the Macrauchenia. 

Mr. Lyell l has arrived at a highly important con- 
clusion with respect to the age of the North American 
extinct inammifers (many of which are closely allied to, 
and even identical with, those of the Pampean forma- 
tion), namely, that they lived subsequently to the period 
when erratic boulders were transported by the agency 
of floating ice in temperate latitudes. Now in the 
valley of the San Cruz, only fifty miles of latitude south 
of the spot where the Macrauchenia was entombed, vast 
numbers of gigantic, angular boulders, which must 
have been transported from the Cordillera on icebergs, 
lie strewed on the plain, at the height of 1,400 feet 
above the level of the sea. In ascending to this level, 
several step-formed plains must be crossed, all of which 
have necessarily required long time for their formation ; 
hence the lowest or ninety feet plain, with its super- 
ficial bed containing the remains of the Macrauchenia, 
must have been formed very long subsequently to the 
period when the 1 ,400 feet plain was beneath the sea, 
and boulders were dropped on it from floating masses 
of ice. 2 Mr. Lyell's conclusion, therefore, is thus far 
confirmed in the southern hemisphere ; and it is the 
more important, as one is naturally tempted to admit 
so simple an explanation, that it was the ice-period 
that caused the extinction of the numerous great 

1 G3ological Proceedings/ vol. iv, p. 36 

2 It must not be inferred fiom these remarks, that the ice-action 
ceased in South America at this comparatively ancient period , for 
in Tierra del Fuego boulders were, probably transported contempo- 
raneously with, if not subsequently to, the formation of the ninety 
feet plain at S. Julian, and at other parts of the coast of Patagonia 



CHAP. xi. concluding Remarks on. 349 

mammifers which so lately swarmed over the two 
Americas. 

Summary and concluding remarks on tJie Pam- 
pean Formation. One of its most striking features is 
its great extent ; I passed continuously over it from the 
Colorado to St. F6 Bajada, a distance of 500 geographical 
miles ; and M. d'Orbigny traced it for 250 miles farther 
north. In the latitude of the Plata, I examined this 
formation at intervals over an east and west line of 
800 miles from Maldonado to the River Carcarana ; and 
M. d'Orbigny believes it extends 100 miles farther 
inland : from Mr. Oaldcleugh's travels, however, I should 
have thought that it had extended, south of the Oordo- 
vese range, to near Mendoza, and I may add that I 
heard of great bones having been found high up the 
River Quinto. Hence the area of the Pampean forma- 
tion, as remarked by M. d'Orbigny, is probably at least 
equal to that of France, and perhaps twice or thrice 
as great. In a basin, surrounded by gravel- cliff (at a 
height of nearly 8,000 feet), south of Mendoza, there 
is, as described in the tenth chapter, a deposit very like 
the Pampean, interstratified with other matter; and 
again at S. Julian's, in Patagonia, 560 miles south of 
the Colorado, a small irregular bed of a nearly similar 
nature contains, as we have just seen, mammiferous 
remains. In the provinces of Moxos and Chiquitos 
(1,000 miles northward of the Pampas), and in Bolivia, 
at a height of 4,000 mitres, M. d'Orbigny has described 
similar deposits, which he believes to have been formed 
by the same agency contemporaneously with the Pam- 
pean formation. Considering the immense distances 
between these several points, and their different heights, 
it appears to me infinitely more probable, that this 
similarity has resulted not from contemporaneousness of 
origin, but from the similarity of the rocky framework 



35O Pampean Formation. PABT 11. 

of the continent : It Is known that in Brazil an Immense 
area consists of gneissic rocks, and we shall hereafter 
see, over how great a length the plutonic rocks of the 
Cordillera, the overlying purple porphyries, and the 
trachytic ejections, are almost Identical in nature. 

Three theories on the origin of the Pampean forma- 
tion have been propounded : First, that of a great 
debacle by M. d'Orbigny; this seems founded chiefly 
on the absence of stratification, and on the number of 
embedded remains of terrestrial quadrupeds. Although 
the Pampean formation (like so many argillaceous 
deposits) is not divided into distinct and separate strata, 
yet we have seen that in one good section it was striped 
with horizontal zones of colour, and that in several 
specified places the upper and lower parts differed, not 
only considerably in colour, but greatly in constitution. 
In the southern part of the Pampas the upper mass (to 
a certain extent stratified) generally consists of hard 
tosca-rock, and tllB^lower part of red Pampean mud, 
often itself divided into two or more masses, varying in 
colour and in the quantity of included calcareous matter. 
In western Banda Oriental, beds of a similar nature, 
but of a greater age, conformably underlie and are 
intercalated with the regularly stratified tertiary forma- 
tion. As a general rule, the marly concretions are 
arranged in horizontal lines, sometimes united into 
irregular strata : surely, if the mud had been tumul- 
tuously deposited in mass, the included calcareous 
matter would have segregated itself irregularly, and 
not into nodules arranged in horizontal lines, one above 
the other and often far apart : this arrangement appears 
to me to prove that mud, differing slightly in composi- 
tion,, was successively and quietly deposited. On the 
theory of a debacle, a prodigious amount of mud, with- 
out a single pebble, is supposed to have been borne over 



CHAP. xi. Theories on its Origin, 351 

the wide surface of the Pampas, when under water: on 
the other hand, over the whole of Patagonia, the same 
or another debacle is supposed to have borne nothing 
but gravel, the gravel and the fine mud in the neigh- 
bourhood of the Eios Negro and Colorado having been 
borne to an equal distance from the Cordillera, or 
imagined line of disturbance : assuredly directly oppo- 
site effects ought not to be attributed to the same 
agency. Where, again, could a mass of fine sediment, 
charged with calcareous matter in a fit state for chemi- 
cal segregation, and in quantity sufficient to cover an 
area at least 750 miles long, and 400 miles broad ; to a 
depth of from twenty or thirty feet to a hundred feet, 
have been accumulated, ready to be transported by the 
supposed debacle? To my mind it is little short of 
demonstration, that a great lapse of time was necessary 
for the production and deposition of the enormous 
amount of mud-like matter forming the Pampas ; nor 
should I have noticed the theory of a debacle, had 
it not been adduced by a naturalist so eminent as 
M. d'Orbigny. 

A second theory, first suggested, I believe 3 by Sir 
W. Parish, is that the Pampean formation was thrown 
down on low and marshy plains by the rivers of this 
country before they assumed their present courses. 
The appearance and composition of the deposit, the 
manner in which it slopes up and round the primary 
ranges, the nature of the underlying marine beds, the 
estuary and sea-shells on the surface, the overlying 
sandstone beds at M. Hermoso, are all quite opposed 
to this view. Nor do I believe that there is a single 
instance of a skeleton of one of the extinct mammifers 
having been found in an upright position, as if it hach 
been mired. ^ 

The third theory, of the truth of which I cannoj 



352 Pampcan Formation. PABT n. 

entertain the srtrillast doubt, is that the Pampean for- 
mation was slowly accumulated at the mouth of the 
former estuary of the Plata and in the sea adjoining it. 
I have come to this conclusion from the reasons assigned 
against the two foregoing theories, and from simple 
geographical considerations. From the numerous shells 
of the Axftra Wwtin lying loose on the surface of the 
plains, and near Buenos Ayres embedded in the tosca- 
rock, we know that this formation not only was formerly 
covered by, but that the uppermost parts were deposited 
in, the brackish water of the ancient La Plata. South- 
ward and seaward of Buenos Ayres, the plains were 
upheaved from under water inhabited by true marine 
shells. We further know from Professor Ehrenberg's 
examination of the twenty microscopical organisms in 
the mud round the tooth of the Mastodon high up the 
course of the Parana, that the bottom-most part of 
this formation was of brackish- water origin. A similar 
conclusion must be extended to the beds of like com- 
position, at the level of the sea and under it, at 
M. Hermoso in Bahia Blanca. Dr. Carpenter finds 
that the harder varieties of tosca-rock, collected chiefly 
to the south, contain marine spongoid bodies, minute 
frao-ments of shells, corals, and Polythalamia ; these 
perhaps may have been drifted inwards by the tides, 
from the more open parts of the sea. The absence of 
shells, throughout this deposit, with the exception of 
the uppermost layers near Buenos Ayres, is a remark- 
able fact : can it be explained by the brackish condition 
of the water, or by the deep mud at the bottom ? I 
have stated that both the reddish mud and the concre- 
tions of tosca-rock are often penetrated by minute, 
linear cavities, such, as frequently may be observed in 
fresh-water calcareous deposits: were they produced 
lag the burrowing of small worms ? Only on this view 



CHAP, xi. Theories on its Origin. 353 

of the Pampean formation having been of estuary 
origin, can the extraordinary numbers (presently to be 
alluded to) of the embedded mammiferous remains be 
explained. 1 

With respect to the first origin of the reddish mud, 
I will only remark, that the enormous area of Brazil 
consists in chief part of gneissic and other granitic rocks, 
which have suffered decomposition, and been converted 
into a red, gritty, argillaceous mass, to a greater depth 
than in any other country which I have seen. The 
mixture of rounded grains, and even of small fragments 
and pebbles of quartz, in the Pampean mud of Banda 
Oriental, is evidently due to the neighbouring and 
underlying primary rocks. The estuary mud was drifted 
during the Pampean period in a much more southerly 
source, owing probably to the east and west primary 
ridges south of the Plata not having been then elevated, 
than the mud of the Plata at present is ; for it was 
formerly deposited as far south as the Colorado. The 
quantity of calcareous matter in this formation, espe- 
cially in those large districts where the whole mass 
passes into tosca-rock, is yery great : I have already 
remarked on the close resemblance in external and 
microscopical appearance between this tosca-rock and 
the strata at Ooquimbo, which have certainly resulted 
from the decay and attrition of recent shells : 2 I dare 

- 1 It is almost superfluous to give the numerous cases (for instance, 
in Sumati a; Lyell's 4 Principles,' vol ni p 825, sixth edit ) of the 
carcases of animals having been washed on t to sea by swollen rivers, 
but I may refer to a recent account by Mr. Bettmgton ('Asiatic Soc.* 
1845, June 21st), of oxen, deer, and bears being carried into the 
Gulf of Cambray ; see, also, the account in my * Journal * (2nd edit, 
p. 133) of the numbers of animals drowned in the Plata during the 
great, often recurrent, droughts 

2 I may add, that there are nearly similar superficial calcareous 
beds at King George s Sound in Australia ; and these undoubted! J 
have been found by the disintegration of marine remains (see Chap- 
ter VII). There is, however, something very remarkable in the 
frequency of superficial, thin beds of earthy calcareous matter, HS 



354 Pampean Formation J?A*T it 

not, however, extend this conclusion to the calcareous 
rocks of the Pampas, more especially as the underlying 
tertiarv strata in Western Banda Oriental show that at 
that period there was a copious emission of carbonate 
of lime in connection with volcanic action. 

The Pampean formation, judging from its similar 
composition, and from the apparent absolute specific 
identity of some of its niammiferous remains, and from 
the generic resemblance of others, belongs over its vast 

area throughout Banda Oriental, Entre Rios, and the 

wide extent of the Pampas as far south as the Colorado, 

to the same geological epoch. The mamnriferous 

remains occur at all depths from the top to the bottom 
oi the deposit; and I may add that nowhere in the 
Pampas is there any appearance of much, superficial 
denudation: some bones which I found near the 
Guarclia del Monte were embedded close to the surface : 
and this appears to have been the case with many of 
those discovered in Banda Oriental : on the Matanzas, 
twenty miles south of Buenos Ayres, a Glyptodon was 
embedded five feet beneath the surface ; numerous 
remains were found by S, Muniz, near Luxan, at an 
average depth of eighteen feet; in Buenos Ayres a 
skeleton was disinterred at sixty feet depth, and on the 
Parana I have descried two skeletons of the Mastodon 
only five or six feet above the very base of the deposit. 
With respect to the age of this formation, as judged of 
by the ordinary standard of the existence of Mollusca, 

districts where the surrounding rocks a r e not calcareous. Major 

Charters m a Paper read before the Eoyal Geographical Society 

(April 13th, 1840, and abstracted In the * Athenasum,' p 317), states 

that this is the case in parts of Mexico, and that he has observed 

^similar appearances in many parts of South Africa. The circum- 

^stance of the uppermost stratum round the rugged Sxerra Ventana 

-consisting of calcareous or marly matter, without any covering of 

Pluvial matter, strikes me as very singular, in whatever manner w 

i%w the deposition and elevation of the Pampean formation. 



CHIP. xr. of Recent Origin. 355 

the only evidence within the limits of the tree Pampas 
which is at all trustworthy is afforded by the still living 
Amm lahiata being embedded in tosca-rock near 
Buenos Ayres. Afc Punta Alta, however, we have seen 
that several of the extinct mammifers, most character- 
istic of the Pampean formation, co-existed with twenty 
species of Mollusca, a barnacle and two corals, all still 
living on this same coast ; for when we remember 
that the shells have a more ancient appearance than 
the bones ; that many of the bones, though embedded 
In a coarse conglomerate, are perfectly preserved ; that 
almost all the parts of the skeleton of the Scelidothe- 
riuni, even to the knee-cap, were lying in their proper 
relative positions ; and that a large piece of the fragile 
dermal armour of a Dasypoid quadruped, connected 
with some of the bones of the foot, had been entombed 
In a condition allowing the two sides to be doubled 
together, It must assuredly be admitted that these 
manimiferous remains were embedded In a fresh state, 
and therefore that the living animals co-existed with 
the co-embedded shells. Moreover, the Macrauchenia 
Patachoniea (of which, according to Professor Owen, 
remains also occur In the Pampas of Buenos Ayres, and 
at Punta Alta) has been shown by satisfactory evidence 
of another kind to have lived on the plains of Pata- 
gonia long after the period when the adjoining sea was 
first tenanted by its present commonest molluscous 
animals. We must, therefore, conclude that the Pani- 
pean formation belongs, in the ordinary geological 
sense of the word, to tjie Recent Period. 1 

At St. Fe Bajada, the Pampean estuary formation, 
with its mammiferous remains, conformably overlies 

1 M d'Orbigny believes (' Voyage, Part. G-e'olog.' p. 81) that this 
formation, though * tres voisine de la notre, est neanmolns de beau- 
coup anterieure 4 uotre creation.' 

M 



356 Pampean Formation PABT n, 

the marine tertiary strata, which, (as first shown by 
M. d'Orbigny) are contemporaneous with, those of 
Patagonia, and which, as we shall hereafter see, belong 
to a very ancient tertiary stage. When examining the 
junction between these two formations, I thought that 
the concretionary layer of marl marked a passage be- 
tween the marine and estuary stages, M. d'Orbigny 
disputes this view (as given in my Journal), and I admit 
that it is erroneous, though in some degree excusable, 
from their conformabihty and from both, abounding 
with calcareous matter. It would, indeed, have been a 
great anomaly if there had been a true passage between 
a deposit contemporaneous with existing species of 
Mollusca, and one in which all the Mollusca appear to 
be extinct. Northward of St. Fe, M. d'Orbigny met 
with ferruginous sandstones, marly rocks, and other 
beds, which he considers as a distinct and lower forma- 
tion ; but the evidence that they are not parts of the 
same, with an altered mineralogical character, does not 
appear to me quite satisfactory. 

In Western Banda Oriental, whilst the marine ter- 
tiary strata were accumulating, there were volcanic 
eruptions, much silex and lime were precipitated from 
solution, coarse conglomerates were formed, being de- 
rived probably from adjoining land, and layers of red 
mud and marly rocks, like those of the Pampean for- 
mation, were occasionally deposited. The true Pampean 
deposit, with mammiferous remains, instead of as at 
St. P6 overlying conformably the tertiary strata, is 
here seen at a lower level folding round and between 
the flat-topped, cliff-bounded hills, formed by the up- 
heaval and denudation of these same tertiary strata. 
The upheaval, having occurred here earlier than at 
St. F6, may be naturally accounted for by the contem- 
poraneous volcanic action. At the Barrancas de S. 



HAP. XL of Recent Origin* 357 

Gregorio, the Pampean deposit, as we have seen, over- 
lies and fills up furrows in coarse sand, precisely like 
that now accumulating on the shores near the mouth of 
the Plata. I can hardly believe that this loose and 
coarse sand is contemporaneous with the old tertiary 
and often crystalline strata of the more western parts 
of the province ; and am induced to suspect that it is 
of subsequent origin. If that section near Oolonia 
could be implicitly trusted, in which, at a height of 
only fifteen feet above the Plata, a bed of fresh-looking 
mussels, of an existing littoral species, appeared to lie 
between the sand and the Pampean niud, I should con- 
clude that Banda Oriental must have stood, when the 
coarse sand was accumulating, at only a little below its 
present level, and had then subsided, allowing the 
estuary Pampean mud to cover far and wide its surface 
up to a height of some hundred feet ; and that after 
this subsidence the province had been uplifted to its 
present level. 

In Western Banda Oriental, we know, from two 
unequivocal sections, that there is a mass, absolutely 
un distinguishable from the true Pampean deposit, be- 
neath the old tertiary strata. This inferior mass must 
be very much more ancient than the upper deposit with 
its mammiferous remains, for it lies beneath the ter- 
tiary strata in which all the shells are extinct. Never- 
theless, the lower and upper masses, as well as some 
intermediate layers, are so similar in mineralogical 
character, that I cannot doubt that they are all of 
estuary origin, and have been derived from the same 
great source. At first it appeared to me extremely 
improbable that mud of the same nature should have 
been deposited on nearly the same spot, during an 
immense lapse of time, namely, from a period equiva- 
lent perhaps to the Eocene of Europe to that of the 



358 Pampean Formation PAKT a. 

Pampean formation. But as, at the very commencement 
of the Pampean period, if not at a still earlier period, 
the Sierra Ventana formed a boundary to the south, 
the Cordillera or the plains in front of them to the 
west, the whole province of Corrientes probably to 
the north, for, according to M. d'Orbigny, it is not 
covered by the Pampean deposit, and Brazil, as known 
by the remains in the caves, to the north-east ; and as 
again, during the older tertiary period, land already 
existed in Western Banda Oriental and near St. Fe 
Bajada, as may be inferred from the vegetable debris, 
from the quantities of silicified wood, and from the 
remains of a Toxodon found, according to M. d'Orbigny, 
In still lower strata, we may conclude that at this an- 
cient period a great expanse of water was surrounded 
by the same rocky framework which now bounds the 
plains of Pampean formation. This having been the 
case, the circumstance of sediment of the same nature 
having been deposited in the same area during an im- 
mense lapse of time, though highly remarkable, does 
not appear incredible. 

The elevation of the Pampas, at least of the southern 
parts, has been slow and interrupted by several periods 
of rest, as may be inferred from the plains, cliffs, and 
lines of sand-dunes (with shells and pumice-pebbles) 
standing at different heights. I believe, also, that the 
Pampean mud continued to be deposited, after parts of 
this formation had already been elevated, in the same 
manner as mud would continue to be deposited in the 
estuary of the Plata, if the mud-banks on its shores 
were now uplifted and changed into plains : I believe 
in this from the improbability of so many skeletons 
and bones having been accumulated at one spot, where 
M. Hermoso now stands, at a depth of between 800 and 
1,000 feet, and at a vast distance from any land except 



CHAP. xr. of Recent Origin* 359 

small rocky islets, as must have been the case, if the 
high tosca-plam round the Ventana and adjoining 
Sierras, had not been already uplifted and converted 
into land, supporting roammiferous animals. At Punta 
Alta we have good evidence that the gravel-strata, 
which certainly belong to the true Pampean period, 
were accumulated after the elevation in that neighbour- 
hood of the main part of the Pampean deposit, whence 
the rounded masses of tosca-rock were derived, and 
that rolled fragment of black bone in the same peculiar 
condition with the remains at Mont Hermoso* 

The number of the mammiferous remains embedded 
In the Pampas is, as I have remarked, wonderful; it 
should be borne in mind that they have almost exclu- 
sively been found in the cliffs and steep banks of rivers 5 
and that, until lately, they excited no attention amongst 
the inhabitants; I am firmly convinced that a deep 
trench could not bo cut in. any line across the Pampas, 
without intersecting the remains of some quadruped. 
It is difficult to form an opinion in what part of the 
Pampas they are most numerous; in a limited spot 
they could not well have been more numerous than 
they were at P. Alta ; the number, however, lately found 
by Seiior F. Muniz, near Luzan, in a central spot in 
the Pampas, is extraordinarily great; at the end of 
this chapter I will give a list of all the localities at 
which I have heard of remains having been discovered. 
Very frequently the remains consist of almost perfect 
skeletons; but there are, also, numerous single bones, 
as for instance at St. F. Their state of preservation 
varies much, even when embedded near each other : I 
saw none others so perfectly preserved as the heads of 
the Toxodon and Mylodon from the white soft earthy- 
bed on the Sarandis in Banda Oriental, It is remarkable 



Pampcan Formation ; 



FAET IL 



that In two limited sections I found no" less than five 
teeth separately embedded, and I heard of teeth having 
been similarly found in other parts : may we suppose 
that the skeletons or heads were for a long time gently 
drifted by currents over the soft muddy bottom, and 
that the teeth occasionally 5 here and there, dropped 

out? 

It may be naturally asked, where did these numerous 
animals live ? Prom the remarkable discoveries of 
MM. Lund and Clausen, it appears that some of the 
species found in the Pampas inhabited the high-lands 
of Brazil : the Mastodon Andium is embedded at great 
heights in the Cordillera from north of the equator J to 
at least as far south as Tarija ; and as there is no higher 
land, there can be little doubt that this Mastodon must 
have lived on the plains and valleys of that great range. 
These countries, however, appear too far distant for 
the habitation of the individuals entombed in the 
Pampas : we must probably look to nearer points, for 
instance to the province of Corrientes, which, as already 
remarked, is said not to be covered by the Pampean 
formation, and may therefore, at the period of its 
deposition, have existed as dry land. I have already 
given my reasons for believing that the animals em- 
bedded at M. Hermoso and at P. Alta in Bahia Blanca, 
lived on adjoining land, formed of parts of the already 
elevated Pampean deposit. With respect to the food 
of these many great extinct quadrupeds, I will not 
repeat the facts given in my Journal (second edit. p. 85), 
showing that there is no correlation between the luxuri- 
ance of the vegetation of a country and the size of its 

1 Hixmbolclt states that tlie Mastodon has been discovered in 
Hew Granada ; it has been found in Quito When at Lima, I saw a 
tooth of a Mastodon in the possession of Don M. Eivero, found at 
Haya Chica on the Maranon, near the G-uallaga Every one has 
heard of the numerous remains of Mastodon in Bolivia. 



CHAP, xt, Mammiferotts Remains of. 361 

mammiferous inhabitants. I do not doubt that large 
animals could now exist, as far as the amount, not kind, 
of vegetation is concerned, on the sterile plains of Bahia 
Blanca and of the E. Negro, as well as on the equally 
if not more sterile plains of Southern Africa. The 
climate, however, may perhaps have somewhat deterior- 
ated since the mammifers embedded at Bahia Blanca 
lived there ; for we must not infer, from the continued 
existence of the same shells on the present coasts, that 
there has been no change in climate ; for several of 
these shells now range northward along the shores of 
Brazil, where the most luxuriant vegetation flourishes 
under a tropical temperature. With respect to the 
extinction, which at first fills the mind with astonish- 
ment, of the many great and small mammifers of this 
period, I may also refer to the work above cited (second 
edit. p. 173), in which I have endeavoured to show that, 
however unable we may be to explain the precise cause, 
we ought not properly to feel more surprised at a species 
becoming extinct than at one being rare ; and yet we 
are accustomed to view the rarity of any particular 
species as an ordinary event, not requiring any extra- 
ordinary agency. 

The several mammifers embedded in the Pampean 
formation, which mostly belong to extinct genera, and 
some even to extinct families or orders, and which differ 
nearly, if not quite, as much as do the Eocene mammifers 
of Europe from living quadrupeds having existed con- 
temporaneously with Mollusca, all still inhabiting the 
adjoining sea, is certainly a most striking fact. It is, 
however, far from being an isolated one ; for, during 
the late tertiary deposits of Britain, an elephant, rhi- 
noceros, and hippopotamus co-existed with many recent 
land and fresh-water shells; and, in North America, 
we have the best evidence that a mastodon, elephant. 



362 Pampean Formation : PABT n. 

megatherium, megalonyx, mylodon, an extinct horse 
and ox, likewise co-existed with numerous land, fresh- 
water, and marine recent shells. 1 The enumeration, of 
these extinct North American animals naturally leads 
me to refer to the former closer relation of the 
mammiferous inhabitants of the two Americas, which 
I have discussed in my Journal, and likewise to the 
vast extent of country over which some of them ranged: 
thus the same species of the Megatherium, Megalonyx, 
ISquus (as far as the state of their remains permits of 
identification), extended from the Southern United 
States of North America to BahiaBlanca, in lat. 39 S., 
on the coast of Patagonia. The fact of these animals 
having inhabited tropical and temperate regions does 
not appear to me any great difficulty, seeing that at 
the Cape of Good Hope several quadrupeds, such as the 
elephant and hippopotamus, range from the equator to 
lat. 85 south. The case of the Mastodon Ancluim is 
one of more difficulty, for it is found from lat. 86 S-, 
over, as I have reason to believe, nearly the whole of 
Brazil, and up the Cordillera, to regions which, according 
to M. d'Orbigny, border on perpetual snow, and which 
are almost destitute of vegetation : undoubtedly the 
climate of the Cordillera must have been different when 
the mastodon inhabited it ; but we should not forget 
the case of the Siberian mammoth and rhinoceros, as 
showing how severe a climate the larger pachyderm ata 
can endure ; nor overlook the fact of the guanaco rang- 
ing at the present day over the hot low deserts of Peru, 
the lofty pinnacles of the Cordillera, and the damp 
forest-clad land of Southern Tierra del Fuego; the 

1 Many original observations, and a summary on this subject, are 
given in Mr. Lyell's paper in the 'Ueolog. Proc!* vol. iv p 3, and in 
his * Travels m North America/ vol i p. 1C4, and vol Ji p. (SO. B\>r 
tiie European analogous cases, see Mr. Ly ell's * Principles of Geology* 
(6th e4it,) vol. L p. 137. 



CHAP, xi. Mammiferons Remains of. 363 

puma, also, Is found from the equator to the Strait of 
Magellan, and I have seen its footsteps only a little 
below the limits of perpetual snow in the Cordillera of 
Chile. 

At the period, so recent in a geological sense, when 
these extinct mammifers existed, the two Americas 
must have swarmed with quadrupeds, many of them 
of gigantic size ; for, besides those more particularly 
referred to in this chapter, we must include in this 
same period those wonderfully numerous remains, some 
few of them specifically, and others generically related 
to those of the Pampas, discovered by MM. Lund and 
Clausen in the caves of Brazil. Finally, the facts here 
given show how cautious we ought to be in judging of 
the antiquity of a formation from even a great amount; 
of difference between the extm.ec and living species in 
any one class of animals ; we ought even to be cautious 
in accepting the general proposition, that change in 
organic forms and lapse of time are at all, necessarily, 
correlatives. 



SUPPLEMENT. 

On the TJiicJtness of the Pampean Formation, near 
Buenos Ayres. 

Repttblished from the ' Proc of the Geological Soc.' Dec. 3, 1862, 

M. Sourdeaux and J. Coghlan, Esq., C.E., have had the 
kindness to send me, through E. B. Webb, Esq., C.E., 
some excellent sections of, and specimens from, two 
artesian wells lately made at Buenos Ayres. I beg 
permission to present these specimens to the Geological 



364 Pampean Formation : PAET ix, 

Society, as they would be of considerable service to any 
one investigating the geology of that country. The 
Pampean formation is in several respects so interesting, 
from containing an extraordinary number of the remains 
of various extinct Mammifers, such as Megatherium, 
Mylodon, Mastodon, Toxodon., &c., and from its great 
extent, stretching in a north and south line for at least 
750 geographical miles, and covering an area fully 
equal to that of France, that, as it appears to me, a 
record ought to be preserved of these borings. South- 
ward, at the Rio Colorado, the Pampean formation 
meets the great Tertiary formation of Patagonia ; and 
northward, at St. Fa Bajada, it overlies this same for- 
mation with its several extinct shells. 

In. the central region near Buenos Ayres no natural 
section shows its thickness ; but, by the borings there 
made in two artesian wells (figs. 31 and 32), the Pampean 
mud, with tosca-roek, is seen to extend downwards 
from the level of the Rio Plata to a depth of sixty-one 
feet, and to this must be added fifty-five feet above 
the level of the river. These argillaceous beds overlie 
coarse sand, containing the Azara laliata (a shell 
characteristic of the Pampean formation), and attaining 
a thickness of about ninety-three feet, 1 So that the 

1 The following extract from the Report of the borers relates to 
this bed The bed of jellow, fluid sands between 18 60 aud47 m 20 
below the ground contains a vsubterranean ascending current, the 
level of which has not varied by a centimetre for three years. The 
level is O m 60 (2 feet over the level of the wells at Barracas) This bed 
(<napa*) is powei fully absorbent. At 68 m 30 a second subterranean cur- 
rent (' ovei flowing'), was met, which *ose one foot over the surface of 
the ground at Barracas. The dischaige was about 50 pipes daily > but 
the water was salt and undnnkable At 73 m 30 was found a third 
subterranean current ('ovei flowing'), which reached with difficulty 
the level of the ground. The discharge might be calculated at 
100 pipes daily. The water was very salt, and absorbed that of 
the hrst oveiflowing current. The great spring was met with at 
77 m *65.' 

As regards the quality and abundance of the water, Mr. Coghlan 
remarks that ' The quantity of water discharged per hour through a 
tube of about 4J inches in diameter, at a level of 6 feet above high* 



CHAP. XL 



On the Thickness of the, 



365 



entire thickness of the great estuarine or Painpean for- 
mation near Baenos Ayres is nearly 210 feet. 

No. 31 

GomparafciYe sections of the Artesian Wells of Barraea? and Bnenos Ayres, 

(Distance, 3 4 5 mi'es ) 

Barracas Kiaclmelo. Buenos Ayres. 

I 



Level of eqoi- 
librmm of 
the princi- 
pal SplUQg 




1st. spring . 



2nd spring 

3rd spring . 
4th spring" . 



High Tvatei 
level 



a. days and Tosca , 
"b. Sand * . 

c. Very sandy clay , ] 

& Dark "blue plastic clay . . f- . 
e Tosca, with calcareous nodules ) 
/. Yellow sands, rery fine and fluid 



a 2nd spring 
|p 3rd spring: 

Ira 4fch spring 
245 feet 



470 feet 

Thickness TMctaess 
at JBarracas at Buenos 
Feet Ayres Feet 
. 57 

13 51 



04 



45 



water mark, was 2,658 gallons. Its temperature was 21 Cent., and 
it bad a slightly disagreeable taste, from its being impregnated with 
salts of lime and magnesia, and a frinall quantity of sulphuretted 
hydrogen, 5 



3 66 



Pampean Formation : 



PABT II. 



Thickness Thickness 
at Banacas at Buenos 
Feet Ayres Feet 

a. Green sands . 66 62 

h Tertiary clay and sandstone (for details see fig- 32) ,34 33 

I t Hai d sandstone at the bottom of the Barracas \\ e 1 4J 

j Very calcareous red clay, becoming moie maily 

beneath ; bored tlirougli to a depth of . . 225 

This formation rests on various marine beds of in- 
durated green clay, sand with corals, sandstone, and 
limestone, altogether 107 feet in thickness. These 

No. 32. 

Detailed section, of the Artesian Well at Barracas. 




Thickness 
in metres 
<7 Sand 4U 

b Very arenaceous clay 8 02 

CFmecl.y 1*05 

c * 1 Blue plastic clay 290 

d Tosea, v*it.h calcareous nodules , . . 2*30 

e. Yellow sand, veiy fine and fluid, with quartz 

pebbles and fluviati e shells . . . . 28 60 
/. Green clay, more 01 less plastic and calcareous, 
with iron pvntes, marine shells, and nodules 
ot lifchogiiiphic scone .... 20 30 
g. Green <-and with shells and quartz pebbles 80 

h Shellv limestone . - 45 

z Calcareous cLiy 2 00 

I Shelly sandstone . 25 

I Gieen arenaceous clay 200 

m Shell} sandstone . 30 

n Speckled sand 70 

o. Very compact arenaceous clay 2 25 

p. Coarse sandstone . . . 1*40 

q. Green sand, very fine and fluid, with quartz 

pebbles' and shells 2 35 



beds contain fragments of the great Ostrea Patafjonica, 
0. Alva/rezii (?), Pecten Paranen&is, and other shells, 
apparently the same (but they have not been rigorously 
compared) with those enumerated by M. A. d'Orbigny 
and by myself as found at St. Fe Bajada, as well as at 
various points on the coast of Patagonia. The already 
enormous continuous extension of the Patagonian ter- 
tiary formation is thus largely increased. Beneath 



CHAP. xi. On the Thickness of the. 367 

these beds a mass of red calcareous clay, becoming In 
the lower part more and more marly, containing layers 
of sand, and of tlie thickness of 213 feet, was bored 
through to a depth of 470 feet from the level of the 
Rio Plata. This lower mass contained no fossils, and 
its age is of course unknown ; l but I may add that I 
saw at two points in Western Banda Oriental, beneath 
the marine tertiary strata, beds of red clay with marly 
concretions, which, from their mineralogical resemblance 
to the overlying Pampean formation, seemed to indicate 
that at an ancient period the Rio Plata had deposited 
an estuarine formation, subsequently covered by the 
marine tertiary beds, and these by the more modern 
estuarine formation, with its remains of numerous 
gigantic Mammalia; and that, finally, the whole had 
been elevated into the present plains of the Pampas. 



Localities within the region of the Pampas where great bones have 
beenfound. 

The folio wing list, which includes every account which I have 
hitherto met with, of the discovery of fossil mammiferous remains 
in the Pampas, may be hereafter useful to a geologist investigating 
this region, and it tends to show their extraordinary abundance. 
I lieard of and saw many fossils, the original position of which I 
could not ascertain j and 1 received many statements too vague to 
be here inserted. Beginning to the south : we have the two 
stations in Bahia Blanca, described in. this chapter, where, at P. 
Alta, the Megatherium, Megalonyx, Scelidotherium, Mylodon, 
Holophractus (or an allied genus), Toxodon, Macrauchenia, and 
an Equus were collected j and at M. Hermoso a Ctenomys, Hydrp- 
cheerus, some other rodents and the bones of a great roegatheroid 
quadruped. Close north-east of the S Tapalguen ; we have the 
R,io * Huesos ' (i e. "bones), which probably takes its name from 
large fossil bones. Near Villa Nuevo, and at Las Aveiias, not 
far from the Salado, three nearly perfect skeletons, one of the 
Megatherium, one of the GLyploion daiipeSj&nd. one of some great 
Dasypuid quadruped, were lound by the agent of Sir W. Parish 

1 It was supposed by Dr. Burmeister to be Silurian. 



368 Pampean Formation 6 PART n. 

(see Ms work ' Bu<*no^ Avres/ c. p. 171). I have seen the tooth 
of a Mastodon from the Salado ; a little northward of this river, 
on the borders of a lake near the G. del Monte, I saw many "bones, 
and one large piece of dermal armour : higher up the Salado, there 
is a place called Monte * Huesos.' On the Matanzas, about twenty 
miles south of Buenos Ayres, the skeleton (vide p. 178, of Buenos 
A} res,' &c by Sir W. Parish) of a Glyptodon was found about 
five feet beneath the surface ; here also (see k Cat. of Royal College 
of Surgeons ') remains of Glyptodon clavipes, G. ornatus, and G. 
retmdatus were found. Signer Angehs, in a letter which I have 
seen, refers to some great remains found in Buenos Ayres, at a 
depth of twenty varas from the surface. Seven leagues north of 
this city the same author found the skeletons of Mylodon robustiLS 
and Glyptodon ornatus. From this neighbourhood he has lately 
sent to the British Museum the following fossils : Remains of 
three or four individuals of Megatherium ; of three species of 
Glyptodon ; of three individuals of the Mastodon Andlum ; of 
Macrauchenia ; of a second species of Toxodon, different from T. 
Platensis ; and, lastly, of the Machairodus, a wonderful large car- 
nivorous animal. M. d'Orbigny has lately received from the Reco- 
late (' Voyage/ Pal. p. 144), near Buenos Ayres, a tooth of Toxodon 
Platensis. 

Proceeding northward, along the west bank of the Parana, we 
come to the Rio Luxan, where two skeletons of the Megatherium 
have been found; and lately, within eight leagues of the town of 
Luxan, Dr. F. X. Muniz has collected (' British Packet,' Buenos 
Ayres, September 25th, 1841), from an average depth of eighteen 
feet, very numerous remains, of no less than, as he believes, nine 
distinct species of mammifeis. At Areco, large bones have been 
found, which are believed, by the inhabitants, to have been changed 
from small bones by the water of the rher! At Arrecifes, the 
Glyptodon, sent to the College of Surgeons, was found ; and I 
have seen two teeth of a Mastodon from this quarter. At S. 
Nicolas, M. d'Orbigny found remains of a Canis, Ctenomys, and 
Kerodon ; and M. Isabelle (< Voyage,' p. 332) refers to a gigantic 
Armadillo found there. At S Carlos I heard of great bones. A 
little below the mouth of the Oarcarana, the two skeletons of 
Mastodon were found ; on the banks of this river, near S. Miguel, 
I found teeth of the Mastodon and Toxodon; and 'Falkner' 
(p. 55) describes the osseous armour of some great animal 5 I beard 
of many other bones in this neighbourhood. I have seen, I may 
add, in the possession of Mr. Caldcleugh, the tooth of a Mastodon 
Andwm said to have been found in Paraguay ; I may here also refer 
to a statement in this gentleman's travels (vol. i. p. 48), of a great 
skeleton having been found in the province of Bolivia in Brazil, on 
the B. de las Contas. The farthest point westward in the Pampas, 
at which I have heard of fossil bones, was high up on the banks of 
the R, Quinto. 

