UNIVERSITY OF CALIFORNIA
G-XFT OP
HENRY DOUGLASS BACON.
1877.
Iccessions No. ^/£Z_/^ Shelf No...
* vv
:.?, OF CJBOLOCJS; ur SENG'S COLLEGE, LOEDOH
THE
UNIVERSITY
OJ0»
CONTENTS
TO
THE SECOND VOLUME.
CHAPTER VI. —continued.
HISTORICAL VIEW OF STRATIFIED ROCKS.
Page
POST-TERTIARY STRATA, continued.
Fluviatile and Lacustrine Deposits - - 1
Ancient Valley Formations - -2
Fluriatile Deposits in - - - 3
Rock Terraces in - - - - 6
FLCVIATILE DEPOSITS -
Waste of the Earth's Surface - - 9
Effects of Rain - - - - - - 10
Effects of Frost - - - - - -11
Effects of Springs - - 19
Effects of Rivers - - - 20
Lakes on the Course of Rivers - - - -23
Deep Lakes on the Course of a River - - -24
New Lands at the Mouths of Rivers - - - - 27
Estuary and Shore Deposits
LACCSTRINE DEPOSITS- - - 36
Classification of Fossil Mammalia - - - - 39
Eocene or Lower Tertiary Period - - - - 41
Organic Remains of the Paris Basin - - 41
Organic Remains of the Quarries of Binstead - -42
Middle Tertiary Period - - - -/ - 43
Fossil Remains of the upper Freshwater Beds of the Paris
Basin - - - - - - 43
Organic Remains of various Freshwater Beds - . 44—47
A 2
IV CONTENTS.
Page
LACUSTRINE DEPOSITS — continued.
Lakes of the Pleiocene and Diluvial Period - - - 48
Fossil Mammalia of the upper Val d'Arno - 48
Series of Deposits in the upper Val d'Arno - 49
Series of Deposits at Bielbecks - - . - 50
Organic Remains at Bielbecks - - - - 50
Fossil Shells of the Valley of the Thames - -51
Charlesworth's Classification of Mammaliferous Strata - 52
Modern Lacustrine Deposits - - - - 53
Analysis of the Deposition - - - -55
SUBTERRANEAN AND SUBMARINE FORESTS - - - - 57
Buried Trees on the Course of a River - - - 57
Series of Beds associated with Tin Ore at Sandrycock, Corn-
wall - - - - - - 60
Turf Moors - .... 62
Antiquity of Subterranean Forests - - - - 64
General Considerations - - - - 68
CHAP. VII.
UNSTRATIFIED ROCKS IN THE CRUST OP THE EARTH.
General Remarks - - - - - - 71
Igneous Origin - ... 71
Geological Age - ... 72
Composition - - - - . - 72
Mineral Composition of Unstratified Rocks 80
Scrope's Synopsis of Volcanic Rocks — Trachyte - - 83
Greystone. — Basalt - - 84
Elements of the Old Rocks of Fusion. Division I. — Felspathic - 84
Division II. — Hornblende, Augite, &c Felspathic - 84
Division III. — Hornblendic, Augitic, &c. - - 85
Mixed Rocks - ... 86
Gradations among Igneous Rocks - - - - 87
Chemical Composition of the Rocks of Igneous Origin - - 90
Analysis of Minerals in Igneous Products - - - 91
Table of Varieties of Mica - - - -92
Table of Varieties of Granite - -92
Table of Varieties of Sienite - « - - 93
Table of Combinations of Felspar - 93
Analysis of Serpentine - - - - - 94
Table of Felspathic Compounds analogous to Granite - 94
Analyses of Pumice, compact Lava of Calabria, Basalt - 95
Exterior Forms of the Masses of Igneous Rocks - . - 95
Interposed Beds - - 95
Overlying Masses - - - 97
Fissures - - - - - - -97
Dykes - - - - - - - 98
Veins - - - - - - - 99
CONTENTS. V
Page
Internal Divisions of Igneous Rocks - - 108
PHENOMENA OBSERVED WHERE IGNEOUS ROCKS COME IN CONTACT WITH
STRATIFIED MASSES - - - - • - 109
Induration of Stratified Rocks ... - 109
Alteration of the Structure of Rocks by Heat - - lit
Metamorphic Rocks
Re-arrangement of the Particles of Rocks - - 126
Alteration of the Chemical Nature of Rocks - - 131
Dolomitic Limestone - - - 133
Generation of New Minerals - - 136
Metamorphic Slates - 139
Succession of Metamorphic Slates - 140
Metamorphic Mica Schist, Gneiss, &c. - 143
Relative Antiquity of Pyrogeuous Rocks - - 145
Table of the Principal Disturbances of the Stratification of the British
Islands, with the Igneous Rocks observed in connection therewith - 152
Class I — Before the Deposition of Old Red Sandstone - 152
i Class II. — Before the Deposition of the Lias -153
Class III. — Before the Deposition of the Lower Green Sand - 154
Class IV. — Since the Deposition of the Chalk - - 154
CHAP. VIII.
MINERAL VEIXS.
Remarks .... - 155
Geographical Distribution - - 156
Occurrence of Mineral Veins near Centres of Igneous Action - 159
Relations of Veins to the Substance and Structure of the Neighbouring
Rocks - - 163
Relation of Veins to each other - - - 171
First Class. — Oldest Tin Veins - - 171
Second Class. — More recent Tin Lodes - - 171
Third Class Oldest East and West Copper Lodes - - 172
Fourth Class Contra Copper Lodes - 172
Fifth Class — Cross Courses - 173
Sixth Class. — More recent Copper Lodes - - 173
Seventh Class. — Cross Flukans - -173
Eighth Class. — Slides - -173
Deposits of Metallic Veins in Cornwall - - - 174
Theory of Mineral Veins - - 177
Veins are of posterior Date to the Rocks which they traverse - 178
Description'of Huel Peever Vein ... 180
Origin of Vein Fissures ... - - 188
Filling of the Fissures - -192
Recapitulation ... - - 196
Vi CONTENTS.
CHAP. IX.
MODERN EFFECTS OF HEAT ON THE GLOBE.
.'Page
Remarks . - - 200
VOLCANIC ACTION ... - 201
Origin of Volcanos - - 202
Volcanos in Action ...
Dispersion of Ashes, Stones, Mud, &c. - -213
Extinction of Volcanos - - 216
Extinct Volcanos - - - - - 220
Geographical Distribution of Volcanos
Asiatic Volcanos - - - - 227
American Volcanos . . . 229
African Volcanos - - 231
Australian - . - 232
Indian Ocean - 232
Pacific Ocean ..... 232
Geological Age of Volcanos - - 233
Volcanic Eruption Forces. _ Earthquakes - - 234
Ejection of Ashes and Stones .... 235
New Mountains formed ... - 236
New Islands raised - - - - - 236
Earthquakes - . - 242
Hypotheses of Volcanic Action - - 248
THERMAL SPRINGS ...... 252
Warm Springs of the British Islands, yielding Nitrogen, &c. - 255
Warm Springs of a Part of Germany, &c., yielding Carbonic
Acid, &c. ..... 256
Warm Springs of the Pyrenees - - - 256
Warm Springs of Volcanic Countries - - - 257
Summary of their Geolsgical Relations to existing Volcanos - 259
Experimental Inquiries into the Heat of the Globe - - 262
First Class of Experiments. — Metalliferous Veins - - 270
Tables of Temperatures of Water at different Depths in the
Mines of Freyberg ..... 270
Account of Temperatures of Water at different Depths in va-
rious Countries - . - 271
Second Class of Experiments. — Stratified Rocks - . 272
Account of the Temperatures of Water at various Depths in
different Mines . 273
Cordier's Summary of Observations in the Coal Mines of
Carmeaux, Littry, and Decise - - 274
Summary of Observations on Subterranean Temperatures in
Rocks •<--_-- 275
Third Class of Experiments. — Artesian Wells - - 276
Tables of Temperatures of Water, with Mean Results - 276
CONTEXTS. Vll
CHAP. X.
STATE OF GEOLOGICAL THEORY.
Page
General Observations - - -277
PHYSICAL GEOGRAPHY ... 286
Distribution of Land and Sea - 286
Heights and Depths - 288
Displacements of Stratified Rocks - - - - 289
Direction .... -292
Production of Longitudinal Fissures - - 299
Formation of Transverse Fissures - SCO
Formation of Fissures in a Conical Elevation - - 300
Faults - - - 301
Periods of Ordinary and Critical Action - - - 301
Primary Period. — Carboniferous Period - - 302
Oolitic and Cretaceous Periods — Eocene Period of Mr.
Lyell - - 303
Modern Period of Ordinary Action - - 304
Climate - - 305
CONCLUSION .--.-.- 315
CHAP. XI.
POPULAR VIEWS AND ECONOMICAL APPLICATIONS OF GEOLOGY.
Introductory Remarks - - 317
Aspect of the Earth's Surface - -319
Outline of Land and Sea - - 320
Undulations of the Interior - - 322
Scenery ... - 324
ECONOMICAL APPLICATIONS OP GEOLOGY - - 326
Agriculture ..-.-. 326
Construction of Roads, Railways, Canals, &c. - - 329
Building Materials - - - 330
Coal and other Mineral Products - 331
A
TREATISE ON GEO
UNIVERSITY
CHAPTER
FLUVIATILE AND LACUSTRINE DEPOSITS.
WE now quit the marine deposits of tertiary and post-
tertiary age, and fix our attention on a parallel series of
accumulations, in valleys, and ancient lakes, for the
most part under the influence of fresh waters. In
treating of formations in valleys, we cannot always con-
fine our illustrations to the operations of fresh waters,
because continued research appears, in several instances,
to show that what appeared at first to be due to lacus-
trine fluctuation or river currents was really the effect
of water-movement in an ancient arm of the sea. This
result is quite to be expected. Valleys have been the
channels of strong sea currents before they were raised
above the ocean and filled with precipitations from the
air : valleys were subaqueous before they became sub-
aerial, and in them we ought to find marks of marine
followed by other marks of fluviatile action.
When shells are absent -(as they most frequently are),
we may not always be able to distinguish between the
beaches left by the retiring sea and the banks left by
rapid inundations formerly flowing at higher levels.
VOL. II. B
2 A TREATISE ON GEOLOGY. CHAP. VI.
No uncertainty of this kind is felt in tracing the
history of the purely lacustrine deposits : for these
seldom are deficient in the characteristic organic forms
of fresh water. Perhaps in both of these classes of
phenomena, we may reasonably look for more zealous
and persevering research than have been lately bestowed
upon them. Old lakes deserve all the attention of
palaeontology and physical geology : for their history
goes far back on the scale of geological time, and by
their contents we know at least somewhat of our
"native" land in pleistocene, tertiary, oolitic, and
perhaps carboniferous periods. Nor is any survey of
the primeval world at all complete which fails to in-
quire into the river action of early geological times, since
this action is an index of the state of the land, and
many of our valleys are even of palaeozoic date, and
contain conglomerates heaped in them by palaeozoic, me-
sozoic, and cainozoic waves. And, even where no trace
of the valley remains, we not unfrequently mark the
positive effect, or the probable vicinity, of a great an-
cient river. Thus, in the Weald of Sussex, we have
such a combination of reliquiae as to mark, not a bay of
the sea, but an estuary nourished by a richly wooded
river ; nor can we easily escape from the conviction
that the alternating sediments of the coal formation in
many cases require the intervention of powerful streams
from the land. To show where that land was posited,
and what was its character, may be an impracticable
problem, but it cannot be prosecuted without some in-
direct advantages, perhaps more than commensurate
with the effort which it requires.
The recent work of Mr. Chambers, entitled tf Ancient
Sea Margins," may be perused with advantage for many
examples of old sea and tide river terraces at various
stated levels, round a great part of the British shores,
and along many of the valleys.
ANCIENT VALLEY FORMATIONS.
I have some time ago proposed this term, for the
CHAP. VI. POST-TERTIARY STRATA.
purpose of combining in one point of view a great
number of remarkable ancient phenomena, attesting
the former action of water in existing valleys, but flow-
ing at higher levels than the actual stream, unless the
land has been raised and sunk. Deposits of gravel at
the mouth of a valley, in the form of terraces, abound
in most mountain countries (e. g. foot of Glen Roy), on
the sides of a valley (as in Tynedale, above Newcastle),
at the head of a valley (as at the head of several Cum-
berland glens).
In Glen Roy, at a very high level, are two parallel
lines, or terraces, which run round the mountain sides,
and communicate with other drainage streams. The
deposit called Loss, on the Rhine, appears of the same
nature, so far, at least, as to indicate the deposition of
sediments in water flowing at a level many hundred feet
above the present River Rhine, and extending beyond
what is now its proper valley on the north side of the
range of the Ardennes.*
In some of these cases there is sufficient proof that
the water was not marine, land shells being not unfre-
quently found in the deposits, especially the finer sorts
of sediments. The level character of the terraces, which
is the most usual form of these accumulations, seems to
indicate the existence of ancient lakes at a high level in
the valleys where they occur.
This, however, is less certain than may be commonly
imagined ; for streams like the rough Arve scatter the
detritus brought down from the glaciers over a surface
gently declining, as the stream runs, but nearly level in
the transverse section. If, by any change of the
* Lyell, in Geol. Proc.
B 2
A TREATISE ON GEOLOGY.
CHAP. VI.
physical conditions, the stream should cut its way to a
greater depth, the banks would have that terrace form
which belongs to the Lune, the Ouse, the Tees, the
Tyne, and many rivers of the North of England. It
not uncommonly happens, that two such terraces, at dif-
ferent levels, can be traced for some distance on the sidet
of a valley, as on the Lune; — occasionally, in the midst
of a valley, rises a low hill of gravel corresponding to the
lateral terraces. Jn most valleys, the materials of the ter-
races are such as the rocks on the sides of the mountains
yield ; but this is not the case on the Lune about Kirkby
Lonsdale, or the Tyne above Newcastle, in both of which
situations boulders and gravel from the Cumbrian
mountains constitute a considerable part of the deposit.
For this reason, they would probably be called diluvial
deposits by some writers, and described as raised breaches
by others. The confused aggregation of the pebbles,
sand, &c. is such as to imply sudden and violent in-
undations, which delivered a vast body of detritus in a
short time, and perhaps followed the line of the valley,
but deposited the coarse earthy matters near the sides
where the velocity was lessened, as powerful streams are
always found to do.
H. W. High water mark.
1. Surface of chalk excavated by water in some ancient period.
2. Surface of ancient tertiary sands, or alluvial sediment left in the chalk
valley.
3. Surface of detrital (diluvial) deposit extended over hill and valley.
4. Surface of comparatively modern alluvial deposit in the valley of the
diluvium, consisting of chalk and Hint gravel.
Existing valleys have, then, in many cases, been tra-
versed by floods of water which have left evidence of
their volume, force, and direction. Did they excavate
the valleys? or merely follow the traces left by earlier
watery violence ? Perhaps we must not yet venture to
CBAP. VI. POST-TERTIARY STRATA. 5
propose a general answer to such questions; — there
exist, however, cases which bear very decided evidence
with reference to them. At a little valley in the chalk
of Yorkshire (represented in the diagram, page 4.),
which opens to the sea near Bridlington, we behold, as
in the above sketch, the solid, laminated chalk, gently
declining to the south, excavated in a broad undulation
across the laminae ; over nearly the whole breadth of the
hollow thus occasioned rests an irregular sandy deposit
very much of tertiary aspect ; above this, a thick mass
of diluvial clay with bouldered stones in great confusion ;
the whole surmounted, in places, by a widely laminated
deposit of chalk and flint gravel. Finally, the channel
of the existing little rill is cut, certainly by that rill, in
places through the whole series of deposits, into the solid
chalk beneath. What does this teach us ? First, the
excavation of the chalk by an agent which wholly swept
away the spoils ; secondly, a less turbulent agency in-
troducing sand and gravel, so as partially to fill up the
hollow, but not to cover the parts of the chalk beyond ;
thirdly, a violent impulse of mud and stones brought
from a distance over this valley, and the surfaces for
miles on each side of it ; fourthly, variable but exten-
sive deposits of local gravel ; fifthly, the work of the
actual stream, which gathered in the ancient hollow.
As we know the chalk to have been raised from the
sea, this upward movement may suggest to us the exca-
vation of the rock by oceanic currents, and the partial
deposition of sand; the general accumulation of boulders
and clay demands a general disturbance affecting other,
and even remote, districts; while the mass of chalk flint
gravel seems the natural effect of a more local and less
violent convulsion. In some instances, local gravel of
this description lies both above and below the proper
diluvium.
The interval of time here supposed to occur between
the original excavation of a hollow or valley in the
rocks, and the accumulation in it of the spoils of a
violent commotion of water, is indeterminate. So, in-
B 3
6 A TREATISE ON GEOLOGY. CHAP. VI.
deed, is that between the cessation of the diluvial floods
(whatever they were) and the commencement of the
actual stream. Judging from a survey of examples in
the North of England, we have no doubt that many of
these old river terraces are the remains of estuary deltas
accumulated when the sea had wider dominion ; and we
are strongly impressed with the conviction that it is
possible now to point out in certain sheltered spots the
pebbly shores which, like the modern Spurn, formed the
seaward barrier of thes£ estuaries.
Rock Terraces in Valleys. — There is a peculiar
class of terraces in valleys, which indicate in the same
manner the successive lowering of the level of descend-
ing water (or the successive rising of the land) ; these
terraces are formed by solid rock, with little or no trace
of gravel, or other detritus. Such cases are frequent in
the mining dales of the North of England, which cut
deep into the " Yoredale Rocks/' or upper mountain
limestone series.*
In this varied series of limestone, sandstone, and shale,
almost every limestone which overlies shale projects into
a terrace ; and this sometimes happens to strong sand-
stones similarly circumstanced. It is easy to see that,
as this occurs in many of the branching lesser dales, as
well as in the principal valley, it may plausibly be argued
that the whole effect is due to atmospheric action. It
is probable, however, that this is not a sufficient cause ;
since additional de'bris might thus be expected to be
falling every day, or, at least, more of this accumulation
should remain than we see. We must further observe,
that the presumed levels of the water are only clearly
marked by continuous terraces when the strata dip nearly
in the plane of the valley. It appears, that just as, at
this day, a mountain stream crossing the Yoredale Rocks
forms waterfalls and cliffs at every ledge of limestone,
by the wearing away of the subjacent shales — so the
great currents which anciently flowed in the valley
* Geol. of Yorkshire, vol. ii.
CHAP. VI.
POST- TERTIARY STRATA.
(whatever they were) excavated the softer strata, and
left the hard prominent in terrace cliffs, as in diag.
No. 72.
m. Millstone grit summit resting op shales and grits to I, which is lime-
stone, and projects over *, the subjacent argillaceous beds. The same
occurs with each lower ledge of limestone /, which, with the gritstone g,
usually found beneath, forms a terrace on the hill sides, above a slope of
shale.
A different case occurs in valleys which cross and
enter deeply into thick masses of red sandstone, such
as occurs at Nottingham, Kidderminster, Bridgnorth,
&c. At Bridgnorth, for example, occurs a remarkable
triple row of terraces on the east bank of the Severn,
which appear decisive as to the successive operations by
which changes of relative level of the land and the water
which excavated the valley were brought about.
All the terraces represented in the diagram No. 73.
fifirfd/e Terrfce,
Lower Terrace.
are formed on the face of the thick and easily excavated
red sandstone ; but it is only on the left (east) bank of
the Severn that they are conspicuous, because this is the
salient angle, — for it is always observed among the
common daily effects of inundations, that such terrace-
8 A TREATISE ON GEOLOGY. CHAP. VI.
like levels are only marked on the projecting land, while
the re-entering angle is excavated to vertical or steep
faces.
FLUVIATILE DEPOSITS.
To discuss fully the origin and history of valleys, is
an object reserved for a later section ; we may now pro-
ceed to consider the effects produced, in valleys already
formed, and partially filled with old detritus, by the
water running therein. This is a large subject ; for,
besides the mechanical and chemical actions of the
rivers and brooks, which vary according to the hardness
and nature of the rocks, there is to be examined the
influence of atmospheric vicissitudes, heat and cold,
moisture, dry ness, frost, &c. ; and all the complicated
effects thus occasioned are, in relation to the valleys,
further modified by the form and slope of the urfaces,
the occurrence of lakes, and other circumstances.
Streams flowing along a valley under the various con-
ditions which we observe, are to be considered both as
eroding and transporting agents ; and it is not only con-
ceivable from the admitted instability of the level of land
and sea, but perfectly demonstrated by observation, that
these seemingly opposite effects have been exhibited at
different times by the same river, at the same points of
a valley. Moreover, in the course of the changes of
level of land and sea, some rivers appear to have quitted
their ancient valleys entirely, and to have taken up new
courses corresponding to the new conditions ; and this,
not merely in marshy countries, where a river's course
is almost accidental, but in hilly and rocky districts like
the vicinity of Ludlow or the borders of Teesdale. It
will, therefore, be proper to present as full an account
of the phenomena relating to the actual configuration of
valleys under different circumstances, as a due regard to
reasonable limits will allow. The first thing to be con-
sidered is the degree in which the earth's surface is
wasted by atmospheric changes and aqueous agency.
CHAP. VI. FLUVIATILE DEPOSITS. 9
Waste of the Earth's Surface.
If we consider that the aggregation of rocks and
minerals, whether we regard it as a fruit of chemical or
mechanical actions, is no otherwise fixed or stable, than
as the forces which tend to keep them united are su-
perior to those which from all sides strive to separate
them, we shall be prepared to comprehend how the vari-
ations of these constringent and divellent forces, accord-
ing to heat, moisture, new elementary combinations, &c.,
bring a silent but sure and often rapid decay on all the
structures of man, and on all the mightier monuments
of nature, which are exposed to the ever-changing atmo-
sphere. It is painful to mark the injuries effected by a
few centuries on the richly sculptured arches of the
Normans, the graceful mouldings of the early English
architects, and the rich foliage of the decorated and
later Gothic styles. The changing temperature and
moisture of the air, communicated to the slowly con-
ducting stone, especially on the western and southern
fronts of buildings, bursts the parts near the surface into
powder, or, by introducing a new arrangement of the
particles, separates the external from the internal parts,
and causes the exfoliation or desquamation, as Maccul-
loch calls it, of whole sheets of stone parallel to the
ornamental work of the mason. From these attacks, no
shelter can wholly protect ; the parts of a building
which are below a ledge, often decay the first ; oiling
and painting will only retard the destruction ; and
stones which resist all watery agency, and refuse to
burst with changes of temperature, are secretly eaten
away by the chemical forces of carbonic acid and other
atmospheric influences. What is thought to be more
durable than granite ? Yet this rock is rapidly con-
sumed by the decomposition of its felspar, effected by
carbonic acid gas, — a process which is sometimes con-
spicuous even in Britain (Arran, Muncaster Fell, Cum-
berland), but is rapidly, performed in Auvergne, where
carbonic acid gas issues plentifully from the volcanic
regions.
10 A TREATISE O.V GEOLOGY. CHAP. VI.
Effects of Rain.
Mere rain is a powerful agent of disintegration ; and
its frequent attacks leave at length, in sandstones and
limestones, otherwise very durable, channels of consider-
able dimensions, which have sometimes been ascribed to
other causes. The Devil's Arrows at Boroughbridge,
in Yorkshire, are fluted from this cause from top to
bottom (except on the underhanging sides, where they
cease not far below the summit) — the work of two or
three thousand years: and when we turn from these
monuments of man to the native crags whence they
were cut, "Brinham rocks/' and regard the awful
waste and ruin there, well marked by the pinnacles
and rocking stones which remain in picturesque desola-
tion, it is difficult to avoid indulging a long train of
reflection on the processes of decay and renovation which
thus seem to visit even the inanimate kingdoms of
nature, subjecting all its material elements to continually
renewed combinations.
On the broad limestone floors which support the
noble mountains of Ingleborough, Penyghent, and
Whernside, the rain channels are so abundant as
to have attracted the attention of artists and tourists ;
and on Hutton roof crags, as well as among the lime-
stones of the Alps, they change their direction with
the slope of the ground, collect into larger furrows like
valleys on a broad surface, and terminate in the large
deep fissures, as small valleys often end in a great hollow
of drainage. Another remarkable phenomenon of the
moorland districts of the North of England, which are
formed on the Yoredale series of mountain limestone,
may perhaps admit of the same explanation. These
are the a Swallow " holes, as they are termed, which
range above the outcrop edge of the limestone beds, and
act as drainage channels from the surface to the jointed
calcareous rocks below. These round or irregular pits
and holes are smoothed on the faces and joints of stone,
CHAP, VI. FLUVIAT1LE DEPOSITS. 11
as if by the action of acidulated water, the origin of
which, from the air or the neighbouring vegetable
substances, is not hypothetical.
Effects of Frost.
In no form is the moisture of the atmosphere in-
efficient in accelerating the disintegration of rocks. Col-
lected in the joints and cavities of mountains, it loosens
every thing by its expansion and relaxation; heaped
into enormous glaciers on the summits and down the
valleys of the Alps, it melts at its lower edges and on
the lower surfaces, and thus is ever in motion down-
wards ; augmented from above and diminished from
below, its moving masses plough up the solid earth, and,
by a wonderful and momentarily insensible energy,
pile up, on each side of the icy valley, vast quantities of
blocks of stone and heaps of earth, which slowly ad-
vance into the lower ground ; and these sometimes bear
trees and admit cultivation ; till, in the course of changes
which these rude climates experience, the whole is
transported away by the river which flows beneath, and
space is left for new augmentations from above. Per-
haps no circumstances are so favourable to the collection
of materials for rivers to sweep away, as the glacial
crown and icy valleys of the Alps, accompanied by the
thundering avalanche and frequent landslips, like those
of the Rossberg and the Righi. What further happens
to these materials belongs to the history of the river.
In modern geological theory, the glacier has become
a power not less influential than in other days the dilu-
vial wave ; but it is a power in daily action, of which
the laws are known and the effects measurable. If, in
applying this power to earlier phenomena, we employ
larger measures than nature now works by, or stretch
our lines in directions where glaciers are now unknown,
we are always amenable to the ascertained laws of
glacial action. If we may -now venture to say these
laws are known, let geology gratefully own her obliga-
tion to the cultivators of physical science, who follow-
12 A TREATISE ON GEOLOGY. CHAP. VI.
ing the adventurous steps of Saussure, Charpentier,
and Agassiz, have, with Mallet, Darwin, Martins,
Forbes, and Hopkins, measured, calculated, and imi-
tated the glaciers of many mountains and various
latitudes.
Snow is the parent of glaciers ; mountains are only
their birth-place. Mountain ranges may by their
mere narrowness and steepness furnish no cradle ; they
may be in so dry a region that snows are not abun-
dant, and glaciers grow but feebly, or have such very
gradual slopes as to allow of only very slow downward
movement. But where the climate favours abundant
precipitation of aqueous vapour, on an expanse of high
land amidst loftier peaks, from which steep valleys
lead down to levels much below the snow-line, the
glacier, fed by a perpetual growth from above, and
wasted by an eternal corrosion at the lower extremity,
is modified by continual transformations of interior
substance, and stimulated by a never-ceasing activity of
descent.
It is, in fact, a river of ice, slowly winding its way
from an inexhaustible upper sea (mer de glace), losing
at every instant a part of its substance, and under-
going change in all its features, till, bent, broken, and
dissolved, it gives birth to a stormy river, or floats
away in icebergs to cool far-distant seas.
The substance of a glacier is not snow, nor is it
wholly pure ice ; it consists of the peculiar icy com-
pounds, and manifests the peculiar structures which
are generated when snow, after partial and interrupted
fusion, is re-aggregated by frost. If this fusion be
complete, pure ice is the refrigerated result, and this
appears in glaciers ; but the greater part of the glacial
mass is derived from neve, which is the partially fused
and re-aggregated snow. Such being its composition, its
parts are not incoherent as snow, nor liquid as water,
nor wholly incapable of mutual displacement as solid
ice: but it has something of all these properties; for it
moves in a coherent mass, which is capable of flexure
CHAP. VI. FLUVIATILE DEPOSITS. 13
and compression, but when overstrained breaks into
fissures, and when overpressed is easily crushed. A
mass with such a constitution, placed so as to glide
down the inclined but very unequal channel of an
Alpine valley, may well be expected to present sin-
gular phenomena ; but these phenomena have not
become really known except after long and patient
scrutiny by most excellent observers. Saussure has
rightly conceived the descent of glaciers to be due
essentially to the downward solicitation of gravity ;
Forbes has measured this descent in different levels of
the glacial stream, at different points on its surface, at
the same level, at different depths, and in valleys of
different characters : Hopkins has made experiments at
home, which throw great light on the interrupted or
gradual descent of the icy currents. Without pre-
tending to analyse the innumerable memoirs on gla-
cial movement and its geological effects *, we may
endeavour to sketch the course of a glacier.
Glaciers do not begin to flow from the loftiest peaks
of mountains which rise above the perpetual snow-line :
there the only downward movement of the snow is by
the " avalanche." But in the zone of variable tempe-
rature, where the summer melts the surface of the
snows which winter had collected, the snowy mass be-
comes first bathed with water, and afterwards more or
less consolidated by frost ; it becomes in fact neve, and,
pressed downwards by gravity, begins to glide on its
bed, or on surfaces of separation formed within itself,
more or less parallel to the local slope of the valley.
As we descend below the limit of perpetual snow, the
ground, growing warmer, maintains fluidity below the
glacier f , the descent of which thus becomes less im-
peded. The glacier moves faster in summer than in
* Saussure, Voyages dans le« Alpes ; Agassiz, Etudes sur les Glaciers ;
Forbes, Travels in the Alps, and Phil. Trans ; Mallet, Proc. of Dublin
Geol. Soc. ; Hopkins, Phil. Magazine, Camb. Phil. Trans., may be specially
cited in regard to glacial movement. De la fieche has colfected a body
of information in his Geological Observer.
t The glacier of the Aar was found by Agassiz to fill a Talley 780 feet
deep.
14 A TREATISE ON GEOLOGY. CHAP. VI.
•winter, faster in a warm day than in a cold night,
faster in some seasons than in others. Its motion is
continual though unequal ; faster in the middle than at
the sides, and at the surface than in the deeper parts.
The daily motion at a point of the side of the
glacier of Montanvert was found by Forbes to be 17'5
inches; and at the centre 27' 1 : the general proportion
of the central to the lateral movement being 1375 to
1000.
In one year the average descent of the Mer de glace
was found to be 563 feet. The velocities vary in
different parts of the glacier. In the upper part of
the glacier above Montanvert 674 feet in a year :
lower down 479 : at the te Angle," 770 : and below
Montanvert, 1000.
While thus moving downward, the glacier is subject
to enormous waste by the action of sun and wind.
The waste of the glacier above Montanvert is thus
given by Forbes : —
1842. ft. ins. Daily Rate.
June 26 to June 30, 1 9 4 -1 inches.
July 28, 10 11 3-6
Aug. 9, 14 10 3-7
Sept. 16, 24 6-5 2 -5
Thus only a small portion of the mass which quitted
the snowy wilds at its source is found to reach the
source of the Arve, which, indeed, is formed by a
portion of that waste, which is thus indicated.
In the uppermost parts of the glacier some alter-
nations appear of the more snowy and more icy parts
of the mass ; a kind of stratification. Farther down a
peculiar structure, first distinctly described and ex-
plained by Professor J. Forbes, appears. This is the
veined or ribboned structure, in which lamina of blue
compact ice alternate with other laminae of ice full
of air bubbles, placed in a vertical direction across the
glacier. Lower down these plates are no longer ver-
tical, but dip toward the source of the glacier ; and
they are no longer plane, but curved, so as to present a
CHAP. VI. FLUVIATILE DEPOSITS. 15
concavity toward the same point. " These alternate
bands have all the appearance of being due to the
formation of fissures in the aerated ice or consolidated
neve, which fissures, having been filled with water
drained from the glacier and frozen during winter,
have produced the compact blue bands."
The farther down the glacier we pass the more nu-
merous are the fissures, the more confused the masses
of ice which they separate. This arises from the in-
equality of the bed and sides of the channel ; for thus
lines of tension are produced, and across these lines of
fracture. Very great fissures appear indeed in all parts
of the glacier, but the displacements which these oc-
casion as the masses move onward grow more and more
remarkable, because of the additional effect of waste on
the surface, in the fissures, and below the glacier.
The glacier thus slowly gliding or flowing down its
channel is like a huge grinding and polishing mass.
Not that the ice of which it consists can wear much
even of the limestone and still less of the gneissic bed
of an Alpine or Scandinavian valley, any more than
pitch can wear hard speculum metal ; but the glacier
has under it hard stones, which, set as it were in the
ice, become as effective agents in wearing away the
rock as emery set in the pitch grinds the hardest
compound of copper and tin. Nor is it necessary for
attrition that the stones should be imbedded ; their
grinding effect when loose is considerable.
The sides, also, of the glacial valley are worn by
similar pressure and similar agency. This is actually
seen to be the case at the "angle" on the Mer de
glace (Forbes), and in other situations. In fact
owing to the circumstance that the glaciers in some
seasons extend themselves far beyond their usual flow,
and in other seasons retreat within their ancient limits,
the scratched, grooved, and rounded rocks which they
once covered, and between which they formerly flowed,
are visible in many places, and leave no doubt of the
power with which glaciers grind their channels.
16 A TREATISE ON GEOLOGY. CHAP. VI.
Some of the materials for this grinding are brought
down by the glaciers themselves, on which we com-
monly see, in the middle, or at the sides, or in both
situations, sinuous lines of rock fragments, which,
fbeing traced up to their source, are always found to be
furnished by rocks on the sides or at the junction of
glaciers. These streams of stones are called moraine :
the lateral streams are furnished by rocks on the side
of the flow ; a central stream may be formed by the
union of two lateral moraines when two glaciers
meet and unite, and thus, in the lower part of a
glacier, which is formed of many confluent streams of
ice, many lines of moraine may be traced. Arrived at
the termination of the glacier, these streams lose their
individuality for the most part, and constitute a great
terminal moraine. Such remain, in many situations,
many hundred yards, and even some miles, beyond the
present range of the glacier which transported ihem.
In the diagram (p. 17.) several of the circumstances
which have been mentioned are represented. It cor-
responds to a part of the Mer de glace above Montan-
vert. Three glacial streams are seen to unite, and
three bands of moraine to run down the main glacier
(marked m). The figures indicate the number of feet
in a year which the glacier moves at the point where
they are placed. (From Forbes's Travels in the Alps.)
Amongst the blocks brought down in this singular
manner by glaciers, without attrition, are many of
enormous magnitude; and, as each moraine band is
only fed from certain rocks, it is easy to see that each
has its own mineral character, and may bring detritus
of a totally different quality from even its next in
position. Much more, in this respect, may different
glaciers disagree. If then, as in Spitzbergen, on the
coast of Greenland, and in Tierra del Fuego, the
glacier masses break off in icebergs, it is quite to
be expected they should, after carrying their loads
of rock to greater or lesser distances, deposit them
in groups, each having a certain character and com-
CHAP. VI.
Jardin
FLUVIATILE DEPOSITS.
IT
bination, just as we see to have been determined by
many travellers on the plains of North Germany,
Russia, North America, and the regions west and
north of the Alps.
The height of the origin of a glacier depends,
as already observed, on the elevation of the line of
perpetual snow ; and this varies, not only with latitude,
but by the influence of local causes and peculiarities
of climate. In all the northern zone's it is above the
isothermal lines of 32°, and is so much the more above
this line, as the difference between winter cold and
VOL. II. 0
18 A TREATISE ON GEOLOGY. CHAP. VI.
summer heat is greater. The lower limit of a glacier
depends also on local climates, on the abundance
of snow, the depth of the glacier, the slope of the
valley, and the rapidity of downward motion : for as
the glacier is subject to continual waste from atmo-
spheric and terrestrial agency, the longer its course the
more is it exposed to this waste. With a long course
on a slight declivity glaciers cannot in general descend
so far below the line of perpetual snow, as with
a shorter course in a steeper glen. In the Alps the
steep glaciers of Grindelwald and the valley of Cha-
mouni descend to the level of 5,300 feet below the snow
line, while that of the Aar, on an easier slope, reaches
only to 2,650 feet. In Norway the glaciers descend
4,400 feet ; but in the Pyrenees only 1,700 feet.*
The average slope of the whole glacier from the
Arveyron to the Col du geant is 8° 52', and this is
nearly the inclination of the upper part. In the
middle part, terminating with Montanvert, it varies
from 4° 1 9' to 5° 5', and below Montanvert grows so
steep as to give measures of 12° and 20° 41'.f
The slopes on which glacier movement is possible
are of course somewhat less than those which are
actually traversed by glaciers, because they are unequal.
In some ingenious experiments made in temperatures
which allowed the lower surface of a mass of ice to be
just losing its solidity, Hopkins has found * the follow-
ing relations between the inclination of the surface on
which motion takes place, and the velocity produced.
Up to 12° the velocity is uniform.
Inclination Hourly Motion Inches in
lination. Jn lnches 24 Hours
3° 0-31 7-44
6° 0-52 17-28
9° 0-96 22'32
1 2°§ 2-00
20° The motion became accelerated.
* Hopkins in Proceedings of Geol. Soc. 1852.
+ Forbes's Travels in the Alps,
j Camb. Phil. Trans.
§ Weight diminished to $.
CHAP. VI. FLUVIATILE DEPOSITS. 19
On reducing the inclination to 1° there was still
a perceptible movement. This table may be compared
with Professor Forbes's measures of the velocities ob-
served in the Mer de glace — already given.
Effects of Springs.
Collected in the atmosphere, the rain is filtered
through the sandy rocks, passes rapidly by the joints of
the calcareous strata, and is stopped by the clays, and
by dykes and faults ; it then issuing in springs. But it
is no longer the same water : rain water is, indeed, far
from being in a state of purity ; it contains always car-
bonic acid, frequently some muriatic acid or chloride of
sodium, besides other irregular admixtures. In passing
through the rocks it absorbs lime, oxide of iron, &c.,
and on issuing in the form of springs, loses its excess
of carbonic acid, and again deposits carbonate of lime,
carbonate of iron, &c. From some springs the quantity
of carbonate of lime deposited is enormous ; with the
water of others, sand, gravel, fossil shells, and zoophy-
tic fragments issue. Thus the first operation of water
in and upon the earth is the same, viz. to consume
away the solid substance of the rocks, and either de-
posit it in new situations not far from the source, or
deliver it to flowing streams to be carried further away.
Springs which have an impeded issue to the surface
are the most general cause of landslips : we may con-
c2
2t3 A TREATISE ON GEOLOGY. CHAP. VI.
sider the great fall of the Rossberg as a case of this
kind, the water entering and moistening a particular
layer of strata, all inclined very highly, so as easily to
acquire a descending force, if the cohesion of the parts
were weakened by interposed moisture.
The spring, or rather river (Arve), which issues from
the foot of the Mer de glace, near Mont Blanc, brings a
vast quantity of detritus, which the grinding motion of
the glacier on its rocky bed had broken and rolled to
pebbles.
Effects of Rivers.
A river thus fed by springs of water not pure, par-
tially filled with earthy matter, flowing with various
velocities through soil and among rocks of unequal re-
sisting power, and formed of particles of different mag-
nitude and specific gravity, must exhibit in its long
course a great diversity of appearances. Some rocks
and soils it may corrode chemically, others it may grind
away by its own force and the aid of the sand and par-
ticles which go with it : from steep slopes it, must, in
general, transport away all the loose materials ; but when
its course relents, these must drop and augment the
land. The finest particles are first taken up and last
laid down ; the larger masses make the shortest transit.
Rivers, on whose course no lake interposes its
tranquillising waters, may be considered as constantly
gathering, incessantly transporting, and continually de-
positing earthy materials. It is, of course, princi-
pally in times of flood that they both gather the most
materials, and transport them farthest ; yet even in
the driest season, the feeblest river does act on its
bed, wears by little and little even the hardest stones,
and works its channel deeper or wider. This it does,
partly by the help of some chemical power, from car-
bonic acid, and other admixtures, but principally by
the grinding agency of the sand, pebbles, £c. which it
moves along. In times of flood, these act with violence
CHAP. VI. FLUVIATILE DEPOSITS. 21
like so many hammers on the rocks, ploughing long
channels on their surface, or whirling round and round
in deep pits, especially beneath a fall, or where the
current breaks into eddies over an uneven floor of stone.
This is admirably seen at Stenkrith Bridge in West-
moreland, under the waterfalls about Blair Athol, and in
North Wales, and, indeed, very commonly. Not un-
frequently, on mountain sides or tops, far from any
stream or channel, phenomena somewhat similar oc-
cur, sometimes the effect of rain, sometimes, we may
suppose, the remaining evidence of the former passage
of running water, when the levels of the country were
differently adjusted.
As the slopes are greatest in the upper parts of
valleys (generally), and gradually flatten towards the sea,
it is commonly observed, that, from all the upper parts
of these valleys, rivers abstract large quantities of the
finer matter, and in times of inundation, not a little of
the coarser fragments of rocks ; much of this is deposited
in the lower ground, where the current is more tranquil,
and generally (unless the river be very deep) slower. We
must, indeed, suppose, that every where some wearing
effect on its bed ard sides is produced by every river,
even to its mouth ; but this effect grows almost insensi-
ble far from the high ground which gives birth to the
streams; and long ere we approach the estuary, the wide
flat meadows, which fill the whole breadth of the valley
for miles in length, show what a mass of materials has
been drifted away from the higher ground. Finally,
where the tides and freshes meet, the sediment of both
is disposed to drop ; and some rivers may be viewed as
sending little or no sediment to the sea.
Thus the whole effect of drainage, including all the
preliminary influences of the atmosphere, rain, springs,
&c., is to waste the high ground, and to raise the low ;
to smooth the original ruggedness of the valley in
which it flows, by removing prominences and filling
up hollows ; and notwithstanding the length of years
that rivers have flowed, they have, in general, net yet
c 3
22 A TREATISE ON GEOLOGY. CHAP. VJ.
completed this work : they still continue to add materials
to the lower ground, and, in a few instances, to carry-
out sediment into the sea.
The whole surface of the earth, then, is changing
its level, by the mere precipitations of the atmosphere,
and their subsequent effects ; the high land sinks, and
the low land rises ; but what is the rate of this pro-
gress, we have no complete means of knowing. Few
ancient measures of the height of the land which has
been wasted, or the area of that which has been accumu-
lated, are worthy of notice; we are, however, sure, from
various causes that many valleys have not been altogether
worked out by the rivers now running in them ; and
some natural chronometers have been pointed out by
De Luc and others, which rudely limit the length of
time during which rivers have flowed, and might be
more usefully employed to determine the rate and
amount of fluviatile action.
Rivers certainly did not excavate the whole valley in
which they flow, for they have not even removed the
diluvial detritus brought into them from other drain-
ages, and heaped on the previously excavated rocks.
Rivers have certainly not excavated more than an
inconsiderable part of their valleys, for otherwise the
Lakes of Geneva and Constance would have been long
since filled by the sediments of the Rhone and the
Rhine, which issue from these lakes of that lovely
hue and transparency which marks their total freedom
from all tinge of earthy impurity. When, indeed, we
look at the small but growing deltas of the heads of
the English lakes, as Derwentwater, Windermere, or
Ulswater, and consider the Derwent or the Rothay
in its time of furious flood, we shall be disposed to set
a high value on De Luc's opinion, sanctioned by Cuvier,
Sedgwick, and others, that these deltas prove the com-
paratively recent date of the present disposition of
drainage on the surface of the earth. Rivers flow in
certain channels, because these were previously formed
by convulsions, and violent movements of water ; they
CHAP. VI.
FLUVIATILE DEPOSITS.
have exerted all their force in merely smoothing and
filling the inequalities of their valleys, and this partial
labour they have not accomplished. Will any one,
after this, require to be told that rivers did not make
their own valleys; and only yield to this truth when, on
the chalk and limestone hills, hundreds of valleys are
shown him, down which water never runs, and which,
indeed, have no trace of a channel ?
The upfillings of a valley by the operations of a
river ever tend to be formed in horizontal laminae ;
or at least their surface is generally level in the direc-
tion across the valley, whatever undulations exist be-
neath, and however rapid may be the longitudinal de-
clivity of the valley. This is well seen in many valleys
of the Swiss Jura, the Cotswold Hills, &c.
a. Irregular surface which is the original basis of the valley, b. The sedi-
ment left in it, with a plane surface'as if deposited in a lake. c. The
surface of the valley, uniformly declining among A, the bordering moun-
tains.
AVhen the materials are gravel and coarse sand, de-
posited by an impetuous stream, the general surface
may be level, and yet the laminae beneath are frequently
much inclined, with slopes in various directions, as
Mr. Lyell has noticed with regard to the detritus left
by the stormy waters of the Arve. The same thing
occurs in many of the stratified rocks which appear to
have been accumulated under violent agitation near the
sea-shore. (See Diag. No. 20. p. 61. Vol. I.)
Lakes on the Course of Rivers.
Plane surfaces existing along the course of valleys,
c 4
24- A TREATISE ON GEOLOGY. CHAP. VI.
are commonly, without further question, supposed to be
indicative of the site of ancient lakes, which have
been slowly but completely filled : the supposition is
often correct, but it is. sometimes erroneous. Rapid
rivers, which, in times of inundation, drift coarse ma-
terials down their rough beds, and deposit them in the
expansions of their valleys, are thus partly choked in
their courses, and turned into new channels. Thus
they wander irregularly over a large area, every where
filling it, to about the same height, with a mass of
partial deposits, related to the successive positions of
the channel, which, when unconfined by man, seeks
always the lowest passage. On a cross section of such
a valley, these many distinct streams of gravel and sands
appear nearly as in the annexed diagram.
But such a distribution of materials appears not to
occur in lakes ; whether they receive sediments from
gentle streams, rapid rivers, or sudden inundations.
The reason of this is the great lateral diffusion of
motion in water. Where any great depth of quiet
water is interposed on the path of a river, the lacus-
trine sediments assume various modes of arrangement,
depending on their own fineness, and the velocity of
the water by which they are hurried along.
Deep Lakes on the Course of a River. — On en-
tering a deep lake, the mingled sediment of a river
is subjected to a new influence, — the descending
force of gravity, in addition to the direct horizontal
force imparted by the current, and the lateral move-
ments which it occasions. Each particle, in conse-
CHAP. VI.
FLUVIATILE DEPOSITS.
25
quence, tends to fall from the surface of the water, as
it moves forward, or to the right and left of the point
of entry of the river, and with an accelerated velocity
in the lower part. The path of each particle will be
more or less influenced by the direct, lateral, or vertical
forces, according to its magnitude and weight. Thus,
in the diagram No. 77-, which is to represent a vertical
section along the path of the river as it enters the lake
at the point o, P p p, particles of unequal magni-
77
tude, entering together, describe curves of unequal cur-
vature (they are all related to the same vertical axis,
G) ; the smallest particles being transported furthest,
because they have, proportionally, the largest surface,
and therefore subside most slowly in the water.
On the horizontal plan (No. 78.) the courses of such
deposits are shown to be concentrical, or nearly so, to
the point of influx of the river. By such deposits, the
Delta of the Rhone in the Lake of Geneva, as well as
that of the Derwent in the Lake of Keswick, has been
78
26 A TREATISE ON GEOLOGY. CHAP. VI.
formed ; and, in fact, in every lake a similar explanation
is found applicable. Returning to the vertical section
(No. 77.) we may remark, that the parabolic lines there
given, if considered as representing successive deposi-
tions, require to be modified above and below : above,
by the shifting of (o) the point of influx forward;
below, by the circumstance that the curve ceases at a
certain depth (n), when it coincides with the line n /,
drawn to represent the greatest slope on which the par-
ticles will rest. This slope varies somewhat in particles
of different size and form. Generally speaking, the
structure of these deltas corresponds to the subjoined
diagram ; where the surface a a' is level ; the lines a n',
a' n' are curved, and lie in surfaces of contemporaneous
depositions ; and the lines n b, n bf are straight lines
corresponding to the angle of rest in deep water.
We may further observe, that the unequal dispersion
of the sediments in water causes another modification of
the lamination of such delta. Fine clay is spread far in
the water, and settles at length in a general thin deposit
over the curved and sloping faces a n b, and on the bed
of the lake b b ", after the agitation of the water produced
by the inundation has ceased, and the coarser sediment
has settled to its place.
If, further, we imagine the waters of such a lake to
be calcareous, and liable to slow decomposition, so that
layers of carbonate of lime (or shelly marls) are formed,
these will be still differently arranged. If the cal-
careous matter be generally diffused, the layers will not
radiate from or collect round a point, but be very ge-
nerally spread over the bed of the lake ; and even
when the calcareous substance enters in solution with
a particular stream (as often happens), it mixes with
the water of the lake so extensively as to yield wider
CHAP. VT. FLUVIATILE DEPOSITS. 2?
and more regular deposits than those produced by
merely mechanical agency.
Shallow lakes, subject to fluctuation, produce on the
deposits of coarse gravel and sand, which are brought
into them by rivers, an effect intermediate between
that of deep water and mere fluviatile currents. The
conoidal lamination due to the former is complicated
with variation of the point of influx arising from the
latter ; and thus the upper ends of such lakes become
irregular in outline, and are filled by insulated sub-
aqueous banks.
New Lands at the Mouths of Rivers.
The deposition of sediments from a river happens in
all parts of a valley, even very near to the sources of
the stream, if the slopes of the ground permit ; but as
towards the sea, generally, the inclination becomes the
most gentle, it is there that the finer sediments drop
most abundantly.
The cross section of the ' straths' or narrow meadows
which are produced in the upper parts of valleys are
usually level, or rather a little highest near the edge
of the river, and a little lowest where the new surface
touches the old (technically 'hard') land. The sedi-
ment is rather coarser near the river edge, rather finer
at a distance from it, but every where laminated accord-
ing to the frequency and continuity of the inundations.
Inland seas, which by their position are exempt from
strong tides and currents, become filled with river sedi-
ments, under the same conditions as large lakes. Their
area is contracted, by the addition of new land on the
margin, and their depth is lessened by the diffusion of
fine sediment over the bed, to various distances, accord-
ing to circumstances already pointed out while treating
of lakes.
Some of the most considerable deltas at the mouths
of rivers have been accumulated in seas of this quiet
character ; as the delta of the Nile, which is a continua-
tion of the long valley of Egypt ; the wide sediments at
28 A TREATISE ON GEOLOGY. CHAP. VI.
the mouths of the Po and the Adige, the Rhone, the
Danube, and the Volga, and the numerous streams which
enter the Gulf of Bothnia. The rate of augmentation
of the deltas in the Mediterranean may be determined
by comparing the descriptions of ancient and modern
geographers ; and in some cases verified by roads,
embankments, and other monuments of ancient civilisa-
tion. Mr. Lyell has collected evidence of this nature
in proof of the considerable increase of land at the
mouth of the Rhone, since the era of Roman power,
and even during the last thousand years. " Notre
Dame des Ports was a harbour in 898, but is now a
league from the shore. Psalmodi was an island in 815,
and is now two leagues from the sea. Several old lines
of towers and sea-marks occur at different distances from
the present coast, all indicating the successive retreat of
the sea, for each line has in its turn become useless to
mariners ; which may well be conceived, when we state
that the Tower of Tignaux, erected on the shore so late
as the year 1737, is already a French mile from it." —
(Princip. of Geol., book ii. ch. iv.)
Lower Egypt is the gift of the Nile ; and Herodotus
estimates the sediments borne by the waters of that river
to be so abundant, that if diverted into the Arabian
gulf (Red Sea), they would fill it up in 20,000, or
even 10,000 years. But the further growth of the
great Nilotic delta is checked by a powerful littoral
current, which washes the African coast from Gibraltar
to Egypt. The accession of new land on the coasts of
the Adriatic is perfectly known, since the Augustan
days of Rome, and the rate of increase is inferred to have
been even augmented during the last 200 years. For
by Prony's account (Cuv. Disc, sur les Rev. du Globe),
the shore was 9000 or 10,000 metres from Adria in
the twelfth century ; 18,500 metres in the year 1600 ;
and between 32,000 and 33,000 metres at present ;
which gives an average yearly increase of breadth of
new land of 25 metres from 1200 to 1600, and 70
metres from 1600 to 1800. This augmentation may
CHAP. VI. FLUVIATILE DEPOSITS. 29
probably be ascribed partly to the shallowing of the
whole upper end of the Adriatic, and partly to the al-
terations of .the system of internal drainage, whereby
the rivers, enclosed in extensive embankments, are pre-
vented from depositing much of their sediment upon
the ancient alluvial lands. " From the northernmost
point of the Gulf of Trieste, where the Isonzo enters,
down to the south of Ravenna, there is an uninterrupted
series of recent accessions of land, more than 100 miles
in length, which within the last two thousand years
have increased from ten to twenty miles in breadth." —
(Lyellj book ii. ch. iv.)
The surfaces of deposition from rivers thus entering
quiet seas are in general inclined at a very moderate
angle : at the mouth of the Rhone the water deepens
gradually from four to forty fathoms, in a length of six
or seven miles (^^4-o), or 1 in 160, a "dip" less than the
average inclination of our so-called tc horizontal" strata.
Reasons are assigned for adopting the opinion that the
Adriatic, now so shallow, was once a deep sea ; if so,
the sediments on its bed, raised into dry land,
would constitute a modern formation equal in import-
ance to a large part of the subapennine tertiaries, and,
according to the testimony of Donati, very similar to
them in mineral composition, and the arrangement of
their organic contents. The sediments consist of mud
and calcareous rock, with shells grouped in families, as
we often find, them in ancient strata. The deposits
from the Rhone are ascertained to be in a considerable
degree calcareous, sheets of limestone indeed ; and the
mud of the Nile contains nearly one half of argillaceous
earth, about -*th of carbonate of lime, and -fDth of car-
bon, besides silica, oxide of iron, and carbonate of
magnesia. (Girard, quoted by Lyell.) Materials of
this description may be deposited together ; but little
doubt can exist that, during their solidification, the arrange-
ment of the particles may be so influenced by peculiar
attractions, as to exhibit many of the circumstances
noticed among old sedimentary rocks, as concretions of
so
A TREATISE ON GEOLOGY. CHAP. VI.
limestone, siliceous nodules, segregations of oxide of
iron, &c.
These recent deposits sometimes are laminated like
the old rocks. De Luc notices, near Groningen and
Enckhuysen, the division of the silt deposit into layers,
by the annual growths of grassy turf buried in sedi-
ments. At Enckhuysen, he also observed between the
layers ("couches") of sediment, sand and shells, and
very justly calls attention to the value of this example
of the different effects which may be occasioned by cur-
rents in the modern ocean, comparable to the appearances
in the solid crust of the globe. (Lettres sur 1'Histoire
de la Terre et de rHomme, vol. v. p. 289.)
The general result of atmospheric and fluviatile action
is to equalise the levels of the land, to smooth and mask
the original inequalities of the surface, partly to deepen,
but principally to elevate the valleys. The sediments
which remain on the course of rivers, are all more or
less inclined, and thus, from their sources down to the
sea, and into the sea, a series of inclined deposits, peb-
bly, sandy, argillaceous, and calcareous, may be always
observed. These deposits are subject to much irregular
wasting, by inundations and change of the river chan-
nels, while unconfined by art ; when embanked, a new
order of phenomena arises.
In rivers whose mouths are carried farther and far-
ther continually into the sea. the moving force of the
stream would be lost, did not the level of the water rise
between the sea and the upland. In a state of nature,
this may be sometimes accomplished by successive
depositions of sediment over all the parts of a large sur-
face ; but there are many cases in which it is evident that
rivers tend to embank themselves, by depositing along
the sides of their channels a greater proportion of sedi-
ment than falls elsewhere. This effect is most striking
along streams which bear gravel and coarse sand, as near
Kirkby Lonsdale, and in all mountainous countries.
Rivers which are forced by artificial barriers to flow in
one channel, across a flat alluvial tract, to the sea, ever
CHAP. VI. PLUVIATILE DEPOSITS. 31
tend to raise their own beds, and the embankments,
rising with them for the protection of the marshes, ex-
hibit in the Po and the numerous rivers of Holland, and
the English fens, the singular spectacle of vase volumes
of water, flowing on levels many feet or yards above
the cultivated fields, and even higher than the houses,
•which are often placed below the shelter of the danger-
ous bank. Hardly any thing can be imagined more
awful than the bursting of river banks in the fen lands
of Norfolk, Cambridgeshire, and Lincolnshire.
Estuary and Shore Deposits.
Rivers which discharge themselves into the ocean,
where tides and currents break with a certain regularity
the quiet of its waters, exhibit always at their mouths,
and often along the lower part of their channels, an-
other set of phenomena.
Where the tide enters a river's mouth, and period-
ically combats the freshes, these are " backed" to
certain distances, their motion is nearly destroyed for a
time, and the sediment, which was only suspended by
the agitation of the water, is dropped in the interval of
quiescence. The stronger the current from the land, the
further toward the open sea are its sediments carried, so
that in many cases large quantities pass beyond the
estuaries and float away on the heavier salt water, even
to hundreds of miles from the coast. (Vol. I. p. 342.)
It is easy to perceive that, by this process, every
river connected with a tidal sea is continually repelling
the salt water, and making new land by its fresh-water
deposits. Thus it happens that many towns to which
the tide formerly reached, in the days of Roman sway,
as Ribchester, Norwich, York, are now wholly or par-
tially deserted by it, and large breadths of marsh land
occupy the sites of ancient tide lakes. It is, however,
true, that the tide waters themselves have contributed some
part of the sediment which forms the wide marsh lands
by the Thames and the Medvvay, the enormous breadths
32 A TREATISE ON GEOLOGY. CHAP. VI.
of fen land in Lincolnshire and Cambridgeshire, and
the warp or silt lands on the Trent, Aire, Ouse, and
Derwent. The latter cases are very instructive, be-
cause, by studying in connection the operation of the
sea on the coast of Holderness, and in the tributaries of
the Humber, we see very plainly an important benefit
arising from the enormous waste of that ill-fated coast
(2£ yards per annum for 30 miles from Kilnsea near
Spurn Point to Bridlington). The mean height of this
wasting cliff being taken at only 10 yards, the total
quantity of fine sediment, coarse sand, pebbles and
boulders, falling into the sea in one year = (1760 x 30)
X (10x2^) = 1,188,000 cubic yards. Now, though
not all this mass of sediment must be supposed to enter
the Humber, a considerable portion of it does, and is
turned to good account by the industrious and intelli-
gent inhabitants, in the practice of warping. This
consists essentially in admitting the muddy waters of
the tide at its height, and especially in spring tides,
to flow through proper channels over the low land
adjoining the rivers, so that by stagnation it may drop
its sediment, and again be returned to the Humber.
By frequent repetition of this simple process, the hollow
places near the rivers which are connected with the large
estuary of the Humber are filled up, and thousands of
acres of land raised in level one foot, or eighteen inches ;
and by the addition of most excellent soil augmented in
value from a mere trifle to above the average of the
country. The annual waste of the Holderness coast
alone would cover to the depth of one foot 3,564,000
yards, or about 737 acres. It is often imagined that
all the " warp" of the Yorkshire rivers descends with
the fresh waters : this is so far from the fact that it is
in dry seasons, when the freshes which bring no sediment
do not dilute the rich tide water, that the process is
most successful. The quantity of sediment contained
in the water in a dry summer is great, and chokes the
channel of the Dun about Thome; but in winter the floods
clear it away.
CHAP. VI. FLL VIATILE DEPOSITS. 33
The water of the Rhine transports, according to Mr.
Homer's experiments at Bonn, about Toiyo^th Part °f
its own volume of nmd ; and the extent of alluvial
land, at the mouth of this and other German rivers
•which enter the North Sea, shows that in some earlier
times the conditions of that sea were such as to favour
accumulation, and permit of secure emhankments. But,
for some hundreds of years, a different scene has been
presented ; both natural and artificial barriers have
yielded to the increased pressure of the sea, large tracts
of the main land are lost in the waves, while the islands
that still fringe the coast, relics of a once continuous
tract, have been diminished, and are still undergoing
waste. In 1421, the wide surface of the Bies Bosch
was overwhelmed ; in the thirteenth century the Zuyder
Zee was excavated; and since the year 800, Heligoland,
with other islands, has been nearly swept away ; and,
from Belgium to Jutland, the whole coast has more or
less changed its form in consequence of the incessant
attack of the sea. The history of Nordstrand and other
islands belonging to Sleswig, formed of alluvial land,
which was deposited, fortified, and afterwards devas-
tated by the sea, as given by De Luc (Geol. Travels,
vol. i.), is extremely instructive, and places in a clear
light the contrast between what may be termed the
ordinary processes, whereby sediment is accumulated,
and the extraordinary and wasteful violence of the
North Sea when swollen by high tides, and urged by
powerful north-westerly winds.
By Capt. Denham's survey of the estuary of the
Mersey, it appears that a cubic yard of water of the
flood tide holds 29 cubic inches of mud in suspension,
and a cubic yard of water of the ebbing tide 33 inches;
and the quantity of water moving up and down is
such, that with every ebb tide 48,065 cubic yards of
sediment pass out of the estuary, and are detained by the
banks outside the Rock Narrows, excepting that part
which the succeeding ebb tide disturbs. The excess of
silt thus accumulated from 730 refluxes of the year's
VOL. II. D
34 A TREATISE ON GEOLOGY. CHAP. VI.
tides amounts to 35,087,450 cubic yards ; and the an-
nual tangible deposit over a certain area (allowance being
made for shrinking to half its bulk) is estimated at
11,695,817 cubic yards. The cross set of the Irish
Channel currents limits the extension outwards of the
shoals.
The proportion of sediment thus found in the Mer-
sey (33 cubic inches in a cubic yard = -j^1^, and 4
cubic inches the quantity really deposited = — ^4,)
may perhaps exceed the average for British estuaries,
but is much below some estimates, or rather conjectures,
collected by Mr. Lyell, from Rennell, Sir G. Staunton,
and others. Mr. Everest found in the water of the
Ganges, during rains, -g-^th of its volume of mud ; and
the total annual discharge of sediment into the Bay of
Bengal 6,368,077,440 cubic feet ( = 235,854,720 cubic
yards). (Biblioth. Universelle, 1834). In the Severn
Mr. Ham found on an average 40'3 grains of sediment
in an imperial gallon of water, weighing about lOlb?.,
or 70,000 grains — proportion of weight as 1737 to 1 :
of bulk as 6948 to 1 nearly. (British Association
Reports, 1837.)
If researches of this nature had been prosecuted in
various quarters of the globe, and on rivers flowing over
different classes of rocks, the results would have been of
great value in geological reasoning.
If the country drained by the Ganges is 300,000
square miles, its average waste, from Mr. Everest's data,
would appear to be 78 '6 cubic yards per square mile of
3,097j600 square yards, = -^Vo of a yard in depth,
which is about ^-jth of an inch per annum from the
whole surface of drainage ! In 8000 years this would
be equal to the mass of the English tertiaries, assumed
to be on average 800 feet thick, and to have a surface
of 6000 square miles. The Brahmaputra is supposed
to discharge as much sediment as the Ganges.
On the narrow bed of the quiet Adriatic we behold
the accumulation of conchiferous mud, hardly different
from the subapennine tertiaries which have formerly been
«HAP. VI. KLUVIATILE DEPOSITS.
raised from out of the Mediterranean ; in the wider Bay
of Bengal the diffusion of river sediments is complicated
by tidal action and periodical winds ; and the North Sea
givesus in addition, all the variations of opposing and con-
current tides, entering from opposite points, and diverted
into a variety of channels by the form of the coast and
the inequalities of the sea bed. How various are the
materials therein deposited ! Boulders of granite and
other rocks, drifted from the Cumbrian mountains, fall
from the Yorkshire cliffs, mixed with oolitic limestones,
and chalk and flints ; blocks of Scandinavian rocks are
mixed with the silt along the coasts and islands of Den-
mark ; the Thames brings tertiary, the Tees secondary,
the Dee primary detritus. And all these ingredients,
distributed over the shallow bed by violent currents and
storms, mix with volcanic sediments from the Rhine,
cretaceous mud from the English Channel, and organic
exuviae drifted from the polar circles, or perhaps brought
by the gulf stream from the tropical shores of America.
This remarkable sea bed is so nearly level, that its
slight inequalities are indiscernible when drawn to a true
scale, yet it is really channelled and undulated, and liable
to change in the form of its surface, since we are in-
formed that currents have cut through Heligoland a
channel 60 feet in clepth.