In Entre Kios, besides the remains of the Mastodon, Toxodon, 



CHAP. xi. Mammiferous Remains of. 369 

Equus, and a great Dasypoid quadruped near St. F6 Bajada, I 
received an account of tones having been found a little 8E. of 
P. G-orda (on the Parana), and of an entire skeleton at Matanzas, 
on the Anoyo del Animal. 

In Banda Oriental, besides the remains of the Toxodon, Mylo- 
dpn, and two skeletons of gieat animals with osseous armour (dis- 
tinct from that of the Glyptodon), found on the Arroyos Sarandis 
and Berquelo, M. Isabelle (' Voyage/ p. 322) says, many bones 
have been found near the R. Negro, and on the'K. Arapey, an 
affluent of the Paraguay, in lat. 30 40' south. I heard oi bones 
near the source of the A. Vivoi as I saw the remains of a Dasy- 
poid quadruped from the Arroyo Seeo, close to M. Video , and 
M d'Orbigny refers ( ( Voyage, Geolog.' p. 24) to another found on 
the Pedernal, an affluent of the St. Lucia ; and Signor Augelis, in 
a letter, states that a third skeleton of this family has been found 
near Oanelones. I saw a tooth of the Mastodon from Talas, 
another affluent of the St. Lucia. The most eastern point at 
which I heard of great bones having been found, was at Soils 
Grande, between M, Video and Maldonado. 



37O Tertiary Formations, PAET n. 



CHAPTEE XIL 

OH THE OLDER TERTIABY FORMATIONS OF PATAGONIA AND 
CHILE. 

jRio Negro S. Josef Port DesireinJiitepntincenusmitdstone with in- 
fusoria Port S. Julian Santa Cruz^asaltiv laid of P. Gallegos 
Eastern Tierra del Fneffo; lerrre? of r>Ttinct leech-trees Sum- 
mary on the Pataqotnan tertiary foima/iicns Tertiary formations 
of the Western Coast ChottOd ana C/iuoe yroups, lolcanic rocks of 
ConeepGion Namdad Coqwimbo Summary Age of the ter- 
tiary formations Lines <f elevation Sihcvfred KQO& Comparatiie 
ranges of the extinct and livwg Mollusca on the West Coast of S 
America Climate of the tertiary perioa On the causes of the 
absence of recent conclvifcrous deposits on the coast? of S America 
On the contemporaneous deposition and preservation of sedi- 
mentary formations. 

Rio Negro. I can add little to the details given by 
M. d'Orbigny l on the sandstone formation of this dis- 
trict. The cliffs to the south of the river are about 
200 feet in height, and are composed of sandstone of 
various tints and degrees of hardness. One layer, which 
thinned out at both ends, consisted of earthy matter, of 
a pale reddish colour, with some gypsum, and very like 
(I speak after comparison of the specimens brought 
tome) Pampean mud : above this was a layer of compact 
marly rock with dendritic manganese. Many blocks of 
a conglomerate of pumice-pebbles embedded in hard 
sandstone were strewed at the foot of the cliff, and had 
evidently fallen from above. A few miles NE. of the 
1 Voyage, Part. GSolog.' pp. 57-G5. 



xn. 



Rio Negro. 



371 



towD, 1 found, low clown in the san cist one, a bc s cl, a few 
inches in thickness, of a white, friable, harsh-feeling 
sediment, which adheres to the tongue, is of easy fusi- 
bility, and of little specific gravity; examined under 
the microscope, it is seen to be puniiceous tuff, formed 
of broken transparent crystals. In the cliffs south of 
the ri\ r er there is, also, a thin layer of nearly similar 
nature, but finer grained, and not so white ; it might 
easily have been mistaken for a calcareous tuff, but it 
contains no lime : this substance precisely resembles a 
most widely extended and thick formation in southern 
Patagonia, hereafter to be described, and which is re- 
markable for being partially formed of Infusoria. These 
beds, conjointly with the conglomerate of pumice, are 
interesting, as showing the nature of the volcanic action 
in the Cordillera during this old tertiary period. 

In a bed at the base of the southern cliffs, M. d'Or- 
bigny found two extinct fresh-water shells, namely, a 
Unio and Ohilina. This bed rested on one with bones 
of an extinct rodent, namely, the Mecjcumys Patagoni- 
ensis-y and this'again on another with extinct marine 
shells. The species found by M. d'Orbigny in different 
parts of this formation consist of: 



1 Ostrea Patagoniea, d'Orblg. 

* Voyage Pal.' (also at St. 
Pe, and whole coast of Pata- 
gonia) 

2 Ostrea Ferraris! , do. 

3 Ostrea Alvarezii, d'Orbig 



Voyage Pal * (also St. F 

and S Josef). 

4. Pecten Patagoniensis, do. 
5 Venus Monster u, do (also St. 

F6). 
6. Area Bonplandiana, do. (do.) 



According to M. d'Orbigny, the sandstone extends 
westward along the coast as far as Port S. Antonio, and 
up the Rio Negro far into the interior : northward I 
traced it to the southern side of the Bio Colorado, where 
it forms a low denuded plain. This formation, thougii 
contemporaneous with that of the rest of Patagonia 3 is 
25 



372 Tertiary Formations. PAKT n a 

quite different in mineralogical composition, being con- 
nected with it only by the one thin white layer : this 
difference may be reasonably attributed to the sediment 
brought down in ancient times by the Rio Negro; by 
which agency, also, we can understand the presence of 
the fresh- water shells, and of the bones of land animals. 
Judging from the identity of four of the above shells, 
this formation is contemporaneous (as remarked by 
M. d'Orbigny) with that under the Pampean deposit in 
ntre Rios and in Banda Oriental. The gravel capping 
the sandstone plain, with its calcareous cement and 
nodules of gypsum, is probably, from the reasons given 
in the eighth chapter, contemporaneous with the upper- 
most beds of the Pampean formation on the upper plain 
north of the Colorado. 

San Josef. My examination here was very short : 
the cliffs are about 100 feet high ; the lower third 
consists of yellowish-brown, soft, slightly calcareous, 
muddy sandstone, parts of which when struck emit a 
fetid smell. In this bed the great Ostrea Patagonica, 
often marked with dendritic manganese and small coral- 
line&, were extraordinarily numerous. I found here the 
folluwmg shells : 

1. Osirea Patagomca, d'Orbis; 'Voyage Pal.' (also at St. F6 and 

whole coast of Patagonia) 

2. Osirea Alvarezu, d'Oibig * V. Pal ' (also St F6 and R. Negro.) 

3. Pecten Parauensis, d'Orbig. 'V. Pal' and PI. Ill f. 30 of this 

work (also St F, S. Julian, and Port Desiie). 

4. Pecten Darwimanus, d'Orbig. V. Pal.' and PI III. f . 28 and 29 

(also St. F6.) 

5. Pecten actinodes, G. B. Sowerby, PI III. f 33 

6. Terebratula Patagomca, G. B. iSowerby, PI. II. f. 26 and 27 

(also S. Julian). 

7. Oasts of a Turntella. 

The four first of these species occur at St. P6 in 
Entie Rios, and the two first in the sandstone of the 
Bio Negro. Above this fossiliferous mass, there is a 



CHAP. xii. Nnevo Gulf and Port Desire. 373 

stratum of very fine-grained, pale brown muds tone, 
including numerous laminse of selenite. All the strata 
appear horizontal, but wlien followed by the eye for a 
long distance, they are seen to have a small easterly 
dip. On the surface we have the porphyritic gravel, 
and on it sand with recent shells. 

N'uevo Gulf. From specimens and notes given me 
by Lieut. Stokes, it appears that the lower bed consists 
of soft muddy sandstone, like that of S. Josef, with 
many imperfect shells, including the Peden Paranensis^ 
d'Orbig., casts of a Turritella and Scutella. On this 
there are two strata of the pale brown mudstone, also, 
like that of 8. Josef* separated by a darker coloured, 
more argillaceous variety, including the Odren Pata- 
(jonica. Prof. Ehrenberg has examined this mudstone 
for me : he finds in it three already known microscopic 
organisms, enveloped in a fine-grained punuceous tuff, 
which I shall have immediately to describe in detail. 
Specimens brought to me from the uppermost bed, 
north of the RioChupat, consist of this same substance, 
but of a whiter colour 

Tertiary strata, such as are here described, appear 
to extend along the whole coast between the Rio Chupat 
and Port Desire, except where interrupted by the under- 
lying claystone porphyry, and by some metamorphic 
rocks ; these hard rocks, I may add, are found at in- 
tervals over "a space of about five degrees of latitude, 
from Point Union to a point between Port S. Julian 
and S. Cruz, and will be described, in the ensuing chapter. 
Many gigantic specimens of the Ot>trea Patagonica 
were collected in the Gulf of St. George. 

Port Desire. A good section of the lowest fossili- 
ferous mass, about forty feet in thickness, resting on 
claystone porphyry, is exhibited a few miles south of 



374 Tertiary Formations. PA.ET n. 

the harbour. The shells sufficiently perfect to be 
recognised consist of: 

1. CKtrea Pata^onica, d Orhig (also at St. Fe and whole coast of 

Pataaoma) 

2. Pecten Paianensis, d'Orbig 'Voy Pal ,' and PI III. 1 30 of this 

work (also at St Fe, S Josef, S Julian) 

3. Pecten centrahs, G- B. Sowerby, PI III. 1 31 (also S. Julian 

and S. Cruz) 

4. Cucullsea alta, do , PI. II f 22, 23 (also S Cruz). 

5. Nucula omata, do , PL II. f 19. 

6. Tumtella Patagomoa, do , PI III. f . 48. 

The fosbiliferous strata, where not denuded, are 
conformably covered by a considerable thickness of the 
fine-grained pumiceous mudstone, divided into two 
masses : the lower half is very fine-grained, slightly 
unctuous, and so compact as to break with a semi- 
conchoidal fracture, though yielding to the nail ; it 
includes laminse of selenite : the upper half precisely 
resembles the one layer at the Rio Negro, and, with the 
exception of being whiter, the upper beds at San Josef 
and Nuevo Gulf In neither mass is there any trace to 
the naked eye of organic forms. Taking the entire 
deposit, it is generally quite white, or yellowish, or 
feebly tinted with green it is either almost friable 
under the finger, or as hard as chalk ; it is of easy 
fusibility, of little specific gravity, is not harsh to the 
touch, adheres to the tongue, and when breathed on 
exhales a strong aluminous odour it sometimes con- 
tains a very little calcareous matter, and traces (besides 
the included laminse) of gypsum. Under the microscope, 
according to Prof. Ehrenberg, 1 it consists of minute, 
triturated, cellular, glassy fragments of pumice, with 
some broken crystals. In the minute glassy fragments, 
Prof. Ehrenberg recognises organic structures, which 
have been affected by volcanic heat : in the specimens 
from this place, and from Port S. Julian, he finds six- 

1 * Monatsberichten der konig. Akad. zu Berlin vom April, 1845.' 



OHAP. XTT, Port S. Julian. 375 

teen Polygastrica and twelve Phj tolitharia. Of these 
organisms, seven are new forms, the others being pre- 
viously known : all are of marine, and chiefly of oceanic, 
origin. This deposit to the naked eye resembles the 
crust which, often appears on \\eathered surfaces of 
feldspathic rocks ; it likewise resembles those beds of 
earthy feldspathic matter, sometimes inter-stratified with 
porphyritic rocks, as is the case in this very district 
with the underlying purple claystone porphyry. From 
examining specimens under a common microscope, and 
comparing them with other specimens undoubtedly of 
volcanic origin, I had come to the same conclusion \\ ith 
Prof. Ehrenberg, namely, that this great deposit, in its 
first origin, is of volcanic nature. 

Port S. Julian. On the south side of the harbour, 
the following section, which 1 here repeat, gives the 
nature of the beds seen in the cliffs of the ninety feet 

No 33 

Section of the strata exhibited in the cliffs of the 9U-feet plain at Port 
fci J uliaii. 




plain. Beginning at the top, 1st, the earthy mass 
(A A), including the remains of the Macrauchenia, with 
recent shells on the surface; 2nd, the porphyritic 
shingle (B), which, in its lower part is inter stratified 
(owing, I believe, to redeposition during denudation) 
with the white pnmiceons mndstone ; 3rd, this white 
mndstone, about twenty feet in thickness, and divided 
into two varieties (0 and D), both closely resembling 
the lower, fine-grained, more unctuous and compact 
kind at Port Desire ; and, as at that place, including 
much selenite ; 4th, a fossiliferous mass, divided into 



376 Tertiary Formations. PART rr, 

three main beds, of which the uppermost is thin, and 
consists of ferruginous sandstone, with many shells of 
the great oyster and Pectin Par une MIS ; the middle 
bed (E) is a yellowish earthy sandstone abounding with 
Scutellne; and the lowest bed (F) is an indurated, 
greenish, sandy clay, including large concretions of 
calcareous sandstone, many shells of the great oyster, 
and in parts almost made up of fragments of Balanidie. 
Out of these three beds, I procured the following twelve 
species, of which the two first were exceedingly numerous 
in individuals, as were the Terebratulaa and Turritello3 
in certain layers r 

1. Ostrea Patagonica, d'Orb 'Voyage Pal/ (also at St. F6 and 

whole coast of Patagonia). 

2. Pecten Paranensis, d'Oibig do , and PI III. f. 30 of this work 

(St Fe, S. Josef, Port Desne) 

3. Pecten centrahs, G-. B, Soweiby, PL III. 1 31 (also P. Desire 

and S Crnz). 
4 Pecten geminatus, do , PI. II f 24 

5. Terebratula Patagonica, do , PI II f . 26 and 27 (also S Josef), 

6. SStruthiolana oinata, do , PI. IV f. (52 (al&o S. Cruz). 

7. Fusus Patagonicus, do , PI IV. f GO. 

8. Fusus Noachinus, do , PI IV. f. 58 and 59. 

9. Scalana rugulosa, do , PI III f. 42 and 43 

10 Turntella arntmlacram, do , PI III f 49 (also S Cruz). 

11. Pyrula, cast of, like P. ventricosa of Rowerby, Tank Cat. 

12. Balamis vanans, G B Sowerby, Pi II f 4 5, 6 

13. Scutella, diifenng from the species from Nuevo Gulf. 

At tlie head of the inner harbour of Port S, Julian, 
the fossihferous mass is not displayed, and the sea-cliffs 
from the water's edge to a height of between 100 and 
200 feet are formed of the white pumiceous mndstone, 
which here includes innumerable, far-extended, some- 
times horizontal, sometimes inclined or vertical laminae 
of transparent gypsum, often about an inch in thick- 
ness. Further inland, with the exception of the 
superficial gravel, the whole thickness of the truncated 
hills, which represent a formerly continuous plain 950 
feet in height, appears to be formed of this white mud- 



CHAP. xn. Port S. Julian and Santa Cruz. 377 

stone : here and there, however, at various heights, thin 
earthy layers, containing- the great oyster, Pecten Para- 
nends and Turrit ella ambulacrum, are interstratified ; 
thus showing that the whole mass belongs to the same 
epoch I nowhere found even a fragment of a shell 
actually in the white deposit, and only a single cast of 
a Turritella. Out of the eighteen microscopic organisms 
discovered by Ehrenberg in the specimens from this 
place, ten are common to the same deposit at Porb 
Desire. I may add that specimens of this white mud- 
stone, with the same identical characters, were brought 
me from two points, one twenty miles north of S. 
Julian, where a wide gravel-capped plain, 350 feet in 
height, is thus composed ; and the other forty miles 
south of S. Julian, where, on the old charts, the clifls 
are marked as c Chalk Hills,' 

Santa Cruz. The gravel-capped cliffs at the mouth 
of the river are 355 feet in height : the lower part, to 
a thickness of fifty or sixty feet, consists of a more or 
less hardened, darkish, muddy, or argillaceous sandstone 
(like the lowest bed of Port Desire), containing very 
many shells, some silicified and some converted into 
yellow calcareous spar. The great oyster is here 
numerous in layers; the Trigonocelia and Turritella 
are also very numerous : it is remarkable that the 
Pecten Paranensis, so common in all other parts of 
the coast, is here absent: the shells consist of: 

1. Oatrea Patagonica, d'Orbi^ * Voyage Pal J (also at St Fe and 

whole coast of Patagonia) 

2. Pecten centralis, G- B Sowerby, PI III. f 31 (also P. Desire 

and S Julian). 

3. Venus mendionuhs of G- B Sowerby, PI II. f. 13. 

4 CrassatellaLjeliii, do PI II 110 

5 Cardmin pulchellum, do PL II. f. 15. 

6 Cardita Patagonica do PI II f. 17. 

7 Maotra ru^ata, do. PI II f. 8. 

8. Mactra Darwimi, do. PL II. f 9 

9. Cucullasa alta, do. PL II f 22, 23 (also P. Desire), 



378 Tertiary Formations. FAET n. 

10, Tugonocelia insolita, do PI II 1 20, 21. 
11 Nucula (?) glabra, do PI II f. IS 
12, Crepidula greuaria, do PI III. f 34. 

13 Valuta alta, do PI. IV f 75. 

14 Tiochus coilans, do PI III f. 44, 45. 

15 Natioa solida (.'), do H HI * 40, 41. 

16 Stmthiolariaoznata, do PI IV f 62 (also P Desire). 

17 Tumiella ainbulacium, do PL III f 49 (also P 8 Julian) 
Imperf ec t f ragments of the geneia Byssoarca, Artemis, and Fusus. 

The upper part of the cliff is generally divided into 
three great strata, differing slightly in composition, but 
essentially resembling the pumiceous mndstone of the 
places farther north; the deposit, however, here is more 
arenaceous, of greater specific gravity, and not so white : 
it is interlaced with numerous thin veins, partially or 
quite filled with transverse fibres of gypsum ; these fibres 
were too short to reach across the vein, have their extre- 
mities curved or bent : in the same veins with the gvp- 

o/ i 

sum, and likewise in separate veins as well as in little 
nests, there is much powdery sulphate of magnesia (as 
ascertained by Mr Reeks) in an uncompressed form : I 
believe that this salt has not heretofore been found in 
veins. Of the three beds, the central one is the most com- 
pact, and more like ordinary sandstone : it includes nu- 
merous flattened spherical concretions, often united like 
a necklace, composed of hard calcareous sandstone, con- 
taining a few shells : some of these concretions were 
four feet in diameter, and in a horizontal line nine feet 
apart, showing that the calcareous matter must have 
been drawn to the centres of attraction from a. distance 
of four feet and a half on both sides. In the upper and 
lower finer-grained strata, there were other concretions 
of a grey colour, containing calcareous matter, and so 
fine-grained and compact as almost to resemble por- 
celain-rock : I have seen exactly similar concretions in 
a volcanic tufaceous bed in Ohiloe. Although in this 
tipper fine-grained strata, organic remains were very 
rare, yet I noticed a few of the great oyster ; and in 



CHAP xii. Santa Cruz. 379 

one included soft ferruginous layer, there were some speci- 
mens of the CucuUwa alto, (found at Port Desire in the 
lower fossil if erous mass) and of the Madra ru<jat(^ which 
latter shell has been partially converted into gypsum. 

In ascending the valley of the S. Cruz, the upper 
strata of the coast-cliffs are prolonged, with nearly the 
same characters, for fifty miles: at about this point, 
they begin in the most gradual and scarcely perceptible 
manner, to be banded with white lines , and after as- 
cending ten miles farther, we meet with distinct thin 
layers of whitish, greenish, and yellowish fine-grained, 
fusible sediments. At eighty miles from the coast, 1 m 
a cliff thus composed, there were a few la}ers of ferru- 
ginous sandstone, and of an argillaceous sandstone with 

No 34. 

Section of the plains of Patagonia, on the bauks of the S Cruz 
Surface of plam with erratic boulders, 1,416 ft above the sea. 



212 ft thick 



322 ft. thick 




592 ft. thick 



Eiver of S Cruz , here 280 ft. above sea 

a. Gravel and boulders 5 Basaltic lava, 

c Sedimentary layers d. Bed of small pebbles. t Talus. 

concretions of marl like those in the Pampas. At 100 
miles from the coast, that is at a central point between 

1 At this spot, for a space of three- quarters of a mile along the 
north side of the river, and for a width of halt a mile, there has'been 



380 Tertiary Formations. PAET n. 

the Atlantic and the Cordillera, we have the preceding 
section. 

The upper half of the sedimentary mass, under the 
basaltic lava, consists of innumerable zones of perfectly 
white, bright green, yellowish and brownish, fine-grained, 
sometimes incoherent, sedimentary matter. The white, 
puniiceous, trachytic tuff-like varieties are of rather 
greater specific gravity than the pumiceous mudstone 
on the coast to the north : some of the layers, especially 
the browner ones, are coarser, so that the broken crys- 
tals are distinguishable with a weak lens. The layers 
vary in character in short distances. With the excep- 
tion of a few of the Obtrea Patagomca, which appeared 
to have rolled down from the cliff above, no organic 
remains were found. The chief difference between 
these layers taken as a whole, and the upper beds both 
at the mouth of the river and on the coast northward, 
seems to lie in the occasional presence of more colouring 
matter, and in the supply having been intermittent : 
these characters, as we have seen, very gradually dis- 
appear in descending the valley, and this fact may 
perhaps be accounted for by the currents of a moie 
open sea having blended together the sediment from a 
distant and intermittent source. 

The coloured layers in the foregoing section rest on 
a mass, apparently of great thickness (but much hidden 
by the talus), of soft sandstone, almost composed of 
minute pebbles, from one-tenth to two-tenths of an 
inch in diameter, of the rocks (with the entire exception 

a great slip, which has formed hills between CO and 70 feet in height, 
and has tilted the strata into highly inclined and even vertical posi- 
tions. The strata generally clipped at an angle of 45 towards the 
cliff from which they had slided. 1 have observed in slips, both on 
a small and large scale, that this inward dip is very general Is it 
due to the hydrostatic pressure of water percolating with difficulty 
through the strata acting with greater force at the base of the 
mass than against the upper part ? 



CHAP. xn. 



Santa Crztz. 



of the basaltic lava) composing the great boulders on 
the surface of the plain, and probably composing the 
neighbouring Cordillera. Five miles higher up the 
valley, and again thirty miles higher up, 1 (that is twenty 
miles from the nearest range of the Cordillera) the lower 
plain included within the upper escarpments is formed, 
as seen on the banks of the river, of a nearly similar 
but finer-grained, more earthy, laminated sandstone, 
alternating with argillaceous beds, and containing nu- 
merous moderately sized pebbles of the same rocks, and 
some shells of the great Ostrea Patagonica. As most 
of these shells had been rolled before being here em- 
bedded, their presence does not prove that the sand- 
stone belongs to the great Patagonian tertiary formation, 
for they might have been redeposited in it when the 
valley existed as a sea-strait ; but as amongst the 
pebbles there were none of basalt, although the cliffs on 
both sides of the valley are composed of this rock, I 
believe that the sandstone does belong to this formation. 
At the highest point to which we ascended, twenty 
miles distant from the nearest slope of the Cordillera, I 
could see the horizontally zoned white beds, stretching 
under the black basaltic lava, close up to the mountains ; 
so that the valley of the S. Cruz gives a fair idea of the 
constitution of the whole width of Patagonia. 

Basaltic Lava of the S. Cruz. This formation is 
first met with sixty-seven miles from the mouth of the 
river ; thence it extends uninterruptedly, generally but 
sot exclusively on the northern side of the valley, close 
up to the Cordillera. The basalt is generally black 
and fine-grained, but sometimes gray and laminated ; 
it contains some olivine, and high up the valley much 

1 I found at both places, but not in situ, quantities of coniferous 
and ordinary dicotyledonous silicified wood, which was examined 
for me by Mr. R. Brown. 



382 Tertiary Formations. *AET n. 

glassy feldspar, where, also, it is often amygdaloidal ; 
it is never highly vesicular, except on the sides of rents 
and on the upper and lower, spherically laminated sur- 
faces. It is often columnar ; and in one place I saw- 
magnificent columns, each face twelve feet in width, 
with their interstices filled up with calcareous tuff. 
The streams rest conformably on the white sedimentary 
beds, but I nowhere saw the actual junction ; nor did I 
anywhere see the white Tbeds actually superimposed on 
the lava ; but some way up the valley, at the foot of 
the uppermost escarpments, they must be thus super- 
imposed. Moreover, at the lowest point down the 
valley, where the streams thin out and terminate in 
irregular projections, the spaces or intervals between 
these projections are filled up to the level of the now 
denuded and gravel-capped surfaces of the plains, with 
the white-zoned sedimentary beds; proving that this 
matter continued to be deposited after the streams had 
flowed. Hence we may conclude that the basalt is 
contemporaneous with the upper parts of the great 
tertiary formation. 

The lava where first met with is ISO feet in thick- 
ness : it there consists of two, three, or perhaps more 
streams, divided from each other by vesicular spheroids, 
like those on the surface From the streams having, 
as it appears, extended to different distances, the terminal 
points are of unequal heights. Generally the surface 
of the basalt is smooth ; but in one part high, up the 
valley it was so uneven and hummocky, that until I 
afterwards saw the streams extending continuously on 
both sides of the valley up to a height of about 3,000 
feet close to the Cordillera, I thought that the craters of 
eruption were probably close at hand. This hummocky 
surface I believe to have been caused by the crossing 
and Leaping up of different streams. In one place, 



CHAP. xn Santa Critz. 383 

there were several rounded ridges about twenty feet in 
height, some of them as broad as high, and some broader, 
which certainly had been formed whilst the lava was 
fluid, for in transverse sections each ridge was seen to 
be concentrically laminated, and to be composed of im- 
perfect columns radiating from common centres, like 
the spokes of wheels. 

The basaltic mass where first met with is, as I have 
said, 130 feet in thickness, and, thirty-five miles higher 
up the valley, it increases to 322 feet. In the first 
fourteen and a half miles of this distance, the upper 
surface of the lava, judging from three measurements 
taken above the level of the river (of which the appa- 
rently very uniform inclination has been calculated 
from its total height at a point 135 miles from the 
mouth) slopes towards the Atlantic at an angle of only 
7' 20" : this must be considered only as an approxi- 
mate measurement, but it cannot be far wrong. Taking 
the whole thirty-live miles, the upper surface slopes at 
an angle of 10' 53" ; but this result is of no value in 
showing the inclination of any one stream, for half-way 
between the two points of measurement, the surface 
suddenly rises between 100 and 200 feet, apparently 
caused by some of the uppermost streams having 
extended thus far and no farther. From the measure- 
ments made at these two points, thirty-five miles apart, 
the mean inclination of the sedimentary beds, over 
which the lava has flowed, is now (after elevation from 
under the sea) only T 52" : for the sake of compari- 
son, it may be mentioned that the bottom of the present 
sea in a line from the mouth of the S. Cruz to the 
Falkland Islands, from a depth of seventeen, fathoms to 
a depth of eighty-five fathoms, declines at an angle of 
1' 22" ; between the beach and the depth of seven- 
teen fathoms, the slope is greater. From a point about 



384 Tertiary Formations, PAET n. 

half-way up the valley, the basaltic mass rises more 
abruptly towards the foot of the Cordillera, namely, 
from a height of 1,204 feet, to about 3,000 feet above 
the sea. 

This great deluge of lava is worthy, in its dimensions, 
of the great continent to which it belongs. The aggre- 
gate streams have flowed from the Cordillera to a dis- 
tance (unparalleled, 1 believe, in any case yet known) 
of about 100 geographical miles. Near their furthest 
extremity their total thickness is 130 feet, which increase 
thirty-five miles farther inland, as we have just Been, 
to 322 feet. The least inclination given by M. E. de 
Beaumont of the upper surface of a lava stream, namely, 
SO', is that of the great subaerial eruption in 1783 
from Skaptar Jukul in Iceland ; and M. E. de Beaumont 
shows 1 that it must have flowed down a mean inclination 
of less than 20'. But we now see that under the 
pressure of the sea successive streams have flowed over 
a smooth bottom with a mean inclination not more 
than 7' 52" ; and that the upper surface of the 
terminal portion (over a space of fourteen and a half 
miles) has an inclination of not more than 7 / 20", 
If the elevation of Patagonia has been greater nearer 
the Cordillera than near the Atlantic (as is probable), 
then these angles are now all too large. I must repeat, 
that although the foregoing measurements, which were 
all carefully taken with the barometer, may not be 
absolutely correct, they cannot be widely erroneous. 

Southward of the S. Cruz, the cliffs of the 840 feet 
plain extend to Coy Inlet, and, owing to the naked 
patches of the white sediment, they are said on the 
charts to be c like the coast of Kent.' At Coy Inlet 
the high plain trends inland, leaving flat-topped outliers, 
At Port Gallegos (lat, 51 35', and ninety miles south 

1 ' M&moires pour rvir,' &c., pp. 178 and 217, 



CHAP. XH. Tierra del Fitcgo. 385 

of S. Cruz), I am informed by Captain Sulivan, E.N"., 
that there is a gravel-capped plain from 20 U to 300 feet 
in height, formed of numerous strata, some fine-grained 
and pale-coloured, like the upper beds at the mouth of 
the S Cruz, others rather darker and coarser, so as to 
resemble gritstones or tuffs ; these latter include rather 
large fragments of apparently decomposed volcanic 
rocks ; there are, also, included layers of gravel. This 
formation is highly remarkable, from abounding with 
inammiferous remains, which have not as yet been 
examined by Professor Owen, but which include some 
large, but mostly small, species of Pachydermata, 
Edentata, and Rodentia. From the appearance of the 
pale-coloured, fine-grained beds, I was inclined to 
believe that they corresponded with the upper beds of 
the S. Cruz; but Professor Ehrenberg, who has examined 
some of the specimens, informs me that the included 
microscopical organisms are wholly different, being 
fresh and brackish water forms. Hence the 200 to 
300 feet plain at Port Gallegos is of unknown age, but 
probably of subsequent origin to the great Patagonian 
tertiary formation. 

Eastern Tieira del Faego. Judging from the 
height, the general appearance, and the white colour 
of the patches visible on the hill sides, the uppermost 
plain, both on the north and western side of the Strait 
of Magellan, and along the eastern coast of Tierra del 
Puego as far south as near Port St. Polycarp, probably 
belongs to the great Patagonian tertiary formation* 
These higher table-ranges are fringed by low, irregular, 
extensive plains, belonging to the boulder formation, 1 
and composed of coarse unstratified masses, sometimes 
associated (as north of C. Virgin's) with fine, laminated, 
muddy sandstones. The cliffs in Sebastian Bay are 

1 Described in the ' Geological Transactions,' vol vi p. 416, 



386 Summary on the Patagonian PAET n. 

200 feet in height, and are composed of fine sandstones 3 
often in curvilinear layers, including hard concretions 
of calcareous sandstone, and layers of gravel. In these 
beds there are fragments of wood, legs of crabs, barnacles 
encrusted with corallines still partially retaining their 
colour, imperfect fragments of a Pholas distinct from 
any known species, and of a Venus, approaching very 
closely to, but slightly different in form from, the 
V. leyiticularis, a species living on the coast of Chile. 
Leaves of trees are numerous between the laminae of 
the muddy sandstone ; they belong, as I am informed 
by Dr. J. D. Hooker, 1 to three species of deciduous 
beech, different from the two species which compose 
the great proportion of trees in this forest-clad land. 
From these facts it is difficult to conjecture, whether 
we here see the basal part of the great Patagonian 
formation, or some later deposit. 

Summary on the Patagonian Tertiary Formation. 
Four out of tie seven fossil shells, from St. Fe in 
Entre Rios 5 were found by M d'Orbigny in the sand- 
stone of the Rio Negro, and by me at San Josef Three 
out of the six from San Josef are identical with those 
from Port Desire and S Julian, which two places have 
together fifteen species, out of which three are common 
to both. Santa Cruz has seventeen species, out of 
which five are common to Port Desire and S. Julian. 
Considering the difference in latitude between these 
several places, and the small number of species altogether 
collected, namely thirty-six, I conceive the above pro- 
portional number of species in common, is sufficient to 
show that the lower fossiliferous mass belongs near'y, 
I do not say absolutely, to the same epoch. What this 
epoch may be, compared with the European tertiary 
stages, M. d'Orbigny will not pretend to determine. 
1 * Botany of the Antarctic Voyage,' p 212. 



CHAP. XXX. 



Tertiary Formation. 387 



The thirty six species (including those collected by 
myself and by If. d'Orbigny) are all extinct, or at least 
unknown | but it should be borne in mind, that the 
present coast consists of shingle, and that no one, I 
believe, has dredged here for shells; hence it is not 
improbable that some of the species may hereafter be 
found living. Some few of the species are closely related 
with existing ones ; this is especially the case, according 
to M. d'Orbigny and Mr. Sowerby, with the Fusus 
Patagonicus ; and, according to Mr. Scwerby, with 
the Pyrula, the Venus meridionalis , the Orepidula 
gregaricu, and the Twrritella ambulacrum, and T. 
Patagonica. At least three of the genera, namely, 
Cucullgsa, Crassatelia, and (as determined by Mr. 
Sowerby) Struthiolaria, are not found in this quarter 
of the world ; and Trigonocelia is extinct. The evidence 
taken altogether indicates that this great tertiary 
formation is of considerable antiquity but when treat- 
ing of the Chilian beds, I shall have to refer again to 
this subject. 

The white pumiceous mudstone, with its abundant 
gypsum, belongs to the same general epoch with the 
underlying fossiliferous mass, as may b inferred from 
the shells included in the intercalated layers at Neuvo 
Gulf, S. Julian, and S. Grass. Out of the twenty-seven 
marine microscopic structures found by Prof. Ehrenberg 
in the specimens from S. Julian and Port Desire, ten 
are common to these two places : the three found at 
Neuvo Gulf are distinct. I have minutely described 
this deposit, from its remarkable characters and its 
wide extension. From Coy Inlet to Port Desire, a dis- 
tance of 230 miles, it is certainly continuous; and I 
have reason to believe that it likewise extends to the 
Bio Ghupat, Neuvo Gulf and San Josef, a distance of 
570 miles : we have, also, seen that a single layer occurs 
26 



388 Summary on the Patagonian PAET n 

afcTho Rio Negro. At Port S. Julian it is from 800 to 
900 feet in thickness ; and at S. Cruz it extends, with 
a slightly altered character, up to the Cordillera. From 
its microscopic structure, and from its analogy with 
other formations in volcanic districts, it must be con- 
sidered as originally of volcanic origin: it may have 
bren formed by the long-continued attrition of va^t 
quantities of pumice, or, judging from the manner in 
which the mass becomes, in ascending the valley of S. 
Cruz, divided into variously coloured layers, from the 
long-continued eruption of clouds of fine ashes. In 
either case, we mut-t conclude, that the southern volcanic 
orifices of the Cordillera, now in a dormant state, were 
at about this period over a wide space, and for a great 
lenjrth of time, in action. We have evidence of this 
fac in the latitude of the Eio Negro in the sandstone- 
conglomerate with pumice, and demonstrative proof of 
it, at S. Cruz, in the vast deluges of basaltic lava : at 
this same tertiary period, also, there is distinct evidence 
of volcanic action in Western Banda Oriental. 

The Patagonian tertiary formation extends continu- 
ously, judging from fossils alone, from S. Cruz to 
near the Eio Colorado, a distance of above 600 miles, 
and reappears over a wide area in Entre Eios and Banda 
Oriental, making a total distance of 1,100 miles ; but 
this formation undoubtedly extends (though no fossils 
were collected) far south of the S. Cruz, and, accord- 
Ing to M. d'Orbigny, 120 miles north of St. Fe. At 
S. Cruz we have seen that It extends across the con- 
tinent ; being on the coast about 800 feet in thickness 
(and rather more at S. Julian), and rising with the 
contemporaneous lava-streams to a height of about 
3,000 feet at the base of the Cordillera. It rests ? 
wherever any underling formation can be seen, on 
plntonic and metamorphic rocks. Including the newer 



xii. Tertiary Formation. 



Pampean deposit, and those strata In eastern Tierra del 
Puego of doubtful age, as well as the boulder formation, 
we have a line of more than twenty-seven degrees of 
latitude, equal to that from the Straits of Gibraltar to 
the south of Iceland, continuously composed of tertiary 
formations. Throughout this great space the land has 
been upraised, without the strata having been in a 
single instance, as far as nay means of observation went) 
unequally tilted or dislocated by a fault, 

Tertiary Formations on the West Ooast* 

Chonos Archipelago. The numerous islands of this 
group, with the exception of Lemus, Ypun, consist 
of metamorphic schists these two islands are formed of 
softish grey and brown, fusible, often laminated sand- 
stones, containing a few pebbles, fragments of black 
lignite, and numerous mammillated concretions of hard 
calcareous sandstone. Out of these concretions at Ypun 
(lat. 40 30' S.), I extracted the four following extinct 
species of shells : 



1. Turritella suturalis, G B. Sowerby, PL IIL f. 50 (also Na 

2. faigaretus subglobos~s, do. PI. IIL 1 36, 37. (do.) 

3, Cytbei^ea (?) sulculosa (?), do. PI. IL 1 14 (also Ghzloe and 

Huafo ?). 

4, Volute, fragments of. 

In the northern parts of this group there are some 
cliffs of gravel and of the boulder formation. In the 
southern part (at P. Andres in Tres Montes), there is 
a volcanic formation, probably of tertiary origin. The 
lavas attain a thickness of from 200 to 300 feet ; they 
are extremely variable in colour and nature, being 
compact, or brecciated, or cellular, or anaygdaloidal 
with zeolite, agate and bole, or porphyritic with glassy 
albitic feldspar. There is also mnch Imperfect rnbbly 



39 Tertiary Formations. FAET n, 

pitch stone, with the Interstices charged with powdery 

carbonate of lime apparently of contemporaneous origin. 
These lavas are conformably associated with strata of 
breccia and of brown toff containing lignite. The 
whole mass has been broken up and tilted at an angle 
of 45, by a series of great volcanic dikes, one of which 
was thirty yards in breadth. This volcanic formation 
resembles one, presently to be described, in Ohiloe. 

Huafa. This island lies between the Chonos and 
Ohiloe groups : it is about 800 feet high, and perhaps 
has a nucleus of metamorphic rocks. The strata which 
I examined consisted of fine-grained muddy sandstones, 
with fragments of lignite and concretions of calcareous 
sandstone. I collected the following extinct shells, of 
which the Turritella was in great numbers : 

1. Bulla cosmophila, G. B. Sowerby, PL HI. 1 35. 

2. Plenrotoma snbsequalis, do. PI. IV". f, 52. 

S. Fusus cleryanns, d'Orbig. ' Toy. Pal' PL XII. 1 6, 7 (also at 
Ooqmmbo). 

4. Triton leuoostomoides, G. B Sowerby, PL IV. 1 64. 

5. Turritella Chiiensis, do. PI IV 1 51 (also Mocha) 

6. Venus, probably a dibticet species, but very imperfect. 

7. Cytfaersea (?) sulculosa ('), do. PL II, f. 14 

8. Dentalium majus, G B. Sowerby, PL II. f. 3. 

Chiloe. This fine island is about 100 miles in 
length. The entire southern part, and the whole 
western coast, consists of "mica-schist, which likewise is 
seen in the ravines of the interior. The central moun- 
tains rise to a height of 8,000 feet, and are said to be 
partly formed of granite and greenstone: there are 
twp small volcanic districts. The eastern coast, and 
large parts of the northern extremity of the island are 
composed of gravel, the boulder formation, and under- 
lying horizontal strata. The latter are well displayed 
for twenty miles north and south of Castro ; they vary 
in character from common sandstone to fine-grained, 
laminated mudstones: all the specimens which I ex- 



CHAP. xn. Ckiloe. 39 * 

amined are easily fusible, and some of tlie beds might 
be called volcanic grit-stones. These latter strata are 
perhaps related to a mass of columnar trachyte which 
occurs behind Castro. The sandstone occasionally In- 
cludes pebbles, and many fragments and layers of lignite ; 
of the latter, some are apparently formed of wood and 
others of leaves: one layer on the N W. side of Lemny 
is nearly two feet In thickness. There is also much 
silicified wood, both common dicotyledonous and coni- 
ferous : a section of one specimen in the direction of the 
medullary rays has, as I am informed by Mr. R. Brown, 
the discs in a double row placed alternately, and not 
opposite as in the true Araucaria. I found marine 
remains only in one spot ? in some concretions of hard 
calcareous sandstone : in several other districts I have 
observed that organic remains were exclusively confined 
to such concretions ; are we to account for this fact, by 
the supposition that the shells lived only atthesepoints^ 
or is it not more probable that their remains were pre- 
served only where concretions were formed ? The shells 
here are in a bad state, they consist of: 

1. Tellinides (?) oblonga, G B. Sowerby, PL IL f. 12 (a solenella 

in M d'Orbigny's opinion). 

2. Natica striolata, GL B. Sowerby, PL IXL f. 39. 

3. Natica (?) pnmila, do, PI III. f 38. 

4. Cytherasa (?) sulculosa, do. PL II. f . 14 (also Ypnn and Huafo f ) 

At the northern extremity of the island 3 near S. 
Carlos, there is a large volcanic formation, between 500 
and 700 feet in thickness. The commonest lava is 
blackish-grey or brown., either vesicular, or amygda- 
loidal with calcareous spar and bole : most even of the 
darkest varieties fuse into a pale-colonred glass. The 
next commonest variety is a rubbly, rarely well charac- 
terised pitchstone (fusing into a white glass) which 
passes in the most irregular manner into stony gray 



592 . Tertiary Formations. PAET n. 

lavas. This pitchstone, as \\ell as some purple clay- 
stone porphvry, certainly flowed in the form of streams. 
These various lavas often pass, at a considerable depth 
from the surface, in the most abrupt and singular 
manner Into wacko. Great masses of the solid rock are 
brcveiutt'd, and it was generally Impossible to discover 
Vrlietlier the recemonting process had been an igneous 
or aqueous action. 1 The beds are obscurely separated 
from each other ; they are sometimes parted by seams 
of tuff and layers of pebbles. In one place they rested 
on y and in another place were capped by ? tuffs and grit- 
stones, apparently of submarine origin. 

The neighbouring peninsula of Lacuy is almost 
wholly formed of tufaceous deposits, connected probably 
in their origin with the volcanic hills just described. 
The tuffs are pale-coloured, alternating with laminated 
mudstones and sandstones (all easily fusible) and passing 
sometimes into fine grained white beds strikingly re- 
sembling the great upper infusorial deposit of Patagonia, 
and sometimes into brecciolas with pieces of pumice in 
the last stage of decay ; these again pass into ordinary 
coarse breccias and conglomerates of hard rocks. With- 
in very short distances, some of the finer tuffs often. 
passed into each other in a peculiar manner, namely, 
by irregular polygonal concretions of one variety in- 
creasing so much and so suddenly in size, that the 
second variety, instead of any longer forming the entire 
mass, was left merely in thin veins between the concre- 

1 In a cliff of the hardest fragmentary mass, I found sevejal 

tortuous, vertical veins, varying in thickness from a few tenths of an 
inch to one inch and a half, of a substance which I have not seen 
described. It is glossy, and of a brown colour j it is thinly laminated, 
with the laminse transparent and elastic ; it is a little harder than 
calcareous spar ; it is infusible under the blowpipe, sometimes decre- 
pitates, gives out water, curls up, blackens and becomes magnetic. 
Boras: easily dissolves a considerable quantity of it, and gives a 
class tinged with green I have no idea what its true nature is, 
On first seeing it, I mistook it for lignite 1 



Chiloc. 



393 



tions. In a straight line of cliffs, at Point Tenuy, J 
examined the following remarkable secticE : - 

No 35, 
i ~- 

L 




Lercl of sea. 



On the left hand, the lower part (A A) consists of regular, 
alternating strata of brown tuffb and greenish laminated 
mudstone, gently inclined to the right, and conformably 
covered by a, mass (B left) of a white, tufaceous and 
brecciolated deposit. On the right hand, the whole 
cliff (B B right) consists of the same white tufaceous 
matter, which on this side presents scarcely a trace of 
stratification, but to the left becomes very gradually 
and rather indistinctly divided into strata quite con- 
formable with the underlying beds (A A) : moreover, a 
few hundred yards farther to the left, where the surface 
has been less denuded, the tufaceous strata (B left) are 
conformably covered by another set of strata, like the 
underlying ones (A A) of this section. In the middle 
of the diagram, the beds (A A) are seen to be abruptly 
cut off, and to abut against the tufacecus non-stratified 
mass; but the line of junction has been accidentally 



394 Tertiary Formations. PAET n* 

not represented steep enough, for I particularly noticed 
that before the beds had been tilted to the right, this 
line must have been nearly vertical. It appears that a 
current of water cut for itself a deep and steep sub- 
marine channel, and at the same time or afterwards 
tilled it up with the tufaceous and brecciolated matter, 
and spread the same over the sarroundiDg submarine 
beds; the matter becoming stratified in these more 
distant and less troubled parts, and being moreover 
subsequently covered up by other strata (like A A) not 
shown in the diagram. It is singular that three of the 
beds (of A A) are prolonged in their proper direction, 
as represented, beyond the line of junction into the 
white tufaceous matter : the prolonged portions of two 
of the beds are rounded ; in the third, the terminal 
fragment has been pushed upwards: how these beds 
could have been left thos prolonged, I will not pretend 
to explain. In another section on the opposite side of 
a promontory, there was at the foot of this same line 
of junction, that is at the bottom of the old submarine 
channel, a pile of fragments of the strata (A A) 5 with 
their interstices filled up with the white tufaceous 
matter: this is exactly what might have been antici- 
pated under such circumstances. 

The various tufaceous and other beds at this northern 
end of Chiloe probably belong to about the same age 
with those near Castro, and they contain, as there, many 
fragments of black lignite and of silicified and pyritous 
wood, often embedded close together. They also con- 
tain many and singular concretions : some are of hard 
calcareous sandstone, in which it would appear that 
broken volcanic crystals and scales of mica have been 
better preserved (as in the case of the organic remains 
near Castro) than in the surrounding mass. Other 
concretions in the white brecciola, are of a hard fer- 



CHAP. SH, 



Chiloe. 



395 



ruginous, yet fusible, nature; they are as round as 
cannon-balls, and vary from two or three inches to two 

feet in diameter ; their msides generally consist either 
of fine, scarcely coherent volcanic band, 1 or of an argil- 
laceous tuff; in this latter case, the external crust was 

quite thin and hard. Some of the spherical balls were 
encircled, in the line of their equators, by a necklace- 
like row of smaller concretions. Again there were other 
concretions, irregularly formed, and composed of a hard ? 
compact, ash-coloured stone, with an almost porcelain- 
ons fracture, adhesive to the tongue, and without any 
calcareous matter. These beds are, also, interlaced by 
many veins, containing gypsum, ferruginous matter, 
calcareous spar, and agate. It was here seen with re- 
markable distinctness, how intimately concretionary 
action and the production of fissures and veins are re- 
lated together. The following diagram is an accurate 



Ground plan showing the relation beta cen veins and concretionary zones 
in a mass of tuff. 




representation of a horizontal space of tuff, about four 
The frequent tendency in iron to form hollow concretions or shell 



396 Tertiary Formations. PAET n, 

feut long by two and a lialf in width : the double lines 
represent the fissures partially filled with oxide of iron 
and a^ate : the curvilinear lines show the course of the 
innumerable, concentric, concretionary zones of different 
shades of colour and of coarseness in the particles of 
tuff. The symmetry and complexity of the arrangement 
gave the surface an elegant appearance. It may be 
seen how obviously the fissures determine (or have been 
determined by) the shape, sometimes of the whole con- 
cretion, and sometimes only of its central parts. The 
fissures also determine the curvatures of the long undu- 
lating zones of concretionary action. From the varying 
composition of the veins and concretions, the amount 
of chemical action which the mass has undergone is 
surprisingly great ; arid it would likewise appear from 
the difference in size in the particles of the concretionary 
zones, that the mass, also, has been subjected to internal 
mechanical movements. 

In the peninsula of Lacuy, the strata over a width 
of four miles have been upheaved by three distinct, and 
some other indistinct, lines of elevation, ranging with- 
in a point of north and south. One line, about 200 
feet in height, i& regularly anticlinal, with the strata 
dipping away on both sides, at an angle of 15, from a 
central ( valley of elevation/ about 300 yards in width. 
A second narrow steep ridge, only sixty feet high, is 
uniclinal, the strata throughout dipping westward; 
those on both flanks being inclined at an angle of from 
ten to fifteen degrees ; whilst those on the ridge dip in 
the same direction at an angle of between thirty and 
forty degrees. This ridge, traced northwards, dies away ; 
and the beds at its terminal point, instead of dipping 
westward, are inclined 12 to the north. This case 

containing incoherent matter is singular ; D'Aubuissoa (' Trait& de 
G&ogo.' torn. I. p. S18) remarks on this circumstance. 



CHAP. xn. Valdhia. Conccpcion. 397 

interested me, as being the first in which I found in 
South America, formations perhaps of tertiary origin, 
broken "by lines of elevation. 

Valdwia: Island of Hocha. The formations of 
Chiloe seem to extend with nearly the same character 
to Valdivia, and for some leagues northward of it : the 
underlying rocks are micaceous ?chisi s, and are covered 
up with sandstone arid other sedimentary beds, including, 
as I was assured, in many places layers of lignite. I 
did not land on Mocha (lat. 88 20'), but Mr. Stokes 
brought me specimens of the gray, fine-grained, slightly 
calcareous sandstone, precisely like that of Huafo, con- 
taining lignite and numerous Turritellae. The island is 
flat topped, 1,240 feet in height, and appears like an 
outlier of the sedimentary beds on the mainland. The 
few shells collected consist of:- 

1. Turrit ella Ghilcnsis, GL B. Sowfrby, PL IV, 1 51 (also at Huafo), 

2. Fiibus, veiy impeifeet, soniewljat resembling F. subrellexus of 

Navidad (PI. IV. f . 57), but piobably diifeient. 

3. Venus, fiagoaents of. 

Conception. Sailing northward from Yaldivia, the 
coast-cliffs are seen, first to assume near the R. Tolten, 
and thence for 150 miles northward, to be continued 
with the same mineralogical characters, immediately to 
be described at Concepcion. I heard in roany places 
of bed sof lignite, some of it fine and glossy, and likewise 
of silicified wood ; near the Tolten the cliffs are low, 
but they soon rise in height ; and the horizontal strata 
are prolonged, with a nearly level surface, until coming 
to a more lofty tract between points Eumena and 
Lavapie. Here the beds have been broken tip by at 
least eight or nine parallel lines of elevation, ranging 
E. or ENE., and W. or WSW. These lines can be 
followed with the eye many miles into the interior; 
they are all uniclinal, the strata in each dipping to a 



398 Tertiary Formations. PAET n, 

point between S. and SSR. with an inclination in 
the central lines of about forty degrees, and in the 
outer ones of under twenty degrees. This band of 
symmetrically troubled country is about eight miles in 
width. 

The inland of Quinquina, in the Bay of Concepcion 5 
LS formed of various soft and often ferruginous sand- 
stones, with bands of pebbles, and with the lower strata 
sometimes passing into a conglomerate resting on the 
underlying metamorphic schists. These beds include 
subordinate layers of greenish impure clay, soft mica- 
ceous and calcareous sandstones, and reddish friable 
earthy matter with white specks like decomposed crystals 
of feldspar ; they include, also, hard concretions, frag- 
ments of shells, lignite, and silicified wood. In the 
upper part they pass into white, soft sediments and 
brecciolas, very like those described at Ohiloe ; as in- 
deed is the whole formation. At Lirguen and other 
places on the eastern side of the bay, there are good 
sections of the lower sandstones, which are generally 
ferruginous, but which vary in character, and even pass 
into an argillaceous nature; they contain hard concre- 
tions, fragments of lignite, silicified wood, and pebbles 
(of the same rocks with the pebbles in the sandstones 
of Quinquina), and they alternate with numerous, often 
very thin layers of imperfect coal, generally of little 
specific gravity. The main bed here is three feet thick ; 
and only the coal of this one bed has a glossy fracture. 
Another irregular, curvilinear bed of brown, compact 
lignite} is remarkable for being included in a mass of 
coarse gravel. These imperfect coals, when placed in a 
heap, ignite spontaneously. The cliffs on this side of 
the bay, as well as on the island of Quiriquina, are 
capped with red friable earth, which, as stated in the 
ninth chapter, is of recent formation. The stratifica- 



. XII. 



Conception. 



399 



tion In tliis neighbourhood is generally horizontal ; but 

Bear Lirguen the beds clip N W. at an angle of 23 ; 
near Conception they are also inclined : at the northern 
end of Quinquina they have been tilted at an angle of 
80 and at the southern end at angles varying from 15 
to 40 : these dislocations must have taken place under 
the sea. 

A collection of shells, from the island of Quinquina, 
has been described by XL d'Orbigny : they are all extinct, 
and from their generic character, SI. d'Orbigny inferred 
that they were of tertiary origin : they consist of: 



1. Scalaria Chilensis, d'Orbig. 

4 Voyage, Part. Pal.* 

2. Natica Araucana, do. 
3 Natica anstralis, do. 
4* Fusus difficilis, do. 

5. Pyrula longirostra, do. 

6. Pleurotoma Araucana, do. 

7. Cardtum auca, do. 



8. Oarditim acuticostatumu 

d'Orfoig. ' Voyages, PaL' 

9. Venus auca, do 

10. Mactra cecile.ma, do. 

11. Mactra Araucana, do. 

12. Aica Aiaucana, do 

13 Nucnla Largilherti, do. 
14. TiigomaHanetiana, do. 



During a second visit of the Beagle to Concepcion, 
Mr. Kent collected for me some silicified wood and 
shells out of the concretions in the sandstone from Tome, 
situated a short distance north of Lirguen ; they consist 
of: 



1. Natica australis, d'Qrbig. 

* Voyage, Pal/ 

2. Mactra Araucana, do. 

3. Tngorda Hanetiana, do. 

4. Pecten, fragments of, pro- 

bably two species, but too 



imperfect for description. 

5. Bacuhtes vagina, B, Forbes, 

PI V. f 3. 

6. Nautilus d'Orbignyanus, K 

Forbes, PL V. f. 1 (a) and 



Besides these shells. Captain Belcher 1 found here an 
Ammonite^ nearly three feet in diameter, and so heavy 
that he could not bring it away ; fragments are deposited 
at Baslar Hospital : he also found the silicified vertebra 
of some very large animal. From the identity in 



* Zoology of Oapt. Belcher*s Vo} age,' p. 163, 



400 Tertiary Formations, PIBT it. 

mineralogifnl nature of the rocks, and from Captain 
Belcher's minute description of the coast between Lirguen 

and Tome, the fossil iferous concretions at this latter 
place certainly belong to the same formation with the 
beds examined by im>elf at Lirguen ; and these again 
are undoubtedly the wmie with the strata of Quinquina; 
moreover, the three first of the shells from Tome, though. 
associated in the same concretions with the Baculite, 
are identical with the species from Quiriquina. Hence 
all the sandstone and hgnitiferous beds in this neigh- 
bourhood certainly belong to the same formation. Al- 
though the generic character of the Quiriquina fossils 
naturally led M. d'Orbigny to conceive that they were 
of tertiary origin, yet as we now find them associated 
with the BacnlHes vnyiia and with an Ammonite, we 
must, in the opinion of M. d'Orbigny, and if we are 
guided by the analogy of the Northern Hemisphere, rank 
them in the Cretaceous system. Moreover, the Baculites 
vagina j which, is in a tolerable state of preservation, 
appears to Professor E. Forbes certainly to be identical 
with a species, so named by him, from Pondicherry in 
India ; where it is associated with numerous decidedly 
cretaceous species, which approach most nearly to Lower 
Greensand or Neoconiian forms : this fact, considering 
the vast distance between Chile and India, is truly sur- 
prising. Again, the Nautilus d'Orbignyanus, as far 
as its imperfect state allows of comparison, resembles, 
as I am informed by Professor Forbes, both in its general 
form and in that of its chambers, two species from the 
Upper Greensand. It may be added that every one of 
the above-named genera from Quiriquina, which have 
an apparently tertiary character, are found in the Pon- 
dicherry strata. There are, however, some difficulties 
on this view of the formations at Concepcion being cre- 
taceous, which I shall afterwards allude to ; and I will 



xii. 2\ T avzdad. 401 



here only state that the Cardium auca Is found also at 
Coquiinbo, the beds at which place 3 there can be no 
doubt, are tertiary. 

Namcl id l The Concepclon formation extends some 
distance northward, but how far I know not ; for the 
next point at which I landed was at Navidad, 160 miles 
north of Concepcion, and 60 miles south of Valparaiso, 
The cliffs here are about 800 feet in height; they 
consist^ wherever I could examine tlienij of fine-grained, 
yellowish, earthy sandstones, with ferruginous veins^ and 
with concretions of hard calcareous sandstone. In one 
part, there were many pebbles of the common meta- 
morphic porphyries of the Cordillera : and near the 
base of the cliff, I observed a single rounded boulder of 
greenstone, nearly a yard in diameter. I traced this 
sandstone formation beneath the superficial covering of 
gravel, for some distance inland : the strata are slightly 
inclined from the sea towards the Cordillera, which 
apparently has been caused by their having been accu- 
mulated against or round, outlying masses of granite, 
of which some points project near the coast. The sand- 
stone contains fragments of wood, either in the state of 
lignite or partially silicified, sharks' teeth, and shells in 
great abundance, both high up and low down the sea- 
cliffs. Pectunculus and Oliva were most numerous in 
individuals, and next to them Turritella and Fusus. 1 
collected in a short time, though suffering from illness, 
the following thirty-one species, all of which are extinct, 
and several of the genera do not now range (as we shall 
hereafter show) nearly so far south : 

1, Gastridium cepa, G. B. Sowerby, PL IT. f. 68, 69. 

2. Monncoros, fragmeDts of, considered by M, d'Orbigny as a new 

species, 

1 I was guided to this locality "by the Beport on M. Gay's *Geolo* 
gical Researches/ in the ' Annales des Scienc Nat.* (1st series) torn. 2& 



402 Tertiary Formations, PAET n, 

3. Vc4uta alfa,G. B Powriby, PL IV. f . 75 (comideiGd by M, 

d'Orbitrnv as fliMinct from tlie V altn of 8 Cma). 

4. Vnluta uiphi-a-a, G. JX SoACiby, PI, IV. f. 7i. 

5. Olua diiu.lL 'a, do. 11 IV !. 7o, 77. 
0. PIeurot<maduscorjs, <to PI IV f 51. 

7 Pleuroloniatarliinflloidcs, do PI IV. f. 53, 

8 Kut-rts Mibri'fl'Mis, <V> PL IV f f>7. 
9. F-sp\riilii>rii'iisdo PI IV f 50 

10. Fubiis, allied to F regular IP, PI IV. 1 55 (considered by il. 

tFOrbi^ny a^ a distinct specie^). 

11. Turnlella su'uralis, Gf- B. Sowerby, PI. Ill f. 50. 

12* Turntella Patagonica (do ), Pi III. 1 48 (fragments of). 

13. Troohns liovis, G. B. Sowerby, PI III. f. 46, 47 

14. Trochus collar is, do, PL III. f. 44, 46 (considered by M. 

d'Orbigny as the young of the T. Issvis). 

15. Cassis mom lifer, G. B, Sowerby, PL IV. 1 65, 

16. Pyrala distans, do , PL J V f. 01. 

17. Triton verruculo^us, do., PI IV. f . 63. 

18. Sigaretus subglobosus, G- B. Sowerby, PL III f. 36, 37. 

19. Natica solida,"do , PI III 1 40, 41 (it is doubtful whether tbe 

N. solida of S. Cruz is tbe same species with this). 
SO. Terebra undulifera, G-. B Sowerby, PL IT. 1 72, T3 

21. Terebra costellata, do., PL IV. f. 70, 71. 

22. Bulla (fragments of). 

23. Dentalium giganteum, do., PL II. f. 1. 

24. Dentalinm snlcosam, do., PI II f. 2. 

25. Oorbis (?) Isavigata, do., PL II. f. 11. 

26. Oardinm naultiradiatum, <3o., PL II. f. 16. 

27. Venus mendionalis, do , PL IL f. 13, 

28. Pecttmculus dispar, ( ? ) Desh (considered by H. d'Orbigny as a 

distinct species). 

29. 30. Cytheraea and Mactra, fragments of (considered by M, 

d'Orbigoy as new species). 
81. Pecten, trsgmenis of. 

oquimbo. For more tBaa 200 miles northward of 
Navidad, the coast consists of plutonic and metamorphic 
rocks, witt the exception of some quite insignificant 
superficial beds of recent origin. At Tonguay, twenty- 
five miles south of Coquinibo, tertiary beds recommence. 
I have already minutely described in the ninth chapter, 
the step-formed plains of Coquimbo, and the upper 
calcareous beds (from twenty to thirty feet in thickness) 
containing shells of recent species, bat in different 
proportions from those on the beach. There remains 
to be described only the underlying ancient tertiary 



CHAP. XII. 



Coquimbo. 403 



beds, represented In the following diagram (here given 
again) by the letters F and E ; 

No 37 

Section of the Teitiary Formation at Coquimbo* 
Surface of plain, 252 feet above sea. 



i-..-',!, T.JJL.. r,. . j^gf. J- T . f y -.,_., *LA, 

IP '.^^^^""^-r- 1 -"^^ -.r 







Level of Sea. 

F Lower Sandstone, with concretions and siiicifierl bones, ) with fossil shells, oil, or 
E -Upper ferinprinou-. sandstone, with numerous Balaui, f nfarlj all, extinct 
C and I) Calcareous beds with recent shells A Stratified sand m a ravine, also 
\uth icceiit bhtlls 

I obtained good sections of bed (F) only in Herra- 
dara Bay : it consists of soft whitish sandstone, with 
ferruginous veins, some pebbles of granite, and concre- 
tionary layers of hard calcareous sandstone. These 
concretions are remarkable from the great number of 
large silicified bones, apparently of cetaceous animals, 
which they contain ; and likewise of a shark's teeth, 
closely resembling those of the Ctircliarias megalodon. 
Shells of the following species, of which the gigantic 
Oyster and Perna are the most conspicuous, are nume- 
rously embedded in the concretions : 

1. Bulla ambigua, d'Orbig * Voyage Pal/ 

2. Monoceros Blainvillii, do. 
3 Cardium anca, do. 

4. Panopaea Coquimbensis, do. 

5. Perna Gaudichaudi do 

6 Artemis ponderosa ; Mr. Sovverby can find no distinguishing 
character between thus fossil and the recent A ponderosa j it 
is ceitamly an Artemis, as shown by the pallial impression. 

7. Ostrea Patagonica ( ? ) Mr Sowerby can point out no distin- 

guishing character between thib species and that &o eminently 
characteristic of the gieat Patagonian formation; bathe will 
not pretend to affirm that they are identical. 

8. Fragments of a Venus and Natica. 

The cliffs on one side of Herradura Bay are capped 
by a mass of stratified shingle, containing a little calca- 

27 



404 Tertiary Formations. PABT n 

ri*otis matter, and 1 did not doubt that it belonged to 
the same recent formation with the gravel on the sur- 
rounding plains, also cemented by calcareous matter, 
until to my surprise, I found in the midst of it, a single 
tliin layer almost entirely composed of the above gigantic 
oyster. 

At a little distance inland, I obtained several sections 
of the bed (E), which, though different in appearance 
from the lower bed (P), belongs to the same formation : 
it consists of a highly ferruginous sandy mass, almost 
composed, like the lowest bed at Port S. Julian, of 
fragments of Balanidae; it includes some pebbles, and 
layers of yellowish-brown mudstone. The embedded 
shells consist of: 

1. JMonoceros BUinvillii, d'Orbig- 'Voyage Pa]' 

2. ambiguua, G. B. So\verby,>l. IV. f. 66, 67. 

3. Anomia alternaas, do PI II. f. 25. 

4. Pecten rndfc, do., PL III f 82 

5. Perna Gaudichandi, d'Oibigr. * Voyage Pal.' 

6. Ostrea Patagomoa(. ? ) do. 

7. Ostrea, small species, in imperfect state; it appeared to me 

like a snuill Kmcl now hvinsr in, but very rare in the bay 

8. IMytilus ChilocxiS'S , Mr Howeiby can hnd no distinguishing 

character between tins fossil, as far as its not very perfect 
condition allows of companion, and the recent species 
9 Balanus Coqaimbensis, G B Sower' y, PL II. i. 7. 
10. Balanus p^ittacas 9 King This appears to Mr. Sowerhy and 
myself identical \\ith a very large and common species now- 
living 021 the coast 

The uppermost layers of this ferragino-saridy mass 
are conformably covered by, and impregnated to the 
depth of several inches with, the calcareous matter of 
the bed (D) called lorn : hence I at one time imagined 
that there was a gradual passage between them ; but as 
all the species are recent in the bed (D), whilst the 
most characteristic shells of the uppermost layers of (E) 
are the extinct Perna, Pecten, and Monoceros, I agree 
with M. d'Orbigny, that this view is erroneous, and that 
there is only a rnineralogieal passage between them, 



CHAP. xn. Coquimbo to Copiapo. 405 

and no gradual transition in the nature of their organic 
remains. Besides the fourteen species enumerated from 
these two lower beds, M. d'Orbigny has described ten 
other species given to him from this locality; namely, 

6. Venus petitiana, d'Orbig. 



1. Fusus Clervanus, d'Orbig 

* Voyage Pal/ 

2 putitianus, do. 

3. Venus ha.net.iaua, do 

4. inceita, ('') do. 

5. Clei>ana, do. 



* Voyage PaL* 

7. Chifensis, do. 

8. Solecurtus hanetianus, do. 

9. Mactra auca, do. 
10. Oliva serena, do. 



Of these twenty-four shells, all are extinct, except, 
according to Mr, Sowerby, the Artemis ponderosa, 
Mytilus Ohiloensis, and probably the great Balanus. 

Coquimbo to Copiapo. A few miles north of Co- 
quimbo, I met with the ferruginous, balaniferous mass 
(E) with many silicified bones; I was informed that 
these silicified bones occur also at Tonguay, south of 
Coquimbo : their number is certainly remarkable, and 
they seem to take the place of the sihcifiecl wood, so 
common on the coast- formations of southern Chile, la 
the valley of Chaneral, I again saw this, same formation > 
capped with the recent calcareous beds. I here left 
the coast, and did not see any more of the tertiary 
formations, until descending to the sea at Copiapo : 
here in one place I found variously coloured layers of 
sand and soft sandstone, with seams of gypsum, and in 
another place, a comminuted shelly mass, with layers 
of rotten-stone and seams of gypsum, including many 
of the extinct gigantic oyster : beds with these oysters 
are said to occur at English Harbor, a few miles north 
of Copiapo. 

Coast of Peru. With the exception of deposits 
containing recent shells and of quite insignificant 
dimensions, no tertiary formations have been observed 
or this coayt, for a space of twenty-two degrees of lati- 
tude north of Copiapo ? until coming to Payta, where 



406 Tertiary Formations : PABT n. 

tin *re is said to be a considerable calcareous deposit : a 

E-w fossils have been described by M. d'Orbigny from 
tills place, namely : 

1 i:<.-*ellana Gamlichaudi, d'Orbig* * Voyage Pal.* 

2 IVctuneulub Pay ten sis, do. 
:-J Vf'nnspetifiana, do. 

4. Otrea Patagomca ' This great oyster (of which specimens 
lia\ e been tfiven me) cannot be distinguished by Mr. Sowerby 
fiom some'of the varieties from Patagonia ; though it would 
be hazaidous to assert it is the same with that species, or 
with that from Coqutmbo. 

Concluding R&vmrks. The formations described 
in this chapter, have, in the case of Chiloe and probably 
in that of Concepcion and Navidad, apparently been 
accumulated in troughs formed by submarine ridges 
extending parallel to the ancient shores of the continent ; 
in the case of the islands of Mocha and Huafo it is 
highly probable, and in that of Tpun and Lemus almost 
certain, that they were accumulated round isolated 
rocky centres or nuclei, in the same manner as mud 
and sand is now collecting round the outlying islets 
and reefs in the West Indian archipelago. Hence, I 
may remark, it does not follow that the outlying ter- 
tiary masses of Mocha and Huafo were ever continuously 
nnited at the same level with the formations on the 
mainland, though they may have been of contempora- 
neous origin, and been subsequently upraised to the 
same height. In the more northern parts of Chile, the 
tertiary strata seem to have been separately accumu- 
lated in bays, now forming the mouths of valleys. 

The relation between these several deposits on the 
shores of the Pacific, is not nearly so clear as in the 
case of the tertiary formations on the Atlantic. Judging 
from the form and height of the land (evidence which 
5t feel feure is here much more trustworthy than it can 
be in sitdh broken continents as that of Europe), from 



CHAP. xn. Concluding Remarks on. 407 

the identity of mineral ogical composition, from the 
presence of fragments of lignite and of silicified wood, 
and from the intercalated layers of imperfect coal, I 
must believe that the coast-formations from central 
Chiloe to Concepcion, a distance of 400 miles, are of 
the same age : from nearly similar reasons, I suspect 
that the beds of Mocha, Huafo, and Ypun, belong also 
to the same period. The commonest shell in Mocha 
and Huafo is the same species of Turritella ; and I 
believe the same Cytheraa is found on the islands of 
Huafo, Chiloe, and Ypun ; but with these trifling ex- 
ceptions, the few organic remains found at these places 
are distinct. The numerous shells from Navidad, with. 
the exception of two, namely, the Sigaretus and Tur- 
ritella found at Ypun, are likewise distinct from those 
found in any other part of this coast. Coqnimbo has 
Curdium auca in common with Concepcion, and Fitsus 
Cleri/anus with Huafo; I may add, that Coquimbo has 
Venus petitiana, and a gigantic oyster (said by 
M. d'Orbigny also to be found a little south of Concep- 
tion) in common with Payta, though this latter place 
is situated twenty-two degrees northward of lat. 27, to 
which point the Coquimbo formation extends. 

From these facts, and from the generic resemblance 
of the fossils from the different localities, I cannot avoi$ 
the suspicion that they all belong to nearly the same 
epoch, which epoch, as we shall immediately see, must 
be a very ancient tertiary one. But as the Baculite, 
especially considering its apparent identity with the 
Cretaceous Pondicherry species, and the presence of an 
Ammonite^ and the resemblance of the Nautilus to two 
upper greensand species, together afford very strong 
evidence that the formation at Concepcion is a Secondary 
one ; I will, in my remarks on the fossils from the other 
localities, put on one side those from Concepcion and 



408 Tertiary Formations : PABT n* 

from Eastern Chiloe, which, whatever their age may be, 
appear to me to belong to one group. I must, however, 
again call attention to tie fact that the Cardiwn aura 
is found both at Concepcion and in the undoubtedly 
tertiary strata of Coquirnbo : nor should the possibility 
be overlooked, that as Trigonia, though known in the 
Northern Hemisphere only as a Secondary genus, lias 
living representatives in the Australian seas, so a Bacu- 
lite, Ammonite, and Trigonia may have survived in this 
remote part of the Southern Ocean to a somewhat later 
period than to the north of the equator. 

Before passing In review the fossils from the other 
localities, there are two points, with respect to the for- 
mations between Concepcion and Chiloe, which deserve 
some notice. First, that though the strata are generally 
horizontal, they have been upheaved in Chiloe, in a set 
of parallel anticlinal and uniclinal lines ranging north 
^nd south, in the district near P. Rumena by eight 
or nine far-extended, most symmetrical, tiniclinal lines 
ranging nearly east and west, and in the neighbourhood 
of Concepcion by less regular single lines, directed both 
NB. and SW , andNW. and SB. This fact is of some 
interest, as showing that within a period which cannot 
te considered as very ancient in relation to the history 
of the continent, the strata between the Cordillera and 
the Pacific have been, broken up in the same variously- 
directed manner as have the old plutonic and meta- 
morphic rocks in this same district. The second point 
is, that the sandstone between. Concepcion and Southern 
Ohiloe is everywhere lignitiferous, and includes much 
silicified wood; whereas the formations in Northern 
Chile do not include beds of lignite or coal, and in place 
of the fragments of silicified wood there are silicified 
bones. Now, at the present day, from Cape Horn to 
near Concepcion, the land is entirely concealed by forests, 



CHAP, xn:. Age of. 409 

which thin out at Concepciorj, and in central and 
Northern Chile entirely disappear. This coincidence iu 
the distribution of the fossil wood and the living forests 
may be quite accidental ; but I incline to take a diffe- 
rent view of it; for, as the difference in climate, on 
which the presence of forests depends, is here obviously 
in chief part due to the form of the land, and as the 
Cordillera undoubtedly existed when the lignitiferous 
beds were accumulating, I conceive it is not improbable 
that the climate, during the ligrutiferous period, varied 
on different parts of the coast in a somewhat similar 
manner as it now does. Looking to an earlier epoch, 
when the strata of the Cordillera were depositing, there 
were islands which even in the latitude of Northern 
Chile, where now all is irreclaimably desert, supported 
large coniferous forests. 

Seventy-nine species of fossil shells, in a tolerably 
recognisable condition, from the coast of Chile and Peru, 
are described in this volume, and in the Palseontological 
part of M. d'Orbigny's ' Voyage ' : if we put on one side 
the twenty species exclusively found at Concepcion and 
Chiloe, fifty-nine species from Navidad and the other 
specified localities remain. Of these fifty-nine species 
only an Artemis, a Mytilus, and Balanus, all from 
Coquimbo, are (in the opinion of Mr. Sowerby, but not 
in that of M. d'Orbigny) identical with living shells ; 
and it would certainly require a better series of speci- 
mens to render this conclusion certain. Only the 
Turritelloj Chilensis from Huafo and Mocha, the T. 
Patagonica and Venus meridionalis from Navidad, 
come very near to recent South American shells, namely, 
the two Turritellas to T. cingulata, and the Venus to 
V. exalbida: some few other species come rather less 
near; and some few resemble forms in the older Euro- 
pean tertiary deposits : none of the species resemble 



Tertiary Formations : 



IL 



secondary forms. Hence I conceive there can be no 
doubt that these formations are tertiary, a point ne- 
cessary to consider, after the case of Concepcion. The 
fifty-nine species belong to thirty-two genera; of these, 
Gasirklluiii is extinct, and three or four of the genera 
(viz. Panupsea, Hostel lana, Corbis ?, and I believe 
Solecurtius) are not now found on the west coast of South 
America. Fifteen of the genera have on this coast 
living representatives in about the same latitudes with 
the fossil species; but twelve genera now range very 
.differently to what they formerly did. The idea of the 



GeueiM, vutli living ami 


Latitudes, in \\ludh found 
to^il on the coasts of 


Southernmost latitude, in 
which found living on the 


u ejb coast of S. AiaentM 


C'hi'e and Peru 


u est coat of S Ainenca 


Bulla . 


,>u' J to 4;; 30' 


12 near Lima 


Cassis . . . 


:M 


137' 


Pyrula. . 


31 (and 36 30' at 


6 Payta 




Conoepcion) 




Fusus . * . 


SO to 43 30' 


23 Mexillones ; re- 






appears at the St. 






ot Magellan 


PleuTotoma . 


34 to 43 30 ; 


2 18' St. Elena 


Terebra . . . 