Upon such a surface some organic bodies will be
entombed entire, where they lived and as they died,
(oyster-beds for example, comparable to the fossil oyster-
beds in the oolitic system,) others will be displaced,
and floated to various distances, and deposited in un-
equal states of imperfection. Some bivalve shells
will be found in the rocks which they have bored, others
with valves just held by the ligament, or widely separa-
ted, or broken among pebbles ; fishes entire, or dis-
integrated ; their scales and teeth drifted away by the
currents, and mixed in various combinations with the
unsettled sediments.
Now, most or all of these circumstances may be
paralleled among many of the strata ; especially among
D 2
36 A TREATISE ON GEOLOGY. CHAP. VI.
the tertiary and certain parts of the oolitic systems of
strata ; and a benefit would be conferred on geology if
a careful and accurate survey were made of the mineral
and organic contents of the whole bed of the German
Ocean, for which object its shallowness (it nowhere
exceeding 30 fathoms in depth between the Humber
and the Elbe) offers unusual facilities.
LACUSTRINE DEPOSITS.
Until the publication of Cuvier and Brongniart on the
Environs of Paris, the attention of geologists was but
feebly turned to the study of the numerous fresh-water
deposits, from which, chiefly, we are to learn the an-
cient condition of the land, as the stratified marine
sediments give us information of the contemporaneous
operations in the sea. The general scale of geological
time most certainly is founded on the series of marine
deposits ; but our views of the changing conditions of
the globe will be very imperfect if we are not able to
arrange on the same scale the monuments which remain
of the contemporaneous operations on the land.
At certain points in the series of tertiary strata this
can be done with certainty, or probabilities of various
value, by the legitimate process of observed interstrati-
fication. Marine post-tertiary deposits are some-
times associated with lacustrine sediments, in such a
manner as to determine a few points of union in times
approaching our own day.
But, for a very large proportion of lacustrine forma-
tions, the important data of interposition among marine
strata are wanting, and we are only able to affirm that
the fresh-water sediments are of a date posterior to a
certain marine formation, because they rest upon it.
Some few of these lacustrine formations can, by some
monuments of art and civilisation, be proved to belong
to the period since the creation of man, or even be
limited within certain historical dates ; but there remains
a large class of desiccated lakes whose antiquity must
CHAP. VI. LACUSTRINE DEPOSITS. 3?
remain indefinite, both as regards the historical and
geological scales of time, unless we can find tests inde-
pendent of successive deposition, and of remains of
human art, and yet comparable with natural monuments
both in the ancient and modern, the geological and the
historical, ages of the world.
These are the organic remains of plants and animals ;
and before employing their powerful and abundant tes-
timony in solving the difficulties which attend a classifi-
cation of lacustrine deposits, we must be satisfied on two
points.
1. That faithful observation and correct inferences
have established the fact that to every successive geolo-
gical period belonged characteristic groups of marine
plants and animals, which, in every region yet explored,
may by comparison of selected genera and species,
be discriminated from marine groups of earlier and
later date, whose remains are buried in that region.
2. That through the whole series of strata, the or-
ganic productions of the land and fresh water, which
are mixed with or interposed in beds among marine
strata, present variations of form and structure similarly
related to geological time.
On these points the reader who consults Vol. I. chap. v.
of this work, and considers the drawings and notices
of the organic remains of the several systems of strata,
will probably need no farther proof, except what the
following investigation may yield. There remains, then,
only the difficulty of deciding how far the relics of
plants, shells, fishes, reptiles, and quadrupeds, which
occur in the lacustrine sediments of all ages, are suf-
ficiently numerous and characteristic to justify positive
inferences. This must be left to the judgment of geo-
logists in each particular case, attention being always
directed to the circumstances which accompany the in-
humation of terrestrial and aquatic beings in the present
condition of nature ; for it is very certain that only a
small proportion of land or fresh-water plants, mollus-
D 3
SB A TREATISE ON GEOLOGY. CHAP. VF.
cous, articulated, or vertebral animals, is entombed in
lacustrine sediments.
Purely lacustrine deposits are almost unknown among
any of the stratified rocks of earlier than tertiary date.
The laminated carboniferous limestones of Burdie house,
near Edinburgh, can hardly be admitted an exception,
any more than the calcareous beds of Ardwick and Le-
bot wood, which lie nearly at the top of the coal form-
ation of England. These deposits may indeed be
thought to mark the influence of fresh water predomi-
nating over that of an estuary, such as we suppose to
have received the sediments and vegetable relics which
constitute the coal formation above millstone grit.
Fresh water products again appear in the midst of
the oolitic strata of Yorkshire, accompanied by circum-
stances almost perfectly comparable to those which cha-
racterise the true coal formations ; the same fact is re-
peated in the strata of the Wealden ; tut in each of
these instances the observers most attentive to the
phenomena have decided that they indicate fluviatile not
lacustrine accumulation. The argillaceous and calca-
reous strata of Purbeck and the upper Wealden beds
certainly come nearer to the notion of quiet sediments,
collected in a lake, than any other deposits of secondary
or earlier date.
It is therefore very interesting and important to study
with care and perseverance the varied mineral characters
of the supracretaceous lacustrine sediments; and to
compare the organic contents of those whose place on
the scale of marine strata is known, in order to obtain
rules for judging of the relative age of others which are
less favourably circumstanced. Some of the results of
this study we propose to exemplify, in the following
brief notices of remarkable lacustrine formations.
Upon a general review of the ossiferous deposits of
Europe, we discover two very distinct assemblages of
animal remains, belonging to two obviously distinct and
widely separated geological periods, both anterior to the
CliAP. VI.
LACUSTRINE DEPOSITS.
completion of the present arrangement of organic life,
and main features of physical geography in these regions;
viz. the eocene or lower tertiary mammalia and the ani-
mals of the diluvial period. Between these two groups,
are many assemblages of intermediate character, and in-
termediate geological position (as in Touraine), and later
than all of them are other deposits which (imperfectly)
unite the diluvial to the existing fauna. The mam-
malia whose remains lie in the lower tertiary rocks may
be considered as having lived on the land previously
to the origin of these strata; and those whose relics
fill caverns and gravel-beds obviously belong to a surface
of the earth which has been modified by subsequent
revolutions. We have therefore the following general
classification of the results arrived at in studying fossil
mammalia : —
Modern period
Diluvial era -
Tertiary period
Supracretaceous era -
Secondary period
Pachydermata almost lost ; ruminant
quadrupeds assume preponderance,
as stag, ox, sheep, &c. wolf.
Pachydermata abound, mostly of living
genera ; as mammoth, hippopotamus,
rhinoceros, tapir, horse, pig ; large
feline and bovine quadrupeds and
deer abound.
Pachydermata of extinct and living
genera abound ; as mastodon, hippo-
potamus, rhinoceros, dinotherium,
anthracotherium, horse, deer ; fe-
line quadrupeds not rare.
Pachydermata of extinct genera first
appear, especially palceotherium, ano-
plotherium, lophiodon.
Marsupial quadrupeds * occur iu one
place ( Stonesfield).
Mr. Lyell's classification of tertiary strata (vol. i.
p. 267.) may be easily reduced to this scale, with sufficient
accuracy for our present purpose, by reading for diluvial,
newer pleiocene (according to the tendency of book iv.
* The true relations of the Stonesfield fossil jaws referred by M. Cuvier,
Mr. Owen, and M. Agassiz to marsupialia, mav now be regarded as
settled.
D 4
40 A TREATISE ON GEOLOGY. CHAP. VI.
chapter xi. of the Principles of Geology), for supra-
cretaceous eocene, and by uniting the meiocene and older
pleiocene periods. Upon this basis it appears worth
while to inquire how far the shells found in lacustrine
sediments support the inferences of the change of or-
ganic life,, since the age of the chalk, which have been
drawn from marine remains and bones of terrestrial
quadrupeds, though there is reason to regret the neglect
which this important subject of research has experienced.
Contemporaneous with the marsupials of Stonesfield,
and with the extinct dinosaurians of Sussex and York-
shire, we have freshwater shells in the oolitic coal
series of Whitby (Unionidse) and others of like af-
finities in the Wealden beds.* A valuable addition to
our knowledge of the lacustrine deposits of Purbeck has
lately been given by Professor E. Forbes, f These truly
lacustrine beds rest without gradation on the truly ma-
rine beds of the Portland oolite. These lowest fresh-
water beds contain modern genera, viz., cyprides, val-
vata, limnsea ; above them are the well-known dirt beds
with the bases of cycadeae in situ ; above the dirt beds
are cypridiferous shales, covered by a varied series de-
posited in brackish water, and containing rissoae and
protocardia, and serpulites. Over these come again
purely freshwater beds marked by cypris, valvata, and
limnaea. Then a thin marine band, — followed by another
group of freshwater beds with cypris, valvata, paludina,
planorhis, limnaea, physa, cyclas, all different from their
congeners in the beds below. With them are some
vesicles of chara (gyrogonites). Marine beds cover
these, and are followed by beds of freshwater and brack-
ish origin, with the same cyprides as below, some fishes,
&c. Again marine beds and brackish beds, and a third
series of freshwater strata with a new series of fossils,
cyprides, paludina, physa, limnsea, planorbis, valvata,
cyclas, unio, — all modern genera. Marine strata come
on above.
* Mantell has described a large Unio from these beds.
t Brit. Association Reports, 1850.
CHAP. VI. LACUSTRINE DEPOSITS. 41
" So similar are the generic types of these raollusca to
those of tertiary freshwater strata and those now ex-
isting, that had we only such fossils before us and no
evidence of the infraposition of the rocks in which they
are found, we should be wholly unable to assign them
a definite geological epoch." In the lapse of time
during the deposition of these Purbeck strata, there was
no great physical disturbance there, nor were the sedi-
ments much varied in mineral character, nor were the
generic forms changed, and these forms are yet con-
tinued in other species which are in existence at the
present day in the same physical region. The scale of
lacustrine life, if formed on the mollusca,, would not be
marked by generic steps, as the contemporaneous scale
of marine life is. Perhaps we may admit a similar
result in the case of aquatic and land insecta*, as com-
pared with marine Crustacea.
Eocene, or lower tertiary Period.
The freshwater sediments of the Paris basin, studied
in connection with those of Auvergne, Velay, and Cantal,
offer a very complete view of the eocene lake deposits,
and lead to the conclusion that the marine and fresh-
water strata of that basin are to be considered as
marking sometimes the independent action of the sea
and land floods in one basin, and sometimes their pe-
riodical alternation ; the land floods always coming from
the south, and the marine sediments from the north or
west.
The gypseous deposit of the Paris basin is a repository
of many extinct species of quadrupeds, while of birds
10 species, and several fishes and reptiles, also extinct,
remain to augment the value, and complete the evidence
presented by these precious relics. Four fifths of the
quadrupeds belong to the division of pachydermata; and
nearly all the species are such as might.be supposed
* See Brodie's Fossil Insects.
42 A TltKATISIl ON (.
habitually to frequent the margins of rivers and Jakes.
Ainung them are
(l/iflroj'firtt, Vi'spiTtilii) I'.n •:• irnsis. — Carnivora, Nasua ;
VIVIMTU I'ansii'iisis, and 'J otlu-rs ; Canis, '2 spirirs.- — Mur-
tupiata, Didulphis Cuviiri, and another. — AW, ,///,,, .M\<>\us,
2 Spt-rii's ; Scnirus. — J'(if/ii/,i,riii,ttn, Adapis 1'arisu-nsis ; Chae-
ropntaimis I'.n I'/u'iisis ; Aiioplotlii'i inni roimmiiie, A. sirunda-
riuin ; \iphodon gracili- ; Dirliohuiu- K-porina, 1). iniirina,
D. obliqilii ; * I'al.-iMitlicriuin inai'iiuni, !'. iiu-diuni, I*, rrassimi,
P. latum, P. curium, P. minus, P. miniinuiu, 1'. iiuli-ti-nnina-
tuin; Ix)pliiodon
Among the reptiles are trionyx Parisiensis, emys
(si'ViTal species) crocodilus.
Palms and other endogenous plants accompany these
remains.
In this list of undoubtedly eocene quadrupeds, \vr
remark, with interest, first, the total absence of rumi-
nant animals ; secondly, the great predominance of the
pachydermata ; thirdly, the deficiency in this group
of the elephant, rhinoceros, hippopotamus, mastodon,
and horse ; and, fourthly, the deficiency of larp,e feline
beasts. Ily all these characters the eocene deposits differ
widely from those which have been generally called di-
luvial.
The quarries of llinstead, and cliff's near Hyde,
have yielded to Mr. Pratt, Mr. \\ ' . 1). Fo\, and Mr.
AV. V. llarcourt, bones of palirotheriu, auoplotheri.i,
diieropotamus, and perhaps dicliohune, as Mr. Owen
lias recently stated to the (Icological Society (Proceed-
ings, Nov. 18,'*8). The species are
1'ul.rothri ium nu'dium.
-• crassuni.
• minus.
' curtuin.
a iii'u
Anoplollu'riiiin i-oinnunu'
Chaeropotamui
Bsoundariuoo,
(Tliis was
dosi-ribi'd as a
. )
The agivi-ment of this list with that of the animals
of the eoi responding beds in the Paris basin is remark-
able.
(JU.M-. VI. LA'1' -ITS. 43
All the land and fn- -h-watcr shells of the; basins of
Paris and Hampshire belong to extinct species. In
Jlonlwi'll cliff Mr. Lyc-11 found viv ipara lenta, melania
conica, in< lanopMs r.uinata, M. brevis, planorbis lens,
P. rotumlatus, Litrmaca fusiforrnis, L. longiscata, L.
(olumellaris, potamidutn margaritaceum, neritina,
ancyhis eleirans, unio solandri, mya gregarea, M.plana,
M. Kubangulata, and 2 species of Cyclas. (Geol. Trans.
2d Series, vol. ii.)
The coeval beds of the Paris basin contain Cyclostoma
mumia ; Lirnna>a longiscata, L. elongata, L. acuminata,
L. ovum, bulimus pusillus, &c.
Middle Tertiary Period.
In the upper fresh-water beds of the Paris basin
(considered eocene by Mr. Lyell) occur many shells
closely approaching recent species, as well as those of
the true pala?otherian age. The series is cyclostoma
truncatum, C.elegansantiquum; Potamidum Lamarckii,
I'hiitnrfii.s rotundatus, P. cornu, P. prevostinus ; lim-
naea cornea, L. fabulum, L. ventricosa, L. inflata,
L. cylindrus ; BulimuH pyymfnu*, JL iwhru ; paludina
carinata ; Pupa Defrancii, P. muscorum ; Helix le-
inana, II. desmarestina.
In tlie fresh-water limestone of Saucats, near Bor-
di aux (considered to be of meiocene date by Mr. Lyell
and M. Deshayes, but ranked with later deposits by
M.Dufrenoy,) are found Cyrena Brongniarti, Planorbis
rotunda tux, and Limnita longiscata.
A strong analogy to existing as well as extinct
species appears in the fresh-water deposits of Aix in
Provence, where, according to Lyell and Murchison, the
series of strata in descending order is as follows : —
150 feet of white calcareous nmrls and limestone, calcareous
and siliceous millstone and resinous flints, — containing I'utam-
iilnm Lnmarhii, Hulimus tt-.rtbra, Ii. jiyymaa ; Cyclasgibbosa,
and another species.
The subjacent strata (marls, with fishes, plants, &c.)
run out into a terrace, beneath which gypsum is exten-
44< A TREATISE ON GEOLOGY. CHAP. VF.
siveiy worked. lf In this upper gypsum fossil insects
occur exclusively in a finely laminated bed of 2 inches
in thickness : still lower are two other ranges of gypsum,
the upper one of which alone is worked ; the marls
associated therewith contain nearly as great a quantity
of fishes as those of the upper calcareous zone. Beneath
these are beds of white and pink coloured marlstone
and marl, inclined at 25° to 30°, containing Potamidum
Lamarckii, and Cyclas aquae Sextiae ; and these pass
downwards into a red sandstone and coarse conglomerate.
The fundamental rock of the whole district is a secondary
limestone, with belemnites, gryphites, and terebratulae."
In the contemporaneous lignites of Faveau, Planorbis
cornu, P. rotundatus, Melania scalaris, cyclades, and a
unio occur ; thus rendering the resemblance of the
testacea of this deposit to those of the Upper Parisian
freshwater beds very striking.
The insects of this deposit consist of Coleoptera 20
species, Orthoptera 8, Hemiptera 20, Neuroptera and
larvae, Hymenoptera 8, Lepidoptera 2, Diptera 15;
there are also Arachnida. In the opinion of Marcel de
Serres and Curtis, they are almost entirely included
in genera now living in the south of Europe ; and
several species, as Brachycercus undatus, Acheta cam-
pestris, Forficula parallela, and Pentatoma grisea, are
supposed to be identical with living types.
The freshwater beds of Alhama yielded to colonel
Silver top —
Planorbis rotundatus of the Isle
of Wight.
————— new species.
Bulimus pusillus.
Paludina pusilla.
Paludina desmarestina.
pyramidalis.
Ancylus.
Cypris.
Limiiiea.
And at Teruel. Aragon, occur? —
Limnaea pyramidalis.
In the freshwater beds of Cantal, according to Lyeli
and Murchison, are found —
Potamidum Lamarckii.
CHAP. VI. LACUSTRINE DEPOSITS. 45
Limnaea acuminata, L. columellaris, L. fusiformis, L. longis-
cata, L. inflata, L. cornea, L. fabulum, L. strigosa, L. pa-
lustris antiqua.
Bulimus terebra, B. pygma^us ? ; B. conicus.
Planorbis rotundatus, P. cornu, P. rotundus.
Ancylus elegans.
At Montabusard, a league west of Orleans, in marls
with Limnaea and Planorbis,, at a depth of 18 feet, bones
of land mammalia were found, belonging to cervus, rhino-
ceros, mastodon tapiroi ties, palaeotherium, and lophiodon.
The deposit is thought to be younger than the millstone
freshwater beds of Paris. In freshwater beds in the
Orleannois, are found Mastodon angustidens, M. maxi-
mus ? ; Hippopotamus, Rhinoceros incisivus, R. minutus,
Dinotherium giganteum, Canis, 2 rodentia, and 1
ruminant.
Lacustrine deposits of undoubtedly meiocene age are
scarcely known ;-the list of quadrupeds of this period
must therefore be chiefly collected from the marine beds
of Touraine, Bourdeaux, Dax, &c.
In the marine beds of Touraine, the following
mammalia are found :
Mastodon angustidens.
Hippopotamus major.
minutus.
Rhinoceros (large).
minutus.
Anthracotherium.
Paljeotherium magnum.
Equus.
Lepus.
Cervus, 2 species.
Dinotherium giganteum.
If this list be compared with that of the Paris basin,
we perceive, that mastodon, hippopotamus, rhinoceros,
dinotherium, anthracotherium, and equus, are introduced
among the pachydermata, but without excluding the
pala&otheria, and that ruminant quadrupeds appear.
At Eppelsheim, on the Rhine, the sandy deposit has
yielded a large suite of animal remains, now in the
museum at Darmstadt, which present a general analogy
to those of Touraine, but possibly are of somewhat later
date. Among them are —
CarniTora - Gulo antediluvianus.
Fells aphanistes.
46
A TREATISE ON GEOLOGY.
CHAP. VI.
Felis ogygia.
prisca.
Rodentia - Palaeomys castoroides.
Aulacodon (Chelodus) typus.
Chalicomys Jageri.
Spermophilus superciliosus.
Myoxus (Arctomys) primigenius.
Cricetus (vulgaris ?) fossilis.
Ruminantia - Moschus antiquus.
Cervus anocerus.
• brachycerus.
trigonocerus.
• dicranocerus.
• curtocerus.
Pachydermata - Rhinoceros Schleiermacheri.
- incisivus,
leptodon.
Mastodon angustidens.
arvernensis.
Equus caballus primigenius.
mulus primigenius
asinus primigenius.
Tapirus priscus (Lophiodon Cuv.)
Lophiodon Goldfussii.
Sus antiquus.
— — palaeochaerus.
Dinotherium bavaricum.
— giganteum.
Edentata - - Manis gigantea.
At Georges Gmiind, near Roth, beds of sandy marl
and whitish concretionary limestone crown low hills of
keuper sandstone, and contain subordinate beds of cal-
careous, ferruginous, and bony breccia.
The catalogue of the bones found at this place by
Count Munster and other observers, is thus given by
Meyer (Palaologica, 1832) : —
Dinotherium bavaricum.
Mustek, new species.
Ursus spelaeus.
A new species of carnivora.
Mastodon angustidens.
arvernensis.
Rhinoceros tichorhinus.
• incisivus.
Lophiodon, 2 species.
PaUeotherium magnum.
aurelianense.
Anthracotherium.
Cheeropotamus Sommeringii.
Cervus.
In Mr. Murchison's account of Gmiind (Geol. Pror.
CHAP. VI.
LACUSTRINE DEPOSITS.
1831), it is said that Mr. Clift has also identified frag-
ments of the teeth and bones of the hippopotamus and
ox. From these data the deposit of Gmund appears to
belong to the middle part of the tertiary series.
The slaty marls and limestones of Oeningen, some of
them bituminous and fetid, which rest upon the
" molasse '' of the Rhine valley, contain plants, insecrs,
one shell, numerous fishes, some reptiles, and mammalia,
of which the following is a synopsis, from Meyer, Mur-
chison, &c.
Mammalia : —
Vespertiiio murinus ? v.
fossilis.
Vulpes fossilis. Mantell.
Mus musculus fossilis.
My ox us.
Lagomys.
Anoema oeningensis. Kb'nig.
Reptilia : —
Chelydra serpentina. Bell.
Salamandra gigantea.
Leuciscus pusillus, heter-
urus.
oeningensis.
Tinica leptosomus, fuscata.
Aspius gracilis.
Rhodius latior, elongatus.
Gobio analis.
Cobitis centrochir, cepha-
lotes.
Acanthopsis angustus.
Lebias perpusillus.
Esox lepidotus.
Perca lepidota,
Cottus brevis.
Anguilla pachyura.
Triton palustris ?
Rana.
Bufo.
Fishes (Agassiz) : —
Mr. Murchison's examination of Oeningen led him to
believe that it was to be referred to one of the most
recent tertiary aeras (Geol. Proc. vol. i. p. l69« and
330.) : but M. Agassiz, finding all the numerous fishes
of this deposit to be of extinct species, regarded it as of
higher antiquity than was generally supposed ; and as
both the tortoise (chelydra serpentina Bell) and the fox
are extinct species, while the analogies offered by the
insects, plants, &c., are in most instances merely generic,
this may prove the most satisfactory conclusion.
Insecta - Formicidee, hymenoptera, libellulidae.
Anthrax, cimex, coccinella, blatta, vespa.
Mollusca - Anodon Lavateri. Al. Brong.
Plants - Fraxinus rotundifolia ? Lind.
Acer opulifolium ? a. pseudoplatanus ?
Populus cordifolia.
48 A TREATISE ON GEOLOGY. CHAP VI,
Lakes of the Pleiocene and Diluvial Period.
In this series of deposits, we hardly ever meet with
limestone strata, comparable to those of older date ; there
are sometimes about the accumulations such considerable
marks of local violence of water, as to render it doubtful
whether the bones and shells have not been drifted from
other situations. The lossjbeds of the Rhine probably
belong to this period.
In the newer pleiocene deposits of the valley of the
Elsa in Tuscany, which consist of several hundred feet
of marl, and shelly travertins disposed horizontally, six
living species of testacea were recognised by M. Deshayes :
viz. Paludina impura, Neritina fluviatilis, Succinea
amphibia, Limntza auricularis,L.peregra, and Planorbis
carinatus. (Lyell, book iv. ch. xi.)
The upper Val d'Arno has yielded in its insulated
freshwater deposits a few apparently lacustrine shells
(anodon, paludina, neritina), and a vast number of mam-
malia : of which the following is a list (principally taken
from Mr. Pentland's communication to Mr. Lyell) : —
Fera - - Ursus spelagus.
cultridens.
Viverra valdarnensis.
Canis lupus ?
Canis .
Hyjena radiata.
• fossilis.
Felis, new species.
Rodentia - - Hystrix.
Castor.
Pachydermata - Elephas indicus (or E. primigenius ?)
Mastodon angustidens.
• tapir old es.
Tapir.
Equus.
Sus scrofa.
Rhinoceros leptorhinus.
Hippopotamus major.
fossilis.
Ruminantia - Cervus euryceros?
CHAP. VI. LACUSTRINE DEPOSITS. 49
Cervus valdarnensis.
, new species.
Bos urus.
taurus.
bubalo affinis.
Cuvier also mentions the bones of a lophiodon from
Val d'Arno. There is no geological evidence of the age
of this deposit, except what its organic contents give.
Mr. Lyell ranks it as meiocene : but, to judge from the
list of mammalia, we should be disposed to place it in a
later geological period ; for here are no palaeotheria nor
anoplotheria of the Parisian eocene beds ; no dinotheria
or anthracotheria of the meiocene strata of Touraine,
Kapfnach, &c. ; while on the other hand, elephas indi-
cus, hyaena radiata, and sus scrofa, if all living species !
and Ursus spelaeus, U. cultridens, Hyaena fossilis, Cervus
euryceros, Bos urus, B. taurus, — all frequent in caverns
and diluvial beds, £c., give to the list of animals a very
modern aspect. By some authors (Meyer) the elephant
of Val d'Arno is considered the same as that of the
ordinary diluvium, and by Nesti it is called a new
species (E. meridionalis).
The series of deposits in the upper Val d'Arno is as
under : —
Upper layer - Thick beds of yellow argillaceous sand.
Second - - Thick masses of pebbles.
Third - - Yellow sand, several fathoms thick, the middle
and lower parts rich in bones.
Lowest bed - Thick blue argillaceous marl, with mica, with
bones in the upper part.
The pebbles are largest and most numerous towards
the north ; the coarse sand abounds in the middle, and the
finer sediment in the southern part of the basin, -the sands
and blue marls lie commonly horizontal. The bones lie in
the middle of the valley, on the right side of the Arno.
The lower Val d'Arno contains only marine deposits.
(Bertrand Geslin, Ann. des Sci. Nat.'}
Agreeing in many respects with the freshwater aggre-
gations in Val d'Arno, is a remarkable lacustrine deposit,
of small extent (one fourth of a mile across), resting in a
VOL, II. E
50 A TREATISE OX GEOLOGY. CHAP. VI.
hollow of the new red sandstone formation, at Bielbecks,
south of Market Weigh ton, in Yorkshire. The surface
here is sandy and gravelly ; for the sake of improving
it the lacustrine marls below were excavated by the
farmer, and in the lower part of the pit many bones and
shells were found.
The excavation, being renewed under the direction of
Mr. W. V. Harcourt, was continued to the bottom of
the deposit, presenting in succession —
1. Black sand at the surface.
2. Yellow sand, with a few pebbles of quartz and
sandstone, to the depth of - - - 3 feet.
3. Gravel, composed of chalk, pebbles, and sharp
flints, to a depth of - - - 4£
4. Grey marl, indented by the gravel No. 3, and con-
taining rolled pebbles of quartz, limestone and
sandstone of the carboniferous system, with
chalk and flint, reaching the depth of - - 10
5. Black marl, with minute pebbles of chalk, and
very few flints ; at the bottom a few fragments
of a fine-grained calcareous sandstone, such as
belongs to the neighbouring red marl. — Ex-
treme depth - - 22£
6. Strong blue marl and some clay nodules.
Flint gravel in marl.
Strong blue marl.
Flint gravel in marl.
7. Red marl, the basis of the whole deposit.
No bones, shells, or vegetable remains were found in
Nos. 1, 2, 3. 6. or 7- In the grey marl, No. 4., hones
and tusks and teeth of the elephant, a bone of the
rhinoceros, and a part of the horn of a deer were found,
but no vegetable reliquiae, and no shells. In the black
marl, No. 5, most of the bones, and all the shells and
vegetable reliquiae occurred. The whole collection con-
tained —
Mammalia- Elephas primigenius, tusks, teeth, vertebra?, &c.
Rhinoceros tichorhinus, teeth, tibia, rib.
Bos urus antiquus, cranium, horns, teeth,
bones of leg, &c.
Stag of great size, parts of horn and meta-
tarsal.
CHAP. VI. LACUSTRINE DEPOSITS. 51
Horse of large size, metatarsal and phalangal
bones.
Felis spelaea, lower and upper jaw, and
several leg bones.
Wolf, humerus, radius, and ulna
of right side, right lower
jaw,condyle of the other.
Birds - - Duck, ulna, clavicle, tibia.
Insects - The green elytron of a species of chrysomela was
recognised.
Mollusca - 13 species of land and freshwater shells, every one
identical with species now living in the vicinity,
were found mixed with bones of elephant,
rhinoceros, viz. : —
Helix nemoralis, caperata.
Pupa margin at a.
Succinea amphibia.
Limrieea liaiosa, palustris.
Planorbis complanatus, vortex,
contortus, nitidus, splrorbis.
Valvata cristata.
Tisidium amnicum.
(GeoL of Yorksh. vol. i. 2d edit.)
Mr. Morris, in his Memoir on the Deposits contain-
ing Mammalia in the Valley of the Thames (Magazine
of Xatural History, Oct. 1838), presents a variety of
information bearing on the contemporaneous races of
mammalia and mollusca. The mammalian remains
are of the ' diluvial' sera (elephant, rhinoceros, hippo-
potamus, horse ; ox ; deer, Irish elk ; vole, bear, lion,
hysena, — occurring at Brentford*, Wickham, Ilford*,
Erith, Grays, Whitstable, Copford, Stutton, Harwich,
Gravesend, Nine Elms, Lewisham, Kingslands. The
shells found at Erith, Grays, Copford, Stutton and
Ilford, are thus enumerated : —
Cyrena trigonvla, at Ilford, Erith, Grays, and Stutton.
Cyclas obliqua, Stutton ; C. cornea, Stutton, Grays ; C. pusilla,
Stutton.
Pisidium amnicum, Stutton.
Anodon cypneus, Grays, Stutton, Erith.
Unio pictorum, Grays, Erith, Ilford ; new species Erith (ex-
amined by Mr. G. B. Sowerby).
Succinea amphibia. Grays, Stutton ; S. dblonga, Ilford.
» Mr. Morris remarks that the shells which occur at these localities are
of land and freshwater kinds, not marine, and agrees with the opinions of
Mr. Charlf-sworth. that mammalian remains are more commonly associated
with fluviatile and lacustrine, than marine and detrital deposits, a conclu-
sion which is acquiring fresh importance every day. We have, in fact,
preglacial and postglacial elephantine remains.
E2
52 A TREATISE ON GEOLOGY. CHAP VI.
Helix hortensis, Ilford, Stutton, Grays ; H. lucida, Stutton ;
H.fusca, Stutton ; H.rufescens, Grays and Stutton ; H.palu-
dosa, Stutton ; H. hispida, Erith, Stutton, Grays, Ilford ;
H. trochiformis, Stutton.
Carychium minimum, Stutton, Erith, Grays.
Pupa marginata, Stutton, Erith, Grays ; P. sexdentata, Stutton,
Erith, Grays.
Bulimus lubricus, Stutton.
Umax lubricus, Stutton.
Limnaea auricularia, Ilford, Stutton ; L.peregra, Stutton, Copford,
Ilford ; L. fossaria, Stutton ; L. palustris, Stutton, Grays.
Planorbis carinatus, Stutton, Erith, Grays ; P. corneus, Ilford,
Stutton, Erith ; P. vortex, Stutton, Erith ; P. contortus,
Stutton ; P. imbricatus. Stutton ; P. nitidus, Stutton.
Paludina impura, Stutton, Grays, Erith, Ilford.
Valvata cristata, Stutton ; V. piscinalis, Stutton, Copford ; V.
antiqua, Grays.
Ancylus lacustris, Stutton ; A. 'fiuviatilis, Stutton , Grays.
Thus, the former co-existence of extinct mammalia,
and numerous mollusca not in the smallest degree dif-
ferent from recent species living in the same climates,
which was first ascertained near Market Weigh ton,
and confirmed by Mr. H. Strickland's researches in
Worcestershire, is abundantly established by a large
induction of instances.
Mr. Charlesworth, whose researches on the supracre-
taceous deposits of the eastern counties have led to other
valuable results, presents, in the following general view
of the beds which there occur above the chalk, a simple
classification of the mammaliferous strata. (Reports of
the British Association, for 1836, p. 85.)
SECTION I. Beds containing numerous remains of terrestrial
mammalia : —
1. Superficial gravel, containing bones of land
animals, probably washed out of stratified
deposits.
2. Superficial marine deposits of clay, sand, &c. , in
which the shells, very few in number (10 or
15 species), may all be identified with such as
are now existing. (Brick earth of the river
Nar, Norfolk.)
3. Fluviatile and lacustrine deposits, containing a
considerable number of land and freshwater
CHAP. VI. LACUSTRINE DEPOSITS. 53
shells, with a small proportion of extinct
shells ; (mammalian remains in great abun-
dance. ( Ilford, Copford, and Grays, in Essex,
Stutton in Suffolk.)
4. Mammaliferous crag of Norfolk and Suffolk,
hitherto confounded with " red crag," con-
taining about 80 species of shells; proportion
of extinct species undecided. (Bramerton,
near Norwich ; Southwold and Thorpe in
Suffolk.)
SECTION II. Beds in which few traces of terrestrial mam-
malia have yet been discovered : —
5. Red crag. (It contains mastodon, £c.)
6. Coralline crag.
7. London clay. (It contains quadrumana, &c.)
8. Plastic clay.
Modern Lacustrine Deposits.
Some small lakes are situated at this day, and many
were in former times, so as to receive no considerable
river, but many small runlets from the adjacent slopes.
Under ordinary circumstances, the running streams
throw into lakes only carbonate of lime, and other dis-
solved or suspended matters, which may be diffused
with great equality in the water, and at length settle on
the bottom in one or more layers. In times of abun-
dant rain, coarser sediments are carried into such lakes
from more numerous points of the margin, and thus
the whole lake is filled toward the edges by narrow con-
centric sloping layers of sand and gravel (*), which are
intermixed with layers of finer clay or marly substance
(c), as in the diagram No. 80. ; which also shows,
above several deposits of coarse and fine earthy mate-
E 3
A TREATISE ON GEOLOGY. CHAP. VI.
rials, a single bed of peat (p), composed of the
disintegrated portions of plants swept down from
the land, or produced by vegetable growth on the spot.
Above such a peat-layer it is usual to find in the middle
parts of old lakes very fine marls, with or without
shells, wholly unmixed with coarser sediments. This
circumstance is commonly observed in many of the
ancient lakes of Holderness, where, usually, the middle
part of the lake-bed contains little or no coarse sand or
gravel.
In these fine marls tubular passages, left by the roots
of aquatic plants, frequently appear ; and shells of fresh-
water (or land) species commonly occur. Heads and
horns, and sometimes entire skeletons of the red deer,
the Irish elk, beaver, &c., are buried in the marls or
peat, under circumstances which indicate in some cases
the drifting of their dead bodies by water, and in others
require the supposition that the animals had entered the
lake through choice or fear, and been drowned and
covered by sediments.
Certain fine layers, in freshwater lakps of Denmark,
have been found by Dr. Forchhammer to be composed
of the siliceous matter arising from the disintegration of
the epidermis of some fresh water plants. Seeds of
Chara occur in others ; and it is probable that the cal-
careous substance of this plant has contributed not a
little to the mass of friable marls which lie in many
lakes.
On the coasts of Yorkshire and Lincolnshire, lacus-
trine deposits occur at many points, and present a con-
siderable variety of circumstances as to level above or
below the sea, sandy, marly, or peaty composition ; but
are always governed by the general condition, that they
occupy small hollows on the surface of the diluvial
accumulations. " All the lacustrine deposits containing
peat, which I have inspected in Holderness, agree in
this generalfact, that the peat does not rest immediately
upon the diluvial formation beneath, but is separated
from it by at least one layer of sediment, which is
CHAP. VI. LACrSTRINE DEPOSIT?, 55
seldom without shells. The peat is very generally
confined to a single layer, and shells are seldom found
above it. Supposing that all the varieties which I
have witnessed in different places existed together, the
section would be nearly in the following general
terms : —
*1. Clay, generally of a blue colour and fine texture.
*2. Peat, with various roots and plants, and, in large deposits,
containing abundance of trees ; nuts, horns of deer,
bones of oxen, &c.
3. Clay of different colours, with freshwater limnaese.
4. Peat, as above.
*5. Clay, with freshwater cyclades, &c., and blue phosphate of
iron.
6. Shaly curled bituminous clay.
7. Sandy coarse laminated clay, filling hollows in the diluvial
formation.
Of these the most constant beds appear to be Nos. 1,
2. and 5. ; and in general these constitute the whole
deposit. The peat varies from 5 feet in thickness to
less than so many inches. In a few instances, the lower
clay, No. 5, contains no shells : the species which so
occur are not always the same: Cyclades and small
Paludinae are the most plentiful: Anodons occur at
Skipsea and Owthorn, but I did not find them elsewhere.
Skeletons, and detached horns of the Irish elk (Cervus
euryceros), red deer, and fallow deer, occur in it at
several points." (Geol. of Yorkshire, vol. i.)
A deposit of similar origin in Berwickshire, full of
limnseana and planorbes, envelops horns of the red
deer and bones of the beaver. At Silverdale, near
Burton in Kendal, and at other points round the bay o
Morecambe, deposits from fresh water, probably of
equal antiquity, occur at such levels that the tide might
easily flow over them. They are usually covered by
peat at the surface, and composed of shell marls in
considerable quantity, the shells belonging to Limnsea,
Planorbis, Cyclas, Pisidium, &c., and apparently iden-
tical with existing species. Occasionally the bones of
the great Irish elk occur in these marls (a fine pair is
E 4
56 A TREATISE ON GEOLOGY. CHAP. YI.
to be seen over a doorway in Garstang) ; and from them
Lee states the head of hippopotamus, figured in the
Natural History of Lancashire, to have been derived.
To this period we may also refer the lacustrine and
peat deposits of the Isle of Man, and Ireland, which
have yielded the fine skeletons of the Irish elk, now-
standing in the museums of Edinburgh and Dublin.
The specimen in the Royal Dublin Society's collection
was obtained by archdeacon Maunsell, at Rathcannon,
near Limerick, in shelly marl, 1^ to 2£ feet thick
under peat 1 foot thick, and above blue clay 12 feet
thick or more. According to Mr. Griffith, it is in
these white shelly marls, under peat, that all the skel-
etons of the Irish elk have been found, which agrees
with what has been observed in England. (Outline
of the Geology of Ireland, 1838.)
" At Milk Pond in New Jersey, countless myriads of
bleached shells of the families limnceana and peristo-
miana, analogous to species now living in the adjoining
waters, line and form the shores of the whole circum-
ference of the lake to the length and depth of many
fathoms. Thousands of tons of these small species, in
a state of perfect whiteness, might be used for agricul-
tural purposes. In one case, a perforation was made
1 0 or 12 feet deep, and did not pass through the mass. It
forms the whole basin of the lake, and may at some
future time become a tufaceous lacustrine deposit." (Lea,
Contrib. to Geol. p. 225.)
Mr. Lyell's description of the deposits which are
still proceeding in Bakie Loch, Forfarshire, offers an
excellent type of comparison for analogous deposits of
older date. The sediments in this lake are principally
two beds of calcareous shelly marls, separated by a loose
sandy deposit, covered by a layer of peat with trees,
and resting on fine sand and detritus. The calcareous
matter is supplied by springs, and in general is of a
soft friable nature ; but near the springs it is solidified,
and receives the title of " rock marl/' It is principally
to the vital functions of limnflese, cyelades, and chara>>
CHAP. VI. SUBTERRANEAN FORESTS. 57
that the separation of the calcareous matter from the
water of the lake is owing; and though, in some parts
of the deposit, all trace of their individual forms is
lost, (as in certain coral reefs the organic structure is
obliterated by the decomposition and recondensation of
the mass), there is reason to think the greater part of
the marls is really a congeries of organic exuviae.
Horns of the stag lie in the marls. There are no
unionidae among the shells.
SUBTERRANEAN AND SUBMARINE FORESTS.
Buried Trees on the Course of a River.
It appears that sometimes the violence of river floods
was so great as to sweep down to the tide-line abundance
of land plants, which, covered by sediment, constitute
by their accumulation one kind of buried or subter-
ranean forest. A very interesting case of this kind was
exhibited some years ago, by the deep cutting of a canal
connected with the Aire and Calder navigation, near
Ferrybridge. At a depth of 1 2 feet from the surface
of the fine alluvial sediment, here occupying the broad
valley of the Aire, a quantity of hazel-bushes, roots, and
nuts, with some mosses, freshwater shells (Limnaea,
Planorbis, &c.), and bones of the stag were met with.
In some part of the superjacent sediments, an English
coin was found, and oars of a boat were dug up. Where
a little water entered this peaty and shelly deposit, from
the adjacent upper magnesian limestone, it produced
in the wood a singular petrification ; for the external
bark and wood were unchanged, but the internal
parts of the wood were converted to carbonate of lime,
in which the vegetable structure was perfectly preserved*
In like manner, some of the nuts were altered ; the
shell and the membranes lining it were unchanged ; but
the kernel was converted to carbonate of lime, not crys-
tallised, but retaining the peculiar texture of the recent
fruit.
58 A TREATISE ON GEOLOGY. CHAP. VI.
What renders this curious case of elective molecular
attraction the more decisive, is the fact that, in the
same deposit, sulphuret of iron was found, but only on
the outside of wood ; and, from the whole we learn that,
just as in the chambers of ancient ammonites, and cells
of the bones of saurians, the carbonate of lime has
passed through shell, membrane, and bone, and pene-
trated precisely to those spots where it might seem most
difficult for it to arrive, so, in the comparatively modern
nuts and woods, the same substance has been similarly
transferred to the interior parts, through solid matter ;
while sulphuret of iron in both cases remains on the
outside.
In this particular case, no reasonable doubt can exist
(we conceive) that the peaty deposit, full of land mosses,
hazel-bushes, and freshwater shells, was water-moved,
and covered^ up by fine sediments from the river and
the tide. In some of the old lakes of Holderness, the
same mechanical explanation appears applicable : an
example has been furnished (Waghen in Holderness),
which shows on the same spot, first, the accumulation of
violently agitated water (" diluvium") ; then a deposit
of fine clay, and several layers of peat and trees of differ-
ent kinds ; and over all, the stumps of pines (Scotch fir),
which seem to be in their place and attitude of growth.
On Chat Moss, near Manchester, and in other situa-
tions, the stumps of oak trees appear in the attitude of
growth, though the proof 'of the trees having grown there
is seldom completed by the actual tracing of the roots
laterally, or, what is still more important, downwards
in the clay. Dr. W. Smith has observed, in the deposits
of trees in East Norfolk, differences according to the
soil ; birches and alders on sand, and oak trees on an
argillaceous bed.
In England, Wales, and Scotland, deposits of this
nature, full of trees and vegetable reliquiae of different
kinds, abound much more on the sea coast, and in allu-
vial land which has been deposited within the ancient
sea boundary, than elsewhere. Occasionally, it is true,
CHAP. VI. SUBTERRANEAN FORESTS. 5Q
amidst the mountains of Westmoreland (as in a small
hollow hetween Kirkby Lonsdale and Kendal) and
Scotland (as at the head of Glencoe), trees, rooted or
prostrate, occur mixed with peat; but it is on the
shores, or in the midst of the alluvial plains of York-
shire, Lincolnshire, Cambridgeshire, West and East
Norfolk, Cornwall, Somersetshire, Swansea, Cheshire,
Lancashire, the mouths of the Clyde, Forth, and Tay,
the shores of the Orkneys and Hebrides, that the most
abundant of these buried forests occur. This general
fact justifies the title of Submarine Forests, commonly
applied to them, and is of great importance in reason-
ing on the circumstances of their accumulation. On
the contrary, the greater part of the Irish bogs are in-
land accumulations ; but they occupy the lower plains
of the country, and are often margined by gravel banks,
and abound on the line of the Shannon, which is a
stream of very little declivity.
The trees contained in these deposits are identical
with those now growing in the vicinity, hazel branches
and nuts being very common ; with them are occasion-
ally found fluviatile or lacustrine shells, and bones of deer
and other land animals; but, as far as we know, no marine
mollusca, and seldom marine remains of any kind. The
level of the buried trees is seldom above, but generally
below, the high-water line, and often level with, or not
unfrequently many feet, or even yards, below, low-water.
On the sides of the Humber, below Hull, submarine peat
and trees are found at various depths below low water ;
at the mouth of the Tay, level with it ; at Swansea and
Owthorne, sloping beneath it ; at Sutton, near Alford,
on the Lincolnshire coast, visible only at the lowest
ebb-tides.
As De Luc suggests, with regard to the layers of peat
resting on clay at Rotterdam (Hist, de la Terre et de
tHomme, torn. v. p. 325.), we may believe the deep-
buried trees and peat of the sides of the Humber to have
beendrifted; but this is not the explanation generally pro-
posed by observers, who appear almost without exception
60 A TREATISE ON GEOLOGY. CHAP. VI.
impressed with the belief that the trees grew on the
spots where now they lie prostrate, and often buried
beneath lacustrine or fluviatile (seldom marine) sedi-
ments.
To account for their occurrence, at levels and under cir-
cumstances which now render the growth of trees almost
impossible, it is sometimes supposed that the waste
of the coast has opened to the sea some secluded valley
of peat, which, originally full of moisture, like a sponge,
was raised thereby above the tide-level, but, on the loss
of its seaward barrier, was drained, and sunk considerably.
(Dr. Fleming, in the Quarterly Journal of Science, 1 830.)
But in most cases a real subsidence of vthe land is ap-
pealed to. (Dr. J. Correa de Serra, in Phil. Trans.
1799.)
The evidence in favour of the opinion that the trees
really grew on the spots where now they appear has
generally been thought satisfactory by geological writers;
it is, however, not always so exact and complete as
might be desired, because the circumstances which ac-
company the submarine forests have seldom been care-
fully inquired into with this object in view. Speaking
of the deposits on the shores of the Frith of Tay, Dr
Fleming observes, that c< the upper portion of the clay,
on which the vegetable accumulation immediately rests,
is penetrated by numerous roots, which are changed into
peat and sometimes into iron pyrites/' Stumps of trees,
with roots attached, are observed on the surface of the
peat. Leaves, stems, and roots of equisetacese, graminea?,
and cyperaceae, with roots, leaves, and branches of birch,
hazel, and probably alder, constitute the mass of the
deposit. Hazel nuts without kernel abound. All these
remains are much flattened where they lie horizontally,
but the stems which remain erect retain their cylindrical
figure. This is exactly similar to the condition of stems
of trees in a coal district.
One of the most interesting deposits of peaty matter is
that associated with drifted tin ore, on the coast of Corn-
wall. The deposit of Sandi-ycock, between the parishes
CTTAP. VI. SUBTERRANEAN FORESTS. 61
of St. Austle and St. Blazy, is described by Mr. P.
Rashleigh (GeoL Trans, of Cornwall, vol. ii. p. 281.)
as occupying a vale, which has received drifts from the
sea, as well as from the country above. The series of
beds is thus noticed : —
ft. in.
}. Vegetable mould, about - - . - 0 3
2. Gravel and micaceous sand, mixed with fine loam,
in alternate beds of various depths, making to-
gether - - - - - 8 3
3. Light-coloured clay, with a little mica, and a few
roots of vegetables nearly decayed - - 5 3
4. Black peat - - 4 1
5. Light coloured clay - - - I 4
6. Stiff clay of a light brown colour, with some de-
cayed roots of vegetables. The clay was spotted
with light blue (phosphate of iron) - - 3 10
7. Sea sand and clay mixed . - 3 0
8. Very fine sea sand, together with mica and small
fragments of shells and killas - - - 4 0
9. Coarser sand without shells - - - 6 0
10. A solid black fen, with a few remains of vege-
tables, in which are round globules of the size
of middling shot, but not harder than the fen.
This substance is not made use of as fuel - 2 10
11. Tin ground, and loose stones of all sorts. This
bed varies in thickness from 1 ft. to - 6 0
1 2. Kilias, the general base of the deposit.
At Mount's Bay (Dr. Boase, in Trans. GeoL Soc.
Cornwall), the vegetable deposit is covered, on the sea
coast, by a thick bed of shingles, and inland, appears
beneath a marsh. Elytra of insects appear in this de-
posit, very little changed from their pristine beauty.
De Luc paid great attention to peat deposits and
buried forests in all situations. In his observations on
Holland he makes frequent mention of the low level of
the peat and silt deposits, attributing this circumstance
to a subsidence of those materials in the course of their
desiccation. From M. Van Swinden he learned that
there were lakes in Friesland, which had once been
woods. " Le Fljuessen Meer, par exemple, grand lac
62 A TREATISE ON GEOLOGY. CHAP. VI.
au N. E. de Staveren, e'toit encore un bois en 489 ; et
ce lac, ne pourroit etre desseche aujourd'hui que par
artifice." The soil of Holland, which has been longer
enclosed in banks than Friesland, is on a lower level.
The same explanation applies to the fact, well known
near Lynn, that the land which has been regained since
the Roman sea banks were made is on a higher level,
and of greater value, than that which was enclosed by
the Romans ; and outside of " Marshland," as this tract
is called, the new foreshores are sometimes still higher.
For the following interesting fact we are also indebted
to De Luc : —
" Pres de la Scanie, dans la mer Baltique, est une
isle nominee Bornholm, environnee de collines de sable,
dont le milieu est une vaste Tourbiere, sous laquelle
on trouve quantite de sapins, couches de la circon.
ference au centre. Cette derniere circonstance, pour le
dire en passant, prouve toujours mieux que ces arbres
n'ont pas ete abattus par des inondations, mais par les
vents. Ici, plongeant du haut des collines, et tout le
tour en differens terns, les vents out renverse ces arbres
quand la tourbe a ete profonde et molle, et les ont ainsi
couches de la circonference vers le centre." (Hist, de
la Terre, Partie X. Lettre cxxvi. torn. v. p. 222.)
He applies this fact to explain the origin of coal from
peat, and enters into a short explanation of the mode
by which he conceives the submerged peat was covered
by the argillaceous schistus of its roof, enveloping the
plants then growing on the peat ; remarking that both
elevations and depressions of land happened before the
final desiccation of our continents, and noticing the dif-
ferences of the ancient and living flora of the peat
moors.
Turf Moors.
Submarine and subterranean forests are almost uni-
versally associated with peat, or turf, as it is called in the
north of England, and indeed, generally, they constitute
CHAP. VI. SUBTERRANEAN FORESTS. 63
a considerable portion of the vegetable mass. There
are, however, peat bogs in which no timber lies buried ;
and many of these are daily and hourly augmenting
their area, and increasing their depth, by the growth of
living, and the accumulation of dead, plants. Though
the gigantic (( peat plant," as described by some writers,
is an imaginary creation, sphagnum palustre and other
humble mosses appear to deserve the epithet, and heather
is a very common accompaniment. To an antiseptic
property, imparted by this latter plant, De Luc was
disposed to ascribe the conservation and accumulation of
the various vegetable substances which occur in peat.
There are few shallow lakes in the interior of Eng-
land, and especially in the sandy tracts, like Cheshire
and Nottinghamshire, which are not, in some part or
other, encroached on by the growth of peat. Preceded
by reeds, this substance slowly advances over the sandy
or pebbly bed, and changes to damp and shaking mea-
dows the surface of the upper end of the lake. The
upper end of Derwentwater, Ulswater, and many of
the mountain lakes in Wales, display this growth of
peat completely ; and in many of the wide bogs of
Ireland, the Isle of Man, and Arran, we see the process
finished, and the lakes wholly obliterated in a spongy
carbonaceous mass. In a similar way, many of the val-
leys without lakes, and many of the elevated slopes
and summits of hills, especially on gritstone or granite
surfaces, both in the south of England (Dartmoor),
among the Yorkshire hills (Watercrag, Great Whern-
side), and the Cumbrian mountains (between Skiddaw
and Saddleback), are covered with great depths of peat,
in which trees are never seen. Similar facts appear
among the Grampians, on the mountains near Ennis-
killen, and in other parts of Ireland ; and these exten-
sive tracts of " moor," as De Luc calls the peat deposits
in the north of Germany, are supposed to be no where
so abundant as in northern latitudes.
The bogs of Ireland lie principally in the central
parts, on the wide plains of mountain limestone, and
64 A TREATISE ON GEOLOGY. CHAP. VI.
are supposed to cover one-tenth of the surface of the
island. The thickness of the peat varies from 12 to
above 40 feet; the upper layers being very fibrous,
and showing clearly the structure of the component
plants ; the lowest, a close dense mass, much resembling
coal, and breaking with conchoidal fracture.
Most of the Irish peat bogs contain trees, which in
some cases lie at the bottom ; and it may be thought
that the whole deposit is little else than the accumu-
lated ruins of a long succession of forests ; in other
cases the vegetable mass, whether thus accumulated or
aggregated by drifting, has served as the basis of a new
race of trees, whose roots remain at the surface. And
it is observed, in the "Reports" on the bogs of Ireland,
that in that country it is common to find trees, in the
place and attitude of growth, rooted on peat seven feet
thick. This is especially the case with fir trees (so at
Waghen, in Yorkshire), but oaks are commonly found
to rest on the gravelly basis of the bog. Shelly marls
frequently lie under the peat, and indicate that, in such
cases, the origin of the bog is to be ascribed to the
same process which is constantly going on to extinguish
gome modern lakes. This is the view adopted by the
ordnance surveyors, in their Report on the County of
Londonderry.
Antiquity of Subterranean Forests,
Closely connected with the determination of the
question whether the trees of the " submarine forests"
grew where now they lie enveloped in peat, are facts
ascertained regarding tlie antiquity of certain of these
deposits. De Luc, who looked on phenomena of this
nature with great interest, on account of their import-
ant bearing on two capital points to which his mind
was continually turning, viz. the origin of coal, and
the antiquity of our continents, — notices, a few leagues
from Winsen (near Hamburg), the occurrence of four
or five inches of vegetable earth (terre vegetable) above
CHAP. VI. SUBTERRANEAN FORESTS. 65
ancient burial mounds, composed of heaps of stones, and
inclosing frequently an urn of burnt bones. Observ-
ations nearly similar may be easily made on the heathy
and peaty moors of the elevated parts of the north of
England, where tumuli and ancient roads and cause-
ways are nearly concealed by the growth of vegetables
and aggregation of sands.
But the accumulation of peat from living plants is in
some places so rapid, that it seems endowed with aff
inexhaustible vitality, and may be cut like a copsewood
every fourteen years. And in countries like Hatfield
Chace, which are one wide turf moor, the occurrence
of Roman coins, and axes yet fixed in the wood, appear
to prove at once the fact that the trees grew on the
spot, and fix the historic date of their destruction.
De Luc mentions the discovery of a medal of Gordian
30 feet deep in peat at Groningen. Besides other proofs of
the modern origin of this substance, near Bremervorde,
a small hill of " hard land" or "geest," is stated to be
overgrown with peat, and its title " Isleberg " shows
the modern date of this overgrowth. (Lettres sur THis-
toire de la Terre et de t Homme, torn. v. p. 264.)
" De Luc ascertained that the very site of the abori-
ginal forests of Hercinia, Semana, Ardennes,, and several
others, are now occupied by mosses and fens ; and a
great part of these changes has, with much proba-
bility, been attributed to the strict orders given by
Severus and other emperors to destroy all the wood
in the conquered provinces." (Lyell, Princip. book iii.
ch. xiii.)
One of the most valuable of all the descriptions
of subterranean forests is that of Hatfield Chace in
Yorkshire, by the Rev. A. De la Pryme (1701). Of
180,000 acres here, constituting the largest chace of
red deer in England which belonged to Charles II.,
about half was yearly drowned by vast quantities of
water. Sir Cornelius Vermuiden drained it, at a cost of
400,000/., cutting amongst other great works a new
channel for the tide river Don, which is now called
VOL. II. F
66 A TREATISE ON GEOLOGY. CHAP. VI.
Dutch River, one of the old channels, which entered the
Aire, being now nearly filled up. In the beds of the
rivers, below the marshland, and all round to the high-
lands of Lincolnshire and Yorkshire, are found " vast
multitudes of the roots and trunks of trees of all sizes,
great and small, and of most of the sorts that this
island either formerly did, or that at present it does,
produce ; as firs, oaks, birch, beech, yew, thorn, willow,
ash, &c. ; the roots of all or most of which stand in the
soil in their natural position as<thick as ever they could
grow, as the trunks of most of them lie by their proper
roots. Most of the large trees lie along about a yard
from their roots (to which they evidently belonged, both
by their situation and the sameness of the wood), with
their tops commonly north-east ; though, indeed, the
smaller trees lie almost every way across the former,
some over and others under them." A third part of
the trees were of the fir tribe (some 30 yards long and
more), and in such condition as to be sold for masts
and keels for ships ; oak, black as ebony, abounded, 35
yards and more long, and useful in carpentry ; ash trees
were the only ones found decayed. " Some of the fir
trees, after they were fallen, have shot up large branches
from their sides, which have grown up to the height and
bulk of considerable trees." (Hutton's Abridgment,
Phil. Trans, vol. xxii.)
Many of the trees, and especially the fir trees, have
been burnt, sometimes quite through ; others chopped,
squared, bored through, or split, with large wooden
wedges and stones in them, and broken axe-heads, some-
what like sacrificing axes in shape, and this at depths,
and under circumstances, which exclude all supposition
of their being touched since the destruction of the forest.
1 ' Near a large root in the parish of Hatfield were found
eight or nine coins of some of the Roman emperors, but
exceedingly defaced with time ; and it is very observ-
able, that, on the confines of this low country, between
Burningham and Brumley in Lincolnshire, are several
great hills of loose sand, under which, as they are yearly
CHAP. VI. SUBTERRANEAN FORESTS. 6?
worn and blown away, are discovered many roots of
large firs, with the marks of the axe as fresh upon them
as if they had been cut down only a few weeks." (Hut-
ton's Abridgment, vol. xxii.y
Hazle nuts, and acorns, and fir cones, in great abund-
ance, lie heaped together at the bottom of the soil ;
and f( at the bottom of a new river or drain (almost
100 yards wide and 4 or 5 miles long), were found
old trees squared and cut, rails, stoops (gateposts),
bars, old links of chains, horse-heads, an old axe some-
what like a battle-axe, and two or three coins of Vespa-
sian. But what is more remarkable, is that the very
ground at the bottom of the river was found in some
places to lie in ridges and furrows, thereby showing that
it had been ploughed and tilled informer days" (Ibid.)
Mr. De la Pry me was informed by Mr. E. Canby,
that he had found an oak tree which was 4 yards
across at the base, 3£ yards in the middle, and
2 yards across the top ; and the length of this
fragment (the top was gone) was 40 yards. The same-,
person found a fir tree 36 yards long, and estimated it
to be deficient 15 yards = 51 yards or 153 feet. (The
highest fir tree which has fallen under our observation
in England, is a spruce fir near Fountain's Abbey, stated
to be 1 1 8 feet above the grass.)
The roots of the fir trees have been observed to be in
the sand, and those of the oak trees in clay.
" About 50 years ago," says Mr. De la Pryme, " at
the very bottom of a turf pit, there was found a man,
lying at his length, with his head upon his arm, as in a
common posture of sleep, whose skin being tanned, as it
were, by the moor water, preserved his shape entire ; but
within, his flesh and most of his bones were consumed."
Another case of this nature was brought under the
examination of the author of this volume, by Mr. W.
Casson, of Thorn, who forwarded to the Yorkshire
Museum (1831), the head of a fallow deer, found in the
peat near that place, in a singular condition. The bones
and teeth were, in fact, changed to leather ; the harden-
6'8 A TREATISE ON GEOLOGY. CHAP. VI.
ing earth having been dissolved in the sulphuric acid,
•which is of ordinary occurrence in the peat of Yorkshire,
and the residuary gelatine changed to leather by the
tannin.
The prostration of the trees towards the north-east has
been noticed by Verstegan and De Luc, in the morasses
of the Netherlands and Germany. De Luc, speaking
of the abundance of trees lying below the peat of the
country near Bremervorde, attributes their direction
from S.W. to N.E. to the prevalent winds and rains
from the S.W. ; he also notices the chopping and burn-
ing of the trees. (Lettres, torn, v.)
The conclusion of Mr. De la Pry me, " that the Ro-
mans were the destroyers of all the great woods and
forests which we now find underground in the bottom of
moors and bogs," has been generally adopted by geolo-
gists ; and, with regard to districts where the Roman
sway was impotent or unknown, as Wales, the Isle of
Man, and Ireland, the destruction of many forests is
charged on later conquerors.
If, from the contemplation of evidence concerning the
historic date of subterranean forests furnished by the coins
of Rome, and ruder works of earlier people, we turn to
the monuments of nature, the remains of men and quad-
rupeds, which occasionally present themselves in drains
and other excavations, we find the impression, that the
overthrow of the forests took place in comparatively
modern geological times, materially strengthened. For,
while the bodies of men and women, which have been
found in Solway Moss, in the bogs of Ireland, and other
parts, agree with the evidence of coins, axes, and canoes,
the bones of quadrupeds belong, almost in every instance,
to existing species, as the red and fallow deer, wolf,
beaver, horse, ox, and sheep ; the insects and mollusca,
and all the trees and plants, are of types yet living in
the same vicinity.
Yet, to this general rule are, at least, two seeming
exceptions. The head of a hippopotamus is figured by
Lee, in his History of Lancashire, and noticed as found
CHAP. VI. SUBTERRANEAN FORESTS. 69
under the peat of Lancashire ; works of human art
being also mentioned ; and bones and antlers of the great
extinct elk of Ireland occur in many of the peaty and
marly Deposits of Ireland, the Isle of Man, Lancashire,
and Yorkshire.
Another example of peat deposits connected with
shell marls, which contain quadrupeds of the same
races as those usually supposed to characterise the di-
luvial deposits, occurs at Wittgendorf, near Sprottau
(Silesia). Here, according to Meyer (Pal&ologica) ,
below a thin bed of drifted sand and pebbles, in the lower
parts of a peat deposit, 6 to 8 feet thick, and t also in
marls below, lie bones of Elephas primigenius, oxen,
deer, and fish, with cyclostomse. • In these cases, the
bones and shells show no sign of abrasion.
If we turn to America, and take as an example the
circumstances which accompany the bones of the great
mastodon, the inference previously adopted as to the
age of the peat deposits is confirmed ; for these certainly
date from an epoch subsequent to the dispersion of
diluvial detritus. But, as regards the animal remains,
we learn that a tooth of the mastodon occurred at Fort
M'Henry, near Baltimore, below " diluvium ; " and it is
wall known that, at Big Bone Lick and in New Jersey,
and elsewhere, nearly complete skeletons of Mastodon
giganteus occur in peat and shelly marls of compara-
tively recent date, along with extinct and living species of
oxen and deer.
" From all the facts before me," observes Professor
Rogers, in his Report to the British Association, 1834,
on the geology of North America, " I have little hesi-
tation in giving my opinion, that the extinct gigantic
animals of this continent, the mastodon, elephant, me-
galonyx, megatherium, fossil bos, and fossil cervus,
lived down to a comparatively recent period, and that
some of them were in existence so long ago as the era
anterior to that which covered the greater part of this
continent with diluvium."
The conclusion here presented may very probably, or
F 3
70 A TREATISE ON GEOLOGY. CHAP. VI.
rather certainly, be extended to the Irish elk, of which
the perfect specimens appear to be of comparatively
modern date ; but various fragments, apparently of the
same species, have been detected in the ossiferous caves
arid gravel of northern regions, which contain the mam-
moth and rhinoceros. It will depend upon farther
research, whether this conclusion may be extended to
the extinct elephant, hippopotamus, and rhinoceros, and
to the living stag, ox, horse, and wolf. Concerning
these latter animals, we can only affirm, that it has
been found -impossible to distinguish, by any constant
marks, the specimens found in ancient caverns and
gravel beds, from those now living in the same regions*
CHAP. VII. t'XSTRATIFIED ROCKS. 71
CHAP. VII.
UNSTRATIFIED ROCKS IX THE CRUST OF THE EARTH.
General Remarks.
IN a former part of tliis work* a general view is given
of the reasons which have guided modern geologists in
ascribing to a large class of rocks in the crust of the
earth an original state of igneous fusion ; and in con-
nection with each system of strata some notice is taken
of the distribution and characteristic phenomena of the
igneous rocks locally associated therewith. We must
now take up the subject in a comprehensive point of
view, and elucidate its bearings on the general problem
of the effects of heat in the crust of the globe. We
must unite into one contemplation the history of the
whole series of igneous rocks of every age, from the sup-
posed " fundamental granite" to the volcanic mounds,
heaped up under daily observation. And in this review
care must be taken, both to combine and to analyse the
knowledge of igneous effects, so as to obtain from the
whole investigation trustworthy conclusions regarding
the true condition of the globe, in respect of heat, at
and below the surface, in successive geological periods.