34 


6 Payta 


Sigaretus 


34 to 44 30' 


12 Lima 


Anonna . . 


30 


7 48' 


Pern a . 


30 


1 23' Xixappa 


Cardium . . 


SO' to 34 (and 3C> 


5 Payta 




30' at Concepcion) 




Artemis * . 


30 


5 Payta 


Voluta , . 


34 to 44 30' 


Mr. Cuming does 






not know of any 






species living on 






the west coast, 






between the equa- 






tor and lat. 43 






south; from this 






latitude a species 






is found as far 






south as Tieira 






del Fuego. 



1 M. d'Orhigny states that the genus Natica is not found on the 
coast of Chile ; but Mr, Cumiug found it at Valparaiso Scalaria 
was fottnd at Valparaiso; Area, at Iquique, in lat 20, by Mr. 
Cuming ; Area, ako, was found by Capt. King 1 , at Juan Fernandez, 
in lat. 33 SO'. 



CHAP. XII 



Age of, 



table on the previous page, in which the difference 
between the extension in latitude of the fossil and existing 
species is shown, is taken from M. d'Orbigny's work ; but 
the range of the lining shells is given on the authority 
of Mr Curaing, whose long-continued researches on the 
conchology of South America are well known. 

When we consider that very few. If any, of the fifty- 
nine fossil shells are identical with, or make any close 
approach to, living species ; when we consider that some 
of the genera do not now exist OB the west coast of 
South America, and that no less than twelve genera out 
of the thirty-two formerly ranged very differently from 
the existing species of the same genera, we must admit 
that these deposits are of considerable antiquity, and 
that they probably verge on the commencement of the 
tertiary era. May we not venture to believe, that they 
are of nearly contemporaneous origin with the Eocene 
formations of the Northern Hemisphere ? 

Comparing the fossil remains from the coast of Chile 
(leaving out, as before, Concepcion and Chiloe) with 
those from Patagonia, we may conclude, from their 
generic resemblance, and from the small number of the 
species which from either coast approach closely to 
living forms, that the formations of both belong to 
nearly the same epoch ; and this is the opinion of M. 
d'Orbigny. Had not a single fossil shell been common 
to the two coasts, it could not have been argued that 
the formations belonged to different ages ; for Messrs. 
Cuming and Hinds have found, on the comparison of 
nearly 2,000 living species from the opposite sides of 
South America, only one in common, namely, the PUT- 
pitra, lapMus from both sides of the Isthmus of Panama : 
even the shells collected by myself amongst the Ohonos 
Islands and on the coast of Patagonia, are dissimilar, 
and we must descend to the apex of the continent, to 



412 Tertiary Formations : *ART n 

TIerra del Fuego, to find these two great concliological 
provinces united into one. Hence it is remarkable that 
four or five of the fossil shells from Navidad, namely, 
Valuta alta, Tnmtella Pat agon ica, Trochus collar is, 
Venus meridionalis, perhaps Natiea solida,, and per- 
haps the large oyster from Coquimbo, are considered by 
Mr. Sowerby as identical with species from Santa Cruz 
and Port Desire. M. d'Orbigny, however, admits the 
perfect identity only of the Trochus. 

On the Temperature of Uie Tertiary Period. As 
the nnnaber of the fossil species and genera from the 
western and eastern coasts is considerable, it will be 
interesting to consider the probable nature of the 
climate under which they lived. We will first take the 
case of Navidad, in lat. 34, where thirty-one species 
were collected, and which, as we shall presently see, 
must have inhabited shallow water, and therefore will 
necessarily well exhibit the effects of temperature. 
Referring to the Table given in the previous page, we 
find that the existing species of the genera Cassis, 
Pyrula, Pleurotoma, Terebra, and Sigaretus, which are 
generally (though by no means invariably) characteristic 
of warmer latitudes, do not at the present day range 
nearly so far south on this Hue of coast as the fossil 
species formerly did. Including Coquimbo, we have 
Perna in the same predicament. The first impression 
from this fact is, that the climate must formerly have 
been warmer than it now is; but we must be very 
cautious in admitting this, for Cardium, Bulla, and 
Fusus (and, if we include Coquimbo, Anomia and 
Artemis) likewise formerly ranged farther south than 
they now do ; and as these genera are far from being 
characteristic of hot climates, their former greater 
southern range may well have been owing to causes 
quite distinct from climate : Voluta, again, though 



CHAP. xn. Temperature of Tertiary Period. 413 

generally so tropical a genns, is at present confined on 
the west coast to colder or more southern latitudes than 
it was during the tertiary period. The Trochns collaris, 
moreover, and, as we have just seen according to Mr. 
Sowerby, two or three other species, formerly ranged 
from Navidad as far south as Santa Cruz in lat. 50. If, 
instead of comparing the fossils of Navidad, as we have 
hitherto done, with the shells now living on the west 
coast of South America, we compare them with those 
found in other parts of the world, under nearly similar 
latitudes; for instance, in the southern parts of the 
Mediterranean or of Australia, there is no evidence 
that the sea off Navidad was formerly hotter than whafe 
might have been expected from its latitude, even if it 
was somewhat warmer than it now is when cooled by 
the great southern polar current. Several of the most 
tropical genera have no representative fopsils at Navi- 
dad ; and there are only single species of Cassis, Pyrula, 
and Sigaretus, two of Pleurotoma and two of Terebra, 
but none of these species are of conspicuous size. In 
Patagonia, there is even still less evidence in the 
character of the fossils, of the climate having been 
formerly warmer. 1 As from the various reasons already 
assigned, there can be little doubt that the formations 
of Patagonia and at least of Navidad and Coquimbo in 
Chile, are the equivalents of an ancient stage in the 
tertiary formations of the northern hemisphere, the 
conclusion that the climate of the southern seas at this 
period was not hotter than what might have been ex- 
pected from the latitude of each place, appears to roe 
highly important ; for we must believe, in accordance 

1 It may be worth while to mention that the shells living at the 
present day on this eastern si<ie of S. America, in lat. 40, have 
perhaps a more tropical chaiacter than those in corresponding 
latitudes on the shores of Europe : for at Bahia Blanca and S. BUs, 
there are two fine species of Voluta and four of Ohva. 



414 On the Absence of PABT n. 

with the views of Mr. Lyell,that the causes which gave 
to the older tertiary productions of the quite temperate 
zones of Europe a tropical character, were of a local 
character mul did not affect the entire globe On the 
other hand. 1 have endeavoured to show, in the ' Geo- 
logical Transactions/ that, at a much later period, Europe 
and North and South America were nearly contempora- 
neously subjected to ice-action, and consequently to a 
colder, or at least, more equable climate than that now 
characteristic of the same latitudes. 

On the Absence of extv/isice modern Oonohiferous 
Deposits in South America; and on the Contempo- 
raneousness of the older Tertiary Deposits at distant 
points being due to contemporaneous movements of 
subsidence. Knowing from the researches of Professor 
E. Forbes, that molluscous animals chiefly abound 
within a depth of 10Q fathoms and under, and bearing 
in mind how many thousand miles of both coasts of 
South America have been upraised within the recent 
period by a slow, long-continued, intermittent move- 
ment, seeing the diversity in nature of the shores and 
the number of shells now living on them, seeing also 
that the sea off Patagonia and off many parts of Chile, 
was during the tertiary period highly favourable to the 
accumulation of sediment, the absence of extensive 
deposits including recent shells over these vast spaces 
of coast is highly remarkable. The conchiferous cal- 
careous beds at Coquimbo, and at a few isolated points 
northward, offer the most marked exception to this 
statement; for these beds are from twenty to thirty 
feet in thickness, and they stretch for some miles along 
shore, attaining, however, only a very trifling breadth. 
At Yaldivia there is some sandstone with imperfect casts 
of shells, which possibly may belong to the recent period : 
parts of the boulder formation and the shingle-beds o 



CHAP. xn. Conckiferous Deposits. 41 ^ 

the lower plains of Patagouia probably belong to tnis 
same period, but neither are fossiiiferous : it also so 
happens that the great Pampean formation does not in- 
clude, with the exception of the Azara, any mollusca. 
There cannot be the smallest doubt that the upraised 
shells along the shores of the Atlantic and Pacific, 
whether lying on the bare surface, or embedded in mould 
or in sand-hillocks, will in the course of ages be destroyed 
by alluvial action : this probably will be the case even 
with the calcareous beds of Coquimbo, so liable to dis- 
solution by rain-water. If we take into consideration 
the probability of oscillations of level and the conse- 
quent action of the tidal waves at different heights, 
their destruction will appear almost certain. Looking 
to an epoch as far distant in futurity as we now are 
from the past Miocene period, there seems to me scarcely 
a chnnce, under existing conditions, of the numerous 
shells now living in those zones of depths most fertile 
in life, and found exclusively on the western and south- 
eastern coasts of South America, being preserved to this 
imaginary distant epoch. A whole conchological series 
will in time be swept away, with no memorials of their 
existence preserved in the earth's crust. 

Can any light be thrown on this remarkable absence 
of recent conchiferous deposits on these coasts, on which, 
at an ancient tertiary epoch, strata abounding with 
organic remains were extensively accumulated ? I think 
there can, namely, by considering the conditions neces- 
sary for the preservation of a formation to a distant 
age. Looking to the enormous amount of denudation 
which on all sides of us has been effected, as evi- 
denced by the lofty cliffs cutting off on so many coasts 
horizontal and once far-extended strata of no great 
antiquity (as in the case of Patagonia), as evidenced 
by the level surface of the ground on both sides of great 



416 On the Absence of 

faults and dislocations,- by inland lines of escarpments, 
by outliers, and numberless other facts, and by that 
argument of high, generality advanced by Mr. Lyell, 
namelv, that every sedinic atari/ formation, whatever its 
thickness may bo, and over however many hundred 
square miles it may extend, is the result and the measure 
of an equal amount of wear and tear of pre-existing 
formations ; considering these facts, we must conclude 
that, as an ordinary rule, a formation to resist such vast 
destroying powers, and to last to a distant epoch, must 
be of wide extent, and either in itself, or together with 
superincumbent strata, be of great thickness. In this 
discussion, we are considering only formations contain- 
ing the remains of marine animals, which, as before 
mentioned, live, with some exceptions, within (most of 
them much. 'within) depths of a hundred fathoms. How, 
then., can a thick and widely extended formation be 
accumulated, which, shall include such organic remains ? 
First, let us take the case of the bed of the sea long re- 
maining at a stationary level : under these circumstances 
it Is evident that concliiferous strata can accumulate 
only to the same thickness with the depth at which 
the shells can live ; on gently inclined coasts alone can 
they accumulate to any considerable width ; and from 
the want of superincumbent pressure, it is probable 
that the sedimentary matter will seldom be much con- 
solidated : such formations have no very good chance, 
when in the course of time they are upraised, of long 
resisting the powers of denudation. The chance will 
be less if the submarine surface, instead of having re- 
mained stationary, shall have gone on slowly rising 
during the deposition of the strata, for in this case their 
total darkness must be less, and each part, before being 
consolidated or thickly covered up by superincumbent 
matter, will have had successively to pass through the 



CHAP. xii. Recent Conchiferous Formations. 4 1 7 

ordeal of the beacli ; and on most coasts, the waves on 
the beach tend to wear down and disperse every object 
exposed to their action. Now, both on the south-eastern 
and western shores of South America, we have had clear 
proofs that the land has been slowly rising, and in the 
long lines of lofty cliffs, we have seen that the tendency 
of the sea is almost everywhere to eat into the land. 
Considering these facts, it ceases, I think, to be sur- 
prising, that extensive recent conchiferous deposits are 
entirely absent on the southern and western shores of 
America. 

Let as take the one remaining case, of the bed of 
the sea slowly subsiding during a length of time, whilst 
sediment has gone on being deposited. It is evident 
that strata might thus accumulate to any thickness, each 
stratum being deposited in shallow water, and conse- 
quently abounding with those shells which cannot live 
at great depths : the pressure, also, I may observe, of 
each fresh bed would aid in consolidating all the lower 
ones. Even on a rather steep coast, though such must 
ever be unfavourable to widely extended deposits, the 
formations would always tend to increase in breadth 
from the water encroaching on the land. Hence we 
may admit that periods of slow subsidence will com- 
monly be most favourable to the accumulation of 
conckiferous deposits, of sufficient thickness, extension, 
and hardness, to resist the average powers of denudation. 

We have seen that at an ancient tertiary epoch, 
fossiliferous deposits were extensively deposited on the 
coasts of South America ; and it is a very interesting 
fact, that there is evidence that these ancient tertiary 
beds were deposited during a period of subsidence. 
Thus, at Navidad,the strata are about 800 feet in thick- 
ness, and the fossil shells are abundant both at the level 
of the sea and some way up the cliffs ; having sent a 



41 8 Formation during Subsidence ?AET n; 

list of these fossils to Professor E. Forbes, lie thinks 
they must have lived in water between one and ten 
fathoms in depth : hence the bottom of the sea on 
which these shells once lived must have subsided at 
least 700 feet to allow of the superincumbent matter 
being deposited. I must here remark, that, as all these 
and the following fossil shells are extinct species, Pro- 
fessor Forbes necessarily judges of the depths at which 
they lived only from their generic character, and from 
the analogical distribution of shells in the Northern. 
Hemisphere; but there is no just cause from this to 
doubt the general results. At Huafo the strata are 
about the same thickness, namely, 800 feet, and Pro- 
fessor Forbes thinks the fossils found there cannot have 
lived at a greater depth than fifty fathoms, or 300 feet. 
These two points, namely, Navidad and Huafo, are 570 
miles apart, but nearly half-way between them lies 
Mocha, an island 1,200 feet in height, apparently formed 
of tertiary stiata up to its level summit, and with many 
shells, including the same Turritella with that found 
at Huafo, embedded close to the level of the sea. In 
Patagonia, shells are numerous at St. Cruz, at the foot 
of the 350 feet plain, which has certainly been formed 
by the denudation of the 840 feet plain, and therefore 
was originally covered by strata that number of feet in 
thickness, and these shells, according to Professor 
Forbes, probably lived at a depth of between seven and 
fifteen fathoms : at Port St. Julian, sixty miles to the 
north, shells are numerous at the foot of the ninety feet 
plain (formed by the denudation of the 950 feet plain), 
and likewise occasionally at the height of several hundred 
feet in the upper strata ; these shells must have lived in 
water somewhere between five and fifty fathoms in depth. 
Although, in other parts of Patagonia I have no direct 
evidence of shoal-water shells having been buried under 



CHAP. xii. of Cone /life rous Deposits. 4x9 

a great thickness of superincumbent submarine strata, 
yet It should be borne In mind that the lower fossil i- 
ferous strata with several of the same species of Hollusca, 
the upper tufaceous beds, and the high summit-plain, 
stretch for a considerable distance southward, and for 
hundreds of miles northward ; seeing this uniformity 
of btructure, I conceive it may bo fairly concluded that 
the subsidence by which the shells at Santa Cruz and 
St. Julian were carried down and covered, up, was not 
confined to these two points, bub was co-extensive with 
a considerable portion of the Patagoinan tertiary forma- 
tion. In a succeeding chapter it will be seen, that we 
are led to a similar conclusion with respect to the 
secondary fossihferous strata of the Cordillera, namely, 
that they also were deposited during a long-continued 
and great period of subsidence. 

Prom the foregoing reasoning, and from the facts 
just given, I think we must admit the probability of 
the following proposition: namely, that when the bed 
of the sea is either stationary or rising, circumstances 
are far less favourable, than when the level Is sinking, 
to the accumulation of eonchiferous deposits of sufficient 
thickness and extension to resist, when upheaved, the 
average vast amount of denudation. This result appears 
to me, in several respects, very interesting : everyone is 
at first inclined to believe that at innumerable points, 
wherever there is a supply of sediment, fossiliferous 
strata are now forming, which at some future distant 
epoch will be upheaved and preserved ; but on the views 
above given, we must conclude that this is far from 
being the case; on the contrary, we require (1st), a 
long-continued supply of sediment ; (2nd), an extensive 
shallow area; and (3rd), that this area shall slowly 
subside to a great depth, so as to admit the accumula- 
tion of a widely-extended thick mass of superincumbent 



420 Formation during Subsidence PART n, 

strata. In how few parts of the world, probably, do 
these conditions at the present day concur ! We can 
thus, also, understand the general want of that close 
sequence in fobSiliferous formations which wo might; 
theoretically have anticipated ; for, without we suppose 
a subsiding movement to go on at the same spot during 
an enormous period, from one geological era to another, 
and during the whole of this period sediment to accu- 
mulate at the proper rate, so that the depth should not 
become too great for the continued existence of mollus- 
cous animals, it is scarcely possible that there should be 
a perfect sequence at the same spot in the fossil shells 
of the two geological formations. 1 So far from a very 
long-continued subsidence being probable, many facts 
lead to the belief that the earth's surface oscillates up 
and down ; and we have seen that during the elevatory 
movements there is but a small chance of durable fos- 
siliferous deposits accumulating. 

Lastly, these same considerations appear to throw 
some light on the fact that certain periods appear to 
have been favourable to the deposition, or at least to 
the preservation, of contemporaneous formations at very 
distant points. We have seen that in South America 
an enormous area has been rising within the recent 
period; and in other quarters of the globe immense 
spaces appear to have risen contemporaneously. Prom 
my examination of the coral-reefs of the great oceans, 

1 Professor EL D Koger 5 ?, in Ms excellent address to the Associa- 
tion of American Geologists; (Siliiman's 'Journal/ vol. xlvii. p. 277), 
makes the following remark : ' T question if we are at all aware bow 
completely the whole history of all departed time lies indelibly re- 
corded with the amplest minuteness of detail in the successive 
sediments of the globe, how effectually, in other words, every 
period of time Jim wntten, its own history, carefully preserving- eveiy 
created form and every trace of action ' I think the correctness of 
such remarks is more than doubtful, even if we except (as I suppose 
he would) all those numerous organic forms which contain no haid 
parts 



CHAP. XTI. of Conckiferous Deposits. 421 

I have been led to conclude that the bed of the sea has 
gone on slowly sinking within the present ora, over truly 
vast areas : this, indeed, is in itself probable, from the 
simple fact of the rising areas having been so large. In 
South America we have dibtinct evidence that at nearly 
the same tertiary period, the bed of the sea off parts of 
the coast of Chile and off Patagonia was sinking, though 
these regions are very remote from each other. If, 
then, it holds good, as a general rule, that in the same 
quarter of the globe the earth's crust tends to sink and 
rise contemporaneously over vast spaces, we can at 
once see, that we have at distant points, at the same 
period, those very conditions which appear to be re- 
quisite for the accumulation of fossiliferous masses of 
sufficient extension, thickness, and hardness, to resist 
denudation, and consequently to last unto an epoch 
distant in futurity. 1 

1 Professor Forbes has some admirable remarks on this subject, 
In his 'Keporfc on the Shells of the ^E^ean Sea ' In a letter to Mr. 
Maclaren (* Edinburgh New Phil. Journal,' January 1843), I partially 
entered into this discussion, and endeavoured to show that it was 
highly improbable, that upraised stolls or barrier-reefs, though of 
great thickness, should, owing to their small extension or breadth, 
be preserved to a distant future period. 



422 Bahia, Brazil : PAET n. 



CHAPTER XIII. 

PLUTONIC AND METAMOEPHIO BOCKS: CLEAVAGE AND 

FOLIATION. 



Brazil, BdhiOi gntiss with disjointed metamorphosed* ctilies 
of Johation Rio de Janeiro^ gneiM-gi'amte, embedded fragment 
^n, deco<mpo8intm of La Plata,, wetamjrjjhu* and old rolcamv rocks 
O j s. Ventana Gladstone p&rpJiyry formation of Patagonia; 
singular metamorpjtio roeT&s ; xpettdo-cli'keB FMlanA Islands, 
paleozoic f*,$ils if Tierra del Fucqo, clay-blate formation, 
cretaceom fossil* of; el&avaffe and foliation ; form of land Chonos 
Arehijp&lctfjO) mica scJusts, foliation distwbed l)y granitic axu> ; 
dikes Cklloe Concepcion, M'es, incc&sive formation of Central 
and Northern Chile Concluding remarks on vleavage andfolia- 
$i on Weir elofi analogy and similar origin Stratification of 
met amor j)Jt 10 schists Foliation of tntrtmre roelts Relation of 
cleavage and foliation totlie fanes of tension during metamorphosis. 

THE metamorpliic and plutonic formations of the several 
districts visited by the Beagle will be here chiefly 
treated of, but only such cases as appear to me new, or 
of some special interest, will be described in detail ; at 
the end of the chapter I will sum up all the facts 
on cleavage and foliation, to which I particularly 
attended. 

BaJiia, Brazil; lat. 13 south. The prevailing 
rock is gneiss, often passing, by the disappearance of 
the quartz and mica, and by the feldspar losing its 
red colour, into a brilliantly grey primitive green- 
stone. Not unfrequently quartz and hornblende are 
arranged in layers in almost amorphous feldspar. 



CHAP. xiii. Rocks of. 423 

There is some fine-grained syenltic granite, orbicularly 
marked by ferruginous linen, and weathering into 
vertical, cylindrical holes, almost touching each other. 
In the gneiss, concretions of granular feldbpar and 
others of garnets with mica occur. The gneiss is 
traversed by numerous dikes composed of black, finely 
crystallised, horubleodic rock, containing a little glassy 
feldspar and sometimes mica, and varying in thickness 
from mere threads to ten feet : these threads, which 
are often curvilinear, could sometimes be traced running 
into the larger dikes. One of these dikes was remark- 
able from having been in two or three places laterally 
disjointed, with unbroken gneiss interposed between 
the broken ends, and in one part with a portion of the 
gneiss driven, apparently whilst in a softened state, 
into its side or wall. In several neighbouring places, 
the gneiss included angular, well-defined, sometimes 
bent, masses of hornblende rock, quite like, except in 
being more perfectly crystallised, that forming the 
dikes, and, at least in one instance, containing (as 
determined by Professor Miller) augite as well as 
hornblende. In one or two cases these angular masses, 
though now quite separate from each other by the solid 
gneiss, had, from their exact correspondence in size 
and shape, evidently once been united ; hence I cannot 
doubt that most or all of the fragments have been 
derived from the breaking up of the dikes, of which we 
see the first stage in the above-mentioned laterally 
disjointed one. The gneiss close to the fragments 
generally contained many large crystals of hornblende, 
which are entirely absent or rare in other parts: its 
folia or laminas were gently bent round the fragments, 
in the same manner as they sometimes are round concre- 
tions. Hence the gneiss has certainly been softened, 
its composition modified, and its folia arranged, sub- 



424 Bahia, Brazil. PAET n. 

seqnently to the breaking up of the dikes, 1 these latter 
also having been at the same time bent and softened. 

I must here take the opportunity of premising, 
that by the term cleavage, I imply those planes of 
division which render a rock, appearing to the eye 
quite or nearly homogeneous, fissile. By the term folia- 
tion, I refer to the layers or plates of different minera- 
logical nature of which most metamorphic schists are 
composed; there are, also, often included in such 
masses, alternating, homogeneous, fissile layers or folia, 
and in this case the rock is both foliated and has a 
cleavage. By stratification, as applied to these forma- 
tions, I mean those alternate, parallel, large masses of 
different composition, which are themselves frequently 
either foliated or fissile, such as the alternating so- 
called strata of mica-slate, gneiss, glossy clay-slate, and 
marble. 

The folia of the gneiss within a few miles round 
Bahia generally strike irregularly, and are often cur- 
vilinear, dipping in all directions at various angles : 
but where best defined, they extended most frequently 
in a NE. by K (or East 50 N.) and SW. by S. line, 
corresponding nearly with the coast-line northwards 
of the bay. I may add that Mr. Gardner 2 found in 
several parts of the province of Ceara, which lies 
between 400 and 500 miles north of Bahia, gneiss with 
the folia extending E. 45 N. ; and in Guyana, accord- 
ing to Sir R. Schomburgk, the same rock strikes E. 
57 N. Again, Humboldt describes the gneiss-granite 
over an immense area in Venezuela and even in Colombia, 
as striking E. 50 N., and dipping to the NW. at an 

1 Professor Hitchcock (< Geolog. of Massachusetts,* vol. ii. p. 673) 
gives a closely similar case of a greenstone dike in syenite. 

a * Geological Section of the Brit. Assoc ' 1840. For Sir R Schom- 
bargVs observations, see 'Geograph. Journal/ 1842, p. 190. See 
also Htunboldt's discussion on Loxodrism in the * Personal Nanacive/ 



CHAP. xm. Rio de Janeiro. 425 

an^le of fifty degrees. Hence all the observations 
hitherto made tend to show that the gneis&ic rocks 
over the whole of this part of the continent have their 
folia extending generally within almost a point of the 
compass of the same direction. 1 

Rio de Janew o. This whole district is almost 
exclusively formed of gneiss, abounding with garnets, 
and porphyntic with large crystals, even three and four 
inches in length, of orthoclase feldspar: in these 
crystals mica and garnets are often enclosed. At the 
western base of the Corcovado, there is some ferruginous 
canons quartz-rock ; and in the Tijeuka range, much 
tine-grained granite. I observed boulders of greenstone 
in several places; and on the islet of Villegagnon, and 
likewise on the coast some miles northward, two large 
trappean dikes. The porph\ritic gneiss, or gneiss- 
granite as it has been called by Humboldt, is only so 
far foliated that the constituent minerals are arranged 
with a certain degree of regularity, and may be said to 
have a fi grain, but they are not separated into distinct 
folia or laminae. There are, however, several other 

1 1 landed at only one place nortli of Bahia, narnelv, at Pernam- 
buco. I found there only soft, horizontally stratified matter, 
formed from disintegrated granitic rocks, and some yellowish im- 
pure limestone, probably of a tertiary ^poch. I have described a 
most singular natural bar of hard sandstone, which protects the 
harbour, in the Appendix to my work, *The Structure and Distribution 
of Coral Beefs,' 2nd edit p. 265. 

ABKOLHOS ISLETS, lat 18 S. off the coast of Brazil Although 
not strictly in place, I do not know where I can moie conveniently 
describe this little group of small islands The lowest bed is a 
sandstone with t err ugmous veins ; it weathers into an extraordinary 
honey-combed mass ; above it there is a d<irk- coloured argillaceous 
shale , above this a coaler sandstone making a total thickness of 
aoout sixty feet; and lastly, abo'.e these sedimentary beds, there is 
a line confoimab'e mass of greenstone, in some parts having a 
columnar structure. All the strata, as well as the surface of the 
land, dip at an angle of about 12 to N. by W. Some of the islets 
at e composed entirely of the sedimentary, others of the trappean 
rock&>, ^eneially, however, with the sands' ones cropping out on th 
southern shores 



426 Rio de Janeiro : PART n. 

varieties of gneiss regularly foliated, and alternating 
with each other in so-called strata. The stratification 
and foliation of the ordinary gneisses, and the folia- 
tion or grain ' of the gneiss-granite, are parallel to 
each other, and generally strike within a point of NB. 
and SYV. clipping at a high angle (between 50 and 60) 
generally to SB. : so that here again we meet witb the 
strike so prevalent over the more northern parts of this 
continent. The mountains of gneiss-gianite are to a 
remarkable degree abruptly conical, which seems caused 
by the rock tending to exfoliate in thick, conically 
concentric layers : these peaks resemble in shape those 
of phonolite and other injected rocks on volcanic 
islands ; nor is the grain or foliation (as we shall after- 
wards see) any difficulty on the idea of the gneiss- 
granite having been an intrusive rather than a meta- 
morphic formation. The lines of mountains, but not 
always each separate hill, range neatly in the same 
direction, with the foliation, and so-called stratification, 
but rather more easterly. 

On a bare gently inclined surface of the porphyritic 
gneiss in Botofogo Bay, I observed the appearance here 
represented. 

A fragment seven yards long and two in width, 
with angular and distinctly defined edges, composed of 
a peculiar variety of gneiss with dark layers of mica 
and garnets, is surrounded on all sides by the ordinary 
gneiss-granite; both having been dislocated by a 
granitic vein. The folia in the fragment and in the 
surrounding rock strike in the same NNB and SSW. 
line; but in the fragment they are vertical, whereas 
in the gneiss -granite they dip at a small angle, as 
shown by the arrows, to SSE. This fragment, con- 
sidering its great size, its solitary position, and its 
foliated structure parallel to that of the surrounding 



XXEL 



Granitic Rocks of. 



427 



rock, is, as far as I know, a unique case : and I will 
not attempt any explanation of its origin. 

No. 38. 
Fragment of Gneiss embedded m another variety of the same rock. 




The numerous travellers * in tMs country, have all 
been greatly surprised at the depth to which the gneiss 
and other granitic rocks, as well as the talcose slates of 
the interior, have been decomposed. "Near Rio, every 
mineral except the quartz has been completely softened, 
in some places to a depth little less than one hundred feet. 2 
The minerals retain their positions in folia ranging in 
the usual direction ; and fractured quartz veins may be 
traced from the solid rock, running for some distance 
into the softened, mottled, highly coloured, argillaceous 
mass. It is said that these decomposed rocks abound 

1 Spix and Martins have collected, in an Appendix to their 
' Tiavels,' the largest body of facts on this subject. See, also, some 
remarks by M Lund, in his communications to the Academy at 
Copenhagen ; and others by M Gaudichaud, in Freycinet's 4 Voyage.' 

- Br Benza describes granitic rock (' Madras Journal of Lit ' &c. 
Oct. 1836, p 246), in the Neelghernes, decomposed to a depth of 
forty feet 



428 La Plata : *AET u. 

with gems of various kinds, often in a fractured state, 
owing, as some have supposed, to the collapse of geodes, 
and that they contain gold and diamonds. At Bio, it 
appeared to me that the. gneiss had been softened before 
the excavation (no doubt by the sea) of the existing, 
broad, flat-bottomed valleys; for the depth of decom- 
position did not appear at all conformable with the 
present undulations of the surface. The porphyritio 
gneiss, where now exposed to the air, seems to with- 
stand decomposition remarkably well ; and I could see 
no signs of any tendency to the production of argilla- 
ceous masses like those here described. I was also 
struck vuth the fact, that where a bare surface of this 
rock sloped into one of the quiet bays, there were no 
marks of erosion at the level of the water, and the 
parts both beneath and above it preserved a uniform 
curve. At Bahia, the gneiss rocks are similarly decom- 
posed, with the upper parts insensibly losing their 
foliation, and passing, without any distinct line of 
separation, into a bright red argillaceous earth, includ- 
ing partially rounded fragments of quartz and granite. 
From this circumstance, and from the rocks appearing 
to have suffered decomposition before the excavation of 
the valleys, I suspect that here, as at Kio, the decom- 
position took place under the sea. The subject 
appeared to me a curious one, and would probably well 
repay careful examination by an able mineialogist. 

The Northern Proimces of La Plata.- According 
to some observations communicated to me by Mr. Fox, 
the coast from Rio de Janeiro to the mouth of the 
Plata seems everywhere to be granitic, with a few 
trappean dikes. At Port Alegre, near the boundary of 
Brazil, there are porphyries and diorites. 1 At the 
mouth of the Plata, I examined the country for twenty- 
1 M. Tsabelle, * Voyage & Buenos Ayres,' p, 479. 



CHAP. xirr. Crystalline Rocks of. 429 

five miles west, and for about seventy miles north of 
Maldonado; near this town, there is some common 
gneiss, and much, in all parts of the country, of a 
coarse-grained mixture of quartz and reddish feldspar, 
often, however, assuming a little dark-green imperfect 
hornblende, and then immediately becoming foliated. 
The abrupt hillocks thus composed, as well as the 
highly inclined folia of the common varieties of gneiss, 
strike NNE. or a little more easterly, and SSW. Clay- 
slate is occasionally met with, and near the L. del 
Potrero, there is white marble, rendered fissile from the 
presence of hornblende, mica, and asbestns ; the cleavage 
of these rocks and their stratification, that is the alter- 
nating masses thus composed, strike NNE. and SSW. 
like the foliated gneisses, and have an almost vertical 
dip. The Sierra Larga, a low range five miles west 
of Maldonado, consists of quartzite, often ferruginous, 
having an arenaceous feel, and divided into excessively 
thin, almost vertical laminse or folia by microscopically 
minute scales, apparently of mica, and striking in the 
usual NNE. and SSW. direction. The range itself is 
formed of one principal line with some subordinate 
ones ; and it extends with remarkable uniformity far 
northward (it is said even to the confines of Brazil), in 
the same line with the vertically ribboned quartz rock 
of which it is composed. The S. de las Animas is the 
highest range in the country ; I estimated it at 1,000 
feet; it runs north and south, and is formed of feld- 
spathic porphyry; near its base there is a NNW. and 
SSE. ridge of a conglomerate in a highly porphyritic 
basis. 

Northward of Maldonado, and south of Las Minas, 
there is an E. and W. hilly band of country, some miles 
in width, formed of dliceous clay-slate, with some quartz, 
rock and limestone, having a tortuous irregular cleav- 



430 



La Plata : PAJBT IL 



age, generally ranging east and west. E. and SE. of 
Las M*nas there is a confused district of imperfect 
gneiss and laminated quartz, with the hills ranging in 
various directions, but with each separate hill generally 
running in the same line with the folia of the rocks of 
which it is composed : this confusion appears to have 
been caused by the intersection of the [E, and W.] and 
[NNB. and SSW.] strikes. Northward of Las Minas, 
the more regular northerly ranges predominate : from 
this place to near Polanco, we meet with the coarse- 
grained mixture of quartz and feldspar, often with the 
imperfect hornblende, and then becoming foliated in 
a N. and S. line with imperfect clay-slate, including 
laminae of red crystallised feldspar with white or black 
marble, sometimes containing asbestus and crystals of 
gypsum with quartz-rock with syenite and lastly, 
with much granite. The marble and granite alternate 
repeatedly in apparently vertical masses : some miles 
northward of the Polanco, a wide district is said to bo 
entirely composed cf marble. It is remarkable, how 
rare mica is in the whole range of country north and 
westward of Maldonado. Throughout this district, the 
cleavage of the clay-slate and marble the foliation of 
the gneiss and the quartz the stratification or alter- 
nating masses of these several rocks and the range 
of the hills, all coincide in direction ; and although the 
country is only hilly, the planes of division are almost 
everywhere very highly inclined or vertical. 

Some ancient submarine volcanic rocks are worth 
mentioning, from their rarity on this eastern side of 
the continent. In the valley of the Tapas (fifty or 
sixty miles N* of Maldonado) there is a tract three 
or four miles in length, composed of various trappean 
rocks with glassy feldspar of apparently metamorphosed 
grit-stones of purplish amygdaloids with large kernels 



CHAP. xiix. Crystalline Rocks of. 431 

of carbonate of lime ] and much of a harshish rock 
with glassy feldspar intermediate in character between 
clay stem e porphyry and trachyte. This latter rock \\ as 
in one spot remarkable ft om being full of drusy cavities, 
lined with quartz cnstals, and arranged in planes, 
dipping at an angle of 50 to the east, and striking 
parallel to the foliation of an adjoining hill composed 
of the common mixture of quartz, feldspar, and im- 
perfect hornblende : this fact perhaps indicates that 
these volcanic rocks have been metamorphosed, and 
their constituent parts re-arranged, at the same time 
and according to the same laws, with the granitic and 
metamorphic formations of this whole region. In the 
valley of the Marmaraya, a few miles south of the 
TapaSj a band of trappean and amygdaloidal rock is 
interposed between a hill of granite and an extensive 
surrounding formation of red conglomerate, which (like 
that at the foot of the S. Animas) has its basis porphy- 
ritic with crystals of feldspar, and which hence has 
certainly suffered metamorphosis, 

Monte Video. The rocks here consist of several 
varieties of gneiss, with the feldspar often yellowish, 
granular and imperfectly crystallised, alternating with, 
and passing insensibly into, beds, from a few yards to 
nearly a mile in thickness, of fine or coarse grained, 
dark-green hornbleadic date ; this again often passing 
into chloritic schist. These passages seem chiefly due 
to changes in the mica, and its replacement by other 
minerals. At Rat Island I examined a mass of chloritic 
schist, only a few yards square, irregularly surrounded 
on all sides by the gneiss, and intricately penetrated 
by many curvilinear veins of quartz, which gradually 
Uend into the gneiss : the cleavage of the chloritic 

1 Near the Pan de Azucar there is some greenish porphyry, in on 
place amygdaloidal with agate. 



432 La Plata : PART u 

schist) and the foliation of the gneiss were exactly 
parallel. Eastward of the city there is much fine- 
grained dark-coloured gneiss, almost assuming the 
character of hornblende-slate, which alternates in thin 
laminae with laminae of quartz, the whole mass being 
transversely intersected by numerous large veins of 
quartz : I particularly observed that these veins were 
absolutely continuous with the alternating laminse of 
quartz. In this case and at Rat Island, the passage of 
the gneiss into imperfect hornblendic or into chl critic 
slate, seemed to be connected with the segregation of 
the veins of quartz. 1 

The Mount, a hill believed to be 450 feet in height, 
from which the place takes its name, is much the 
highest land in this neighbourhood : it consists of horn- 
blendic slate, which (except on the eastern and disturbed 
base) has an east arid west nearly vertical cleavage; 
the longer axis of the hill also ranges in this same line. 
Near the summit the hornblende-slate gradually be- 
comes more and more coarsely crystallised, and less 
plainly laminated, until it passes into a heavy, sonorous 
greenstone, with a slaty conchoiclal fracture ; the 
lamina on the north and south sides near the summit 
dip inwards, as if this tipper part had expanded or 
bulged outwards. This greenstone must, I conceive, be 
considered as metamorphosed hornblende-slate. The 
Cerrito, the next highest, but much less elevated 
point, is almost similarly composed. In the more 
western parts of the province, besides gneiss, there is 
quartz-rock, syenite, and granite ; and at Colla, I heard 
of marble. 

1 Mr, Greenongh. (p. 78, < Critical Examination, 1 &c.) observes that 
quartz ia mica-slate sometimes appears in beds and sometimes m 
veins Von Buch also, ia ais * Travels in Norway ' (p. 236), remarks 
on alternating laminas of quartz and hornbleade-slate replacing mica- 

ficbist. 



CHIP, HIT. Crystalline Rocks of. 433 

Near M. Video, the space which I more accurately 
examined was about fifteen miles in an east and west 
line, and here I found the foliation of the gneiss and the 
cleavage of the slates generally well developed, and ex- 
tending parallel to the alternating strata composed of the 
gneiss, homblendic and chioritic schists. These planes 
of division all range within one point of east and wesfe, 
frequently east by south and west by north ; their dip 
is generally almost vertical, and scarcely anywhere 
under 45 : this fact, considering how slightly undula- 
tory the surface of the country is, deserves attention. 
Westward of M. Video, towards the Uruguay, wherever 
the gneiss is exposed, the highly inclined folia are 
seen striking in the same direction ; 1 must except one 
spot where the strike was NW. by W. The little 
Sierra de S. Juan, formed of gneiss and laminated 
quartz, must also be exceptecl, for it ranges between 
[N. to NE.] and [S. to SW.j and seems to belong to 
the same system with the hills in the Maldonado 
district. Finally, we have seen that, for many miles 
northward of Maldonado and for twenty-five miles 
westward of it, as far as the S. de las Animas, the folia- 
tion, cleavage, so-called stratification and lines of hills, 
all ranges NNE. and SSW., which is nearly coincident 
with the adjoining coast of the Atlantic. Westward of 
the S. de las Animas, as far as even the Uruguay, the 
foliation, cleavage, and stratification (bat not lines of 
hills, for there are no defined ones) all range about E. 
by S. and W. by N., which is nearly coincident with 
the direction of the northern shore of the Plata : in the 
confused country near Las Minas, where these two great 
systems appear to intersect each other, the cleavage, 
foliation, and stratification run in various directions, 
but generally coincide with the line of each separate 
hill. 



434 Let Plata. PABT n. 

Southern La Plata. The first ridge, south of the 
Plata, which projects through tbe Pampean formation, 
is the Sierra Tapalgaen and Vulcan, situated 200 miles 
southward of the district just described. This ridge is 
only a few hundred feet in height, and runs from C. 
Corrientes in a WNW. line for at least 150 miles into 
the interior : at Tapalguen, it is composed of unstrati- 
fied granular quartz, remarkable from forming tabular 
masses and small plains, surrounded by precipitous cliffs: 
other parts of the range are said to consist of granite I 
and marble is found at the S. Tinta. It appears from 
M. Parchappe's * observations, that at Tandil there is a 
range of quartzose gneiss, very like the rocks of the S. 
Larga near Malcionado, running in the same NNE. and 
SSW. direction so that the framework of the country 
here is very similar to that on the northern shore of 
the Plata. 

The Sierra G-uitru-gueyu is situated sixty miles 
south of the S. Tapalguen : it consists of numerous 
parallel, sometimes blended together ridges, about 
twenty-three miles in width, and 500 feet in height 
above the plain, and extending in a NW. and SB. 
direction. {Skirting round the extreme SB termination, 
I ascended only a few points, which were composed of 
a fine-grained gneiss, almost composed of feldspar with 
a little mica, and passing in the upper parts of the 
hills into a rather compact purplish-clay state. The 
cleavage was nearly vertical, striking in a EW. by W. 
and SB. by E. line, nearly, though not quite, coinci- 
dent with the direction of the parallel ridges. 

The Sierra Ventana lies close south of that of Guitru- 
gueyu ; it is remarkable from attaining a height, very 

1 M. d'0rbigny*s * "Voyage, Part. Gfiolog/ p. 46. I liave given a 
short account of the peculiar forms of the quartz hills of Tapalguen, 
so untipml in a metamorphic formation, in my ' Journal of JEte 
searches* (2nd edit ), p, 116. 



CHAP. xin. Patagonia* 435 

unusual on this side of the continent, of 8,310 feet. Ifc 
consists up to Its summit, of quartz, generally pure and 
white, but sometimes reddish, and divided into thick 
laminae or strata: in one part there is a little glossy 
clay-slate with a tortuous cleavage. The thick layers 
of quartz strike in a W. 30 N. line, dipping southerly 
at an angle of 45 and upwards. The principal line of 
mountains, with some quite subordinate parallel ridges, 
range about W. 45 N. : but at their SE. termination, 
only W. 25 "N". This Sierra is said to extend between 
twenty and thirty leagues into the interior. 

Patagonia. With the exception perhaps of the 
hill of S. Antonio (600 feet high) in the Gulf of S. 
Matias, which has never been visited by a geologist, 
crystalline rocks are not mefc with on the coast of Pata- 
gonia for a space of 380 miles south of the S. Ventana. 
At this point (lat. 43 50'), at Points Union and Tombo, 
plutonic rocks are said to appear, and are found, at 
rather wide intervals, beneath the Patagonian tertiary 
formation for a space of about 300 miles southward, to 
near Bird Island, in lat. 48 56'. Judging from speci- 
mens kindly collected for me by Mr. Stokes, the pre- 
vailing rock at Ports St. Elena, Camerones, Halasplna, 
and as far south as the Paps of Pineda, Is a purplish- 
pink or brownish claystone porphyry, sometimes la- 
minated, sometimes slightly vesicular, with crystals of 
opaque feldspar and with a few grains of quartz ; hence 
these porphyries resemble those immediately to be de- 
scribed at Port Desire, and likewise a series which I have 
seen from P. Alegre on the southern confines of Brazil. 
This purphyritic formation further resembles in a 
singularly close manner the lowest stratified formation 
of the Cordillera of Chile, which, as we shall hereafter 
see, has a vast range, and attains a great thickness. 
At the bottom of the Gulf of St. George, only tertiary 
29 



436 Patagonia : PART it* 

deposits appear to be present. At Cape Blanco, there 
is quartz rock, very like that of the Falkland Islands, 
and some hard, blue, siliceous clay-slate. 

At Port Desire there is an extensive formation of 
the claystone porphyry, stretching at least twenty-five 
miles into the interior : it has been denuded and deeply 
worn into gullies before being covered up by the ter- 
tiary deposits, through which It here and there projects 
in hills; those north of the bay being 440 feet in 
height. The strata have in several places been tilted 
at small angles, generally either to NKW. or SSE. 
By gradual passages and alternations, the porphyries 
change incessantly in nature. I will describe only 
some of the principal mineralogical changes, which are 
highly Instructive, and which I carefully examined. 
The prevailing rock has a compact purplish base, with 
crystals of earthy or opaque feldspar, and often with grains 
of quartz. There are other varieties, with an almost truly 
trachytic base, full of little angular vesicles and crystals 
of glassy feldspar ; and there are beds of black perfect 
pitchstone, as well as of a concretionary imperfect 
variety. On a casual inspection, the whole series would 
be thought to be of the same plutonic or volcanic 
nature with the trachytic varieties and pitchstone ; but 
this is far from being the case, as much of the porphyry 
is certainly of nietamorphic origin. Besides the true 
porphyries, there are many beds of earthy, quite white 
or yellowish, friable, easily fusible matter, resembling 
chalk, which under the microscope is seen to consist of 
minute broken crystals, and which, as remarked in a 
former chapter, singularly resembles the upper tufaceous 
beds of the Patagonian tertiary formation. This earthy 
substance often becomes coarser, and contains minute 
rounded fragments of porphyries and rounded grains of 
quartz, and in one case so many of the latter as to 



CHAP. xrn. Porphyritie Rocks of, 437 

resemble a romrnon sandstone. These beds are sometimes 
marker! with true lines of aqueous deposition, separat- 
ing particles of different cleoiws of coarseness ; in other 

cases there are parallel ferruginous lines not of true 
deposition, as shown by the arrangement of the par- 
ticlcs 5 though singularly resembling them. The more 
indurated varieties often include many small and some 
larger angular cavities, which appear dae to the re- 
moval of earthy matter: some varieties contain mica. 
All these earthy and generally white stones insensibly 
pass into more indurated sonorous varieties, breaking 
with a conchoidal fracture, yet of small specific gravity ; 
many of these latter varieties assume a pale purple tint, 
being singularly banded and veined with different shades } 
and often become plainly porphyritie with crystals of 
feldspar. The formation of these crystals could bo 
most clearly traced by minute angular and often par- 
tially hollow patches of earthy matter, first assuming a 
fibrous structure, then passing into opaque imperfectly 
shaped crystals, and lastly, into perfect glassy crystals. 
When these crystals have appeared, and when the 
basis has become compact, the rook in many places 
could not be distinguished from a true clay stone por*- 
phy ry without a trace of mechanical structure. 

In some parts, these earthy or tufaceous beds pass 
into jaspery and into beautifully mottled and bandecl 
porcelain rocks, which break into splinters, translucent 
at their edges, hard enough to scratch glass, and fusible 
into white transparent beads : grains of quartz included 
in the porcelainous varieties can be seen melting Into 
the surrounding paste. In other parts, the earthy or 
tufaceous beds either Insensibly pass into, or alternate 
with, breccias composed of large nnd small fragments 
of various purplish porphyries, with the matrix gene- 
rally porphyritie: these breccias, though their sub- 



438 Patagonia* PART n* 

aqueous origin is in many places shown both by the 
arrangement of their smaller particles and by an oblique 
or current lamination, also pass into porphyries, in 
which every trace of mechanical origin and stratifica- 
tion has been obliterated. 

Some highly porphyritic though coarse-grained 
masses, evidently of sedimentary origin, and divided 
into thin layers, differing from each other chiefly in 
the number of embedded grains of quartz, interested 
me much from the peculiar manner in which here and 
there some of the layers terminated in abrupt points, 
quite unlike those produced by a layer of sediment 
naturally thinning oot ? and apparently the result of a 
subsequent process of metarnorpliic aggregation. In 
another common variety of a finer texture, the aggre- 
gating process had gone further, for the whole mass 
consisted of quite short, parallel, often slightly curved 
layers or patches, of whitish or reddish finely granulo- 
crystalline feldspathic matter, generally terminating at 
both ends in blunt points j these layers or patches fur- 
ther tended to pass into wedge or almond shaped little 
masses, and these finally into true crystals of feldapar, 
with their centres often slightly clrusy. The series was 
so perfect that I could not doubt that these large 
crystals, which had their longer axes placed parallel to 
each other, had primarily originated in the metamor- 
phosis and aggregation of alternating layers of tuff; 
and hence their parallel position must be attributed 
(unexpected though the conclusion may be), not to 
laws of chemical action, but to the original planes of 
deposition. I am tempted briefly to describe three 
Other singular allied varieties of rock ; the first with- 
out examination would have passed for a stratified 
porphyritic breccia, but all the included angular frag- 
ments consisted of a border of pinkisli crystalline feld~ 



CHAP. xni. Pseudo-Dikes. 439 

spathic matter, surrounding a dark translucent siliceous 
centre, in which gtains of quartz not quite blended 
into the paste could be distinguished: this uniformity 
in the nature of the fragments shows that tlioy are not* 
of median Ira 1 ? but of concretionary origin, having 1 re- 
sulted perhaps from the self- breaking up anc! aggrega- 
tion of lajers of indurated tuff containing numerous 
grains of quartz, into which, indeed, the whole mnsa 
in one part passed. The second variety is a reddish 
non-porpln ritic claystone, quite full of spherical 
cavities, about half an inch in diameter, each lined with 
a collapsed crust formed of crystals of quartz. The 
third variety also consists of a pale purple non-porphy- 
ritic claystone, almost wholly formed of concretionary 
balls, obscurely arranged in layers, of a less compacts 
and paler coloured claystone; each ball being on one 
side partly hollow and lined with crystals of quartz. 

Pseudo-Dikes. -Some miles up the harbour, in a 
line of cliffs* formed of slightly metamorphosed tuface- 
ons and porphyritic claystone beds, I observed three 
vertical dikes, so closely resembling in general appear- 
ance ordinary volcanic dikes, that I did not doubt, 
until closely examining their composition, that they 
had been injected from below. The first is straight, 
with parallel sides, and about four feet wide ; its con- 
sists of whitish, indurated tufaceous matter, precisely 
like some of the beds intersected by it. The second 
dike is more remarkable ; it is slightly tortuous, about 
eighteen inches thick, and can be traced for a con- 
siderable distance along the beach ; it is of a purplish- 
red or brown colour, and is formed chiefly of round eil 
grains of quartz, with broken crystals of earthy feld- 
spar, scales of black mica, and minute fragments of 
claystone porphyry, all firmly united together in a hard 
sparing base. The structure of this dike shows obviously 



440 Falkland Islands. PART 



that, it Is of mechanical and sedimentary origin; jet 
it thinned out upwards, and did not cut through the 
uppmituht fat ntt a in the eliflk, This fact at first appears 
to ihdiniU" that the inaitrr could not have "been washed 
in from abou; ! but if we reflect on the suction which 
would it'MiIt from a deep-seated fissure "being formed, 
we iaj admit that If the fissure were In any part open 
to the surface, nnid and water might well be drawn 
it its whole course. The third dike consisted 

of a hard, rough, white rock, almost composed of broken 
crjfitstls of tflawsy feldspar, with numerous scales of black 
mica, cemented in a scanty ba^c ; there was little in 
the app."ai.ucc of this reck, to preclude the idea, of its 
having bt'4-n a true injected iVklspathic dike. The 
matter flu m time pseudo-dikes, especially 

the *"Toud one, to have suffered, like the sur- 

rounding strata, a certain degree of metamorphic 
action; thin hag much aided the deceptive appear- 
At Baliifij in Biazil, we hare seen that a true 
injected horubl*ndic dike, not only has suffered meta- 
rnorphos*is, but lias b^en dislocated and even diffused 
in the surrounding gwi>s, xmder the form of separate 
crystals and of fru^iwnts. 

FulLland Ixlaiidii.! have described these islands 

in a publWifd ia the third volume of the Geo- 

Jourual/ The mountain-ridges consist of quartz, 

and the lower country of clay-slate and sandstone, the 

paleozoic fossils. These fossils have 

described by Messrs. Morris and Sliarpe: 

of reBemble Silurian, and others Devonian 

forms. In the eastern part of the group the several 

of quartz extend in a west and east line; 

1 figures are known to occur both in volcanic and In 

WGiawitarjr fonmtions. At the Galapagos Archipelago 

( V. of thin work), there are some striking ezampies of 

of haxd tntf 



XITI. Ticrra del Fitcgo. 441 

but farther westward the line becomes "WXW. and ESB., 
and even still more northerly. The cleavage-planes of 
the clay-sly to arc highly inclined, generally at an angle 

of above 50, and often vertical; they strike almost 
invariably in the same direction with the quartz ranges. 
The outline of the indented shores of the two main 
islands, and the relative positions of the smaller islets, 
accord with the strike both of the main axes of elevation 
and of the clotu age of the clay-slate. 

Tiemt del Fiwgo* My notes on the geology of 
this country are copious, but as they aro unimportant, 
and as fossils were found only in one district, a brief 
sketch will be here sufficient. The east coast from the 
Straits of Magellan (where the boulder formation is 
largely developed) to St. Polycarp's Bay is formed of 
horizontal tertiary strata, bounded some way towards 
the interior by a broad mountainous band of clay-slate. 
This great clay-slate formation extends from St. Le 
Maire westward for 140 miles, along both sides of tlio 
Beagle Channel to near its bifurcation. South of this 
channel, it forms all Navarin Island, and the eastern 
half of Hoste Island and of Hardy Peninsula ; north of 
the Beagle Channel it extends in a north-west line on 
both sides of Admiralty Sound to Brunswick Peninsula 
in the Straits of Magellan, and I have reason to believe, 
stretches far up the eastern side of the Gordiilera, The 
western and broken side of Tierra del Fuego towards 
the Pacific is formed of metamorphic schists, granite 
and various trappean rocks : the line of separation be- 
tween the crystalline and clay-slate formations can 
generally be distinguished, as remarked by Captain 
King, 1 by the parallelism in the clay-slate districts of 
the shores and channels, ranging in a line between 
[W. 20 to 40 K] and [K 20 to 40 S.]. 

1 * Geographical Journal, 1 vol. i. p, 155, 



442 Tierra del Fuego . PABT a 

The clay-slate is generally fissile, sometimes siliceous 
or ferruginous, with veins of quartz and calcareous 
spar ; it often assumes, especially on the loftier moun- 
tains, an altered feldspathic character, passing into 
feldspathic porphyry : occasionally it is associated with 
"breccia and grauwacbe. At Good Success Bay, there 
is a little intercalated black crystalline limestone. At 
Port Famine much of the clay-slate is calcareous, and 
passes either into a mudstone or into giauwacke, in- 
cluding odd-shaped concretions of dark argillaceous 
limestone. Here alone, on the shore a few miles north 
of Port Famine, and on the summit of Mount Tarn 
(2,600 feet high), I found organic remains ; they con- 
sist of: 

1. Ancyloceras simplex, d'Orbig * Pal. Franc '(PL V f. 2) Mount Tarn. 

2. FUMIS (in iinpei tect state) do. 

3. Natica do. do. 

4. Pentacrioras do. do. 

6. Lucina excontnca, G B, Sowerby (PL V. fig. 21), Port Famine. 

6. "Venus (in imperfect state) do. 

7. Turbmolia ? do. do. 

8. Hamitcs elatior, O. B. Sowerby, do, 

M. d'Orbigny states 1 that MM. Hombron and 
Grange found in this neighbourhood an Ancyloceras, 
perhaps A. simple, an Ammonite, a Plicatula and 
Modiola. M. d'Orbigny believes from the general 
character of these fossils, and from the Ancyloceras 
being identical (as far as its imperfect condition allows 
of comparison) with the A. sim/jjl&v of Europe, that 
the formation belongs to an early stage of the Ci etaceous 
system. Professor E. Forbes, judging only from my 
specimens, concurs in the probability of this conclusion, 
The Ho/mites elatior of the above list, of which a de- 
scription is given by Mr. Sowerby in the Appendix, and 
*whleli is remarkable from its large size, has not been 
1 ' Voyage, Part. GSolog.' p. 2i2. 



CHAP. xm. Crystalline Rocks of. 443 

seen either by M. d'Orbigny or Professor E. Forbes, as, 
since my return to England, the specimens have been 
lost. The great clay-slate formation of Tierra del Fnego 
being cretaceous, Is certainly a very Interesting fact, 
whether we consider the appearance of the country, 
which, without the evidence afforded by the fossils, 
would form the analogy of most known districts, pro- 
bably have been considered as belonging to the Palaeo- 
zoic series, or whether we view it as showing that the 
age of this terminal portion of the great axis of South 
America, is the same (as will hereafter be seen) with 
the Cordillera of Chile and Peru. 

The clay-slate in many parts of Tierra del Fuego, 
is broken by dikes * and by great masses of green stone 3 
often highly hornblendic: almost all the small islets 
within the clay-slate districts are thus composed. The 
slate near the dikes generally becomes paler-coloured, 
harder, less fissile, of a feldspathic nature, and passes 
into a porphyry or greenstone : in one case, however, 
it became more fissile, of a red colour, and contained 
minute scales of mica, which were absent in the un- 
altered rock. On the east side of Ponsonby Sound, 
some dikes composed of a pale sonorous feldspathic 
rock, porphyritic with a little feldspar, were remarkable 
from their number, there being within the space of a 
mile at least one hundred, from their nearly equalling 
in bulk the intermediate slate, and more especially 
from the excessive fineness (like the finest inlaid car- 
pentry) and perfect parallelism of their junctions with 
the almost vertical laminae of clay-slate. I was unable 
to persuade myself that these great parallel masses had 
been injected, until I found one dike which abruptly 

1 In a greenstone-dike in tlie Magdalen Channel, the feldspar 
cleaved with the angle of albite. This dike was crossed, as well as 
the suiroundmg slate, by a large vein of quartz, a circumstance of 
unusual occurrence. 



444 Tierra del Fuego* PAET n. 

thinned out to half its thickness, and had one of its 
walls jagged, with fragments of the slate embedded 
in it. 

In soul hern T. del Fuego, the clay-slate towards 
its SW. boundary, becomes much altered and feld- 
spathic Thus on Wollaston Island slate and grauwacke 
can be distinctly traced passing into feldspathic rocks 
and greenstones, including iron pyrites and epidote, 
but still retaining traces of cleavage with the usual 
strike and dip. One such metamorphosed mass was 
traversed by large vein-like masses of a beautiful 
mixture (as ascertained by Professor Miller) of green 
epidote, garnets, and white calcareous spar. On the 
northern point of this same island, there were various 
ancient submarine volcanic rocks 3 consisting of amyg- 
dalolds with dark bole and agate, of basalt with 
decomposed olivine, of compact lava with glassy 
feldspar, and of a coarse conglomerate of red scorise, 
parts being amygdaloidal with carbonate of lime. The 
southern part of Wollaston Island and the whole of 
Hermite and Horn Islands, seem formed of cones of 
greenstone : the outlying islets of II Defenso and D. 
Raminez are said * to consist of porphyritic lava. In 
crossing Hardy Peninsula, the slate still retaining 
traces of its usual cleavage, passes into columnar feld- 
spathic rocks, which are succeeded by an irregular tract 
of trappean and basaltic rocks, containing glassy feld- 
spar and much iron pyrites : there is, also, some harsh 
red claystone porphyry, and an almost true trachyte, 
with needles of hornblend, and in one spot a curious 
Blaty rock divided into quadrangular columns, having 
a base almost like trachyte, with drusy cavities lined 
by crystals, too imperfect, according to Professor Millerj 

1 Determined by Professor Jameson. Weddell's * Voyage,' p. 169. 



CHAP. xm. Cleavage of Clay-Slate. 445 

to be measured, but resembling Zeagonite. 1 In tlie 
midst of tbese singular rocks, no doubt of ancient sub- 
marine volcanic origin, a high Mil of feldspathic clay- 
elate projected, retaining its usual cleavage. Near this 
point, there was a small hillock, having the aspect of 
granite, but formed of white albite, brilliant crystals of 
hornblende (both ascertained by the reflecting gonio- 
meter) and mica 5 but with no quartz. No recent 
volcanic district has been observed in any part of Tierra 
del Fuego. 

Five miles west of the bifurcation of the Beagle 
Channel, the slate-formation, instead of becoming, as 
in the more southern parts of Tierra del Faego, feld- 
spathic, and associated with trappean or old volcanic 
rocks, passes by alternations into a great underlying 
mass of fine gneiss and glossy clay-slate, which at no 
great distance is succeeded by a grand formation of 
mica-slate containing garnets. The folia of these 
metamorphic schists strike parallel to the cleavage- 
planes of the clay-slate, which have a very uniform 
direction over the whole of this part of the country: 
the folia, however, are nndulatory and tortuous, whilst 
the cleavage-laminse of the slate are straight. These 
schists compose the chief mountain chain of southern 
T. del Fuego, ranging along the north side of the north- 
ern arm. of the Beagle Channel, in a short WNW. 
tod ESB. line, with two points (Mounts Sarmiento and 
Darwin) rising to heights of 6,800 and 6,900 feet. 
On the south-western side of this northern arm of the 
Beagle Channel, the clay-slate is seen with its strata 
dipping from the great chain, so that the metamorphic 
schists here form a ridge bordered on each side by clay- 
slate. Farther north, however ; to the west of this 

1 See Mr, Brooke's Paper in the 'London Phil. Mag,' vol. x. 
This mineral occurs in an ancient volcanic rock near Borne. 



446 Tierra del F^lego. PAET n. 

great range, there is no clay-slate, but only gneiss, mica, 
and bornblendic slates, resting on great barren bills of 
true granite, and forming a tract about sixty miles in 
width. Again, westward of these roots, the outermost 
islands are of trappean formation, which, from infor- 
mation obtained during the voyages of the Adventure 
and Bougie, 1 seem, together with granite, chiefly to 
prevail along the western coast as far north as the en- 
trance of the St. of Magellan : a little more inland, on 
the eastern side of Clarence Island and S. Desolation, 
granite, greenstone, mica-slate, and gneiss appear to 
predominate. 1 am tempted to believe, that where the 
clay-slate lias been metamorphosed at great depths 
beneath the surface, gneiss, mica-slate, and other allied 
rocks have been formed, bat where the action has taken 
place nearer the surface, feldspathic porphyries, green- 
stones, etc., have resulted, often accompanied by sub- 
marine volcanic eruptions. 

Only one other rock, met with in both arms of the 
Beagle Channel, deserves any notice, namely a granulo- 
crystalline mixture of white albite, black hornblende 
(ascertained by measurement of the crystals, and con- 
firmed by Professor Miller), and more or less of brown 
mica, but without any quartz. This rock occurs in 
large masses, closely resembling in external form 
granite or syenite : in the southern arm of the Channel, 
one such mass underlies the mica-slate, on which clay- 
slate was superimposed: this peculiar plutonic rook 
which, as we have seen, occurs also in Hardy Peninsula, 
is interesting, from its perfect similarity with that 
(hereafter ofcen to be referred to under the name of 

1 See tbo Paper by Capt. King, in the * Geograpn Journal ; ' also 
a Letter to D* Fit ton in * Geolog Proc/ vol. i. p 2$ j also some ob- 
servations by Capt Kitzlloy, Voj ages/ vol. i. p 375. I am indebted 
also to Mr. LyeJl for a series of specimens collected by Lieut, 
Graves. 



CHAP. xin. Cleavage of Clay -Slate. 447 

andesite) forming tie great injected axes of the Cordil- 
lera of Chile. 

The stratification of the clay-slate is generally very 
obscure, whereas the cleavage is remarkably well defined: 
to begin with the extreme eastern parts of T. del Puego ; 
the cleavage -planes near the St. of Le Maire strike 
either W, and E. or WSW. and ENS., and are highly 
inclined ; the form of the land, including Staten Island, 
indicates that the axes of elevation have run in this 
same line, though I was unable to distinguish the planes 
of stratification. Proceeding westward 3 I accurately 
examined the cleavage of the clay-slate on the northern, 
eastern, and western sides (thirty-five miles apart) of 
Navarin Island, and everywhere found the laminse 
ranging with extreme regularity, WNW. and ESE., 
seldom varying more than one point of the compass 
from this direction. 1 Both on the east and west coasts, 
I crossed at right-angles the cleavage-planes for a space 
of about eight miles, and found them dipping at an 
angle of between 45 and 90, generally to SSW., 
sometimes to NNE., and often quite vertically. The 
SSW. dip was occasionally succeeded abruptly by a 
NNE. dip, and this by a vertical cleavage, or again by 
the SSW. clip ; as in a lofty cliff on the eastern end of 
the island the laminae of slate were seen to be folded 
into very large steep curves, ranging in the usual WNW. 
line, I suspect that the varying and opposite dips may 
possibly be accounted for by the cleavage-laminee, 
though to the eye appearing straight, being parts 
of large abrupt curves, with their summits cut off and 
worn down. 

In several places I was particularly struck with the 

1 The clay- slate in this island was in many places crossed by 
parallel smooth joints Out of five cases, the angle of intersection 
between the strike of these joints and that of the cleavage-lammaa 
was in two cases 45 and in two others 79. 



448 Tierra del Fuego. PABT n. 



fact, that the fine lammse of the clay-slate, where cut- 
ting straight through the bands of stratification, and 
therefore indisputably true cleavage-planes, differed 
slightly in their greyish and greenish tints of colour, in 
compactness, and in some of the laminae having a rather 
more jaspery appearance than others. I have not seen 
this fact recorded, and it appears to me important, for 
it shows that the same cause which has produced the 
highly fissile structure, has altered in a blight degree 
the mineralogical character of the rock in the same 
planes. The bands of stratification, just alluded to, 
can be distinguished in many places, especially in 
Navarin Island, but only on the weathered surfaces of 
the slate ; they con&ist of slightly undulatory zones of 
different shades of colour and of thicknesses, and re- 
semble the marks (more closely than anything else 
to which I can compare them) left on the inside of a 
vessel by the draining away of some dirty slightly 
agitated liquor: no difference in composition, corre- 
sponding with these zones, could be seen in freshly 
fractured surfaces. In the more level parts of 
Navarin Island, these bands of stratification were 
nearly horizontal ; but on the flanks of the mountains 
they were inclined from them, but in no instance that 
I saw at a very high angle. There can, I think, be no 
doubt that these zones, which appear only on the 
weathered surfaces, are the last vestiges of the ori- 
ginal planes of stratification, now almost obliterated 
by the highly fissile and altered structure which the 
mass has assumed. 

The clay-slate cleaves in the same WNW. and ESE. 
direction, as on Navarin Island, on both sides of the 
Beagle Channel, on the eastern side of Hoste Island, on 
the NE. side of Hardy Peninsula, and on the northern 
point of Wollaston Island; although in these two 



CHAP. xni. Cleavage of Clay-Slate. 449 

latter localities the cleavage has been much obscured 
by the metamorphosed and feldspathic condition of the 
slate. Within the area of these several islands, in- 
cluding Navarin Island, the direction of the stratifica- 
tion and of the mountain-chains is very obscure ; though 
the mountains in several places appeared to range in 
the same WNW. line with the cleavage : the outline 
of the coast, however, does not correspond with this 
line. Near the bifurcation of the Beagle Channel, 
where the underlying metamorphic schists are first seen, 
they are foliated (with some irregularities) in this same 
WNW. line, and parallel, as before stated, to the main 
mountain-axis of this part of the country. Westward 
of this main range the metamorphic schists are foliated, 
though less plainly, in the same direction, which is 
likewise common to the zone of old erupted trappean 
rocks forming the outermost islets. Hence the area, 
over which the cleavage of the slate and the foliation of 
the metara orphic schists extends with an average WN W. 
and ESB. strike, is about forty miles in a north and 
south line, and ninety miles in an east and west line. 

Further northward, near Port Famine, the stratifi- 
cation of the clay-slate and of the associated rocks is 
well defined, and there alone the cleavage and strata- 
planes are parallel. A little north of this port there is 
an anticlinal axis ranging NW. (or a little more westerly) 
and SE. : south of the port, as far as Admiralty Sound 
and Gabriel Channel, the outline of the land clearly 
indicates the existence of several lines of elevation in 
this same NW. direction, which, I may add, is so uoi- 
forni in the western half of the St. of Magellan, that, 
as Captain King * has remarked, * a parallel ruler placed 
on the map upon the projecting points of the south 
shore, and extended across the strait, will also touch 
1 * Geograph. Journal,' vol. i. p. 170. 



450 C/ionos Archipelago* PAUT n 

the headlands on the opposite coast/ It would appear, 
from Captain King's observations, that over all this 
area the cleavage extends in the same line. Deep-water 
channels, however, in all parts of Tierra del Fuego 
have burst through the trammels hoth of stratification 
and cleavage ; most of them may have been formed during 
the elevation of the land by long-continued erosion, 
but others, for instance, the Beagle Channel, which 
stretches like a narrow canal for 120 miles obliquely 
through the mountains, can hardly have thus originated. 

Finally, we have seen that in the extreme eastern 
point of Tierra del Fuego, the cleavage and coast-lines 
extend W. and E. and even WSW. and ENE. : over a 
large area westward, the cleavage, the main range of 
mountains, and some subordinate ranges, but not the 
outlines of the coast, strike WNW. and ESE. ; in the 
central and western parts of the Strait of Magellan, the 
stratification, the mountain-ranges, the outlines of the 
coast, and the cleavage all strike nearly NW. and SE. 
North of the strait, the outline of the coast, and the 
mountains on the mainland, run nearly north and 
south. Hence we see, at this southern point of the 
continent, how gradually the Cordillera bend, from 
their north and south course of so many thousand miles 
in length, into an E. and even ENE. direction, 

West Coist, from the Southern Chortos Islands to 
Northern, Chile. The first place at which we landed 
north of the St. of Magellan was near Cape Tres Montes, 
in lat. 47 S. Between this point and the northern 
Chonos Islands, a distance of 200 miles, the ' Beagle * 
visited several points, and specimens were collected for 
me from the intermediate spaces by Lieut. Stokes. 
The predominant rock is mica-slate, with thick folia 
of quartz, very frequently alternating with and passing 
into a chloriticj or into a Hack, glossy, often striated, 



CHA.P. xin. Chonos Archipelago. 45 1 

slightly anthracitic schist, which soils paper, and be- 
comes white under a great heat, and then fuses. Thin 
layers of feldspar, swelling at intervals into well crystal- 
lised kernels, are sometimes included in these black 
schists ; and I observed one mass of the ordinary black 
variety insensibly lose its fissile structure, and pass into a 
singular mixture of chlorite, epidote, feldspar, and mica. 
Great veins of quartz are numerous in the mica-schist ; 
wherever these occur the folia are much convoluted* 
In the southern part of the Peninsula of Tres Montes f 
a compact altered feld spathic rock with crystals of 
feldspar and grains of quartz is the commonest variety ; 
this rock l exhibits occasionally traces of an original 
brecciated structure, and often presents (like the altered 
state of Tierra del Fuego) traces of cleavage-planes, 
which strike in the same direction with the folia of 
mica-schist farther northward. At Inchemo Island, a 
similar rock gradually becomes granule-crystalline and 
acquires scales of mica ; and this variety at S. Estevan 
becomes highly laminated, and though still exhibiting 
some rounded grains of quartz, passes into the black, 
glossy, slightly anthracitic schist which, as we have 
seen, repeatedly alternates with and passes into the 
micaceous and chloritic schists. Hence all the rocks 
on this line of coast belong to one series, and insensibly 
vary from an altered feldspathic clay-slate into largely 
foliated, true mica-schist. 

The cleavage of the homogeneous schists, the folia- 
tion of those composed of more or less distinct minerals 
in layers, and the planes of alternation of the different 
varieties or so-called stratification are all parallel, and 
preserve over this 200 miles of coast a remarkable 

1 The peculiar, abruptly conical form of the hills in this neigh- 
bourhood, would have led any one at first to have supposed that they 
had been formed of injected or intrusive rocks. 

30 



452 Chonos Archipelago. PAET n. 

degree of uniformity in direction. At the northern 
end of the group, at Low's Harbour, the well-defined 
folia of mica-schist everywhere ranged within eight 
degrees (or leES than one point of the compass) of 
N. 19 W. and S. 19 E.; and even the point of dip 
varied very little, being always directed to the west and 
generally at an angle of forty degrees : I should mention 
that I had here good opportunities of observation, for I 
followed the naked rock on the beach, transversely to 
the strike, for a distance of four miles and a half, and 
all the way attended to the dip. Along the outer islands 
for 100 miles south of Low's Harbour, Lieutenant Stokes^ 
during his boat-survey, kindly observed for me the strike 
of the foliation, and he assures me that it was invariably 
northerly, and the dip with one single exception to the 
west. Farther south, at Vallenar Bay, the strike was 
almost universally N. 25 W., and the dip, generally at 
an angle of about 40 to W. 25 S., but in some places 
almost vertical. Still farther south, in the neighbour- 
hood of the harbours of Anna Pink, S. Estevan, and S, 
Andres, and (judging from a distance) along the southern 
part of Tres Montes, the foliation and cleavage extended 
in a line between [N. 11 to 22 W.] and [S. 11 to 
22 E.] ; and the planes dipped generally westerly, but 
often easterly, at angles varying from a gentle incline^ 
tion to vertical. At A. Pink's Harbour, where the 
scMsts generally dipped easterly, wherever the angle 
became high, the strike changed from N* 11 W. to 
even as much as N. 45 W. : in an analogous manner 
at Vallenar Bay, where the dip was westerly (viz. on an 
average directed to W. 25 S.), as soon as the angle 
became yery high, the planes struck in a line more 
than 25 west of north. The average result from all 
the observations on this 200 miles of coast, is a strike 
of N. 19 W. and S. 19 E. : considering that in each 



CHAP. DEL Foliation of Mica-Schist. 453 

specified place my examination, extended over an area 
of several miles, and that Lieut. Stokes' observations 
apply to a length of 100 miles, I think this remarkable 
uniformity is pretty well established. The prevalence, 
throughout the northern half of this line of coast, of a 
dip in one direction, that is, to the west, instead of being 
sometimes west and sometimes east, is, judging from 
what I have elsewhere seen, an unusual circumstance, 
In Brazil, La Plata, the Falkland Islands, and Tierra 
del Fuego, tie re is generally an obvious relation be- 
tween the axes of elevation, the outline of the coast, 
and the strike of the cleavage or foliation : in the 
Chonos Archipelago, however, neither the minor details 
of the coast-line nor the chain of the Cordillera, nor 
the subordinate transverse mountain-axes, accord with 
the strike of the foliation and cleavage : the seaward 
face of the numerous islands composing this archi- 
pelago, and apparently the line of the Cordillera, range 
N. 11E. 5 whereas, as we have just seen, the average 
strike of the foliation is N. 19 W. 

There is one interesting exception to the uniformity 
in the strike of the foliation. At the northern point 
of Tres Montes (lat. 45 52') a bold chain of granite, 
between 2,000 and 3,000 feet in height, runs from the 
coast far into the interior, 1 in a ESE. line, or more 
strictly E. 28 S. and W. 28 N. In a bay, at the north- 
ern foot of this range, there are a few islets of mica- 
slate, with the folia in some parts horizontal, but mostly 
inclined at an average angle of 20 to the north. On 
the northern steep flank of the range, there are a few 
patches (some quite isolated, and not larger than half-a* 

1 In the distance, other mountains could be seen apparently 
ranging NNE. and SSW. at right angles to this one. I may add, 
that not far from Yallenar Bay there is a fine range, apparently of 
granite, which has burst through the mica-slate in a Njfi by B. and 
SW. by S. line. 