Igneous Origin. — In asserting, concerning granite,
basalt, porphyry, and other rocks, that they are of ig-
neous origin, we must be careful to explain that it is not
meant to affirm, that the materials of which these rocks
consist have not existed together in any other combi-
nation, or been subject to other conditions previously.
* See VoL I. p. 45.
f 4
72 A TREATISE ON GEOLOGY. CHAP. VI I.
Fusion obliterates all or most of the marks of earlier
states of material arrangement, and it is only in a few
cases that direct or indirect evidence remains, by which
to form a correct judgment respecting them. Granite
may have been derived from the fusion of previously
formed strata, a mode of origin confidently ascribed td
certain ancient porphyritic rocks, and probable with re-
gard to some modern lava. The origin of all natural
phenomena is obscure; and with regard to the rocks
above named, and others like them, all that it is now
necessary to admit, is that, through whatever previous
conditions the matter of which they consist has passed,
their last combination, in which they now appear, has
been caused by the agency of heat.
Geological Age. — Heat, though a simple cause, is pro-
ductive of most complicated effects ; not only because of
the unequal action of different degrees of heat, or the
various habitudes of the substances operated on, taken
singly or in combination, but because extraneous circum-
stances, such as pressure, the passage of electrical currents,
&c., affect the condition of the fused mass, and modify
the aspect and arrangement of the solidified products.
The mere antiquity of an igneous rock is a circumstance
absolutely inefficient in accounting for any other of its
characters than the degree of superficial waste, or in-
ternal change by particular agencies; and therefore an
inquiry into the composition and structure of such rocks
must in the first instance include the whole series of
igneous products, if we wish to determine, in the first
place, the conditions to which particular phenomena are
due, and, finally, to obtain a correct general history of
the change of these conditions in the order of geological
time.
Composition. — Reduced to their last molecules, all
igneous rocks appear to be oxides of various metallic
and metalloid bodies, oxygen constituting about one
half of their weight ; silicium, aluminum, magnesium,
calcium, potassium, sodium, iron, &c., are the most
CHAP. VII. UXSTRATIFIED ROCKS. 73
prevalent elementary bases, of even the most dissimilar
rocks.
Silica, or silicium combined with oxygen, is found
abundantly in perhaps every igneous rock, and very
commonly Is combined in definite atomic proportions
with lime, alumina, &c., so as to form a peculiar class
of compounds, called silicates, bisilicates, and trisili-
cates, according to the atomic proportion of silica in the
mineral. So general is this fact that, considering the
easy fusion of most earthy substances in contact with
silica, and the well known fact that in most of the
igneous rocks some superabundant silica remains (in the
state of quartz), we may contemplate the whole mass of
these rocks as having existed in the state of a siliceous
glass, from which, according to the admixture of other
elements, silicates, bisilicates, &c., would be formed by
crystallisation ; or, according to the rate of cooling, pres-
sure, and other circumstances, earthy aggregates, com.
pact stones, or glassy products, result.
According to this view, the differences between some
of the most remarkable igneous rocks are merely in the
degrees of arrangement to which their particles have
been subjected. As lava, obsidian, and pumice, are merely
three states of the same volcanic product, so probably
the granitic, porphyritic, and homogeneous rocks, gene-
rated by heat in ancient times, have derived their
characteristic structures from the conditions of their
solidification. On this subject it is satisfactory to refer
to the capital experiments of Mr. Gregory Watt (Phil.
Trans. 1804), which are among the most interesting
and instructive on record, and have been repeated by
other observers with like success.
Mr. Watt's experiments were made on the amor-
phous basalt of Rowley, in Staffordshire, a fusible, fine-
grained, confusedly crystalline stone, of dark colour, and
opaque. It affects the magnetic needle, and has a spe-
cific gravity of 2'868.
Seven hundred weight of this rock was placed in a
reverberatory furnace, on the elevated part of the inte-
74- A TREATISE ON GEOLOGY. CHAP. VII.
rior, between the fire and the chimney, from whence,
as it melted, it flowed into the deeper part, where the
melted iron is usually collected. When the whole was
melted, it formed a liquid glass, rather tenacious. From
this a large ladleful was taken ; which being allowed to
cool, retained the characters of perfect glass. The fire
was maintained throughout, with gradual diminution,
for more than six hours, after which time the draught
of the chimney was intercepted ; the surface of the glass
was covered with heated sand, and the furnace was filled
with coals, which were consumed very slowly. By these
precautions the heat was so slowly conducted away, that
it was eight days before the mass in the furnace was suf-
ficiently cool to be extracted, and even then it retained
considerable warmth.
The form of the mass, being derived from the bottom
of the furnace, was considerably irregular, approaching
to the shape of a wedge, whose lower angles were
rounded. It was nearly three feet and a half long, two
feet and a half wide, about four inches thick at one end,
and above eighteen inches at the other. From this di-
versity of thickness, and from the unequal action of the
heat of the furnace, too great an irregularity had pre-
vailed in the refrigeration of the glass to permit the
attainment of a homogeneous texture. These circum-
stances might probably have been counteracted by better
devised precautions ; but the inequality of the product
is not to be regretted, since it disclosed some very sin-
gular peculiarities in the arrangement of bodies passing
from a vitreous to a stony state, which might have
remained unobserved, if the desired homogenity of the
result had been obtained.
1. This substance is easily fused into glass, with few
air-bubbles ; it then possesses an undulated conchoidal
fracture, is black and opaque, except in thin fragments,
and harder than felspar. Its sp. gr. is 2'743, and it
has no action on the magnetic needle.
2. The tendency towards arrangement, in the particles
of the fluid glass, is first developed by the formation of
CHAP. VII. U.VSTRATIFIED ROCKS. 75
minute globules, which are generally nearly spherical,
but sometimes elongated, and which are thickly dissemi-
nated through the mass. The colour of these globules
is considerablylighter than that of the glass ; they are
commonly greyish brown, sometimes inclining to cho-
colate-brown ; and when they have been formed near the
interior surface of the cavities in the glass, they project,
and resemble a cluster of small seeds. Their diameter
rarely exceeds a line, and seldom attains that size, as in
general they are so near to one another that their surfaces
touch before they can acquire considerable magnitude.
In the process of cooling, they adapt their form to their
confined situation, fill up every interstice, and finally
present a homogeneous body wholly unlike glass, and
equally unlike the parent basalt. When the union of
the little globules has been imperfectly effected, the
fracture of the mass indicates its structure by numerous
minute conchoidal surfaces, which display the form of
each globule.
But, if the arrangement has extended a little farther,
all these subdivisions are entirely lost ; the mass becomes
perfectly compact ; has an even or a flat conchoidal frac-
ture; is nearly of the same hardness as the glass; is com-
monly of a chocolate colour, graduating into a brownish
black; and the intensity of the colour increases in pro-
portion to the degree to which the arrangement has ex-
tended. Its aspect is rather greasy; and it much
resembles some varieties of jasper in the compactness
of its texture, and in its opacity. Its magnetic action
is extremebly feeble. Sp. gr. 2'938.
8. If the mass were now rapidly cooled, it is obvious
that the result would be the substance just described ;
but if the temperature adapted to the further arrange-
ment of its particles be continued, another change is
immediately commenced, by the progress of which it
acquires a more stony texture, and much greater tena-
city, and its colour deepens as these changes advance,
till it becomes absolutely black. Sometimes this alter-
ation is effected by a gradual transition, the limits of
76 A TREATISE ON GEOLOGY. CHAP. VII.
which cannot be assigned, but more generally by the
formation of secondary spheroids in the heart of the
compact jaspideous substance. These spheroids differ
essentially from those first described ; the centres of their
formation are more remote from each other, and their
magnitude is proportionably greater, sometimes extend-
ing to a diameter of two inches, and seeming only to be
limited by contact with the peripheries of other sphe-
roids. They are radiated, with distinct fibres : some-
times the fibres resemble those of brown haematites, and
sometimes they are fasciculated irregularly, so as to be
very similar in appearance to the argillaceous iron ores
rendered prismatic by torrefaction. They are generally
well defined, and easily separable from the mass they are
engaged in ; and often the fibres divide at equal dis-
tances from the centre, so as to detach portions of the
spheroid in concentric coats. The transverse fracture
of the fibres is compact and fine-grained; the colour
black; and the hardness somewhat inferior to that of
the basaltic glass. When two of the spheroids come
into contact by mutual enlargement, no intermixture of
their fibres seems to take place : they appear equally
impenetrable, and in consequence both are compressed ;
their limits are defined by a plane, at which a separation
readily takes place, and each of the sides is invested
with a rusty colour. When several spheroids come in
contact on the same level, they are formed by mutual
pressure into pretty regular prisms, whose division is
perfectly defined; and when a spheroid is surrounded
on all sides by others, it is compressed into an irregular
polyhedron.
4. The transition from this fibrous state to a different
arrangement seems to be very rapid ; for the centre of
most of the spheroids becomes compact before they attain
the diameter of half an inch. As the fibrous structure
propagates itself by radiating into the unarranged mass,
the compact nucleus which supplies its place gradually
extends till it finally attains the limits of the spheroids;
and the same arrangement pervades the matter compre-
CHAP. VII. UNSTRATIFIED ROCKS. 77
bended between them. The mass has now assumed a
compact stony texture, and possesses great tenacity. Its
hardness is somewhat inferior to that of the glass from
which it was' formed. Its action on the magnetic
needle is very considerable. Sp. grav. 2'938. Its
colour is black, inclining to steel grey ; it is abso-
lutely opaque, and only reflects light from a few minute
points. Though the divisions between the spheroids are
rendered imperceptible to the eye, they are not oblite-
rated, and their rusty surfaces ure often disclosed by an
attempt to fracture the mass.
5. A continuation of the temperature favourable to
arrangement speedily induces another change. The tex-
ture of the mass becomes more granular, its colour rather
more grey, and the brilliant points larger and more nu-
merous; nor is it long before these brilliant molecules
arrange themselves into regular forms ; and, finally, the
whole mass becomes pervaded by thin crystalline laminae,
which intersect it in every direction, and form project-
ing crystals in the cavities. The hardness of the basis
seems to continue nearly the same ; but the aggregate
action of the basis and of the imbedded crystals on the
magnetic needle is prodigiously increased. The sub-
stance now appears to possess some polarity, and minute
fragments of it are suspended by a magnet. Its spe-
cific gravity is somewhat increased, as it is now 2*949.
The crystals contained in it, when examined by a mi-
croscope, appear to be fasciculi of slender prisms, nearly
rectangular, terminated by planes perpendicular to the
axis : they are extremely brilliant; their colour is greenish
black ; they are harder than .glass, and fusible at the
blowpipe ; they are suspended by the action of a magnet.
They are arranged nearly side by side, but not accumu-
lated in thickness, so that they present the appearance
of broad thin laminae; they cross one another at all
angles, but always on nearly the same plane ; and the
lamina thus formed is often three or four lines long, and
from a line to a line and a half broad, but always ex-
tremely thin.
78 A TREATISE ON GEOLOGY. CHAP. VII.
The cavities which existed in the glass are not obli-
terated during the subsequent processes, though changed
on the surfaces.
All these steps in this remarkable experiment may be
compared with parallel instances in the products of vol-
canos.
Thus, from homogeneous obsidian we pass to that va-
riety of it which envelopes small globular concretions ;
and these, by increasing in number and size, convert the
whole into a finely granular mass.
The increase of arrangement is traced through the
lavas with interspersed crystals, becoming decidedly por-
phyritic, until at length we find the whole a congeries
of crystals.
In the older rocks of igneous origin a similar gra-
dation is observable — through homogeneous pitchstone,
pitchstone with globules, to pitchstone with crystals ; —
through claystone, claystone with concretions, with
felspar crystals, with felspar, and quartz crystals ; —
through amorphous felspar, with felspar crystals, with
felspar and quartz crystals, with felspar, quartz, and
hornblende crystals, passing to sienite, — with felspar,
quartz, and mica, scarcely distinct from granite.
The process of crystallisation being determined by the
attractions of the particles, it by no means follows that
the most infusible substance in an igneous fluid, or the
most insoluble in an aqueous solution, should be the
first to crystallise. In either case the particles of dif-
ferent kinds are mixed together; and it depends upon
their relative elective attractions and cohesive forces, what
crystals shall be the first generated. Now as the elective
attractions between particles of different nature, super-
added to the common force of cohesion, will tend to
bring these together with more energy than the homo-
geneous particles, it follows that, in most instances, crystals
compounded of several ingredients should be formed
before those which consist of one simple substance ; and
this seems to explain the remarkable general fact, that
quartz, the most infusible portion of granite, should be
CHAP. VII. UNSTRATIFIED ROCKS. 79
impressed by the previously formed crystals of felspar
and mica.
Nevertheless, the' degree of infusibility of the ingre-
dients must be allowed to have a considerable influence in
determining the order of crystallisation ; because, in the
first place, no crystal can be formed at a heat sufficient
for its entire fusibility ; and, 2dly, the action of heat
seeming to be directly opposed both to elective attraction
and the force of cohesion, if the fusing points of the
materials be very unequal, the refractory substance may
be collected together at a heat too great to permit any
other part of the compound to solidify.
However, as in real solution and fusion we must in
general suppose the materials resolved into their atomic
constituents, the former state of things seems likely to
be most common ; and we ought in consequence to ex-
pect that a portion of the most abundant substance should
remain till the last, and appear as a homogeneous enve-
loping base, whether crystallised or not.
This is remarkably the case with granite, which ap-
pears to have been once a melted fluid, consisting of the
ingredients of felspar and mica, with an excess of silica;
and this often remains not exactly as an enveloping paste,
but in detached and irregular masses, filling the vacuities
between the crystals of felspar and mica.
The rate of cooling is shown by Mr. Watt's experi-
ments to have a most decided influence on the ultimate
condition of earthy masses solidified from igneous fusion ;
the degree of pressure under which the solidification
happens is also influential, by introducing a new force, to
modify the relative molecular attractions. Of this sir
James Hall's experiments on powdered limestone offer a
satisfactory proof. Under a pressure which prevents the
escape of its carbonic acid, limestone undergoes fusion,
and assumes different degrees of consolidation and crys-
tallisation, according to the pressure.
The principal products of volcanic action are known
to us in the form of slender lava currents, and scattered
scoria and ashes, which are all cooled and solidified in
SO A TREATISE ON GEOLOGY. CHAP. VII.
the air with greater rapidity, and under less pressure,
than under the deep roots of a volcanic mountain. The
same materials which, cooled at the surface of the earth,
may be of glassy nature, as obsidian, or cellular, as most
lava, may be, and probably are, at great depths in the
earth's crust, or even under the sea, solidified with struc-
tures as highly crystalline, and in masses as dense, as
those of granite or greenstone. And as in fact we know,
from careful observation, that granites, greenstones, and
other ancient rocks of igneous origin, were solidified
under the pressure of the sea, and generally below a
great mass of strata on its bed, it is not without good
reason that modern geologists have drawn a- line of dis-
tinction between the plutonic rocks, elaborated in the
deep recesses of the earth, and the volcanic products,
which are solidified at or near the surface. This dis-
tinction is indeed one of degree, and may be misapplied,
and is neither complete nor exact when used, as it fre-
quently is, absolutely to separate the consideration of
the old and the modern products of heat. There are crys-
tallised rocks among the products of modern volcanos,
and glassy lavas among the ancient strata ; basalt is
both an ancient and a modern product ; yet, as a general
rule, it is true that the ancient igneous rocks possess those
characters which we may believe to belong to slower
cooling under greater pressure than the lavas which flow
from subaerial volcanos have experienced. A philo-
sophical consideration of the subject will always recog-
nise the essential differences of subterranean, submarine,
and subaerial solidification, as independent of geological
antiquity ; and philosophical observation will gradually
enable us to detect these differences, and to employ
them in tracing the changing conditions of the terra-
queous globe.
Mineral Composition of Unstratvfied Rocks.
In those rocks of igneous origin, which permit the
ingredients of which they are composed to be clearlv
CHAP. VII. UNSTRATIFIED ROCKS. 81
distinguished, one mineral substance is almost universally
found, viz. felspar, which equally abounds in the oldest
granites and most fecent lavas, and occurs, though not
in equal abundance, in rocks of very different weight,
colour, and chemical composition.
Very frequently, though not universally, we detect
another mineral, which, under two forms, has been called
by two distinct names, augite and hornblende (pyroxene
and amphibole of Haiiy). These, by the admirable
researches of Rose and Mitscherlich, have been shown to
acquire their characteristic differences of crystallisation
from the rateof cooling to which they have been subjected.
This protean mineral (which varies greatly in its chemi-
cal composition, by the substitution of different ingre-
dients in combination with silica) constitutes a great
proportion of the substance of greenstone and basalt,
and many congeneric rocks. In general they present
themselves under different circumstances from those
which accompany rocks allied to granite, but offer near
approximations to some of the products of actual volcanos,
the flags of melting furnaces, and other fruits of artificial
heat.
These two minerals, felspar and hornblende, appear
at opposite points of the circle of plutonic and volcanic,
of ancient and modern igneous products ; so that mine-
ralogists have generally found reason to coincide with the
opinions of Cordier and Scrope, and to adopt them as
the elements for a fundamental classification of the rocks
of fusion.
Thus we have two series of rocks, viz. felspathic and
augitic (or hornblendic) rocks, of every geological age,
which, in the extremes (as granite and basalt, among the
ancient, and trachyte and basalt, among the modern
rocks), are perfectly and strikingly different ; but yet
graduate into one another by innumerable variations,
which demonstrate the similarity of origin of all the un-
stratified rocks, and at the same time open wide fields
of inquiry into the causes and effects of their differences.
Besides these predominant and typical minerals, others
VOL. II. G
82 A TREATISE ON GEOLOGY. CHAP. VII.
are frequently observed to modify very much the cha-
racters of igneous rocks, as mica, quartz, garnet, schorl
zircon, olivine, mesotype, epidote, hypersthene, diallage
oxydulous iron, iron pyrites; cyanite, pinite, spodumene>
topaz, beryl, corundum, chromate of iron, prehnitQ
apatite, sphene, molybdena, &c. also occur — in particultf
rocks even abundantly.
According to the views previously established, every
definite chemical mixture of earthy substances in fusion
may be of crystalline, earthy, or vitreous texture; of uni-
form or unequal aspect in its parts ; compact, cellular,
or spumous ; according to the circumstances of solidi-
fication.
The most correct way of describing a rock would be
to give the formula of its mineral composition ; but in
uncrystalline masses this cannot be done, and the che-
mical composition of the same rock is not the same in
even neighbouring parts. Geologists, therefore, whose
more immediate object is to record the principal pheno-
mena associated with rocks, have generally preferred to
give distinctive names to those aspects of solidified ig-
neous products which depend rather on the circumstances
of their solidification, and indicate characteristic physical
conditions of the globe, than on original and real dif-
ferences of their own nature. Thus igneous rocks, with
crystals lying detached in an uncrystallised basis, are
generally called porphyries (as felspar porphyry, clay por-
phyry, trap porphyry, &c.) ; such as have concretions of
quartz or mesotype, in place of those cavities which occur
in modern lavas, are called amygdaloids. This method,
though not strictly scientific, will perhaps always prevail;
because the variations to which these rocks are subject are
such as to baffle all mineralogical strictness ; and because
the most prominent and characteristic circumstances
which accompany them, the form and manner of their
exhibition, their relative antiquity, and the induration,
metamorphism, and elevation of strata, appear but very
indistinctly related to the formulae which represent their
chemical or mineralogical nature. On this ground Dr.
CHAP. VII. TJNSTRATIF1ED ROCKS. 83
MacCulloch justifies his classification ; in which rocks are
often grouped under one head, not because they consist
of the same ingredients, or of similar combinations of
related minerals, hut because they are related in age or
position with regard to the strata, or fulfil other geological
functions in common. In popular language, the mutual
mixture of the crystals constitutes granitic; the sepa-
ration of certain crystals defines the porphyritic; and
peculiar divisional planes characterise the basaltic rocks;
but every one of these circumstances belongs to almost
every combination of felspar, quartz, mica, and hornblende.
If we bear in mind that, in describing phenomena (for
which chiefly technical names are useful), the first ques-
tion to be answered is always with what these phenomena
are associated, we shall see great reason to regret the
neglect of eminent modern observers, who are satisfied
with such terms as " trap " (which may be felspathic or
hornblendic, porphyritic or amygdaloidal), or "granite,"
which may be a binary compound of felspar and quartz ;
a ternary mixture of quartz, felspar and mica ; a quater-
nary union of quartz, felspar, mica, and hornblende, with
or without large interspersed crystals of felspar, tita-
niferous iron, molybdena, apatite, &c., or may have the
mica replaced by other congeneric substances.
This has been forcibly pointed out by Mr. Scrope, who
has proposed a very intelligible plan of arrangement for
volcanic rocks, on the basis of the relative abundance of
the two conspicuous minerals felspar and hornblende (or
augite), which, as before observed, compose the greater
part of the igneous rocks of every age.
Mr. Scrope's synopsis of the species of volcanic rocks
is as follows. (Journal of Science, vol. xxi.)
Trachyte.
A. Compound trachyte with mica, hornblende, or augite,
sometimes both, and grains of titaniferous iron.
B. Simple trachyte, without any visible ingredient but felspar.
C. Quartziferous trachyte, containing numerous crystals of
quartz.
8* A TREATISE ON GEOLOGY. CHAP. VII.
D. Siliceous trachyte, when there appears to have been in-
troduced a great quantity of silex into its compo-
sition.
Greystone.
A. Common, consisting of felspar, augite (or hornblende), and
iron.
B. Leucitic greystone, when leucite supplants the felspar.
C. Melilitic greystone, when melilite is substituted for that
mineral, &c.
Basalt.
A. Common basalt, composed of felspar, augite, and iron.
B. Leucitic, when leucite replaces the felspar.
C. Basalt, with olivine in lieu of felspar.
P. Basalt, with hauyne in lieu of felspar.
E. Ferruginous basalt, when iron is the predominant^ingre-
dient.
R Augitic basalt, when augite or hornblende composes nearly
the whole of the rock.
If our knowledge of the true composition of many of
the old rocks of fusion were perfect, we might propose
for them a scale of classification parallel to that which
Mr. Scrope has given for volcanic rocks. Of such a
scale the following would appear to be the elements : —
DIVISION I. — Felspathic.
Rocks in which the characteristic and most abundant
mineral, felspar, is not at all or but slightly mixed with
hornblende, augite, or their congeners, hypersthene,
diallage, &c,
Ancient. Modern.
Granitic and most porphy- I Trachytic rocks of Von Buch,
ritic rocks. Cordier, Scrope, &c.
DivmoN II.-
\ Augite,
Rocks in which felspar is mixed in nearly equal pro-
portion with hornblende or augite, or their congeners,
hypersthene, diallage, &c.
CHAP. VII. TINSTRATIFIED ROCKS. 85
Ancient. Modern.
Sienitic and greenstone rocks. | Greystones of -Mr. Scrope.
DIVISION III. — ffornblendic, Augitic, $c.
Rocks in which hornblende, augite, hypersthene, or
diallage predominates over the felspar (or its represent-
ative olivine, &c.), and sometimes constitutes the whole
mass of the rock.
Ancient. Modern.
Basaltic series of most authors. | Basaltic series of Scrope.
To each of these three divisions belong the granular,
earthy, compact, resinous, and vitreous textures; por-
phyritic, concretionary, amygdaloidal, and cellular struc-
tures ; cuboidal, prismatic, spheroidal, or irregular divi-
sional planes. (Among recent igneous rocks the cellular
and vitreous structure passes to spumous and filament-
ous : — pumice and scoria.)
To each of them belongs also a peculiar set of stratified
analogues — as gneiss to granite ; some hornblende slates
to greenstones ; wacke to basalt, — which are often em-
barrassing to the observer, and perplexing to the reasoner,
even with the advantage of Mr. LyelTs views of " me-
tamorphic " rocks, (for which consult a future section).
Exposed to the wasting agency of the atmosphere and
water, few resist decomposition, and then yield clay or
sand, often of great fertility.
A classification and nomenclature upon this system,
which should embrace the igneous rocks of all ages,
might, if accepted generally among observers, confer
great benefits on geology. It would, however, neces-
sitate an almost total change of descriptive names, and
would render it indispensable for geologists to study
mineralogy with more care than is now given to that
rather difficult subject. It seems therefore unlikely that
success would attend such a system if proposed at this
time, more especially when we remember how very little
~egard has been paid in England to the classification and
nomenclature of mixed rocks devised by M. Brongniart.
G 3
86 A TREATISE ON GEOLOGY. CHAP. vn.
The system alluded to is, however, well worthy of con-
sideration ; and being much and usefully employed on the
Continent, it appears proper to offer the following brief
account of that portion which relates to our present
subject.
Mixed Rocks.
I. Crystallised isomerous * rocks, in which the constituent
parts are equally blended.
A. Felspathic rocks, the characteristic mineral being
felspar.
1. Granite. — Composed of laminated felspar, quartz,
and mica.
2. Protogine. — Composed of felspar, quartz, steatite,
or talc, or chlorite, with little or no
mica.
3. Pegmatite, or graphic granite. — Consisting of lami-
nated felspar and quartz.
4. Mimose. — Laminated felspar and augite.
B. Hornblendic rocks, the characteristic mineral being
hornblende.
1. Sienite — Composed of laminatedfelspar,hornblende,
and quartz, the first predominating.
One of the most remarkable varieties
is the zircon sienite of Norway.
2. Diabase, er greenstone. — Composed of dissemi-
nated hornblende and compact felspar.
(The orbicular greenstone of Corsica is
a singular variety.)
II. Crystallised anisomerous rocks, in which the constituent
parts are not equally mixed.
A. Basis of serpentine with imbedded minerals.
Ophiolite. — In this occur oxydulous iron, chromate
of iron, diallage, garnet, &c.
B. Basis of cornean, with imbedded minerals.
1. Variolite.— It contains nodules or veins, calcareous
or siliceous, not older than the base.
2. Vakite. — The base is wacke, with augite, mica, &c.
imbedded.
* From ifost equal, and fAt(os, & portion.
CHAP. VII. UNSTRATIFIED ROCKS. 87
C Basis of hornblende or basalt, with imbedded minerals.
1 . Amphibolite. — Basis of hornblende.
2. Basanite. — Basis of compact basalt, with dissemi-
nated minerals. (Basalt is viewed as a
mixture of augite, olivine, and tita-
niferous iron.)
3. Trappite — The basis hard and compact, holds mica,
felspar, &c.
4. Melaphyre, or trap porphyry. — The basis is a black
petrosiliceous hornblende (by other
writers said to be augite), withcrystals
of felspar.
s •< * ' '^\* \vS
D. Basis of petrosilex coloured by hornblende.
1. Porphyry. — Basis a paste red or reddish, with
crystals of felspar.
2. Ophite. — Basis a paste green, with crystals of
felspar.
3. Amygdaloid. — Holds nodules similar (except in
colour) to the basis.
4. Euphotide, or diallage rock. — Encloses crystals of
diallage.
E. Basis of petrosilex, or compact felspar.
1. Eurite. — The disseminated minerals are mica,
felspar, garnets, &c.
2. Leptenite. — Basis of granular felspar with mica and
quartz.
3. Trachyte. — Encloses crystals of glassy felspar in a
dull (earthy) basis.
F. Basis of claystone (an earthy or granular felspar).
1. Clay porphyry. — The enclosed crystals are felspar.
2. Domite porphyry. — The enclosed crystals are mica. ,
G. Basis of pitchstone or obsidian.
Stigmite. — Encloses crystals of felspar (pitchstone por-
phyry of authors).
H. Base undetermined.
Many kinds of lava.
Gradations among Igneous Rocks.
The rocks of igneous origin exhibit among one another
particular relations and gradations, which it is important
to attend to before proceeding to discuss some other
G 4
88 A TREATISE ON GEOLOGY. CHAP. VII.
points of their history. That such variations should take
place among the felspathic rocks on the one hand, and
among the augitic rocks on the other, was quite to be
expected ; but, in fact, between these generally opposite
groups some transitions are known. Dr. Hibbert Ware
has noticed, in his work on the Shetland islands, a
gradation from binary granite (composed of quartz and
felspar) to a basaltic rock (composed of hornblende
and some felspar). He also describes a transition from
felspar porphyry into granite, near Hillswick Ness.
M. Necker informs us, that, in the depth of the
valley of the Valteline, which is in the anticlinal axis of
the Alps north of Como, three great protuberances of
granite arise, surmounted by gneiss and mica schist.
The granite resembles that of the Valorsine and Mit-
tenwald, in the Tyrol, being composed of grey quartz,
white felspar, and black mica, and it throws up veins into
the schistore rocks. This granite is seen to pass, by an
easy gradation, first to common sienite, then to sienitic
hypersthene, some of which has white felspar and black
hypersthene, some green hypersthene, and greenish
felspar. This rock varies also in the size of the grain
and the reflections of the hypersthene ; it partly re-
sembles diallage rock and partly greenstone ; the dif-
ferent varieties are intermingled, and the complication
is augmented by contemporaneous veins of fine-grained
granite entering the hypersthene. The granite is tra-
versed by veins of quartz enclosing black tourmaline.
(Bibliotheque Universelle, 1829.)
This description of M. Necker will remind the geo-
logist who has examined the granitic region of the
Caldew, in Cumberland, of what is there a probable, but
not a certain, inference, the connection of the granite
of the base of Saddleback (which, like that of the Val-
teline, is composed of grey quartz, white felspar, and
black mica) with the hypersthenic sienite of Carrock
Fell, which passes into common sienite, and in places
cannot be distinguished from diallage rock or green-
stone. It often encloses magnetic iron ore.
CHAP, VTL rXSTRATIFrED ROCKS. 89
Von Buch speaks of the transition of <e gabbro," or
diallage rock, to granite, in the island of Kielvig.
No author has given more attention to the transitions
which obtain between the various pyrogenous rocks, nor
with greater success, than the late Dr. MacCulloch, to
whom, indeed, modern geologists owe a large debt, for
the clear and masterly conceptions he has published on
this subject. He tells us, concerning the granites of
Aberdeen shire, which are generally composed of quartz,
felspar, and mica, that in this compound hornblende is
occasionally substituted for mica ; that the quartz some-
times fails; that this hornblendic mass becomes fine-
grained, and passes to greenstone, basalt, and an earthy
trap-like claystone.
Von Dechen, in the German translation of De la
Beche's manual, expresses very clearly the state of
opinion among geological observers, as to the gradation
in character from one to another, of all the igneous
rocks. Thus granite, by replacement of its mica
with hornblende, changes to sienite ; by containing de.
tached felspar crystals, it becomes porphyritic ; and
when reduced to very fine grains, we can entirely cor-
roborate Von Dechen in saying that it is undistinguish-
able from felspar porphyry. A more earthy basis gives
us clay porphyry ; a concentric internal arrangement
makes globular porphyry (kugel porphyr).
Trachyte and porphyritic trachyte are a parallel
series to granite and porphyritic granite ; in an earthy
state they constitute domite.
Sienite and felspar porphyry pass by variation of
mineral ingredients to the vague group of greenstones or
traps, in which hornblende or augite forms a prominent
part of the mass. Of these, diorite (diabase or green-
stone) is related to sienite (the gradations being called
greenstone sienite, and sienitic greenstone, &c.). The
total absence of felspar turns such greenstones into horn-
blende rocks ; diorites with extremely fine grains are
called aphanite, and these cannot often be separated from
the more quartzose rocks, usually called hornstone (by
90 A TREATISE ON GEOLOGY. CHAP. VII.
other writers, petrosilex or cornean). Such a basis, with
crystals of felspar and hornblende, is often called green-
stone porphyry, green porphyry, &c.
Dolerite (mimose of Brongniart) differs from diorite
by holding augite instead of hornblende ; its fine-grained
varieties pass into the vague group of basalts or whin-
stones, which, if restricted to a common definition,
should contain magnetic (titaniferous) iron ore.
Augite alone rarely constitutes a rock (Iherzolite, or
augite rock). The compact rocks, like aphanite, com-
pact basalts, &c., change to amygdaloids, when they
include masses of extraneous minerals, which fill, or
appear to fill, cavities in the stone like those common in
lava ; the basis of many amygdaloids is earthy, and is
called wacke. The rock called gabbro (euphotide, dial-
lage rock, hypersthene rock) is characterised by its
mixed felspar and diallage, or hypersthene ; and ser-
pentine is a corresponding but uncrystallised mates of
felspar and schiller spar, usually enclosing several talc-
ose minerals.
Felspar, the most abundant of all the minerals in
rocks of igneous origin, is variable as to the alkaline
portion of it ; for in some (common felspar), potash —
in others (labradorite), soda — in others (albite), lime
and soda, are found. Von Dechen tells us that common
felspar is mostly found in quartziferous and hornblendic
mixtures ; labradorite in mixtures with augitic minerals ;
while albite, though sometimes mixed with common
felspar, constitutes but a small part of the masses of
igneous rocks.
Chemical Composition of the Rocks of Igneous Origin.
The permutations which take place among the mineral
ingredients of igneous rocks are easily and clearly in-
telligible by considering the chemical composition of
these minerals, which, as in the case of hornblende,
augite, hypersthene, and diallage, often differ from one
another, rather by the crystalline arrangement of the
CHAP. VII.
L'NSTRATIFIED ROCKS.
91
parts, or the substitution of mutually replacing sub-
stances, than by any essential and constant characters.
If the pyrogenous rocks of every age be restored in
imagination to their ancient state of fluidity, and their
chemical constitution in this state be calculated from the
analysis of their integrant minerals, we shall find a
remarkable general analogy running through them,
and be able to perceive, in some instances, the reason
of those gradations in mineral characters, which link
into on*; system a long series of ^seemingly different
rocks.
Mr. De la Beche has given some calculations on this
subject, founded on the assumed elementary compo-
sition of minerals which are of frequent occurrence
in igneous rocks. Some of the analyses adopted by
Mr. De la Beche, and the calculations founded on them,
are appended, with a few additions of our own.
Analysis of Minerals in Igneous Products.
Felspar, common
Felspar, albite
Mica
Hornblende
Augite of Etna f
Tourmaline
Hypersthene
Diallage
1
09
64-0
69-5
46-1
45-7
52-0
36-0
54-2
47-2
Aluminc.
3
.3
%
4
1
13-7
10-1
0-7
io:o
2-0
Oxides of Iron
and Manganese.
S
I!
1
M
6-5
3:5J
-
|
2-0
4:8
1-0
3-2
18-9
19-4
26-2
12-2
3-3
35-8
2-3
3-7
0-8
0-2
0-4
138
13-2
0-3
1-5
13-1
o"i
5-0
18-8
10-0
4-4
14-0
24-4
0-7
0-3
8-8
7'5»
16-7
15-3
24*5
7-4*
In this list, the most variable substances are mica,
augite, and hornblende ; the most uniform is felspar.
The variety of composition in mica is extraordinary,
as the following comparative table, in which the four
» Protoxide of iron.
| Boracic acid.
Black augite analysed by Vauquelin.
92 A TREATISE ON GEOLOGY. CHAP. VII.
varieties are classed according to the predominance of
magnesia, alumina, potash, or oxide of iron, will show.
g|
rf
II
I
o
Analysts
j
£
B
tl)
«
-^
0
co
•<
£
fc
C ~
C
Mica, magnesian of Siberia
aluminous of Sweden
ferruginous of Siberia
Potash of Moscow
42-5
46-4
42-5
40-0
16'0
34-8
11-5
ll'O
26-0
9-0
19'0
7'6
8-8
10-0
20'0
pooop
«J 10 OJOO
07
C'8
Rose.
Hose(3analys.)
Klaproth.
Vauquelin.
171-4
73-3
54'0
4fi-4
40-8
Average
42-8
18-3 |13-5
11-3
10-i!
0-4
= 96-5.
The sum =iOO gives
44-3
18-9J14-9
117
Krii
0-4
= 99-9.
Granite, of the ordinary kind, compounded of quartz,
felspar, and mica, varies greatly in the proportion of
these substances, yet the fused glasses from which these
various products have crystallised, might differ only
by small variations in the proportions of the ingre-
dients.
Granite, composed of quartz 2 parts, felspar 2 parts,
and mica 1 part, would, according to Mr. de la Beche's
calculation, be represented in column 1. of the table
below ; and porphyritic granite, composed of quartz
2 parts, felspar 3 parts, and mica 1 part, in column
2.; and we have added binary gianite (felspar 3 parts,
and quartz 2 parts) in column 3.
1.
2.
3.
Silica -
74-84
73-04
75-1
Alumina
12-80
13-83
10-9
Potash
7-48
8-51
9-8
Magnesia •,
0-99
0-83
Lime - «
0'37
0-44
0-5
Oxide of iron
1-93
1-73
0-4
Oxide of manganese
0-12
o-io
Fluoric acid .
0-21
0-18
i
CHAP. VII. tXSTRATIFIED ROCKS. 93
The differences of the ultimate analysis are very much
smaller than the different aspect of the rocks might lead
us to expect.
Sienite, composed of quartz, felspar, and hornblende,
in equal proportions, would be represented in the sub-
joined table by column 1. ; sienitic granite in which
quartz, felspar, and mica shonld appear in equal pro-
portions, in column 2. ; schorl rock, composed of equal
parts of quartz and schorl, in column 3.
1.
2.
2
Silica ...
69-91
63-96
68-01
Alumina
10-37
14-32
17-91
Potash
4-55
5-94
S3}-*
Lime
4-86
3-73
0-14
Magnesia
6-26
5-94
2-22
Oxide of iron
2-69
4-06
6-85
Oxide of manganese
0-07
0-21
0-81
Fluoric acid
0-50
0-65
1-79
j
Turning from these rocks, in which quartz is an
essential constituent, to those which are composed of
felspar united with hornblende or some analogous mine-
ral, we have greenstone (felspar and hornblende in equal
parts) represented in the first column of the next table ;
1.
2.
S. \
Silica
54-86
59-14
58-42
Alumina
Jo '56
10-59
13-86
Potash -
6-83
6-83
9-10
Lime
7-29
1-13
4-87
Magnesia
9-39
7-00
8-13
Oxide of iron
4-03
12-62
2-00
Oxide of manganese
Fluoric acid
0-11
0-75
Water -
.
0-50
1-05
94 A TREATISE ON GEOLOGY. CHAP. VII.
hypersthene rock (common felspar and hypersthene in
equal parts) in column 2. ; and diallage rock (two thirds
of common felspar and one third of diallage) in co-
lumn S.
Serpentine, usually considered to be little else than
diallage or schiller spar, seems to be well represented in
general, by supposing it a hydrated subsilicate of mag-
nesia ; and contains besides chrome and other metals,
alumina, &c. (in all 5 per cent.) : —
Silica about
Magnesia —
Water —
42
38
15
A subsilicate of magnesia would contain very nearly
the same proportions of the earths.
Among the rocks known to be of volcanic origin,
porphyry, which graduates to claystone, and trachyte, —
trachyte, which in a vitreous state becomes one kind of
obsidian, — and pumice, which is a spumous or filamentous
form of obsidian, — appear to compose one long series of
felspathic compounds, remarkably analogous to granite,
both by mineral variations (where these can be clearly
seen) and by chemical composition. The analysis of
obsidian from Hecla, by Vauquelin, yielded the results
in column 1.; while in column 2. is the composition of
a siliceous granite, which we have calculated from the
proportions of quartz 3 parts, common felspar, albite,
and mica, each 1 part. In column 3. is the analysis of
1.
2.
3.
4.
Silica
78
80-1
•80-2
80-9
Alumina
10
10-0
12-7
10-2
Potash
6
4-0
_
1-7
Lime
1
0-7
1-1
0-2
Magnesia •
_
„
-
0-8
Soda
1-6
1-7
1-9
3-3
Oxide of iron and"!
manganese J
1-0
1-5
1-1
1-5
Fluoric acid & water
•
0-5
-
0-5
CHAP. VII. UNSIRATIFIED ROCKS. 95
Newry pitchstone by Knox (W. Phillips's Mineralogy,
the bitumen and water omitted) ; and in column 4. a
granite of 3 parts quartz, 2 parts albite, and 1 part
mica.
Pumice, the last term of this siliceous series, is stated
by W. Phillips to be composed of
Silica, 77-5. I Potash and soda, 3-0.
Alurr.ina, 17-5. Oxide of iron, 1*7.
As an example of greystone ? lava, Dr. Kennedy's
analysis of the compact lava of Calabria may be
quoted : —
Silica, 51.
Alumina, 19.
Lime, 1 0.
Soda, 4.
Iron, 14.
Water, 1,
Basalt, which belongs to almost every geological age,
constitutes the last term of this series, in which silica
is diminishing continually. It is very irregular in com-
position, as might be expected from the character of its
predominant ingredient, hornblende or augite. The
basalt of Hasenberg in Saxony, according to Klaproth,
is composed of
Silica, 44-50.
Alumina, 16 '75.
Lime, 9 '50.
Magnesia, 2 '25.
Soda, 2-60.
Oxide of iron, 20-00.
Oxide of manganese, 0-12.
Water, 2-00.
That of Staffa, according to Dr. Kennedy,
Silica, 48.
Alumina, 16.
Oxide of iron, 16.
Lime, 9.
Soda, 4.
Muriatic acid, 1 .
Water, &c., 5.
Exterior Forms of the Masses of Igneous Rocks.
Interposed Beds. — As before observed, the want of
stratification is one of the characters of igneous rocks ;
yet there are two cases in which they show themselves
in stratiform masses, which seem exceptions to the rule.
9f) A TREATISE ON GEOLOGY. CHAP. VII.
One of these cases has been amply treated by Maccul-
loch, in his account of the Island of Skye j examples
of it may also be seen in the Island of Arran. The
reader will understand the circumstance alluded to by
consulting /#. 81., where (d) represents a vertical mass
of igneous rock (greenstone in Skye, pitchstone in Arran)
filling & fissure in the stratified rocks, (s) and (6) an in-
terposed bed of the same igneous rock forced in a liquid
state between two strata originally contiguous.
The second case is exemplified in the basaltic form-
ation of Antrim, where several successive layers of melted
rock, the fruit of many successive volcanic eruptions,
are heaped one upon another as they were originally
poured out upon ihe chalky bed of the ancient sea. —
Another example is furnished by the volcanic rock called
fe toadstone*," which in Derbyshire lies in one or more
stratiformed masses between the beds of mountain lime-
stone, as probably it was originally effused on the sur-
face of the lower bed. The upper surface of the toad-
stone is said to be remarkably undulated. A third example
is found in the region round Crossfell, where a basaltic
formation, called the ' ( whin sill," is widely spread in the
midst of the limestones and sandstones, over some of
which it appears to have poured as a submarine current
of lava, while through and amongst others it was per-
* Is this word originally todtsiein, derived from German miners ? It
would in thi? case signify rock, which in a mining country is dead, or un-
productive of mineral treasures, a character generally applicable to this
rock.
CHAP. VII. UNSTEATIFIED ROCKS. 97
haps forcibly injected. The diagram No. 82. shows
the manner in which the basaltic mass (6) grows thinner
in one direction (towards the west), and also the occur-
rence of a mineral vein (v) (yielding sulphuret of lead)
in a fissure which divides equally the limestone and the
" whin sill," and yields valuable metallic ores in each.
Overlying Masses. — In the preceding instances,
igneous rocks are included between sedimentary strata;
overlying masses, as they are called, spread irregularly
over a surface of other rocks without being themselves
covered by any. The same overflow of melted rock may,
in one part, appear an overlying mass, and, in another,
an interposed bed, as in the Clee Hills, in Salisbury
Craig, near Edinburgh, &c. The porphyritic summit
of Ben Nevis is an overlying mass, which has burst up
through the granitic base of the mountain ; the porphy-
ritic mass at the lower end of St. John's Vale, Cumber-
land, is similarly circumstanced in relation to the slate
rocks of that region; and the phenomenon is common. It
is perfectly paralleled by what happens in many erup-
tions of lava, and was well illustrated by the great Ice-
landic lava currents in 1783.
Fissures. — In all these cases the situation of the
once melted rocks is easily explicable by supposing,
what in some cases is known to be the fact, that the
horizontally extended masses of igneous rocks have been
forced upwards through tubular passages or fissures, as
happens at this day at the summit or on the sides of
active volcanos. Such fissures or tubular passages oc-
casionally appear connected in one long or in several
short parallel lines ; as, for example, among the silurian
strata the line of eruptions marked by the trap rocks of the
VOL. II. H
98 A TREATISE ON GEOLOGY. CIIAP. VII.
Wrekin, the Lawley, Caer-Caradoc, &c. ; and,, among
existing volcanos on a greater scale, the linear volcano*,
to which Von Buch was the first to direct attention.
Great fissures, such as here alluded to, may be ex-
tremely irregular ; the strata through which they break
may be thrown into great confusion ; their parts may be
disjoined and separated by cavities. Into these irregular
hollows the fused matter sometimes has been forced ;
and not unfrequently large and small portions of the
broken strata are inclosed in the midst of the igneous
rock ; while sometimes portions of the latter have flowed
into cavities in the stratified masses, from which it is dif-
ficult to trace their connection with the main stream.
Such phenomena may be well studied in Salisbury
Craigs, and other localities near Edinburgh ; in Teesdale;
the Caradoc Hill, &c.
Dykes. — A still more common form of appearance
among igneous rocks is what is called a dyke, which
agrees with the general description of similar rocks
occupying a fissure ; nor in some cases is there any dis-
tinction. But dykes, when seen in perfection, as in the
Island of Arran,the coal-field of Durham and Newcastle,
the limestone of Teesdale, the lias near Stokesley, the
silurian rocks of Shropshire, or the slates of Snowdonia,
present characters of greater symmetry, and claim a some-
what different origin. The fissures which inclose these
trap dykes present often no trace of violent movement
of the strata, which, on the contrary, sometimes appear
level and undisturbed on both sides ; these sides are re-
markably parallel, plane, and either vertical, or slightly
inclined, so that the inclosed mass of rock looks like a
continuous wall. On the surface the dyke lies usually
in a straight line from a few hundred yards to ten,
twenty, and more miles in length.
Archdeacon Verschoyle has described several trap
dykes which range on the coast of Mayo and Sligo : one
of them extends altogether, in an east and west direc-
tion, sixty or seventy miles. One of the dykes, which
is represented in the diagram No. 83., continues in a
CHAP. VII. UXSTRATIFIED ROCKS. 99
83
rf'
T. The great mass of basalt in Teesdale.
d. A straight dyke passing East 20° North.
d'. Another, passing generally to the South of East.
perfectly straight line, across the Durham coal-fields,
twenty miles, in a direction E.N.E. ; the other, start-
ing from the same point (near Middleton in Teesdale),
extends into the eastern part of Yorkshire, nearly reach-
ing Robin Hood's Bay, a distance of seventy miles, in an
E.S.E. direction.
In some districts, rock dykes are wonderfully nu-
merous. Forty-four trap dykes of various kinds were
carefully noticed and measured by the author of these
remarks, in a few miles of the coast of the Island of
Arran, between Brodick and Lamlash. They abound
no less on the western side of the same island at
Tormore.
Veins. — One of the most interesting forms of occur-
rence of igneous rocks is that of veins, which penetrate
and ramify irregularly in the fissures of the neighbour-
ing rocks. These veins sometimes appear insulated in
the midst of rocks more or less different from them in
composition, except at the common surfaces, where the
substance of the vein and the inclosing rock are inti-
mately united by intermediate characters of mineral com-
position or undistinguishable blending of the parts. In
this manner granite frequently incloses parts in which
hornblende, or mica, are particularly abundant or remark-
ably deficient; the redundancy and defect being equally
referrible to circumstances which operated during the
crystailisation of the stone. To such spherical, nodular,
or elongated parts of a rock, the title of contemporane-
H 2
100 A TREATISE ON GEOLOGY. CHAP. VII.
ous veins has been given by professor Jameson : they
may also be called veins of segregation.
But the veins to which attention is now directed had
a different origin, and disclose a different history. They
sometimes may appear insulated in a mass of quite dif-
ferent rock, but there is little, or no gradation of mineral
character at the common surface, and, when carefully
traced, the veins are found connected with larger masses
of their own substance at no great distance. (See dia-
gram No. 84. p. 76.) Recollecting that all the igneous
rocks, found intermixed with the strata, have been pressed
by considerable mechanical force, it is an unexpected
fact that veins, such as are now described, branching off
into the" minute cracks and fissures of the stratified masses,
should be witnessed almost exclusively in granitic and
sienitic compounds. Nor is our surprise lessened, when
we find the lava or existing volcanos occasionally as-
suming the shape of veins, as well as of dykes, in the
fissured substance of the crater and sides of the moun-
tain.
Why, for example, should it almost never occur that
the substance of porphyritic and basaltic dykes, whether
they pass through slate, coal, sandstone, or limestone, is
extended from the main body into the numerous small
cracks and fissures which margin the dyke ; while, on
the other hand, there are few situations where granite
comes in contact with gneiss, clay slate, limestone, mica
slate, or hornblende slate, without throwing off many
branches into those rocks ?
One reason may be, that the porphyritic and other
1 trappean' dykes, injected among the strata while they
were cold, lost, like lava at the surface, their heat and
fluidity too rapidly to penetrate the small fissures ; while
the enormous masses of granite in contact with the
strata which they penetrate, may have retained their
fluidity through a considerable period. But this is pro-
bably not the whole truth. One effect of the igneous
rocks is to produce fissures in the stratified masses; and
it is very conceivable that the small lateral fissures
CHAP. VII. UNSTRATIFIED ROCKS. 101
alluded to did not exist till after the partial or complete
solidification of the rock which filled the dyke.
Examples of granite veins are innumerable, though
a few years only have passed since they were deemed
too rare to be of much value in supporting the Hutto-
nian doctrine of the crystallisation of this rock from
igneous fusion. Their importance was most fully under-
stood by Dr. Hutton, and his able supporter Play fair,
whose notices have not lost their value in the eyes of
modern inquirers. Distinguishing between the veins
which are clearly and completely traced to the large
masses of granite rock, and such as appear insulated,
Playfair describes the latter class as occurring in the
Western Islands, particularly in Coll, where they traverse
the beds of gneiss and hornblende schist. They are several
fathoms in thickness, obliquely intersecting the nearly
vertical planes of the strata. The beautiful Portsoy
granite is a vein or dyke ; a similar granite is found
inland, near Huntly. The bed of the river Tilt, in the
distance of little more than a mile, is intersected by no
less than six very powerful veins of granite, all of them
accompanied with such marks of disorder and con-
fusion in the strata, as indicate very strongly the vio-
lence with which the granite was here introduced into
its place. (Dr. Macculloch's view of these phenomena
in Glen Tilt is different.) " The second kind of granite
vein is one which proceeds visibly from a mass of that
rock, and penetrates into the contiguous strata. The
importance of this class of veins, for ascertaining the
relation between granite and other mineral bodies, has
been pointed out (§ 82.) j and by means of them it has
been shown that thje granite, though inferior in position,
is of more recent formation than the schistus incumbent
on it ; and that the latter, instead of having been quietly
deposited on the former, has been, long after its depo-
sition and consolidation, heaved up from its horizontal
position by the liquid body of the granite forcibly im-
pelled against it from below." *
* Illustrations of the Huttonian Theory, Works, p. 312.
H 3
102 A TREATISE ON GEOLOGY. CHAP. VII.
Among the cases quoted by Playfair in his further
discussion of this subject, is the series of veins which
accompany the junction of the granite and schist of
Galloway. Sir J. Hall and Mr. Douglas, following the
previous indications of Dr. Hutton and Mr. Clerk, traced
the line of separation between the granite and schist all
round a tract of country about eleven miles by seven,
extending from the banks of Loch Ken westward ; and
in all this tract they found that wherever the junction
of the granite with the schistus was visible, veins of the
former, from fifty yards to the tenth of an inch in
width, were to be seen running into the latter, and per-
vading it in all directions, so as to put it beyond all
doubt that the granite of these veins, and consequently
of the great body itself, which was observed to form with
the veins one uninterrupted mass, must have flowed in
a soft or liquid state into its present position.
Perhaps no better example of granite veins is known
than in the mountain of Tornidneon, above Loch Ranza,
which was examined by sir J. Hall. From a careful
personal survey of this case, in 1826, the following notes
and diagram (No. 84.) are extracted. The junction of
granite and a dark quartziferous clay slate, with rather
wavy laminae, takes place nearly in a vertical line, rudely
parallel to the lamination of the slate. The granite at
a distance from the slate is very coarse grained (com-
posed of quartz, felspar, and mica, occasionally with
cavities inclosing those minerals distinctly crystallised),
and sometimes porphyritic; but where it touches the
slate it appears fine grained and much more compact.
Veins pass from the granitic mass in various directions :
a great vein, which incloses fragments of slate, divides
itself, and crosses at different angles the slaty laminae,
but is not ramified into many small strings. In the
large vein the granite is coarse, but in the small veins
it is fine grained.
The substance of granite veins is sometimes undistin-
guishable from that of the great mass whence they spring,
as in some of the veins which surround the granitic
CHAP. VII.
UNSTRATIPIED ROCKS.
103
8. The slaty rock.
G. The mass of granite.
g. One of the veins. The style of dotting is intended to express th
fineness or coarseness of grain in the granitic mass and veins.
*. Portions of slate included in the granite vein.
region of Galloway, and some of the veins in Glen Tilt;
in other cases it is very much more fine in grain, and
otherwise dissimilar to the parent rock, as at St.
Michael's Mount, and in the ease already mentioned at
Toruidneon ; and sometimes it is said by Tlayfair to
H 4
104- A TREATISE ON GEOLOGY. CHAP. VII.
be more crystallised in the veins than in the mass.
These differences probably depend on several circum-
stances. The rate of cooling, if at all rapid, would
cause the thinker veins to be of fine grain, while the
broader veins would more nearly approximate to the
parent rock. This is exactly what occurs at Tornid-
neon. The remoteness of the point in the vein from
the mass of igneous rock, and the nature of the strata
penetrated, may also have influenced the particular mode
of aggregation of the substance of the veins.
No part of the world equals Cornwall in the abun-
dance of opportunities afforded b) its sea cliffs, streams,
and mines, for studying the veins which at almost every
point branch off from the great subjacent masses of
granite into the everywhere incumbent " killas." Pro-
fessor Sedgwick, Dr. Forbes, sir H. Davy, Mr. Came,
Mr. Kenwood, Mr. De la Beche, Dr. Boase, Von Dechen,
and many other eminent geologists, have paid great at-
tention to their occurrence and characters, which cer-
tainly are very complex, and, to judge from the diversity
of the published opinions concerning them, very per-
plexing. When, indeed, we see on the plans given by
Von Dechen (Phil. Mag. 1829), granite veins ramified
in almost every direction, of almost every size and form
of sides, plane or indescribably twisted, of large or small
grain, pure or holding fragments of the neighbouring
killas, or mixed with greenstone — crossed by quartz and
schorl veins, and by metallic lodes which displace the
veins of granite and quartz — variously connected with
serpentine masses and veins of steatite, — it is surely not
surprising that phenomena so various and remarkable,
exhibited incompletely, should, if studied without refer-
ence to other and less complicated examples, be the
source of confusion and discord between perfectly im-
partial observers and reasoners. Nor is this all the diffi-
culty : the general relation of the laminar structure of
killas to the faces of the granite masses is extremely
difficult to reduce to a clear statement. The killas is of
most indefinite composition; the granite includes con-
CHAP. VII. UNSTRATIFIED HOCKS. 105
temporaneous veins ; and this same country is broken
into innumerable parts by metallic lodes, elvan courses,
and other accompaniments of subterranean dislocations.
Most thankful,, therefore, should geologists be, that
further investigation of the facts, on which so many
hands have been employed, has been performed by Mr.
De la Beche, whose report, accompanying the geological
survey of Devon and Cornwall, has now passed through
the press.
From professor Sedgwick's description of the magni-
ficent phenomena of granite veins at Trewavas Head,
about two miles west of Forth Leven (Cambridge Philo-
sophical Trans.), we extract the following notice: —
" On reaching the beach, we first found the killas
rocks intersected by many contemporaneous veins of
quartz. Not many feet farther west we were surprised
to observe an appearance of alternation between the slate
on which we were advancing, and several thin beds of
granite. One more especially, which towards its southern
extremity was lost under the waters, preserved its thick-
ness and conformity to the laminae of the schist for more
than 100 feet. But its true nature was easily deter-
mined in the other direction ; for it gave out several
smaller veins, then cut obliquely through the laminae of
slate, and at length contracted its dimensions, started
entirely from its previous direction, and ran in a flicker,
ing line across the perpendicular cliffs. This vein is in
no part more than two feet wide ; yet it may be traced
from the edge of the water to its termination in the
cliff, nearly 400 feet.
"In the cliffs further west there are several granitic
veins, which would be considered of no great interest
if they had not been intersected by two other veins of
different character, which must be classed either with
the metalliferous lodes or the cross course of the country.
One of them ranges nearly in the magnetic meridian,
is about one foot and a half wide, and underlies east,
two feet in a fathom. The other underlies in an op-
posite direction. They both contain quartz, oxide of
106 A TREATISE ON GEOLOGY. CHAP. VII.
iron, and apparently some fragments of clay slate. At
the time of their formation, the mineral masses which
they traverse must have undergone a considerable dis-
turbance ; for the broken ends of the schistose beds and
granite veins, where they pass, are distinctly heaved
from their original position.
" Still further west we found the rocks beautifully inter-
sected by granitic veins ; the higher part being traversed
by innumerable ramifications, while the lower part is cut
through by one well-defined vein about a foot thick, which,
after keeping nearly in the direction of the beds of slate for
about sixty feet, suddenly starts off at right angles to its
former direction, and rises up to the top of the cliff.
The whole system of veins here described afterwards
unites in one trunk, which traverses a projecting ledge
of rock, and descends obliquely into a mass of granite
which forms the eastern side of the entrance into a sin-
gular natural cavern. Both sides of its entrance are of
granite, but the roof is formed by undisturbed beds of
killas. The granitic masses, however, soon contract
their dimensions, and wedge out in the schistose rocks,
which form both the roof and walls of the cavern, about
50 feet from its commencement.
" From the very point which is marked by so much
confusion, two large veins, separated by a lancet-shaped
mass of slate, rise towards the west at an angle of
about 15°. Within a few feet of the other two, a
third vein starts out nearly at the same angle, and pro-
ceeds in the same direction. These three veins are
throughout nearly of the same thickness, viz. each about
five feet. The highest, at some distance from its base,
begins to ascend more rapidly, and is lost in the alluvial
soil at the summit. The other two preserve their
course, without being much deflected, for some hun-
dred feet from the place where we first remarked them,
and disappear behind a projecting part of the cliff.
On turning this projecting ledge, we suddenly reached
a recess, the lower part of which was filled with the
ruins from the higher part of the overhanging rocks.
CHAP. VII. UXSTRATIFIED BOCKS. 107
The western side of this recess is composed of killas
intersected by some small granitic veins. A protruding
mass of granite forms the base of the eastern side to the
height of twenty-five or thirty feet. It is of a very
singular outline, yet does not appear to have thrown
the slaty laminae reposing on it out of their usual
direction.
" The mound of rubbish in the recess enables us to
ascend more than half way up the cliff, and trace the
two large veins before mentioned into an enormous
bunch of granite, which here reposes on the top of the
cliff, and is supported by undisturbed beds of slate ; the
line of demarcation being nearly horizontal, and at an
elevation of sixty or seventy feet above the level of the
beach. The denuded face of this bunch of granite
is thirty or forty feet thick, and, in a section made
farther from the cliffs, would probably be much more
considerable ; for the ground rises rapidly to the north,
and it is impossible even to form a conjecture how
far the cap of granite may extend in that direction.
" Two or three veins appear to take theirorigin from this
anomalous overlying mass. One spreads out in minute
ramifications towards the part of the cliffs which abuts
against Trewavas Point, at the termination of the killas
in that direction. Two others descend obliquely, and
are lost behind the large mound of rubbish before men-
tioned."
Granitic vans, which ramify and pass irregularly
for short distances from the great mass, are frequent; but
dykes, which are of simple form, and cross with a certain
regularity great breadths of strata, where no parent mass
of the same nature is known, are very rarely grani-
tic. If this seem a paradox, its solution may lead to
important results. Could we behold enormous masses of
porphyry, or basalt, below vast breadths of stratified
sediments, as granite is commonly seen, there would
probably be found porphyritic or basaltic veins passing
from them into the cracks of the strata. If this is
never the case, does it not show the peculiar mineral
108 A TREATISE ON GEOLOGY. CHAP. VII.
character of granite, and its peculiar effects on the ad-
joining rocks, to be the fruit of the local circumstances
of its deep 'plutonic' origin? It is a 'hypogene'
rock very slowly cooled; in other circumstances it
would not appear as granite. In thin veins and parts
remote from the great body it becomes a fine-grained
or even compact mass, hardly different from the base of
porphyry. What then prevents us from believing that
many felspathic dykes, like the elvans of Cornwall and
Cumberland, which are so very generally found on the
borders of granitic districts, are really of granitic origin ?
This is a view which has become familiar to our minds,
while traversing the vale of St. John's, Wastdale, and
Shapfells, and which has already been advanced by
MM. Oeynhausen and Von Dechen, while speaking of
the geology of Cornwall. (Geol. Proceedings, vol. i.)
Amorphous Masses under all the Strata. — If granitic
veins surprise us by their smallness and the perfection
with which they have been injected into all the rami-
fications of a stratified rock, the vastness of the masses
from which they arise is even more remarkable. For it
is certainly true, that in every place, yet completely ex-
plored, the veins end downwards in granite formations,
so extensive and unbounded, and appearing at so many
points beneath the lowest strata, as to deserve, more
than any other assemblages of mineral masses yet made
known, the title of an universal formation. The differ-
ences which obtain between different sorts of granite are
more striking to the eye than important in reasoning;
for it has already appeared, that even when one of the
constituent minerals, mica, is wholly absent, the che-
mical contents of this remarkable stone vary almost
imperceptibly. (Seep. 92.)
INTERNAL DIVISIONS OF IGNEOUS ROCKS.
On this head it has not been found necessary to add
to the remarks which will be found in Vol. I. p. 62.
CHAP. VII. L'XSTBATIFIED ROCKS. 109
PHENOMENA OBSERVED WHERE IGNEOUS ROCKS COME IN
CONTACT WITH STRATIFIED MASSES.
Induration of Stratified Rocks.
One of the most usual effects of moderate heat upon
argillaceous and arenaceous compounds is to indurate
and condense their substance : considerable heat causes
the grains to agglutinate into a " grit;" extreme heat
fuses most argillaceous and many arenaceous rocks into
a slaggy or glassy matter, which upon cooling remains
vitreous, earthy, or crystalline, just as Mr. Watt found
to happen to the basalt of Rowley Hills. In the slags of
furnaces, several minerals have been found crystallised.
The effects of the heated rocks which fill veins and
dykes, and spread above and below argillaceous strata,
are very similar. When dykes are of small breadth,
the alteration which is seen in the neighbouring rocks is
very slight. Of forty-four dykes composed of green-
stone, claystone, and other igneous rocks, which were
carefully observed and described by the author, as they
occur on the shore of the Island of Arran, between Bro-
dick and Lamlash, very few were found to have pro-
duced in the adjacent red sandstone more than a slight
induration, in a very narrow space close to the dyke.
Where two dykes crossed, it happened sometimes that
a vitreous substance ran along the line of intersection.*
But on the sides of large dykes, 20 to 60 feet wide
(as, for example, the great dyke of Cockfield fell in
Durham), the shales are highly indurated and otherwise
altered, and the sandstones rendered as hard and solid
as some sorts of quartz rock.t In Salisbury Craigs,
* These descriptions are unpublished.
t Mr. Murchison has found numerous examples of this effect in his
survey of the trap rocks of the Silurian system, as in Caer Caradoc, the
Corndon Hills, the Stiperstone ridge, and many others. One of the Corn-
don dykes, forty feet wide, with prisms lying across'the dyke, composed of
greenstone varying to felspar, has indurated the neighbouring argillaceous
beds for two or three inches, so as to make them like the substance known
AS porcelain jasper j and for twelve feet the induration is remarkable.
110 A TREATISE ON GEOLOGY. CHAP. VII.
the greenstone which is intermixed with the soft sand-
stones and shales of the coal formation has hardened
these beds at the surfaces of contact so as to convert
them into a kind of jasper, which takes a good polish.