454 Chonos Archipelago. PAET m 

crown!) of the mica-schist, foliated with the same 
northerly dip. On the broad summit, as far as the 
southern crest, there is much mica- slate, in some places 
even 400 feet in thickness, with the folia all dipping 
north, at angles varying from 5 to 20, but sometimes 
mounting up to 30. The southern flank consists of 
bare granite. The mica-slate is penetrated by small 
veins 1 of granite, branching from the main body. 
Leaving out of view the prevalent strike of the folia in 
other parts of this archipelago, it might have been 
expected that here they would have dipped N. 28 E. ? 
that is, directly from the ridge, and, considering its 
abruptness, at a high inclination ; but the real dip, as 
we have just seen, both at the foot and on the northern 
flank, and over the entire summit, is at a small angle, 
and directed nearly due north. From these considera- 
tions it occurred to me, that perhaps we here had the 
novel aad curious case of already inclined laminae 
obliquely tilted at a subsequent period by fche granitic 
axis. Mr. Hopkins, so well known from his mathe- 
matical investigations, has most kindly calculated the 
problem : the proposition sent was, take a district 
composed of laminae, dipping at an angle of 40 to 
W. 19 S., and let an axis of elevation traverse it in an 
E. 28 S. lin, what will the position of the laminae be 
on the northern flank after a tilt, we will first suppose, 
of 45 ? Mr. Hopkins informs me, that the angle of 
the dip will be 28 31', and its direction to north 
30 33' west. 2 By varying the supposed angle of the 

1 The granite within these veins, as well as generally at the 
junction with the mica-slate, is more qnartzose than elsewhere. The 
granite, I may add, is traversed by dikes running for a very great 
length in the line of the mountains ; they are composed of a some- 
what laminated eurite, containing crystals of feldspar, hornblende, 
and octagons of quartz. 

* On the south side of the axis (where, however, I did not see any 
mica-slate) the dip of the folia would be at an angle of 77 55' t 



sin. Foliation of Mica-Schist 455 

tilt, our previously inclined folia can be thrown into 
any angle between 26, which is the least possible angle, 
and 90 ; but if a small inclination be thus given to 
them, their point of dip will depart far from the north, 
and therefore not accord with the actual position of the 
folia of mica-schist on our granitic range. Hence It ap- 
pears very difficult, without varying considerably the ele- 
ments of the problem, thus to explain the anomalous strike 
and dip of the foliated mica-schist, especially in those 
parts, namely, at the base of the range, where the folia 
are almost horizontal. Mr. Hopkins, however, adds, 
that great irregulaiities and lateral thrusts might be 
expected in every great line of elevation, and that these 
would account for considerable deviations from the 
calculated results : considering that the granitic axis, 
as shown by the veins, has incli&putably been injected 
after the perfect formation of the mica- slate, and con- 
sidering the uniformity of the strike of the folia through- 
out the rest of the archipelago, I cannot but still think 
that their anomalous position at this one point is 
someway directly and mechanically related to the in- 
trusion of this WNW. and ESE. mountain-chain of 
granite. 

Dikes are frequent in the metamorphic schists of the 
Ohonos Islands, and seem feebly to represent that great 
band of trappean and ancient volcanic rocks on the 
south-western coast of T. del Fuego. At S. Andres I 
observed in the space of half a mile, seven broad, parallel 
dikes, composed of three varieties of trap, running in a 
NW. and SE. line, parallel to the neighbouring moun- 
tain-ranges of altered clay-slate ,* but they must be of 
long subsequent origin to these mountains; for they 

directed to the west 35 33' south. Hence the two points of clip on 
the opposite sides of the range, instead of being as in ordinary cases 
directly opposed to each other at an angle of 180, would heie be 
only 86 50' apart. 



456 Chiloe and Concepcion. FAET ir. 

intersected the volcanic formatioB described in the lasfc 
chapter. North of Tres Montes, I noticed three dikes 
differing from each other in composition, one of them 
having an enritic base including large octagons of 
quartz ; these dikes, as well as several of porphyritic 
greenstone at Vallenar Bay, extended NB. and SW. ? 
nearly at right angles to the foliation of the schists, 
but in the line of their joints. At Low's Harbour, 
however, a set of great parallel dikes, one ninety yards 
and another sixty yards in width, have been guided by 
the foliation of the mica-schist, and hence are inclined 
westward at an angle of 45 : these dikes are formed of 
various porphyritic traps, some of which are remarkable 
from containing numerous rounded grains of quartz. 
A porphyritic trap of this latter kind, passed in one of 
the dikes into a most cnrions hornstone, perfectly white, 
with a waxy fracture and pellucid edges, fusible, and 
containing many grains of quartz and specks of iron 
pyrites. In the ninety yard dike several large, appa- 
rently now quite isolated fragments of mica-slate were 
embedded ; but as their foliation was exactly parallel 
to that of the surrounding solid rock, no doubt these 
now separate fragments originally formed wedge-shaped 
depending portions of a continuous vault or crust, 
once extending over the dike, but since worn down and 
denuded. 

GMloe Valdiwa,, Conception. In Chiloe, a great 
formation of mica-schist strikingly resembles that of 
the Chonos Islands. For a space of eleven miles on 
the SEL coast, the folia were very distinct, though 
slightly convoluted, and ranged within a point of NNW. 
and SSB., dipping either ENTE. or more commonly 
WSW, 5 at an average angle of 22 (in one spot, however, 
at 60), and therefore decidedly at a lesser inclination 
than amongst the Chonos Islands. On the west and 
north-western shores, the foliation was often 



xiii. Chi Ice and Conception. 457 

though, where best defined, it ranged within a point of 
N. by W. and S. by E., dipping either easterly or 
westerly, at varying and generally very small angles. 
Hence, from the southern part of Tres Montes to the 
northern end of Ohiloe, a distance of 300 miles, we 
have closely allied rocks with their folia striking on an 
average in the same direction, namely, between N". 11 
and 22 W. Again, at Valdivia, we meet with the 
same mica-schist, exhibiting nearly the same minera- 
logical passages as in the Chonos Archipelago, often, 
however, becoming more ferruginous, and containing 
so much feldspar as to pass into gneiss. The folia were 
generally well defined ; but nowhere else in South 
America did I see them varying so much in direction : 
this seemed chiefly caused by their forming parts, as I 
could sometimes distinctly trace, of large flat curves : 
nevertheless, both near the settlement and towards the 
interior^ a NW. and SE. strike seemed more frequent 
than any other direction ; the angle of the dip was 
generally small. At Concepcion, a highly glossy clay- 
slate had its cleavage often slightly curvilinear, and 
inclined, seldom at a high angle, towards various points 
of the compass ; * but here, as at Valdivia, a NW. and 

1 I observed in some parts that the tops of the laminas of the 
clay-slate (b of the diagram) under the superficial detritus and soil 
(a) were bent, sometimes without be- 
ing broken, as represented in the 
accompanying diagram., which is 



la Beche (p 42, * Geological Manual') 

of an exactly similar phenomenon in 

Devonshire Mr B A 0. Austen, also, 

in his excellent paper on S.E Devon 

(* Geolog. Transact.' vol. vi. p. 437), has described this phenomenon ; 

he attributes it to the action of frosts, but at the same time doubts 

whether the frosts of the present day penetrate to a sufficient depth. 

As it is known that earthquakes particularly affect the surface ot the 

ground, it occurred to me that this appearance might perhaps be due, 

at least at Concepcion, to their frequent occurrence j the superficial 

layers of detritus being eithei }erked in one direction, or, where the 



458 Chiloe and Concepcion. PABT it, 

SE* strike seemed to be the most frequent one. In 
certain spots large quartz veins were numerous, and 
near them the cleavage, as was the case with the folia- 
tion of the schists in the Chonos Archipelago, became 
extremely tortuous. 

At the northern end of Quinquina Island 3 in the 
Bay of Concepcion, at least eight rudely parallel dikes, 
which have been guided to a certain extent by the 
cleavage of the skte 7 occur within the space of a quarter 
of a mile. They vary much in composition, resembling 
in many respects the dikes at Low's Harbour: the 
greater number consist of feldspathic porphyries, some- 
times containing grains of quartz : one, however, was 
black and brilliant, like an augitic rock, but really 
formed of feldspar ; others of a feldspathic nature were 
perfectly white, with either an earthly or crystalline 
fracture, and including grains and regular octagons of 
quartz ; these white varieties passed into ordinary green- 
stones. Although, both here and at Low's Harbour, 
the nature of the rock varied considerably in the same 
dike, yet I cannot but think that at these two places 
and in other parts of the Chonos group, where the dikes, 
though close to each other and running parallel, are of 
different composition, that they must have been formed 
at different periods. In the case of Quinquina this is a 
rather interesting conclusion, for these eight parallel 
dikes cut through the metamorphic schists in a NW. 
and SB. line, and since their injection the overlying 
cretaceous or tertiary strata have been tilted (whilst 
still under the sea) from a NW. by N. and SE by 

surface was inclined, pushed a little downwards during each strong 
vibration. In North Wales I have seen a somewhat analogous but 
less regular appearance, though on a greater scale (' London PhiL 
Mag.* vol. xxi p. 184), and produced by a quite different cause,, 
namely, by the stranding of great icebergs ; this latter appearance 
has also been observed in North America. 



CHAP. xm. Central and Northern Chile. 459 

S. line; and again, during the great earthquake of 
February 1835, the ground in this neighbourhood was 
fissured in N W. and SB. lines ; and from the manner in 
which buildings were thrown down, it was evident that 
the surface undulated in this same direction. 1 

Central and Northern Chile. Northward of Oon- 
cepcion, as far as Copiapo, the shores of the Pacific 
consist, with the exception of some small tertiary basins, 
of gneiss, mica-schist, altered clay-slate, granite, green- 
stone and syenite : hence the coast from Tres Montes 
to Copiapo, a distance of 1,200 miles, and I have reason 
to believe for a much greater space, is almost similarly 
constituted. 

Near Valparaiso the prevailing rock is gneiss, 
generally including much hornblende : concretionary 
balls formed of feldspar, hornblende and mica, from 
two to three feet in diameter, are in very many places 
conformably enfolded by the foliated gneiss: veins 
of quartz and feldspar, including black schorl and well- 
crystallised epidote, are numerous. Epidote likewise 
occurs in the gneiss in thin layers, parallel to the" folia- 
tion of the mass. One large vein of a coarse granitic 
character was remarkable from in one part quite 
changing its character, and insensibly passing into a 
blackish porphyry, including acicular crystals of glassy 
feldspar and of hornblende : I have never seen any other 
such case, 2 

I shall in the few following remarks on the rocks of 
Chile allude exclusively to their foliation and cleavage. 
In the gneiss round Valparaiso the strike of the foliation 
is very variable, but I think about N. by W. and S. by 

1 Geolog. Trans/ vol. vi. pp. 602 and 617. * Journal of Ee 
searches ' (2nd edit.), p. 307. 

2 Humboldt (' Personal Narrative,' vol iv. p 60) has described 
with much surprise, concretionary balls, with concentric divisions, 
composed of partially vitreous feldspar, hornblende, and game s, 
included within great veins of gneiss, which cut across the mica- 
slate near Venezuela. 



460 Cleavage and Foliation. PART n. 

E. is the commonest direction ; this likewise holds good 
with, the cleavage of the altered feldspathic clay -slates, 
occasionally met with on the coast for ninety miles north, 
of Valparaiso. Some feldspathic slate, alternating with 
strata of clay-stone porphyry in the Bell of Quillota 
anJ at Jajuel, and therefore, perhaps 3 belonging to a 
later period than the metatnorphic schists on the coast, 
cleaved in this same direction. In the eastern Cordillera, 
In the Portillo Pass s there is a grand mass of L'ioa- 
slate, foliated in a north and south line, and with a 
high westerly dip : in the Uspallata range, clay-slate 
and gran wacke have a highly inclined, nearly north and 
south cleavage, though in some parts the strike is irreg- 
ular : in the main or Cambre range, the direction of the 
cleavage in the feldspathic clay-slate is NW. and SE. 

Between Coquimbo and Guasco there are two con- 
siderable formations of mica slate, in one of which the 
rock passed sometimes into common clay-slate and some* 
times into a glossy black variety, very like that in the 
Chonos Archipelago. The folia and cleavage of these 
rocks ranged between [N. and NW. by N.] and [S.and 
SW by S.j Near the Port of Guasco several varieties 
of altered clay-slate have a quite irregular cleavage. 
Between Guasco and Copiapo, there are some siliceous 
and talcaceons slates cleaving in a north and south line, 
wifch an easterly dip of between 60 and 70 : high up, 
also, the main valley of Copiapo, there is mica-slate 
with a high easterly dip. In the whole space between 
Valparaiso and Copiapo an easterly dip is much more 
common than an opposite or westerly one. 

Concluding Remarks on Cleavage and Foliation. 

In this southern part of the Southern Hemisphere, 
we have seen that the cleavage-laminae range over wide 



CHAP. xin. Cleavage and Foliation. 461 

areas with, remarkable uniformity, cutting straight 
through, the planes of stratification, 1 bat yet being 
parallel in strike to the main axes of elevation, and 
generally to the outlines of the coast. The dip, how- 
ever, is as variable, both in angle and in direction (that 
is, sometimes being inclined to the one side and some-? 
times to the directly opposite side), as the strike is 
uniform. In all these respects there is a close agree- 
ment with the facts given by Professor Sedgwick in his 
celebrated memoir in the c Geological Transactions,' and 
by Sir B. I. Murchison in his various excellent dis- 
cussions on this subject. The Falkland Islands, and 
more especially Tierra del Fuego, offer striking instances 
of the lines of cleavage, the principal axes of elevation, 
and the outlines of the coast, gradually changing 
together their courses. The direction which, prevails 
throughout Tierra del Fuego and the Falkland Islands, 
namely, from west with some northing to east with 
some southing, is also common to the several ridges in 
northern Patagonia and in the western parts of Banda 
Oriental : in this latter province, in the Sierra Tapalguen, 
and in the western Falkland Island, the W. by N"., or 
WNW. and ESE., ridges, are crossed at right angles by 
others ranging NNE. and SSW. 

The fact of the cleavage-laminae in the clay-slate of 
Tierra del Fuego, where seen cutting straight through 
the planes of stratification, and where consequently 
there could be no doubt about their nature, differing 
slightly in colour, texture, and hardness, appears to me 
very interesting. In a thick mass of laminated, feld- 
spathic and altered clay-slate, interposed between two 

1 In my paper on the Falkland Islands (vol. iii. p 267 * Geolog- 
ical Journal*), I have given a curious case on the authority of Capt. 
Suhvau, E N" , of much folded beds of clay-slate, in some of which the 
cleavage is perpendicular to the horizon, and in others it is perpen- 
dicular to each curvature or fold of the bed j this appears a new case. 



462 Cleavage and Foliation. P^JRT n. 

great strata of porphyritic conglomerate in central 
Chile, and where there could be but little doubt about 
the bedding, I observed similar slight differences in com- 
position, and likewise some distinct thin layers of 
epidote, parallel to the highly inclined cleavage of the 
mass. Again, I Incidentally noticed in North Wales, 1 
where glaciers had passed over the truncated edges of 
the highly inclined laminse of clay-slate, that the surface^ 
though smooth, was worn into small parallel undula- 
tions, caused by the component laminas being of slightly 
different degrees of hardness. With reference to the 
slates of North Wales, Professor Sedgwick describes the 
planes of cleavage, as * coated over with chlorite and 
semi-crystalline matter, which not only merely define the 
planes in question, bat strike in parallel flakes through 
the whole mass of the rock/ 2 In some of those glossy 
and hard varieties of clay-slate which may often be 
seen passing into mica-schist, it has appeared to me that 
the cleavage-planes were formed of excessively thin ? 
generally slightly convoluted, folia, composed of micro- 
scopically minute scales of mica. Prom these several 
facts, and more especially from the case of the clay- 
slate In Tierra del Fuego, it must, I think, be con- 
cluded, that the same power which has impressed on 
the slate its fissile structure or cleavage has tended 
to modify its mineralogical character in parallel 
planes. 

Let us now turn to the foliation of the meta- 
morphic schists, a subject which has been much less 
attended to. As in the case of cleavage-laminae, the 
folia preserve over very large areas a uniform strike : 
thus Humboldt 3 found for a distance of 300 miles in 

8 London Phil. Mag. 1 vol. xxi. p 182. 

8 Geological Trans.* vol. iii. p. 471. 

9 ' Personal Narrative/ vol vi p. 591, et sec^ 



CHAP. nn. Cleavage and Foliation. 463 

Venezuela, and indeed over a much larger space, gneiss, 
granite, mica, and clay-slate, striking very uniformly 
NE. and SW. 5 and dipping at an angle of between 60 
and 70 to NW. : it would even appear from the facts 
given in this chapter, that the metamorphio rocks 
throughout the north-eastern part of S. America are 
generally foliated within two points of NE. and SW. 
Over the eastern parts of Banda Oriental, the foliation 
strikes with a high inclination, very uniformly NNE. to 
SSW., and over the western parts, in a W. by N. and 
E. by S. line. For a space of 800 miles on the shores 
of the Ohonos and Chiloe Islands, we have seen that the 
foliation seldom deviates more than a point of the com- 
pass from a K 19 W. and S. 19 E. strike. As in the 
case of cleavage, the angle of the dip in foliated rocks 
is generally high but variable, and alternates from one 
side of the line of strike to the other side, sometimes 
being vertical : in the northern Ohonos Islands, however, 
the folia are inclined almost always to the west; in 
nearly the same manner, the cleavage -laminae in 
southern Tierra del Fuego certainly dip much more 
frequently to SSW. than to the opposite point. In 
eastern Banda Oriental, in parts of Brazil, and in some 
other districts, the foliation runs in the same direction 
with the mountain-ranges and adjoining coast-lines: 
amongst the Ohonos Islands, however, this coincidence 
fails, and I have given my reasons for suspecting 
that one granitic axis has burst through and tilted the 
already inclined folia of mica-schist: in the case of 
cleavage, 1 the coincidence between its strike and that 
of the main stratification seems sometimes to fail. 
Foliation and cleavage resemble each other in the planes 
winding round concretions, and in becoming tortuous 

1 Cases are given by Mr. Jukes, in his * Geology of Hewfoundland/ 
p. 130. 



464 Cleavage and Foliation. PAEP n 8 

where veins of quartz abound. 1 On the flanks of the 
mountains both in Tierra del Fuego and in other 
countries, I have observed that the cleavage-planes fre- 
quently dip at a high angle inwards ; and this was long 
ago observed by Von Buch to be the ease in Norway : 
this fact is perhaps analogous to the folded, fan-like or 
radiating structure in the metamorphic schists of the 
Alps, 2 in which the folia in the central crests are vertical 
and on the two flanks inclined inwards. Where masses 
of fissile and foliated rocks alternate together, the cleav- 
age and foliation, in all cases which I have seen, are 
parallel. Where in one district the rocks are fissile, 
and in another adjoining district they are foliated, the 
planes of cleavage and foliation are likewise generally 
parallel: this is the case with the feldspathic homo- 
geneous slates in the southern part of the Chonos group, 
compared with the fine foliated mica-schists of the 
northern part; so again the clay-slate of the whole 
eastern side of Tierra del Fuego cleaves in exactly the 
same line with the foliated gneiss and mica-slate of the 
western coast; other analogous instances might have 
been adduced. 3 

With respect to the origin of the folia of quartz, 
mica, feldspar, and other minerals composing the meta- 
morphic schists, Professor Sedgwick, Mr. Lyell and 
most authors believe, that the constituent parts of each 
layer were separately deposited as sediment, and then 

1 I have seen in Brazil and Chile concretions thus enfolded by 
foliated gneiss j and Macculloch ('Highlands/ vol. i p 64) has 
described a similar case. For analogous cases in clay-slate, see 
Prof. Henslow's Memoir in ' Cambridge Phil Trans ' vol i p 379, 
and Macculloch's * Class, of Rocks,' p. 3S1. With respect to both 
foliation and cleavage becoming tortuous where quartz- veins abound, 
I have seen instances near Monte Video, at Concepcion, and in the 
Chonos Islands. See also Mr. Greenough's ' Critical Examination,' 



work. 



* 

Studer in * Bdin. New Phil Journal,' vol xxm p. 144. 

I have given a case in Aus ralia See Chapter VII of this 



CHAP. xin Cleavage and Foliation. 465 

metamorphosed. This view, in the majority of cases, I 
believe to be quite untenable. In those not uncommon 
instances, where a mass of clay-slate, in approaching 
granite, gradually passes into gneiss, 1 we clearly see 
that folia of distinct minerals can originate through the 
metamorphosis of a homogeneous fissile rock. The de- 
position, it may be remarked, of numberless alternations 
of pure quartz, and of the elements of mica or feldspar, 
does not appear a probable event. 2 In those districts 
in which the metamorphic schists are foliated in planes 
parallel to the cleavage of the rocks in an adjoining 
district; are we to believe that the folia are due to 
sedimentary layers, whilst the cleavage-laminse, though 
parallel, have no relation whatever to such planes of 
deposition ? On this view, how can we reconcile the 
vastness of the areas over which the strike of the folia- 
tion is uniform, with what we see in disturbed districts 
composed of true strata : and especially, how can we 
understand the high and even vertical clip throughout 
many wide districts, which are not mountainous, and 
throughout some, as in western Banda Oriental, which 
are not even hilly ? Are we to admit that in the 
northern part of the Chonos Archipelago, mica-slate w\s 
first accumulated in parallel horizontal folia to a thick- 
ness of about four geographical miles, and then upturned 
at an angle of forty degrees ; whilst, in the southern 
part of this same archipelago, the cleavage-laminae 
of closely allied rocks, which none would imagine had 
ever been horizontal, dip at nearly the same angle, to 
nearly the same point ? 

Seeing, then, that foliated schists indisputably are 

1 I have described (in Chapter VII. of this work) a good instance 
of such a passage at the Cape of Good Hope. 

3 See some excellent remarks on this subject, in D'Aubxrisson's 
*Tiaite de G6og' torn 1 p 297, Also, some remarks by Mr. Dana 
19 Silliman's l American Journ.' vol. xlv. p. 108. 



466 Cleavage and Foliation. P\ET n. 

sometimes produced by the metamorphosis of homo- 
geneous fissile rocks ; seeing that foliation and cleavage 
are so closely analogous in the several above-enumerated 
respects; seeing that some fissile and almost homo- 
geneous rocks show incipient mineralogical changes 
i*long the planes of their cleavage, and that other rocks 
with a fissile structure alternate with, and pass into 
varieties with a foliated structure, I cannot doubt that 
in most cases foliation and cleavage are parts of the 
same process : in cleavage there being only an incipient 
separation of the constituent minerals ; in foliation a 
much more complete separation and crystallisation. 

The fact, often referred to in this chapter, of the 
foliation and the so-called strata in the metamorphic 
aeries that is, the alternating masses of different 
varieties of gneiss, mica-schist, and hornblende-slate, 
&c. being parallel to each other, at first appears quite 
opposed to the view that the folia have no relation to 
the planes of original deposition. Where the so-called 
beds are not very thick and of widely different minera- 
logical composition from each other, I do not think that 
there Is any difficulty In supposing that they have 
originated in an analogous manner with the separate 
folia. We should bear in mind what thick strata, 
in ordinary sedimentary masses, have obviously been 
formed by a concretionary process. In a pile of volcanic 
rocks on the Island of Ascension, there are strata, dif- 
fering quite as much in appearance as the ordinary 
varieties of the metamorphie schists, which undoubtedly 
have been, produced, not by successive Sowings of lava, 
but by internal molecular changes. Near Monte Video, 
where the stratification, as it wo aid be called, of the 
metamorphic series is, in most parts, particularly well 
developed, being as usual, parallel to the foliation, we 
liavo seen that a mass of chloritic schist, netted with 



CHAP. xm. , Cleavage and Foliation. 467 

quartz-? eins, is entangled in gneiss, in sucli a manner as 
to show that it had certainly originated in some pro- 
cess of segregation : again, in another spot, the gneiss 
tended to pass into hornblendic schist by alternatin * 
with layers of quartz ; but these layers of quartz aln os 3 
certainly had never been separately deposited, for they 
were absolutely continuous with the numerous intersect- 
ing veins of quartz. I have never had an opportunity of 
tracing for any distance, along the line both of strike 
and of dip, the so-called beds in the metamorphic 
schists, but I strongly suspect that they would not be 
found to extend with the same character, very far in the 
line either of their dip or strike. Hence I am led to 
believe, that most of the so-called beds are of the nature 
of complex folia, and have oot been separately de- 
posited. Of course, this view cannot be extended to 
thicl masses included m the metamorphic series, which 
are of totally different composition from the adjoining 
schists, and which are far extended, as is sometimes the 
case with quartz and marble ; these must generally be 
of the nature of true strata. 1 Such strata, however, 
will almost always strike in the same direction with the 
folia, owing to the axes of elevation being in most 
countries parallel to the strike of the foliation; but 
they will generally dip at a different angle from that of 
the foliation ; and the angle of the foliation in itself 
almost always varies much : hence, in crossing a meta- 
morphosed schistose district, it would require especial 
attention to discriminate between true strata of depo- 
sition and complex foliated masses. The mere presence 
of true strata in the midst of a set of metamorphic 
schists, is no argument that the foliation is of sedimen- 

1 Macculloch states (' Classification of Rocks,* p. 364) that prim- 
ary limestones are otten found in irregular masses or great nodules, 
1 which can scarcely be said to possess a stratified shape.' 

31 



468 Cleavage and Foliation. PAET n. 

tary origin, without it be further shown in each case, 
that the folia not only strike, but dip throughout in 
parallel planes with those of the true stratification. 

As in some cases it appears that where a fissile rock 
has been exposed to partial metamorphic action for 
instance, from the irruption of granite the foliation 
has supervened on the already existing cleavage-planes ; 
so perhaps, in some instances, the foliation of a rock may 
have been determined by the original planes of deposi- 
tion or of oblique current-lamina): I have, however, 
myself, never seen such a case, and I must maintain that 
in most extensive metamorphic areas, the foliation is 
the extreme result of that process, of which cleavage 
is the first effect. That foliation may arise without any 
previous structural arrangement in the mass, we may 
infer from injected, and therefore once liquefied, rocks, 
both of volcanic and plutomc origin, sometimes having 
a 'grain' (as expressed by Professor Sedgwick), and 
sometimes being composed of distinct folia or larmnas of 
different compositions. In the earlier chapters of the 
present work, I have given several instances of this struc- 
ture in volcanic rocks, and it is not uncommonly seen in 
plutonic masses thus, in the Cordillera of Chile, there 
are gigantic mountain-like masses of red granite, which 
have been injected whilst liquefied, and which neverthe- 
less, display in parts a decidedly laminar structure. 1 

Finally, we have seen that the planes of cleavage 
and of foliation that is, of the incipient process and of 
the final result generally strike parallel to the principal 

1 As remarked In a former part of this chapter, I suspect that 
the boldly conical mountains of gneiss-giamte, near Rio de Janeiro, 
in which the constituent minerals are ananged in parallel planes, 
are of intrusive origin We must not, howe\er, foiget the lesson of 
caution taught by the curious clay-stone porphyries of Port Desire, 
in tvhich we have seen that the breaking up and aggregation of a 
fchmly stratified tufaceous mass, has yielded a rock semi-porphyritio 
with crystals of feldspar, arranged in the planes of original deposition- 



CHAP. xiii. Cleavage and Foliation. 469 

axes of elevation, and to the outline of the land the 
strike of the axes of elevation (that is, of the lines of 
fissures with the strata on their edges upturned), ac- 
cording to the reasoning of Mr. Hopkins, is determined 
by the form of the area undergoing changes of level, 
and the consequent direction of the lines of tension and 
fissure. Now, in that remarkable pile of volcanic rocks 
at Ascension, which has several times been alluded to 
(and in some other cases), I have endeavoured to show, 1 
that the lamination of the several varieties,, and their 
alternations, have been caused by the moving mass, just 
before its final consolidation, having been subjected (as 
in a glacier) to planes of different tension, this differ- 
ence in the tension affecting the crystalline and concre- 
tionary processes. One of the varieties of rock thus 
produced at Ascension, at first sight, singularly resembles 
a fine-grained gneiss ; it consists of quite straight and 
parallel zones of excessive tenuity, of more and less 
coloured crystallised feldspar, of distinct crystals of 
quartz, diopside, and oxide of iron. These considera- 
tions, notwithstanding the experiments made by Mr. 
Fox, showing the influence of electrical currents in pro- 
ducing a structure like that of cleavage, and notwith- 
standing the apparently inexplicable variation, both in 
the inclination of the cleavage-lamina and in their dip- 
ping first to one side and then to the other side of the line 
of strike, lead me to suspect that the planes of cleavage 
and foliation are intimately connected with the planes 
of different tension, to which the .area was long sub- 
jected, after the main fissures or axes of upheavement 
had been formed, but before the final consolidation of 
the mass and the total cessation of all molecular move- 
ment. 

1 See Chapter III. of the present work 



470 Central Chile. 



n. 



CHAPTER XIV. 

CENTKAL CHILE; STKUCTURE OF THE OOKDILLERA. 

Central Chile Basal formations of the Cordillera, Origin of fht 
porphyritic clay-stone conglomerate Anaesite Volcanic rochs 
Section of the Cordillera by the Peuquenes or Portillo Pass Great 
gypseous formation Pnuquenes line; thickness of strata, fossils of 
Portillo line^ conglomerate, orthitic granite^ mica MJti&t, and 
rolcanic rochx of Conclwlwfj remarks on tliedeniidatwn and dela- 
tion of the Portillo line Section by the Cumbre or UspaVata Pass 
Porphyries Gypseous strata Section 'near Puente del Inca ; 
fossils of Great subsidence- Intrmwe porphyries Plain of Us- 
pallata Section of the Uspallata chain Structure and nature of 
the strata jSili&jied vertical trees Great subsidence- Granitic 
rocks of axis Concluding r&marlts on the Uspallata range ; origin 
subsequent to that of the main Cordillera ; two periods of ub#id 
cncc , comparison with the Portillo cJiain. 

THE district between the Cordillera and the Pacific, OB 
a rude average, is from about eighty to one hundred 
miles in width. It is crossed by many chains of moun- 
tains, of which the principal ones, in the latitude of 
Valparaiso and southward of it, range nearly north and 
south ; but in the more northern parts of the province, 
they run in almost every possible direction. Near the 
Pacific, the mountain-ranges are generally formed of 
syenite or granite, or of an allied euritic porphyry ; in 
the low country, besides these granitic rocks and green- 
stone, and much gneiss, there are, especially northward 
of Valparaiso, some considerable districts of true clay- 
slate with quartz veins, passing into a feldspathic and 
porphyritic slate $ there is also some grauwacke and 



CHAP. xiv. Central Chile. 47 



quarfczose and jaspery rocks, the latter occasionally 
assuming the character of the basis of clay-stone por- 
phyry : trap-dikes are numerous. Nearer the Cordillera 
the ranges (such as those of S. Fernando, the Prado, 1 
and Aconcagua) are formed partly of granitic rocks, 
and partly of purple porphyritic conglomerates, clay- 
stone porphyry, greenstone porphyry, and other rocks, 
such as we shall immediately see form the basal strata 
of the main Cordillera. In the more northern parts of 
Chile, this porphyritic series extends over large tracts 
of country far from the Cordillera ; and even in Central 
Chile such occasionally occur in outlying positions. 

I will describe the Carnpana of Quillota, which 
stands only fifteen miles from the Pacific, as an instance 
of one of these outlying masses. This hill is conspicuous 
from rising to the height of 6,400 feet : its summit 
shows a nucleus, uncovered for a height of 800 feet, of 
fine greenstone, including epidote and octahedral mag- 
netic iron ore; its flanks are formed of great strata 
of porphyritic clay-stone conglomerate, associated with 
various true porphyries and amygdaloids, alternating 
with thick masses of a highly feldspathic, sometimes 
porphyritic, pale-coloured slaty rock, with its cleavage- 
laminse dipping inwards at a high angle. At the base 
of the hill there are syenites, a granular mixture of 
quartz and feldspar, and harsh quartzose rocks, all be- 
longing to the basal metaniorphic series. I may ob- 
serve that at the foot of several hills of this class, where 
the porphyries are first seen (as near S. Fernando, the 
Prado, Las Vacas, &c.), similar harsh quartzose rocks 
and granular mixtures of quartz and feldspar occur, as 
if the more fusible constituent parts of the granitic 
series had been drawn off to form the overlying por- 
phyries. 

1 Meyen, Beise urn Brde, 1 Th. 1, S. 235, 



472 Basal Strata of the Cordillera. PAETIZ, 

In Central Chilej the flanks of the main Cordillera, 
into which 1 penetrated by four different valleys, gene- 
rally consist of distinctly stratified rocks. The strata 
are inclined at angles varying frcnr sometimes even 
under ten, to twenty degrees, very rarely exceeding 
forty degrees : in some, however, of the quite small, 
exterior, spur-like ridges, the inclination was not unfre- 
quently greater. The dip of the strata in the main 
outer lines was usually outwards or from the Cordillera, 
but in Northern Chile frequently inwards, that is, 
their basset-edges fronted the Pacific. Dikes occur in 
extraordinary numbers. In the great, central, loftiest 
ridges, the strata, as we shall presently see, are almost 
always highly inclined and often vertical. Before giving 
a detailed account of my two sections across the Cor- 
dillera, it will, I think, be convenient to describe the 
basal strata as seen, often to a thickness of 4,000 or 
5,000 feet, on the flanks of the outer lines. 

Basal Strata of the Cordillera. The prevailing 
rock is a purplish or greenish, porphyritic clay-stone 
conglomerate. The embedded fragments vary in size 
from mere particles to blocks as much as six or eight 
inches (rarely more) in diameter ; in many places, where 
the fragments were minute, the signs of aqueous depo- 
sition were unequivocally distinct; where they were 
large, such evidence could rarely be detected. The 
basis is generally porphyritic with perfect crystals of 
feldspar, and resembles that of a true injected clay- 
stone porphyry: often, however, it has a mechanical 
or sedimentary aspect, and sometimes (as at Jajuel) is 
jaspery. The included fragments are either angular, 
or partially or quite rounded; 1 in some parts the 

1 Some of the rounded fragments in the porphyritic conglomerate 
near the Baths of Cauquenes, were marked with radii and concentric 
Bones of different shades of colour ; any one who did not know that 



. Porphyritic Clay stone Conglomerate, 473 

rounded, in others the angular, fragments prevail, and 
usually both kinds are mixed together: hence the word 
Irecda ought strictly to be appended to the term par- 
pliyritic conglomerate. The fragments consist of many 
varieties of clay-stone porphyry, usually of nearly 
the same colour with the surrounding basis, namely, 
purplish-reddish, brownish, mottled or bright green; 
occasionally fragments of a laminated, pale-coloured, 
feldspathic rock, like altered clay-slate, are included ; 
as are sometimes grains of quartz ; but only in one in- 
stance in Central Chile (namely, at the mines of Jajuel) 
a few pebbles of quartz. I nowhere observed mica in 
this formation, and rarely hornblende ; where the latter 
mineral did occur, I was generally in doubt whether 
the mass really belonged to this formation, or was of 
intrusive origin. Calcareous spar occasionally occurs 
in small cavities ; and nests and layers of epidote are 
common. In some few places in the finer-grained 
varieties (for instance, at Quillota), there were short, 
interrupted layers of earthy feldspar, which could be 
traced, exactly as at Port Desire, passing into large 
crystals of feldspar : I doubt, however, whether in this 
instance the layers had ever been separately deposited 
as tufaceous sediment. 

All the varieties of porphyritic conglomerates and 
breccias pass into each other, and by innumerable 
gradations into porphyries no longer retaining the least 
trace of mechanical origin : the transition appears to 
have been effected much more easily in the finer-grained, 
than in the coarser-grained varieties. In one instance, 
near Cauquenes, I noticed that a porphyritic conglo- 

pebbles for instance, flint pebbles from the chalk are sometimes 
zoned concentrically with their worn and rounded surfaces, might 
have been led to infer that these balls of porphyry were not true 
pebbles, but had originated in concretionary action. 



474 Basal Strata of the Cordillera. PAET n. 

merate assumed a spheroidal structure, and tended to 
become columnar. Besides the porphyritic conglomerates 
and the perfectly characterised porphyries of meta- 
morphic origin, there are other porphyries which, 
though differing not at all or only slightly in composi- 
tion, certainly have had a different origin : these consist 
of pink or purple clay-stone porphyries, sometimes 
including grains of quartz, of greenstone porphyry, 
and of other dusky rocks, all generally porphyritic with 
fine, large, tabular, opaque crystals, often placed cross- 
wise, of feldspar cleaving like albite (judging from 
several measurements), and often amygdaloidal with 
silex, agate, carbonate of lime, green and brown bole. 1 
These several porphyritic and amygdaloidal varieties 

1 This bole is a very common mineral in the amygdaloidal rocks; 
it is generally of a greenibh-brown colour, with a radiating structure; 
externally it is black with an almost metallic lustre, but often 
coated by a bright green film. It is soft and can be scratched by a 
quill ; under the blowpipe swells greatly and becomes scaly, then 
fuses easily into a black magnetic bead. This substance is evidently 
similar to that which often occurs in submarine volcanic rocks. 
An examination of some very curious specimens of a fine poiphyry 
(from Jajuel) leads me to suspect that some of these amygdaloidal 
balls, instead of having been deposited in pre-existing air- vesicles, 
are of concretionary origin ; for in these specimens, some of the 
pea-shaped little masses (often externally marked with minute pits) 
are formed of a mixture of green earth with stony matter, like the 
basts of the porphyry, including minute imperfect crystals of feldspar ; 
and these pea-shaped little masses are themselves amygdaloidal with 
minute spheres of the green earth, each enveloped by a film of white, 
apparently feldspathic, earthy matter: so that the porphyry is doubly 
amygdaloidal. It should not, however, be overlooked, that all the 
strata here have undergone metamorphic action, which may have 
caused crystals of feldspar to appear, and other changes to be 
eftected, in the originally simple amygdaluidal balls Mr. J. D 
Dana, in an excellent paper on Trap rocks (' Edin New Phil Jouin.' 
vol f xli. p. 198). has argued, with great force, that all amygdaloidal 
minerals have been deposited by aqueous infiltration I may take 
this opportunity of alluding to a curious case, described in Chapter 
II. of the present work, of an amygdaloidal rock, with many of the 
cells only half filled up with a mesotypic mineral 

M. Eose has described an amygdaloid, brought by Dr Meyen 
(<lleise urn Erde,' Th 1, S. 316) fiom Ch'le, as consisting of crystall- 
ised quartz, with crystals of stilbite within, and lined externally by 
green earth. 



CHAP, 



'. Tzv.Porpkyritic Clay stone Conglomerate. 475 



never show any signs of passing into masses of sedi- 
mentary origin : they occur both in great and small 
intrusive masses, and likewise in strata alternating with 
those of the porphyritic conglomerate, and with the 
planes of junction often quite distinct, yet not seldom 
blended together. In some of these intrusive masses, 
the porphyries exhibit, more or less plainly, a brecciated 
structure, like that often seen in volcanic masses. These 
brecciated porphyries could generally be distinguished 
at once from the metamorphosed, porphyritic breccia- 
conglomerates, by all the fragments being angular and 
being formed of the same variety, and by the absence 
of every trace of aqueous deposition. One of the por- 
phyries above specified, namely, the greenstone porphyry 
with large tabular crystals of albite, is particularly 
abundant, and in some parts of the Cordillera (as near 
St. Jago) seemed more common even, than the purplish 
porphyritic conglomerate. Numerous dikes likewise 
consist of this greenstone porphyry ; others are formed 
of various fine-grained trappean rocks ; but very few 
of clay stone porphyry : I saw no true basaltic dikes. 

In several places in the lower part of the series, but 
not everywhere, thick masses of a highly feldspathic, 
often porphyritic, slaty rock occur interstratified with 
the porphyritic conglomerate : I believe in one or two 
cases blackish limestone has been found in a similar 
position. The feldspathic rock is of a pale grey or 
greenish colour ; it is easily fusible ; where porpliyritic, 
the crystals of feldspar are generally small and vitreous; 
it is distinctly laminated, and sometimes includes 
parallel layers of epidote ; * the lamination appears to 

1 This mineral is extremely common in all the formations of Chile ; 
in the gneiss near Valparaiso and in the granitic veins crossing it, in 
the in;jected t greenstone crowning the C.of Quillota, in some gram tic 
porphyries, in the porphj ritic conglomerate, and in the f eldspathia 
clay-slates. 



476 Basal Strata of the Cordillera. 

be distinct from stratification. Occasionally this rock 
is somewhat carious ; and at one spot, namely, at the 
0. of Quillota, it had a brecciated structure. Near the 
mines of Jajnel, in a thick stratum of this feldspathic, 
porphyritic slate, there was a layer of hard, blackish, 
siliceous, infusible, compact clay-slate, such as I saw 
nowhere else : at the same place I was able to follow 
for a considerable distance the junction between the slate 
and the conformably underlying porphyritic conglo- 
merate, and they certainly passed gradually into each 
other. Wherever these slaty feldspathic rocks abound, 
greenstone seems common; at the 0. of Quillota a bed 
of well-crystallised greenstone lay conformably in the 
midst of the feldspathic slate, with the upper and lower 
junctions passing insensibly into it. From this fact, 
and from the frequently porphyritic condition of the 
shite, I should perhaps have considered this rock as an 
erupted one (like certain laminated feldspathic lavas 
in the trachytic series), had I not seen in T. del Fuego 
how readily true clay-slate becomes feldspathic and 
porphyritic, and had I not seen at Jajuel the included 
layer of black, siliceous clay-slate, which no one could 
have thought of igneous origin. The gentle passage 
of the feldspathic slate, at Jajuel, into the porphyritic 
conglomerate, which is certainly of aqueous origin, 
should also be taken into account. 

The alternating strata of porphyries and porphyritic 
conglomerate, and with the occasionally included beds 
of feldspathic slate, together make a grand formation ; 
in several places within the Cordillera I estimated its 
thickness at from 6,000 to 7,000 feet. It extends for 
many hundred miles, forming the western flank of the 
Chilian Cordillera j and even at Iquique in Peru, 850 
miles north of the southernmost point examined by me 
in Chile, the coast-escarpment, which rises to a height 



CHiP. XIV, 



. Porphyritic Clay stone Conglomerate. 477 



of between 2,000 and 3,000 feet, is thus composed. In 
several parts of Northern Chile this formation extends 
much farther towards the Pacific, over the granitic and 
metamorphic lower rocks, than it does in Central Chile ; 
but the main Cordillera may be considered as its cen- 
tral line, and its breadth in an east and west direction 
is never great. At first the origin of this thick, mass- 
ive, long but narrow formation, appeared to me very 
anomalous : whence were derived, and how were dis- 
persed the innumerable fragments, often of large size, 
sometimes angular and sometimes rounded, and almost 
invariably composed of porphyritic rocks ? Seeing that 
the interstratified porphyries are never vesicular and 
often not even amygdaloidal, we must conclude that the 
pile was formed in deep water ; how then came so many 
fragments to be well rounded and so many to remain 
angular, sometimes the two kinds being equally mingled, 
sometimes one and sometimes the other preponder- 
ating? That the clay-stone, greenstone, and other 
porphyries and amygdaloids, which lie conformably be- 
tween the beds of conglomerate, are ancient submarine 
lavas, I think there can be no doubt ; and I believe we 
must look to the craters whence these streams were 
erupted, as the source of the breccia-conglomerate : 
after a great explosion, we may fairly imagine that 
the water in the heated and scarcely quiescent crater 
would remain for a considerable time 1 sufficiently 
agitated to triturate and round the loose fragments 
lying within it : these rounded fragments, few or many 
in number, would be shot forth at the next eruption, 
associated with a few or many angular fragments, ac- 
cording to the strength of the explosion. Theporphyr- 

1 This certainly seems to have taken place in some recent volcanic 
arcbij; elagos, as at the Gaiapaeos, where numerous craters are exclus- 
ively formed of tuff and fragments of la\ a. 



47 8 Phttonic Rocks of the Cordillera. PAET n, 

itic conglomerate being purple or reddish, even when 
alternating with dusky-coloured or bright green por- 
phyries and amygdaloids, is probably an analogous 
circumstance to the scoria of the blackish basalts be- 
ing often bright red. The ancient submarine orifices 
whence the porphyries and their fragments were ejected 
having been arranged in a band, like most still active 
volcanos, accounts for the thickness, the narrowness, and 
linear extension of this formation. 

This whole great pile of rock has suffered much 
metamorphic action, as is very obvious in the gradual 
formation and appearance of the crystals of albitic 
feldspar and of epidote in the blending together 
of the fragments in the appearance of a lami- 
nated structure in the feldspathic slate and ? lastly, 
in the disappearance of the planes of stratification, 
which could sometimes be seen on the same mountain 
quite distinct in the upper part, less and less plain on 
the flanks, and quite obliterated at the base. Partly 
owing to this metamorphic action, and partly to the 
close relationship in origin, I have seen fragments of 
porphyries taken from a metamorphosed conglomerate 
from a neighbouring stream of lava from the nucleus 
or centre (as it appeared to me) of the whole submarine 
volcano and lastly from an intrusive mass of quite 
subsequent origin, all of which were absolutely undis* 
tinguishable in external characters. 

One other rock, of plutonic origin, and highly im- 
portant in the history of the Cordillera, from having 
been injected in. most of the great axes of elevation, and 
from having apparently been instrumental in meta- 
morphosing the superincumbent strata, may be con- 
veniently described in this preliminary discussion. It 
Eas been called by some authors Andesite ; it mainly 



CHAP. xiv. Andesitic and Volcanic Rocks. 479 

consists of well-crystallised white albite 1 (as determined 
with the goniometer in numerous specimens both by 
Professor Miller and myself), of less perfectly crystall- 
ised green hornblende, often associated with much 
mica, with chlorite and epidote, and occasionally with 
a few grains of quartz : in one instance in Northern 
Chile, I found crystals of orthitic or potash feldspar, 
mingled with those of albite. Where the mica and 
quartz are abundant, the rock cannot be distinguished 
from granite ; and it may be called andesitic granite. 
Where these two minerals are quite absent, and when, 
as often then happens, the crystals of albite are imper- 
fect and blend together, the rock may be called andes- 
itic porphyry, which bears nearly the same relation to 
andesitic granite that euritic porphyry does to common 
granite. These andesitic rocks form mountain masses 
of a white colour, which, in their general outline and 
appearance in their joints in their occasionally in- 
cluding dark-coloured, angular fragments, apparently of 
some pre-existing rock and in the great dikes branch- 
ing from them into the superincumbent strata, manifest 
a close and striking resemblance to masses of common 
granite and syenite : I never, however, saw in these 
andesitic rocks, those granitic veins of segregation 
which are so common in true granites. We have seen 
that andesite occurs in three places in Tierra del Fuego; 
in Chile, from St. Fernando to Copiapo, a distance of 

1 I here, and elsewhere, call by this name, those feldspathic mine- 
rals which cleave like albite * but it now appears (' Edm. New Phil. 
Journ.' vol. sxiv p. 181) that Abichbas analysed a mineral from the 
Cordillera, associated with hornblende and quartz (probably the same 
rock with that here under discussion), which cleaves like albite, but 
which is a new and distinct kind, called by him Anfasine. It is 
allied to leucite, with the greater proportion of its potash replaced by 
lime and soda. This mineral seems scarcely distinguishable from 
albite, except by analysis. 



480 Plutonic Rocks of the Cordillera. PAUT n. 

450 miles, I found it under most of the axes of elevation ; 
in a collection of specimens from the Cordillera of Lima 
in Peru, I immediately recognised it ; and Brnian J 
states that it occurs in eastern Kamtschatka. From 
its wide range, and from the important part it has 
played in the history of the Cordillera, I think this 
rock has well deserved its distinct name of andesite. 

The few still active volcanos in Chile are confined 
to the central and loftiest ranges of the Cordillera ; and 
volcanic matter, such as appears to have been of sub- 
aerial eruption, is everywhere rare. According to 
Meyen, 2 there is a hill of pumice high up the valley 
of the Maypu, and likewise a trachytic formation at 
Colina, a village situated north of St. Jago. Close to 
this latter city, there are two hills formed of a pale 
feldspathic porphyry, remarkable from being doubly 
columnar, great cylindrical columns being subdivided 
into smaller four or five sided ones ; and a third hillock 
(Cerro Blanco) is formed of a fragmentary mass of 
rock, which I believe to be of volcanic origin, inter- 
mediate in character between the above feldspathic 
porphyry and common trachyte, and containing needles 
of hornblende and granular oxide of iron. Near the 
Baths of Cauquenes, between two short parallel lines of 
elevation, where they are intersected by the valley, there 
is a small, though distinct volcanic district , the rock 
is a dark grey (andesitic) trachyte, which fuses into a 
greenish-grey bead, and is formed of long crystals of 
fractured glassy albite (judging from one measurement) 
mingled with well-formed crystals, often twin, of augite. 
The whole mass is vesicular, but the surface is darker 
coloured and much more vesicular than any other part. 
This trachyte forms a cliff-bounded, horizontal, narrow 

1 Geogxaph. Journal,' vol ix. p 510. 

a Beise urn Bide/ Th. 1, SS. 338 und 362. 



CHAP. xiv. Section by the Portillo Pass. 481 

strip on the steep southern side of the valley, ao tne 
height of 400 or 500 feet above the river-bed ; judging 
from an apparently corresponding line of cliff on the 
northern side, the valley must once have been filled up 
to this height by a field of lava. On the summit of a 
lofty mountain some leagues higher up this same valley 
of the Cachapual, I found columnar pitchstone porphy- 
ritic with feldspar ; I do not suppose this rock to be 
of volcanic origin, and only mention it here, from its 
being intersected by masses and dikes of a vesicular 
rock, approaching in chaiacter to trachyte; in no other 
part of Chile did I observe vesicular or amygdaloidal 
dikes, though these are so common in ordinary volcanic 
districts. 



Passage of the Andes "by the Portillo or PeucjiieneB 
Pass. 

Although I crossed the Cordillera only once by this 
pass, and only once by that of the Cumbre or Uspallata 
(presently to be described), riding slowly and halting 
occasionally to ascend the mountains, there are many 
circumstances favourable to obtaining a more faithful 
sketch of their structure than would at first be thought 
possible from so short an examination. The mountains 
are steep and absolutely bare of vegetation ; the atmo- 
sphere is resplendently clear ; the stratification distinct ; 
and the rocks brightly and variously coloured : some of 
the natural sections might be truly compared for dis- 
tinctness to those coloured ones in geological works. 
Considering how little is known of the structure of this 
gigantic range, to which I particularly attended, most 
travellers having collected only specimens of the rocks, 
I think my sketch-sections, though necessarily imper- 
fect, possess some interest. The section given in Plate I, 



482 Section by the Portillo Pass. PART n, 

fig. 1, winch 1 will now describe in detail, is on a 
horizontal scale of a third of an inch to a nautical mile, 
and on a vertical scale of one inch to a mile or 6,000 
feet. The width of the range (excluding a few out- 
lying hillocks), from the plain on which St. Jago the 
capital of Chile stands, to the Pampas, is sixty miles, as 
far as I can judge from the maps, which differ from each 
other and are all exceedingly imperfect. The St. Jago 
plain at the mouth of the Maypu, I estimate from ad- 
joining known points at 2,300 feet, and the Pampas at 
3,500 feet, both above the level of the sea. The height 
of the Peuquenes line, according to Dr. Gillies, 1 is 
13,210 feet; and that of the Portillo line (both in the 
gaps where the road crosses them) is 14,845 feet; the 
lowest part of the intermediate valley of Tenuyan is 
7,530 feet all above the level of the sea. 

The Cordillera here, and indeed I believe throughout 
Chile, consist of several parallel, anticlinal and unichnal 
mountain-lines, ranging north, or north with a little 
westing, and south. Some exterior and much lower 
ridges often vary considerably from this course, pro- 
jecting like oblique spurs from the main ranges : in 
the district towards the Pacific, the mountains, as be- 
fore remarked, extend in various directions, even east 
and west. In the main exterior lines, the strata, as also 
before remarked, are seldom inclined at a high angle ; 
but in the central lofty ridges they are almost always 
highly inclined, broken by many great faults, and often 
vertical. As far as I could judge, few of the ranges are 
of great length : and in the central parts of the Cor- 
dillera, I was frequently able to follow with my eye a 
ridge gradually becoming higher and higher, as the 
stratification increased in inclination, from one end 
where its height was trifling and its strata gently inclined 
1 * Journal of Nat. and Geograph. Science,' August, 1830. 



CHAP, xiv. Section by the Porfillo Pass. 483 

to the other end where vertical strata formed snow-clad 
pinnacles. Even outside the mam Cordillera, near the 
baths of Cauquenes, I observed one such case, where a 
north and south ridge had its strata in the valley in- 
clined at 37, and less than a mile south of it at 67: 
another parallel and similarly inclined ridge rose at the 
distance of about five miles, into a lofty mountain with 
absolutely vertical strata. Within the Cordillera, the 
height of the ridges and the inclination of the strata 
often became doubled and trebled in much shorter dis- 
tances than five miles : this peculiar form of upheaval 
probably indicates that the stratified crust was thin, 
and hence yielded to the underlying intrusive masses 
unequally, at certain points on the lines of fissure. 

The valleys, by which the Cordillera are drained, 
follow the anticlinal or rarely synclinal troughs, which 
deviate most from the usual north and south course ; or 
still more commonly those lines of faults or of unequal 
curvature (that is, lines with the strata on both hands 
dipping in the same direction, but at a somewhat 
different angle) which deviate most from a northerly 
course. Occasionally the torrents run for some distance 
in the north and south valleys, and then recover their 
eastern or western course by bursting through the ranges 
at those points where the strata have been least inclined 
and the height consequently is less. Hence the valleys, 
along which the roads run, are generally zigzag ; and, 
in drawing an east and west section, it is necessary to 
contract greatly that which is actually seen on the road. 

Commencing at the western end of the coloured 
section [Plate I.] where the K. Maypu debouches on the 
plain of St. Jago, we immediately enter on the por- 
phyritic conglomerate formation, and in the midst of 
it find some hummocks [A] of granite and syenite, 
which probably (for I neglected to collect specimens) 

33 



484 Section by the Portillo Pass. PAET 11 

belong to the andesitic class. These are succeeded by 
some rugged hills [B] of dark-green, crystalline, felcl- 
spathic and in some parts slaty rocks, which I be- 
lieve belong to the altered clay-slate formation. Frora 
thh point, great mountains of purplish and greenish, 
generally thinly stratified, highly porphyritic conglo- 
merates, including many strata of amygdaloidal and 
greenstone porphyries, extend up the valley to the 
junction of the rivers Yeso and Volcan. As the valley 
here runs in a very southerly course, the width of the 
porphyritic conglomerate formation is quite conjectural ; 
and from the same cause, I was unable to make out 
much about the stratification. In most of the exterior 
mountains the dip was gentle and directed inwards; 
and at only one spot I observed an inclination as high 
as 50. Near the junction of the R. Colorado with the 
main stream, there is a hill of whitish, brecciated, 
partially decomposed feldspathic porphyry, having a 
volcanic aspect but not being really of that nature : at 
Tolla, however, in this valley, Dr. Meyen L met with a 
hill of pumice containing mica At the junction of 
the Yeso and Volcan [D] there is an extensive mass, in 
white conical hillocks, of andesite, containing some 
mica, and passing either into andesitic granite, or into 
a spotted, semi-granular mixture of albitic (?) feldspar 
and hornblende: in the midst of this formation Dr. 
Meyen found true trachyte. The andesite is covered 
by strata 'of dark-coloured, crystalline, obscurely por- 
phyritic rocks, and above them by the ordinary por- 
phyritic conglomerates, the strata all dipping away at 
a small angle from the underlying mass. The surround- 
ing lofty mountains appear to be entirely composed 
of the porphyritic conglomerate, and I estimated its 
, thickness here at between 6,000 and 7,000 feet. 
* 'Eeise urn Erde,' Th 1. SS. 338, 341. 



CHAP. xiv. Section by the Portillo Pass. 485 

Beyond the junction of the Yeso and Volcan, tie 
porphyritic strata appear to dip towards the hillocks of 
andesite at an angle of 40 ; but at some distant points 
on the same ridge they are bent up and vertical. 
Following the valley of the Yeso, trending NE. (and 
therefore still unfavourable for our transverse section.), 
the same porphyritic conglomerate formation is pro- 
longed to near the Cuestadel Indio, situated at the 
western end of the basin (like a drained lake) of Yeso. 
Some way before arriving at this point, distant lofty 
pinnacles capped by coloured strata belonging to the 
great gypseous formation could first be seen. Prom 
the summit of the Cuesta, looking southward, there is 
a magnificent sectional view of a mountain-mass, at 
least 2,000 feet in thickness [E], of fine andesitic 
granite (containing much black mica, a little chlorite 
and quartz), which sends great white dikes iar into the 
superincumbent, dark-coloured, porphyritic conglome- 
rates. At the line of junction the two formations are 
wonderfully interlaced together : in the lower part of 
the porphyritic conglomerate, the stratification, has 
been quite obliterated, whilst in the upper part it is 
very distinct, the beds composing the crests of the 
surrounding mountains being inclined at angles of 
between 70 and 80, and some being even vertical. 
On the northern side of the valley, there is a great 
corresponding mass of andesitic granite, which is 
encased by porphyritic conglomerate, dipping both 
on the western and eastern sides, at about 80 to west, 
but on the eastern side with the tips of the strata bent 
in such a manner, as to render it probable that the 
whole mass had been on that side thrown over and 
inverted. 

In the valley-basin of the Yeso, which I estimated 
at 7,000 feet above the level of the sea, we first reach 



486 Section by the Portillo Pass. PAET n, 

at [F] the gypseous formation. Its thickness is very 
great. It consists in most parts of snow-white, hard, 
compact gypsum, which breaks with a saccharine frac- 
ture, having translucent edges; under the blowpipe 
gives out much vapour; it frequently includes nests 
and exceedingly thin layers of crystallised, blackish 
carbonate of lime. Large, irregularly shaped concre- 
tions (externally still exhibiting lines of aqueous 
deposition) of blackish-gray, but sometimes white, 
coarsely and brilliantly crystallised, hard anhydrite, 
abound within the common gypsum. Hillocks, "formed 
of the hardest and purest varieties of the white gypsum, 
stand up above the surrounding parts, and have their 
surfaces cracked and marked, just like newly baked 
bread. There is much pale brown, soft, argillaceous 
gypsum; and there were some intercalated green beds 
which I had not time to reach. I saw only one frag- 
ment of selenite sOr transparent gypsum, and that 
perhaps may have come from some subsequently formed 
vein. From the mineralogical characters here given, 
it is probable that these gypseous beds have undergone 
some metamorphic action. The strata are much hidden 
by detritus, but they appeared in most parts to be 
highly inclined; and in an adjoin ing lofty pinnacle they 
could be distinctly seen bending up, and becoming 
vertical, conformably with the underlying porphyritic 
conglomerate. In very many parts of the great moun- 
tain-face [F], composed of thin gypseous beds, there 
were innumerable masses, irregularly shaped and not 
like dikes, yet with well-defined edges, of an imperfectly 
granular, pale greenish or yellowish- white rock, essen- 
tially composed of feldspar, with a little chlorite or 
hornblende, epidote, iron-pyrites, and ferruginous pow- 
der : I believe that these curious trappean masses have 
been injected from the not far distant mountain-mass 



CHAP. XIY. Gypseous Formation. 487 

[B] of andesite whilst still fluid, and that owing to the 
softness of the gypseous strata they have not acquired 
the ordinary forms of dikes. Subsequently to the 
injection of these feldspathic rocks, a great dislocation 
has taken place ; and the much shattered gypseous 
strata here overlie a hillock [G], composed of vertical 
strata of impure limestone and of black highly calcare- 
ous shale including threads of gypsum : these rocks, as 
we shall presently see, belong to the upper parts of the 
gypseous series, and hence must here have been thrown 
down by a vast fault. 

Proceeding up the valley-basin of the Yeso, and 
taking our section sometimes on one hand and some- 
times on the other, we come to a great hill of stratified 
porphyritic conglomerate [H] dipping at 45 to the 
west ; an,d a few hundred yards farther on, we have a 
bed between 300 or 400 feet thick of gypsum [I] dip- 
ping eastward at a very high angle : here then we have 
a fault and anticlinal axis. On the opposite side of 
the valley, a vertical mass of red conglomerate, con- 
formably underlying the gypsum, appears gradually to 
lose its stratification and passes into a mountain of 
porphyry. The gypsum [I] is covered by a bed [K], 
at least 1,000 feet in thickness, of a purplish-red, 
compact, heavy, fine-grained sandstone or mudstone, 
which fuses easily into a white enamel, and is seen 
under a lens to contain triturated crystals. This is 
succeeded by a bed [L], 1 3 000 feet thick (I believe I 
understate the thickness) of gypsum, exactly like the 
beds before described ; and this again is capped by 
another great bed [M] of purplish-red sandstone. All 
these strata dip eastward ; but the inclination becomes 
less and less, as we leave the first and almost vertical 
bed [I] of gypsum. 

Leaving the basin-plain of Yeso, the road rapidly 



488 Section by the Portillo Pass. PAET n, 

ascends, passing by mountains composed of the gypseous 
and associated beds, with their stratification greatly 
disturbed and therefore not easily intelligible : hence 
this part of the section has been left uncoloured. 
Shortly before reaching the great Peuquenes ridge, the 
lowest stratum visible [N] is a red sandstone or mud- 
stone, capped ty a vast thickness of black, compact, 
calcareous, shaly rock [0], which has been thrown 
into four lofty, though small ridges : looking northward, 
the strata in these ridges are seen gradually to rise in 
inclination, becoming in some distant pinnacles abso- 
lutely vertical. 

The ridge of Peuquenes, which divides the waters 
flowing into the Pacific and Atlantic Oceans, extends in 
a nearly NNW. and SSE. line , its strata dip eastward 
at an angle of between 30 and 45, but in the higher 
peaks bending up and becoming almost vertical. Where 
the road crosses this range, the height is 13,210 feet 
above the sea-level, and I estimated the neighbouring 
pinnacles at from 14,000 to 15,000 feet. The lowest 
stratum visible in this ridge is a red stratified sandstone 
[P] ; on it are superimposed two great masses [Q and 
S] of black, hard, compact, even having a conchoidal 
fracture, calcareous, more or less laminated shale, pass- 
ing into limestone : this rock contains organic remains, 
presently to be enumerated. The compacter varieties 
fuse easily in a white glass ; and this I may add is a 
very general character with all the sedimentary beds in 
the Cordillera : although this rock when broken is 
generally quite black, it everywhere weathers into an 
ash-gray tint. Between these two great masses [Q and 
S], a bed [B] of gypsum is interposed, about 300 feet 
in thickness, and having the same characters as hereto- 
fore described. 1 estimated the total thickness of these 
three beds [Q, E 5 S] at nearly 3,000 feet; and to this 



CHAP. xiv. Gypseous Formation. 489 

must be added, as will be immediately seen, a great 
overlying mass of red sandstone. 

In descending the eastern slope of this great central 
range, the strata, which in the upper part dip eastward 
at about an angle of 40, become more and more curved, 
till they are nearly vertical; and a little farther on wards 
there is seen on the farther side of a ravme, a thick 
mass of strata of bright red sandstone [T], with their 
upper extremities slightly curved, showing that they 
were once conformably prolonged over the beds [S] : 
on the southern and opposite side of the road, this red 
sandstone and the underlying black shaly rocks stand 
vertical, and in actual juxtaposition. Continuing to 
descend, we come to a synclinal valley filled with 
rubbish, beyond which we have the red sandstone [T 2 ] 
corresponding with [T], and now dipping, as is seen 
both north and south of the road, at 45 to the west ; 
and under it, the beds [S 2 , R 2 , Q 2 , and I believe P 2] 
m corresponding order and of similar composition, with 
those on the western flank of the Peuquenes raoge, but 
dipping westward. Close to the synclinal valley the 
dip of these strata is 45, but at the eastern or farther 
end of the series it increases to 60. Here the great 
gypseous formation abruptly terminates, and is suc- 
ceeded eastward by a pile of more modern strata. 
Considering how violently these central ranges have 
been dislocated, and how very numerous dikes are in 
the exterior and lower parts of the Cordillera, it is 
remarkable that I did not here notice a single dike. 
The prevailing rock in this neighbourhood is the black, 
calcareous, compact shale, whilst in the valley-basin of 
the Yeso the purplish-red sandstone or mudstone pre- 
dominates, both being associated with gypseous strata 
of exactly the same nature. It would be very difficult 
to ascertain the relative superposition of these several 



490 Section by the Portilto Pass. PAKT n 

masses, for we shall afterwards see in tie Cumbre Pass 
that the gypseous and intercalated beds are lens-shaped, 
and that they thin out, even where very thick, and 
disappear in short horizontal distances: it is quite 
possible that the black shales and red sandstones may 
be contemporaneous, but it is more probable that the 
former compose the uppermost parts of the series. 

The fossils above alluded to in the black calcareous 
shales are few in number, and are in an imperfect 
condition; they consist, as named for me by M. d'Or- 
bigny, of 

1. Ammonite, indeterminable, near to A recticostaius, D'Orbig. 

* Pal. Franc.' (Neocomian formation) 

2. Gryphcea, near to @. Couloni (Neocomian formations of France 

and Neufch^tel) 

3. Natica, indeterminable 

4 Cjprmarostrata, D'Oibig 'Pal Franc.' (Neocomian formation). 

5. II htellanaangulosa(2) D'Orbig. 'Pal del'Am^r. Mer' 

6. Terebtatula 1 

Some of the fragments of Ammonites were as thick 
as a man's arm : the Gryphaea is much the most 
abundant shell These fossils M d'Orbigny considers 
as belonging to the Neocomian stage of the Cretaceous 
system. Dr. Meyen, 1 who ascended the valley of the 
Rio Volcan, a branch of the Yeso, found a nearly 
similar, but apparently more calcareous formation, with 
much gypsum, and no doubt the equivalent of that 
here described : the beds were vertical, and were pro- 
longed up to the limits of perpetual snow : at the height 
of 9,000 feet above the sea, they abounded with fossils, 
consisting, according to Von Buch, 2 of 

1. Exogyra (Gryphsea) Couloni, absolutely identical with specimens 

from the Jura and South of France 

2. Xrigonia costata, \ identical with those found m the upper 

3. Pecfcen stnatus, J Jurassic beds at Hildesheim. 



* Keise um Erde/ Th. 1. S. 355. 

* Descnpt. Phys. des lies Canaries/ p. 471. 



CHAP. xiv. Neocomian Fossils. 491 

4. Cucullsea, corresponding in form to C. longirostris, so frequent 

in the upper Jurassic beds of Wetstphaha. 
6. Ammonites, resembling .4. 



Von Buch concludes that this formation is intermediate 
"between the limestone of the Jnra and the chalk, and 
that it is analogous with the uppermost Jurassic beds 
forming the plains of Switzerland. Hence M. d'Orbigny 
and Von Buch, under different terms, compare these 
fossils to those from the same late stage in the Secondary 
formations of Europe. 

Some of the fossils which I collected were found a 
good way down the western slope of the main ridge, 
and hence must originally have been covered up by a 
great thickness of the black shaly rock, independently 
of the now denuded, thick, overlying masses of red 
sandstone. I neglected at the time to estimate how 
many hundred or rather thousand feet thick the 
superincumbent strata must have been : and I will 
not now attempt to do so. This, however, would have 
been a highly interesting point, as indicative of a great 
amount of subsidence, of which we shall hereafter find 
in other parts of the Cordillera analogous evidence 
during this same period. The altitude of the Peu- 
quenes range, considering its not great antiquity, is 
very remarkable ; many of the fossils were embedded at 
the height of 13,210 feet, and the same beds are pro- 
longed up to at least from 14,000 to 15,000 above the 
level of the sea. 

The Porfillo or Eastern Chain. The valley of 
Tenuyan, separating the Peuquenes and Portillo lines, 
is, as estimated by Dr. Gillies and myself, about twenty 
miles in width ; the lowest part, where the road crosses 
the river, being 7,500 feet above the sea-level. The 
pass on the Portillo line is 14,865 feet high (1,100 feet 
higher than that on the Peuquenes), and the neigh- 



49 2 Section of the Portillo Chain, PAET n, 

bouring pinnacles must, I conceive, rise to nearly 16,000 
feet above tlie sea. The river draining the intermediate 
valley of Tenuyan, passes through the Portillo line. 
To return to our section : shortly after leaving the 
lower beds [P 2 ] of the gypseous formation, we come to 
grand masses of a coarse, red conglomerate [V], totally 
unlike any strata hitherto seen in the Cordillera. This 
conglomerate is distinctly stratified, some of the beds 
being well defined by the greater size of the pebbles : the 
cement is calcareous and sometimes crystalline, though 
the mass shows no signs of having been metamorphosed. 
The included pebbles are either perfectly or only par- 
tially rounded : they consist of purplish sandstones, of 
various porphyries, of brownish limestone, of black 
calcareous, compact shale precisely like that in situ in 
the Peuquenes range, and containing some of the same 
fossil shells ; also very many pebbles of quartz, some of 
micaceous schist, and numerous, broken, rounded crys- 
tals of a reddish orthitic or potash feldspar (as deter- 
mined by Professor Miller), and these from their size 
must have been derived from a coarse-grained rock, 
probably granite. From this feldspar being orthitic, 
and even from its external appearance, I venture posi- 
tively to affirm that it has not been derived from the 
rocks of the western ranges ; but, on the other hand, 
it may well have come, together with, the quartz and 
metamorphic schists, from the eastern or Porfcillo line, 
for this line mainly consists of coarse orthitic granite. 
The pebbles of the fossihferous slate and of the purple 
sandstone, certainly have been derived from the Peu- 
quenes or western rang*es. 

The road crosses the valley of Tenuyan in a nearly 
east and west line, and for several miles we have on 
both, hands the conglomerate, everywhere dipping west 
and forming separate great mountains. The strata, 



CHAP. XIY. Section of the Portillo Chain. 493 

where first met with, after leaving the gypseous forma- 
tion, are inclined westward at an angle of only 20, 
which farther on increases to about 45. The gypseous 
strata, as we have seen, are also inclined westward : 
hence, when looking from the eastern side of the valley 
towards the Peuquenes range, a roost deceptive appear- 
ance is presented, as if the newer beds of conglomerate 
dipped directly under the much older beds of the 
gypseous formation. In the middle of the valley, a 
bold mountain of unstratified lilac-coloured porphyry 
(with crystals of hornblende) projects ; and farther on ? 
a little south of the road, there is another mountain, 
with its strata inclined at a small angle eastwards, which 
in its general aspect and colour, resembles the porphy- 
ritic conglomerate formation, so rare on this side of the 
Peuquenes line and so grandly developed throughout 
the western ranges. 

The conglomerate is of great thickness : I do not 
suppose that the strata forming the separate mountain- 
masses [V, V, Y] have ever been prolonged over each 
other, but that one mass has been broken up by several, 
distinct, parallel, uniclinal lines of elevation. Judging 
therefore of the thickness of the conglomerate, as seen 
in the separate mountain-masses, I estimated it at least 
from 1,500 to 2,000 feet. The lower beds rest con- 
formably on some singularly coloured, soft strata [W], 
which I could not reach to examine ; and these again 
rest comformably on a thick mass of micaceous, thinly 
laminated, siliceous sandstone [X], associated with a 
little black clay-slate. These lower beds are traversed 
by several dikes of decomposing porphyry. The lami- 
nated sandstone is directly superimposed on the vast 
masses of granite [Y, Y] which mainly compose the 
Portillo range. The line of junction between thia 
latter rock, which is of a bright red colour, and the 



494 Section of the PortilLo Chain. 

whitish sandstone was beautifully distinct; the sand- 
stone being penetrated by numerous, great, tortuous 
dikes branching from the granite, and having been 
converted into a granular quartz rock (singularly like 
that of the Falkland Islands), containing specks of an 
ochery powder, and black crystalline atoms, apparently 
of imperfect mica. The quartzose strata in one spot 
were folded into a regular dome. 

The granite which composes the magnificent bare 
pinnacles and the steep western flank of the Portillo 
chain, is of a brick-red colour, coarsely crystallized, and 
composed of orthitic or potash feldspar, quartz, and im- 
perfect mica in small quantity, sometimes passing into 
chlorite. These minerals occasionally assume a laminar 
or foliated arrangement. The fact of the feldspar being 
orithic in this range, is very remarkable, considering 
how rare, or rather, as I believe, entirely absent, this 
mineral is throughout the western ranges, in which 
soda-feldspar, or at least a variety cleaving like albite, 
is so extremely abundant. In one spot on the western 
flank, and on the eastern flank near Los Manantiales 
and near the crest, I noticed some great masses of a 
whitish granite, parts of it fine-grained, and parts con- 
taining large crystals of feldspar ; I neglected to collect 
specimens, so I do not know whether this feldspar is 
also orthitic, though I am inclined to think so from its 
general appearance. I saw also some syenite and one 
mass which resembled andesite, but of which I likewise 
neglected to collect specimens. From the manner in 
which the whitish granites formed separate mountain- 
masses in the midst of the brick-red variety, and from 
one such mass near the crest being traversed by nume- 
rous veins of flesh-coloured and greenish eurite (into 
which I occasionally observed the brick-red granite 
insensibly passing), I conclude that the white granites 



CHAP. xiv. Section of the Portillo Chain. 495 

probably belong to an older formation, almost over- 
whelmed and penetrated by the red granite. 

On the crest I saw also, at a short distance, some 
coloured stratified beds, apparently like those [W] at 
the western base, but was prevented examining them 
by a snow-storm: Mr. Caldcleugb, 1 however, collected 
here specimens of ribboned jasper, magnesian lime- 
stone, and other minerals. A little way down the 
eastern slope a few fragments of quartz and mica-slate 
are met with ; but the great formation of this latter 
rock [Z], which covers up much of the eastern flank 
and base of the Portillo range, cannot be conveniently 
examined until much lower down at a place called Mai 
Paso. The mica-schist here consists of thick layers 
of quartz, with intervening folia of finely-scaly mica, 
often passing into a substance like black glossy clay- 
slate : in one spot, the layers of quartz having disap- 
peared, the whole mass became converted into glossy 
clay-slate. Where the folia were best defined, they 
were inclined at a high angle westward, that is, towards 
the range. The line of junction between the dark 
mica-slate and the coarse red granite was most clearly 
distinguishable from a vast distance : the granite sent 
many small veins into the mica-slate, and included 
some angular fragments of it. As the sandstone on the 
western base has been converted by the red granite into 
a granular quartz-rock, so this great formation of mica- 
schist may possibly have been metamorphosed at the 
same time and by the same means; but I think it 
more probable, considering its more perfect metamor- 
phic character and its well-pronounced foliation, that it 
belongs to an anterior epoch, connected with the white 
granites : I am the more inclined to this view, from 
having found at the foot of the rang the mica- schist 
1 * Travels/ &c , vol. p. 308. 