Under Stirling Castle, in Teesdale, on the flanks of the
Caradoc, by the Plas Newydd dykes on the Menai, and
indeed generally where the rocks of igneous origin appear
in great masses, this effect of consolidating the stratified
rocks is conspicuous, and leads to important reflections
concerning the changes which, on a greater scale, the
whole series of stratified rocks may have undergone.
The induration of the strata is an effect quite dis-
tinct from their deposition, and appears to require the
supposition of long continued application of heat. In
surveying the different systems of strata in succession,
we readily perceive that, independent of the local influ-
ence of particular masses of igneous rocks, whose influ-
ence extends only a few yards at most from their
bounding surfaces, the formations of different ages are
unequally indurated, — the oldest being by far the most
consolidated, while the newest appear but little harder
than the analogous deposits which at this day are known
to be produced in freshwater lakes, at the mouths of
rivers, on the sea coast, or on the bed of the ocean.
This may be satisfactorily proved by a short compa-
rison of the three principal varieties of stratified rocks,
viz. arenaceous, argillaceous, and calcareous beds. In
the tertiary series loose sands not only occur, but, in
fact, constitute a large part of the whole series in Europe;
for the sandstones of Fontainbleau, and the " grey-
weathers'1 of the Wiltshire downs, and the molasse of
Switzerland, seem only exceptions to the general rule.
Clays abound under London, in Hampshire, and the
sub-Apennine hills; and even the limestones, as the
stony crag of England, the Leitha kalk of Transylvania,
and the calcaire grossier of Paris, have a softness and
looseness of texture not common in strata below the
chalk. (Some freshwater beds in the Cantal, and near
Weimar, are hard.)
CHAP. VII. UNSTRATIFIED ROCKS. Ill
In the oolitic system there are still some beds of
sand, hut sandstones predominate ; there are also clays,
but they grow denser toward the lower or lias form-
ation ; and the limestones exhibit the same gradations.
In these respects the saliferous system differs but little,
and still shows clays and sands and soft limestones;
among the carboniferous rocks we lose almost totally the
trace of loose sands, and soft clays (until brought to the
surface) and the limestones acquire that compact and
solid character which belongs to almost all the strata be-
low the old red sandstone. Below the Silurian rocks the
induration of the strata is rapidly accelerated ; the clays
have become slate, the sandstones are changed to quartz
rocks, and the limestones have undergone an equal meta-
morphosis. The superior consolidation of the primary
strata has struck every intelligent observer, and, allow-
ance being made for difference of materials and local
igneous agency, there can be no doubt of the justice of
referring this quality to the higher degree in which they
have been influenced by general subterranean heat.
ALTERATION OF THE STRUCTURE OF ROCKS BY HEAT.
The influence of heat in altering the structure of
rocks is no less decided than in condensing their sub-
stance. For by this agency the original stratified arrange-
ment of rocks is greatly obscured, and in some cases
almost wholly extinguished, while entirely new struc-
tures are introduced to supplant those formerly imparted
by water. The general character of the divisional planes
in rocks has been already noticed*; it is desirable,
however, to extend the description formerly given of
slaty cleavage, the most striking and important of all
these structural changes. We shall previously give
some illustrations of the evidence on which some ge-
ologists have attributed these effects to subterranean
heat, and others to electrical currents.
A case which has fallen under our own observation
* Vol. L p. 65, &c.
112
A TREATISE ON GEOLOGY.
CHAP. VII.
at the celebrated waterfall called the " High Force/'
in the upper end of Teesdale, Yorkshire, will first re-
quire attention. At this romantic spot the river Tees
dashes down a precipice of 69 feet, which to the artist
shows two distinct forms of
rocks : the upper part is
boldly prismatic, and the
lower part stratified. Across
the prisms run bands of
stratification, and to the
hasty observer this will ap-
pear a case of stratified ba-
salt. But careful inspection
demonstrates a more curi-
ous truth. The annexed
sketch (taken from the Illus-
trations of the Geology of
Yorkshire, vol. ii. pi. xxiii.)
will explain the peculiar
circumstances alluded to.
a. Basalt, rudely prismatic, grey with lichen.
b. Thin " plate," not very much indurated.
c. Bed of plate, sub-prismatic.
d. Beds of plate, laminated.
e. Thin limestone bed with a superficial layer of pyrites.
/. Bed of hard pyritous limestone.
g. Several beds of common dark limestone, with white shells and corals.
Here we see a new structure, commonly found in
great masses of igneous rocks, communicated to the
adjoining strata; but this is not very obvious in Tees-
dale, except where the basaltic rock is in very great
quantity and thickness. At a distance from the heated
rock, the shale or " plate" resumes its usual divisional
surfaces, caused by nearly vertical joints which cross and
intersect in rhomboidal or rectangular figures. (Com-
pare cuts No. 86. and No. 87.) Both of these differ
from those produced by the local application of heat,
but neither of them is the effect of violent disturbance ;
both arise from the condensation of the matter of the
CHAP. VII.
UX?TRATIFIEr> ROCKS.
113
strata, under the influence of heat or other causes com-
petent to induce particular arrangements, — prismatic,
87
cubical, rhomboidal, &c., according to the nature,
thickness, and position of the rocks, the degree in which
the polarities of their particles are controlled by the dif-
ferent qualities of neighbouring mineral masses, and
other important circumstances. Another case which also
fell under the author's notice at Coley Hill, near New-
castle, appears strongly to confirm the view here pre-
sented, and at the same time to remove part of the ob-
scurity which has always been supposed to overhang
the origin of the " cleavage " of slate (see Vol. I.
p. 67, &c.). In the annexed cut,
88
d , it a basaltic dyke, nearly vertical, and between twenty and thirty
feet across, ranging east and west, and appearing at the surface.
*, u the ordinary coal shale, which is, as usual, very much laminated at
a moderate distance (a few yards) from the dyke, and contain* fern leaves
and other plants between the lamins.
VOL. II. I
114 A TREATISE ON GEOLOGY. CHAP. VII.
At the sides of the dyke the horizontal lamination is
obscured, the shaly mass is indurated, and traversed by
numerous vertical divisional planes parallel to the faces
of the dyke, most numerous near the dyke, so as to
occur in every half inch of breadth, but becoming less
and less abundant in the parts removed from the dyke,
till they entirely vanish. On the surface section, the
lines of these vertical planes would, on a minute scale,
represent the ee cleavage" edges of slate.
This fact is an example of a large class of phenomena,
often to be seen on the sides of basaltic and porphyritic
dykes, which traverse argillaceous strata ; and it is one of
the most prominent illustrations which we have, ever
met with in favour of the opinion that the cleavage of
slate is a metamorphic structure produced by the action
of heat. Heat, however, is certainly not the only agent
for generating cleavage.
We are acquainted with instances in which a similar
structure (though certainly less perfect) is found pa-
rallel to, and limited to the region of, great fractures
of the strata where no dyke of basaltic or other pyro-
genous rocks occurs. This is seen in limestone cliffs
which border the north side of the Great Craven fault
in Yorkshire, where it crosses Giggleswick Scar, near
Settle, and certainly no igneous action is otherwise in-
dicated or probable there.
Mr. R. Fox, in prosecuting his curious researches
regarding the changes effected in metallic bodies by
electrical currents, has been conducted to an unexpected
result, which appears to be of importance in reasoning
on the laminated structures of mineral masses generally,
and especially on the " cleavage" planes. The following
notice of the experiments is extracted from the Report
of the Royal Cornwall Polytechnic Society for 183?.
" Some clay was exhibited by R. W. Fox, esq.,
which had become laminated by long- continued voltaic
action, so as to resemble clay slate in its structure.
CHAP. VII.
UNSTRATIFIED ROCKS.
115
" The above figure may serve to illustrate the process
by which this was accomplished. Let abed represent
the top or rim of an earthenware cup or basin; e, a
piece of copper pyrites ; /, the upper edge of a plate of
zinc ; t, copper wire by which the two latter were con-
nected ; and g, h, the top of a mass or wall of clay be-
tween the copper ore and the zinc, and forming for each
of them a watertight cell. The cell containing the
copper ore was filled with a metallic solution — the sul-
phate of zinc, for instance — and the other with water
mixed with a little sulphuric acid. The water with
which the clay was worked up was also acidulated.
Thus circumstanced, the apparatus was set aside three
or four months, and was not disturbed till some little
time after the water had evaporated, and the clay had
become perfectly dry throughout.
" It then exhibited, on breaking off a portion of its
upper part, lines of cleavage of a schistose character,
parallel to the sides of the clay and plate of zinc, or at
least as nearly so as was consistent with their undu-
latory form. In other words, the lines or laminse were
at right angles to the direction of the electrical forces.
" They are indicated by the lines on g, h; and the
strongly marked line a c represents a principal line of
division which separated the clay into two portions
from the top to the bottom.
" These seemed to form, as it were, two voltaic
i 2
116 A TREATISE ON GEOLOGY. CHAP. VII.
plates, in opposite states of electricity, and one of them,
consequently, more favourable than the other for the
reception of metallic deposits and other bases from their
solutions.
" Indeed, the general laminated structure of the
clay appears to indicate that a series of voltaic poles
were produced throughout the clay, the symmetrical
arrangement of which had a corresponding effect on the
structure of the clay. This view is still more strik-
ingly confirmed by the occurrence, in several instances,
of veins, or rather laminae, of oxide of iron, the edges
of which are shown by the shaded lines k, I, m. In
these cases sulphate of iron was substituted for sulphate
of zinc ; and laminae of oxide of copper were sometimes
formed, in like manner, when a solution of that metal
was employed ; and moreover, numerous minute insu-
lated portions or specks of the oxide of copper were
detected in different parts of the mass of clay when
broken."
These facts appear highly favourable to the opinion
that the direction of cleavage planes in slate depends on
some form of electrical excitement, and currents of elec-
tricity passing in given directions ; but they do not at
all negative the probability, from other and more gene-
ral facts, that it is to the application of heat that the
electrical currents owed their origin. In fact, when we
remember that it is only among dislocated primary
strata that real clay slate occurs, and that it is only in
the vicinity of pyrogenous rocks, or fractures of the
strata, that rocks of later date assume, however imper-
fectly, the slaty aspect, and that dislocations of the
strata with unequal conducting powers for heat and
electricity necessarily generate electrical disturbance
and currents to restore the equilibrium, we see that the
general opinion which geologists had adopted, of the
dependence of the directions of cleavage and other sym-
metrical structures in rocks, upon local or general appli-
cation of heat, may be very correct, though certainly
it is incomplete. Mr. Fox's experiments will doubtless
CHAP. VII. UNSTRATIFIED ROCKS. 117
be repeated in other forms, but their present value is
great, and they may, as he suggests, lead to practical
results of value in mining operations.
We must, however, add some further details of the
phenomena of cleavage, and discuss their bearing on
another hypothesis, which ascribes to pressure this
beautiful superposition of structure.*
The occurrence of cleavage at all in any given dis-
trict is in some degree dependent on the nature of the
rocks therein. Still more obvious is it that perfect ex-
amples of it only occur in certain argillaceous deposits.
In a country consisting of alternations of thick argilla-
ceous beds with coarse conglomerates, hard sandstones,
limestones, quartz rock, and felstone, or greenstone, we
shall find the cleavage, after passing through the argilla-
ceous bed, more or less constantly interrupted by the
other strata, — through which, however, a certain
fissility, occasionally twisted and otherwise modified, is
often traceable.
We have also for many years observed a beautiful
case of the bending of the cleavage surfaces when they
pass from one bed, or part of a bed, to another bed
or mineralogically different part of a bed. Mr. Sharpe
also admits this fact. This bending is always in such
a manner as to render the angle of intersection between
the cleavage and the stratification more acute, just as
sometimes happens when a mineral vein crosses ob-
liquely a strong throw, or when strata rise with an up-
lifting fault. The law is the same in all cases. These
phenomena deserve the utmost attention from those
who speculate on the theory of cleavage.
Beyond these completely or partially interrupting
layers the cleavage recurs in the next band of argillaceous
rock, with planes parallel to those first observed.
There are, however, cases in which alternating beds
* Consult on this subject, besides Memoirs by the Author, (Geol. Trans.
1820, and Brit. Assoc. 1843), and Professor Sedgwick (Geol. Trans. 1835),
the later writings of Sharpe, (Proceedings of Geol. Soc. 1847. 1849), and
Hopkins (Phil. Mag. &c.) See also De la Beche, in Geol. Observer, 1851.
118
A TREATISE ON GEOLOGY.
CHAP. VII*
of more and less argillaceous rock manifest cleavage, but
not in parallel planes, and when this happens, the an-
gular difference of the planes is such that those in the
finer grained or more argillaceous bed meet the planes
of stratification at more acute angles than those do
which traverse the coarser and more sandy or more in-
durated bed. An example of this in secondary cleavage
("bate") is given in the author's paper on Craven rocks
(Geol. Trans. 1828). He has since collected examples
more obviously dependent on the difference of the
mineral quality of the adjacent beds. Mr. Sharpe
has admitted this peculiarity (Geol. Proc. 1848).
The above diagram shows a remarkable case observed
in old red sandstone near Cork, (1843); * being soft
red marly beds, h harder beds, / a laminated sandstone
without cleavage, but jointed.
Another of the characteristic phenomena of cleavage
was frequently presented to us, while surveying (in
1839) the Palaeozoic strata of North Devon. Surfaces
of stratification are usually found to be ridged and fur-
rowed by the edges of cleavage, in such a way that the
CHAP. VII.
896
UNSTRATIFIED BOCKS.
119
120 A TREATISE ON GEOLOGY. CHAP. VII.
outlines of shells and other organic remains are dis-
torted, and their surfaces crumpled and waved. Thus
the symmetrical forms of leptsense, orthides and spiriferse
become abbreviated in one direction, and (relatively)
lengthened in another, and if they were laid obliquely
to the direction of cleavage they have become distorted.
So the trilobites of Llandeilo appear, in some instances,
much narrowed, in others much widened, and in other
instances obliquely elliptical, but in every instance the
result was a contraction of the space across the edges of
cleavage, and what may be called a minute folding, or
furrowing ; in fact, a '•' creep," in the direction of the
dip. This " creep" is such as in the case of specimens
of Ogygia Buchii from Llandeilo to contract them J
and even % an inch.
We may illustrate this by a diagram. Let ss be the
line of strike, and D the line of dip on the surface of the
stratum. Let o be the semicircular smaller valve of an
orthis, with r its radius, perpendicular to the diameter
d. Let such a figure be placed in 1 with its diameter
in the line of the dip, in 2 at right angles to it, and in
3 at some lesser angle, say 50° to it. Then let all the
stratum be subject to compression along the line of the
dip, the result will be that 1 becomes shortened di-
ametrically, r remaining unchanged, 2 becomes short-
ened on the radius r, but unchanged on the diameter d,
while 3 is shortened both on the line r and on the line
d, and is distorted*, so that r is no longer at right
angles to d. If we had assumed an extension of the
rock in the line D, we should have had d lengthened
in 1, r in 2, both d and r in 3 ; 1 and 2 retaining their
symmetry, and 3 being distorted in a different manner.
Hence arises distinctly the idea of pressure as a cause
of cleavage ; an idea which has been the subject of ela-
borate illustration by Mr. Sharpe. j~
Mr. Sharpe has given examples of elongation due to
expansion in the direction of the dip of the cleavage ;
* Brit. Assoc. Reports for 1843.
t Geol. Proceedings, 1847, 1349.
GHAP. VII. UNSTBATIFIED ROCKS. 121
but it does not yet appear that any change of dimensions
can be shown in the direction of the strike of the cleav-
age. No one can doubt that here we have indications
of exact mechanical laws, operating on masses of matter,
so regularly as to emulate the results of crystalline force
on the molecules. But the latter force is free to arrange
molecules singly by polar attractions, the former is con-
strained to obey certain axes in the mass.
Cleavage is remarkably developed in some districts
which are formed upon one or more axes of anticlinal
elevation and synclinal depression : for example, in
Cumbria, Wales, and Devonshire. In each of these
cases the fact is patent that the cleavage runs for 20 or
30 miles in one continuous direction, which is observed
by all the cleavage planes over a considerable breadth of
country. This direction is parallel to the great axes of
movement in that district, almost exactly so on a great
scale, though deviating slightly from the strike of the
beds in particular places, especially when the strata are
in any degree twisted.
The cleavage is in fact but little, if at all, affected
by small irregular twists of the beds, and is, on the
whole, more regular in its strike than they are. It is
related to the great axes, not to the local bedding. May
we from this infer that the general pressure on the
axes of movement has been a determining cause of the
new structures parallel to these axes ?
Another thing is remarkable. The cleavage is less
frequently vertical than inclined at a high angle, say
70°. It is also found at 45°, 30°, 20°, and even at
much lower angles. Most frequently, when the strata
are much inclined, the cleavage is inclined still more ;
but this has exceptions.
As the cleavage strike is not really dependent on the
strike of the beds at a particular place, so is its dip not
really dependent on the dip of the strata there : there
may be more than one anticlinal and synclinal of strata
(besides minor folds) and yet only one cleavage system.
122 A TREATISE ON GEOLOGY. CHAP. VII*
According to Mr. Sharpe, a cleavage system may be re-
garded as bounded by parallel lines along which the
cleavage is vertical, and in all intermediate points less
than vertical, in the middle of the space horizontal or
nearly so ; and he imagines these cleavage surfaces to be
portions of great curves, everywhere perpendicular to
pressures emanating from the axis of t'hat space ; that
is to say, they would be so many parts of cylindrical
sheets of uniform tension.
Upon this view we are not perhaps obliged to take
into account any one of the axes of movement in a
district, but the pressure on a whole district ; and we
are even released from referring the slaty cleavage to
the date of their axes ; it may be posterior to them all,
and be only related to a general subterranean cause, of
which they are some of the external manifestations.
A curious investigation of the component parts of
non-fossiliferous slates has convinced Mr. Sharpe that the
parts of such rocks have undergone that compression
across the planes of cleavage, and extension in the
direction of the dip, which had been inferred for other
slates from evidence of altered fossils.
On the foundation of facts which have thus brought
out the idea of internal pressure as an antecedent to the
production of cleavage, Mr. Hopkins* has endeavoured
to point out the accurate mechanical conditions of the
problem, and to indicate the points to which the atten-
tion of future observers should be specially directed for
the purpose of ascertaining the data required for a com-
plete theory. Though we cannot here give an analysis
* Camb. Phil. Trans. 1847.
CHAP. Vn. DNSTRATIFIED ROCKS. 123
of this investigation, a short statement of the bearing of
it may suffice to put geologists on the right track for
further inquiry, and perhaps to show them how much
of beautiful illustration of geology is lost by those who
permit themselves to be deterred by mathematical ex-
pressions from a close survey of physical truths. Pres-
sure and tension being taken as of opposite meanings,
and coexistent in a mass of rock, we may admit as re-
presenting their directions three coordinate axes passing
through a central point at right angles to each other.
Along these axes the effects of pressure and of tension
will be direct and total, so that a small plane situated
at right angles to one of these lines will be subject to
the pressures or tensions of that line only, and will be
moved, if at all, along that line ; but a small plane
placed in some other position will be moved in a line
not having the same direction. As these pressures and
tensions are assumed to be general, and so to affect all
the particles, it is obvious that we shall have three co-
ordinate planes, parallel to which direct forward or
backward motion is possible, and between them other
(tangential) planes in which the possible motions are
oblique.
Now in the case before us one of the axes of direct
pressure or tension may be regarded as of little or no
effect, viz., that which coincides with the strike of the
cleavage and the strike of the strata. And from this it
follows, that direct motion from pressure should take
place along lines lying in one plane only, viz., that
which is perpendicular to the anticlinal, and only in two
directions crossing each other at right angles in this plane,
— one of these directions being that of pressure, the
other that of tension. Planes perpendicular to these
two lines will be planes of direct tension or pressure,
and their strike will be that of the beds. There will be
also crossing these planes (but having the same strike
with them) two other (tangential) planes, making
with them angles of 458, but with each other angles
124 A TREATISE ON GEOLOGY. CHAP. VII.
of 90°, in which oblique motions will be at a maximum.
One of these (tangential) planes, therefore, will dip in
the same direction (but not necessarily at the same
angle) as the beds, and the other in the opposite
direction.
These things premised, we may by referring the
pressures to the plane of stratification discover their
effect on the outlines of organic remains, which, for the
sake of comparison with our observations already re-
corded, we shall assume to be semicircular, and always
laid with the hinge or diametral line parallel to the line
of dip.
First, let it be supposed that pressure is applied per-
pendicular to the stratification and tension produced
parallel to the strata. In this case there will be a sym-
metrical extension of the figure in the direction of the
line of dip. If tension be applied perpendicular to the
strata and pressure exerted parallel to them, the semi-
circle will be symmetrically contracted to a semiellipse,
as in the example already represented in the diagram
(p. 119.); and, finally, if either pressure or tension be
applied in a direction meeting the plane of stratification
at 4-5°, so that a plane of maximum tangential action
shall coincide with the stratification, the semicircle will
be unsymmetrically changed in form, so as to become
elliptical with its diameter lying obliquely across the
line of dip — in fact, to be angularly distorted.
When, therefore, angular distortion occurs in an
equilateral shell placed symmetrically with respect to
the line of dip, we may be sure the result is due to the
tangential movements developed by pressure. If this
happens chiefly or exclusively when the cleavage nearly
coincides with the stratification, and happens rarely or
not at all when the cleavage meets the strata at or about
an angle of 45°, we may conclude that the cleavage plane
is not perpendicular to any axis of antecedent pressure
or tension, but is coincident with one of the two planes
of maximum tangential movement.
CHAP. Til. UNSTRATTFIED ROCKS. 125
Thus a delicate and critical inquiry is opened out for
geologists who may have been trained to the accurate
use of graduated instruments.
Metamorphic Rocks.
For the application of the useful term, "Metamorphic
Rocks," in the description of phenomena connected with
the occurrence of igneous rocks, and reasoning on their
causes, we are indebted to Mr. Lyell ; and there is,
perhaps, no part of the study of ancient nature more
worthy of attention from philosophic minds. For thus,
and thus only in many instances, are we enabled to ar-
rive at probable and intelligible views of the course of
changes which even the most solid materials of the
globe have undergone. The Pythagorean maxim,
" Nihil est toto quod perstet in orbe,"
comes into full credit when we approach the great masses
of felspathic and augilic rocks which have been effused
in a melted state above and amongst the ordinary pro-
ducts of water. As we pass from the districts where no
igneous rocks appear at the surface, towards the moun-
tain regions where they abound, the strata acquire hard-
ness, assume new structures, and in their innermost
texture and substance appear under new and peculiar
aspects. In order to trace these phenomena, so that the
picture may not only be interesting but instructive, it
will be necessary to distinguish the effects which we call
" metamorphic" into three classes.
1. There are rocks which, by the local influence of
heated rocks, are locally changed as to the arrangement
of their mineral ingredients ; so that earthy substances
become crystalline ; and the view thus arising is capable
of being generalised so as to explain the corresponding
appearances of similar rocks, by a similar but more
general cause.
2. There are stratified masses which have undergone,
126 A TREATISE ON GEOLOGY. CHAP. VII.
near pyrogenous rocks, a loss of some portions of their
substance.
3. There are cases in which the rocks near igneous
dykes have not only been hardened, fissured in a certain
manner, and subjected to re-arrangement of their ingre-
dients ; but further, there have been introduced into their
substance, minerals not known in the same rocks else-
where. This is also found to have a general application
to rocks exhibiting like phenomena, but upon a scale so
vast as to require the supposition of very general appli-
cation of heat.
From these facts and inferences we pass immediately
and inevitably to the great geological problem naturally
arising out of such data, viz. the degree in which the
peculiar mineral characters and admitted absence of
monuments of organic life among the oldest strata are
to be relied on as conclusive testimony concerning the
primeval condition of the globe.
Re-arrangement of the Particles of Rocks.
One of the earliest notices of an extensive mass of
limestone changed by the action of igneous rock, is that
of the district of Strath in the Isle of Skye. Dr. Maccul-
loch's observations in this island led him, in 18 16, to
believe that certain laminated shelly limestones, which
occupy a considerable breadth, and cross the island
from Broadford to Loch Slapin, are altered in various
ways, by contact with and proximity to sienitic rocks,
so as, in a considerable space of country, to have lost all
stratification, and in sr"ae instances to have assumed
the character of a pure white marble of fine grain. In
its chemical composition it is generally a pure carbonate
of lime ; but where in contact with the sienite or the
trap veins, becomes overloaded with silica, magnesia,
and argil. In such situations it often contains veins
and nodules of greenish transparent serpentine, and ap-
pears in a variety of colours, grey, dove-colour, dark
blue, grey, striped, mottled, veined, pure white. At
GHAP. VII. TJNSTRATIF1ED ROCKS. 127
points removed from the sienite, the pectines, and other
shells which this rock contains, and its position with
regard to other secondary rocks above and below, have
satisfied not only Dr. Macculloch, but Mr. Murchison and
professor Sedgwick, that it is a part of the lias form-
ation, which also occurs in Pabba, &c.
A case of the same kind, on an equally extensive
scale, which occurs in connection with the " whin sill,"
or stratiform basalt of High Teesdale, especially in that
portion of the country where the trap rock is very thick,
has been made known by Professor Sedgwick. The
limestone of this district, both above and below the
basalt, is usually of a very dark grey or even blackish
colour (some beds are very black) ; but in contact with
that rock it loses its obscure blackness (probably by
loss of bitumen), becomes of a clear blue tint, and
finally, the change being complete, of a clear or greyish
white. The arrangement of the particles is altered in
an equal degree. The stone usually is compact, or
partially varied by laminar shells, or crystallised plates
of calcareous spar, representing the stems of crinoidea.
Near the f ' whin " these characters change ; the stone
becomes granular and crystalline (in the sense that
statuary marble deserves this term), and in some cases
the crystalline grains separate by disintegration of the
mass. In these metamorphic limestones small cavities
sometimes occur ; but the most interesting fact that
remains to be noticed, is the occurrence of crinoidal
columns in the midst of the granular crystalline mass
(our own observation). They are, however, not common.
These phenomena may be seen over some square miles
of surface in the vicinity of the High Force and Caldron
Snout, chiefly, perhaps, in the limestone which overlies
the basalt.
In connection with the ancient volcanic rocks of% the
Kaiserstuhl mountain (in the Rhine valley), limestone
of the Jura formation (or oolitic system) is similarly
altered to a really crystallised mass of calcareous spar ;
128 A TREATISE ON GEOLOGY, CHAP. VII.
and, in addition, mica and other minerals are inter-
mixed with the limestone. The broad flakes of carbonate
of lime are here very remarkable.
The basaltic district of Antrim furnishes abundant
and precise evidence of the conversion of chalk into
granular marble by the action of basaltic dykes.
" The Irish chalk is seldom of a texture sufficiently
loose to soil the hand ; and in the few instances where
this does take place, it is in a very slight degree : its
general colour is either perfectly white, or white with a
very slight tinge of yellow ; towards the lower part it
passes into a uniform ash-colour; the texture then becomes
still more compact." "At many points near Belfast,
Glenarm, Moira, &c., the chalk is frequently traversed
by basaltic dykes, and often undergoes a remarkable
alteration near the point of contact j where this is the
case, the change sometimes extends 8 or 10 feet from
the wall of the dyke, being at that point greatest, and
thence gradually decreasing till it becomes evanescent.
The extreme effect presents a dark brown crystalline
limestone, the crystals running in flakes as large as those
of coarse primitive limestone ; the next state is saccha-
rine, then fine grained and arenaceous ; a compact variety
having a porcellanous aspect, and bluish grey colour suc-
ceeds ; this towards the outer edge becomes yellowish
white, and insensibly graduates into the unaltered chalk.
The flints in the altered chalk usually assume a grey
yellowish colour ; the altered chalk is highly phospho-
rescent when subjected to heat." *
In the island of Raghlin, directly over against
Kenbaan Head, a singular combination of dykes occur
(seeming to be a continuation of those which at the
latter place have been attended by such extraordinary
disturbances). Here, within a distance of 90 feet, these
dykes may be seen traversing the chalk, which is con-
verted into a finely granular marble, where contiguous
» Dr. Berger on the Geological Features of the North of Ireland, GeoL
Trans, vol. iii. p. 172.
CHAP. VIT.
UNSTRATIFIED ROCKS.
129
to the two outer dykes, and through the whole of the
masses included between them and the central one.
The following diagram, copied from Mr. Conybeare's
section (Geological Transactions, vol. i. pi. 10.), will
be useful for reference. It represents the ground plan
of the dykes as they appear on the shore.
d 1. Dyke, 35 feet wide.
d 3. Dyke, 20 feet wide.
m. Granular marble.
d 2. Dyke, 1 foot wide,
c. Chalk.
One of the most direct objections to that part of the
Huttonian system'of geology in which the induration
of rocks is attributed to the action of heat, was drawn
from the calcareous strata, which, it was said, would
have parted with their carbonic acid, and thereby have
ceased to be limestone. That such an effect would take
place in the open air, in the ordinary state of limestone
(not perfectly dry), is a matter of invariable experience;
but Dr. Hutton, with his accustomed sagacity, pro-
posed the hypothesis that the carbonic acid gas would
not be liberated by heat under great pressure, such as
the weight of the ocean pressing on its bed. This hy-
pothesis, sir J. Hall, with equal sagacity, put to the
test of accurate and conclusive experiments. In the
breech of a gun-barrel he placed an earthen tube half
filled with calcareous matter in powder, and strongly
compressed, the rest of the space being filled with
powdered silica. The tube was then closed hermetically
by a mixture of fusible metal. The end of the barrel
where the powdered earth was, being heated in a furnace,
a part of the fusible racial yielded to the heat, and came
VOL. II. K
130 A TREATISE ON GEOLOGY. CHAP. VII.
nearly into contact with the porcelain tube (separated
by aqueous vapour and air) ; the rest remained solid.
After the heat had been sufficiently applied, and the
whole had become cool, the fusible metal which stopped
the tube was melted out by moderate heat, and the
calcareous powder in the porcelain tube was examined.
Similar experiments were made in porcelain tubes alone,
with different modes of hermetical sealing. The general
result was, that, under mechanical pressure, carbonate of
lime may be exposed to great heat without calcination ;
while, by the effect of great heat and pressure combined,
the calcareous powder was agglutinated into a solid
limestone, nearly as hard and as heavy as the natural
rock. Some portions might even be polished as marble.
By a mechanical contrivance, the degree of pressure
on the materials exposed to heat was varied and measured ;
and it appeared, that with a pressure of 52 atmospheres,
equal to a column of 1700 feet of sea- water, powdered
limestone was converted to hard stone ; with 86 atmo-
spheres, equal to a column of 3000 feet of sea-water,
it is changed to marble; with a pressure of 173 atmo-
spheres, equal to a column of 5700 feet of sea-water,
it is completely fused, so as to act strongly on other
earthy substances.
The celebrated marble of Carrara is probably an
altered limestone of the oolitic era.
Having now seen many examples of the conversion of
common limestone into crystalline marble, both by
actual experiment, by volcanic action, and the heat
communicated from pyrogenous rocks of different kinds,
the application of these truths to the history of the
" Primary Strata" is obvious. For primary limestones
differ from secondary and tertiary calcareous deposits
merely by their mode of aggregation, which is not such
as water ever produces in carbonate of lime, but is
exactly comparable to that occasioned by heat. And
this general analogy is strengthened by collateral cir-
cumstances, as, for example, the frequent occurrence of
serpentine in some of the " primary" limestones is a
CHAP. VII. UNSTRATIFIED ROCK?. 131
fact exactly parallel to the introduction of serpentine
among the crystallised metamorphic limestone of Skye
(noticed by Macculloch). In Radnorshire, Mr. Mur-
chison observed the ramification of serpentinous strings
through limestone which was otherwise altered in con-
tact with a felspathic trap ; and in this and other places,
anthracitic coatings and nests, and crystals of copper and
iron pyrites, complicate the effects. In one place, a
serpentinous rock of this kind is 20 or 30 feet wide.
If therefore, in conformity with so many and such
strong analogies, we admit the inference that the crys-
talline primary limestones have acquired this character
by the action of heat, it must follow that this heat was
of a very general, if not universal, application below
the primary strata, for there is, perhaps, no considerable
district known where the gneiss and mica schist systems
are devoid of such crystalline limestone, and the occur-
rence of it is not specially connected with the local ap-
pearance of igneous rocks. This important inference
will, however, be invested with a higher degree of pro-
bability if it be also found, as a matter of fact, that the
other strata with which this limestone is associated show
independent signs of having been subjected to a general
heat.
Alteration of the Chemical Nature of Rocks.
One of the most popular of all the proofs of the
pyrogenous origin of basalt and greenstone, is the effect
they produce on coal and bituminous shales, for by their
action the coal is often turned to coke, and the dark shales
assume a very light colour. These effects are almost
too common in Scotland and the North of England to
deserve especial notice. Thus the Kyloe dyke, which
crosses the Tweed below Lennel, has converted the coal-
seams intersected by it into a sort of cinder, the bitu-
minous matter having been entirely dissipated. (MttitB
on the Geology of Berwickshire.} Several of the dykes
in the collieries of Newcastle and Durham (as the dyke
K 2
132 A TREATISE ON GEOLOGY. CHAP. VII.
in Walker colliery, the Coley Hill dyke, the Cockfield
fell dyke, &c.) have expelled the bitumen from the
coals and shales, to various distances, according to the
width of the dykes, and other less known conditions of
the adjoining strata. The anthracite has in some
instances been injected into the cracks of neighbouring
sandstones. Analogous facts on a smaller scale are
found in connection with the trap dykes in Radnor-
shire, &c., which are frequently accompanied by anthra-
citic nests and coatings.
The following notice of the effects of the remarkable
Cockfield dyke is from an eye witness, whose observ-
ations were communicated to me by my friend John
Ford, esq.
" In working the coal towards the dyke, when within
50 yards of it the coal begins to change. It first loses
the white spar in its joints and faces; looks dull, tender,
and short; and loses its quality for producing flame.
Nearer the dyke it has the appearance of half-burnt
cinder: still nearer it decreases in thickness, and be-
comes a hard cinder 2 feet 6 inches thick. Eight yards
from the point at which the coal becomes a real cinder,
that is, 8 yards nearer the dyke, the coal assumes the
appearance of soot caked together ; it is called fdawk'
or ' swad : ' when it touches the dyke, the coal is re-
duced from 6 feet to 9 inches."
" On each side of the dyke, betwixt it and the regular
strata, there is a thin layer of clay, or, as it is called, a
' gut ' or ' core,' about 6 inches thick, which turns the
water from the rise to the dip side of the dyke, and
forces it to the surface in several springs, in the direction
of the dyke, where it crosses the country/' The da-
mage done by the dyke is thus estimated: "25 yards
of tender, short, spoiled coal; 16 yards of cinder;
and 10 yards of dawk or swad," making a total of 100
yards of spoiled coal throughout Cockfield fell. The
dyke is nearly vertical, and 18 yards in width; the
strata of coal, sandstone, &c. are dislocated by it about
CHAP. VII. UNSTRATIFIED ROCKS, 133
three fathoms. In other situations the " throw" is
greater.
The application of these facts to the explanation of
the condition of ancient strata is important. "For it is
a general fact, that the carbonaceous substances which
are associated with any part of the primary or transi-
tion strata, are of the nature of anthracite, which is
devoid of bitumen. Whether it will be proper to
extend this explanation to the large anthracitic beds of
Pennsylvania, South Wales, Devonshire, Brittany, &c.,
some of which lie among secondary strata, is at present
uncertain.
Dolomitic Limestone. — One of the effects of the sie-
nite of Skye, in contact with the lias limestone, which
it converts to fine granular marble of many colours, is the
introduction of silica, alumina, and magnesia, into its
composition. (Macculloch, Geol. Trans, vol. iii. p. 42.)
This sienite is principally a felspathic mass, varying
from claystone to clinkstone and compact felspar, from
which no transfer of magnesia could be supposed. Von
Buch, in the course of his extensive and laborious ex-
aminations of plutonic and volcanic rocks, was led to
attribute to a rock of quite another kind, the melaphyre
(black or pyroxenic porphyry) of the southern flank of
the Alps, not only an important function in the elevation
of mountain ranges like the Alps, but the peculiar che-
mical and mineral change which is locally noticed in
some of the limestones. By this change carbonate of lime
becomes a double carbonate of lime and magnesia ; the
compound is crystalline, and often of a dazzling white-
ness. This is the case with the dolomite of St. Gothard,
and with much of that which occurs on the Lago
Lugano.
This last is the vicinity to which Von Buch has
specially directed the attention of geologists, and as
melaphyre, granite, dolomite, and common limestone
here occur in abundance and in varied circumstances of
exposure, perhaps no better locality can be chosen for
134 A TREATISE ON GEOLOGY. CHAP. VII.
investigating the truth and applicability of the opinion
of this eminent geologist.
Between Varese and Tresa is seen the section pre-
sented below. In this section the main facts commonly
01
Mt. Beuscer
1. Gneiss. 2. Mica schist. 3. Granite. 5. Melaphyre.
6. Tuff. 8. Sand and gravel. 9. Limestone. 10. Dolomite.
noticed as to the association of melaphyre with the other
rocks are well typified, and it is seen that the occur-
rence of dolomitic limestone is not uniformly connected
with the appearance of melaphyre ; sometimes it adjoins
granite, in other localities mica schist : it also appears
that limestone is not always dolomitised in contact with
melaphyre, or granite ; and those geologists who have
imagined that Von Buch supposed there was a real trans-
fer of carbonate of magnesia from the augitic rock, have
very naturally arrived at the inference that this district
lends no countenance to the speculation. But we learn
from M. Elie de Beaumont (Ann. des Sc. Nat. vol.
xviii.), that this was not Von Buch's meaning, and
indeed, that would easily appear from the facts quoted
by him in support of his opinion. The true notion
advocated by Von Buch, of these transformations of
limestone, is that the eruption of melaphyre was coin-
cident with violent disturbances and fractures of the
country in a particular line parallel to the melaphyre ;
and that along the fissures then produced, gaseous sub-
limations of different kinds found their way to the
surface, and altered particular rocks in their passage.
The ordinary and obvious form of objection above
noticed therefore fails ; and it remains to be seen whether
the occurrence of dolomite in definite relation to lines
of meJaphyre, or, to take the problem in a still more
CHAP. VII. UNSTRATIFIED ROCKS. 135
general sense, to fractures of the earth's crust, is a
circumstance well proved ; and if so, whether the sub-
limation of carbonate of magnesia would be chemically
probable. On this latter subject, Dr. Daubeny and Dr.
Dalton stated facts in confirmation of the view of Von
Buch (Reports of the British Association, for 1 835),
and on the former question, we have related, in describing
the geology of Yorkshire, the dolomitisation of common
limestone by the sides of faults and mineral veins, far
away from igneous rocks of any kind. It seems, there-
fore, unsafe to reject Von Buch's remarkable hypothesis,
without a patient investigation of many collateral points;
and, on the other hand, the dolomitic masses of Fran-
conia, which form a part of the Jura kalk, and the
magnesian limestones of England (extensive deposits
which are unconnected with pyrogenous rocks), appear
to show that subterranean heat is not the only nor the
principal means of introducing magnesia as an ingredient
of limestone. We may, indeed, choose further to suppose
that the submarine springs, which probably gave origin
to the magnesian limestones of Durham, were a con-
sequence of that great disturbance of the earth's crust
which is so manifest in the coal districts of England ;
and this easy and probable explanation for these cases,
while it recognises the general principle which connects
magnesian limestones with dislocations of the strata,
may possibly be found applicable to other examples.
One of the points favourable to investigation of the
relation of dolomitic limestones to volcanic forces, is
Gerolstein in the Eifel, where, round a particular vent,
for a considerable space, the " transition " limestone
(corresponding exactly to the "Wenlock" limestone in
the silurian system of England) is converted to dolo-
mite, and appears in the usual unstratified, fissured, and
antiquated forms of that rock, while further off it is a
thin-bedded rock; organic remains occur in both thecom-
mon and dolomitic limestone (observed 1829). To tne
facts which appear in this volcanic region, Von Buch
appealed in proof of his hypothesis ; but Dr. Daubeny
136 A TREATISE ON GEOLOGY. CHAP. VII.
{On Volca nos, p. 51.), after describing the cellular cha-
racter of the lava, and the way in which it is related to
the present form of the surface, observes, " It seems diffi-
cult to reconcile the hypothesis of Von Buch with the age
which we are compelled to assign to the volcanic opera-
tions here, as well as in other parts of the Eifel. As it is
evident that no foreign ingredient could penetrate the
substance of the rock in its present hardened condition,
so as to unite with the other constituents, and diffuse it-
self uniformly through the mass, it seems necessary for
Von Buch's hypothesis to suppose the limestone to have
previously been at least softened by the heat, which
occasioned the sublimation of the magnesia. Hence we
should be obliged to fix the period at which this process
took place as antecedent to the formation of the valleys,
for these would be necessarily obliterated by any soft-
ening of the limestone which now overhangs them.
" Indeed it would be necessary to carry back this
supposed softening of the calcareous rocks'to some period
antecedent to the retirement of the ocean, when sufficient
pressure might be exerted to prevent the carbonic acid
from being driven off from the limestone when exposed
to the heat required for softening it.
' « But all this is contradicted by the phenomena of the
volcanic products in question, the cellular appearance of
which plainly indicates the absence of pressure, and
which even seem, from the existence in them of craters,
and by the manner in which they have accommodated
themselves to the present slope of the valleys, to have
been formed since the commencement of the present
order of things.'*
Dolomitic limestone is not at all common among pri-
mary strata, though these early limestones often contain
serpentine in strings and veins, augite (as at Tiree)^
mica, and other magnesian minerals.
Generation of New Minerals.
Perhaps no more interesting or satisfactory evidence
CHAP. VII. UNSTRATIFIED ROCKS. 137
of the generation of new minerals in strata which ad-
join a " trap " rock has ever appeared than in the
description of the great dyke south of Plas Newydd in
Anglesea, hy professor Henslow. (See Camb. Phil. Trans,
vol. i.) The substance of this dyke is basalt, composed
of felspar and pyroxene; its width is 134 feet, and it
cuts perpendicularly through strata of shale and lime-
stone. The strata on each side form an abrupt cliff,
against the Menai shore, about 15 feet high, but the
dyke, through decomposition, offers a gradual slope.
The Plas Newydd dyke crosses the Menai. The cliff
which bounds the dyke at Plas Newydd is composed of
clay shale, and argillaceous limestone. The lowest por-
tion (thin calcareous shaly bed), on approaching the
dyke, undergoes various changes. At 15 feet from
the contact it forms a compact bluish grey mass, with
spots of a fainter colour. In contact it is bluish green,
very compact and hard. The shaly structure disappears,
in a great measure, near the dyke (as at Coley Hill).
The next portion of the cliff, proceeding upwards,
consists, at 50 feet from the dyke, of a soft dark-co-
loured plastic clay shale, thinly laminated. At 35 feet
from the dyke this becomes indurated; at 10 feet it is
a cherty mass, inclosing patches of highly crystalline
limestone; in contact it is a hard porcellanous jasper of
various colours. (Impressions of shells remain in it.)
The third division of the cliff consists of dark argil-
laceous limestone, which in contact is found of a
speckled dull green and brown colour.
Above this is a thick body of clay shale, which, near
the dyke, is partially turned to a flinty mass, while the
rest of the shale assumes a confused appearance of crys-
tallisation and globular structure. Perfect crystals are
recognised in this mass of two distinct kinds, and ex-
hibiting every gradation of aspect from a globular and
concretionary to a perfectly crystalline character. Some
of the crystals (analcime) have twenty-four trapezoidal
faces. Shells of brachiopoda are enveloped in globules and
crystals. Other crystals have twelve rhomboidal faces,
138 A TREATISE ON GEOLOGY. CHAP. VII.
and prove to be garnet of specific gravity 3'353. The
crystals were examined by professor Gumming, and
those of analcime analysed by him, and found to have a
specific gravity of 2*293, or 2 '394. Minute garnets in
the form of rhombic dodecahedrons were found by the
Rev. J. Harrison under the basaltic mass which over-
hangs the Tees, below Caldron Snout in Teesdale, in
altered shale and limestone.
The segregation of mineral substances in rocks ad-
joining trap dykes is noticed by Mr. Milne, in his ac-
count of the geology of Dumfriesshire.
Since it thus appears that in many instances where
the masses of igneous rock were considerable, perfect
garnets have been produced by heat in the neigh-
bouring sedimentary strata, though these were not in
other respects re-crystallised, we turn with interest to
the well known and general (though not universal) fact
of the occurrence of garnets in the ancient strata of
gneiss and mica schist, as a valuable addition to the
evidence brought by the crystalline limestone associated
with the same strata, in favour of the opinion that the
whole mass of these rocks has been subjected to a per-
vading high temperature. For the occurrence of garnets
in mica shist and gneiss is entirely unconnected with
any local effect of heat derived from particular masses
of granite, greenstone, &c. ; nor can their occurrence
be often accounted for by any supposition of their
having formed part of more ancient rocks, which by
disintegration yielded them to the watery currents con-
cerned in accumulating the primary strata; for they are
in general perfectly crystallised, among fragmentary
scales of mica, and worn and broken felspar and quartz,
or granular aggregates of those substances, scarcely dif-
fering in arrangement or aspect of the parts from par-
ticular sandstones and coarse argillaceous slates. The
term so commonly employed of " crystalline schists,"
for mica schist, gneiss, &c., appears to be seldom jus-
tified by accurate examination ; for frequently, we
CHAP. VII. UNSTRATIFIED ROCKS. 139
believe, the parts of these rocks are not individually
crystals (as mica and felspar are in granite), nor en.
velop crystals (as quartz often envelops the other sub-
stances in granite), nor are in a state of crystalline
aggregation, as the grains and plates of most primary
limestone, but are parts of crystallised bodies frag-
mented and worn in various degrees, aggregated in
laminae under the influence of water (perhaps in a
peculiar state), and subsequently consolidated, but not
melted, nor re-crystallised, by the application of heat.
It is, however, thought by some geologists that the
whole mass of the primary schistose rocks is to be viewed
as metam orphic ; as transformed from some other sort
of sedimentary rock — grauwacke, for instance — and re-
arranged into a crystalline rock of granitic aspect and affi-
nity. We must therefore pay attention to some of the
evidence which is adduced in support of this important
hypothesis.
Metamorphic Slates.
As containing examples of metamorphic rocks, on a
considerable scale, and of interesting if not remarkable
variety, the district of the Cumbrian mountains may be
advantageously quoted. In connection with the granite
of the Caldew occurs the remarkable mass of chiasto-
litic and hornblendic slates, which form the base of the
clay slate system of Cumberland ; and it is thought that
these rocks are, at least in part, metamorphic, similar
combinations being found in analogous situations else-
where. Dr. Macculloch ascribes a metamorphic origin
to hornblende schist, viewing this rock as the extreme
term of a series of changes commencing with clay or
shale, and passing through siliceous schist or Lydian
stone. Argillaceous schist, when in contact with granite,
is sometimes (as in Shetland) converted into hornblende
schist.
The hornblende schist of the Cumbrian granitic
district is in places similar to that which adjoins
140 A TREATISE ON GEOLOGY. CHAP. VII.
the granite of Glen Tilt ; and in each case its slaty
structure is parallel to the crystalline faces of the prisms
of hornblende. Some of this rock is almost pure crys-
tallised hornblende ; in other parts hornblende and fel-
spar appear ; but in Cumberland at least, and, judging
from specimens, we think also in Cornwall, it is not
quite correct to call another metamorphic rock gneiss.
There appears to be produced, in connection with the
granite of the Caldew, a combination (in small quan-
tity) of crystallised mica and uncrystallised quartz,
which has been called mica slate. The main fact to be
attended to with regard to these phenomena of contact
is, whether the parts of the altered rocks called gneiss,
hornblende schist, mica schist, &c., are really crystals,
andm crystalline aggregation, — circumstances often erro-
neously admitted with regard to primary strata, in con-
sequence of the very inaccurate use of these important
and characteristic terms.
In professor Sedgwick's account of the succession of
the strata above the granite of the Caldew, given below,
he seems to refer all the interpolated crystals of the
upper part of the series to chiastolite. Some of the
rocks appear, however, to be genuine hornblende slate
crystallised, and one of our specimens is traversed by a
granite vein.
Skiddaw slate. — Generally a fine glossy clay slate, much
penetrated by quartz veins.
Crystalline slaty rocks : —
1. Skiddaw slate, with interspersed crystals of chiasto-
lite, alternating with and passing into the pre-
ceding group.
2. A similar slate, with numerous crystals of chisato-
lite, passing in the descending order into a crystal-
line slate, sometimes almost composed of matted
crystals of chiastolite.
3. Mica slate spotted with chiastolite
4. Quartzose and micaceous slates, sometimes passing
into the character of gneiss.
Granite. — (White felspar, grey quartz, and black mica.)
CHAP. VII. rXSTHATIFIED ROCKS. ' 141
A different series of changes may be traced among
different rocks in Borrowdale and Wastdale, where the
members of the middle division of slate rocks abut
against the granitic mass which forms the base of Sea-
fell, and occupies considerable breadths- in Eskdale.
The slaty rocks alluded to are bedded and laminated;
but besides the cleavage structure, which has been super-
added, and which crosses all the beds of fine, coarse,
and laminated grauwacke, we notice (as in the rocks
which overhang the Bowder Stone) extreme induration,
and the plentiful occurrence of spots and strings of
epidote. In other beds the stratification remains, but
the mineral composition is complicated by the segre-
gation of spots of green earth, and nodules of green
earth, calcareous spar, quartz, or even calcedony, so
that the stone would, by most persons, be called amyg-
daloid. It is, however, a widely stratified rock, and
passes by perfect gradation in Borrowdale, near Ulpha
Park, on Grasmere, and in Patterdale, to the common
bedded and spotted slate* On approaching yet nearer
to the granitic mass, other changes appear; the slaty
stone becomes very hard and compact, is traversed by
abundance of fissures, acquires a peculiar spotting,
which finally assumes the character of felspar, till the
whole mass becomes what is often called clay porphyry,
and at length can in no manner be distinguished from
variolites and porphyries with a compact base. (Some
of these rocks have been called greenstones.) This
series of changes may be traced in a breadth of two
miles, by walking over the summit of drainage betweea
Borrowdale and Wastdale, called Stye Head.
What renders these alterations the more interesting,
is the abundant occurrence of garnets of a fine red co-
lour and perfect crystallisation (rhombic dodecahedron)
in the porphyritic, partially porphyritic, and even brec-
ciated rocks. Such specimens may be gathered on the
slopes of the Gable Mountain, or obtained from the rocks
near the summit of the pass of Stye Head (observed
by the author 1838). How many of the porphyiitic
142 A TREATISE ON GEOLOGY, CHAP. VII.
masses of this interesting region may hereafter be ranked
as metamorphic slates, we cannot predict ; but many
rocks at the base of Helvellyn and in the Vale of St.
John's (some of which contain garnets) appear to the
author to deserve examination in this respect.
On a great scale, the alternation of porphyritic and
schistose rocks in this region is established by professor
Sedg wick's laborious researches, still only partially known
to geologists. The results of his corresponding examin-
ation of the parallel series of rocks in North Wales
appear very similar to those obtained in the Cumbrian
mountains. (See Geol. Proceedings, vol. i. p. 400.)
The alterations produced upon the argillaceous slaty
rocks of Cornwall, by the proximity of granite, are
differently reported by different observers; but in ge-
neral they appear to be inconspicuous, and perhaps can-
not be described in a smaller compass than in the words
of Oeynhausen and Von Dechen, who say, — " The killas
is, at its junction with the granite, rather hornblende
slate and greenstone than clay slate. The transition
from clay slate into hornblende slate and greenstone is
commonly so gradual, that we have not been able to
trace any where a line of junction between both rocks."
(Phil. Mag. and Annals, 1829.) The slightness of
the changes which are remarked near many of the gra-
nite veins of Cornwall is not an unusual circumstance
elsewhere, among argillaceous slates inclosing green-
stones and porphyries ; and perhaps the reason may be,
that these substances had already undergone great heat,
and suffered a great degree of change from their first
condition.
Speaking with reference to the granite of Cligga
point, and the porphyritic elvan courses of St. Agnes,
the Rev. J. Conybeare observes, — " The killas, which
is traversed and covered by these more crystalline rocks
has, for the most part, the character usually ascribed to
clay state, and its strata occasionally present singular
curvatures ; in many places it passes into chlorite slate.
CF1AP. VII. UXSTRATIFIRD ROCKS. 143
and in the immediate neighbourhood of these dykes it
usually presents either a highly crystallised form of that
rock, or such an intermixture of it with quartz and fel-
spar as might fairly be esteemed a variety of gneiss."
(Geol. Trans, iv. p. 403.)
Metamorphic Mica Schist, Gneiss, S$c.
From cases like those already mentioned, where argil-
laceous slates, on approaching granite, appear in every
intermediate state of change till they finally are con-
verted to clay porphyry or to hornblende slate, we pass
to consider other supposed transformations, in which
the original substances are similar, but the product is
different. Speaking of the altered rocks round Dart-
moor, Mr. De la Beche (Manual, p. 479-) observes, —
" The grauwacke slates in many parts of the country
surrounding the granite of Dartmoor have suffered from
its intrusion, some being simply micaceous, others more
indurated and with the characters of mica schist and
gneiss, "while others again appear converted into a hard
zoned rock strongly impregnated with felspar."
Von Dechen's account of the changes effected by
the granite of the Hartz on the grauwacke of that
region, appears not dissimilar to the description we have
given of the Cumbrian rocks, for flinty slate, quartz rock,
greenstone, &c. are stated to be the result of the igneous
action. Mr. Griffith has found it convenient to express
by a particular colour the metamorphic portion of the
slaty series of the South-east of Ireland which surrounds
the granite of Wicklow and Wexford. He describes
them as ef altered rocks in the neighbourhood of granite,
clay slate, passing into greenstone or greenstone slate, or
serpentine, or crystalline micaceous slate, or micaceous
shining slate, or flinty slate." Similar phenomena are
recorded by the same geologist, in a considerable breadth
round the Mourne mountains. (See his Map, 1838.)
Von Buch first made known the interesting circum-
stances under which the syenite of Christiania touchea
144 A TREATISE ON GEOLOGY. CHAP- VTT.
and partially overlies the " transition " rocks of that
country, which yield trilobites, orthocerata, &c. in con-
siderable abundance. Mr. Lyell has recently explored
this district, and, fully confirming the important infer-
ence of Von Buch, that the sienite was of posterior date
to these transition strata, observed those changes which
are now known to be the frequent concomitants of the
contact of igneous and stratified rocks. The limestone,
usually of very dark colour, is turned into white marble,
the schist into Lydian stone, and " sometimes into mica
schist," of which Mr. Lyell saw one striking example
at Grorud, north-east of Christiania. Traces of fossils
are not unfrequently discoverable in some of the crys-
talline and altered rocks of the transition formation, so
that the actual conversion of the latter into metamorphic
strata is unequivocal. (Lyell, in Brit. Assoc. Reports,
1837-) The rocks here termed syenite are considered
by Mr. Lyell to be (geologically speaking) of the granitic
family; they seem to pass into trap porphyry, and divide
the gneiss and less ancient schists in a very irregular
manner, but do not spread widely over them in any part
of the district. Tabular masses of igneous rocks are no
where seen to spread over the fossiliferous rocks, except
where they have assumed the usual aspect and charac-
ters of trap.
The oolitic system of strata, as described by De Beau-
mont, Necker de Saussure, and Brochant de Villers, in
the Tarentaise, Dauphine, and the valleys near Mont
Blanc, puts on a very different aspect from that which
is usual in the more level regions of Germany, France,
and England; and this difference appears similar to
some occurrences mentioned by Studer and De Beau-
mont, which are obviously dependent on the heat of
contiguous granitic rocks. In the Tarentaise, siliceous
limestones, micaceous quartz rocks, and gypsum, cor-
respond to the lias and lower oolitic rocks of England ;
and contain the fossils common in these rocks. It is
further remarkable, that at the Col du Chardonnet
(Hautes Alpes), plants, supposed to be of species which
CHAP. VII. UNSTBATIFIED ROCK?. 14.5
also occur in the coal formation, lie in beds which alter-
nate with others containing belemnites of the lias. In
the upper part of the Buet, Necker de Saussure has ob-
served the following series of strata : viz., mica schist
covered by various sandstones and schists ; Triack slaty
beds with talcose impressions of ferns ; dark impure
limestones ; black slaty clay with nodules of Lydian
stone, alternating with talcose slaty clay, both contain-
ing ammonites ; and over all a grey calcareous belem-
litic shale, to the top of the Buet.
Relative Antiquity of Pyrogenous Rocks*
The determination of the relative antiquity of the
unstratified rocks is a point of much importance, and
of great difficulty. Taken generally, it is an indeter-
minate problem ; for though, in a vague sense, we may
easily be satisfied that granitic and other felspathic rocks
are more ancient than basaltic and other augitic rocks,
yet there can be little doubt that some of these latter,
as, for example, the bedded greenstones of Wales and
Cumberland, are of higher antiquity than the granitic
rock of Weinbohla, which rests on members of the
cretaceous formation.
When we consider this question with reference to a
small district, as, for example, the Island of Arran, so
rich in various rocks of igneous origin, the result to
be looked for is like that which may be gained by ex-
amining a volcanic mountain, where certain different
rocks have at different times been ejected by the same
volcanic forces. In Arran, for instance, we have
granite, sienite, porphyries of many kinds, claystone,
hornstone, pitchstone, greenstone, basalt. These cross
and complicate one another ; and it is possible, upon
certain suppositions or admissions, to determine their
relative antiquity. If the conclusion be substantially
correct, and the order of production among these rocks
be known, the interpretation may be trusted to the
small extent of inferring, that below this small tract,
VOL. n. L
146
A TREATISE ON GEOLOGY.
CHAP. VII.
at different successive times, rocks of different chemical
composition existed in a melted state, and were forced
upwards through rifts in the strata. The same thing is
known with respect to modern volcanic accumulations,
which change with time ; and there remains for each case
the same further question of the cause of these mineral
changes under a given area of the earth's face.
The principle upon which the inquiry proceeds in
the case of the older rocks, was strongly enforced and
applied by Werner ; but is not universally, though
perhaps it is generally, admitted. Dykes fill fissures
in stratified and unstratified rocks ; mineral veins appear
under the same circumstances. Where the rocks are
distinctly stratified, and are of different qualities in the
different beds, and contain organic remains in some or
all of the beds, the proof that the fissures alluded to
are of later date than the formation of the rocks is con-
clusive: therefore the dykes, which fill these fissures,
are of still later date ; and the same conclusion is ex-
tended to unstratified rocks : nor is it limited lo the
great masses of rocks. When dykes or veins intersect
one another, that which is divided is the older, that
which cuts through another is the newer. Thus, in
the diagram (No. 92.), taken from Dr. Macculloch's
drawing in the Geological Transactions, vol. iv. pi. 6.
(S) the schist rock is divided by veins of granite (G),
£. Schist.
G, Granite veins.
P. Porphyry dykes.
CHAP. VII. UNSTBATIFIED ROCKS. 14
which fill ramified fissures, and are themselves crossed and
cut through by straight dykes of porphyry (P). This
occurs in Ben Cruachan, by the shore of Loch Awe.
Upon this principle Werner speaks confidently of the
relative age of mineral veins ; and it is the general
impression of miners and geologists, that he is right in
so doing.
On a greater scale, the same problem is presented to
us by examinations of large districts, like Ireland, the
Pyrenees, Cornwall, or the Bohemian mountains. But
the data necessary for the solution of this problem are
quite different, and the result becomes a part of the
history of the formation of the crust of the globe. It
is requisite to know in this case what relation the several
rocks of igneous origin bear to the stratified rocks among
which they appear. In this inquiry we must not assume
that all the masses of igneous rocks of the same nature
have been forced among the strata at the same time ;
this would be sometimes erroneous, always insecure.
One of the most certain proofs of the exact age of a
particular mass of igneous rock, is also one of the
rarest. When strata a, 6, c, d are traversed by a trap
dyke, and these strata, together with the dyke, are over-
laid by the next stratified rock in order of time e, it is
evident that the dyke was formed in the interval
(whether long or short) between the deposition of d
and e. Such a case is believed to occur on the line of
a trap dyke which crosses the Durham coalfield from
Eggleston to Quarrington, dividing the coal strata, but
not the superincumbent magnesian limestone. A similar
dyke, starting from near the same point, passes into the
oolitic system ; and thus we learn that the igneous
action in Teesdale, which commenced in the early car-
boniferous period, continued to produce similar basaltic
rocks till after the deposition of part of the oolites ;
and there is nothing which prevents us from supposing
that this last eruption may have been of much later
date, as the great eruption in the north of Ireland is
known to have been.
148 A TREATISE ON GEOLOGY. CHAP. Vlf.
The great basaltic plateau in the counties of Antrim
and Londonderry rests upon chalk ; there are no tertiary
strata above it : its date is therefore only known ap-
proximately : it was effused during the tertiary eras.
The great basaltic masses of Mull and Skye, of Arran
and Ayrshire, the Ochill Hills, &c., appear in directions
and under circumstances which seem to connect them
with the same seat of volcanic action as the Irish
basalts ; but data are* wanted for determining the age of
their eruption.
Mere association of igneous rocks with particular
strata only proves that such rocks are at least not older
than these strata : the case of the dyke traced by Mr.
Murchison from theBreiddyn Hills (amid primary strata)
and under and into the new red sandstone of Acton
Reynolds, shows how very little propriety there is in
classing trap rocks by the strata among which they have
been injected ; since this is, in fact, " a geological ac-
cident/*
It is remarkable with regard to granite and rocks
closely allied to it, that, excepting at a very few spots,
among which Weinbohla on the Danube is the most
remarkable, these igneous products are not seen in
contact with any of the strata of the secondary or
tertiary class. Granite touches gneiss at Strontian j
mica schist in Ben Nevis ; hornblende schist, argil-
laceous schist, and primary limestone in Glen Tilt ; clay
slate and grauwacke slate in Wicklow, Anglesea, Devon,
and Cornwall.
It has been supposed that granites of different an-
tiquity possess distinguishable mineral characters. The
opinion is not improbable ; but it is difficult to assure
ourselves of its truth, because, as Humboldt confesses,
it would be difficult to mention a granite which
geognosts unanimously consider as anterior to every
other rock. The same author observes, while speaking
of " primitive " granite, " it appears to me that in both
hemispheres, particularly in the New World, granite is
most ancient when it is richer in quartz and less
CHAP. vii. L-.VSTRATIFIED BOCKS. 149
abundant in mica ; and he notices the addition of horn
blende as characterising the most modern granites. As
before observed, the three granitic masses in the midst
of the Cumbrian mountains present as many distinct
sorts of granite, and each belongs to a distinct place in
the series of slates. The Skiddaw granite is quartzose
and micaceous, and underlies the lowest slate rocks ; the
Eskdale granite is quartzose with little or no mica, and
lies among green slates of the middle division ; the
Shap granite contains but little quartz, is porphyritic in
structure, and lies near the base of the upper Cumbrian
series of slates. Whether these granites are .of the
same or very different geological eras, cannot be known
without the most careful study of the district under-
taken for the purpose.
Those geologists who think that the culmiferous
strata of Devon form part of the carboniferous system
of England, which overlies old red sandstone, may believe
the granite of Dartmoor to have been erupted since the
age of the mountain limestone ; for the culm measures
are greatly contorted where they approach the igneous
rock.
At Weinbohla on the Danube, according to professor
Weiss, confirmed by many subsequent authorities, occurs
a real superposition of granite (or sienite) on chalk
and green sand, which strata, usually horizontal, dip
suddenly beneath the granite in some places, and rest
upon it in others. (See De la Beche's Manual, for a
detailed account.)
In the Pyrenees we learn from M. Dufrenoy, that
granite sends veins into chalk, and converts it into
granular crystallised limestone, and generates in it
valuable veins of iron ore. This range of mountains
is remarkable for showing contacts of granite with cal-
careous beds of the several eras of transition rocks,
lias, and chalk, and in each of these cases the lime-
stone become crystalline and metalliferous.
Our view of the history of igneous rocks will be both
more complete and accurate by considering them in
connection with the lines and points where the strata
L 3
150 A TREATISE ON GEOLOGY. CHAP. VII.
have been subjected to remarkable disturbance. By this
means their true origin becomes, if possible, more clear,
their relative antiquity less doubtful, their affinity to the
products of modern volcanos more definite. As by the
modern earthquake the ground is opened far beyond the
reach of lava currents, so in earlier times great fractures
were not every where filled with melted rock ; but yet it
is only along and near to lines of subterranean disturb-
ance that the "hypogene" rocks have risen to the
day. Their dependence on such dislocations is very
unequal : granitic rocks show themselves in distinct
connection with the principal ranges of mountains which
mark the most considerable effects of modern subter-
ranean disturbance. Minute scrutiny may show in many
mountain chains that the granite, which is almost uni-
versally present, does not uniformly occupy the mineral
or geographical axis or centre of the rocky group ; —
amidst the complicated displacements which there
occur, this could seldom be exactly the case; but a
glance at all good geological maps will satisfy the im-
partial student that the connection of granitic elevation,
uplifted primary strata, and mountain country, is real,
if not necessary, and of high theoretical importance.
(See Vol. I. p. 38.)
Rocks which in some degree share with granite this
character of central position, with respect to mountain
ranges of primary strata, are hypersthenic syenite and com-
mon syenite, and certain porphyries which graduate into
granite, and sha^e its geological history. But the trap
rocks generally, including in this term the augitic and
hornblendic rocks, and the porphyries which are related
to them, are differently circumstanced. Von Buch has
remarked, concerning augitic porphyry, that it ranges
parallel to, and is found constantly at the base of, great
chains of mountains ; and he attributes to this porphyry
a powerful influence in the elevation of the mountains.
If we consider the granites as supporting lines of prin-
cipal movement among the stratified masses, and re-
collect that, on a great scale, the angle of elevation
CHAP. VII. UNSTRATIFIED ROCKS. 151
quickly diminishes as we proceed from the mountains,
till, in plains not far remote, the strata retain their hori-
zontality, we may say that the trap rocks are most
abundant in points and in lines distributed between the
granitic axis and the level plains. In some instances
trap rocks occupy an extent of country not inferior to the
area of granite. The Ochill 'Hills, the Campsie Hills
the Pentland Hills, and others connected with them, form
one great trappean country filling the vale of the Forth
and Clyde, which is a great natural hollow between the
ranges of the Grampians and the Lammermuir moun
tains, both elevated on axes of granite and syenite.
Large breadths of trap rocks appear in Skye, Rum, Eigg,
Mull, Arran, and Antrim ; but in none of these cases
is their appearance connected with ridges of stratified
rocks, as granitic masses almost invariably are. More-
over these trap rocks, whether in the shape of dykes or
overlying masses, are usually so disposed as to suggest
the idea of volcanic action, determined to particular
points, and bursting out and overflowing from particular
lines, rather than a general expansion beneath immense
areas of strata which seems best to agree with granitic
elevations.
Trap dykes are frequently manifested along the lines
of faults, and these may sometimes be determined in
geological age by the circumstances which accompany
the disturbed strata.
Keeping in mind these general facts, but disregard-
ing the crude notions which attribute to granite or trap
rocks the elevations and fractures which have merely
opened to us their subterranean repository, or given
them channels to the surface, we shall be able to con-
strucc a table of the relative antiquity of igneous rocks,
by comparing their distribution with the principal phe-
nomena of convulsion in the crust of the earth. Such
a table, however, would be very incomplete if founded
upon small geographical areas ; as the imperfection of
the following sketch, based on the examination of the
British islands, will abundantly prove.
152
A TREATISE ON GEOLOGY.
CHAP. VII.
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CHAP. VIII. MINERAL VEINS. 155
CHAP. VIII.
MINERAL VEINS.
WERNER, in his valuable treatise on veins, distinguishes
between "true veins" and some other appearances which
he thinks undeserving of the title. " Veins " he declares
to be particular mineral repositories, of a flat or a tabu-
lar shape, which in general traverse the strata of moun-
tains, and are filled with mineral matter differing more
or less from the nature of the rocks in which they occur.
They cross the strata, and have a direction different from
theirs j they are rents which have been formed in moun-
tains, and have been afterwards filled up by mineral
matter.
In this definition rock dykes are included, and it
sometimes happens that those dykes are metalliferous ;
but the substances associated with tin, copper, lead, and
the other minerals for which veins are valued, are
usually quite different from the matter of rock dykes.
Felspar and augite, so common in trap rocks, are almost
unknown in metalliferous veins, which contain, in fact,
few silicates of any kind, though quartz (of a peculiar
aspect) is very frequent therein. Besides the metals,
in combination with sulphur, carbonic acid, &c., salts of
lime and barytes abound, and clays of different qualities
appear.
Thus the distinction between rock veins and rock
dykes is in their contents; and since we find both in the
same districts, in similar fissures, and under similar
circumstances, this difference is of such importance,
that, however strong may be the arguments which tend
to show that mineral veins are the result of igneous
action among the masses of the globe, we cannot fail
156 A TREATISE ON GEOLOGY. CHAP. VIII.
to perceive that this action was materially different in
the two cases.
Geographical Distribution.
On no part of the history of veins has observation
pronounced a more positive decision, than on the rela-
tion borne by their distribution to physical geography.
The truth is universally recognised, that while exten-
sive plain countries are utterly deprived of all indi-
cations of these valuable mineral deposits, and others
contain them but rarely and in small quantity, there are
few mountain countries in which mineral veins are not
found in abundance and variety. They are, indeed, not
equally nor uniformly distributed even in their more
favoured regions : their occurrence is sufficiently depen-
dent on other causes, besides the mere form of the
surface, to keep alive the curiosity and inflame the
enterprise of the miner, as well as to conduct the phi-
losopher one step further in his research into the myste-
rious structure of the earth. Taking a general view
of the mining districts (not herein counting the collieries)
of Great Britain, we see the Grampians, and Lammer-
muir, and Cumbrian mountains; the great ridges of
Northumberland, Durham, Yorkshire, and Derbyshire;
the anticlinal axes of the Isle of Man, Anglesea, Snow-
donia, and Shropshire ; the elevated boundaries of the
coal tracts of Wales, and Somerset ; the mountain chain
of Devon and Cornwall; the elevated ranges of Wicklow,
and Wexford, of Leitrim, Sligo, Mayo, and Galway ;
all rich in lead, copper, zinc, tin, &c., with some silver,
and traces of .gold. On the other hand, the broad val-
leys of the Forth, Clyde, and Tweed ; the wide vales
which surround the Cumbrian, Yorkshire, Welsh, and
Devonian mountains, contain almost no mines ; and the
central plains of Ireland hardly yield any metallic
treasures. The same contrast appears on the continent
of Europe, between the mountainous and metalliferous
tracts of Brittany, the Pyrenees, the Harz, Eregebirge,
CHAP. VIII. MINERAL VEINS. 157
Oural, &c., and the great Plains of France, Germany,
and Russia.
In considering further the situations of mineral veins,
•we are struck by another feature of their geographical
distribution. There are some general directions, com-
mon not to all, but yet to a very great majority of the
veins of the British islands. More than half of the
productive veins pass in east and west lines, or rather a
little N. of East, and S. of West, in the mining dis-
tricts of Cumberland, Yorkshire, Derbyshire, North
Wales, Shropshire, and Cornwall. The same directions
prevail in Brittany, the Harz, Hungary, and, according
to Mr. J. Taylor, in Mexico. Hence, veins running
east and west are commonly called " right running"
veins, while others, which in the same districts are
generally unproductive, and run very often north and
south, across the productive veins, are often called
" cross" veins. (For proofs of these truths, Werner
on Veins, Williams's Mineral Kingdom, Forster and
Sopwith's Accounts of Aldstone Moor, and Farcy's
Derbyshire ; Mr. Carne, in the Geol. Trans, of Corn-
wall ; Mr. J. Taylor on Veins, in the Brit. Assoc.
Reports, may be consulted.) Now as the directions of
the mountain masses to which these veins are geogra-
phically related are various ; the greater number rang-
ing N. E. and S. W.; some (Yorkshire, Derbyshire,
Flintshire) north and south ; others, Pyrenees, Harz,
Carpathians, E. S. E. ; it is requisite to take other
circumstances into account, before deciding to what
extent these prevalent directions of the mineral veins
are dependent on the direction of the mountains which
they enrich.
One of the most obvious and interesting points of
inquiry is the dependence of the occurrence of metal-
liferous veins on the age of the rocks ; and Werner, as
might be expected from the tenor of his generalisations,
ventured boldly to pronounce concerning many metals,
the order of their antiquity in the crust of the earth.
Judging from the rocks in which they frequently occur,
158 A TREATISE ON GEOLOGY. CHAP. VIII.
tin, molybdena, tungsten, and wolfram are ranked as the
most ancient metals ; uranium and bismuth stand next,
" having been found in veins in transition or second-
ary strata." Gold and silver are considered compara-
tively new ; copper, lead, and zinc occur in deposits of
various ages ; arsenical pyrites ranks as an old product,
cobalt as new, magnesia is of intermediate, and iron
ores are of all ages.
Though these doctrines of the relative antiquity of
the metals must now be greatly modified, the subject of
the distribution of metallic ores according to the place
of the rocks in the scale of stratification, is still one of
the most curious in geology, and valuable in mining.
It is certain that such a dependence exists, and probable
that the accurate knowledge of it would be important in
clearing up some great difficulties in the theory of mining.
The variety of metallic and earthy minerals in the
veins which traverse primary slates in Cornwall, Cum-
berland, and the Lead Hills, is very great and remarkable
when compared to the small catalogue of these found
in the secondary limestones of Flintshire, Derbyshire,
and Durham. While argentiferous lead ore, and salts of
lead, copper ore, blende, calamine, pyrites, carbonate
of iron, quartz, carbonate of lime, sulphate of barytes,
fluor spar, &c., are common to these and the Cornish
districts, the latter yield ores of silver, tin, bismuth,
cobalt, arsenic, antimony, uranium, &c., opal, jasper,
garnet, zoolites, tourmaline, schorl, epidote, asbestus,
steatite, &c.
There is a remarkable circumstance in the distribu-
tion of metallic veins in the same class of stratified
rocks, — a peculiarity depending on local influences ;
such, that while the slates of Cornwall near the gra-
nitic eruptions, yield tin and copper, and the Snow-
donian slates, and those of Coniston Water Head yield
copper; those of Loweswater, Borrovvdale, Patterdale,
and Caldbeck fells yield lead, or lead and copper.
Copper ore and red oxide of iron occur in the lime-
stone of Furness; lead ore and calamine in that of
CHAP. VIII. MINERAL VEINS. 15Q
Derbyshire, Flintshire, and Mendip. In the same
manner the veinstones vary; even the calcareous spar
is crystallised with quite different planes in the mines
of Aldstone and Derbyshire.
The limits of mining districts are often very decided.
In the rich mining tract round Cross fell, dissected like
a map by mineral veins, and worked with an enterprise
worthy of all praise, no instance (we believe) has yet
occurred of a single vein being traced to the western
side of the mountain range, across the great Penine
fault, so as to penetrate the slaty rocks that rise in the
line of dislocation. The same fact is witnessed again,
in almost precisely similar circumstances, in the Flint-
shire veins, which do not, in a single instance, enter
the subjacent silurian rocks of the Moel Fammau range,
which rises on the line of a great axis of movement.
Numerous instances of this remarkable dependence of
the occurrence of mineral veins, in limited portions of
country definitely related to particular lines of dis-
turbed strata, are well and familiarly known.
Occurrence of Mineral Feins near Centres of Igneous
Action.
Ever since the analogy of mineral veins and rock
dykes has been clearly perceived, and the dependence of
these latter on disturbance of subterranean temperature
recognised, the dependence of the occurrence of mineral
veins on the general influence of heat has been con-
tinually more and more apparent. This appears to have
been strongly felt by Boue and Humboldt ; there are
also passages in the writings of Von Buch which con-
duct to the same conclusion. M. Necker presented to
the Geological Society, in 1832, an attempt to bring
under general geological laws the relative position of
metalliferous deposits with regard to the rock formations
of which the crust of the earth is constructed. The doc-
trine of the sublimation of the metalliferous contents of
veins from igneous matter occurred to the author, twelve
160 A TREATISE ON GEOLOGY. CHAP. VIII.
years previously, from observing the deposition of spe-
cular iron on the crust of a stream of lava flowing down
the side of Vesuvius; and he was induced, from that
circumstance, to institute an investigation of the subject
with reference to the following questions : —
First, Is there, near each of the known metalliferous
deposits, any unstratified rock ?
Secondly, If none is to be found in the immediate
vicinity of such deposits, is there no evidence, derived
from the geological constitution of the district, which
would lead to the belief that an unstratified rock may
extend under the metalliferous district, and at no great
distance from the surface of the country ?
Thirdly, Do there exist metalliferous deposits entirely
disconnected from unstratified rocks ?
With respect to the first of these questions, the
author showed, by copious references to England,
Scotland, Ireland, Norway, Fiance, Germany, Hun-
gary, the Southern Alps, Russia, and the northern
shores of the Black Sea, that the great mining districts
of all these countries are immediately connected with
unstratified rocks : and in further support of this solu-
tion of the first question, he mentions the metalliferous
porphyries of Mexico, and the auriferous granite of the
Orinoco; tut he observes, that his knowledge of the
mining countries of South America is not sufficient to
enable him to state their general geological connection.
Locally, this truth is well known. Mr. R. Fox, in his
excellent summary of facts regarding the veins of
Cornwall, observes: — "The copper and tin mines are ge-
nerally situated at or near some of the junctions of the
granite and killas, or of killas and elvan," &c. : and
both of these metals have been found in great abund-
ance in each of these rocks ; and it is, perhaps, difficult
to decide in which of them either metal has, upon the
whole, predominated.
With reference to the second question, — the probable
association of metallic veins with unstratified rocks,
though the latter are not visible in the immediate neigh-
CHAP. VIII. MINERAL VEIN?. l6l
bourhood of the former, — the author gives a section of
the country between Valorsine and Servoz, and points
out the probable extension of the granite of Valorsine
under the Aiguelles Rouges and Mont Breven, com-
posed of protogine, chlorite, and talcose schists, to the
immediate vicinity of the mines of Servoz, which are
situated in the latter formation. He also refers the
reader for further illustration to the metallic deposits of
Wanlockhead and the Lead Hills; to the mines of
Huelgoet and Poullauen in Brittany ; to those of Ma-
cagnaga and Allayna at the foot of Mount Rosa ; to
those of Sardinia, Corsica, and Elba ; to the metallife-
rous veins of the Vosges, Brescina in the Alps, and the
Altai chain ; all of which occur in districts where un-
stratified rocks are known to exist.
In reply to the third question, — Do their exist me-
talliferous deposits entirely disconnected from unstrati-
fied rocks ? — the author enumerates the mines of the
Netherlands, those of quicksilver at Idria, the lead
mines of Poggau in the valley of the Mur ; Pezay and
Macoz in the Tarentaise, and the veins of galena in the
mountain limestone of the south-west of England. (See
Geological Proceedings, 1832.)
On considering the cases mentioned by Mr. Necker,
of metalliferous veins entirely unconnected with great
masses of unstratified rocks, we perceive they are not un-
accompanied by great dislocations of the strata, such as
are usually associated with the appearance of trap rocks
at the surface. It is probably not to the " Whin Sill "
that the rich and abundant lead mines of the whole
district extending from the Tyne to the Aire are due,
— for indeed, through all the southern portion of this
tract, almost no igneous rock appears, — but to the mighty
and continuous disruption of strata 'caused by disturb-
ance of interior heat, which bounds the mining district.
In like manner, the very rich mining tract of Flintshire
is unconnected with igneous rocks, but is defined, and
is obviously dependent on the great disruption of strata
along the eastern side of the vale of Clwydd. The
162 A TREATISE ON GEOLOGY. CHAP. VIII.
Men dip hills offer a similar example of veins which
depend on an axis of movement, though no igneous
rocks appear on the line.
Again, in several smaller instances, the relation of
lead and copper veins to axes of dislocation is obvious ;
witness the lead veins which cross the anticlinals of
Greenhow Hill, Bolton Bridge, Bolland, &c. (see Illus-
trations of the Geology of Yorkshire), in none of which
situations is there the smallest indication of igneous
rocks near the surface.
Now, as in all these cases the subterranean move-
ment has opened a passage to the interior regions of the
earth, we see that M. Necker's propositions are not
negatived, provided we suppose these communications
to have been traversed by the sublimations to which
he ascribes the origin of the substances in veins.
Whether the particular mode of igneous action (sub-
limation from heated rocks), proposed by Mr. Necker
for investigation, be the true method of nature or not,
it is clear that his researches, followed out, justify a
confident belief that proximity to, or communication with,
masses of igneous rock, is a condition remarkably and
generally influential on the production of metalliferous
veins in the stratified rocks.
Taking, then, the element of heat as of great import-
ance in explaining the leading facts connected with mi-
neral veins, we are prepared at once with answers to the
obvious question, Why are the metalliferous veins, beyond
all comparison, most plentiful in primary and early
secondary (transition rocks of Buckland) strata? —
Because these rocks, as being nearer to the ignigenous
masses below, must have experienced, more than those
of later origin, the general influence of heat, We are
also enabled to account for the exceptions to this rule in
the Pyrenees, where, according to M. Dufrenoy's inter-
esting examination (Memoires sur les Mines de Per de*
Pyrenees, 1834), ores of iron accompany the ramifica-
tions of granite even in the cretaceous formation. There
CHAP. VIII. MINERAL VEINS. 163
are, in fact, in the Pyrenees, three repositories of iron
ores.
1 . At the separation of transition strata and granite in the
slopes of the Canigou.
2. In limestone of the lias epoch, at Rancie.
3. In the cretaceous formation, accompanying granitic ra-
mifications, at St. Martin in the valley of Gly.
All these deposits of iron ore are found where the
rocks touch or approach very near to the granite ; and
from all the circumstances, M. Dufrenoy is apparently
well justified in viewing the occurrence of the ores as
dependent on the proximity of granite, and independent
of the antiquity or other characteristic differences of the
rocks in which they lie.
Lest this result should lead us too far, and confound
all the variety of phenomena connected with mineral
veins in the vague and valueless notion of " the effects of
heat," it appears right to point the reader's attention
to such localities as the Island of Arran, where the
proximity of the granite is marked by abundance of rock
dykes, but shows almost no trace of mineral veins.
The dependence of metallic veins upon local centres of
igneous action, is certainly very different from that of
rock dykes, as might be safely inferred from many es-
sential differences between them in countries where they
occur together.
Relation of Veins to the Substance and Structure of
the neighbouring Rocks.
Before proceeding to trace the relations which really
exist between the substance of the veins and the neigh-
bouring rocks, a more minute description of the forms
and contents of veins must be attempted than was
necessary for the preceding inquiries.
The fissures now occupied by veins pass through all
the rocks met with in their downward descent. Though
a few instances are supposed to be known of their ter-
mination, at some considerable depth, all large vein*
M 2
1(34 A TREATISE ON GEOLOGY. CHAP. VIII.
continue beyond the reach of the deepest mine. Their
horizontal extent is various: some veins run 5, 10,
or more miles through a country ; and, in fact, their
termination is not really known, except that they are
lost in mere cracks not worth the miner's attention.
But so variable is the breadth of veins, that extreme
contractions and considerable expansions sometimes con-
fuse all regularity, and render doubtful even the con-
nection of the seemingly disunited parts of such veins.
" If we take a vein of 3 or 4 feet to represent a fair
average size, it may be only an inch or two wide in
one place and 8 or 10 feet in another. Such extremes
not unfrequently occur within a few fathoms of each
other." * Other veins preserve an almost unvarying
breadth and freedom from these perplexing contractions ;
and we believe these differences of character may be dis-
tinctly referred to the natural structure of the rocks, and
the movements to which they have been subjected.
Veins,, in their descent through the rocks, approach
more or less to a vertical position ; their deviation from
it seldom exceeds 10 degrees in the mining countries of
the north of England ; but in Cornwall, so rich in com-
plicated phenomena, the underlie, or deviation from
the vertical, is supposed by Mr. Fox to average 20
degrees, but seldom to exceed 45. The mechanical
theory of these inclinations of veins is yet altogether
imperfect ; we do not know in what degree these pecu-
liarities depend on original jointed structure of the rocks,
nor how to refer their various directions to sudden frac-
tures or gradual pressures, such as Werner pictured to
himself. Nor shall we escape from this ignorance, until
the directions taken by the veins, or, to speak more ac-
curately, the planes of their fissures, are compared geo-
metrically with the planes of the joints, the planes of
stratification, and the local axes of elevation and depres-
sion. In the lead mining districts of the North of
* Fox, in the Report of the Polytechnic Society.
CHAP. VIII. MINERAL VEINS. ] 65
England, a notion exists that the greater number of veins
are at right angles to the planes of stratification : this
idea is put as a general assertion by Williams (Mineral
Kingdom, vol. i. p. 317-)> a writer whose extensive ex-
perience in mining renders even a dogma of this nature
worth recording. His words are, " rake veins have a
greater or lesser hade or slope in proportion to the de-
clivity of the strata, as the mineral fissure, or vein, is a
transverse section cut at right angles to the lay or bed of
the strata;" — " whatever be the slope of the strata one
way, the hade or slope of the vein is as much from the
perpendicular the other way." And he then confines
this remark to veins which range with the bearing of
the strata ; distinguishing them from others which " cut
right across the strata," and a third group cutting them
diagonally, which he rightly terms " oblique veins."
The reader who compares this description of the ordi-
nary relation of the deviations and dip of veins, with
Mr. Murchison's notices of the prevalent character of the
joint planes in the silurian rocks, will not fail to per-
ceive the conformity of two independent sets of observ-
ations, and gather in consequence a useful notion of the
affinity of vein fissures, and the divisional planes which
constitute a part of the structure of all stratified rocks.
It is much to be wished that the triple co-ordination re-
commended above, as necessary to a just view of the
origin of vein fissures, should be carefully executed on
many of the complicated phenomena of the Cornish
mines. The cleavage planes of the slaty rocks, which
inclose mineral veins, should also be included in the
survey.
Some veins, like rock dykes, occupy one t( clean "
fissure of the rocks; others branch off into strings, or
become divided into forks, which continue for a longer
or shorter space till they are lost in clefts of the rocks,
or turn to re-unite themselves with the main trunk.
Such " strings," or " feeders," as they are called in Corn-
wall, appear under very various circumstances, both on
the horizontal and vertical sections. Occasionally a poor
166 A TREATISE ON GEOLOGY. CHAP. VIII.
vein is worth following for its rich lateral strings ; and
it is a common notion of miners that such appendages
are influential on the productiveness of a vein.
One of the most curious accidents which affect a vein
fissure, is its bending or expanding against particular
layers of rock, so as to constitute what, in the mining
country of Aldstone Moor, are called '* flats," or lateral
extensions parallel to the stratification. These are often
cavernous in the middle, and yield beautiful crystallis-
ations.
Veins sometimes appear as one united mass, due to
one single or uninterrupted deposition of mineral sub-
stances ; in other cases there are divisions in the veins,
or by the side of them, which contain clay or quartz
ribs, or in some other way give indications of successive
rents in the same general direction. Such appearances
have been often noticed (as by Werner, Came, Fox, &c.),
and considered as capable of explaining, in some in-
stances, the curious and very common accident of por-
tions of the neighbouring rocks, enveloped in the mass
of the veins, always near to and even opposite to the
parts whence they were disjoined. Such portions of
the neighbouring rocks are called " rider" and being
frequently traversed and impregnated by the vein sub-
stances, acquire a characteristic aspect; which being
found again not unfrequently in the rock on the sides of
the vein, especially where "strings" pass off from the
mass of the vein, such bounding rocks are said to be
" ridered."
In this manner, by (successive ?) nearly parallel rifts
in the rocks, which all received mineral depositions, a
" strong vein " becomes of almost indefinite width, even
30, 40, or more feet across, and often bewilders the
miner, unable to interpret or follow the seemingly ca-
pricious manner of the mineral aggregation.
The rocky boundaries of the veins are often some-
what peculiar in character near the vein : sometimes, as
in the case of rock dykes, they appear harder than the
rest of the rock; at other times some difference of
CHAP. VIII. MINERAL VEIN?. 167
mineral impregnation, pyritous, or serpentinous admix-
ture, appears, which distinguishes the so-called "walls"
of a vein. But this term is apt to mislead a geologist
into the notion that some definite parallel band always
insulates the vein from the inclosing rock ; which is, in
general, not the fact. In Cornwall generally, it is
thought by Mr. Fox that the rocks diminish in hard-
ness near a vein ; and similar facts are mentioned by
Werner.
A curious circumstance is noticed by Mr. Fox and
others, regarding the arrangement of the quartz in the
cross courses of Cornwall. This mineral does not in
such cases appear in its usual pyramidal or prismatic
crystallisation, but is of a fibrous structure, the axes of
the fibres lying across the vein, exactly as we may see
in hundreds of examples in thin quartz veins which
divide argillaceous slate, and other rocks. There are in
some cases several parallel plates of this fibrous quartz,
marking successive small rents.
In the cross courses of Cornwall, which contain
quartz, clay, and other substances, these are very com-
monly arranged in alternate layers parallel to the walls.
(Mr. Fox.) The same thing obtains very generally,
though not universally, in veins of all ages and contents ;
as the small specimens commonly sold in Derbyshire
very prettily illustrate. It is generally to be observed
in such cases, that the crystallisations are so arranged
that the terminal faces point inwards each way from
the walls of the vein, and that those bands of crystal-
lisation which are nearest to the walls, have themselves
served as surfaces of attachment for the next layer,
which is usually moulded on the other as if that had
been deposited first. This appearance "has suggested
successive irruptions of melted matter, successive secre-
tions from solution, successive accumulations from sub-
limation, and successive depositions by electrical currents,
to persons whose views led them thus diversely ; but a
succession of operations is commonly (not universally)
admitted to explain these appearances.
168 A TREATISE ON GEOLOGY. CHAP. VIII.
Another peculiar appearance in mineral veins, noticed
by Williams, Fox, Henwood, and others — and which
from personal inspection the author knows to be fre-
quent both in primary and secondary mining tracts — is
the segregation of the metallic contents of a vein into
portions inclined at various angles in different veins,
but nearly parallel in the same vein. These are called
" pipes " or " shoots ; " and their occurrence is of such
importance, as to mark, in a long vein, a series of
parallel spaces more than usually metalliferous. The
relation of these pipes of ore to the natural structures of
the neighbouring rocks is a subject of research strongly
to be recommended to intelligent mine agents, both for
its practical and scientific value. Mr. Fox observes,
from the information of Mr. R. Tregaskis, that when
veins are nearly at right angles to the beds of killas,
the masses of ore which they contain are generally con-
formable, in their underlie, to the direction or dip of
such beds ; in other words, they usually take an oblique
direction in. the veins, and form what the miners call
" shoots" of ore: and when the directions of the beds
and veins are nearly parallel to each other, the ore has
not usually any independent dip or shoot in a lode; it is
then termed a "pipe " of ore.
According to Mr. Kenwood (Mining Review}, the
*' shoots " usually dip from the granite, and towards the
slate, whichever of them may be the containing rock.
The reality of the dependence of the distribution of
metallic ores, in a continuous vein, upon some qualities
of the surrounding rocks, is very perfectly demonstrated
by facts known in the north of England. The
mining districts of Aldstone Moor, Teesdale, Swaledale,
£c. consist of shales, grits, and limestones, traversed by
east and west and north and south veins, which variously
dislocate the strata. In the course of these unequal
dislocations, coupled with unequal thicknesses of the
strata, various oppositions of the argillaceous, arenaceous,
and calcareous rocks happen ; and there are simple rules
which seldom fail in determining what parts of a vein
CHAP. VJir. MINERAL VEINS. ifig
may be found productive. First, it is chiefly in the
limestone district that the veins are productive, though
the fissures traverse a vast thickness of superincumhent
shales, grits, and coal. Secondly, in a series of lime-
stones, gritstones, and shales, which margin a vein, it
will happen that, when inclosed between walls or cheeks
which are both argillaceous, the vein will be unproduc-
tive, and generally " nipped," or reduced in width ;
with argillaceous beds on one side, and gritstones or
limestones on the other, the same effects appear, but in
an inferior degree; gritstone opposing gritstone yields
irregular results, according to the mass and quality of
the gritstone, so that in several districts (Grassington,
Allenhead, &c.) much lead ore has been found in such
situations ; but when limestone is opposite to limestone,
the vein is always most productive. Now, if we con-
sider that, in the many displacements of veins, a thick
limestone rock will be less frequently carried altogether
away from its fellow beds than a thinner one, we see at
once a reason why the " main limestone" of Swaledale
(or <e twelve fathom" limestone of Aldstone) is by far
the most productive among the "bearing beds" of those
counties ; for it is the thickest limestone there known.
There may be other reasons in addition; but this is ob-
vious and important, and agrees with an opinion of
those countries, which affirms that veins of small amount
of dislocation (or " throw" as it is called) are, on the
whole, more regularly productive than those attended by
enormous displacement. (See Forster and Sopwith on
the Veins of Aldstone Moor; and Geology of Yorkshire,
vol. ii.)
In Cornwall, some veins bear tin or copper both in
granite and killas; others yield more in one of these
rocks ; the veins are also very unequal in their produce
in relation to depth from the surface ; yet, as a general
result, it seems to be admitted by all writers, that the
contents of the veins undergo real and decided variations
wherever the bounding rocks (or " country," as the miners
term the mass of rocks adjoining a vein) experience
170 A TREATISE ON GEOLOGY. CHAP. VIII.
changes of their nature or structure. (See the papers of
Mr. Carne, Fox, &c. in Trans, of Geol. Soc. of Corn-
wall ; Mr. Taylor's Report ; Kenwood's Survey, &c.)
The same truth of the dependence of the contents of
mineral veins upon the containing rocks is put in a
strong light by Von Dechen, in his translation of De la
Beche's Geological Manual. He notices the mecha-
nical dependence of the width of the vein upon the so-
lidity of the neighbouring strata, and points out other
phenomena analogous to what have been mentioned
above. " The veins of Kupferberg, in Silesia, bear ore
only in hornblende schist, and become impoverished in
mica schist." " At Stadtberg, veins which divide zech-
stein, kupferschiefer, and the subjacent clay slate and
flinty slate, never bear ore above the kupferschiefer."
At Bieber, cobalt veins traverse the kupferschiefer, and
are unproductive in the subjacent red mica schist."
It has been generally thought that depth below the
surface of the earth was influential on the quantity and
quality of ore contained in a vein. Pryce, writing in
1778, says, — " The richest strata for copper is be-
tween 40 and 80 fathoms deep ; and for tin between
20 and 60; and though a great quantity may be
raised of either at fourscore or 100 fathoms, yet the
quality is often decayed, or dry of metal" * This does
not appear confirmed by recent experience, which has
in some instances (Dolcoath mine) gone to the depth of
260 fathoms without exhausting the supply. That
copper, upon the whole, occupies greater depths than
tin, is a common opinion in Cornwall. Mr. W. Phillips
observes, " At about 80 or 100 feet under the sur-
face, the first traces of copper or tin are usually found ;
rarely nearer to it than 80 feet. If tin be first dis-
covered even without a trace of copper, it is not unusual
that, in the course of sinking 80 or 100 feet or
more, all trace of it is lost, and copper only is found ;
but if, instead of tin, copper be first discovered at a
. * Mineralogia Cornubiensis, p. 79.
CHAP. VIII. MINERAL VEINS. 171
depth of 80 or 100 feet, it seldom or never happens
that tin is found below it in the same vein." Mr. Fox
adds, — " There are, however, many instances of tin ore
accompanying copper ore to a great depth; and in
Dolcoath mine it is found in a copper lode more than
200 fathoms below the surface, and even under the
copper." Mr. Carne observes, — " In general an ochre-
ous oxide of iron (gossan) is found in the upper part of
the copper veins, to which sulphuret of iron (' mundic')
frequently succeeds, below which the miners confidently
expect to obtain copper ore."
Relation of Feins to each other.
Adopting the opinion of Werner, that veins which
cross and cut through others are of newer formation,
we shall find great interest in the description given
by Mr. Carne of the principal vein systems of Corn-
wall *, and Werner's earlier classification of the veins
of Freyberg.
Mr. Carne, distinguishing between contemporaneous
veins and those which he considers as " true veins t,"
arranges the latter according to the difference of their
antiquity, as inferred from their observed intersections,
in eight classes.
The first Class includes the oldest tin veins.
The underlie of these oldest tin veins is to the north ;
they are traversed by those of the second class. They
form a very large majority of the whole.
The Second Class includes the more recent tin lodes.
There are few veins of this class ; they underlie to the
south. The tin veins are generally east and west
veins ^, ranging from 5° to 1 5° south of east and north
of west ; in some cases due east and west ; and less fre-
quently north of east and south of west. In St. Just,
• In the Trans, of the Geol. Soc. of Cornwall, vol. ii.
t In Cornwall, metalliferous veins are called " lodes."
J The directions are by compass, whose westerly variation ii in Cornwall
172 A TREATISE ON GEOLOGY. CHAP. VIII.
nearly S.E. and N.W. In Polgorth one is north and
south.
The veinstones of tin lodes are quartz, chlorite, capel
(quartz and schorl, or quartz and mica, or quartz, schorl,
and chlorite), and rarely schorl, or fluor. The width
of tin lodes varies from 36 feet to a mere string;
the average being from 1 to 4 feet. The average
underlie is about 2 feet in a fathom : extreme cases
give 10 feet; or, in contact with copper lodes, 16 feet.
Most of the productive tin lodes have been found in a
slaty country.
To the Third Class belong the oldest east and west
copper lodes. These form the great majority of the
copper lodes of Cornwall. Their veinstone is generally
quartz ; sometimes fluor, quartz and fluor, capel, chlo-
rite, hornstone and porphyry, or calcedony. The aver-
age width is not more than 3 feet.
The direction is mostly south of east, and north of
west, about 10° upon an average; sometimes E. and W.;
or north of east and south of west. The underlie is
various, but generally northwards ; in a particular tract
mostly southwards ; in some cases the same vein changes
its underlie from north to south. The average amount
of underlie is 2 feet per fathom, the greatest 8. These
copper lodes always traverse tin lodes. They are usually
accompanied by small veins or partings of clay, called
by miners " flukan."
The Fourth Class is composed of the contra * copper
lodes. These are similar to the third class, except-
ing in their direction, their greater width, and their
having more flukan in their composition. The average
width may be stated at 4 feet.
. Their direction is in general from 30 to 45 degrees
south of east and north of west; some, however, run in an
opposite direction, namely, north-east and south-west.
Their underlie is much the same as that of the other
copper lodes, to which they are much inferior in number,
* Veins which range from 30 to 60 degrees north or south of the east and
west points are called CONTRAS.
CHAP. VIII. MINERAL VEINS. 173
The Fifth Class includes the "cross courses:" these
are sometimes composed wholly of quartz, but they
usually contain, besides quartz, a large portion of flukan,
and sometimes of gossan.
Their width is usually greater than that of the veins
previously mentioned, averaging at least 6 feet.
Their direction is usually west of north and east of
south, but sometimes north and south, or east of north
and west of south.
Their underlie is various: most of those which point
east of north, underlie towards the west ; and on the
contrary, those which point west of north, underlie to-
wards the east.
Cross courses have been traced for several miles:
they rarely yield tin or copper ; lead is the principal
metal found in them.
In the Sixth Class, the more recent copper lodes, which
are not numerous, nor in their size, direction, or under-
lie, materially different from older veins of this metal
which have been described. They have more clay in
them than is usually seen in the cross courses.
The Seventh Class contains the cross flukans, or cross
courses which are composed wholly of clay ; they are
seldom more than one foot wide, but no water passes
through them.
Their general direction is nearly north and south •
their underlie is much the same as that of the cros
courses, generally towards the east.
In the Eighth Class are ranked the slides, which ar<
composed wholly of slimy clay, and appear like natura
partings in the rock.
They run in all directions, but in general are nearl;
parallel to the tin and copper lodes, which they throv
up or down. They are narrow, and underlie ver
fast.
It has been observed by Mr. Carne, as a result of
the preceding investigations, that " veins which con-
lain the greatest quantity of flukan or clay, are gene-
rally found to traverse those which contain a less quan-
174 A TREATISE ON GEOLOGY. CHAP. VIII.
tity or none at all of that substance ; " and this gene-
ralisation is confirmed by several facts communicated to
Mr. Fox by the intelligent mine agents of Cornwall.
Werner used the same method of classification as
that employed by Mr. Game, for the phenomena which
attend the mineral veins in a district as rich in metallic
treasures as Cornwall ; and the examination is the more
valuable in comparison, because the treasures are gene-
rally different, and lie in different strata. Gneiss is the
great repository of metallic veins in the Freyberg dis-
trict, and aigentiferous lead ore the principal product.
The ancient mining district in question is only about
two German miles long, and one broad ; yet, within "
these limits, Werner observed at least eight principal
deposits of metallic veins, perfectly distinct from one
another, and for the most part containing different
metals. Of the veins which are thus distinguished, the
first four intersect one another, so as to give a definite
scale of antiquity, but the last four are obscurely cha-
racterised in this respect from other considerations.
The first, and decidedly the most ancient, of these de.
posits, which yields argentiferous lead glance (galena),
is one of the most important of the whole district,
having constantly yielded, since the earliest period of
working the mines of Freyberg, a large quantity of
lead and silver, and a smaller of copper. It consists of
coarse granular lead ore, with silver in the proportion of
1^ to 2i- oz. in the quintal ; common arsenical pyrites ;
black blende in large grains ; common iron and liver
pyrites ; a little copper pyrites ; a little sparry ironstone.
The veinstones are quartz ; and sometimes a little brown
spar, and calc spar. The various substances here
named are not believed by Werner to be all of the same
antiquity, but to have been formed successively in the
vein, the oldest being nearest the sides.
These veins are from 2-*- to 6 feet across, and are
chiefly northern veins.
The second metalliferous deposit yields lead mixed
with a larger proportion of silver than any other. It
CHAP. VIII. MINERAL VEINS. 175
contains lead glance, very rich in silver ; black blende,
small granular ; common iron and liver pyrites ; a little
arsenical pyrites. Dark red silver ore, brittle silver
ore, white silver glance, and plumose antimony ore also
occur. The veinstones are principally quartz, much
brown spar, and calc spar. There is a difference of
situation in the rein, characteristic of these substances ;
quartz is generally on the outside. The veins are from
2 feet to 10 inches wide, and are south and south-west
veins.
The third deposit yields lead glance, with but little
silver. Its contents are lead glance, with nearly an
ounce of silver to the quintal ; much iron pyrites ;
some black blende j a little red iron ochre. The vein-
stones are quartz ; sometimes also chlorite, mixed and
surrounded with clay. These are all northern veins,
The fourth deposit is also composed of lead glance,
with but little silver (from a quarter to three quarters
of an ounce of silver to the quintal). Besides the lead
ore, there is radiated pyrites, and sometimes a small
quantity of brown blende. The veinstones are very
distinct, and consist of heavy spar, fluor spar, a little
quartz, and rarely calcareous spar. The veins are
from 1 foot to a fathom in width, and have generally
a western direction.
(To this vein system, Werner refers many deposits
beyond the Saxon districts, not hesitating to include the
Derbyshire mines, which certainly offer several interest-
ing analogies as to the veinstones, the direction, and
contents of the veins.)
The fifth deposit contains native silver, silver glance,
and glance cobalt, besides a small portion of grey copper
ore ; lead glance rich in silver ; a little brown blende ;
and sparry ironstone. The veinstones are disintegrated
heavy spar, and blue fluor. It always occurs at the in-
tersection of the southern and western veins (or first and
fourth vein systems here described), or in the middle of
the western veins.
The sixth deposit consists of native arsenic and red
176 A TREATISE ON* GEOLOGY. CHAP. VIII.
silver ore, with sometimes a little orpiment ; and rarely
a little copper nickel, glance cobalt, native silver, lead
glance, iron pyrites, and sparry ironstone. The vein-
stones are heavy spar, green fluor, calcareous spar, and
a little brown spar. Occurs in the intersections or in
the middle of veins.
(The distinction of age between this and the last
system is obscure.)
The seventh deposit consists of red ironstone, con-
taining also a little iron glance, quartz, and heavy spar.
Occurs in the upper parts of veins.
The eighth deposit contains copper pyrites, mountain
green, malachite, red and brown iron ochre ; with vein-
stones of quartz and fluor. It is of small importance.
In the valuable lead mines of Aldstone Moor, cases
of intersection so complicated as those of Cornwall and
other tracts of primary strata seldom or never occur.
The main facts are the general east and west direction
(by compass) of the lead veins, and the intersection of
these by cross courses which range, like these in Corn-
wall, mostly west of north and south of east. Their
' ' throw " is sometimes very great. The underlie of the
veins is seldom considerable ; and being mostly in the
same direction in each mining field, intersections of
the veins are not commonly met with. The cross courses
are, as in Cornwall, commonly wider than the veins,
and seldom produce any thing valuable. The veinstones
are quartz, fluor, carbonate of lime, sulphate of barytes,
&c.
That veins are enriched near the places where they
are intersected by cross courses, is an opinion common
in Cornwall, and for which good evidence appears :
sometimes this happens only on one side of the cross
course, as at Huel Creber mine, near Tavistock. Re-
ciprocally, the cross courses are productive near the
places where they cut the veins. When veins cross one
another, it is supposed that the intersections are seldom
enriched if the veins differ much in underlie.
Slides often contain ore, in the part between the
CHAP. VIII. MINERAL VEINS. 177
separated portions of the veins which they divide and
dislocate.
Theory of Mineral Veins.
There is, perhaps, no portion of geological science
less satisfactory than the variety of opinions, and con-
jectures, which, till within a few years, constituted what
was called the " Theory " of mineral veins. In no de-
partment of geology is it so difficult to observe accu-
rately the phenomena which form the basis of reasoning,
or to obtain from experience the data which ought to
limit and direct speculation. A short inspection of a
mine, with the disadvantage of confused lights and
noises, and explanations hid in a phraseology of very
difficult interpretation, leaves on the mind a feeling of
disquieting disappointment. The important facts of
the intersection of veins are not seen ; the segregations
of ore in a vein, the change of the contents with the
change of ground, with the depth, the underlie, and
other influential conditions, must all be taken on the
affirmation of the agent, in whose office the stranger
expects in vain to find a complete record of the subter-
ranean operations, with all the scientific data which they
have revealed. Dr. Boase was so impressed with
these difficulties, that in his examination of the veins of
Cornwall, with a view to understand their formation, he
declined to enter the mines at all. preferring to trust his
reasonings on the few phenomena in the sea cliffs, which
he could accurately examine, than on the almost innu-
merable facts which the mining art has disclosed, only
to be, in many cases, lost for ever to science. The
want of a national system of mining records is now
acknowledged, and ought to be remedied.* Werner's
views on this subject are not unworthy of his high re-
putation. (See his work " On the Origin of Veins.")
* This subject has attracted the attention of the British Association lor
the Advancement of Science, who directed a repiesentation to bt sub-
nutted to the government. The result is a Mining Record Office.
Vol.. 11. N
178 A TREATISE ON GEOLOGY. CHAP. VIII.
Even under these extreme disadvantages with respect
to the facts, the theory of mineral veins might have
heen more rapidly advanced, had a right method been
followed in the interpretation of them ; but this subject
fell under the general misfortune of geology, and was
considered rather as a boundless arena for Neptunists
and Plutonists, for Wernerian and Huttonian contro-
versy, than as a storehouse of more curious truths than
those contained in the rude notions of injection by heat,
or solution by water.
In the unfortunate dissociation of reasoners and ob-
servers, which is not even yet remedied, the imperfec-
tions of the closest speculations were too apparent to the
miner to leave him the slightest confidence in the ex-
planations proposed ; and when, moreover, to every
general rule regarding the position and contents of
veins, gathered from observation, and seemingly esta-
blished, further experience brought exceptions, how can
we wonder that practical men gave up the problems as
desperate, rejected mechanical and chemical causes alto-
gether, and, resolute in ignorance, believed the veins to
be contemporaneous with and an essential part of the
stratified rocks, in whose history they felt no interest ?
This was the " vulgar notion " in the time of Agricola
(1556), but it has been revived among men of science
in the ipth century.
This, in fact, is the fundamental question in the
theory of mineral veins ; and though the state of know-
ledge on the point is so much advanced since the days
of Werner and Play fair, that Macculloch thought, and
most geologists feel, the question to be completely de-
cided, we do not think it unnecessary to substantiate the
truths which they have rather assumed than proved,
and examine the objections which they neglected.
Veins are posterior to the Rocks which they traverse.
Werner, in his definition already given, assumes as a
truth, that veins are of posterior date to the rocks which
CHAP. VIII. MINERAL VEINS. 179
they traverse, because they Jill fissures in them, but he
was aware of the opinion which had, and still has, sup-
porters, that veins were formed at the same time, and
are of the same age, as the rocks in which they occur.
He takes the trouble to examine this point, and to es-
tablish the origin of veins by the rilling up of originally
open fissures as a fundamental point of theoretical and
practical importance. He offers nine proofs in support
of this unequivocal statement, hoping to " remove all
doubt of its truth from the mind of every intelligent
and unprejudiced geognost and miner." These proofs,
though not very skilfully managed, appear sufficient to
establish the conclusion as far as regards the pheno-
mena described by Werner, and commonly met with in
mining experience. Practical miners, in all but a few
districts, seldom express the slightest doubt of the truth
of the Wernerian postulate, from which we have here
retrenched the part which affirms that the veins were
open in the upper parts.
Those who in modern times reject this origin of
veins, and revive the notion that they are contempo-
raneous with, and a part of the rock formation, in
which they lie, are influenced in their views, first, by
the difficulty of explaining, according to simple mecha-
nical laws, the displacements which, on the Wernerian
supposition, the fissured rocks must have experienced ;
secondly, by the admitted fact, that there is some gene-
ral, and often some special, affinity between the contents
of the vein and the nature of the including rock ;
thirdly, there are cases in which substances of the same
nature as those in veins, and combined in the same
manner, are found in cavities which are unconnected
with veins.
These circumstances have been regarded as of much
importance, especially in Cornwall, where numerous
veins, occurring under various circumstances, and in-
closing a vast variety of minerals, have been worked
extensively to unusual depths, by men of great expe-
rience. If, then, in a country so favourably circumstanced,
N "Z
180 A TREATISE ON GEOLOGY. CHAP. VIII.
we find the theory of veins halting at the first step, we
must admit that the general argument by which this
step is fixed, is far from clear, or be prepared to en-
counter peculiar difficulties in the application of it to
Cornwall. That the general argument is not really de-
fective, we shall endeavour to shew, by examining the
three classes of objections which have been referred to.
1. The mechanical difficulty of explaining the
movements of the masses of rock in which the veins
lie, is more considerable in Cornwall than in any other
mining country yet investigated. In Vol. I. p. 40. we
have given a sketch of the usual relation (a, b, d, e) of
the planes of displacement to those of stratification, and
an example of the contrary (c). Now this latter case,
so rare in general, is not unfrequent in Cornwall. An-
other cause of difficulty is the excessive abundance of the
veins, and the variety of direction, inclination, and in-
equality of apparent displacement, which they manifest.
The accompanying plan and section of Huel Peever
mine will explain many points peculiar to the Cornish
veins.
On the ground plan it will be seen that six parallel
courses (a tin vein, two copper veins, an elvan course,
and two " slides ") are "shifted" to the south by the
cross course y, and again still further to the south by
the cross course #, each through the same horizontal
space.
In the vertical transverse section (taken from north to
south), it is seen that the two " slides" c and d pass
through and interrupt, in their inclined courses, both
the copper vein &, which is inclined in the same way
(to the north) as the slides, and the tin vein a, which
is inclined the contrary way (see the points marked
A, B, C, D, G) : also, it is seen that the copper vein b
passes through and displaces the tin vein a (compare the
points F and E) ; moreover, it appears that, excepting
the displacements from A to C, B to D, F to E, and at
G, there is no irregularity, the divided parts of the vein
being respectively parallel.
CHAP. VIII.
MINERAL VEINS.
181
GROUND FLAN OF HUEL PEEVER.
n, a', a". Tin vein worked.
bV. Copper vein, called" John's
Gossan."
c. North " slide."
& South ditto.
e. Copper vein.
/. Vein of clay. (" Elvan.")
x, y, %. Cross courses.
The ordinary explanation is that the tin vein, now
appearing in four parts, a, a', a", a'", is the oldest
vein, and was formed in one straight line ; after its
formation the copper vein b b' was formed by filling a
straight continuous fissure, which was made by violent
fracture of the mass of the rocks across the tin vein.
This was accompanied by a dislocation of the rocks in-
closing the tin vein ; so that the line was broken and
182
A TREATISE ON GEOLOGY.
CHAP. VIII.
94
TRANSVERSE SECTION OF HUEL TEEVBR.
the parts separated by the distance F E. At some later
period the slide c was formed by a similar fracture and
displacement, crossing both the copper vein and the
tin vein, and shifting the parts of them both, so that
the copper vein was divided into two parts, b and &', se-
parated by the interval A C ; and the tin vein again
divided and its parts a and a' separated by the interval
B D (which is equal to A C). At the same or some
other time, the slide d produced a slighter effect on the
tin vein a at G. What other effects may have accom-
panied the other intersections, which are indicated as
possible, viz. c and d, 6 and d, the locality does not
shew.
Finally, after all these fractures, three fissures in a
north and south direction, #, y, z in the ground plan
(not seen in the vertical section), have been formed
across a, b, c, d} e,f, and have been accompanied by
CHAP. VIII. MINERAL VEINS. 183
dislocation in a horizontal direction along nearly ver-
tical planes. (These drawings are from Mr. William's
paper on Huel Peever Mine, in the Geol. Transactions,
vol. iv. plate 7-)
The mine in question was supposed to present an
unusual complication of phenomena ; and, in fact, the
practical men were baffled by the " accidents" to which
the veins were found subject in the course of the work-
ings. It will be seen that the horizontal displacements
indicated on the plan follow, in this plane, the general
law given in Vol. I. p. 40. for a vertical plane, thus
bringing the Cornish veins in this respect into analogy
with those of other districts, as, for example, Aldstone
Moor, in Cumberland. There is no difficulty in this
respect.
On turning to the vertical section across the veins from
north to south, we find three apparent displacements:
one to a small extent, at the intersection of b and a,
which is contrary to the common law above referred to ;
a second, of twice the extent, at the intersection of c
and b, and c and a, which agrees with that law ; and a
third, of small extent, where d and a meet, which is
again exceptional. Now, that the movements supposed
are possible, without inconsistency, in this case, any one
can satisfy himself by a model ; and that the result, i. e.
the new position of all the masses, is perfectly explained
by such movements, is obvious from the following facts :
first, the displacement of each of the veins 6 and a, on
the line of fissure c e is equal ; in the next place, the
divided parts retain their parallelism ; and, which is not
of least importance, they agree in their characteristic
contents.
Such cases do not oppose, but strongly confirm, the
opinion that veins are posterior to the rocks which they
traverse, and of unequal antiquity as compared with
one another. But it must not be thought that the
Cornish geologists, who have revived the opinion of
Stahl, that the veins are contemporaneous with the
rocks, have no stronger case than that of Huei Peever.
184 A TRBATISK ON GKOLOGY. CHAP. VIII.
Mr. Kenwood, in his communication to the Geological
Society (Nov. 1832), mentions several instances of re-
markable intersections, some of which are, and others
are not, easily explicable by the supposition of real
movements in right lines.
Thus, if, " in Weeth mine, two cross courses are tra-
versed by the same east and west lode, arfd one is
heaved to the left, and the other to the right/' (in a hori-
zontal plane,) this would necessarily happen if the cross
courses dipped in contrary directions, and the movement
on the plane of dislocation were vertical. In all such
cases, precise and complete measures are necessary, to
enable a candid inquirer to form a satisfactory opinion
as to the mechanical solution of the problem of dis-
placements involved in the data ; and such a case Mr.
Kenwood presented to the Section of the British Asso-
ciation at Liverpool. Most of the phenomena described
in that communication were capable of explanation by
simple movements in right lines, but some were not ;
particularly the case of two veins, dipping in opposite
directions, and yet heaved the same way, contrary to the
mechanical necessity of the case, had the movement been
real. In such cases, angular movements of the masses,
which are known, by examples of common faults, to be
real causes, may be appealed to.
It is impossible now to enter into a minute examin-
ation of this and other such cases of embarrassment,
which change their aspect when a whole district of re-
lated veins is submitted to consideration ; but having
examined many of the published examples of intersec-
tion of veins in Cornwall, it is our opinion at present
that much of the difficulty has arisen from the incom-
plete description of the phenomena, and the division of
the general problems belonging to a considerable extent
of displaced ground, into a multitude of minor cases,
the key to which is in their connection. There can be
no doubt that the great mass of these phenomena are
perfectly reconcileable with the hypothesis of real dis-
placement of the masses of rock, and it appears to us
CHAP. VIII. MINERAL VEINS. 185
.hat little is wanting to reduce the whole to understood
laws, except a greater attention to the influence which
the jointed structure of the rocks must be admitted to
have exerted in modifying the result of mechanical
movements.
In the plan and section of Tin Croft mine, given by
William Phillips in his Outlines of Mineralogy and
Geology, p. 165. , one of two parallel copper veins is
represented as sending off two branches on one side,
probably into joints of the rocks. Had the veins there
represented been traversed by a " slide " underlying to
the south, the phenomena, now so clear, might have
been rendered very difficult to comprehend. We have
made models of some of the possible cases of real move-
ment, the complexity of which in the case of the
Cornish veins appears to us greater than any thing yet
found in mining.
Turning from this district to others of less com-
plexity, we shall see immediately the impossibility of a
reasonable doubt as to the fact of veins now occupying
what were fissures in the rock. In the mining districts
of Wales, Derbyshire, Yorkshire, Cumberland, where
sandstones, shales, coal, basalt, and limestones, alternate
in one or more successions, and are all divided by the
same vein, to which of these strata of unequal antiquity
is the vein contemporaneous ? When, on the opposite
sides of such a vein, are seen the separated parts of large
corals, and in innumerable cases of the small strings
passing off from a vein, the division of shells like Pro-
ducta, Euomphalus, &c. ; all further discussion is
useless, and the facts thus proved in cases free from
complexity, are with justice employed to interpret, in
other dictricts, results which are marked by additional
influences.*
2. The affinity between certain rocks and the veins in
* But it is not now necessary to appeal to such evidence in districts dis-
tant from Cornwall, since Mr. de la Heche has discovered encriniies and
other organic remains imbedded in killas igrauwafke), close to the walls of
Great Crinnis copper and tin lode, — says Mr. Fox, in his Summary of
3henomena in the Veins of Cornwall, p. ^5.— Report qf Polytechnic Society,
186 A TREATISE ON GROT,OGY. CHAP. VIIT.
them is real, and sometimes leads to an intimate union
of their substance by mutual penetration. To this,
considered as an objection to his theory of veins, Wer-
ner makes the following reply.
" The union between a vein and a rock, on some oc-
casions, is so intimate as to give the appearance of their
having been melted together, if I may so express myself."
"In places where this peculiarity occurs, the rock has
had a strong attraction for the substance of the vein in-
troduced into the rent, and has become so intimately
mixed with it, that they now appear to be one and the
same substance ; at least, it is not easy to mark a line of
separation between the rock and the vein. This is par-
ticularly the case with veins of quartz and hornblende,
when they occur in newer gneiss of a quartzy nature ;
but veins of pyrites in this rock do not present this ap-
pearance, which is, upon the whole, a rare occurrence.
In general, the vein and rock are very distinctly sepa-
rated from each other; and there are sometimes inter-
spersed between them thin layers of an earthy matter
called besteg. A vein is very seldom united to the rock
so as to adhere intimately with it through its whole
course; but this only takes place in certain parts."
(Werner on Veins, p. 90.)
To this it seems only necessary to add, that in what-
ever manner the ingredients of mineral veins were placed
in their present situations, it is not possible to doubt
that the specific relations alluded to must have been
manifested. Were all the mineral masses injected by
fusion, as Hutton thought, there would be segregations,
and peculiar arrangements, produced by the conditions
of cooling, the conducting power of the rocks, and their
inherent molecular forces. Were they introduced by
solution, as Werner believed, what menstruum capable
of dissolving such a heterogeneous mixture could be
without power on the walls of the fissure, or some part
of them ? Were the elementary parts of the substance
of veins raised by sublimation, molecular attractions
would be exerted unequally by the different parts of the
CHAP. VIII. MINERAL VEINS. IS?
sides of the fissure ; and if electrical currents were the
agents of transferring the metallic substances to their
peculiar repositories, the conditions of the rocks as to
conduction of heat and electricity become of paramount
influence. The specific affinities which the contents of
one vein display to the different rocks which bound it
(as in the lead mining districts of the north of Eng-
land), when rightly viewed, offer a most convincing
proof that the substance of veins was introduced among
these rocks after they had acquired such conditions of
hardness, position, &c. as to exert unequal powers in
determining the arrangement of the substances pre-
sented to their influence.
3. Strings and branches of metallic and sparry sub-
stances, like those which occur in veins, but inclosed
on all sides in rock, are of sufficiently frequent occur-
rence to demonstrate that not all mineral repositories
have been open fissures, filled by depositions from above,
as Werner taught, or by injection from below, as Hut-
ton contended, or by mere sublimation, as other writers
besides M. Necker have advanced on good though
limited evidence. We have shewn, while treating of
the " forms of igneous rocks," that such " contempo-
raneous veins," as Jameson properly calls them, have
arisen from the same play of affinities as the spherical
arrangements of the orbicular greenstone of Corsica ;
they are " segregations" of parts of a fluid compound,
depending on circumstances which affect its transition
to a solid state, £uch results may be admitted to have
happened with metallic veins, whenever the evidence is
equally clear. They are admitted by some writers for
some of the veins in Cornwall.
But yet, a general contemplation of insulated metallic
and sparry masses, which fill cracks and other cavities
in rock, will not allow us to adopt this as a general
explanation. These cracks and cavities have existed as
tuch in the limestones of the north of England, before
the introduction of their crystallised contents. For
some of these cavities are the inner hollows of bivalve
188 A TREATISE ON GEOLOGY. CHAP. VIII.
shells, which shut close and have no opening (Producta) ;
others are the closed chambers of cephalopodous shells
(Orthoceras, &c.). Nor is it doubtful that many, if not
all, the cracks and joints which, near a metallic vein,
hold sulphuret of lead,, or carbonate of copper, have been
produced during the condensation of the stone, since we
not uncommonly find them crossing and dividing the
substance of shells and corals (Wensleydale) and fishes
(Whitley quarry, near Cullercoats).
Upon the whole, therefore, whether the mineral sub-
stances occur in distinct regular fissures, occupy plane
joints, lie in irregular cracks or holes of rock, or line
secret hollows in shells — in all of these cases the exist-
ence of a cavity to receive the crystallised substances is
demonstrated, as the most ordinary antecedent to the
production of the mineral mass. It follows as a con-
sequence, that ordinarily, when veins cross, and one
passes through and divides the other, the " cross vein "
is of later origin than that which is cut through. But
as to the vein fissures having been originally open above
or below, and as to the manner of their being filled,
these points remain for further consideration.
Origin of Vein Fissures.
The theory of the origin of veins being thus to a cer-
tain degree insulated from that of the rocks in which
they lie, the next thing to be determined is the origin
of the fissures in -which the metallic and other mineral
combinations have been effected. The fundamental
facts for this inference are the prevalent parallelism of
directions of the several systems of veins which, in a
given district, belong to successive periods of formation;
the penetration of these fissures through a great variety
of rocks ; their length on the surface (some extending
even several miles) ; their depth, which in large veins
exceeds the range of mining enterprise ; the displace-
ments of the rocks which they divide ; their various
intersections and mutual relations. It is obvious tha;
CHAP. VIII. MINERAL VEINS. 189
the inferences to be adopted from these data, will be
trustworthy in proportion to the variety of sources from
which they are gathered, and especially if the seem-
ingly peculiar phenomena of vein fissures can be re-
ferred to general laws which extend beyond the mining
districts.
Now that this reference to general laws can be ef-
fected, will appear evident from the consideration that
similar parallelism of structural fissures, passing through
various rocks for greater length than mineral veins, to
unknown depths, with the same variety of mutual re-
lations, have been found in other than mining countries,
by the observation of rock dykes, and the symmetrical
structures of rocks called joints, and cleavage. The
most prevalent direction of the Cornish veins (east by
north), is that of certain characteristic joints in a con-
siderable portion of England, beyond the region whence
the results contained in Vol. I. p. 65. were derived ; and
the lines of the great cross courses of the Penine chain,
Flintshire, and Cornwall (north-north-west), are also
coincident with a very general divisional structure of
the rocks in most parts of Great Britain and several
other parts of Europe. Mr. Kenwood and Dr. Boase
expressly state, that the cross courses and principal veins
more or less <i coincide with the lines of symmetrical
structures by which all the rocks of Cornwall are
divided." (Kenwood, in Mining Review.')
The symmetrical structures of rocks, are, however,
different from the fissures now filled by veins and rock
dykes ; for they are seldom so continuous, either in
length or depth ; they are almost universally unaccom-
panied by displacement of the side ; and they often
change their width, frequency, and other characters,
according to the nature of the rocks. It is obvious,
therefore, that it is not merely by the filling of joints
of the rock that veins and dykes were produced ; the
rocks have been disturbed in position, opened to a greater
extent than the original divisional structures, or else
these last are only to be regarded as minor effects of
190 A TREATISE ON GEOLOGY. CHAP. VIII.
great disturbing forces which broke the strata along the
lines of vein fissures and rock dykes. The following
remarks are intended to show that symmetrical divisional
planes, such as joints and cleavage, are due to other
causes than disruption of the strata.
1. It is a fact, that from divisional planes ranging for
many yards or even hundreds of yards, and separated
by wide intervals, to the fine parallel, almost invisible,
cleavage of coal (called "cleat."), and of clay slate,
there is an almost perfect gradation of structures, which
have a definite relation to the different nature of rocks,
while subject to the same mechanical pressures and
movements. In coal, shale, clay slate, and laminated
limestone, it is in vain to attribute these regular divisions
to any thing but the molecular arrangement which ex-
plains the structure of basalt.
2. In different beds of rock, as shale, limestone,
and gritstone, which alternate, it is not uncommon to
find the slopes or inclinations of the joint planes to vary,
nearly as in different beds of slate the planes of cleavage
will deviate from parallelism.
3. The joints are, for the most part, not continuous
through all these alternating strata, but in each rock
are characteristic divisions which enter no other.
4. In symmetry, extent, and frequency, joints are
not at all less, but rather more, remarkable at points far
removed from axes and centres of disturbance of the rocks.
5. Near such axes of movement, many irregular frac-
tures of the rocks occur, and predominate over the natu-
ral joints, which appear not uncommonly to have been
obscured, closed up, or complicated by irregular pres-
sures and cracks in such situations.
It follows from these considerations, that whatever
analogy of direction may appear between the lines of
mineral veins and those of the natural structures of
rocks, this only indicates the influence which such lines
of weakness would necessarily exert on the direction of
fractures produced by mechanical pressure. Now, as,
in addition to joints, many other circumstances, as the
CHAP. VIII. MINERAL VEINS. 1Q1
unequal loading of the parts broken, and the varying
thickness of unequally resisting masses, &c., must have
contributed to the weakening of parts of the crust of
the earth, the want of perfect accordance between the
joints and all the lines of vein fissures, is no sufficient
argument against the anteriority and real influence of
the former over the latter.
The curious circumstance, not uncommonly seen in
the mining district of Aldstone Moor, of the change of
the " hade/' or inclination of the vein, in its passage
through different rocks, is perhaps explained by this
admission of the relation of vein fissures and joints.
The veins which pass perpendicularly through lime-
stone beds, acquire an inclination in the alternating
shales, and they are usually wider in the limestone than
in the shale. Now, in both of these circumstances, the
vein fissures resemble common joints, which not un-
commonly are more inclined and much narrower in
shales, than in the limestone strata of the same district.
Another curious fact, noticed in Cornwall, appears
intelligible by considering the disturbing force as having
opened at once two parallel discontinuous natural joints;
so that opposite the point where one fissure ended, the
other became open enough to receive substances of the
same kind, and thus, as the miners say, to " splice "
the vein.
All the principal circumstances which attend the dis-
locations of the strata along the planes of mineral veins,
are equally witnessed in the cases of common rock
dykes, and faults ; the same general laws as to the rela-
tion of planes of strata and planes of dislocation apply,
with similar exceptions ; nor are there wanting in all
these cases, proofs of the fact that some of the fissures
have been subject to more than one movement. In
mineral veins this is manifested by the striated surfaces
of rock and veinstones (:c slickenside ") ; it equally ap-
pears on the lines of disturbed strata (coal shales, car-
boniferous limestones), and with equal variation and con-
fusion of direction, so as in many cases to suggest the
192 A TREATISE ON GEOLOGY. €HAP. VIII.
probability that the great movements were, as indeed
could hardly be otherwise, complicated with many dis-
placements of small masses in different directions. In
some instances,, as already explained (Vol. I. p. 42.), the
striation is in one only direction,, marking a great sim-
plicity of movement : this is also the most common
case of mineral veins.