496 Section of the Portillo Chain. PABT n. 

surrounding a hummock [Y 2 ] 5 exclusively composed of 
white granite. Near Los Arenales, the mountains on 
all sides are composed of the mica-slate ; and looking 
backwards from this point up to the bare gigantic 
peaks above, the view was eminently interesting. The 
colours of the red granite and the black mica-slate are 
so distinct, that with a bright light these rocks could 
be readily distinguished even from the Pampas, at a 
level of at least 9,000 feet below. The red granite, 
from being divided by parallel joints, has weathered 
into sharp pinnacles, on some of which, even on some 
of the loftiest, little caps of mica-schist could be clearly 
seen: here and there isolated patches of this rock 
adhered to the mountain-flanks, and these often corre- 
sponded in height and position on the opposite sides of 
the immense valleys. Lower down the schist prevailed 
more and more, with only a few quite small points of 
granite projecting through. Looking at the entire 
eastern face of the Portillo range, the red colour far 
exceeds in area the black ; yet it was scarcely possible 
to doubt that the granite had once been almost wholly 
encased by the mica-schist. 

At Los Arenales, low down on the eastern flank, the 
mica-slate is traversed by several closely adjoining, 
broad dikes, parallel to each other and to the "foliation 
of the schist. The dikes are formed of three different 
varieties of rock ? of which a pale brown feldspathic 
porphyry with grains of quartz was much the most 
abundant. These dikes with their granules of quartz, 
as well as the mica-schist itself, strikingly resemble the 
rocks of the Ohonos Archipelago. At a height of about 
1,200 feet above the dikes, and perhaps connected with 
them, there is a range of cliffs formed of successive 
lava-streams [AA], between 300 and 400 feet in thick- 
ness, and in places finely columnar. The lava consists 



CHAP, XIT. Section of the Portillo Chain. 497 

of dark- grayish, harsh rocks^ intermediate in character 
between trachyte and basalt, containing glassy feldspar, 
olivine, and a little mica, and sometimes amygdaloidal 
with zeolite : the basis is either quite compact, or crenu- 
lated with air-vesicles arranged in laminae. The 
streams are separated from each other by beds of frag- 
mentary brown scorias, firmly cemented together, and 
including a few well-rounded pebbles of lava. From 
their general appearance, I suspect that these lava- 
streams flowed at an ancient period under the pressure 
of the sea, when the Atlantic covered the Pampas and 
washed the eastern foot of the Cordillera. 1 On the 
opposite and northern side of the valley there is another 
line of lava-cliffs at a corresponding height; the valley 
between being of considerable breadth, and as nearly as 
I could estimate 1,500 feet in depth. This field of 
lava is confined on both sides by the mountains of 
mica-schist, and slopes down rapidly but irregularly to 
the edge of the Pampas, where, having a thickness of 
about 200 feet, it terminates against a little range of 
clay-stone porphyry. The valley in this lower part 
expands into a bay-like, gentle slope, bordered by the 
cliffs of lava, which must certainly once have extended 
across this wide expanse. The inclination of the 
streams from Los Arenales to the mouth of the valley is 
so great, that at the time (though ignorant of M. Elie 
de Beaumont's researches on the extremely small slope 
over which lava can flow, and yet retain a compact 
structure and considerable thickness) I concluded that 
they must subsequently to their flowing have been 

1 This conclusion might, perhaps, even have been anticipated, 
from the general rarity of volcanic action, except near the sea or 
laige bodies of water. Comformably with this rale, at the present 
day, there are no active volcanos on tins easternsideof the Cordillera ; 
nor are severe earthquakes experienced here. 



498 Section of the Portillo Chain. PABT is. 

upheaved and tilted from the mountains: of this con- 
clusion I can now entertain not the smallest doubt. 

At the month of the valley, within the cliffs of the 
above lava-field, there are remnants, in the form of 
separate small hillocks and of lines of low cliffs, of a 
considerable deposit of compact white tuff (quarried for 
filtering-stones), composed of broken pumice, volcanic 
crystals, scales of mica, and fragments of lava. This 
mass has suffered much denudation, and the hard mica- 
schist has been deeply worn, since the period of its 
deposition ; and this period must have been subsequent 
to the denudcation of the basaltic lava-streams, as at- 
tested by their encircling cliffs standing at a higher 
level. At the present day, under the existing arid 
climate, ages might roll pasb without a square yard of 
rock of any kind being denuded, except perhaps in the 
rarely moistened drainage-channel of the valley. Must 
we then look back to that ancient period, when the 
waves of the sea beat against the eastern foot of the 
Cordillera, for a power sufficient to denude extensively, 
though superficially, tbis tufaceous deposit, soft al- 
though it be ? 

There remains only to mention some little water- 
worn hillocks [B B], a few hundred feet in height, and 
mere mole-hills compared with the gigantic mountains 
behind them, which rise out of the sloping, shingle- 
covered margin of the Pampas. The first little range 
is composed of a brecciated purple porphyntic clay- 
stone, with obscurely marked strata dipping at 70 to 
the SW. \ the other ranges consist of a pale-coloured 
feld spathic porphyry, a purple clay-stone porphyry 
with grains of quartz;, and a rock almost exclusively 
composed of brick-red crystals of feldspar. These 
outermost small lines of elevation extend in a NW. by 
W. and SE. by S. direction. 



CHAP. SIT. The Portillo Range. 499 

Concluding Remarks on the Portillo Range. When 
on tlie Pampas and looking southward, and whilst travel- 
ling norbh ward, I could see for very many leagues the 
red granite and dark mica-schist forming the crest and 
eastern flank of the Portillo line. This great range, 
according to Dr. Gillies, can be traced with little inter- 
ruption for 140 miles southward to the R. Diamante, 
where it unites with the western ranges : northward, 
according to this same author, it terminates where the 
E. Mendoza debouches from the mountains; but a 
little farther north in the eastern part of the Cumbre 
section, there are, as we shall hereafter see, some 
mountain-masses of a brick-red porphyry, the last in- 
jected amidst many other porphyries, and having so 
close an analogy with the coarse red granite of the Por- 
tillo line, that I am tempted to believe that they belong 
to the same axis of injection ; if so, the Portillo line is 
at least 200 miles in length. Its height, even in the 
lowest gap on the road, is 14,365 feet, and some of the 
pinnacles apparently attain an elevation of about 
16,000 feet above the sea. The geological history of 
this grand chain appears to me eminently interesting. 
We may safely conclude, that at a former period the 
valley of Tenuyan existed as an arm of the sea, about 
twenty miles in width, bordered on one hand by a ridge 
or chain of islets of the black calcareous shales and 
purple sandstones of the Gypseous formation ; and oa 
the other hand, by a ridge or chain of islets composed 
of mica-slate, white granite, and perhaps to a partial 
extent of red granite. These two chains, whilst thus 
bordering the old sea-channel, must have been exposed 
for a vast lapse of time to alluvial and littoral action, 
during which the rocks were shattered, the fragments 
rounded, and the strata of conglomerate accumulated 
to a thickness of at least 1,500 or 2,000 feet The 

33 



5OO Concluding Remarks on PAET n. 

red orthitic granite now forms, as we have seen, the 
mam part of the Portillo chain : it is injected in dikes 
not on] y into the mica- schist and white granites, but 
into the laminated sandstone, which it has metamor- 
phosed, and which it has thrown off, together with the 
conformably overlying coloured beds and stratified 
conglomerate, at an angle of forty-five degrees. To 
have thrown off so vast a pile of strata at this angle, 
is a proof that the main part of the red granite 
(whether or not portions, as perhaps is probable, 
previously existed) was injected in a liquified state after 
the accumulation both of the laminated sandstone and 
of the conglomerate ; this conglomerate, we know, was 
accumulated, not only after the deposition of the fos- 
siliferous strata of the Peuquenes line, but after their 
elevation and long-continued denudation : and these 
fossiliferous strata "belong to the early part of the 
Cretaceous system. Late, therefore, in a geological 
sense, as must be the age of the main part of the red 
granite, I can conceive nothing more impressive than 
the eastern view of this great range, as forcing the mind 
to grapple with the idea of the thousands of thousands 
of years requisite for the denudation of the strata 
which originally encased it, for that the fluidified 
granite was once encased, its mineralogical composition 
and structure, and the bold conical shape of the moun- 
tain-masses, yield sufficient evidence. Of the encasing 
strata we see the last vestiges in the coloured beds on 
the crest, in the little caps of mica- schist on. some of 
the loftiest pinnacles, and in the isolated patches of this 
same rock at corresponding heights on the now bare and 
steep flanks. 

The lava-streams at the eastern foot of the Portillo 
are interesting, not so much from the great denudation 
which they have suffered at a comparatively late period 



CHAP. xiT 8 the Portillo Range. 501 

as from the evidence they afford by their inclination 
taken conjointly with their thickness and compactness, 
that after the great range had assumed its present 
general outline, it continued to rise as an axis of eleva- 
tion. The plains extending from the base of the 
Cordillera to the Atlantic show that the continent has 
been upraised in mass to a height of 3,500 feet, and 
probably to a much greater height, for the smooth 
shingle-covered margin of the Pampas is prolonged in a 
gentle unbroken slope far up many of the great valleys. 
Nor let it be assumed that the Peuquenes and Portillo 
ranges have undergone only movements of elevation; 
for we shall hereafter see, that the bottom of the sea 
subsided several thousand feet during the deposition of 
strata, occupying the same relative place in the Cor- 
dillera, with those of the Peuquenes ridge ; moreover, 
we shall see from the unequivocal evidence of buried 
upright trees, that at a somewhat later period, during 
the formation of the Uspallata chain, which corresponds 
geographically with that of the Portillo, there was 
another subsidence of many thousand feet : here, in- 
deed, in the valley of Tenuyan, the accumulation of the 
coarse stratified conglomerate to a thickness of 1,500 
or 2,000 feet, offers strong presumptive evidence of 
subsidence ; for all existing analogies lead to the belief 
that large pebbles can be transported only in shallow 
water, liable to be affected by currents and movements 
of undulation and if so, the shallow bed of the sea on 
which the pebbles were first deposited must necessarily 
have sunk to allow of the accumulation of the super- 
incumbent strata. What a history of changes of level, 
and of wear and tear, all since the age of the latter 
Secondary formations of Europe, does the structure of 
this one great mountain-chain reveal ! 



5O2 Section by the Cumbre Pass. 



PAET H. 



Passage of {lie Andes by tlie Cumbre or Uspallata 
Pass. 

THs Pass crosses the Andes about sixty miles north 
of that just described : the section given in Plate I. 
fig. 2, Is on the same scale as before, namely, at one- 
third of an inch to a mile in distance, and one inch to 
a mile (or 6,000 feet) in height. Like the last section, it 
Is a mere sketch, and cannot pretend to accuracy, though 
made under favourable circumstances. We will com- 
mence as before, with the western half, of which the 
main range bears the name of the Cumbre (that is the 
Eidge), and corresponds to the Peuquenes line in the 
former section ; as does the Uspallata range, though on 
a much smaller scale, to that of the Portillo. Near the 
point where the river Aconcagua debouches on the basin 
plain of the same name, at a height of about 2,300 feet 
above the sea, we meet with the usual purple and 
greenish porphyritic clay-stone conglomerate. Beds of 
this nature, alternating with numerous compact and 
amygdaloidal porphyries, which have flowed as sub- 
marine lavas, and associated with great mountain- 
masses of various, injected, non-stratified porphyries, 
are prolonged the whole distance up to the Cumbre or 
central ridge. One of the commonest stratified por- 
phyries is of a green colour, highly amygdaloidal with 
the various minerals described in the preliminary dis- 
cussion, and including fine tabular crystals of albite. 
The mountain-range north (often with a little westing) 
and south. The stratification, wherever I could clearly 
distinguish it, was inclined westward or towards the 
Pacific, and, except near the Cumbre, seldom at angles 
above 25. Only at one spot on this western side, on a 
lofty pinnacle not far from the Cumbre, I saw strata 
apparently belonging to the Gypseous formation, and 



xiv. Section by the Cumbre Pass. 503 

conformably capping a pile of stratified porphyries. 
Hence, both in composition and in stratification, the 
structure of the mountains on this western side of 
the divortmm aquarum, is far more simple than in the 
corresponding part of the Peuquenes section. In the 
porphyritic clay-stone conglomerate, the mechanical 
structure and the planes of stratification have generally 
been much obscured and even quite obliterated towards 
the base of the series, whilst in the upper parts, near 
the summits of the mountains, both are distinctly dis- 
played. In these upper portions the porphyries are 
generally lighter coloured. In three places [X, Y, ZJ 
masses of andesite are exposed : at [Y], this rock con- 
tained some quartz, but the greater part consisted of 
andesitic porphyry, with only a few well-developed crys- 
tals of albite, and forming a great white mass, having 
the external aspect of granite, capped by much dark 
unsiratified porphyry. In many parts of the moun- 
tains, there a.re dikes of a green colour, and other white 
ones, which latter probably spring from underlying 
masses of andesite. 

The Cumbre, where the road crosses it, is, according 
to Mr. Pentland, 12,454 feet above the sea ; and the 
neighbouring peaks, composed of dark purple and 
whitish porphyries, some obscurely stratified with a 
westerly dip, and others without a trace of stratification, 
must exceed 13,000 feet in height. Descending the 
eastern slope of the Cumbre^the structure becomes very 
complicated, and generally differs on the two sides of 
the east and west line of road and section. First we 
come to a great mass [A] of nearly vertical, singularly 
contorted strata, composed of highly compact red sand- 
stones ; and of often calcareous conglomerates, and pene- 
trated by green, yellow, and reddish dikes ; but I shall 
presently have an opportunity of describing in some 



504 Section by the Cumbre Pass. PAET H. 

detail an analogous pile of strata. These vertical beds 
are abruptly succeeded by others [B], of apparently 
nearly the same nature but more metamorphosed, alter- 
nating with porphyries and limestones ; these dip for a 
short space westward, but there has been here an extra- 
ordinary dislocation, which, on the north side of the 
road, appears to have determined the excavation of the 
north and south valley of the R. de las Ouevas. On 
this northern side of the road, the strata [B] are pro- 
longed till they come in close contact with a jagged 
lofty mountain [D] of dark-coloured, unstratified, in- 
trusive porphyry, where the beds have been more highly 
inclined and still more metamorphosed. This moun- 
tain of porphyry seems to form a short axis of elevation, 
for south of the road in its line, there is a hill [C] 
of porphyritic conglomerate with absolutely vertical 
strata. 

We now come to the Gypseous formation : I will 
first describe the structure of the several mountains, and 
then give in one section a detailed account of the nature 
of the rocks. On the north side of the road, which here 
runs in an east and west valley, the mountain of por- 
phyry [D] is succeeded by a hill [E] formed of the 
upper gypseous strata tilted, at an angle of between 
70 and 80 to the west, by an uniclinal axis of elevation 
which does not run parallel to the other neighbouring 
ranges, and which is of short length ; for on the south 
side of the valley its prolongation is marked only by a 
small flexure in a pile of strata inclined by a quite 
separate axis. A little farther on the north and south 
valley of Horcones enters at right angles our line of 
section; its western side is bounded by a hill of 
gypseous strata [PJ 5 dipping westward at about 45, 
and its eastern side by a mountain of similar strata 
Gr] inclined westward at 70, and superimposed by an 



CHAP. SIT. Gypseous Formation. 505 

oblique fault on another mass of the same strata [HJ 5 
also inclined westward, bot at an angle of only about 
30: the complicated relation of these three masses 
[P, Gr, H] is explained by the structure of a great 
mountain-range lying some way to the north, in which 
a regular anticlinal axis (represented in the section by 
dotted lines) is seen, with the strata on its eastern side 
again bending up and forming a distinct uniclinal axis, 
of which the beds marked [H] form the lower part. 
This great uniclinal line is intersected, near the Puente 
del Inca, by the valley along which the road runs, and 
the strata composing it will be immediately described. 
On the south side of the road, in the space correspond- 
ing with the mountains [E, F and Cr], the strata every- 
where dip westward generally at an angle of 30, occa- 
sionally mounting up to 45, but not in an unbroken 
line, for there are several vertical faults, forming 
separate uniclinal masses, all dipping in the same 
direction, a form of elevation common in the Cordil- 
lera. We thus see that within a narrow space, the 
gypseous strata have been upheaved and crushed to- 
gether by a great uniclinalj anticlinalj and one lesser 
uniclinal line [E] of elevation ; and that between these 
three lines and the Cumbre, in the sandstones, con- 
glomerates and porphyritic formation, there have been 
at least two or three other great elevatory axes. 

The uniclinal axis [I] intersected near the Puente 
del Inca 1 (of which the strata at [H] form a part) 

1 At this place, there are some hot and cold springs, the warmest 
having a temperature, according to Lieut Brand ( 4 Travels/ p. 240), 
of 91 , they emit much gas According to Mr. Brand e, of the Koyal 
Institution, ten cubical inches contain forty-five grains of solid 
matter, consisting chiefly of salt, gypsum, carbonate of lime, and 
oxide of iron. The water is charged with carbonic acid and 
sulphuretted hydrogen. These springs deposit much tufa in the 
form of spherical balls. They burst forth, as do those of Cauquenes, 
and probably those of Villa Yicencio, on a line of elevation. 



506 Section by the Cumbre Pass. PAET H, 

ranges N. by W. and 8. by E., forming a cliain of 
mountains, apparently little inferior in .height to the 
Cumbre : the strata, as we have seen, dip at an average 
angle of 30 to the west. The flanks of the mountains 
are here quite bare and steep, affording an excellent 
section so that I was able to inspect the strata to a 
thickness of about 4,000 feet, and could clearly dis- 
tinguish their general nature for 1,000 feet higher, 
making a total thickness of 5,000 feet, to which must 
be added about 1,000 feet of the inferior strata seen a 
little lower down the valley. I will describe this one 
section in detail, beginning at the bottom. 

1st. The lowest mass is the altered clay-slate de- 
scribed in the preliminary discussion, and winch in this 
Hue of section was here first met with. Lower down 
the valley, at the R. de las Vacas, I had a better oppor- 
tunity of examining it ; it is there in some parts well 
characterised, having a distinct, nearly vertical, tortuous 
cleavage, ranging NW. and SE., and intersected by 
quartz veins : in most parts, however, it is crystalline 
and feldspathic, and passes into a true greenstone often 
including grains of quartz. The clay-slate, in its upper 
half, is frequently brecciated, the embedded angular 
fragments being of nearly the same nature with the 
paste. 

2nd. Several strata of purplish porphyritic con- 
glomerate, of no very great thickness, rest conformably 
upon the feldspathic slate. A thick bed of fine, purple, 
clay-stone porphyry, obscurely brecciated (but not 
of metamorphosed sedimentary origin), and capped 
by porphjritic conglomerate, was the lowest bed 
actually eiamined in this section at the Puente del 
Inca. 

3rd. A stratum, eighty feet thick, of hard and very 
compact) impure whitish limestone, weathering bright 



CHAP. XIY. Gypseoiis Formation. 507 

red, with included layers brecciated and re-cemented. 
Obscure marks of shell are distinguishable in it. 

4th. A red, quartzose, fine-grained conglomerate, 
with grains of quartz, and with patches of white earthy 
feldspar, apparently due to some process of concretionary 
crystalline action: this bed is more compact and 
metamorphosed than any of the overlying conglome- 
rates. 

5th. A whitish cherty limestone, with nodules of 
blueish argillaceous limestone. 

6th. A white conglomerate, with many particles of 
quartz, almost blending into the paste. 

7th. Highly siliceous, fine-grained white sand- 
stone. 8th and 9th. Red and white beds not ex- 
amined. 

10th. Yellow, fine-grained, thinly stratified, mag- 
nesian (judging from its slow dissolution in acids) lime- 
stone : it includes some white quartz pebbles, and little 
cavities, lined with calcareous spar, some retaining the 
form of shells. 

llth. A bed between twenty and thirty feet thick, 
quite conformable with the underlying ones, composed 
of a hard basis, tinged lilac-gray porphyritic with 
numerous crystals of whitish feldspar, with black mica 
and little spots of soft ferruginous matter : evidently a 
submarine lava. 

12th. Yellow magnesian limestone, as before, part- 
stained purple. 

13th. A most singular rock; basis purplish gray, 
obscurely en stalline, easily fusible into a dark green 
glass, not hard, thickly speckled with crystals more or 
less perfect of white carbonate of lime, of red hydrous 
oxide of iron, of a white and transparent mineral like 
analcime, and of a green opaque mineral like soap-stone $ 
the basis is moreover amygdaloidal with many spherical 



508 Section by the Cwnbre Pass. PAET u 

balls of white crystallised carbonate of lime, of which 
some are coated with the red oxide of iron. I have no 
doubt, from the examination of a superincumbent 
stratum (19), that this is a submarine lava ; though in 
Northern Chile, some of the metamorphosed sedimentary 
beds are almost as crystalline, and of as varied com- 
position. 

14th. Red sandstone, passing in the upper part into 
a coarse, hard, red conglomerate, 300 feet thick, having 
a calcareous cement, and including grains of quartz and 
broken crystals of feldspar ; basis infusible ; the pebbles 
consist of dull purplish porphyries, with some of quartz, 
from the size of a nut to a man's head. This is the 
coarsest conglomerate in this part of the Cordillera : in 
the middle there was a white layer not examined. 

15th. Grand thick bed, of a very hard, yellowish- 
white rock, with a crystalline feldspathic base, including 
large crystals of white feldspar, many little cavities 
mostly full of soft ferruginous matter, and numerous 
hexagonal plates of black mica. The upper part of 
this great bed is slightly cellular; the lower part 
compact : the thickness varied a little in different parts. 
Manifestly a submarine lava; and is allied to bed 11. 

16th and 17th. Dull purplish, calcareous, fine- 
grained, compact sandstones, which pass into coarse 
white conglomerates with numerous particles of quartz. 

18th. Several alternations of red conglomerate, 
purplish sandstone, and submarine lava, like that singu- 
lar rock forming bed 13. 

19th. A very heavy, compact, greenish-black stone, 
with a fine-grained obviously crystalline basis, contain- 
ing a few specks of white calcareous spar, many specks 
of the crystallised hydrous red oxide of iron, and some 
specks of a green mineral ; there are veins and nests 
filled with epidote : certainly a submarine lava. 



CHAP, xiv. Gypseous Formation. 509 

20th. Many thin strata of compact, fine-grained, 
pale purple sandstone. . 

21st, Gypsum in a nearly pure state, about 300 feet 
in thickness : this bed, in its concretions of anhydrite 
and layers of small blackish crystals of carbonate of 
lime, exactly resembles the great gypseous beds in the 
Peuquenes range. 

22nd. Pale purple and reddish sandstone, as In bed 
20 : about 300 feet in thickness. 

23rd. A thick mass composed of layers, often as 
thin as paper and convoluted, of pure gypsum with 
others very impure, of a purplish colour. 

24th. Pure gypsum, thick mass. 

25th. Bed sandstones, of great thickness, 

26th. Pure gypsum, of great thickness. 

27th. Alternating layers of pure and impure gypsum, 
of great thickness. 

I was not able to ascend to these few last great 
strata, which compose the neighbouring loftiest pin- 
nacles. The thickness, from the lowest to the uppermost 
bed of gypsum, cannot be less than 2,000 feet : the beds 
beneath I estimated at 3,000 feet, and this does not 
include either the lower parts of the porphyritic conglo- 
merate, or the altered clay-slate ; I conceive the total 
thickness must be about 6,000 feet. I distinctly 
observed that not only the gypsum, but the alternating 
sandstones and conglomerates were lens-shaped, and 
repeatedly thinned out and replaced each other : thus 
in the distance of about a mile, a bed 300 feet thick of 
sandstone between two beds of gypsum, thinned out to 
nothing and disappeared. The lower part of this section 
differs remarkably, in the much greater diversity of 
its mineralogical composition, in the abundance of 
calcareous matter, in the greater coarseness of some 
of the conglomerates, and in the numerous particles 



510 Section by the Cumbre Pass. PAET n 9 

and well rounded pebbles, sometimes of large size, of 
quartz, from any other section hitherto described in 
Chile. From these peculiarities, and from the lens- 
form of the strata, it is probable that this great pile of 
strata was accumulated on a shallow and very uneven 
bottom, near some pre-existing land fotmed of various 
porphyries and quartz-rock. The formation of por- 
phyritic clay-stone conglomerate does not in this section 
attain nearly its ordinary thickness; this may "be partly 
attributed to the metamorphic action having been here 
much less energetic than usual, though the lower beds 
have been affected to a certain degree. If it had been 
as energetic as in most other parts of Chile, many of 
the beds of sandstone and conglomerate, containing 
rounded masses of porphyry, would doubtless have been 
converted into porphyritic conglomerate; and these 
would have alternated with, and even blended into, 
crystalline and porphyritic strata without a trace of 
mechanical structure, namely, into those which, in the 
present state of the section, we see are unquestionably 
submarine lavas. 

The beds of gypsum, together with the red alternat- 
ing sandstones and conglomerates, present so perfect 
and curious a resemblance with those seen in our former 
section in the basin- valley of Yeso, that I cannot doubt 
the identity of the two formations : I may add, that a 
little westward of the P. del Inca, a mass of gypsum 
passed into a fine-grained, harb , drown sandstone, which 
contained some layers of black, calcareous, compact, 
shaly rock, precisely like that seen in such vast masses 
on the Peuquenes range. 

Near the Puente del Inca, numerous fragments of 
limestone, containing some fossil remains, were scattered 
on the ground : these fragments so perfectly resemble 
the limestone of bed No. 3, in which I saw impressions 



CHAP. xiv, Neocomian Fossils. 511 

of shells, that I have no doubt they have fallen from It. 
The yellow magnesian limestone of bed No. 10, which 
also includes traces of shells, has a different appearance. 
These fossils (as named by M d'Orbigny) consist of 

Gryphfea, near to G Couloni (Neocomian formation) 
Area, perhaps A. GaJbnelu, d'Orbig ' Pal B\anc ' (Neocomian for- 
mation). 

Mr. Pentland made a collection of shells from this 
same spot, and Von Buch * considers them as consisting 
of 

Trigonia, resembling in form T. costata. 

Pholadomya, like one found by M Dufresnoy near Alen^on, 

Isocardiaescentrica, Voltz., identical with that from the Jura. 

Two of these shells, namely, the Gryphsea and 
Trigonia, appear to be identical with species collected 
by Meyen and myself on the Peuquenes range ; and in 
the opinion of Von Buch and M. d'Orbigny, the two 
formations belong to the same age. I must here add, 
that Professor E. Forbes, who has examined my speci- 
mens from this place and from the Peuquenes range, 
has likewise a strong impression that they indicate the 
Cretaceous period, and probably an early epoch in it : 
so that all the palaeontologists who have seen these 
fossils nearly coincide in opinion regarding their age. 
The limestone, however, with these fossils here lies at 
the very base of the formation, just above the porphyritic 
conglomerate, and certainly several thousand feet lower 
in the series, than the equivalent, fossiliferous, black, 
shaly rocks high up on the Peuquenes range. 

It is well worthy of remark that these shells, or at 
least those of which I saw impressions in the limestone 
(bed No. 3), must have been covered up, on the least 
computation, by 4,000 feet of strata : now we know 

1 ' Descript. Phys des lies Can/ p 472. 



512 Section by the Cumbre Pass. PABT n. 

from Professor E. Forbes's researches, that the sea at 
greater depths than 600 feet becomes exceedingly 
barren of organic beings, a result quite in accordance 
with what little I have seen of deep-sea soundings. 
Hence, after this limestone with its shells was deposited, 
the bottom of the sea where the main line of the 
Cordillera now stands, must have subsided some thou- 
sand feet to allow of the deposition of the superincum- 
bent submarine strata. Without supposing a movement 
of this kind, it would, moreover, be impossible to 
understand the accumulation of the several lower strata 
of coarse , well-rounded conglomerates, which it is 
scarcely possible to believe were spread out in profoundly 
deep water, and which, especially those containing 
pebbles of quarfcz, could hardly have been rounded in 
submarine craters and afterwards ejected from them, as 
I believe to have been the case with much of the 
porphyritic conglomerate formation, I may add that, 
in Professor Forbes's opinion, the above-enumerated 
species of Mollusca probably did not live at a much 
greater depth than twenty fathoms, that is only 120 
feet. 

To return to our section down the valley : standing 
on the great N. by W. and S. by E, uniclinal axis of 
the Puente del Inca, of which a section has just been 
given, and looking north-east, great tabular masses of 
the Gypseous formation [K K] could be seen in the 
distance, very slightly inclined towards the east. Lower 
down the valley, the mountains are almost exclusively 
composed of porphyries, many of them of intrusive 
origin and non-stratified, others stratified, but with the 
stratification seldom distinguishable except in the 
u PP er parts. Disregarding local disturbances, the beds 
are either horizontal or inclined at a small angle east- 
wards : hence, when standing on the plain of Uspallata 



CHAP. xrv. Section by the Cumbre Pass. 523 

and looking to the west or backwards, the Cordillera 
appear composed of huge, square, nearly horizontal, 
tabular masses : so wide a space, with such lofty moun- 
tains so equably elevated, is rarely met with within the 
Cordillera. In this line of section, the interval between 
the Puente del Inca and the neighbourhood of the 
Cumbre, includes all the chief axes of dislocation. 

The altered clay-slate formation, already described, 
is seen in several parts of the valley as far down as Las 
Vacas, underlying the porphyritic conglomerate. At 
the Casa de Pujios [L], there is a hummock of (ande- 
sitic ?) granite ; and the stratification of the surrounding 
mountains here changes from W. by S. to SW. Again, 
near the R. Vacas there is a larger formation of (ande- 
sitic?) granite [M], which sends a mesh-work of veins 
into the superincumbent clay-slate, and which locally 
throws off the strata, on one side to NW. and on the 
other to SE. but not at a high angle: at the junction, 
the clay-slate is altered into fine-grained greenstone. 
This granitic axis is intersected by a green dike, which 
I mention, because I do not remember having elsewhere 
seen dikes in this lowest and latest intrusive rock, 
from the R Vacas to the plain of Uspallata, the valley 
runs NE., so that I have had to contract my section ; 
it runs exclusively through porphyritic rocks. As far 
as the Pass of Jaula, the clay-stone conglomerate forma- 
tion, in most parts highly porphyritic, and crossed by 
numerous dikes of greenstone-porphyry, attains a great 
thickness : there is also much intrusive porphyry. From 
the Jaula to the plain, the stratification has been in. 
most places obliterated, except near the tops of some of 
the mountains ; and the metamorphic action has been 
extremely great. In this space, the number and bulk 
of the intrusive masses of differently coloured porphyries, 
injected one into another and intersected by dikes, is 



514 Section by the Cumbre Pass. PAET n. 

truly extraordinary. I saw one mountain of whitish 
porphyry, from which two huge dikes, thinning out^ 
"branched doivnwards into an adjoining blackish por- 
phyry. Another hill of white porphyry, which had 
"burst through dark-coloured strata, was itself injected 
Tby a purple, brecciated, and recemented porphyry, both 
being crossed by a green dike, and both having been 
upheaved and injected by a granitic dome. One brick- 
red porphyry, which above the Jaula forms an isolated 
mass in the midst of the porphyritic conglomerate 
formation, and lower down the valley a magnificent 
group of peaked mountains, differs remarkably from 
all the other porphyries. It consists of a red feldspathic 
base, including some rather large crystals of red feldspar, 
numerous large angular grains of quartz, and little bits 
of a soft green mineral answering in most of its charac- 
ters to soap-stone. The crystals of red feldspar resemble 
in external appearance those of orthite, though, from 
being partially decomposed, I was unable to measure 
them ; and they certainly are quite unlike the variety, 
so abundantly met with in almost all the other rocks of 
this line of section, and which, wherever I tried it, 
cleaved like albite. This brick-red porphyry appears 
to have burst through all the other porphyries, and 
numerous red dikes traversing the neighbouring moun- 
tains have proceeded from it : in some few places, 
however, it was intersected by white dikes. From this 
posteriority of intrusive origin, from the close general 
resemblance between this red porphyry and the red 
granite of the Portillo line, the only difference being 
that the feldspar here is less perfectly granular, and 
that soap-stone replaces the mica, which is there im- 
perfect and passes into chlorite, and from the Portillo 
line a little southward of this point appearing to blend 
(according to Dr. Gillies) into the western ranges, I 



CHAP. xiv. Plain of Uspallata. 515 

ata strongly urged to believe (as formerly remarked) 
that the grand mountain-masses composed of this brick- 
red porphyry belong to the same axis of injection with 
the granite of the Portillo line : if so, the injection of 
this porphyry probably took place., as long subsequently 
to the several axes of elevation in the gypseous forma- 
tion near the Curnbre, as the injection, of the Portillo 
granite has been shown to have been subsequent to the 
elevation of the gypseous strata composing the Peu- 
quenes range ; and this interval, we have seen, must 
have been a very long one. 

The Plain of Uspallata has been briefly described 
in Chap. X.; it resembles the basin-plains of Chile; 
it is ten or fifteen miles wide, and is said to extend for 
180 miles northward; its surface is nearly 6,000 feet 
above the sea ; it is composed, to a thickness of some 
hundred feet of loosely aggregated, stratified shingle, 
which is prolonged with a gently sloping surface up the 
valleys in the mountains on both sides. One section 
in this plain [Z] is interesting, from the unusual 1 cir- 
cumstance of alternating layers of almost loose red and 
white sand with lines of pebbles (from the size of a nut 
to that of an apple), and beds of gravel, being inclined 
at an angle of 45, and in some spots even at a higher 
angle These beds are dislocated by small faults : and 
are capped by a thick mass of horizontally stratified 
gravel, evidently of subaqueous origin. Having been 
accustomed to observe the irregularities of beds accu- 
mulated under currents, I feel sure that the inclination 
here has not been thus produced. The pebbles consist 
chiefly of the brick-red porphyry just described and of 
white granite, both probably denved from the ranges 
to the west, and of altered clay-slate and of certain 

1 I find that Mr Smith, of Jordanhill, has described (* Edinburgh 
New Phil Journ ' vol. xxv p, 392) beds of sand and gravel, near Edin- 
burgh, tilted at an angle of 60, and dislocated by miniature faults 

34 



5 1 6 Section of the Uspallata Range. PART n. 

porphyries, apparently belonging to the rocks of the 
Uspallata chain. This plain corresponds geographically 
with the yalley of Tenuyan between the Portillo and 
Peuquenes ranges ; but in that valley the shingle, 
which likewise has been derived both from the eastern 
and western ranges, has been cemented into a hard con- 
glomerate, and has been throughout tilted at a con- 
siderable inclination; the gravel there apparently attains 
a much greater thickness, and is probably of higher 
antiquity. 

The Uspallata Range. The road by the Villa 
Vicencio Pass does not strike directly across the range, 
but runs for some leagues northward along its we&tern 
base : and I must briefly describe the rocks here seen, 
before continuing with the coloured east and west section. 
At the mouth of the valley of Caiiota, and at several 
points northwards, there is an extensive formation of a 
glossy and harsh, and of a feldspathic clay-slate, includ- 
ing strata of grauwacke, and having a tortuous, nearly 
vertical cleavage, traversed by numerous metalliferous 
veins and others of quartz. The clay-slate is in many 
parts capped by a thick mass of fragments of the same 
rock, firmly recemented ; and both together have been 
injected and broken up by very numerous hillocks, 
ranging north and south, of lilac, white, dark and 
salmon-coloured porphyries : one steep, now denuded, 
hillock of porphyry had its face as distinctly impressed 
with the angles of a fragmentary mass of the slate, with 
some of the points sfcill remaining embedded, as sealing- 
wax could be by a seal. At the mouth of this same 
valley of Oanota, in a fine escarpment having the strata 
dipping from 50 to 60 to the NE., 1 the clay-slate 

1 Nearly opposite to this escarpment, there is another correspond- 
ing- one, with the strata dipping pot to the exactly opposite point, or 
BW., but to S3 W. : consequently the two escarpments trend towards 



CHAP. xiv. Section of the Uspallata Range. 517 

formation is seen to be covered by (1st), a purple clay- 
stone porphyry resting unconforrnably in some parts 
on the solid slate, and in others on a thick fragmentary 
mass : (2nd), a conformable stratum of compact blackish. 
rock, having a spheroidal structure, full of minute 
acicular crystals of glassy feldspar, with red spots of 
oxide of iron : (3rd), a great stratum of purplish-red 
clay-stone porphyry, abounding with crystals of opaque 
feldspar, and laminated with thin, parallel, often short, 
layers, and likewise with great irregular patches of 
white, earthy, semi-crystalline feldspar; this rock 
(which I noticed in other neighbouring places) per- 
fectly resembles a curious variety described at Port 
Desire, and occasionally occurs in the great porphyritic 
conglomerate formation of Chile : (4th), a thin stratum 
of greenish-white ; indurated tuff, fusible and containing 
broken crystals and particles of porphyries: (5th), a 
grand mass, imperfectly columnar and divided into 
three parallel and closely joined strata, of cream- 
coloured claystone porphyry : (6th) 5 a thick stratum of 
lilac-coloured porphyry, which I could see was capped 
by another bed of the cream-coloured variety : I was 
unable to examine the still higher parts of the escarp- 
ment. These conformably stratified porphyries, though 
none are either vesicular or amygdaloidal, have evi- 
dently flowed as submarine lavas: some of them are 
separated from each other by^seams of indurated tuff, 
which, however, are quite insignificant in thickness 
compared with the porphyries. This whole pile 
resembles, but not very closely, some of the less 
brecciated parts of the great porphyritic conglomerate 
formation of Chile ; but it does not probably belong to 
the same age, as the porphyries here rest unconformably 

each other, and some miles southward they become actually united s 
this is a form of elevation which I have not elsewhere seen. 



5 1 8 Stratification of PAET n, 

on the altered feldspathic clay-slate, whereas the por- 
phyritic conglomerate formation alternates with and 
rests conformably on it. These porphyries, moreover, 
with the exception of the one blackish stratum, and of 
the one indurated, white tufaceous bed, differ from the 
beds composing the Uspallata range in the line of the 
Villa Vicencio Pass. 

I will now give, first, a sketch of the structure of the 
range, as represented in the coloured section, and will 
then describe its composition and interesting history. 
At its western foot, a hillock