Whatever difficulties these phenomena maybe thought
to present, they are common to all cases of displaced
strata, and must be parts of one general investigation.
In this sufficient progress has already been made, to
assure us that, when the data and measures necessary to
form a right conception of the conditions are furnished,
the mechanical problems of displacement are not be-
yond solution.
Filling of the Fissures.
We are thus conducted to that point in the history
of veins, which was reached by Von Oppel (in 1769),
and are stopped by the same impediment. In his Essay
on the Working of Veins (quoted by Werner), he says :
— " The natural structure of the globe seems to show
us, that after the formation of the primitive and principal
secondary mountains, they had suffered great desiccation,
and been exposed to violent shocks. In consequence of
these changes, the rocks and mountains, which formerly
composed one continuous mass, were split asunder ;
whilst this took place, it might easily happen that one
of the rocks split from the other without ceasing to
touch it ; or these parts might be separated from each
other, leaving between them open spaces, which were
afterwards filled up, in part at least, with different
mineral substances. The greater part of these grand
events belong to that part of subterranean natural
history, which can only be elucidated by a consideration
of the facts which the earth presents to our view ; for
all these great revolutions took place at a period long
before the globe became habitable to the human species.
But whether fissures and veins were actually formed in
th" ~v**iner we have described, or not, it is no less tru-'
CHAP. VIII. MINERAL VEIN'S. 193
that this manner of representing their mode of form-
ation, and the relative situation which they bear to one
another in the mountain, is the most simple way of ac-
counting for them. It explains the uniform law of
their formation both in a general and more particular
manner, and, consequently, we shall admit it as the real
one. This hypothesis would be still more satisfactory
to the naturalist, if it were equally easy for him to con-
ceive how a new mineral substance could be formed in
these fissures, of a nature different from the rocks in
which the veins occur."
One of the early attempts to conquer this difficulty
is that of Lehman, who deserved more attention than
Werner's somewhat contemptuous notice.
" What is called a rent, is an open fissure in a
mountain, which has been produced by a division of
the rocks ; and veins are, in my opinion, nothing but
fissures which have been filled by nature with stones,
minerals, metals, and clay — in short, which are of a very
different nature from the rock itself." Farther on he
says, — " The veins which we find in mines, appear to
be only the branches and shoots of an immense trunk,
which is placed at a prodigious depth in the bowels of
the earth ; but, in consequence of its great depth, we
have not yet been able to reach the trunk. The large
veins are its principal branches, and the slender ones its
inferior twigs. What I have said, will not appear in-
credible, when we consider, that in the bowels of the
earth, according to every observation, is the workhouse
where nature carries on the manufacture of the metals ;
that from time immemorial she has been working at,
and elaborating their primitive particles ; that these
particles issue forth, in the form of vapours and exhal-
ations, to the very surface of the globe, through the rents,
in the same manner as the sap rises and circulates
through vegetables, by means of the vessels and fibres
of which they are composed." *
Another effort to penetrate the mystery of metallic
* Lehman, Abhandlung von den Metahniittern und der Erzeugungder
Mctalle. 1753, quoted by Werner.
VOL. JI. O
194) A TREATISE ON GEOLOGY. CHAP. VIII.
depositions, was that of Werner, who, in 1791, gave
what he considered a " New Theory of Mineral Veins,"
of which the principal points of novelty are, the appli-
cation of the phenomena of intersections to determine
the ages of veins, and the hypothesis of aqueous solution
for the filling of the fissures. In proof that the fissures
of veins were filled from above, Werner mentions the
occurrence of rounded pebbles at the depth of 180
fathoms in the vein Elias in Danielstollen at Joachim-
sthal, and similar instances in the Stoll rerier near
Riegelsdorf in Hessia, and in Dauphine.
His notion of the manner in which veins were
filled, partakes of the errors which belong to all the
Wernerian hypotheses of the origin of mineral masses.
He says, — " The same precipitation which in the humid
way formed the strata and beds of rocks (also the
minerals contained in these rocks), furnished and pro-
duced the substance of veins; this took place during
the time when the solution from which the precipitate
was formed, covered the already existing rents, and
which were as yet wholly or in part empty, and open
in their upper part." *
The Huttonian hypothesis of the earth's construction,
opposed in almost every point to that of Werner, con-
ducted naturally to a different interpretation of the
same facts. The fissures were produced by forces
depending on subterranean heat, and were filled by
injection like rock dykes ; and tlje parallel bands in the
vein, which Werner ascribed to successive aqueous de-
position, were referred by Hutton and Playfair to suc-
cessive igneous injection. In support of this explanation,
the acknowledged impossibility of solution in water of
native, sulphuretted, and oxidised, metals, and many of
the veinstones, was alleged, as fatal to the Wernerian
but favourable to the Huttonian view.
The complicated phenomena of veins led some English
* On Veins, p. 50. — See also p. 110. for a further development of this very
crude notion, mixed with some very ingenious suggestions, and important
views of the relations of geology and mining.
CHAP. VIII. MINERAL VETXS. 1Q5
writers, who admitted the posteriority of veins to the
rocks which inclose them, to suppose their contents to
have been collected from the neighbouring strata, by
some peculiar process of segregation, depending on
electrical currents. Thus it was supposed the suc-
cessive depositions, and peculiar positions of the various
substances which occur in veins, might be accounted
for.
Lastly, the vague suggestion of electrical agency, in
depositing the materials of mineral veins, has been
reduced to a regular system by Mr. Fox, who, uniting
the knowledge of veins to a zeal in conducting ingenious
experiments which has led to most valuable results,
has successively matured his views and advanced his
experiments, till they have attracted very general atten-
tion. Perhaps the most complete account of his hypo-
thesis is that which appeared in connection with a
valuable collection of facts regarding mines, in the
Report of the Polytechnic Society for 1837.
In this paper, Mr. Fox assumes as sufficiently proved,
the origin of fissures, from various causes, and at various
intervals, and the enlargement of them from time to
time ; the progressive rilling up of these fissures ; and
their penetration to great depths and regions of high
temperature. In such fissures, he shows the probability
of the circulation of heated water by ascent and descent ;
and the deposition of quartz and other earthy substances
in cool parts, which had been dissolved by the water in
hotter parts. In such fissures, filled with metallic and
earthy solutions, the different sorts of matter on the
sides must necessarily produce electrical action, which
might be exalted by the peculiar distribution of tempe-
rature. The currents of electricity generated would
pass more easily in the fissures than through the rocks,
and in directions conformable to the general magnetical
currents of the district. These would be east and west,
or somewhat north or south of these points, according
to the position of the magnetical poles at the period
when the process was going on. Electrical currents
o 2
1Q6 A TREATISE ON GEOLOGY. CHAP. VIII.
thus circumstanced, would deposit the bases of the
decomposed earthy and metallic salts on different parts
of the rocky boundaries of the veins, according to the
momentary electrical state and intensity of the points ;
in which conditions the nature and position of the rocks
would be influential. When by such processes parti-
cular arrangements had happened, new actions might
arise, and secondary phenomena, such as the transform-
ation of ores, without change of form, which are otherwise
very difficult to understand ; lateral rents might also be
filled by virtue of these new actions, even though they
were not in the most favourable lines of electrical cir-
culation.
The general hypothesis being admitted, it appears to
follow, that the observed influence of cross courses on
the quality and abundance of particular accumulations
of ore in the veins which they divide, affords strong
ground to believe that, in such cases, the depositions of
these ores was subsequent to the displacement of the vein
fissure by the cross course. It appears to be Mr. Fox's
opinion, that the clays in the flukans and cross courses
were introduced mechanically, and that they affected, in
a particular manner, the metallic distributions.
Not the least striking among the arguments in favour
of Mr. Fox's electrical theory of mineral veins, is the
fact, that he has formed experimentally many well de-
fined metalliferous veins by voltaic currents, operating
under circumstances expressly arranged in imitation of
those which really occur in Cornwall. (See Reports
of the Newcastle Meeting of the British Association,
1838.)
Recapitulation.
In considering these various views of the repletion of
mineral veins, it must appear evident that some things
at least are very probably established ; the successive
enlargement of some veins, the progressive repletion of
most of them, and the influence of general polarities in
CHAP. VIII. MINERAL VEINS. 197
the distribution of, at least, the crystallised materials.
The more closely the investigation is made, the less cer-
tain appears the connection in time between the production
of the fissure and its repletion. If the relative ages of
vein fissures may be known by their intersections, this
does not so clearly apply to their contents ; and thus we
find it quite possible that no long geological period, such
as Werner contemplated, may have intervened between
the older and the younger vein-fissures of a given
district.
It certainly appears at present unsafe to adopt any
one of the views here noticed exclusively. Sublimation
and re-crystallisation of metallic matters (whether pure
metals, sulphurets, or oxides) are common phenomena ;
and the passage of veins downwards to heated regions is
too probable to render it doubtful that such operations
have sometimes contributed to fill the fissures of rocks.
Mr. Patterson's experiment of the influence of steam in
causing the sublimation of galena in an earthen tube
heated in the middle (Phil. Journal, 1829), is an im-
portant illustration.
The deposition of blende, sulphuret of iron, carbonate
of lime, sulphate of barytes, quartz, &c. in cavities of
organic bodies, and in other situations, by the agency of
water, must exempt Werner from the charge of ab-
surdity in attributing to aqueous solution some of the
phenomena of the repletion of mineral veins ; but, as a
general explanation, his system is of no value.
Nor does it appear, at present, just to attribute a much
larger measure of success to Playfair's application of the
Huttonian hypothesis. ^Jt is, indeed, certain, in many
instances, that metallic impregnations are mixed with
rock dykes, or lie in veins by the side of them. Some
veins may have been filled by injection, especially such
as appear very simple in their structure, uniform in
their composition, and wholly independent of the neigh-
bouring rocks in the distribution of their contents.
Such veins there are ; but this speculation does no weU
meet the cases of many parallel bands in a vein,
o 3
198 A TREATISE ON GEOLOGY. CHAP. VIII.
gations in lines of particular rocks, and in closed cavi-
ties of rocks, the mixture of fusible and infusible sub-
stances, and the variation of the contents of veins ac-
cording to their directions, and other characteristic facts,
All of these excepted facts, indeed, appear indicative
of other agencies and polarities accompanying and
governing the deposition of metallic ores. Jt is diffi-
cult to doubt the truth of the views which ascribe these
peculiar and characteristic arrangements to electrical
action, and perhaps the principal problem now remain-
ing, is to determine whether, as Mr. Fox believes, the
electrical currents were voltaic, generated by the chemi-
cal action of particular solutions on particular substances,
or thermo-electric, depending on the application and
conduction of heat. As far as experimental research
goes, the labours of Becquerel, Crosse, Fox, and Bird
appear at present to give the advantage to voltaic elec.
tricity as the agent of arrangement in metallic deposits.
The other source of electrical power has been less inquired
into in this respect; and yet, when we consider the facts
of the communication established by metallic veins of
different conducting power, from the cold surface to the
hot interior of the globe, and recollect that permanent
differences of subterranean temperature are commonly
observed among contiguous rocks (as the killas and
granite of Cornwall, which differ 3°), it is difficult to
check the belief that thermo-electric currents, however
weak in intensity, are now important in their agency, and
may formerly have been much more so.
In these remarks we have chiefly in view the ar-
rangement of the substances in a vein ; the accumula-
tion of these may be due to quite different causes. In
some cases it really appears that a complete account of
the accumulation of the substances is very difficult to
collect, except we call in successively the solvent powers
of water and heat. The formation of sulphurets is
obviously one of the most important of all the facts re-
quiring explanation in mineral veins, because a very
large proportion of metallic ores (tin is the principal
CHAP. VIII. MINERAL VEINS. 199
exception) appears in this state. Heat, by sublimation,
sulphuretted hydrogen, by decomposition of metallic
salts, may give us the sulphurets; but. in the latter
case, from what prior condition is the sulphuretted
hydrogen derived? Mr. Fox proposes the decomposi-
tion of other sulphurets, by electrical action. Thus we
make no advance, and again turn to the simple action
of heat, which, in like manner, stops at the origin Ot
these sulphurets, and only accounts for their transfer
from the deeper parts of the earth. This, perhaps,
measures our possible knowledge as to the origin of the
metallic ores. They have been transferred from the
interior of the earth toward its surface, principally along
the fissures opened by violent movements.
But this conclusion does not necessarily apply to the
sparry contents of the veins. Aqueous solution of
most of these is possible, but of some it gives no suffi-
cient account. Some, as salts of lime, abounding in a
limestone country, may reasonably be attributed to the
action of water passing through the rocks ; others, as
quartz, may be thought to require much heat for their
solution j the clays and rolled fragments mark mecha-
nical action of water ; and thus, finally, it appears that
the present aspect of mineral veins is the result of many
secondary chemical, electrical, and mechanical actions,
the general antecedent to which is the influence of &
high temperature below the surface of the earth.
o 4
200
A TREATISE ON GEOLOGY. CHAP. IX.
CHAP. IX.
MODERN EFFECTS OF HEAT IN THE GLOBE.
To know the temperature of the interior parts of the
globe at the present period, and the effects depending
on its condition in this respect, is important, as furnish-
ing one, and that, perhaps, the most instructive, of the
elements for computing the changes which have, in
earlier times, affected its structure and configuration, and
varied its adaptations for organic life. By combining
such knowledge of the subterranean parts of the earth
as they now are, with inferences concerning more ancient
periods, we are to seek the laws of action and variation
of terrestrial heat, and, with the help of chemical and
mechanical philosophy, to arrive at a general contem-
plation or f< theory " of this part of geological science.
Once well established, such a " theory " Avill be fertile
of deductions bearing on all the known phenomena of
organic and inorganic action : the recorded facts of
geology form, on the other hand, a parallel series of
terms, which involve the same elements : by comparison
of these two scales, the progress made in the interpret-
ation of nature will readily appear, and the lines of
further research will be clearly indicated.
The phenomena indicative of the presence arid de-
gree of heat below the surface of the earth, are either
such as mark its ordinary and regular state, as HOT
SPRINGS, which, with a few exceptions, are not known
to vary in their temperature, and VOLCANOS, which mark,
in their epochs of critical action and their periods of
repose, the measure of the intermitting agencies con-
nected with their origin, growth, and decay. The con-
clusions which arise from these cognate phenomena may
CHAP. IX. MODERN EFFECTS OF HEAT. 201
be further tested by experimental inquiries into the
statical temperature at small depths below the surface
of the earth.
VOLCANIC ACTIOX.
Volcanic action, considered in its full meaning, in-
cludes, perhaps, the largest class of phenomena, attribut-
able to one predominant agent, which falls within the
province of geology. These phenomena are the more
interesting and instructive, because they extend through
an immensity of past duration, with many variations
distinctly related to geological and historical time. The
facts known by history and tradition respecting par-
ticular vents of subterranean fire, go back to the origin
of history and civilisation, and other phenomena of the
same volcanoes are undoubtedly to be referred to a part
of the scale of geological succession, corresponding to
the forms of plants and animals which lived and died
before the present races occupied the surface. Each
volcanic mountain has its own peculiar history, its acci-
dent of origin, its law of progressive increase, its period
of inevitable decay ; it is a monument more venerable
than the pyramids ; recalling, by its mysterious agitation
of the fertile plains around, the remembrance of move-
ments affecting other lands and seas than those on whose
boundaries volcanic fires are now excited.
What augments the interest naturally attached to
problems regarding the long duration and varying
energy of volcanic fires, is the completeness of the series
of phenomena which, taken collectively, they present.
New vents are opened in every few years to show us the
origin of volcanic accumulations on the land or in the
sea; an hundred ignivomous mountains bring up to the
surface abundant examples of substances most instruc-
tive on points which otherwise could only be sources of
vain conjecture; and the last stage of these frightful
disorders of nature is seen in many districts where, only
at particular points, mephitic vapours rise to darken the
smiling picture of general fertility.
202 A TREATISE ON GEOLOGY CHAP. IX.
Origin of Volcanos.
A mountain which has long been silent, and on whose
slopes the cultivation has spread for ages, is yet the
centre of great subterranean disturbance, shaken by
earthquakes, and surrounded by hot springs and sulphu-
reous exhalations. It cannot be known, from such
phenomena alone, whether the volcanic energy of this
particular region is sinking slowly to the entire decay,
which the perishing craters of the Eifel indicate, or re-
awakening to violent efforts, like those which Vesuvius
made in the year 79 °f our era> after many centuries
of entire repose, while the older crater of Monte Somma
was falling in decay.
The renewal of action in an old volcano, after a long
period of repose, may be looked upon as exhibiting, in
a considerable degree, the phenomena which accompany
the first origin of a volcanic vent. Earthquakes, sub-
terranean noises, the bursting forth of new springs, and
the suppression of old sources, are symptoms of a par-
ticular kind of subterraneous disturbance, of which they
record the violence, and in some degree moderate the
effects. Volcanic forces are in action wherever such
phenomena appear ; and, unless the imprisoned powers
acquire an extraordinary intensity, these are their only
effects ; volcanic eruptions are the consequence of forces
which have accumulated beyond the relief afforded by
displacements of the crust of the earth.
The terrific aspect of a burning mountain, and the
immense volumes of melted rocks and scattered ashes
which remain as measures of its fury, affect the ima-
gination too strongly ; and in this scene of temporary
violence we forget the less marked, but really important,
changes occasioned by the disturbance of interior tem-
perature, which in sudden earthquakes, or more gradual
and extensive changes of position among the masses of
matter, is slowly modifying the aspect of the globe.
But, independent of the information to be gathered
from the renewed activity of particular volcanos, like
CHAP. IX. MODERN EFFECTS OF HEAT. 203
Etna and Vesuvius, whose changes of condition are
matter of history, the prolific energy of heat has raised
up islands in the sea, and mountains on the land, within
our own days; and though these new volcanos are always
near to the situation of old ones, and are really only new
chimneys to the same subterranean fires which those con-
ducted to the surface, the circumstances of their origin
are very instructive.
In what form does the ground open for the form-
ation of a new volcanic vent ? This question has been
answered by Von Buch's hypothesis of " craters of
elevation," which, taken as the origin of a volcanic
mountain, are described as being formed by the up-
lifting of the ground in a dome-shaped or conical ele-
vation, with a central aperture. The correctness of
this opinion has been disputed by Mr. Lyell, and both
observation and calculation have been employed to de-
termine the truth. What is now seen of volcanic
mountains in general, proves them to be accumulations
of ashes and lava currents, heaped in a conical shape
round a central aperture. Supposing the aperture made,
it is obvious that lava streams from its edges would
flow only to limited distances, and scoria and dust
would fall in showers round the opening: and thus
every volcanic cone would show, in a vertical section_,
' 95., layers (T) more or less irregular, sloping
each way from the crater (e). In a horizontal sectirn,
the layers of ashes and streams of lava would be dis-
tinguished, as in fig. 96.
[The dotted parts correspond to the depositions of
ashes falling all round the crater, and enveloping the
lava currents, which ran down different sides of the
mountains at different times. In one part the lava is
seen filling a cross rent in the mountain, like a dyke of
older rocks.]
204
TREATISE ON GEOLOGY.
CHAP. IX.
Mountains thus constituted have been, doubtless,
formed by successive eruptions ; they may be called
" craters of eruption;" but still the question recurs, —
"What was the origin of the opening through which
those ejections began, which in their continuance have
formed craters of eruption?
In several cases which have occurred within the
reach of authentic history, eruptions on Etna and Ve-
suvius have commenced in the opening of a fissure
through the previously aggregated masses of volcanic
substances. This happened in 1538, \\hen the Monte
Nuovo rose (the greater portion in a day and a night)
on the shore near Puzzuoli, which had been previously
(for two years) disturbed by earthquakes. Fissures
appeared en Etna in 16'6'9, when the Monte Rossi,
which is a double cone of 450 feet in height, was formed
by explosion, and lava currents ran down the mountain.
The year 1759 witnessed the formation of a new
volcanic vent, and the accumulation of the new moun-
tain of Jorullo (1695 feet high), west of the city cf
Mexico. According to Humboldt's relation, " a tract
of ground from. 3 to 4 square miles in extent rose
up in the shape of a bladder ;" and the bounds of
this convulsion are still distinguishable from the irac-
CHAP. IX. MODERN EFFECTS OF HEAT. 205
tured strata. This important statement has been con-
troverted by the opponents of Von Buch's hypothesis of
•* Erhebungs Cratere," and defended by its favourers ;
and if Humboldt's account remains the only authority
for such a mode of origination of a crater on land, we
must also remember that it is the only authority for
any mode of origin of the opening of a new volcanic
region.
But it may be asked, — Are there no characteristic ar-
rangements of the volcanic rocks, which maybe employed
to determine whether they were accumulated in a level,
or in an inclined conical position ? are there no charac-
ters of form or fissures by which a mountain of eleva-
tion can be distinguished from a crater of eruption ?
It is maintained by De Beaumont and Dufrenoy that
there are. If we attend to the forms necessarily
assumed by lava flowing from the crater of a volcano,
we shall see the almost impossibility, that the melted
matter should flow equally on all sides, so as every
way to invest the cone with a concentric strata of
rock. Wherever the crater is lower, or the slope of
the cone depressed, there the liquid would be directed,
and long streams (or coulees), not zones of rock, be
solidified. If then, in any case, the structure of
volcanic masses is such that the distribution of once
melted rock is concentric to the conical surface, and
not in narrow streams parallel to the slope, such a mass
of rocks may be thought to have been raised by ex-
pansion, by elevation from an originally nearly horizon-
tal strata. If, indeed, we suppose the lapse of immense
time, many streams of lava may successively flow down,
and cover the whole conical slope ; but not regularly,
nor with that uniformity and mutual union here meant
by the term concentric sheet of rock.
The cases are few in which this arrangement of
the volcanic layers appears. The insulated hills of
trachyte ("domite") near Clermont, in Auvergne, are
supposed by Dr. Daubeny to be of this nature ; the
Mont d'Or and Plomb du Cantal have been specially
206 A TREATISE ON GEOLOGY. CHAP. IX.
quoted and illustrated in proof of Von Buch's specula-
tion, by MM. De Beaumont and Dufrenoy. Distin-
guishing clearly, in their prefatory remarks, between
the enveloping of a mountain slope by many streams
of lava, and the elevation, with fractures, of broad
floors of rock, into a conical mass, they attempt, by
a consideration of the structure, form, and fissures
of these mountains, to determine rigorously to which
of the two cases they belong. In this argument the
fissures yet existing in a volcanic mountain are an
important part of the data ; — it requires no great
exercise of calculation to see plainly that, on the sup-
position of a conical elevation, the fissures will grow
wider and wider, till they meet in a large subcentral
hollow ; and the sum of their breadth, will vary as the
inclination of the cone ; and it depends upon a careful
examination of the district whether these conditions be
fulfilled. In the opinion of the able geologists quoted,
the state and appearance of the sheets of rock which
concentrically form the Plomb du Cantal, is such as
to agree with the hypothesis, which, besides, is sup.
ported by an examination of the nature of the rocks.
The Plomb du Cantal, they observe, is in no manner
assimilated to a denuded cone of eruption: this sup-
position of its origin is, on several accounts, inadmis-
sible ; it is, on the contrary, by all its characters, the
result of elevation operated on a great basaltic plateau,
resting on trachyte. The group of Mont Dor requires,
on this hypothesis, several centres of elevation ; on Mr.
Lyell's view, as many points of eruption.
The conclusion of Dufrenoy and De Beaumont has
been objected to by Mr. Lyell on various grounds,
principally the unequal thickness of the presumed
plateaux of volcanic rock now found sloping from the
Plomb du Cantal ; for these, according to Prevost, are
thickest toward the centre. It is satisfactory to refer
to an independent inquirer, very competent to deliver a
just decision on all the bearings of this subject. Pro-
fessor Forbes, visiting Auvergne in 1835, directed his
CHAP. IX. MODERN EFFECTS OF HEAT. 207
attention to Von Buch's hypothesis, and has recorded
the result (Edinb. New Phil. Journal, July, 1836).
He noticed the radiation of valleys from the Cantal,
their narrowing from the centre of the elevation out-
wards, and their wanting lateral valleys. These radi-
ating valleys, so numerous, from a single mountain, appear
to have originated in fissures of disruption. The
alternation of " stratified " tufa, with trachyte, under
a capping of basalt, in the slopes of the mountain, is an
argument of weight with professor Forbes, and leading
to the same conclusion. " Upon the whole," says this
careful observer, ' ' it seems to me that the evidence of
earthquakes subsequent to the deposition (in whatever
way) of the Cantal and Mont Dor, is a fact so indis-
putable as to render the argument about craters of
elevation to a great extent merely verbal." — " There
seems, therefore, so much of probability, and so little
of extravagance, in Von Buch's theory, that we won-
der how it could possibly have given rise to such
animated opposition."
Let us turn from volcanic districts to others in which
stratified rocks have been subjected to vertical displace-
ment, in order to see in what forms the dislocated
rocks are combined. Are there in such rocks <{ hol-
lows of elevation " such as may be compared with the
erhebungs cratere of Von Buch ? It appears that there
are such elevations, unless, with regard to the lake of
Laach, we reject the obvious inference from its general
figure, and are prepared to doubt the exactitude of the
description of the f' valley of elevation " of Woolhope.
Such cases are, however, rare ; they seldom occupy an
exactly, or even approximately, circular area : the
AVoolhope valley is elongated, the Laach crater imper-
fect ; the valley of elevation of Kingsclere is very
little allied to a conical mountain ; Greenhow Hill, in
Yorkshire, though a double or transversely divided
elliptical elevation, is, perhaps, as good a case in point as
any that can be mentioned in England, to show the
analogy which really obtains between the elevation of
208 A TREATISE ON GEOLOGY. CHAP. IX.
ancient strata and that of some modern volcanic tracts.
To what extent the admission of this analogy bears on
the origin of particular groups of mountains remains
to be seen, but it seems probable that most of the
volcanic mountains are, like Vesuvius,, Etna, and Strom-
boli, craters of eruption, while a few may be better
explained by a general or partial elevation, at the origin
or during the continuance of their action.
It must.not be thought that the discussion regarding
the first opening of voicanos is unimportant : the his-
tory of ancient elevations of the strata is closely con-
nected with that of modern earthquakes; and the
occurrence of volcanic fires along mountain lines is a
circumstance very intelligible, upon the supposition
that they were caused by the opening of the ground
along a great fissure, and perhaps hardly to be explained
otherwise. If volcanic regions, arranged in line, owe
their origin to the rupture of the ground along that
line, its length, and die degree of displacement of the
rocks on its sides, are measures of the repressed force
which at length found vent. "Voicanos in line," as Von
Buch calls them, are thus connected with the traces of
the grandest movements which the crust of the earth has
experienced ; arid those who contend against the origin,
by elevation, of single volcanic hills, oppose the doc-
trine of mountain elevation by one or a few violent
struggles of nature, anterior to volcanic eruptions along
them, and attribute the elevation of ranges like the
Andes to many successive efforts of the volcanic action
seated below them. The further discussion of this
subject is part of a general inquiry, comprehending
alike the modern and ancient movements of the land,
which will be found in the next chapter.
Voicanos in Action.
Earthquakes, and the other premonitory symptoms of
a volcanic crisis, are succeeded by eruptions from conical
CHAP. IX. MODERN EFFECTS OF HEAT. 209
hills which have previously yielded passage to the fiery
floods pressed upwards to the surface, from new orifices
on the flanks or at the base of ancient cones, or from
situations where volcanic action is a novelty. The ef-
fects vary according to the diversity of conditions. The
materials issue in the form of melted rocks (lava), or
are driven up in the state of ashes and dust (scoria, &c.),
or burst forth as gas or steam. The lava, lifted by
great mechanical pressure from some depth in the earth,
rises in the tubular passage of the mountain toward its
summit ; and if the sides of the cone are strong enough
to resist the accumulating pressure, it may even over-
flow the top, as has happened in the Peak of Teneriffe,
to whose very summit Humboldt traced a stream of
vitreous lava. But, generally, the slowness with which
an eruption proceeds, is such as to allow of the lava
making for itself lateral passages to the surface, on the
flanks of the mountain, through fissures which yield to
the pressure of the column above, or are opened by
earthquakes. Such lateral eruptions have raised many
minor cones on the slopes of Etna, and round the base
of Vesuvius. Portions of the lava which enter fissures
in the sides of the mountain, and are consolidated
therein, may be compared to the dykes of the older
pyrogenous rocks.
Lava, whatever be its chemical composition, puts on
very different appearances, according to the circum-
stances which accompany its consolidation. The main
circumstances which thus modify its aspect, are the
volume of melted rock, the exposure of its surface to
air or water, the nature and position of the surface on
which it rests. Prismatic structures seldom appear in
the rocks, except where the mass of the lava was great ;
cooled in sea-water, the lava of Torre del Greco became
more dense than that which was cooled in air, and as-
sumed rudely prismatic structures. OIL sloping sur-
faces it is found that the cellular cavities, common to
lava which is cooled in the air, are elongated in a di-
rection parallel to the slopes, — an effect clearly intelligible
VOL. II. p
210 A TREATISE ON GEOLOGY. CHAP. IX.
by considering the viscidity of the moving mass, and
easily imitable by art.
The minerals which enter into the composition of
lava are, as already stated (p. 83.), chiefly felspar,, augite,
and titaniferous iron. But besides these, many varieties
of substances are produced in a crystallised state during
the cooling of the fused mass ; and, as is commonly ob-
served among the old rocks, such as granite and basalt,
these occur most plentifully, and in the finest crystallis-
ations, in cellular cavities and small fissures of the lava.
Eighty-two species of minerals are enumerated in a
catalogue of the products of Vesuvius by Monticelli and
Covelli, and others have been added to the already large
list of this unusually rich locality.
" Lava, when observed as near as possible to the point
from whence it issues, is, for the most part, a semifluid
mass of the consistence of honey, but sometimes so liquid
as to penetrate the fibre of wood. It soon cools exter-
nally, and therefore exhibits a rough unequal surface ;
but, as it is a bad conductor of heat, the internal mass
remains liquid long after the portion exposed to the air
has become solidified. That of 1 822, some days after
it had been emitted, raised the thermometer from 59° to
95° at a distance of 12 feet; 3 feet off, the heat greatly
exceeded that of boiling water. The temperature
at which it continues fluid is considerable enough to
melt glass and silver, and has been found to render a
mass of lead fluid in 4 minutes, when the same mass,
placed on red-hot iron, required double that time to
enter into fusion." — " Even stones are said to have been
melted when thrown into the lava of Vesuvius and Etna.
On the other hand, the temperature in some cases does
not appear to have been sufficient to fuse copper ; for,
when bell-metal was submitted to the action of the lava
of I794>> the zinc was separated, but the copper re-
mained unaffected." (Daubeny, On Volcanos, p. 381.)
These experiments on the heat of lava at the surface are
not at all discordant with what is known of the easy
fusibility of basaltic and trachytic compounds. In lava
CHAP. IX. MODERN EFFECTS OF HEAT. 211
at such temperatures it might happen that fragments of
granite, mica schist, &c. should escape fusion ; and such
are stated, on good authority, to have been found in the
midst of the lava of Vesuvius, Etna, and the Ponza Isles ;
while limestone in a similar situation is found of that
crystalline texture often observed in calcareous rocks
which have undergone fusion.
The volume of melted rocks poured forth in a single
short eruption of Vesuvius is considerable ; far greater
during some of the long-continued periods of activity of
the Icelandic volcanos ; enormous, if we contemplate the
united effect of a whole chain of volcanos like those of
South America. In 1737, the current of lava from
Vesuvius which destroyed Torre del Greco, and ran
into the sea, is supposed to have accumulated no less
than 33,587,058 cubic feet (equal to a cube of above
322 feet by the side, or a cone of the same height and
above 6'30 feet diameter at the base). In 1794, another
current, which flowed also through the same ill-fated
town, was calculated by Breislac, who saw the eruption,
to equal 46,098,766 cubic feet.
Etna, which rises above 10,000 feet in height, and
embraces a circumference of 180 miles, Dr. Daubeny
assures us, is composed entirely of lavas, which appear to
have been emitted above the surface of water, and not un-
der pressure. " In the structure of this mountain, every
thing wears alike the character of vastness. The pro-
ducts of the eruptions of Vesuvius may be said almost
to sink into insignificance, when compared with these
' coulees,' some of which are 4 or 5 miles in breadth,
15 in length, and from 50 to 100 feet in thickness;
and the change made on the coast by them is so con-
siderable, that the natural boundaries between the sea
and land seem almost to depend upon the movements
of the volcano." (On Volcanos, p. 203.) The great
current of 1669, which destroyed Catania, is estimated
by Borelli to contain 93,838,950 cubic feet.
But it is in the great eruptions of Iceland, as that of
Skaptaa Jokul (in 1783), that the effect of the continued
p 2
212 A TREATISE ON GEOLOGY. CHAP. IX.
energy of the subterranean fires, in ejecting matter to
the surface, becomes most astonishing. The fearful
eruption alluded to did not entirely cease till the end of
two years : in its course the lava filled valleys 600 feet
in depth ; dried and took the place of lakes ; accumu-
lated in rocky gorges ; spread in wide plains till they
became broad burning lakes, sometimes from 12 to
15 miles wide, and 100 feet deep. The lava may
be said to have taken two principal and nearly opposite
directions ; flowing in one 50, and in the other 40
miles, with a breadth in the former case of 15 miles,
in the latter of 7- The ordinary depth of the ac-
cumulated mass was about 100 feet, but in narrow de-
files it sometimes amounted to 600 feet. Mr. Lyell,
from whose admirable summary of this destructive
eruption the above abstract is taken, makes an ingenious
comparison of this prodigious mass of modern pyro-
genous rock with older effects of the interior heat of
the globe, and illustrates its effect on the geology of
England, if spread like the basaltic plateau of Antrim.
Spread upon the stratified rocks of England, before
their elevation from the sea bed, the lava would have
occupied a vast continuous surface ; and, after the rising
of the rocks and their waste by watery action, the ori-
ginal extent might be traced. The Skapta branch of
the lava might rest on the high oolitic escarpment
which commands the vale of Gloucester, 100 feet in
thickness, and from 10 to 15 miles broad, exceeding
any which can be found in Central France. Great
tabular masses might occur at intervals, capping the
summit of the Cotswold hills, between Gloucester and
Oxford, by Northleach, Burford, and other towns.
The same rocks might recur on the summit of Cumnor
and Shotover hills, and all the other oolitic eminences
of that district. Plateaus 6 or 7 miles wide might
have crowned the chalk of Berkshire, and masses 500
or 600 feet thick might have raised the hills of High-
gate and Hampstead to rival or surpass Salisbury Craigs
and Arthur's Seat. {Principles of Geol. book ii. ch. xiL)
CHAP. IX. MODERN EFFECTS OF HEAT. 213
To this prodigious fiery flood, there are certainly few
phenomena of superior grandeur among the "wonders'*
of geology.
Dispersion of Asltes.
The currents of lava, though they may appear to flow
with a certain regularity, are really urged hy forces
which continually rise to explosive energy, and dissipate
parts of the liquid columns within the crater into scoriae
and ashes. This effect appears in no small degree due
to a circumstance almost universally observed in vol-
canic excitement, — the extrication of vast volumes of
aqueous vapour. To the mechanical energies which
steam exerts at the base of the fiery funnel, and in the
substance of the mass of lava, we may, perhaps, refer
most of the phenomena attesting great expansive power.
The ashes, scoriae, and stones which are shot upwards
from the mouth of the volcano, and fall in showers
around, are of the same mineral composition as the
solidified parts of the lava : they mostly rest on the
slopes, and augment by external layers of growth the
diameter of the volcanic mound. The white lapilli, and
black ashes, remind us, in this pulverulent state, of the
felspathic and augitic rocks whence they are derived ;
and it is probable that in this way much larger accu-
mulations happen on and around Vesuvius, Etna, and
some other volcanos, than those which are produced
from flowing lava. Pompeii, Stabiae, and Herculaneum
were buried in ashes and sediments derived from ashes,
to depths of 60, 80, and 100 feet ; and it has been cal-
culated that the masses ejected from Vesuvius vastly
exceed the whole bulk of the mountain. (Daubeny on
Volcanos, p. 155.)
The ashes, instead of falling round the volcanic cone,
are sometimes carried for great distances by the winds.
Owing to the commotion of the atmosphere during
these paroxysms of the earth, rains often descend, and
sweep away the falling ashes in rivers of mud (c< lava
P 3
A TREATISE ON GEOLOGY. CHAP. IX.
d'acqua"), which flow according to the slopes of the
ground, and cover up cities, and fill lakes and valleys.
To this cause a part of the accumulation covering Her-
culaneum has been ascribed, while Pompeii was over-
whelmed in dry ashes. It is easy to perceive that
alluvial accumulations will from this cause spread over
a large extent of country round the base of an ignivo-
mous mountain, the arrangement of which is purely th«
effect of water, though the materials are exclusively the
products of heat. Such volcanic sediments will be ar-
ranged in a consistent geological classification as aqueous
deposits; they may contain as well as cover many organic
productions, wood, shells, bones, &c., and be thus, in some
cases, referred to their true geological age.
" Volcanic sandstones/' as Mr. Murchison calls the
marine deposits of ashes and disintegrated trap rocks,
which are interlaminated among the rocks of the silu-
rian system, may have had, in some instances, a similar
origin.
Another mode of aggregation of similar ingredients is
exemplified by some part of the (t trass" deposit, as it is
called, in the country near Andernach, where it abounds
on the borders of the Eifel volcanos. Showers of ashes
falling in lakes would be arranged therein exactly as
other sediments from a different source, except that the
areas and depths of the distributed substances must vary
according to the circumstances of their admission to the
water. Much of the trass in the Valley of Brohl is,
however, in too irregular a state of arrangement to admit
of this view. It probably was deposited rather as a
mass of liquid mud, bursting from some old crater, and
bearing the spoils of the surface (wood and rock frag-
ments) with it. The wood in this trass is carbonised.
The puzzolana of Naples is of similar nature to the trass,
and contains shells and bones, with fragments of pu-
mice, obsidian, and trachyte. It forms considerable hills
round Naples, some of which have regular craters.
When, as in the case of Graham Island, a new vol-
cano bursts up in the sea, and scatters ashes and scoriae,
CHAP. IX. MODERN EFFECTS OF HEAT. 215
these, falling in the sea, are variously disposed of, and
may be borne by currents far from their origin. If,
like the same island, the volcanic heap, after subsisting
for a time, is wasted away by the waves, we can easily
predict the effect on the sea bed near j — sloping strata
of volcanic sediments, which may cover or envelop
abundance of mollusca, and even fishes poisoned by me-
phitic gases, which frequently break forth in points not
far from the centre of the eruption. Among the singu-
larities of the eruptions of Vesuvius is the pouring forth
of boiling water from the sides of the mountain (Dau-
beny, 156.). Eruptions of this nature are less rare
in the New World. Humboldt mentions the singular
fact, that with these aqueous eruptions pass multitudes
of small fishes along with abundance of mud.
" When (on the 19th of June, 1698) the Peak of
Carguairazo sunk down, more than four square leagues
around were covered with clayey mud, called in the
country "lodozales" Small fish known by the name of
"prenadillas" (Pymelodes Cyclopum), — a species which
inhabits the streams of the province of Quito, — were
enveloped in the liquid ejections of Carguaiiazo.
These are the fish said to be thrown out by the
volcano, because they live by thousands in subterranean
lakes, and, at the moment of great eruptions, issue
through crevices, and are carried down by the impulsion
of the muddy water that descends on the declivity of
the mountains. The almost extinguished volcano of
Imbaburu ejected, in 1691, so great a quantity of pre-
nadillas, that the putrid fever, which prevailed at that
period, was attributed to miasmata exhaled by the fish."
(Humboldt on Rocks, p. 455.)
Fetid mud, called " moya," burst, in enormous quan-
tity, from the foot of the volcano of Tunguragua, in
Quito, in 1797, and filled valleys and dammed the
course of rivers. Sulphuric acid is mixed with the waters
which flow from Purace, in Quito, and some other ex-
tinct volcanos.
Besides ashes, scoriae and stones even of consider-
216 A TREATISE ON GEOLOGY. CHAP. IX.
able size are thrown out by the volcanic forces, and
sometimes take their course with the drifts of mud, so
as to form part of the re- aggregated mass of trass, or
constitute a volcanic conglomerate.
The last class of volcanic products which come to the
surface are the gaseous and vaporous substances, to which
much of the grandeur of the exhibition, as well as much
of its general power and momentary energy, is owing.
The most abundant of these is steam, which rises in
white clouds over the craters of active, and from rents
in extinct, volcanos. The most abundant of the gases
are muriatic acid, sulphuretted hydrogen, sulphurous
acid, carbonic acid, and nitrogen. (Daubeny.) Subli-
mations of particular solids occur, as boracic acid in the
crater of Volcano, muriate of ammonia, muriate of soda,
specular iron ore. The boracic acid cannot be sub-
limed by the heat of our furnaces; but Dr. Daubeny
has shown by experiment, that, when heated and tra-
versed by steam, a portion is taken up and carried with
the steam.
Extinction of Volcanos.
The suppression of volcanic excitement lasts so long
in some cases, that the long and quiet sleep is not to
be distinguished from a real extinction of the local
energy of heat. Between two eruptions in Ischia seven-
teen centuries elapsed. In this respect the history of
Vesuvius is very instructive, especially when compared
with the aspect of the long decayed volcanic mounds of
the Eifel and Auvergne, whose fires were, perhaps, never
beheld by man.
The cone of Vesuvius is of comparatively modern
date, formed within the, larger and more ancient crater
of Monte Somma. The descriptions given by Latin
writers seem applicable to this latter mountain, up to
the great eruption of A. D. 79> which Pliny's narrative
has rendered famous. Previous to that event the
mountain was cultivated; its crater, perhaps, served as
CHAP. IX. MODERN EFFECTS OF HEAT. 217
the encampment of Spartacus ; and only obscure tra-
dition or uncertain inference raised the conjecture that
this smiling tract was based on subterranean fire. If
the passage of Lucretius (vi. 748.) has any reference to
Vesuvius, the only symptoms of activity of heat were
sulphureous exhalations, such as might rise many cen-
turies after the volcano had sunk to rest, such as now
rise in the Solfatara, and have risen, with little differ-
ence, for 1600 years ! (See Dr. Daubeny on Volcanos,
p. 166. first edition.)
The great eruption of A.D. 79 was followed by six
others, at long intervals, averaging l64> years, till 1036,
when, for the first time, the flowing of lava is men-
tioned, the previous eruptions being of ashes and lapilli.
Three eruptions are on record between 1036 and 1306.
Vesuvius has never, since the first outbreak on record,
been at rest for so long a period as between 1306 and
1631, between which epochs only one slight revival of
action happened in 1500. Throughout this period
Etna was in a state of unusual activity, as if the rival
craters of Sicily and Campania were connected to the
same subterranean channels. Before the eruption of
1631, the crater of Vesuvius was a pasture for cattle, its
sides were covered with brushwood, in which wild boars
sheltered. The old surface was all blown into the air, and
seven streams of lava poured at once from the crater,
committing enormous destruction. Since that time the
mountain can hardly be said to have been ever tranquil,
and the frequency of eruptions appears to have progres-
sively augmented to the present time. In the seventeenth
century, the intervals between the outbreaks of Vesuvius
are, on an average, twenty years ; in the eighteenth, five
years ; and since 1 800, two years.
Etna has experienced, within the reach of history,
sufficient variations of volcanic energy to justify the
use made of its changes in the Pythagorean philosophy.
Nee quae sulphureis ardet fornacibus JEtna,
Ignea semper erit; neque enim fuit ignea semper.
Ovid. Metam. XT.
218 A TREATISE ON GEOLOGY. CHAP. IX.
The speculations with which this opinion is accom-
panied, show the activity of inquiry which was excited
among the people adjoining the Mediterranean volcanos.
The early eruptions of Etna are lost in the obscurity
of history, and the great mass of the mountain was
probably accumulated during the later tertiary periods
of geology. The first recorded eruption, in 480 B. c.,
was followed by others, 427 and 396 B. c. ; the in-
tervals averaging 42 years. After 256 years, in
which no eruptions are recorded, four more are noticed
between 140 and 122 B. c. ; average interval 6 years.
After 66 years of rest, three other eruptions appear
between 56 and 38 B. c. ; average interval, 9 years.
No eruption is mentioned till 40 A. D. ; interval, 78
years; a pause till 251 A. D. ; another, still longer,
till 812 A. D.; a third to 1169 A. D. ; and then,
after twelve centuries of rarely interrupted quiet, the
mountain became, agitated, and has since continued
to manifest its violence, more and more frequently,
to the present century. In the twelfth and thirteenth
centuries, 3 eruptions ; in the fourteenth century, 2 ;
in the fifteenth, 4 ; in the sixteenth, 3 of unexampled
duration ; in the seventeenth, 8 ; in the eighteenth,
14 ; in the nineteenth, to 1832, 6 eruptions. (See
Dr. Daubeny on Volcanos, and Mr. Lyell's Principles
of Geology, for details, which are here unnecessary.)
The Lipari Isles present us with yet another vari-
ation in the phases of volcanic action and rest. Strom-
boli is always active, but almost never violent ; no
cessation having ever been noticed in its operations,
which are described by writers antecedent to the Chris-
tian era in terms which would be well adapted to its
present appearances ; while in Lipari, the only indi-
cations of volcanic action now existing are the hot
springs ; and the island of Volcano, in an intermediate
state, still emits gaseous exhalations.
Since the first colonisation of Iceland by the Nor-
wegians, the eruptions of the volcanos in that country
CHAP. IX. MODERN EFFECTS OF HEAT. 219
have been frequent, and almost regularly distributed,
through the ten centuries during which it has been
known to us. Dr. Daubeny notices as the first erup-
tion recorded, that at the end of the ninth century
(894 A. D.). One also occurred in 900. The sub-
sequent dates of eruptions are, 1000, 1004, 1029 j
1104, 1113, 1157, 1158; 1245, 1262, 1294; 1300,
1311, 1332, 1340, 1359, 1374, 1390; 1416, 1436,
1475; 1510, 1554,1580, 1587; 1619, 1622, 1625,
1636, 1660, 1693; 1717, 1720, 1724, 1728, a
series of eruptions, 1748 to 1752, 1753, 1772, 1783.
In 1724 occurred the first eruption of Krabla. Erup-
tions have subsequently occurred in 1821, 1823.*
During this period submarine eruptions happened
from 1224 to 1240; in 1422; in 1563; 1783; and
new islands were thrown up in 1563, 1783.
Here, therefore, we have the recorded history of four
volcanic systems, which appear very unequal in their
progress toward decay, as if their energy depended
upon conditions differently apportioned to the several
regions. Without repeating all the hypotheses in Ovid,
which commence with the notion of the earth being an
animal that breathes flame through many variable spi-
racles, we may inquire whether the fluctuation of
volcanic energy in particular districts depends upon
local and temporary stoppage of the^ channels to the
surface, or upon the failure in some of the essential
conditions of igneous excitement? To answer this
• The total number of recorded eruptions appears to be the following? —
From Hekla, since the year
From Kattlagiaa Jokul
From Krabla
In different parts of the Guldbringd Syssel
At sea ...
From the lake Grimsvatn, in
From Eyafialla Jokul
From Eyrefa Jokul, in -
From Skaptaa Jokul, in
1004 inclusive, 22
900—7
1724 —
1000 —
1583 —
1716 —
1717 —
1720 —
1783 —
42
Mackenzie's Travels in Iceland, p. 25L
2£0 A TREATISE ON GEOLOGY. CHAP. IX.
question we must survey volcanic phenomena in a
variety of other aspects.
Extinct Volcanos.
The Solfatara, near Puzzuoli, is in shape like other
volcanic cones, with craters at the summit ; it is formed
of a trachytic rock, naturally hard and dark-coloured,
but in proportion as it is exposed to the vapours given
off from the " fumaroles " in the crater (the steam
contains sulphuretted hydrogen and a minute proportion
of muriatic acid), its texture and colour undergo a re-
markable alteration. It passes through various stages
of decomposition, and finally appears a white siliceous
powder. Saline compounds effloresce on the surface
of the rock (muriates of ammonia, &c., sulphates of
alumine, lime, soda, magnesia, iron, &c.), and sulphur
(not sublimed alone, but derived from sulphuretted
hydrogen) lines the walls of its cavities. The ground
is hollow (probably in fissures) below, and a stream of
trachyte has formerly flowed from it, and formed the
promontory called the Monte Olibano.
Craters in which the volcanic fires are utterly extinct
are sometimes filled by water, as the Lago Agnano, and
the more celebrated Lake Avernus, where no longer rise
the sulphureous fumes which once procured it the for-
midable character of a gate of hell. (Mneid, vi.) They
may be compared with some of the craters of the extinct
Rhenish volcanos, as the Laacher See, near Andernach,
which is about 2 miles in circumference, the Meer-
feld, and other circular lakes or te maars " of the Eifel
district. Sulphureous exhalations, which resemble those
of the Solfatara, and lakes in craters like those of the
Eifel, occur in Hungary and Transylvania ; and the
central districts of France show us, in addition, a variety
of facts, to complete the view of the condition of coun-
tries where, though volcanic action, as commonly under-
stood, is entirely extinct, the effects of subterranean
CHAP. IX. MODERN EFFKCTS OP HEAT. 221
heat and chemical decompositions are manifested by
evolutions of particular gases, and the issue of hot
springs.
Geographical Distribution of Volcanos.
Though volcanic accumulations abound in all quarters
of the globe, the area which they occupy on the land is
not to be compared to that of any one of the systems of
stratified rocks, and is inferior to that of most of the
individual formations. On a first view, volcanic moun-
tains seem to be so many insulated points of ignition,
productive of distinct mineral compounds^ and subject
entirely to independent local conditions. The history
of eruptions, though very incomplete, is, however, suffi-
cient to destroy this notion, by showing on the line of
the Andes corresponding movements of the land, and
ejections of ashes into the air, at points very far removed
from each other.
Thus, a few days after the earthquake which de-
stroyed Concep9ion, on the 20th of February, 1835
several volcanos within the Cordilleras, to the north of
Concep9ion, though previously quiescent, were in great
activity, and the island of Juan Fernandez, 360 miles
to the north-east of the city, was violently shaken. The
volcanos of Osorno, Aconcagua, and Coseguina (the
first and last being 2700 miles apart), burst into sudden
activity early on the same morning (June 20. 1835).
This connexion and sympathy of the phenomena of
volcanos and earthquakes at considerable distances, is an
important element for the determination of the true
condition of the subterranean spaces where these phe-
nomena are excited. The town of Riobamba, near
Tunguragua, was destroyed by a tremendous earthquake
on the 4th of February, 1797 i and at this moment, the
smoke which had been seen to issue in a thick column
from the volcano of Pasto, 65 leagues north of Rio-
bamba, suddenly ceased. Volcanic mountains appear
to act as safety-valves to a boiler, and some of them
222 A TREATISE ON GEOLOGY. CHAP. IX.
relieve completely and continually the subterranean
pressure, so as to free from earthquakes a considerable
region round their bases. Thus, while earthquakes
agitate the neighbouring islands of the Canary group,
the Peak of Teyde appears to be the cause of the com-
parative immunity from these disasters which the island
of Teneriffe enjoys.
By combining observations of this nature with con-
siderations of the grouping of volcanic craters, the
direction and extent of earthquakes, the ebullition of
hot springs, and analogous phenomena, we arrive at the
notion of volcanic regions, and may by this means class
the active and extinct volcanos, which are scattered over
the globe into a modern number of systems, convenient
for description, even if the association rests on an un-
certain basis.
In Europe, the purely volcanic phenomena which are
from time to time manifested, appear at points referrible
to one of seven centres of action. Iceland, with its
Geysers and six or more active volcanos, Hecla, Skaptaa
Jokul, Skaptaa Syssel, Eyafialla Jokul, and Kattlagiaa,
and its formidable eruptions and coast elevations, stands
almost alone ; Jan May en, visited by Scoresby, being its
only volcanic neighbour. The Azores form another
region of considerable importance, where the rising of
islands has happened within the reach of history.
Sicily, like Iceland, has, besides the great chimney of
Etna, lateral escapes of the imprisoned forces labouring
below ; and Sciacca, the island which rose and dis-
appeared in 1 831, is a remarkable proof of their energy.
The Lipari Isles form another group, where Stromboli
and Vulcano are still feebly active ; while Vesuvius stands
and burns amidst many older vents, long since ex-
tinguished, and Ischia and the Ponza isles bear to it
the same relation that the Lipari group does to Etna.
The last centre of activity in European volcanic
systems is in the Greek Archipelago, where Santorini
has undergone many violent displacements, and some
igneous exhibitions since the Christian sera.
CHAP. IX. MODERN EFFECTS OF HEAT. 223
Similarly the extinct volcanos of Europe may be
grouped very conveniently in a few systems of connected
groups. The basaltic mountains and cliffs of the Faro
Isles are stated to be on many points allied to those of
Staffa and Antrim, and perhaps the whole region in
which igneous rocks are scattered, from the Faro Isles
to Antrim, Arran, the Vales of Clyde and Forth, if not
to Teesdale and Derbyshire, should be viewed as the
theatre of one great and long enduring system of sub-
marine volcanic forces.
Another great system, of more recent date, is the tri-
partite volcanic tract of Central France, included in the
districts of Auvergne, Cantal, Velai, and Vivarais, to
which we may attach some points scattered about the
Cevennes mountains near Rodez, at Agde near Mont-
pellier, and Beaulieu, near Aix en Provence.
Just before the Rhine enters the Low Countries, which
conduct it to the sea, it divides hilly districts, principally
of transition rocks, among which, on the left bank, is a
large exhibition of ancient volcanic energy, in the
numerous cones and " maars " of the Eifel country,
lying east of the Ardennes. On the right bank, lower
down, are the celebrated trachytic and basaltic moun-
tains, called the Siebeng'ebirge, which by some detached
rocks of like nature, lying to the east, appear to be con-
nected with the great basaltic masses of the Wester-
wald.
The \Vesterwald, Vogelsgebirge, and Rhongebirge,
may be taken as the principal volcanic group of Western
Germany. Many insulated cones and masses of basaltic
rocks about Li m berg and Wetzlar, the Habichtwald
near Cassel, some basaltic hills near Eisenach, Fulda,
Hanau, and Frankfort, may perhaps be contemplated as
parts of this ancient system.
The Kaiserstuhl mountain, near Freyburg in the
Brisgau, the cone of Hohentwiel, and some small points
in Wiirtemberg may be grouped together, though it is
not known that they have really any particular geological
relations.
224 A TREATISE ON GEOLOGY. CHAP. IX.
A few detached basaltic cones appear near Egra,
amidst the Fichtelgebirge. A much larger volcanic
tract begins in the Mittelgebirge, and extends parallel
to the Erzgebirge, and across the Elbe to near Zittau.
The line of this system is continued by many detached
cones across the range of the Riesengebirge into Silesia.
Volcanic appearances are mentioned near Ho£ north
of Olmutz.
In Hungary, as described by Beudant, the effects of
extinct volcanic action are extensive and remarkable.
Five distinct groups of mountains,, composed wholly of
trachyte, are enumerated by Beudant, who attributes
to each group a separate origin. One of these
groups, larger than that of the vicinity of Clermont,
being 20 leagues long, and 15 broad, is situated in the
porphyritic mining district of Schemnitz and Krem-
nitz ; another, smaller, but similarly circumstanced as
to the porphyry, crosses the Danube, near Grau ;
another, extending east and west elliptically, forms
the mountains of Matra, near Eger ; the fourth, a
large mass, ranging north and south, for 25 or 30
leagues, from Tokai to Eperies; the fifth is the group
of Vihorlet, east of the last, apparently related to the
trachytic mountains of Marmarosch, in Transylvania.
Most of the Hungarian volcanic rocks can be classed
as varieties of trachyte, according to a method of M.
Beudant ; opal, opalised wood, pearl-stone, and pumice,
and scorified masses, abound ; and from the porphyries
of earlier date, there appears to be an easy mineral
gradation to some of the trachytes. The latest vol-
canic action is placed by Mr. Lyell in the Meiocene
tertiary period. The subjacent strata are mostly of
the transition sera. Another group of Hungarian vol-
canos adjoins the Flatten See, on the north-west side.
In the eastern part of Transylvania volcanic rocks
of tertiary aera occur in a range of hills covered with
thick wood, extending from the hills of Kelemany,
north of Remebyel, to the hill of Budoshegy, 10
or 12 miles north of Vascharhely. The principal
CHAP. IX. MODERN EFFECTS OP HEAT. 225
mass of the range is trachytic conglomerate, from
beneath which, at intervals, trachyte of different kinds
emerges, and encloses craters at the southern end of
the range. Some of these craters are, like those in
the Eifel, converted to lakes. Exhalations of hot sul-
phureous vapours are poured out from rents in the hill
of Budoshegy ; sulphureous, chalybeate, and carbonated
waters rise at the foot of this mountain in many
places.
In Styria, the Gleichenberg, a trachytic mountain
enveloped in strata of ashes, perhaps accumulated in
water, indicates considerable volcanic energy during the
tertiary sera. At several other points in Styria volcanic
masses appear.
The Euganean hills south of Padua constitute a
very remarkable mass of volcanic deposits, consisting
principally of trachytic rocks, associated with semi-
vitreous masses, and at Monte Venda with basalt. The
subjacent calcareous strata of " scaglia " contain many
fossils of the European chalk. North of Vicenza, the
variety of volcanic products is considerable, and it is
thought their differences are partly related to the place
which they occupy in the series of strata there occur-
ring, between the primary slates and the scaglia. On
the volcanic rocks rest calcareous and tufaceous de-
posits; and at particular places, especially Monte Bolca,
fishes occur abundantly in slaty bituminous marls, which
alternate with volcanic sediments, often containing
shells, like the trass and puzzolana.
Near Viterbo (Monte Cimini), trachytic rocks
abounding in leucite, associated with basalt, and beds
of pumiceous tufa, covering bones of quadrupeds, are
connected with tertiary marls and shells. Near Radi-
cofani the same trachyte occurs in the Monte Amiata.
A few miles south-west of Volterra, near Monte
Rotondo, and near Monte Cerboli, sulphuretted hydro-
gen rises abundantly from little crater-shaped openings
(lagunes), and boracic acid is sublimed therewith, as
well as in the crater of the island of Volcano.
VOL. II. Q
226 A TREATISE ON GEOLOGV. CHAP. IX.
Mount Albano, 12 miles from Rome, from which
a current of lava is traced nearly to the city, as well as
the volcanic tuff which alternates with other sediments
below the soil of Rome, sufficiently prove the former acti-
vity of volcanic forces in this vicinity. Near Albano are
four lakes, once probably craters. The Rocca Monfina,
a mountain of great antiquity, on the road from Rome
to Naples, surrounded with igneous volcanic deposits,
carries on the line, of connection to the Phlegrean fields
and Vesuvius.
In the Ponza Islands, Mount Vultur, the Lake
Amsanctus, volcanic action, though long extinct, has
left proofs of its former force and extent at points more
or less connected with Vesuvius ; while in the Val di
Note, the early energies of Etna are manifested among
tertiary strata.
Some of the Grecian islands and shores have ex-
hibited volcanic fire, and great elevations of land in
modern times, as Santorini ; and extinct volcanic action
is manifested in the Solfatara of Milo, and the convul-
sions of Methene and Troezena, mentioned by Strabo
and Ovid.
If we compare this brief notice of the situations
where active and extinct volcanos have poured erup-
tions on the land and in the sea, with the extent of
country included by Mr. Lyell in his " Volcanic
Region from the Caspian to the Azores/' it will imme-
diately appear, that, with the exception of Iceland and
Jan May en, all the points in Europe which have pro-
duced eruptions during the reach of history, are in-
cluded in that region. The whole space between the
Caspian and the Azores, a distance of 1000 miles,
within the parallels of 35° and 45° north latitude,
has been from time immemorial agitated by earth-
quakes ; which also extend their effects farther to the
north, so as perhaps to unite the Mediterranean band
of volcanic energy with the distant fires of the Ice-
landic group. Near to and beyond the latitude of 4-5°
are situated many of the most conspicuous of the older
CHAP. IX. MODERN EFFECTS OF HEAT. 22?
volcanic systems, but the most modern lie farther to
the south. The western continuation strikes the Azores.
As a general conclusion, it appears that earthquakes
extend the evidence of subterranean disturbance much
beyond the area covered by volcanic ejections.
If, taking another view of the subject, we inquire the
relation of this distribution of volcanic vents to the
features of European physical geography, it immediately
appears that all the active volcanos are situated in islands
or peninsulas, or, in general, very near to the sea-side.
Further, it is evident that the same law of proximity to
water applies to the ancient volcanos of Auvergne, the
Rhine valley, the Hungarian and Transylvanian vol-
canos, and the Euganean hills, &c. ; for these points,
now far removed from wide sheets of water, were bathed
by fresh waters (Auvergne, Transylvania), or the sea
(Euganean hills, &c.), at the time when they were theatres
of igneous violence.
Asiatic Volcanos.
Proximity to the sea, or to large surfaces of inland
waters, characterises, in like manner, the points where
volcanic action is now, and has formerly been, manifested
on the continent and islands of Asia. On either side
of the sea of Marmora, from the Dardanelles to Con-
stantinople, volcanic accumulations appear. Syria and
Palestine, often desolated by earthquakes in early periods,
abound in volcanic appearances. Near Smyrna these
are extensive *, and the vicinity of the Dead Sea is
volcanic. The Caucasian chain of mountains is full of
volcanic accumulations ; Ararat is of this character.
At Bakur, on the western side of the Caspian, is the
celebrated " field of fire/' where excavations in the soil
yield naphtha, and gas rises, which is easily inflamed.
The Elburz range of mountains, on the southern side of
the Caspian, presents one important volcano in action,
• Strickland, in Geol. Proceedings, 1837.
I
228 A TREATISE ON GEOLOGY. CHAP. JX.
the Peak of Demavend, which is 1 4,000 feet above the
sea.
On the Arabian side of the Red Sea, volcanic phe-
nomena appear at Aden, Medina, Mount Sinai, and other
points ; the island of Zibbel Teir is said to contain an
active volcano. Volcanic phenomena are mentioned at
the mouth of the Persian Gulf, in the island of Ormus,
and at some distance inland north of Kerman.
Beyond the limits of the Mediterranean and Caspian
volcanic regions just described, Humboldt has added to
the previous reasons for admitting the existence of some
volcanic action in the midst of the Altai Mountains
(lat. 42° to 4-6° N., long. E. 80° to 87°). These vol.
canos, which are 400 leagues from the Caspian Sea,
are nevertheless situated among some considerable lakes
so as to invalidate in no degree the generality of the
inference drawn from the consideration of European
volcanic districts.
On the eastern border of Asia is an immense sigmoidal
band of intense volcanic activity, which constitutes one
of the most remarkable physical features of the globe.
Commencing with Barren Island, in the Bay of Bengal,
the line passes south-eastward through Sumatra, where
Marsden describes four existing volcanos, one of which
is 12,000 feet high. Through Java the line passes
nearly east and west, amidst thirty-eight large volcanic
mountains, conical in figure, and rising separately from
a plain to 5000, 11,000 and even 12,000 feet above
the sea. In 1772 one of the largest fell in, so that
an extent of ground 15 miles long and 6 broad, with 40
villages, and 2957 persons, were destroyed.
From Java the volcanic hue continues eastward
through Sumbawa, known from the formidable eruption
recorded by sir Stamford Raffles, and Flores, and Timor,
where the burning peak sunk in 1637, and is changed
to a lake. Between Timor and Ceram, also, in one of
the Banda Isles, in the northern part of Celebes, the
volcanic action is manifested among the Molucca Isles.
Ternate, Tidore, and Sangir, continue the line in a
CHAP. IX. MODERN EFFECTS OF HEAT. 229
northerly direction to the Philippine Islands, Mindanao,
Fugo, and Lucon. From Formosa, by the Loo Choo
Isles to Japan, the line runs north-eastward ; a course
which it continued through the ten volcanos of Japan,
and the nine active vents of the Kurilian islands to the
burning mountains of the peninsula of Kamschatka.
The Aleutian Islands continue the line of volcanic
activity (an island having been thrown up in 1795
3000 feet in height, according to Langsdorff) to the
point of Russian America called Alaschka, which is
believed to be also volcanic.
American Volcanos.
Traces of powerful volcanic action, now extinct, ap-
pear about the head waters of the Columbia and Missouri
rivers ; and probably along more southern parts of the
lofty ranges of the Rocky Mountains, yet but imperfectly
known to Europe. The peninsula of California pos-
sesses, besides the lofty Mount St. Elia (17,875 feet
above the sea), two other active volcanos. The line of
igneous action is continued through Mexico, but not in
the general direction of the high mountain range. This
goes to the south-east, and it is in a line crossing it
obliquely, nearly east and west, that the fire active vents
of Mexico, Tuxtla, Orizaba, Popocatepetl, Jorullo, and
Colima, are situated. The distance of Jorullo from the
sea is 36 leagues, and that of Popocatepetl somewhat
greater ; and this circumstance may be thought to in-
validate the seeming necessity of proximity to water as
an element of volcanic excitement. But it appears not
unreasonable to admit the existence here of a great
transverse fissure, on whose prolongation westward are
situated the volcanic (extinct) group of the Revillagigedo.
Several intermediate points of extinct volcanic action
connect the five active vents above noticed in Mexico.
Between Mexico and the Isthmus of Darien, in the
provinces of Guatimala and Nicaragua, are no less than
twenty-one active volcanos, running in the line of the
230 A TREATISE ON GEOLOGY. CHAP. IX.
great mountain chain. On the southern side of the isth-
mus three volcanos occur in the province of Pasto, as
many in Popayan, and six of surpassing height and
grandeur in Quito, viz. Cayambe, Cotopaxi, Pichincha,
Antisana, 1' Altar, and Tunguragua. The fire comes out
from one or other of these giant cones, but, according to
Humboldt, they all are parts of a single swollen mass,
or immense volcanic wall, covering a surface of 6*00
square leagues. In Peru one active volcano is known,
and there is no other between Quito and Chili, but the
whole country is so remarkably subject to earthquakes,
that it must be presumed the subterranean connection is
continued from Quito to Chili.
In Chili, at least nineteen points of eruption are
ranged in the general mountain line of the Andes, here
passing southwards : Villarica, one of these, burns con-
tinually, but is seldom subject to violent excitement.
One point of eruption appears to have been ascertained
by captain Hall, in Tierra del Fuego. This extraor-
dinary range of volcanos, which appears to indicate a
continuous area of excitement as much as 6*000 miles
in length, is equally remarkable for the narrowness of
its area, and its proximity and uniform parallelism to
the boundary of the Pacific. According to Humboldt,
all the volcanos of America have burst through older
igneous products, such as basalts, trachytes, and por-
phyries. Granite is the basis of the trachytic masses of
Mexico.
If the line of the great Mexican volcanos be pro-
longed to the eastward, it enters the volcanic portion of
the West Indian Islands, on the west it cuts the Revil-
lagigedos. The Gallapagos Islands are volcanic, and
the same may be the case with Juan Fernandez.
In a large proportion of the West Indian Islands,
volcanic appearances have been recognised ; and in se-
veral the igneous action is still important. The large
islands exhibit least of this. In Trinidad is a great
expanse of asphaltum ; in Jamaica the Black Hill is vol-
canic : but all the smaller islands are either of volcanic
CHAP. IX. MODERN EFFECTS OF HEAT. 231
or coralligenous growth. Grenada, St. Vincent, St. Lucia,
Dominica, Montserrat, Nevis, St. Christopher, St. Eu-
stachia, are entirely volcanic ; Martinique, Guadaloupe,
Antigua, St. Bartholomew, St. Martin, St. Thomas, are
partially volcanic, and partially calcareous. The line
of these volcanic islands forms an arch convex to the
eastward.
African Volcanos.
On the continent of Africa, the notices of volcanic
districts are slight and incomplete. Perhaps between
the Nile and the Red Sea, as Ruppell and Jomard state,
volcanic action is not extinct. In Mount Atlas hasaltic
eruptions appear. The African islands, on the contrary,
are nearly all, almost exclusively, volcanic. From the
Azores, which are usually reckoned as European, the
Madeira Isles continue the Atlantic system of volcanic
action to the group of the Canaries. Further south,
the Cape de Verde Isles, Ascension, Fernando Po,
Prince's Island, St. Helena, Tristan d'Acunha, Gough's
Island, are so many points of active or. extinct volcanic
fire. Madagascar, Bourbon, and Mauritius contain
abundantly the effects of the same cause.
The circumstances observed in these various groups
differ extremely. In Madeira and Porto Santo, Ascen-
sion, St. Helena, Tristan d'Acunha, the volcanic fires
are extinct, and their effect has generally been to up-
heave stratified rocks covered by volcanic accumulations.
The Canary group has, in Lanzerote, a low volcanic tract
liable to burst suddenly after long intervals (from 1736
to 1834-), and a vent immensely elevated for the escape
from gaseous emanations and explosions, in the Peak of
Teneriffe, which rises to between 11,000 and 12,000
feet, out of a concentric base of basaltic jocks, between
3000 and 4000 feet high. Von Buch believes this iact
to be in favour of his general doctrine of craters of
elevation, which is also supported by him upon the evi-
dence of the form of Palma, another of these islands,
which have all (according to this view) been raised from
Q 4
232 A TREATISE ON GEOLOGY. CHAP. IX.
the sea, by the upheaving of submarine lava and sedi-
ments.
Australia exhibits traces of former volcanic action, in
the " Dividing Range," New South Wales ; and when
the interior of this vast region shall have been fully ex-
plored, such may, perhaps, be found extensively.*
Indian Ocean. — A submarine volcano is noticed on
the maps in lat. 7° S., long. 87° E. St. Paul's Isles,
lat. 38° S., long. 77° E., are also volcanic.
Pacific Ocean. — This great expanse of water appears
to be really one vast theatre of volcanic action ; for
almost every island raised above the water to a consider-
able height is more or less full of volcanic rocks, some
having high and powerfully active craters; while the low
islands are of coralligenous growth, and appear in forms
that suggest (though Mr. Darwin offers another ex-
planation) the belief of their being founded on volcanic
mountain tops. The volcanic systems of the Pacific
appear connected with the great littoral band of Asia,
already described, by the line of the Banda Isles, New
Guinea, New Britain, New Ireland, and other neigh-
bouring islands. The New Hebrides, Norfolk Island,
the Friendly Isles, the Society Islands, and the Sand-
wich Islands, and many of the detached islets which
adorn the Tropical part of the Pacific, are principally of
volcanic origin. The Ladrone Islands constitute a
mountain chain of active volcanos. In Tahiti (Otaheite)
there is an extinct crater at a height of many thousand
feet ; in Hawaii (Owhyhee), the enormous crater of
Kirauea has been described by Mr. Ellis in his Mission-
ary Tour. After traversing a vast surface of consolidated
lava, the crater was seen at a distance, in a vast plain,
sunk below a high precipice, which encircled the plain
with a rugged border 15 or 16 miles round. The
crater was of a crescent shape, 2 miles long (N. E. and
S.W.), 1 mile broad, and 800 feet deep. Lava melted,
and in violent agitation, filled this singular furnace,
» See Geol. Proceedings, Dec. 1834.
CHAP. IX. MODERN EFFECTS OF HEAT. 233
round which fifty -one conical islands rose, twenty-
two of them emitting smoke and flame, and many
ejecting great streams of lava, which rolled down to the
fiery gulf below. This had evidently, at some time
previous, been full to its edge, and was now partly
emptied by lateral subterranean discharge. All Hawaii
is of volcanic origin.
Geological Age of Volcanos.
Volcanos, properly so called, may perhaps have existed
during all the periods of geology marked by the succes-
sion of stratified rocks ; but volcanic eruptions on the
surface of the land or bed of the sea are rarely known
by their effects previous to the commencement of the
tertiary eras. Perhaps the earliest certain exceptions
to this generalisation have been found by Mr. Mur-
chison, and Mr. De la Beche, in the silurian and
Devonian rocks. In each of these instances, the evidence
of volcanic eruptions such as are here meant, is found
in the occurrence of layers of volcanic sediments, ana-
logous to trass and puzzolana, in alternating succession
with the ordinary deposits of water. Such facts abound
on the borders of the Malvern Hills, the range of the
Caradoc Hills, the Corndon Hills, and among the trap-
pean rocks which border the granite of Dartmoor.
If the great masses of basalt, which, under the name
of the whin sill, are interstratified with carboniferous
limestone in the mining dales of Northumberland, were
(as Mr. W. Hutton believes) spread out like lava on
the bed of the sea, the occurrence of volcanic eruptions
is proved from the early carboniferous eras. The
mixture of porphyritic pebbles and red sandstone in
Germany, on the east side of the Harz, and near Exeter,
seems to render plausible the conjecture that volcanic
eruptions were not unfrequent during the poecilitic era.
(See De la Beche s Manual, 2d edit. p. 365.)
The trap rocks of Skye and other islands on the west
of Scotland, which are in contact with lias and other
234 A TREATISE ON GEOLOGY. CHAP. IX.
rocks of the oolitic system, can scarcely, upon good
grounds, be admitted as originating in volcanic eruptions:
they are mostly unerupted lavas.
In tertiary periods of geology, traces of eruptions
became frequent. According to Lyell, the oldest vol-
canic rocks of the Limagne d'Auvergne belong to the
eocene tertiary period, being associated with freshwater
strata at Pont du Chateau near Clermont, and in the
Puy de Marmont near Veyres. None of the volcanic
eruptions of Central France had, however, commenced
when the older subdivisions of the freshwater groups
originated.
The newer portions of the Mont Dor and Plomb du
Cantal are stated by this author to be of meiocene
date, as well as some cones which stretch from Au-
vergne, through Velay, into the Vivarais, where they
are seen in the basin of the Ardeche. Finally, Etna,
which commenced its operations during the newer
pleiocerie era, has continued them down to recent times
with undiminished energy.
Had we included in this review the cases of un-
erupted lavas (basaltic and porphyritic dykes and inter-
posed masses), there would have been an unbroken
series of igneous products, cooled in subterranean, sub-
marine, or subaerial situations, from the earliest primary
eras down to the present day ; and from the whole we
should clearly see how very probable, or rather certain,
it is, that granitic and other plutonic, as well as volcanic,
rocks are not so much the products of the particular
times as of the particular circumstances in which
igneous action has been manifested.
Volcanic Eruption Forces. — Earthquakes.
The degree of mechanical pressure under which lava
is effused, and ashes are ejected, from volcanic vents, is
of importance in the theory of their action ; and when
combined with indications of the same kind in earth-
quakes, enters among the data requisite for comparing
CHAP. IX. MODERN EFFECTS OF HEAT. 2 35
the agencies of subterranean movements in ancient and
modern periods.
Ejections of Ashes and Stones. — The distance to
•which these are transported after leaving the volcano,
is a useful indication of the quantity ejected, and
thereby of the general power of an eruption, but not a
measure of its momentary violence. During the erup-
tion bf Vesuvius in 472 — 473, the ashes thrown out
were transported by the winds even to Africa, Syria,
and Egypt, and fell in Constantinople. In 1631, ships
were covered with ashes 20 leagues from Vesuvius. In
1812, the eruption of the Souffrier Mountain, in St. Vin-
cent's, gave forth ashes which were carried by the winds
to Barbadoes. During the terrific eruption of Tomboro,
in Sumbawa (1815), clouds of ashes obscured the sun,
and fell, inches deep, on the streets and houses in Java,
at a distance of 300 miles.
The intensity of the volcanic force can be better ap-
preciated by the magnitude of the stones ejected from
the crater, and the height and distances to which they
are thrown, than by any other criterion. It appears
that stones 8 Ib. in weight were thrown from Vesuvius
to Pompeii, a distance of 6 miles ; and stones were
observed by sir W. Hamilton to be thrown so high
above the mountain top, that they occupied 1 1 " in
falling, which gives a height of 2000 feet, and an
initial velocity of above 350 feet in a second. In 1798,
during a violent eruption in Teneriffe, the mountain
Chahorra threw out stones to such a height that
from 12 to 15 seconds were reckoned during their
descent. The height was consequently from 2500 to
3600 feet, and the initial velocity from 380 to 480 feet
per second. The pressure of a whole column of lava,
which should overflow the crater of Tenerifie, would,
according to Daubuisson, be equal to 1000 atmospheres,
and might eject lava, at the base, with a velocity of
nearly 850 feet per second. These forces are much
inferior to those with which cannon balls are projected.
The intermitting character of these " fits" of volcanic
236 A TREATISE ON GEOLOGY. CHAP. IT.
violence is favourable to the notion of their principally
depending on the sudden evolution of the force of steam,
with whose operation in this way we have been fami-
liarised by the steam gun of Mr. Perkins.
The formation of New Mountains is another pheno-
menon which strongly indicates the importance of vol-
canic operations in changing the aspect of the globe.
The cases are numerous. In 1538, in or near the site
of the ancient Lucrine Lake, in the Bay of Baise,
the Monte Nuovo was thrown up, in 48 hours, to a
height of 440 feet, with a circumference of 8000 feet,
from a crater of eruption, which has been measured to
the depth of 418 feet in the middle. In 1669, the
Monte Hossi was thrown up on the slope of Etna, 450
feet in height, and 2 miles in circumference ; this was
accomplished in three or four months. The formation
of Jorullo, in 1759, to a height of 1695 feet, is one of
the most remarkable effects of this kind. (See page 204.)
The New Islands which have been raised from the
sea by volcanic explosion or movement of the sea bed,
furnish additional facts; and probably a large proportion
of these striking phenomena is unrecorded, and many
more must pass away without notice, notwithstanding
the increased facilities which extended commerce and
general scientific education have afforded for recording
them in future.
The changes which have occurred in and about the
Island of Santorini, from an epoch 237 years before
Christ, to almost the present year, are remarkable, the
general effect being an augmentation of the land. The
new island of Sciacca, which appeared in July, 1831,
and disappeared in the course of the following winter,
is one of the most interesting events of this kind known
in modern times. It appears that a line of earthquakes
may be traced from Corfu, by Calabria, to Etna, which,
in its extension westward, .nearly strikes the volcanic
island of Pantellaria. Between Pantellaria and Sicily,
on this line, submarine movements were noticed in
June, 1831 : soon afterwards the signs of an eruption
CHAP. IX. MODERN EFFECTS OF HEAT. 237
were seen by Neapolitan fishermen ; and on the 18th of
July, a British man of war passing near the spot, white
columns were seen in the sea, rising from a dark
hillock, which threw up stones and ashes. It was then
judged by captain Swinburne to be 70 or 80 yards
in diameter, and about 20 feet high. In August it had
grown to a circumference of 3240 feet, its height being
107 feet; and in the middle was a crater 780 feet in
circumference ; the columns of ashes rose to a height of
3000 or 4000 feet. The evolution of gases was incon-
siderable. When examined, the mass of the island was
found to be a dark vesicular lava, with a few fragments
of limestone, and other non- volcanic rocks. On the
28th of September, according to Prevost, the circum-
ference of the island was 2300 feet, and the height
from 100 to 230 feet. In the winter of 1831-2, its
loose and perishable fabric had yielded to the action of
the waves, and disappeared from the surface. It is
now a dangerous shoal, shelving gradually to the deep
sea bed (100 fathoms), out of which it originally
sprung ; on the neighbouring parts of the sea bed,
probably, a considerable deposit of volcanic sediment is
spread. Such is the history of the vanished island of
Sciacca.
In the Azores, in 1628, an island rose from 160
fathoms water, in 15 days, to a height of 360 feet above
the sea ; Mr. De la Beche has found in the MS. of the
Royal Society, a notice of another island, which had been
thrown up in 16QO, but soon afterwards, like Sciacca,
was dissolved and sunk again in the sea.
In 1811, off St. Michael's, in the same group of
islands, a volcano was observed to be active in the sea,
on the 13th of June. On the 17th it shot up black
columns of cinders to the height of 700 or 800 feet
above the sea, and at other times clouds of vapour ; the
eruptions being accompanied by great noises and vivid
lightnings. On the 4th of July, the island which was
formed was 1 mile in circumference, almost circular,
and about 300 feet high ; the crater discharged hot
238 A TREATISE ON GEOLOGY. CHAP. IX.
water. This island, to which the name of Sabrina was
given, disappeared like Sciacca.
In 1 783, a new island rose in the sea near Rey-
kiavich, in connection with the Icelandic volcanic
system : it was 1 mile in circumference, but soon
disappeared like so many of these already mentioned.
The ejections from the summits and sides of vol-
canos go to enlarge the mean diameter of the globe,
whether they be heaped on the land or laid on the bed
of the sea. The amount of this augmentation of
diameter has never been estimated (we believe), nor
would the estimate, perhaps, be worth the slight trouble
of the calculation, were it not useful to moderate the false
impressions which a contemplation of the violence of
ignivomous mountains occasions. If we suppose the
volcanic lines and groups known on the globe to be col-
lected in one line, it would not equal a great circle of the
sphere. If we take as the breadth of this volcanic band
a surface of 10 miles, we shall much exceed the average.
To assume that half the mass of active or extinct
volcanic mountains above the sea is the product of sub-
aerial or submarine eruptions is an ample allowance.
Finally, if the figure of the mixed volcanic and rocky
mass be taken as a series of cones, 2 miles in height,
which is far above the truth, the mean volume of
igneous products resulting from the calculation is
24000 x 10 x 2
~~ m^es = 80,000 cubic miles ; which,
if spread over all the globe equally, would augment its
diameter about 2^ feet. Now, as all the conditions have
been taken in a sense the most favourable for the
magnitude of the result, we see how feeble, after all,
is the change of the general conditions of the globe,
produced by the agents of violence put in action during
volcanic excitement.
The cavities left within the globe, by the ejection of
this mass of matter, are probably so circumstanced by
the overarching of their roofs, that they may resist for
a long time the tendency of the superincumbent weights
CHAP. IX. MODERN EFFECTS OF HEAT. 239
to fall in ; but there is a limit to this resistance. When
the superficial accumulations are of vast height and
great lateral extent, as in some of the mighty volcano*
of America, the internal heat rises upward, in the sub-
stance of the mountain, so as to re-absorb the base of
the cone, and weaken its strength. From this cause,
perhaps, it happens that sometimes volcanic mountains
fall into the cavity below them, and are swallowed up.
Thus the great mountain mass of Papandayang, in
Java, fell into the greater cavity out of which it had
been raised ; and 1'Altar, in Quito, lost its command-
ing summit.
The subterranean connection of even distant volcanic
mountains, and the reciprocity of action between what
appear on the surface to be distinct volcanic groups,
justify the belief that the sources from whence the
eruptions are supplied with mineral matter spread
widely around the volcanic vents ; an inference still
further strengthened by the extension of earthquakes
beyond the regions of burning mountains. It follows
that movements of subsidence, which are occasionally
witnessed in really volcanic districts, may, and indeed
must, happen sometimes in other situations, where
lines or surfaces of weakness fxist, in the earth's crust,
Such depressions may be either gradual or sudden, ac-
cording to the circumstances which determine the points
and degrees of relative weakness in the earth's crust,
and from all the considerations it is easy to perceive
that the real change of the earth's diameter, by the
explosive action of volcanos, is very small, and much
counterbalanced, in all periods, by the contrary effects
of subsidence ; and that in the progress of volcanic oper-
ations a limit must at last be reached, when the two
opposite effects of the same cause must be exactly
balanced, though not necessarily in the same physical
regions. The general result, then, is an augmentation
of the heights by volcanic energy, and a deepening of
the depths by the consequent subsidence.
Far from the centres of volcanic excitement, the
240 A TREATISE ON GEOLOGY. CHAP. IX.
compensating depressions of the earth's crust would
probably be gradual and almost insensible: in such
situations there may also occur equally gradual and
almost imperceptible elevations of particular tracts of
land, because if there be a real sinking over lines and
surfaces of weakness, there will be relatively a rising
over points having the contrary properties. There
may also be a real rising of such parts, with a relative
sinking of others, if the arrangement of the rocks is
such as to give maxima of strength in opposite direc-
tions. The ordinary and well-known forms of anti-
clinal and synclinal axes are examples of such figures ;
for an upward general pressure, such as accompanies
volcanic violence, may more easily extend and raise an
anticlinal mass, and a subsequent general collapse would
act with more force on the synclinal surfaces of strati-
fication. Other causes concur to augment these effects,
which are certainly exemplified in observed phenomena
of the relative levels of land and sea.
In conformity with this reasoning, we find, on the
testimony of all writers who have examined the history
of earthquakes, that they are by far most abundant
and most violent, in countries which surround or lie
between volcanic districts. Before and during volcanic
excitements, earthquakes abound, so as evidently to
make part of the same phenomenon ; and, even under
countries where volcanic fires are dormant or extinct,
these convulsions of the solid framework of the earth are
more powerful than in remoter districts. It is in vol-
canic countries that proofs have been found of the
real displacement and positive elevation of land, on
particular days, and during particular earthquakes;
while at points far remote from Vesuvius and Hecla,
the land is slowly rising in Scandinavia, perhaps slowly
sinking in Greenland, perhaps alternately elevated and
depressed on some parts of the shores of Britain.
Examples of permanent displacements of land, arising
from convukive movements near the seats of igneous
activity, are furnished by the Calabrian earthquakes of
CHAP. IX. MODERN EFFECTS OF HEAT. 24-1
1783, the Lisbon earthquake of 1755, the Chilian earth-
quakes of 1822 and 1835. In 1822, according to
Mrs. Graham, the Chilian coast was agitated by a move-
ment which extended in length 900, 1000, or perhaps
1200 miles (including Copiapo and Valdivia), and raised
the whole line of coast for a distance of 100 miles; at
Valparaiso 3 feet ; at Quintero 4 feet ; the greatest
movement being about 1 5 miles N. E. of Valparaiso :
the beds of oysters and other shells were raised clear to
the surface. The whole region between the Andes and
a line far out in the sea is supposed to have been per-
manently raised, 2, 3, or more feet (in the interior
the elevation is said to have reached even 7 feet). The
area under which, ashore, the earthquake extended, is
estimated at 100,000 square miles.* If, as Mr. Lyell
supposes, the whole of this vast area was raised, and
the elevation be taken at 1 foot on the average, the whole
augmentation of the earth's diameter caused by it will
be T0^^th part of that which we attribute to the whole
mass of visible volcanic accumulations on the surface.
It is unnecessary to re-open the discussion of the accu-
racy of the data above assumed, because in 1835 simi-
lar phenomena happened on another part of the same
coast.
This second great disaster on the Chilian coast has
been described by Mr. Caldcleugh, from his own and
other observations, with much care. It was heralded
by the landward flight of immense flocks of sea-birda
(the same thing occurred previous to the shock of 1822),
and by the remarkable activity of the volcanos of the
Andes, An enormous wave, rising 28 feet in height,
destroyed Talcahuano, and was followed by a greater.
Columns of smoke rose in the sea, followed by whirl-
pools. In the Bay of Conception the strata of clay
slate were elevated about 3 or 4 feet. At San Vicente,
* Journal of Science, TO!, xvii. p. 46. It is not here asserted that 100,000
•quare miles were •' permanently altered In level" It is stated that the
" principal force was exerted in a circle of 50 miles diameter, having its
centre S. E. of Valparaiso," and again the force diminished in proportion
to the distance from Valparaiso.
VOL. II.
242 A TREATISE ON GEOLOGY. CHAP. IX,
a. port a little south of Talcahuano, the land rose about
1 foot and a half. In the small island of Santa Maria,
the rise was estimated by Captain Fitzroy at 8, 9, and
1 0 feet ! At Nuevo Bilbao,, 70 leagues north of Con-
cepcion, the earthquake was violent, but there is no
permanent elevation of the land. Throughout the
entire provinces of Canquenes and Conception, the
crust of the earth has been rent and shattered in every
direction. An hundred miles from the coast vessels
experienced the shock. The island of Juan Fernandez
was included in the area of the submarine disturbance,
which below the land reached northward as far as
Coquimbo.
It is remarkable that Acosta speaks of very similar
effects of waves and violent movements in the same
range of coast, in the 16th century; and other instances
have been collected by Mr. Woodbine Parish.
Though, for reasons before stated, we cannot expect
to find cases of sudden depression in volcanic regions
so frequent or extensive as those of elevation, enough is
known to assure us that in and beyond these regions,
earthquakes have very often caused subsidence of land.
We read, that in the year 541 Pompeiopolis was half
swallowed up in an earthquake ; that in 867 Mount
Acraus fell into the sea ; that in 1112, the city of Liege
was flooded by the Meuse, and that of Rotemburg on
the Neckar was ruined. In 1186, a city on the Adri-
atic shore is described as sinking into the sea; in 1596
the sea covered many towns in Japan ; in 1638 St,
Euphemia became a lake; and in l6Q2 Port Royal is
commonly believed to have sunk. In 1755, the great
earthquake caused a new quay at Lisbon to subside, and
its place was occupied by water 100 fathoms deep, and
other similar cases of engulphment occurred on the
Portuguese and African shores. In 1819, extensive
subsidence occurred with the submersion of a town and
large tracts of country, at the mouth of the Indus, and
in the same vicinity rose a compensating elevation, called
" the Ullah Bund."
CHAP. IX. MODERN EFFECTS OP HEAT.
That earthquakes are experienced over regions far
from volcanic mountains is easily ascertained by con-
sulting the imperfect records which have been preserved
of these phenomena in Europe. For it thus appears
that in Norway, Scotland, England, Belgium, and many
parts of Germany and France, considerable earthquakes
have occurred, not only at a distance from European
volcanos, but also without any definite relation of time
to the eruptions' of the Icelandic or Mediterranean vol-
canos. In a long catalogue which we have drawn up
for the purpose of comparing the dates of earthquakes
in Great Britain with the recorded eruptions of those
volcanos, &c.,the last 1000 years, we have found scarcely
any accordance.
The movement of the ground during an earthquake
is described variously, — as a vibration, a rolling, an un-
dulation, a shock ; but it is to be regretted that these
terms do not always convey a definite and exact notion
of the kind of disturbance which really takes place.
Some observers speak only of vertical movements, such
as were experienced during the Lisbon earthquake by
a vessel far west in the Atlantic ; others mention hori-
zontal movements, as during the Chilian earthquake of
1835. In general, there is an impression that the move-
ment of the ground travels in one certain direction, like
a wave upon water j this direction was remarked to be
different in the northern and southern portions of country
shaken in Chili in 1822. There is sometimes one shock,
in other cases several, seldom many successive impulses
from below. The most violent movements appear to
have been experienced on the sea- side, and in the sea
itself, which, retiring and returning with mighty waves,
10, 20, or even 60 feet high (in the Lisbon earthquakes
of 1755), produce incalculable mischief and destruction
of life and property.
Were the globe a solid mass at great distances from
the seat of the original disturbance, these effects could
not happen, unless, as Mr. Mallet has shown, a wave
of elastic compression were generated, which should
R2
244 A TREATISE ON GEOLOGY. CHAP. IX.
travel like a great wave of translation in water, with
velocities corresponding to the elasticity of the rocks, so
as to reach Lisbon, Loch Lomond, Italy, and the West
Indies. Rocks, we know, are elastic in their parts,
but very imperfectly so in their mass, owing to the nu-
merous divisions which intersect them. Earthquakes
cannot be compared to the vibrations of a string, or the
pulsations of sound, gradually falling to rest; the motion
observed is more similar to the undulation of a flexible
lamina over an agitated liquid ; — as when a long cloth
is shaken in a particular manner, so that a wave of air
travels below its parts successively to the end.
Mitchell, to whom physical geology is largely in-
debted, was the first to explain earthquakes by wave
motion, and he employs for the purpose the mechanism
of a fluid thrown into undulation, or vapour operating
by expansion beneath or between the strata.* He as-
signs 1750 feet per second for the velocity of the Lisbon
earthquake. Professors H. D. and W. B. Rogers, fol-
lowing in the same track, make the phenomena of
earthquakes depend on undulations propagated in molten
rock below the solid crust, trace the path of some of
these phenomena, and give measures of the rate of pro-
gress of the wave : viz., 27 to 30 miles per minute, or
about twice as fast as the wave of sound in air. They
find for the velocity of sea waves generated by the
earthquake shock, 3| and 5 miles an hour.t They find
the area agitated by earthquakes at any one epoch to be
very long and narrow, corresponding to the great wave
of translation, and trace the synchronous lines of move-
ment for several hundred miles in length.
Mr. Mallet, in a paper communicated to the Royal
Irish Academy^,1 followed by a Report to the British
Association, has entered fully on the dynamics of
earthquakes, and on the history of these phenomena ;
and has performed some capital experiments on the rate
of movement of earth waves in incoherent sand, and in
granite of perhaps the average degree of consolidation. §
* Phil. Trans. 1760.
t Reports of the British Association, 1843. J Ibid. 1846.
.§ Communicated to the British Association in 1851.
CHAP. IX. MODERN EFFECTS OF HEAT. 245
From the point where the earthquake originates, two
sets of waves proceed in the solid crust of the earth,
viz., the wave of elastic compression, propagated in every
direction with a velocity proportioned to the elas-
ticity and density of the parts of the earth-crust in
its path. In different sorts of rock the velocity will not
be the same : it will be greatest in the solid, and least
in the loose aggregations of matter. Another set of
waves is that of sound. And, if the origin of the earth-
quake be under the sea, a water wave of translation will
be generated in the sea, of much less velocity than that
in the earth. Sound waves will be communicated to
the water and to the air ; but of these we need not say
much. If the earthquake originate under the land, and
be propagated under the sea, it will reach the extreme
border of the sea, and raise the shore so as to force the
water to appear to retire, and afterwards to return and
flow higher than before, a phenomenon distinctly ob-
served. Supposing the first shock to have happened
under the sea, and all the waves to be noticed on the
extreme edge of the water, we should have,
1 . The earth waves of shock and sound together, or
nearly so.
2. The forced sea wave lost upon the beach.
3. The sound wave through the sea.
4. Sound waves (possibly) through the air.
5. The great water-wave, which has been found so
destructive. *
According to Mr. Mallet, the velocities to be expected
in the sound-wave would be 4700 feet per second in
water, 1140 feet in air; and, judging from the elas-
ticity, in lias 3640 ; in coal measure sandstones 5248 ;
in oolite 5723 ; in primary limestone 6696 ; in carbon-
iferous limestone 7075 ; and in hard slate 1 2,757 j and
in granite and igneous rocks still higher rates. Perhaps
the speed of the great earth-wave may be nearly the
same ; but the Vnasses of rock in the earth are so much
interrupted by joints, by unequal condensation, varying
* Mallet in Brit. Assoc. Reports for 1850.
B 3
246 A TREATISE ON GEOLOGY. CHAP. IX.
•
inclination, and other circumstances, that as appears
in the case of the Lishon earthquake, in Mitchell's,
Rogers's, and Humboldt's estimates, (^ to i a mile in
a second,) the real velocity is much less. Mr. Mallet
has ascertained it in the case of sand and granite to be
even less than the above instances, and his experiments
were so arranged in the sand at Killiney and the granite
of Dalkey, as to give very accurate results. For his
beautiful process the reader must be referred to the
Brit. Assoc. vol. for 1852.
It appears very desirable, for the completion of this
theory of earthquakes, to carry out the seismometrical
observations recommended by the British Association,
especially at the great public observatories.
Mr. Hopkins in treating this subject mathematically,
has shown how, by proper observations of this kind, the
local origin of the earthquake can be determined in
depth, as well as in geographical position.*
The force of an earthquake shock diminishing at
points removed from its origin as the square of the dis-
tance increases, we see how great must have been the
shock in the case of the Guadaloupe earthquake (1 843),
when, as Rogers has shown, an area not less than 2300
geographical miles in length by 770 in breadth was
agitated. According to the observations made on this
occasion, the shock was simultaneous in lines nearly
north and south, and felt moving in opposite directions
from a curved central axis, at the rate of 27 miles in a
minute. This seems to indicate a linear subterranean
fracture of great length — a fault geologically speaking
— such as might occur over a cavity left by the with-
drawal of a fluid support to the earth's crust.
By a mathematical investigation of this subject,
founded on the phenomena of precession and nutation
which arise from the action of the sun and moon on the
unspherical mass of the earth, Mr. Hopkins has shown
that whether the earth be partially fluid or wholly solid
within, there would be no material difference in the
* Brit. Assoc. Reports, 1847.
CHAP. IX. MODFRN EFFECTS OF HEAT. 247
precession and nutation, provided the ellipticities of the
interior and exterior surface of the supposed solid crust
were equal, and the density of the crust and fluid equal
and uniform. But if these limitations were not ob-
served ; if the solid shell and interior fluid were hetero-
geneous, and the ellipticities of the interior and exterior
surface of the crust different, then the amount of the
precession and nutation would depend on the difference
between the ellipticities of the interior and exterior
surface of the crust, and on its thickness : or on this
latter quantity alone, if the solidity of the shell resulted
from refrigeration. And the result of the whole inquiry
appears to be, that the thickness of the solid crust can-
iiot be less than 1th or 4th of the radius of its external
surface.* This conclusion is probably decisive against
any universal ocean of molten rock below us, at depths
accessible to the disturbing agents which generate earth-
quakes and volcanos : but it seems not to preclude the
admission of limited fluid masses, at various and far
smaller depths than 1000 or 800 miles. In harmony
with this view is the opinion of Mr. C. Darwin, who,
from considering the circumstances which accompany
volcanos and earthquakes in the Cordilleras of the Andes,
proposes, as a fundamental point of reasoning, the re-
cognition of the existence of a vast internal sea of melted
rock below a large part of South America, t
This conclusion appears liable to so little objection ;
it is, besides, so perfectly in harmony with the fact his-
torically proved of the perpetual readiness of volcanos
for action, and with the geological inference of the
perhaps unlimited extent below our feet of rocks once
fused ; that we shall venture to adopt it as a datum suf-
ficiently established, and applicable to the whole series
of volcanic phenomena, in every country, and during
all past periods of time.
But this ocean of melted rock may sleep, and does
remain at rest, beneath enormous areas, for centuries, or
much longer periods, till some particular causes concur
ito " change (as Mr. Darwin expresses it) the form of
* Phil. Trans. 1839, 1840, 1842. f Geol. Proceedings, 1838.
R 4;
248 A TREATISE ON GEOLOGY. CHAP. IX.
the fluid surface," and develop extraordinary chemical
energy and fearful mechanical violence. What are
these causes ? and what is the condition of the sub-
jacent fluid masses whose repose they disturb ?
Hypotheses of Volcanic Action.
To answer the questions just proposed, is the object
of a just theory of volcanic action. The conditions al-
ready established, of the great extent of the phenomena,
the appearance of volcanic fires in every kind of rock,
and the continuity of such operations not only through
historical but through earlier geological periods, negative
completely the trifling notion of any particular combus-
tible substances, or decomposable chemical compounds,
being sufficient to maintain such long-enduring and
powerful operations of heat. We must adopt larger and
yet more definite views on the subject. No supposition
will be of the smallest value, which provides an agency
inferior to the area, unequal to the mechanical violence,
or inconsistent with the chemical characters of volcanic
excitement.
Accordingly, only two hypotheses have been deemed
worthy of attention in the "modern consideration of this
subject. Humboldt, Cordier, and other eminent geolo-
gists, reviving the opinion of Leibnitz, look upon vol-
canic action as the necessary result of the influence
exerted by the heated interior upon the cooled exterior
masses of the globe. If the earth be now generally
hot within, it must formerly have been hotter j in the
process of cooling, the exterior solidified part and the
interior fluid parts contract unequally, a general pressure
and tension result, and the crust breaks locally to
restore the equilibrium. Hence earthquakes, and fis-
sures, on some of which volcanic vents are established,
which serve more or less to relieve the subterranean
pressure, as earthquakes also do. If, in addition to
this general view, we suppose the admission of water
through fissures to particular parts of the " ocean
CHAP. IX. MODERN EFFECTS OF HEAT. 249
of molten rock," it is easy to see that the observed me-
chanical phenomena of volcanos and earthquakes will
result as the effect of a local excitement superadded to a
general operation. Such is an outline of the explanation
offered by the hypothesis of a general heat pervading the
interior of the globe.
Mr. Darwin, in his summary of the phenomena
attending earthquakes on the coast of Chili, in 1835,
regards, very justly, the submarine outbursts, the re-
newed volcanic activity, and the permanent elevation of
the land, as forming parts of one great action, and
being effects of one great cause, modified only by local
circumstances ; and that, therefore, " no theory of the
cause of volcanos, which is not applicable to continental
elevations, can be considered as well established." This
appears a just inference. He is further
the following conclusions may be dn
nomena of earthquakes.
1st. That the primary shoe
caused by a violent rending of tl
coast of Chili and Peru, seems \jei6fally to occur
the bottom of the neighbouring sea.
2d. That this is followed by many
which, though extending upwards, do not, except in
submarine volcanos, actually reach the surface.
3d. That the area thus fissured extends parallel, or ap-
proximately parallel, to the neighbouring coast mountains.
Lastly. That the earthquake relieves the subterranean
force precisely in the same manner as an eruption through
an ordinary volcano.
Now every thing here said may be adopted, without
hesitation, into the general speculation of Humboldt, of
which, in fact, these inferences from observation are
strongly illustrative.
Another view, which is strongly supported, is usually
considered by its defenders as " the chemical hypo-
thesis" of volcanic action. It presented itself both to
Davy and Gay-Lussac, as a natural consequence of the
discovery of the metallic and metalloid bases of the
250 A TREATISE ON GEOLOGY. CHAP. IX.
earths and alkalis ; and though the former eminent phi-
losopher abandoned his speculation, it has found able
support in Dr. Daubeny. The account given by Dau-
buisson will clearly exhibit the opinion of Gay-Lussac.
" If we admit, what is in fact almost certain, that water
enters in great quantity to the foci of volcanos, and
there comes in contact with the metalloid bases of the
earths and alkalis, and some chlorides (especially the
chloride of sodium), the following effects will happen: —
One part of the liquid will be quickly decomposed;
the metals and the chlorides will seize oxygen, and be
thereby converted to silica, alumina, lime, magnesia,
soda, &c. — substances which predominate in lavas; the
hydrogen will be liberated in the state of gas, or in
combination with chlorine will form hydrochloric acid,
which is known to be very often present in the vaporous
exhalations of volcanos."* The heat generated by the
primary chemical action (oxygenation) and the ener-
getic action of steam, to which part of the water is con-
verted, are thought sufficient to account for the mecha-
nical phenomena of volcanos.
Dr. Daubeny has given to this speculation a character
of greater completeness, by an examination of the actual
products of volcanos, for comparison with a regular de-
duction of chemical phenomena from the fundamental
postulates of Gay-Lussac and Davy.
If, at a depth of 3 or 4 miles, the nucleus of the
earth consists of the metalloid bases of the earths and
alkalis, with iron and other metals, partially combined
wrth sulphur, — the new oxygenation to which, under
ordinary conditions, they would be subject, may be pro.
ductive of no other phenomena than a moderate rise of
temperature in the neighbouring rocks or in thermal
springs.
But with access of water, and especially sea water,
the effects of the heat generated will become more for-
midable. Oxygenation on an extensive scale ; evolution
* Traite de Geologie, torn. i. p. 206. ; and Ann. de Chiraie, torn. xxii.
CHAP. IX. MODERN EFFECTS OP HEAT. 251
of a large volume of hydrogen, again to combine with
oxygen (supposing atmospheric air present), or with
sulphur, at a high temperature. In the former case,
nitrogen gas will be liberated, which may rise uncom-
bined, or may unite with hydrogen to form ammonia;
and this will be neutralised by free muriatic acid, and
produce sal ammoniac.
The hydrogen not thus disposed of may combine
with sulphur to form sulphuretted hydrogen gas ; but
this may be again decomposed by rising and meeting
with oxygen; as long, therefore, as oxygen abounds,
there will be evolution of water and sulphurous acid ;
afterwards sulphuretted hydrogen will prevail toward
the end of the eruption. As long as heat remains in
the lava, the combustion of sulphur, and the decompo-
sition of the sulphurous acid by sulphuretted hydrogen,
would regenerate water, to maintain, by combination
with metals and metalloids, a continuance of similar
though feebler actions.
There is not, we believe, any attempt on record to
deduce all the chemical phenomena of volcanos from the
hypothesis of general heat below the surface of the earth:
we must therefore, at present, suppose this is difficult,
except upon the admission of that powerful absorption
of oxygen from water, which the " chemical" hypo-
thesis provides. Granting, then, the truth of these
opinions as to the origin of the substances ejected from
volcanos, do they involve the rejection of the hypothesis
of a pervading high temperature below the surface GL
our planet ? Surely not.
For what account does the peculiar series of gaseous
and earthy ejections from a volcano give of the origin of
the volcanic action ? What opens the fissure and gives
passage for the water to the base of volcanic mountains ?
The whole crust of the globe, stratified and unstratified,
is a mass of metallic oxidation ; how can there yet re-
main, at so many points, access for water through this
oxidated crust, to the unseen primitive nucleus ? How
happens it, that really volcanic effusions are so limited
252 A TREATISE ON GEOLOGY. . CHAP. IX.
and so few among the older strata, which were formed
when the stratified crust of the globe was thinner, and
(by this hypothesis) the un saturated metalloid bases
were more plentiful near the surface ?
It appears to us very clear, that the union of the two
speculations here brought into comparison is not only
practicable, but reasonable, and even necessary. A general
cause of change of form of the earth's surface and inte-
rior parts is supplied by the doctrine of a change of
interior heat ; abundant admission for water is afforded
by the fractures necessary (upon this view) to adjust the
balance of pressures; and the chemical products can
only be properly understood by a suitable hypothesis of
chemical action. The interior mass of the globe may
yet retain the uncombined bases of earths and alkalis; but
the chemical products resulting from admission of oxy-
gen to these are not at all the less intelligible, if we sup-
pose the whole mass of the interior to have those general
conditions of heat which appear to suit the mechanical
disturbances of the land and sea. On this point, how-
ever, further researches on collateral phenomena may be
prosecuted with advantage, and to these we now proceed.
Thermal Springs.
In general, the springs which issue from the earth
derive their origin from rain which has descended
through fissures of the rocks (especially calcareous
rocks), and, in consequence of meeting with natural
impediments to further descent, — as beds of clay, dykes,
mineral veins, faults, — collects in the rocky reservoirs,
rises to the surface, and issues at the point to which
access is easiest, whether it be the lowest point of the
vicinity or not. The rains which supply such springs
descend irregularly ; yet, if the subterranean reservoirs
be considerable, the discharge is nearly constant in all
parts of one year, and in many succeeding years. To
each of such springs usually one particular chemical
quality is imparted by the rocks through which the
CRAP. IX. MODERN EFFECTS OF HEAT. 253
water passes ; and one particular average temperature
belongs to each, generally identical with that of the
ground through which it passes.
This temperature seldom differs much from the mean
annual heat of the locality, and, unless the stream be
subject to variation of quantity, hardly varies with
seasons or years.
It has, however, been found that the small differences
which appear between the mean temperature of the
air and of springs at particular localities, are of a
somewhat regular character, and bear a general if not
a precise relation to latitude. It was found, for instance,
by Dalton (1793), that the springs at Kendal gave a
somewhat higher range of temperature than the air :
the same observation has been made at Berlin, Paris,
and other places in the North Temperate Zone ; but in
the equatorial region the contrary appears to be the
fact. The tables of Kupffer (which may be consulted
in De la Beche's Manual of Geology), constructed from
observations of Humboldt, Von Buch, Cordier, Wah-
lenberg, Kupffer, &c., appear to give as much as from
1° to 5° superiority of air temperature above that of
the ground ; while in latitude 54° to 60°, in Russia, the
springs were warmer than the air by 5° or 6°. — This
fact appears to show clearly that the temperature of the
earth and of springs is influenced by gome general
cause independent of solar heat.
Besides the class of ordinary springs, which may
thus differ by small amounts from the temperature ot"
the air, there are " thermal springs" which often deserve
the name commonly assigned to them of " hot springs,"
and sometimes approach even the boiling point. These
are usually found to be almost, or even absolutely,
constant in their discharge, uniform in their tempe-
rature, and unvarying in their chemical composition.
Some of the sources frequented by the luxurious nations
of antiquity still retain their efficacy, — in Greece, in
Belgium, and at Bath ; and the inquiry into the cause
of this continued heat becomes the more important
254 A TREATISE ON GEOLOGY. CHAP. IX.
when we consider the great geographical area over
which hot springs are scattered, the singularity of their
association with cold and mineral waters, which is often
noticed, the variety of their contents, and the geological
circumstances which accompany their efflux.
It is unnecessary to dwell at any length on the
question, how far any peculiar chemical quality is cha-
racteristic of hot waters, so as to offer a satisfactory
explanation of their warmth from chemical action. There
is no such peculiarity. Thermal waters are found to
be, on the average, neither more nor less pure than
springs of common temperature ; they exhibit, in fact,
the same scale and variations of chemical constitution
as common waters. The chemical quality of hot waters,
offers no explanation of their heat, though, combined
with other considerations, it may help to guide to a
right view of the manner in which that heat has been
acquired.
There is no one product of thermal springs, con-
stantly found in them, which never occurs in cold
waters; but it appears from Dr. Daubeny's import-
ant researches, that nitrogen gas is very common in hot
springs, and perhaps very rare in cold waters. This
circumstance appears to him of great importance in the
argument whereby he connects the origin of hot springs
with volcanic action. In Dr. Daubeny's admirable
Essay on Mineral and Thermal Waters*, the catalogue
of thermal waters exhibits the prevalence of nitrogen,
among the gases evolved, in a striking degree ; car-
bonic acid is also plentiful, and, in particular districts
(Nassau), predominant. As examples, we may select the
notices of the warm springs of the British islands, and
of those which adjoin the Ardennes and Nassau moun-
tains, — in both instances only obscurely dependent on
volcanic formations; the Pyrenean and other springs
may also be noticed.
* Reports of British Association, 1836.
CHAP. IX. MODERN EFFECTS OF HEAT. 255
WARM SPRINGS OF THE BRITISH ISLANDS, YIELDING NITROGEN,
&c.
1. Bath. — The King's Bath spring rises through lias*, at a
temperature of 66° above that of the neighbourhood ;
contains saline ingredients, 1 5 grains in a pint (muriate
of lime and magnesia); evolves 96'5 per cent, nitrogen,
3 -5 oxygen, and some carbonic acid.
2. Bristol. — The Hot Well rises in carboniferous limestone, at
a temperature of 25° above that of the place ; contains
saline ingredients, 6 grains in a pint (sulphate of soda and
muriate of lime) ; evolves 92 per cent, nitrogen, and 8
oxygen.
3. Buxton, Derbyshire. — St. Anne's Well rises in carboniferous
limestone, at a temperature of 33° above the vicinity ;
contains saline ingredients, only 1-8 grains in a pint
(muriates of magnesia and soda) ; evolves nitrogen only.
4. Baltewell, Derbyshire. — The Bath spring rises in carboniferous
limestone, at a temperature of 1 3° above the vicinity ;
contains saline ingredients, 3| grains in a pint (sulphate
of lime and muriate of soda) ; evolves nitrogen only.
5- Stony Middleton, Derbyshire. — The spring rises in carboni-
ferous limestone, at a temperature of 14° above that of
the vicinity ; contains saline ingredients, 2 grains in a pint
(sulphate of soda and magnesia, and muriate of lime) ;
evolves nitrogen only.
6. Taafes Well, near Cardiff. — Rises from coal strata, at a
temperature of 21° above that of the vicinity ; contains
saline ingredients, only 1 -2 grain in a pint (sulphate of
magnesia) ; evolves 96i per cent, of nitrogen, and 3% per
cent, of oxygen.
?. Mallow, Co. Cork. — The Spa well rises in carboniferous
limestone, at a temperature of 23° above that of the
vicinity; contains saline ingredients, only 0-3 grain in a
pint (carbonate of lime); evolves nitrogen 93i per cent.,
and oxygen 65.
It is very surprising that the only hot springs of
Great Britain should all rise through strata of the car-
boniferous system (mostly below the coal), or through
others which rest unconformably upon them.
* Dr. Daubeny places the source of this spring in red sandstone, but we
conjecture that it is likely the spring originates iu the mountain limestone
which lies unconformably below the lias and new red sandstone.
256 A TREATISE ON GEOLOGY, CHAP. IX.
WARM SPRINGS OF A PART OP GERMANY, &c., YIELDING
CARBONIC ACID, &c.
Aix-la-Chapelle. — The Kaiserquelle rises at the junction of
clay slate and carboniferous limestone, with a temperature
85^° above that of the vicinity ; contains of saline in-
gredients 32 grains in a pint (muriate, carbonate, and
sulphate of soda, &c.); evolves nitrogen 69 -5, and car-
bonic acid 30.
JBorset. — The Miihlenbend rises with the same geological
relations as the last, with a temperature 121 '5° above that
of the place ; contains of saline ingredients 34 grains in a
pint (muriate, carbonate, and sulphate of soda, &c.);
evolves nitrogen 80 per cent., oxygen 2, and carbonic
acid 18.
Ems. — The Rondul rises in argillaceous slate, with a tempe-
rature of 81° above that of the place; contains of saline
ingredients 28-9 grains in a pint (carbonate, muriate,
and sulphate of soda) ; evolves carbonic acid gas only.
Wiesbaden. — The Kochbrunnen rises in chloride slate, with
a temperature of 108° above that of the vicinity ; contains
of saline ingredients 57 '6 grains in a pint (muriate of
soda, lime, and potash) ; evolves nitrogen 27 per cent., and
carbonic acid 73.
(The above springs all rise in or adjoining the slaty
rocks.)
WARM SPRINGS OP THE PYRENEES.
Those of Aries, Preste, Fernet, and Molitz, in the Dep. des
Pyrenees Orientales, having temperatures above the vicinity
of 85 -3°, 71 '0°, 72 -2°, and 40° ; contain of saline ingredients
2, 1, 1*3, 1*3 grains respectively (sulphuret of sodium,
&c. ) ; and evolve nitrogen gas only. They rise from
granite.
The following are in the same department : —
That of Sorede, having a temperature above the vicinity of 9° ;
contains of saline ingredients 6 '8 grains in a pint (car-
bonate, sulphate, and muriate of iron) ; and evolves car-
bonic acid gas only.
Those of Reynez, Enn, and Thuez, having temperatures above
that of the vicinity of 23 -7°, 62 -0°, and 7 ] ° have almost no
CHAP. IX. MODERN EFFECTS OF HEAT. 257
saline contents; and evolve no gases. The two former rise
in mica slate, the latter at the junction of granite and
limestone.
Those of Enaldes, Dorros, and Los rise at the boundary of
granite, with temperatures 47-1°, 44 '4°, and 24-2° above
the vicinity ; contain very little saline admixture (1 grain
hydrosulphuret of soda, &c. ) ; and yield nitrogen gas only.
The waters of Bartge and Cauteretz, in the Pyrenees (51 -9°
and 70*1° above the temperature of the place), rise in
primary rocks, and yield nitrogen only.
The baths of Loueche (74*1° above the temperature of the place)
yield nitrogen only.
To complete this view of the chemical characters of
hot springs, we may notice some of those which rise in
volcanic countries.
At Mont Dor, Caesar's Bath rises in trachyte, with a tem-
perature 52° above that of the country ; contains of saline
ingredients 11-4 grains in a pint (carbonate, muriate,
and sulphate of soda) ; and evolves 9 '85 nitrogen, 0*85
oxygen, and 90 carbonic acid.
The springs of Chaudes Aigues, near Aurillac, rise in gneiss,
with a temperature 118° above that of the place; contain
14'5 grains of saline ingredients In a pint (carbonate and
muriate of soda, magnesia, lime, and oxide of iron) ;
evolve from 12 to 30 nitrogen, 1 to 15 oxygen, 57 to 87
carbonic acid.
None of the facts disclosed by chemical analysis of
these springs, justify the belief that it is to any peculiar
chemical action in their channels that their heat above
the atmosphere is owing. On the contrary, their heat
is derived by communication from the heated rocks
through which {hey pass, whatever may be the cause of
their chemical differences. (See professor Forbes's
remarks, Ph il. Trans. 1836, p. 5?6.) That the heat
of the rocks, and therefore that of the springs, is de-
rived from volcanic action, appears to Dr. Daubeny
probable, because nitrogen gas, so commonly evolved
from hot springs, is also a product of volcanos, both
subaerial and submarine, and because " the majority of
thermal waters arise, either from rocks of a volcanic
nature, from the vicinity of some uplifted chain of
VOL. u.
258 A TREATISE ON GEOLOGY. CHAP. XT.
mountains, or, lastly, from clefts and fissures caused by
disruption."
These arguments, when taken in connection, appear
to us to prove that the heat of the springs is derived
from the depths of the channels in which they flow
below the surface. The presence of nitrogen may
establish the existence of substances, at considerable
depths, capable of decomposing atmospheric air ; but
when we find that in volcanic Ischia a whole group of
springs yields no nitrogen, and that it is not in volcanic
regions, but on the borders of granitic elevations, and
fractures of ancient strata, that nitrogen is most uni-
formly the predominant gaseous product, it seems
unnecessary to appeal to local volcanic excitement for
an effect which apreads both in time and area far be-
yond the traces of purely volcanic phenomena.
That hot springs are numerous in volcanic regions is
a certain and even necessary truth ; but they appear
quite as abundant on the ancient lines of uplifted rocks,
like the Pyrenees, where professor Forbes has traced
so many to their origin at the junction of stratified
and unstratified rocks, that it seems in that region
almost an invariable concomitant circumstance.* " The
general connection of the hot springs with the granite
is so remarkable in that country, as to strike the ob-
server at once; but there are several other peculiarities
worthy of note. The abundance of hot springs in-
creases in a very remarkable manner as we advance
eastward in the range ; nor can any one have a just
idea of the prodigal abundance of these thermal waters,
who has not visited the departments of the Arriege
and the Pyrenees Orientales. Their temperatures are
also the highest. In this part of the chain, granitic
formations preponderate; yet in almost every case which
I have examined, if springs rise in granite, it is just at
the boundary of that formation with a stratified rock.
* Phil. Trans. 1836, part ii.
CHAP. IX. MODERN EFFECTS OF HEAT. 259
More striking instances of the immediate connection
between thermal waters and disturbed strata, than the
Pyrenees afford, cannot be desired. The same thing,
however, is very generally true; even in England, under
the Bath springs, at the Buxton spring, at the Bristol
spring, the dislocations of the strata are very remark-
able. In connection with professor Forbes's result,
Mr. Henwood's curious observation, already stated, that
the temperature of the waters issuing from the granite
of Cornwall is always lower than that of such as flow
from slate rocks at the same depth, deserves to be re-
membered. This is found to be the case at the surface,
and to the depth of more than 200 fathoms.
Thermal springs are thus found to have, as their
most general characteristic of origin, a peculiar geolo-
gical position; — they burst forth (more remarkably
than other springs) at points of extreme displace-
ment of the strata, anticlinal elevations, &c., or, in
general terms, at points where it is conceivable that a
communication exists downward to the regions of in-
terior heat. For this important generalisation we are
indebted to Dr. Daubeny.
Further, it appears that these springs are scarcely less
abundant or less heated in countries far removed from
the regions of powerful volcanic excitement, than amidst
active or extinct volcanos. Dr. Daubeny supplies an
excellent catalogue of European springs, in his Report
to the British Association, 1836' ; and Mr. De la Beche
has collected examples of hot springs in all quarters of
the globe.* The following brief summary will suffice
for the purposes of reasoning on their geographical
relations to existing volcanos.
In the British Islands, the average of 7 springs connected
with carboniferous limestone gives an excess of temperature
above that of the atmosphere of 28°.f
* Geological Manual, p. 17.
f St Amand, near Valenciennes, in the same strata, has the same ex-
cess of temperature.
s 2
260 A TREATISE ON GEOLOGY. CHAP. IX.
In Germany, the average temperature of 20 springs is 58 '9°
above that of the atmosphere.
In France, connected with its central volcanic chain, 12 springs
average 6 9 '2° above the air.
In France, connected with the granitic Vosges mountains,
4 springs average 80-2° above the atmosphere.
Connected with the Alps of Dauphine, rising in Jura lime-
stone, &c., 3 springs average 46*7° above the air.
Connected with the Pyrenees, 3G springs average 48 '6° above
the air.
Connected with the Swiss Alps, 16 springs average 44 -8°
above the air.
In Croatia, 5 springs average 58*2° above the temperature of
the region.
In Styria and Carinthia, 5 springs average 44*6° above the
temperature of the place.
In volcanic Hungary, 14 springs average 47° above the tem-
perature of the air.
In volcanic Iceland, springs of various temperatures occur,
from the boiling Geysers to a moderate warmth ; the hot-
test being near the site of active volcanos.
In the volcanic island of Ischia, 6 springs average 55 '9° above
the air.
In Sicily, 2 springs average 55° above the air.
In Italy generally, 19 springs average 52 -4° above the air.
In Sardinia, 4 springs average 57 -7° above the air.
In Corsica, 2 springs average 59° above the air.
In Portugal, 35 springs average excess of temperature above
that of the country about 30°.
In the Caucasus, average of those mentioned by De la Beche,
about 60° above the air.
In the Himalaya, on the Jumna River, the temperature of
springs appears to exceed that of the air at least 80°.
In China, 3 springs, which issue from granite, probably exceed
the temperature of the air from 70° to 1 20°.
In Japan (volcanic) is a boiling spring.
In Ceylon are springs which exceed the mean temperature
about 30°.
On the American continent, the most remarkable collection of
springs is on the Ozark mountains ; the 70 springs, which
here rise in slate rocks, have temperatures which exceed those
of the vicinity by 40° to 100°. Others occur in the Rocky
Mountains.
In Jamaica, the bath springs in St. Thomas in the East are
about 50° above the mean temperature.
CHAP. IX. MODERN EFFECTS OF HEAT. 26l
It is to be regretted that the information concerning
the temperature of hot springs is, in general, insufficient
to determine whether they suffer periodical variations
with seasons or cycles of years. Until lately, the means
of instrumental research were inadequate for delicate
experiments such as those required in this branch of
study, nor has much been done to furnish future ob-
servers with the power of settling these questions. It
appears probable that thermal springs may vary their
temperatures, because it is an established fact, that a
part of the contents of some of them is withdrawn, by
cutting off their connection with subterranean springs
of cold water.* Variation of temperature is asserted as
a fact, in respect of the spring of Gargitello in Ischia,
Pfeffers Baths, a spring at Cannea in Ceylon, and
Bagneres de Luchon in the Pyrenees. During earth-
quakes and volcanic violence, thermal springs have been
affected, both in their quantity and in their temperature :
in 1755, the year of the Lisbon earthquake, the tem-
perature of the Source de la Reine at Bagneres de
Luchon was raised 75°. In 1660, a great earthquake
desolated the country from Bordeaux to Narbonne,
displacing large masses of ground, and caused one of
the hottest of the Pyrenean springs to become so cool
as to be no longer of any value. (Kircher, Mundus
Subterraneus.} On the contrary, two springs in South
America, far from any native volcano, have increased
in temperature by 4° centigrade, in the interval be-
tween an observation by Humboldt and its repetition
by Boussingault. (Forbes, On Pyrenean Springs, Phil.
Trans. 1836.)
The general conclusions fairly derivable from a study
of thermal springs are few, but important. Their heat
» This appears to be ascertained in the case of the hot spring of Aix, in
Provence * and though, in the late diminution of the Bath waters by sink-
ing a well In Bath (1836), the new well was filled by warm water, it was
believed, that during the sinking of the Batheaston Trial coal pit, the Baih
waters were reduced. The water was slightly warm in the Batheaston pit,
if we correctly remember the statement of Dr. Smith, who was employed
on the occasion.
262
A TREATISE ON GEOLOGY. CHAP.
is not the effect of local causes peculiar to each locality,
but is communicated to water which has fallen on the
surface, and penetrated to great depths in the earth.
Returned to the surface by hydrostatic pressure,
these springs bring with them the temperature of the
interior, modified and slightly diminished by the com-
paratively cool rocks near the surface of the earth.
This diminution of their heat is perhaps but slight,
owing to the feebly conducting power for heat which
the rocks possess ; yet upon some very small streams it
may have a powerful influence. Most of the very
warm waters, as those of Bath, Aix-la-Chapelle, the
springs of Nassau, and the Pyrenees, are very abundant.
To see these rivers of hot water pouring forth for a
thousand years undiminished in heat or abundance, is
one of the most remarkable and even (as professor
Forbes truly says) romantic circumstances which fall
under the notice of geology. The conclusion to which
they obviously point of the existence of a general heat
below the surface of the earth, is indisputable, whether,
with Dr. Daubeny, we view that heat as the result of
chemical action, and call it volcanic, or, with Humboldt
and Arago, regard it as the residue of the original
ignition (chaleur d'oriaine) of our planet.
Experimental Inquiries into the Heat of the Globe.
That the earth has below its surface a source of great
heat, independent of solar influence, is perfectly ascer-
tained by volcanic phenomena ; that this heat is very
generally diffused, is equally certain, from the extent of
country in which thermal springs are found ; that it is
universally spread below our feet, becomes continually
more and more probable from experimental researches
in countries uninfluenced by any chemical actions sup-
posed to go on at the base of volcanos, where no hot
springs burst to the surface, and where the fractures of
the strata yield both pure and mineralised waters at
common temperatures. Before, however, stating the
CHAP. IX. MODERN EFFECTS OF HEAT. 263
important facts thus established, it is convenient to
direct attention to the conditions of the experiments;
for thus the truth and applicability of the inferences
drawn from them will more clearly appear.
No truth is more firmly established in meteorology,,
than the primary dependence of the temperature of
each point on the earth's surface upon the calorific
influence radiated from the sun. The evidence is found
in the conformity of the diurnal and monthly changes
of temperature, at each place, to the changing position
of the sun, and the proportionality of the annual mean
temperatures at different places to the quantity of solar
rays received.
Neither of these satisfactory parts of evidence can,
however, be completely gathered, except by long averages
of years, which neutralise the irregularities of par-
ticular years ; nor properly understood, without attending
to many secondary influences.
The heating influence of the sun, though continually
acting, has not been found to have any cumulative effect
on the globe ; which, upon the whole, has perhaps under-
gone no perceptible change in this respect since the
reach of history ; but many parts of its surface have
experienced real alterations of climate from drainage,
inclosures, destruction of forests, and other causes. There
is a cooling as well as a heating power constantly at
work. The earth is a warm body plunged in a rela-
tively cold medium, for the planetary spaces are cold
compared to our globe, and the incessant radiation from
the surface of the earth into the vast spaces around is
uncompensated by any counteracting influence, though
diminished in the cold regions of the world by peculiar
provisions of a beneficent Providence.
The temperature of the ethereal spaces around is
supposed to be pretty well represented by the minimum
of observation on the earth's surface, during the
long absence of the sun. It is therefore generally
taken at about 50° centigrade, below the freezing point,
264 A TREATISE ON GEOLOGY. CHAP. IX.
— a supposition confirmed by some astronomical con-
siderations, and sanctioned by Fourier and Swanberg.
Preserving between their joint effects a variable equili-
brium of temperature at the surface of the earth, the calo-
rific power of the sun arid the refrigerating influence of
the planetary spaces affect every point on the terraqueous
globe ; and, as far as geographical position with respect
to the poles and equator is concerned, the result may
be nearly calculated. The mean temperature of any
zone of land and sea is, in fact, nearly proportional to
the cosine of its latitude. *
But the globe is enveloped in an atmosphere, which
produces further modifications of climate, according to
the elevation of places above the level of the sea. The
sun's rays traverse this atmosphere without heating it ;
the warmth which it possesses is derived from the
earth by conduction, and dissipated by radiation. Owing
to the diminution of density in the upper regions of
the atmosphere, the air heated near the earth's surface
expands into larger and still larger spaces as it rises, and
thus the upper parts of the atmosphere have a tem-
perature always growing lower and lower as the density
grows less and less. The variations of heat in the
atmosphere are greatest at and near the earth's surface;
they may become insensible in the upper aerial regions,
above the clouds. The cold, thus permanently fixed in
the high atmospheric spaces, necessarily reacts upon the
land which is raised above the general level of the sea.
The temperature of the surface of such land is the
resultant of the general influence of the sun, planetary
spaces, atmospheric modifications, and conducting power
of the ground. In general, the effect of elevation
above the sea level in diminishing the heat of the
surface of the ground, is nearly in proportion to the
* The mean annual temperature of the equator being taken at 81'5°,
that of any other lat. — 81 5° X nat. cosine iat. This is in error toward
the north pole, owing to the distribution of land and water, which makes
two poles of maximum cold in Asia and America, nearly coincident with
the magnetic poles. See a paper by sir D. Brewster (Transactions of the
Royal Society of Edinburgh).
CHAP. IX. MODERN EFFECTS OF HEAT. 265
height, in all latitudes.* Hence it happens, that as
the mean temperature of the equator is about 81±°, the
height in the air at which the mean snow line should
be found = 49-i° X 352 feet = 17,424. (obs. 1 6,829),
and in any other lat. = (81i° N. cos. lat.- 32) 352.
In W. lat. 56° 50', nearly that of Ben Nevis, this
gives (44-6-32-) 352 = 4435 feet; and as Ben Nevis
is 4350 feet high, and is not covered perpetually with
snow (which melts in July and August, except in
shaded parts), the rule appears exact enough for the
longitude of Britain.
Another cause productive of differences of temperature
on surfaces equally exposed to the sun's influence, is the
peculiar distribution of land and water ; for these dis-
similar parts of the globe unequally absorb and unequally
give out heat ; and one of them diffuses itself so as to
obliterate many original differences of climate. Thus,
on different circles of longitude, places which, having
the same latitude, should have the same mean annual
temperature, may, and do, differ in this respect several
degrees, from the dissimilitude of the ground, and from
the different relations they bear to the masses of land
and surfaces of sea. Under the equator the land is ge-
nerally hotter than the sea ; towards the poles the reverse
obtains. The sea climate admits of less extreme va-
riations from the torrid to the frigid zone,. than the land,
and sea-shores participate in this mildness. Thus
we have oceanic, littoral, insular, and continental cli-
mates, which differ sometimes by several degrees. The
formula, therefore, given above (which expresses the
average mean temperature in terms of the latitude) re-
quires modification from this cause, as sir D Brews ter
has shown in the essay already quoted. From what has
* About 1° of Fahrenheit for every 100 yards of ascent is a common cor-
rection used with the mountain barometer. A rcore exact proportion is
supposed to be 1° for every 352 feet, as found by comparing Geneva and
Great St Bernard. Mr. Atkinson, in Memoirs of the Astronomical Society,
Professor Challis (Cambridge Phil. Trans.), have treated the subject mathe-
matically. A general view of the state of knowledge on the distribution of
terrestrial heat may be found in Professor Forbes's Report on Meteorology
to the British Association.
266 A TREATISE ON GEOLOGY. CHAP. IX.
been said, it is plain that the principal causes which
influence the earth's surface temperature are known.
One of the circumstances which mask the regularity of
the results, and their real dependence on the position of
the sun, is the delay which occurs between the moment
of exertion of the greatest heating and cooling power
and its visible effect on the surface of the land and sea.
In the influence of the moon on the tide, we have an
instance of the same kind lately reduced to law : the
highest tides take place after the moon has passed her
point of power. Just so the warmest epoch of the day is
after the sun has crossed the meridian, when most rays fall
on the earth : the hottest and coldest epochs of the year
follow by an interval of about three weeks (in northern
latitudes) the summer and winter solstices. When
these allowances of time are made, and the local cir-
cumstances previously adverted to allowed for, the co-
incidence of calculation for hourly, daily, monthly, and
annual temperatures, with the result of long continued
and regular observation, is surprisingly close, and fully
justifies the general conclusion that the earth's surface
temperature is the balance of the variable heating energy
of the sun and the uniform cooling power of the ethereal
spaces in which the earth's orbit is situated. (What effect
on surface temperature the peculiar condition of the inte-
rior of the earth may occasion, will be seen hereafter.)
This being established, we may appeal to observation
for proof that it is at the surface of the earth the greatest
variations of temperature take place, and from this sur-
face they are propagated upwards with diminishing force
into the air above, and into the water and earth below,
tiD in each direction they terminate, or become insensible.
The communication of solar heat into the earth consti-
tutes the first branch of our inquiry, and it has been
quite sufficiently prosecuted to authorise the following
positive statements.
1. By Leslie's experiments, made in 1816, 1817, at
Abbotshall, in Fife, with long thermometers, plunged in
CHAP. IX. MODERN EFFECTS OF HEAT. 26?
the earth at depths of 1, 2, 4, 8 feet, their stems rising
above the surface, so as to be easily inspected, we find
that the variations of temperature continually diminish
downwards; — at 1 foot, the extreme monthly differ-
ences corresponding to summer and winter were 21° and
196°; at 2 feet, l6'5° and l6'3°; at 4 feet, 12'8°
and 11-5° ; at 8 feet, 8'0° and 8'2°.
2. The epochs of highest and lowest temperature
continually differ more and more from the summer and
winter solstices, according as the depth in the earth is
greater ; or, in other words, the time taken by the sun's
rays to penetrate and warm the ground augments with
the depth.
Thus, at 1 foot from the surface, January is the
coldest and July the hottest month ; at 8 feet from the
surface, February and March are the coldest months,
and September the hottest.
3. The average mean temperature of the year aug-
ments from the surface downwards ; but does not reach
the average of the air temperature, in the range of these
experiments.
These results have been more than confirmed — they
have been enlarged — by the experiments of Arago in
Paris, Quetelet in Brussels, and Forbes in Edinburgh,
and extended to the depth of 25 feet. M. Quetelet has
founded on the experiments at Brussels a mathematical
investigation of the highest interest.
Among the data for computation employed by M.
Quetelet are experiments analogous to those of Leslie,
made in 1762 at Zurich by M. Ott ; a series made at
Strasburg by Herrenschneider, in 1821, 1822, and
1823 ; another at Heidelberg by M. Muncke ; one made
at Upsal in J 832-3, by M. Rudberg ; others at the ob-
servatories at Paris and Brussels descending to 25 feet.
The original memoir* must be consulted for the mathe-
matical part of the subject ; but we shall present the
conclusions which the investigation has established.
» Sur les Variations des Temperatures de la Terre. Bruxelles, 1837.
268 A TREATISE ON GEOLOGY. CHAP. IX.
1. In descending from the surface of the earth, to
depths continually augmenting, the mean temperature of
the year augments gradually ; yet, immediately below
the surface, and at depths of half a foot or a foot, the
mean temperature is found to be a minimum.
2. The rate at which the annual variations of tem-
perature are transmitted to the interior of the earth,
may be estimated at 6 or 7 days for 1 foot thickness of
earth.*
3. Observation and theory agree in showing that the
extreme temperatures of the year decrease in geometrical
progression, while the depths below the surface are taken
in arithmetical progression.
4. The annual variations of temperature may be
considered as insensible at depths from 60 or 75 feet ;
that is to say, at the depths where the maxima and
minima will occur at the same epochs (after an interval
of one year !) as at the surface.
5. On descending several feet below the surface, the
annual variations of temperature are as the sines of the
elapsed times, in a circle whose circumference cor-
responds to the period of one year.
6. When different latitudes are compared, it appears
that the annual variations of temperature penetrate to
the least depths in the higher latitudes.
7. The rate with which diurnal variations of tem-
perature are transmitted to the interior of the earth, may
be stated at somewhat less than 3 hours for 1 decimetre
in thickness (3*9 inches English).
8. The diurnal variations become insensible at a
depth of 1-3 metre (51 inches), which is 19 times less
than the depth reached by the annual variations, as
theory also indicates.
The important conclusion of the entire disappearance
* Forbes's experiments in different sorts of rock show the effect of these,
in modifying the ranee of subterranean temperature, in altering the rate
of its progress, and changing the epochs of maximum and minimum tem-
perature. (Edinb. Traus. 1846 )
UHAP. IX. MODERN EFFECTS OF HEAT. 269
of all trace of annual or diurnal variation of temperature
at a depth so moderate as from 60 to 100 feet, is per-
fectly confirmed by the well known experiments in the
caves under Paris ; and is the more satisfactory, that it
falls much within the limits assigned to the annual va-
riation by Fourier in his mathematical theory of heat.
The condition of the interior of the earth below the
point of invariable temperature cannot be assumed upon
any ground of probability independent of geological ob-
servations, nor foretold by any mathematical theory of
heat, nor determined by any experiments made at the
surface ; but may be easily detected by direct thermo-
metric experiments, even at the moderate depths already
reached by human enterprise. If the earth be very
cold within, the influence of the interior cold will begin
to be felt below the depth of 100 feet; if very hot
within, the rate of increase of this heat may be inferred
from exact and numerous observations.
The experimental inquiries for this object have been
prosecuted with great success in Europe, and partially
in America, to depths amounting in England to 1584
feet (atMonkwearmouth), and about 1800 feet inMexico.
They consist of three divisions. In the first case, the
experiments are made in or very near to mineral veins,
which, by their character of filling fissures on lines of
disruption, remind us of the general geological conditions
of appearance of hot springs ; the second set of experi-
ments takes place in collieries and other excavations of
like nature, among the stratified rocks, with or without
dislocations. In each of these cases, either the tem-
perature of the rock, of air, or of a constant subterranean
spring may be tried. In the third case, wells or bore-
holes are sunk, in a country where little or no water
naturally springs to the surface, to considerable
depths, and till strong streams of water are let up,
bringing with them the temperature of the subterranean
regions at those depths.
270
A TREATISE ON GEOLOGY.
CHAP. IX.
First Class of Experiments. Metalliferous Feins. (From
Daubuissons Traite de Geognosie.) The degrees are
centigrade.
In the middle of the last century, Gensanne, director
of the mines of Giromagny (Vosges), concluded that
At 100 metres depth, the temperature was 12-0°
308 - - 18-8
432 - 23-1
Ratio deduced, 333 metres = 1 1 '1° centig.
or 30 - =. 1-0 —
M. Dauhuisson made, in 1802, a large series of experi-
ments on the waters in the mines of Freyberg, where
the mean surface temperature is 8° cent. The general
results are contained in the following table.
Depth
in
Metres.
NAME OF THE MINE.
Beschertgluck.
Himraelfahrt.
Kiihschacht.
Junghohebirke.
0
8°
8°
8°
8°
80
.
.
_
10
100
.
10
_
10
120
10
_
_
11
160
-
.
-
12J
180
.
1$
200
.
.
14
220
12J
-
121
240
14
is
260
14&15
141
14
280
-
-
16
300
151
-
15&16
320
•
-
17
The general result is an augmentation of 8° for 300
metres; or, all observations included, 1° for 40 metres:
if the extremes alone be taken, 1° in 35 metres.
This conclusion was confirmed by new experiments,
in 1805, under the direction of Mr. Trebra. The tern-
perature of the rock was now tried, with great care, for
two years, the observations being registered thrice in
each day. The temperature never varied in this time.
CHAP. IX. UODERN EFFECTS OF HEAT. 271
At the surface (as before) 8°
180 metres - ll\
260 - - 15
as M. Daubuisson had found in 1802.
The ratio deduced is about 1° in 37 metres ip the upper part,
and 1° in 22-2 metres in the lower part.
Again, under the same direction, thermometers placed
in gneiss in the mine called Alte Hoffnung Gottes, gave
At the surface (as before) 8-00°
72 metres - 8 '75
170 - - 12-80
270 - - 15-00
382 - - 18 '75
From these experiments it is concluded that the
augmentation of temperature is 1° in 38 metres.
In the mines of Poullaouen and Huelgoat, in Brittany,
M. Daubuisson found results which he considered to be
partly influenced by local causes. In Poullaouen, at
140 fathoms, the augmentation was 3*1° or 1° for 45
metres. In Huelgoat, at 230 metres, the augmentation
was 8-7°, or 1° in 26'4 metres.
In Cornwall, Mr. Fox's obervations, at various periods,
yield corresponding results. In a spring Dolcoath
copper mine, 439 fathoms deep, the temperature was
27'8°, and that of the surface 10°.
In the same mine, 421 fathoms deep, the temperature
of the rock of a gallery for 18 months was 24'2°.
Lately (1837) Mr. Fox communicated to the British
Association some further observations, made below the
lowest workings, in the Levant tin and copper mine, and
the consolidated copper mine. At 230 fathoms from the
surface, in the Levant mine (in granite), a thermometer,
sunk 3 feet below the " sump," stood at 80°; another,
sunk only a few inches, was at 78*5°; and the air in the
mine 67°. At 190 fathoms, the corresponding indications
were 78°, 72*5°, and 67°. The general ratio is 1° Fahr.
for 16 feet English; or, allowing 10 fathoms to the in-
variable temp., 1° in 46 feet.
272 A TREATISE ON GEOLOGY. CHAP. IX.
In the consolidated mines, at a depth of 290 fathoms,
thermometers sunk in a cross course of the rock (killas)
indicated at the vein 92° and 88°; 10 fathoms from it,
86-3° and 85°; 24 fathoms from it, 85'3° and 84°. Here
the metallic vein is the hottest part ; Mr. Fox thinks,
because of its allowing hot waters to ascend. The
temperature 85*3° is at least 35° above that of the
climate, and the ratio is consequently 1° in 49'6 feet;
or, allowing 10 fathoms to the depth of variable temper-
ature, 1° in 48 feet.
And still more lately, experiments made by Captain
Oats inTresavean copper mine gave the following results.
Rock.
Depth. Air. No. 1. No. 2.
26 feet In granite 53-3° 57 -0° 52-8°
200 lode 77-2 76-0 75-5
200 again 77 -7 76-0 75 "5
250 lode 83-2 82 '5 82-0
262 lode 85-5 82 "5 82-0
Ratio, 1° in 48 feet from the surface ; or,
1° - 46 - from a point 10 fathoms below surface.
Humboldt observed, in mines near Guanaxuato (Mexico),
At 502 metres depth in Valenciana mine 36 -8° centig.
193 - llayas 33 -7 —
134 - Villalpand 29 '4 —
The surface temperature is 16°. The volcanic cha-
racter of the country is perhaps unfavourable for accurate
inferences.
Second Class of Experiments. In Stratified Roclts.
Saussure, in the salt mines of Bex, found
At 108 metres depth the temperature 14-4°
183 - . - 15-6
220 - - - 17-4
Ratio deduced, 1° centigrade for 37 metres.
Kr. Hodgkinson, at the request of the British Asso-
CHAP. IX. MODERN EFFECTS OF HEAT. 2 73
elation, has made some experiments in the comparatively
shallow salt mines of Cheshire which evince an aug-
mentation of 1° in 70 feet from the surface.
But the greatest strength of observation, independent
of mineral veins, has been concentrated in the coal
districts. Mr. Bald, Mr. Buddie, and other observers,
have long since collected much information in the
collieries of the Tyne and Wear ; of which, however, we
can make only partial use, because the experiments were
mostly made on the air, which, for many reasons besides
miners' lights and chemical actions, is unlikely to yield
accurate ratios, such as are now attainable.
The following are some of Mr. Bald's results, pub-
lished in the Edinburgh Royal Transactions. The scale
is Fahrenheit's.
\Vhitehaven. — Spring at surface - - 49°
480 feet 60
Ratio from surface, 1° for 44 feet.
Workington. — Spring at surface - - 48°
504 feet - 60
Ratio from surface, 1° for 42 feet.
Percy Main Colliery, Northumberland. — Mean
temperature at surface - 49° *
900 feet depth - 70
Ratio from surface, 1° for 43 feet.
Jarrow colliery. — Surface assumed - - 49 '5°
Water at 882 feet - 68 -0
Ratio from surface, 1° for 48 feet.
Killingworth colliery. — Surface assumed - 48°
Water at 1200 feet depth - 74
Ratio from surface, 1° for 46 feet.
The near accordance of these results is remarkable.
The ratios are all in error by a small quantity, because
HO allowance is made for the depth of variable heat.
* It is really under 48°. — Author.
VOL. H. T
274? A TREATISE ON GEOLOGY. CHAP. IX.
It is a very usual and easy objection to these results,
that the lights, the respiration of horses and men,
pyritous decompositions, &c. raise the temperature. The
contrary is generally true, as we have shown in narrating
the particulars of an experiment (1834) at Monk-
\vearmouth, where the coal had been reached only a
few days previous, no horses had entered the mine, few
miners were at work, no chemical decompositions ap-
parent, and the air supposed to be heated was many
degrees cooler than the coal and rocks, and grew hotter
only in proportion to their influence.* The depth of
this pit was 1584 feet; mean temperature at the surface
47*6°; thermometer at the bottom, in coal, 71'5°,
72-0° and 72'6°. Ratio deduced 1° Fahr.for 20 yards
English. «
This ratio, lower than Mr. Bald's, derived from the
water in the coal mines, may perhaps be more correct ;
and it is supported by experiments at Wigan, under
the care cf Mr. Peace, which give 6'0 feet for 1°. At
Manchester, Mr. Hodgkinson obtained a ratio from the
surface, of 1° in 6'9 feet; while at Bedminster, under
the care of Mr. W. Sanders, the ratio was found to be
as high as 1° in 30 feet, and some anomalous facts were
observed. (In each case 100 feet are deducted from
the depth as an allowance for the depth of variable
heat.)
M. Cordier gives the following summary of observa-
tions in the coal mines of Carmeaux, Littry and Decise
(1827)
Carmeaux.
Water in the well Veriac, at 6-2 metres 12-9° cent.
•Bigorre 11 '5 - 13'1 —
Rock at the bottom of Ravin mine 181-9 - 17'1 —
Castelkm 192'0 -
* Phil. Mag. and Annals, 1834.
CHAP. IX. MODERN EFFECTS OF HEAT.
Littry.
275
Surface temperature 0 me'tre 11*00° cent.
Rock at the bottom of St. Charles
mine ... 99 - 16-13 —
Decise.
Water of the well Pelisson at 8 -8 metres 1 1 -40° —
Puits des Pavilions 16 '9 - 11'67 —
Rock in the Jacobe mine - 107-0 - 17-78 —
Ditto - 171-0 - 22-10 —
The general result of a complete discussion of these
observations on subterranean temperature made in mines
and collieries, appears, to give a ratio of 1° cent, for about
25 metres, or 1° Fahr. for 45 feet English.
Mr. Kenwood's observations on subterranean tem-
peratures in the rocks, made on the waters issuing from
them, extend to no less than 95 in slate, and 39 in
granite, andfromthe surface to SOOfathoms and upwards.
The following is a summary.
SLATE.
GRANITE.
Average
Depth.
No. of Ob-
servations.
Temper-
ature.
Average
Depth.
No. of Ob-
serrations.
Temper-
ature.
35ft.
21
57-0°
31ft.
7
51-6°
73
19
61-3
79
17
55-8
127
29
68-0
133
12
65-5
170
21
78-0
221
5
85-6
237
3
81-3
Thus at all depths the slate appears to be about 3*9°
warmer than the granite at the same level.
The progressive increase of temperature in descending
is in a mean of
95 observations on slate 1° for 6-5 fathoms (39 feet).
39 - granite 1° - 6-9 - (41'4).
(Reports of British Association for 1837.)
T 2
276
A TREATISE ON GEOLOGY. CHAP. JJC.
The Third Class of experiments includes chiefly Ar-
tesian weils. One of the most important is the well of
La Rochelle, described by M. Fleuriau de Bellevue.
The mean temperature of the district is
Air at the surface - 1 -87°
Water in the well, at 316 feet depth - 16-25
Ditto S69£ - - 18-12
Ratio from surface, 1 ° cent, for .58 -5 to 72 feet, or 20 metres.
At Southampton, a well 133 yards deep was found to have a
temperature of 56^° Fahr. ; the mean temperature of sur-
face being 50°. The ratio deduced is 1° Fahr. in 46 feet
English.
The importance of this branch of evidence induced
M. Arago to publish a short but valuable notice of
Artesian wells, which is inserted in Jameson's Journal
for 1835, p. 235. The following table is extracted,
and the ratios appended to each observation : —
Metres. Ratio.
Pan's. — Mean temp, of surface 10-6°
Well of Port St. Ouen 12'9 66 I°in29'00
Departement du Nard.— Mean temp. 10 '3
Well of Marquette 12-5 56 1 - 25 '5
Aire 13-3 63 1 - 21 -0
StVenant 14-0 100 1 - 27'0
Sheerness. — Mean temp, of surface 10 '5
Well - - 15-5 110 1 - 220
Tours. — Mean temp, of surface 11*5
Well - - 17-5 140 1 - 23-3
Mean result, 1° cent, for 24-6 metres; or,
1 Fahr. for 45 feet.
The coincidence of this with the former result is
unexpected.
The conclusion from experimental observation is in
harmony with that authorised by hot springs, that the
earth has a general and pervading high temperature
below the surface.
277
CHAP. X.
STATE OF GEOLOGICAL THEORY.
ALL branches of the study of nature, in their pro-
gress from the period of observation to that of gene-
ralisation and theory, appear destined to endure the
same storm which astronomy has weathered ; and, like
that noble science, to come forth renewed and purified
in the struggle ; strengthened by popular applause, and
fertile of public benefit.
To quicken the inertness of prejudice, and rouse the
despair of ignorance, among the masses of mankind,
may appear unnecessary for the ' ' advancement " of
science, which must ever be intrusted to a few superior
minds ; but the opinion which would separate the ac-
quisition from the diffusion of knowledge is no less
erroneous than ungenerous, since the highest and most
comprehensive truths in natural science are but the
concentration of common phenomena, the laws of com-
mon experience. In the determination of these phe-
nomena, in the correct association of them into laws
and systems, immense preliminary labours must be
undergone before the most powerful intellect, however
deeply versed in abstract science and the philosophy of
causation, can ascend to that comprehensive view of a
whole series of dependent truths which constitutes a
general theory.
Perhaps no term of importance in estimating the
state of science is employed in more various and incon-
sistent senses than this word theory, which few branches
of human knowledge have ventured to claim, but which
is actually used as a term of reproach by men entirely
ignorant of them. When correctly used, with the
T 3
278 . A TREATISE ON GEOLOGY. CHAP. X.
masters of Inductive Philosophy, it signifies the high
point to which every faithful inquirer after truth ia
advancing, however slowly, in his peculiar branch of
study ; it is the unchangeable summit of a cone whose
base continually enlarges to include every known fact
appertaining to the subject ; and whose every part is
linked in harmony according to one simple and intelli-
gible principle. Science is perfect only when it is in
the form of a truly general theory ; and perhaps it is
not too much to believe that the utmost efforts of the
human mind may fail in the attempt to comprehend
all natural phenomena perceptible by our organisation in
one such theory.
Even if, hereafter, it should be found possible to
include the most comprehensive theory of ponderable
matter, gravitation, and the undulatory theory of light
and heat, into one wider generalisation for all inorganic
matter, there would still remain the mysterious phe-
nomena of life ; and beyond all these the relation of
mind and sensation. Now these are a few of the legi-
timate branches of the study of nature, which the
providence of the Almighty Creator of the universe
has committed to human reason. Their development
is for man a physical revelation, continually enlarging
its power and influence on the mind and heart ; yet it
leaves, almost without touching, except to support, a
large circle of moral and religious truths of yet higher
importance, and more lasting and powerful interest.
Geology dares not claim, as yet, the possession of a
sound and general theory, such as is here described ;
but in common with astronomy, and chemistry, and
mechanics, and every ether part of natural science, its
infancy was amused with baseless speculations, and
hypotheses which have fallen into contempt. For
these errors of their fathers its modern cultivators have
dearly paid, and fairly atoned. The wanton and igno-
rant abuse lavished on the magnificent problems to which
their lives are devoted, has been endured with patience;
the principles which have guided other and easier
CHAP. X. STATE OP GEOLOGICAL THEORY.
branches of philosophy in their successful progress,
have been wisely copied ; they have begun at the
foundations of the temple of truth ; they have col-
lected an inconceivable number of individual facts; they
have combined these into correct,, though incomplete,
generalizations ; and have called on zoology and botany,
en chemistry and mechanics, to furnish the interpret-
ation.
Geology has thus been placed, by the energy and
prudence of its living advocates, in the circle of in-
ductive science ; no more to be dissociated from the
ether parts of knowledge ; advancing with them, and
often leading them forward, by the proposal of new
and remarkable problems, to the solution of which all
the collected resources of modern science are sometimes
scarcely equal. In this career the Geological Society
of London has proceeded, without faltering, for thirty
years, and the reward of their labours is in the just
and candid acknowledgment of one most competent
to pronounce, that " Geology, in the magnitude and
sublimity of the objects of which it treats, undoubtedly
ranks, in the scale of the sciences, next to astronomy." *
If the object of this treatise were to produce merely
the entertaining parts of geological discussion, it might
l)e very proper to introduce a notice of the many fanci-
ful and absurd systems of cosmogony and philosophy,
falsely called " theories of the earth." Perhaps, not-
withstanding the discredit which such mistaken attempts
have brought upon philosophy generally, rather than
geology in particular, some useful result might be de-
rived from a dispassionate survey of them. For if
Woodward, Whiston, and Burnet, — Buffon, De Luc,
and Werner, have failed in the great attempt to unveil
the natural history of the earth, it was not so much
because of any inferiority of intellect, want of patient
research, or deficiency of information, that their
" theories " have fallen into oblivion ; but because the
* Sir John Herschel, in his Discourse on the Study of Natural Philosor
phy, p. 287.
T 4
280 A TREATISE ON GEOLOGY. CHAP. X*
process of induction, without which no true theory can
arise concerning the works of nature, was not at all, or
imperfectly followed out.
There has been, moreover, from early times, in
consequence, perhaps, of an imperfect apprehension
of the nature and object of revealed religion, as com-
pared with the physical truths which are left to the
discovery of human reason, a singular propensity to
supply the deficiency of philosophical research by
arbitrary appeals to the authority of scripture. The
danger to religion of such a reckless course is too well
understood by the enlightened theologians of this age
to render more than a passing remark necessary ;
though, even in the nineteenth century, it occasion-
ally happens that astronomical truth is questioned,
because the scriptures, addressed to an unlearned peo-
ple, speak popularly of the sun " standing still ;" and
the established inferences of the successive revolutions
in the state of the globe, which are not mentioned by
Moses, but which invest with new interest the study
of the ancient earth, are thrown aside in favour of
some physical and theological absurdity, such as that
which makes the stratified crust of the earth the effect
of one tumultuous flood, and turns the " fountains of
the great deep " into submarine volcanos, or hides
a world of waters within the globe.
The mention of these unhappy errors would be pain-
ful, could we believe that the progress of pure religion
or sound philosophy could be checked by their influence.
Let it be remembered that the Bible teaches no physical
science, and that philosphy has made little progress in
physical truth, if it does not recognise among all the
multiform changes of the universe the power and the
will of ONE SUPREME. From this highest point of
true philosophy, as from a sure foundation, a pure re-
ligious faith must spring. Of the importance and in-
dependence of physical truth none of the distinguished
ornaments of the Christian faith, from St. Augustin to
Boyle and Chalmers, have been ignorant ; and to their
CHAP. X. STATE OF GEOLOGICAL THEORY. 281
immortal works we beg to direct the attention of those
inconsiderate persons who think to advance Christianity
by denying philosophy, and to confirm revelation by
making its very truth depend upon their own narrow
interpretations of nature.
Lest, however, we should fall into as great absurdities
of another kind as these we have mentioned, it will be
prudent to determine, if possible, the true character of a
general theory of the earth ; for in this there is a great
liability to error. Geology, regarded as a body of facts,
comprises not exclusively, nor specially, the phenomena
which are now, or have been at any one former time, in
progress on and within the earth, but embraces the
whole succession of these occurrences, from the earliest
operation of natural laws on the globe to the present
hour. Each of the phenomena, taken singly, is the
subject of interpretation by some special branch of
natural science: the characters of organic fossils are
referred to the zoologist and botanist ; mineral com-
pounds are examined chemically and crystallographically ;
the fractured crust of the earth receives explanation
from the application of mechanical philosophy. The
general view of these and other phenomena, manifested
at one epoch, or during one period, and the survey of
the condition of the globe at several such periods, are
the proper objects of geological observation ; and the
successive states of the globe being thus ascertained, it
is the business of inductive philosophy to discover the
general antecedent condition or proximate cause upon
which these successive states depend. If the research
be successful, the result is a general theory of the earth;
that is to say, a sufficient natural cause is found to
explain, in combination with other agencies really
existing, all the characteristic changes which have been
observed in the earth's condition, in the degree, com-
bination, and sequence which actually belong to them.
Perhaps an illustration may be usefully taken from
exact science. la mathematical inquiries, a particular
282
A TREATISE ON GEOLOGY. CHAP. X.
result or condition of things is frequently capable of
distinct representation by means of a series of quantities,
unequal in value, and combined in different propor-
tions ; yet the origin, formation, and succession of this
series of dissimilar combinations of unequal quantities
may be perfectly simple, and often is perfectly known,
though the series be demonstrably boundless in one di-
rection. Now, in this case, the " theory" of that series
is really known ; and, in exactly the same sense, the
" theory" of the series of dissimilar combinations of
unequal phenomena, which succeeded one another in a
certain order of time, upon and within the earth, ap-
pears attainable by the human intellect.
Every attempt to ascertain the law of succession among
the phenomena manifested in the structure of the earth
must entirely fail, unless, at least, the characteristic facts,
and combinations of facts, belonging to each successive
geological period be completely known, and these periods
completely defined. It is therefore necessary, before
noticing the attempts which have been made to establish
a geological theory, to ascertain how far these, indis-
pensable preliminary conditions have been fulfilled.
The historical view of the series of stratified rocks, con-
tained in the first part of this work, will show to what
extent the author has been able to reduce to rule and
system the known phenomena occasioned by the action
of water on the globe ; in the succeeding part a similar
attempt is made to unfold the parallel series of truths
concerning the unstratined rocks, and other effects of
heat. Though neither of these attempts ought to be
taken as a measure of the progress made in similar in-
quiries by other individuals, and still less as a sum-
mary of the whole knowledge on the subjects, the in-
telligent reader will easily perceive that, with regard to
the mechanical and chemical agency of water in de-
positing earthy sediments, and the changes of organic
life on the globe at several successive epochs, the mo-
numents of nature have been extensively collected,
ranged in their real order, and in a great measure truly
CHAP. X. STATE OF GEOLOGICAL THEORY. 283
interpreted. Very large portions of the land and sea
are however still unknown in this respect.
Hardly so much can be said regarding the effects of
heat ; for though these are for the most part clearly,
they are not completely, interpreted, nor is the order
of their succession sufficiently known. It appears, how-
ever, that the products and effects of heat at different
times have not varied so much as those of water, so that
the order of succession among them is of less import-
ance.
In a complete geological theory, not only the order of
succession among the several groups of phenomena
would be deducible from the principles on which it was
based, but also, in proportion to the completeness of the
facts indicating the lapse of time, the real duration of
the several successive geological periods would be at
least approximately known. It would be very unwise
to attempt this at present, because of the imperfection
of the data in every part of the series of strata ; and in
this respect geological theory is not singular, for even
the most perfect mathematical theorem is equally inap-
plicable to incomplete data. This was strongly felt by
the geologists of England, who gave a fair proof that
hypotheses were out of fashion, when they declined to
compete for the medal which the Royal Society offered
to encourage researches into the antiquity of the globe.
(See on this subject of geological time, Vol. I. chap, i.)
It may perhaps be thought, that the limits which
have been fixed for a legitimate *' theory of the earth "
are sufficiently wide to include an immense number of
general speculations ; and that many conflicting hypo-
theses, advanced by Neptunists and Plutonists, should
now be compared and condemned. But, in truth, a
little consideration will prove that there have not been,
and can never be, more than two hypotheses really
genera] on the subject. Nature, as we see it, exists
under the influence of particular forces and conditions,
vital, chemical, and mechanical; and the sum of the
phenomena that now occur in a given time is the
284 A TREATISE ON GEOLOGY. CHAP. X.
measure of those forces and conditions. The exterior in-
fluence of the sun, and the ethereal spaces ; the mass and
quality of the atmosphere ; the size, figure, density, and
motions of the earth ; the distribution of land and sea,
— are all circumstances of great importance, to which
the vegetable and animal productions of the globe, as
well as the chemical and mechanical operations upon
it, are adjusted.
It is soon apparent to the inquiring mind, that many
of these conditions and forces ^ary, and with them, from
time to time, suddenly or gradually, the characteristic
phenomena of life and inorganic matter. If we knew
the measure of these variations, the real state and mo-
mentary condition of the earth at the present, in former,
and in future periods, would become a practicable pro-
blem.
Now it must be evident that we have not such know-
ledge ; for the variations in question, though quite
sensible, are too complicated to be understood, except
through an immensity of recorded observations ; and of
these we have few that are trustworthy, except in
astronomy. In astronomy, with the help of the general
theory, it has been found possible to determine the
" limits of variation " due to the disturbing forces of
the planetary system; but it is impossible to effect this
in geology, from a survey of existing nature, for want
of such a theory. Incapable, therefore, of learning from
the most perfect survey of nature as it is, whether ter-
restrial phenomena are subject to progressive and per-
manent changes, or to a limited circle of compensating
variations, the leaders of geological speculation have
assumed one or other of these views — the only really
general ones which the subject permits ; and thus we
have, on the one hand, Leibnitz deducing the principal
geological phenomena from the gradual refrigeration of
an ignited glebe ; and, on the other hand, Lyell, and the
followers of Button, maintaining the sufficiency of
" modern causes," acting with their present intensity, to
account for all, even the earliest traceable changes of
CHAP. r. STATE OF GEOLOGICAL THEOKY 285
conditions of our planet. The real distinction between
these celebrated speculations consists not in the nature
of the physical agencies which are assumed to have ac-
complished geological revolutions — for there is little
difference, in this respect, between Playfair and Leibnitz,
Lyell and De Beaumont — but in the measure of intensity
assigned to them in different geological periods. In
both, the same laws of material action are invoked, the
same causes are recognised in their effects ; in both, the
combinations among these causes are admitted to vary
locally and periodically; both contemplate periods of im-
mense duration as necessary for the production of
observed phenomena. But in one, the Leibnitzian
" theory," the globe is supposed to have undergone a
general and progressive loss of interior heat ; in the
other, to have experienced only local or periodical
variations of surface temperature ; in one, great and
general revolutions in the condition of the globe are
deduced from a gradual refrigeration of its substance ;
in the other, general revolutions, properly speaking,
have no place, but local changes, and new combinations,
arise in endless succession: in one, the mechanical,
chemical, and vital phenomena must necessarily pro-
ceed with an entirely different rate of progress, in dif-
ferent geological periods, because the powerful influence
of heat was continually changing ; in the other, these
phenomena exhibit an undeviating general uniformity,
such that " equal effects are produced in equal times."
Taken on a great scale, time, in arithmetical series, is
the element of a cycle of variations in one hypothesis ;
the product of time and force (one increasing as the
other decreases in geometrical series) is the principle of
continual progression in the other.
To enter fully into the consideration of these rival
hypotheses would be at present fruitless ; but we may
try their power and truth on some of the more im-
portant and fundamental points in the structure of the
earth, such as the actual physical geography, and the
ancient climates of the globe.
A TREATISE ON GEOLOGY. CHAP. X.
PHYSICAL GEOGRAPHY.
Distribution of Land and Sea.
No truth is more certain or important in geological
reasoning than the formation of all our continents and
islands by causes acting below the sea. As far as relates
to the stratified rocks this is obvious ; but it is not the
less certain for the unstratified rocks, these having un-
doubtedly been uplifted to our view from beneath the
strata. It is possible there may yet be found some gra-
nitic rocks which were raised above the general spherical
surface before the production of any deposits from water,
and which may therefore be presumed to form an excep-
tion to this general rule; but such truly " primitive "
rocks have nowhere been seen, nor is there any ground
of expectation that they will be discovered. The ele-
vation of the dry land out of the sea is therefore one of
the great truths to which we must compare general
speculations ; and it affords a test, and prescribes con-
ditions, which no false " theory " can fulfil.
The actual distribution of land and sea is very re-
markable. London being taken as the centre of a hemi-
sphere, nearly all the land is included therein. The
antipodal hemisphere includes a vast abundance of small
islands ; but there are no considerable antipodal surfaces
of land, except where Chili and Patagonia oppose the
eastern part of China, and the volcanic islands of Suma-
tra, &c., oppose the volcanic mountains of Quito. The
continent of Australia is opposite to the deep centre of
the Atlantic Ocean. Only ^th part of the present con-
tinents and islands has land opposed to it.*
The meridian of least land (about 16° W. long.)
passes by Kamschatka, the east side of Hecla, the west
coast of Africa (near Madeira. Teneriffe, the Cape de
Verde islands), the west side of New Caledonia, and
* Gardner, in Geol. Proceedings, 1853.
CHAP. X. STATE OP GEOLOGICAL THEORY. 2SJ
near the west side of New Zealand. On this line it is
nearly all sea. The distribution of land and water pre-
sents little symmetry; yet a meridian at right angles to
that above noticed leaves, east and west of it, nearly
equal masses of land. The poles are believed to be
situated in the midst of extensive oceans, though the
progress of modern research has augmented our know-
ledge of antarctic land. These circumstances, though
they indicate little of symmetry in the rugged and irre-
gular surface of the globe, supply some points not un-
important. The general spheroidal figure of the earth
is obviously not the result of superficial waste and minute
arrangements, as the hypothesis of the invariability of
natural forces would seem to. require ; on the contrary,
this figure appears clearly due to the general conditions
of the interior masses, which are only marked and
rendered irregular by the changes that have happened at
the surface. Upon the Leibnitzian supposition, that the
crust cf the globe is cooled over an ignited nucleus,
which is still further undergoing refrigeration, it appears
possible to understand the accumulation of water about
the poles, since, in the direction of the polar diameter, the
contraction of bulk would be in no degree balanced by
the augmented centrifugal force, corresponding to a
determinate velocity and a diminished diameter. But,
on the supposition of the spheroidal earth having been
originally a sphere, and having derived its actual
figure from superficial processes, the polar regions
should have been very elevated land, and the equatorial
zone deep sea. This neither is, nor appears to have
been, the case.
Again, the remarkable contrast of a hemisphere of
land opposing one of sea marks very clearly the influ-
ence of some great and general alterations of surface level.
The supposition of a cooling globe undoubtedly meets
this case ; but it appears difficult to see how the rival
speculation can be applied to phenomena on so vast a
scale, even if unlimited time be given to the operation
of " modern causes."
288 A TREATISE ON GEOLOGY. CHAP. X.
Heights and Depths.
The elevations on the land rise at most to about five
miles above the level of the sea; and the depths of the
Atlantic may perhaps be justly estimated at nine miles,
from the data furnished in Mr. Whewell's Essays on
Cotidal Lines.* The labour would probably not be
wasted which should be given to a careful estimate of
the mass of the sea, as compared with the mass of land
raised above its surface ; on the hypothesis of a gradual
refrigeration of the globe, it is perhaps not impossible
to determine by calculation the relation of these masses;
and from a comparison of these independent results
there would arise an important test of the truth of the
speculation. The heights and depths of the land and
sea appear to require the supposition of co-extensive up-
ward and downward movements, and, as Mr. Lyell rias
shown, it is probable the depressions exceeded the ele-
vations. These effects appear unintelligible, except upon
the admission of subterranean surfaces of melted rock,
capable of yielding to subsidence inward, and eruptive
forces outwards.
But this conclusion becomes more decided when we
take into account the continuity of mountain chains
and oceanic depths, the abrupt borders of the sea-coasts,
the large areas of tertiary and secondary strata which
were formed in the old sea bed, and are now raised, with
little mark of local violence, into almost boundless
plains and vales, within a border of bold mountains.
All these circumstances are the natural consequences of
extensive depression of the crust of the globe, followed
by elevations; both being determined in greater in-
tensity to points, lines, and areas of weakness, in a solid
crust above a fluid of small compressibility, like melted
rock.
» Phil. Transactions, 1833.
CHAP. X. STATE OF GEOLOGICAL THEORY. 289
Displacements of Stratified Rocks.
The notices in a former chapter (Vol. I.) will pro-
bably suffice to satisfy the inquirer after geological
truth, that the elevation of stratified rocks to their
present height above the sea is not merely relative, not
merely caused by great depressions of the earth's surface
elsewhere, but, in part at least, dependent on a real up-
lifting of mountain chains and other groups of dislocated
strata. The most obvious argument in support of
this is the well-known fact, that, in approaching the
mountains, three orders of phenomena rise together to
importance ; the inclination of the strata becomes more
and more decided and violent, till they appear vertical
or even reversed ; the marks of violent displacement
augment in a corresponding degree; and the exhibition
of igneous rocks becomes continually more frequent
among the fractured and contorted strata. Now, if the
mountain lines and groups had been points of rest,
while all the spaces round them sank, something like
the present distribution of land and sea would have
appeared, but these signs of violent displacement would
not have predominated in the vicinity of the mountains.
There is no doubt, therefore, that these have been local
centres of violence and not of rest.
The elevation of mountains has been too much re-
garded in the light of an insulated phenomenon :
Mr. Darwin has truly pointed out its relation to con-
tinental elevation, which may be regarded as the great
effect of a general cause manifesting itself at particular
points in greater intensity. Just as, in experimental
pressures, on solids of every form, the weakest part
alone yields to a force which, up to a certain point, was
borne equally by all, we may easily conceive a general
continental elevation to a certain point, but beyond this,
a partial rupture and relief of the pressure along a
particular fissure. This is Mr. Darwin's view of the
phenomena of uplifted land in and on either side of
the Andes.
VOL. u. IT
290 A TREATISE ON GEOLOGY. CHAP. X.
The same eminent observer has applied the same
consideration of extensive displacements of land and
sea to explain the alternate bands of elevation and sub-
sidence, which are inferred from his survey of modern
coralligenous reefs and islands. (See Vol. I. p. 336.)
In this generalisation it appears that the points of vol-
canic eruption all fall on bands of general elevation,
where the uplifting force is at a maximum. Volcanic
action might thus suggest itself as the local cause of
this local maximum of elevation, did we not know that
exactly the same relation of continental and mountain
elevation obtains for areas of land and groups of
mountains where no volcanic eruptions have happened.
(Nevertheless, it is not to be denied, that the effect of
volcanos is, generally, to augment the inequalities of level
of the earth's surface.) If this view of Mr. Darwin
be well established, it will go far to confirm the general
probability of a refrigerating globe ; for movements of
such regularity and extent require a corresponding
slowly and powerfully acting cause, such as a general
change of temperature must be acknowledged to be. " A
change of the form of the interior fluid surface of the
globe," as Mr. Darwin very correctly expresses the ge-
neral condition on which all these phenomena of simul-
taneous elevation and subsidence may be made to
depend, is a result strictly deducible from the hypothesis
of a refrigerating globe ; and the interesting examples
of gradual and prolonged elevation in Scandinavia, and
perhaps of subsidence in Greenland, appear natural and
obvious consequences of that doctrine, while more
violent upward and downward movements in other
parts of the globe are not at all opposed to it.
The elevation of mountains is, in the doctrine of
refrigeration, a local, critical, and more or less sudden
result of a general and gradually accumulated force;
the contrary hypothesis supposes a vast multitude of
minor movements, such as earthquakes, which now
happen in volcanic regions ; and that these successively
contribute their effects in one direction. The magnitude
CHAP. X. STATE OP GEOLOGICAL THEORY. 2pl
of single movements of the stratified rocks thus becomes
a criterion of importance in estimating the value of
these contrary views.
Anticlinal axes, such as that of Snowdonia, great
faults, like that of the Penine chain, will perhaps he
easily acknowledged to be absolutely unparalleled in
historic periods ; but this inequality of mere magnitude
will not furnish a shadow of evidence against the ap-
plication of the doctrine of the sufficiency of modern
causes, unless it be proved, or shown to be probable, that
the chain of Snowdon, and the ridge of the English
Apennines, were thrown up by one, or, at most, a few
efforts. Now this is probable in each case, for reasons
based on observation, and, as will hereafter appear, not
improbable for reasons founded in mechanical science.
Observation detects on the line of these great move-
ments of the earth's crust no trace of the minutely
confused and fragmentary condition of the strata, which
must have been the result of an indefinite number of
small convulsions, like those of the Chilian earthquakes
in 1822 and 1835, when the ground rose convulsively
a few feet; on the contrary, the simplicity and com-
pleteness of the anticlinals of Snowdon and the Isle of
Wight, and the violent single fracture and few bold
contortions on the Penine fault (which ranges for above
a hundred miles, and may possibly extend much farther),
speak of one or a few powerful efforts. This is so much
the .more to be trusted, as the effect of the friction on
the surfaces of motion has the same character of
simplicity. The area uplifted by the Penine fault may
be roughly estimated at 2000 square miles ; and the
vertical extent of the movement may be taken, on the
average, at 2000 feet. The Chilian earthquake, even
if the ground were uplifted 4 feet for 100,000 square
miles (neither of which assumptions seems at all sup-
ported by the narratives which are published*,) would
yield, at most, only ^th part of this mass of land.
* See p. 241. On the subject of the Chilian earthquake*, consult, gene-
rally, the Geological Society Proceedings, vols. i. and ii.
u a
292 TREATISE ON GEOLOGY. CHAP. X.
Direction.
The direction of anticlinal lines and other great dis-
locations of the strata has become of importance in a
theoretical point of view, ever since Humboldt, Von
Buch, and De Beaumont, strove to link these features
of physical geography with particular epochs of geo-
logical time. If the parallelism of the Carnarvonshire
and Radnorshire axes of movement is an indication of
their being contemporaneous — and this analogy and
conclusion can be extended to the primary slates of
Cumberland, the Lammermuir, Isle of Man, and
Grampian mountains — the inferences justly drawn from
one district, as to the mechanism of its elevation, be-
come confirmed in a very exalted degree. It is, there-
fore, most important to inquire, not merely what foun-
dation there may be for the particular system on this
head, which is supported by the learning and talent
of De Beaumont*, but further, within what limits
observation or mechanical science allow us to consider
it possible to determine the geographical extent of con-
temporaneous disturbances of the strata.
The propositions of M. De Beaumont, in their ut-
most extent, may be thus understood. The principal
dislocations of the same geological age range in lines
parallel to one and the same great circle of the sphere;
those of different ages are parallel to different circles.
The geological era of the elevation of , mountains may
be known from the direction of their axes of move-
ment. The mode of proof will be understood from
the following abstract relating to the system of dislo-
cations, referred by De Beaumont to the period pre-
ceding the deposits of green sand and chalk ; and the
extension, by analogies, from a limited proof to a large
range of probabilities, will appear in the short notice
of two other systems of later date.
Three small granite eminences, in the Cote d'Or,
near Sombernon, which have occasioned the disruption
* In Ann. des Sciences Naturelles for 1829—30.
CHAP. X. STATE OF GEOLOGICAL THEORY.
of Jura limestone there, range in a line N.E. and S.W.
parallel to the summit ridge of the Cote d'Or. The
line of these granite points being considered part of
a geodesical circle, and prolonged in each direction, is
found to coincide with several remarkable geological
accidents or disturbances. In the N. E., for instance,
it coincides with dolomitic oolite and steep dips at Sury,
between Langres and Dijon ; with the hot springs and
magnesian muschelkalk of Bourbonne les Bains ; with
the basaltic eminence of Essey, of Luneville, and with
the granitic protuberance of Albersweiler, between
Annweiler and Landau.
Another line of disturbance, parallel to the preceding,
is indicated ; and it is observed that from Paray (Saone
et Loire) to Plombieres (Vosges), the great line of val-
ley watered by the Bourbonne and Saone is perfectly
parallel. This line, prolonged into Germany, passes
along the valleys of the Mayn and the Saal, through
Mittenberg to Leipzig, and is parallel to the Erzegebirge
and Mittelgebirge.
Now all these dislocations were probably produced at
the same geological epoch ; which, though inferred
from the general phenomena along the line, is deter-
mined more exactly in consequence of an extension of
this system of faults by a series of parallels retiring to
the S. E., till we arrive in the department of the
Rhone, where the chalk and Jura limestones are found
together — the latter dislocated, the former undisturbed.
The direction of this line of disruption is N.E. and
S. W. at Dijon.
In the Jura, a great number of undulations in the
strata range parallel to a line N. 40° E., or N. 45° E.;
and, being sometimes filled with green sand deposits,
are clearly of the same date as the above disruptions.
In abstracting the proofs of the other grand systems of
elevations, we shall attend less to the minute than to the
general analogies. The insulated chain of the Pyrenees,
one of the most remarkable in Europe, forms the base of
the system. Many observations prove that the chalk
u 3
2p4 A TREATISE ON GEOLOGY. CHAP. X.
and green sand are here uplifted with the primary
rocks ; but the later marine lacustrine deposits lie level
upon their slopes, and were clearly deposited from a
sea which washed the base of the already elevated
mountains.
The general direction of the chain from Cape Or-
tegal in Galicia to Cape Creuss in Catalonia, is a little
south of east ; but this general chain is composed of
partial ridges, whose axes are parallel to one another,
and directed W. N. W. and E. S. E.
This direction belongs to the disturbances of the same
date in Provence, and near Nice, and is recognised in
the Apennines, at least in the northern part, and in
the country of Naples, and along the south shore of
Sicily. The south western boundary of the Nagelflue
in Switzerland appears to correspond with the Pyrenseo-
Apennine line ; as do likewise the Dalmatian and
Croatian summits, the valleys of the Save and the
Drave, the line of the Rhodopian mountains, and the
ridge which crosses the straits of the Bosphorus. Simi-
lar directions seem to be traceable in Greece ; and, as far
as the evidence yet collected goes, the date of the eleva-
tion of all these mountains may be the same. The Carpa-
thian range, parallel to the Dniester, falls into the same
system, with a small line of granitic and sienitic rocks
along the Elbe near Dresden, and the mean courses of
the metallic veins of the Hartz. Finally, the well-
known disturbances of the strata in Sussex and Hamp-
shire have the same age, and lie in the same parallel.
Extending his views, M. De Beaumont finds some
traces of the Pyrenaeo-Apennine system in Africa,
and Syria, in the Caucasus, and in the Ghauts of
India ; but the imperfect state of information concern-
ing the geology of these countries renders the in-
ferences concerning them far from precise.
On prolonging the Pyrenaeo-Apennine circle across the
Atlantic, by Hecla and Greenland, to the New World, we
find it descend parallel to the Alleghanies and their north-
ern connexions, which have determined the form of the
CHAP. X. STATE OF GEOLOGICAL THEORY.
eastern shore of the United Slates, and, as De Beaumont
collected from the statements of transatlantic geologists,
were probably uplifted between the age of the chalk and
the latest of the stratified rocks.
Such remarkable accordances of epoch and linear
direction, over so enormous a length upon the surface of
the globe, cannot, says De Beaumont, be the result of
chance, but of a regularly acting internal cause.
M. de Beaumont has entered into a minute examin-
ation of dislocations affecting the molasse, one of the
most recent of the tertiary deposits. He has connected
the line of these disturbances in the south of France with
those which may be observed in the western Alps from
the Grande Chartreuse near Grenoble to the Saleve near
Geneva, and in the primary chain from the mountain
of Taillefer to Mont Blanc, in the direction north, 26°
east. Numerous observations in the valley of the
Durance, though full of discordances, are reduced by the
author to the same general line north, 26° east, which
agrees with the opposite escarpments of Mont Blanc and
Mont Rosa, and nearly with the line of a remarkable
dislocation parallel to the Jura from Molezon to Aarburg,
and with the depressed region occupied by the Lungern
See, Sarner See, Alpnach, Kussnacht, and the lower parts
of the lakes of Zug, Zurich, and Constance. The volcanic
cone of Hohentwiel, beyond Schaffhausen, being upon
the same line, gives occasion for the remark, that a
system of disruption of the same age has thus been traced
in one direction for above 100 leagues.
In the prolongation of this line to Nova Zembla, no
instance is mentioned of corresponding disruptions ;
but the long Scandinavian Alps, and particularly the
Dovrefeld Mountains, are parallel to it ; and it was in
consequence of their elevation that so large a quantity of
Norwegian rocks have been scattered over northern Eu-
rope : the late date of this dispersion ot blocks proves the
late date of the elevation of these mountains.
Some traces are supposed to be found in Africa of the
•ame line of disturbance, and even the chain of the south-
u 4
29(3 A TREATISE ON GEOLOGY. CHAP. X.
east coast of Brazil, from Cape Roque to the Plata, though
400 leagues distant from the great circle of Zurich and
Marseilles, might, perhaps, upon this hypothesis, be re-
ferred to the same epoch.
The most striking difficulty to the reception, at pre-
sent, of any hypothetical connections between geogra-
phical lines and the irregular lines of disruption of strata,
arises from the excessive number of these disturbances,
and the variety of their directions. Brongniart has ex-
pressed, in strong terms, his impression on this subject,
by saying that there is hardly a square myriameter of
the earth's surface which has been left in its original
position.
This difficulty, however, would only perplex the
observer, not obscure the reasoning. There is another
of more importance. The exact geological date of a
dislocation of strata is very difficult to determine, and
in most cases is merely known within wide limits. Who
can prove the contemporaneity of the elevation of Snow-
donia and the Grampians, when the strata dislocated are
not the same, and the covering deposits are different ?
In the north of England the rothetodteliegende and
magnesian limestone cover dislocated coal; in some
parts of the south of England they are not traceable.
The dislocations of the coal may be of the same age in
both districts, but it is impossible to prove it.
These are difficulties in the examination of De Beau-
mont's views, not objections to their truth. There is,
apparently, only one mode of discussion which is likely
to be at all satisfactory : we may compare together the
directions of dislocations, which are probably of the same
geological period, and afterwards some of those which
are known to belong to different periods.
The first class of dislocations, which, in this vague
sense, may be called contemporaneous, belongs to the
period anterior to the whole carboniferous and old red
eandstone series of rocks. To this period the anticlinal
axes of the Highlands and Lammermuirs, prolonged to
Donegal and Cavan, the Cumbrian mountains, the Isle
CHAP. X. STATE OF GEOLOGICAL THEORY. 2.97
of Man, and North Wales belong. Now all these axes
of elevation range north-east and south-west, and thus
appear to support De Beaumont's hypothesis. Professor
Sedgwick, in a recent communication to the Geological
Society (May, 1838), speaks of the importance of at-
tending to this conformity of direction in the axes of
elevation, while attempting to join into one classification,
according to geological age, the formations of distinct
regions. He states further, in support of the same general
views, the probable contemporaneity of the parts of
another and later system of dislocations passing east and
west in Cornwall, Devon, and South Wales, after the
deposition of the coal strata. Lastly, he notices a system
of dislocations which have brought up a portion of pri-
mary rocks, at Dudley, on both sides of the Coventry
coalfield., and in Charnwood forest. At all these localities
the " strike" is the same, and the lines of the greatest
movement are nearly parallel, all being about N.N.W.
and S.S.E. ; and all these movements belong to one
epoch, having been completed after the deposition of the
lower new red sandstone (rothetodteliegende), and before
the period of the upper sandstone and gypseous marls.
Hence we have three great systems of elevation, which
occurred during three distinct geological periods, and
range in three distinct geographical directions.
This favourable testimony to the hypothesis of De
Beaumont might perhaps be further extended : it is,
however, met by the following facts : —
Dislocations almost perfectly parallel to those of
Devonshire and South Wales range across the cre-
taceous and tertiary systems of Hampshire, Dorsetshire,
and Sussex. In the counties of Radnor and Brecon,
anticlinal axes range N.E. and S.W. through districts
where the old red sandstone is conformed to the primary
strata; and the same direction is observed extensively
in the south-western part of Yorkshire, in anteclinals
which cross the upper part of the mountain limestone
series.
Here, then, dislocations of very different ages appear
298 A TREATISE ON GEOLOGY. CHAP. X.
conformed in direction to some that have been men-
tioned before.
With such uncertainty in the data for reasoning and
such contrariety and complexity in their indications, it is
obvious that no definite and satisfactory conclusion can
be at present adopted on the question of the parallelism
of mountain elevations which belong to one geological
age.
The great ranges of mountains, &c. marking the dislo-
cations of the strata, cannot at present be accommodated
to the strictness of a general geographical system ; it is,
however, not the less desirable to examine the same
question on a smaller scale, with the aid of mechanical
science and rigorous observations.
The well-established facts of the local parallelism of
particular classes of mineral veins, already put in evi-
dence in a preceding chapter, leave no doubt of the
existence of some real symmetry of the systems of dis-
location in every limited district. In several instances
approximate parallelism has been observed between mi-
neral veins and the numerous divisional planes of strati-
fied rocks ; and in others a peculiar dependence has been
traced between the direction of a vein-fissure and that
of an axis Of elevated strata. Phenomena of this nature
would for ever remain unexplained, if mathematical
methods of research could not be applied to them ; nor
can they be applied except upon certain assumed con-
ditions of mechanical action.
The first step in this career of discovery has been
taken by Mr. Hopkins, whose memoir in the Cambridge
Philosophical Transactions is remarkable for the sim-
plicity and probability of its fundamental postulates, and
the ready applicability of its conclusions to the results
of observation. That the crust of the earth is elastic
and capable of extension, earthquakes demonstrate ;
that cavities exist below parts of it is certain ; and
that these have a considerable horizontal extent is pro-
bable. There is no room for doubt that similar con-
ditions existed in early geological times; for such cavities
CHAP. X. STATE OF GEOLOGICAL THEORY. 299
below the earth's crust would probably arise either from
general refrigeration of the globe, or from local variation
of heat. In such cavities the accumulation of elastic
vapours is almost a necessary consequence, and it is con-
ceivable that the crust of the globe would in parts yield
to their force.
But Mr. Hopkins's reasoning would be in no degree
invalidated, if for this mechanism of elastic vapours and
cavities, an outward pressure derived from some other
cause were hypothetically substituted, provided only
that the area of its operation were sufficiently large, and
its force continuously augmented until the earth's crust
broke with the accumulated strain. The direction of
the fissure at the instant of fracture can be determined
mathematically, whether the intensity of the elevatory
force be uniform at every point of the surface, or greater
at particular points ; provided the boundaries of the
surface and the resistance offered by the cohesive power
of the mass raised and broken be known. This last
condition, indeed, does not require to be very precisely
fulfilled, except in a horizontal direction ; for in a ver-
tical plane, the cohesive power may vary according to
any discontinuous law, as must happen in every series
of dissimilar strata. (The pre-existence of joints in the
rocks raised offers greater difficulty; but as few of these
traverse great masses of rock, and each stratum has
some peculiarity in the distribution of the joints, it does
not appear to us necessary to except even this case.)
The following are among the results of the investi-
gation when applied to a case resembling the actual
condition of the stratified crust of the globe.
1. Production of longitudinal fissures. — If the
mass of ground raised by an elevatory force of uniform
intensity be of indefinite length, and bounded laterally
by two parallel lines, the extension and therefore the
tension at any point will be in a direction perpendicular
to the length ; and the line of fracture will necessarily
cross this direction, so that fissures cannot be produced
under these circumstances, except in a longitudinal di-
300 A TREATISE ON GEOLOGY. CHAP. X.
rection, or parallel to what may be called the axis of
elevation. It appears that these fissures will not com-
mence at the surface, but at some lower part of the
mass. The whole series of stratified masses will be
affected by the tension in the same manner, but under
some conditions the fissures may not reach to the surface.
The fissures will be of nearly uniform width at all
depths, except that unequal elasticity in the dislocated
strata will cause some differences. It is not inconsistent
with mechanical principles to admit that more than
one parallel fissure may originate simultaneously, and
they may be subsequently prolonged, so that many pa-
rallel fissures (especially below the surface) may exist
together, the fruit of one general action. No sooner,
however, are the fissures extensively formed than new
conditions arise, and any further fracture can be pro*
duced only in new directions. Wherever such a system
of parallel fissures is found to exist in the same mass of
strata, it is physically impossible that they can have
originated at considerably different times, though the
prolongation of a fissure may have been effected long
after its origin.
2. Formation of transverse fissures. — In a district,
circumstanced as stated, the application of any further
force would cause extension of the now free parallel
parts of the mass only in the direction of their length,
and consequently produce ruptures at right angles to the
former fissures. One or more of these transverse fissures
might in like manner be produced in each of the paral-
lel bands of displaced strata. In any country which
manifests two systems of parallel fissures, one at right
angles to the other, it is absolutely certain that the effects
are due to no more than one general elevatory force, and
One continuous effect for each system of parallels; a series
of partial forces at particular points or different times
could not produce the effects.
3. Formation of fissures in a conical elevation. — If
the mass of strata moved offer a uniform resistance, a
conical elevation of a part can only be occasioned by
CHAP. X. STATE OF GEOLOGICAL THEORY. 301
forces of great intensity determined to a limited area.
Fissures will in this case be formed so as to pass through
the axis and radiate from the centre of the cone, as is
observed to be the case in the Plomb du CantaL If in
addition to a general elevatory force, supposed to act
in the production of longitudinal fissures, a partial force
was simultaneously acting at a particular point, the
fissures would deviate from parallelism to approach that
point. An instance of this was observed by Hopkins,
in connection with a limited elevation of millstone grit,
through the coal strata of Derbyshire.
4. Faults. — The masses thus separated by fissures
might, upon the weakening of the elevatory force, fall
back in some confusion, so as to occasion faults of dif-
ferent kinds.
We shall only observe further on this subject, that a
circumstance of importance in determining the direction
of the lines of fissure is the weighting of the masses,
which for many reasons must be supposed to have been
often very unequal. The more general the mechanical
agency, and the more uniform the resistance of the
masses, so much the more perfectly straight and paral-
lel the systems of simultaneous and successive fissures.
The conclusions thus obtained seem to apply with
special accuracy to the veins and cross courses of Corn-
wall, Brittany, Cumberland, and Northumberland, the
Hartz, the Erzgebirge, and other districts, and assist
very much to strengthen the conviction derived from
other phenomena, that the great faults and other forms
of disturbance may have been occasioned by single con-
tinuous efforts of general subterranean forces. If so,
it is difficult to believe they can have been due to such
effects as those made by modern earthquakes.
Periods of Ordinary and Critical Action
Whatever may be the fate of De Beaumont's speculation
regarding the elevation of mountain groups, at particular
geological aeras, and in certain geographical parallels, tne
502 A TREATISE ON GEOLOGY. CHAP. X.
investigations to which it has conducted are likely to
have an important and permanent influence on geologi-
cal observation and theory. Already, in the countries
best examined, — in England, France, Germany, in
Europe generally, and in North America, it is found
possible to determine one or more periods when great
and extensive subterranean pressures broke the sub-
marine crust of the earth, and raised particular tracts
of land above the reach of further marine deposits.
Comparatively short periods of widely extended dis-
turbance in the equilibrium of heat are thus clearly
established, in alternation with far longer periods of
repose in the same regions ; and though it may be
rather a coincident than a dependent phenomenon, it is
not to be doubted that, among the older strata, these
critical periods of disturbed equilibrium of heat corre-
spond to critical periods in the revolutions of organic
life. That either of these results is true universally
would be a ridiculous affirmation, in the present state of
our ignorance concerning immense areas of the globe ;
but it will not be the less useful to exemplify their truths,
chiefly by application to the British islands. The fol-
lowing table is intended for this purpose, and may be
compared with that on page 152., which contains some
of the same elements ; —
Primary period, of ordinary action, among the aque-
ous and igneous agencies ; the ancient bed of the sea
was filled with sediments, the most recent of which
obviously were derived from tracts of land, which are
now for the most part submerged. The organic re-
mains of this whole period really compose but one series,
in the same sense that the fossils of the oolitic or creta-
ceous system are one varied group. There were local
disturbances of the sea bed in the Cumbrian and other
districts.
An interval of dislocations followed, in which all
the primary strata of England, in every part (excepting
perhaps the silurian region), were raised to angular
positions, so that the next system rests unconformedly
upon them.
CHAP. X. STATE OP GEOLOGICAL THEORY. 303
Carboniferous period, of ordinary action; the sea
filled with new sediments by inundations from the land
which had been lately and previously uplifted. The
series of organic remains undergoes an entire and appa-
rently sudden change of species.
Another interval of dislocations, so general and re-
markable, that there is not a coal field in Europe which
appears to have been exempt from them. The geological
date is not always assignable, except within the limits of
the uppermost coal deposits, and the base of the new red
sandstone. The whole period of rotheliegende and
magnesian limestones may be included in this interval,
and some of the peculiarities of the saliferous system are
probably the effects of this great disturbance.
The oolitic and cretaceous periods appear to have been
scarcely broken by any violence in the region of the
British isles, but the whole bed of the sea underwent a
gradual and continual rise, which brought up progres-
sively the north-western parts of the oolitic rocks. (On
the continent of Europe the oolitic and cretaceous
periods were divided by an interval of great disturbance.)
An interval of extensive dislocations has been recog-
nised by M. de Beaumont and others, under the title of
the Pyreneo-Apennine system ; in England the effects
of disturbance are chiefly exemplified in the conglo-
merates and pebbles which abound in the lower tertiary
strata.
The eocene period of Mr. Lyell succeeds, with a pro-
digious number of organic forms, almost wholly distinct
from those of the older strata.
The dislocations of the western and eastern Alps,
combined with the evidence afforded by diluvial phe-
nomena and raised sea breaches in many parts of the
world, appear to show a separation between the eocene
and modern periods by a period of violent disturbances,
connected with the rising of some of the highest moun-
tain ranges in the world. The conjecture of De Beau-
mont, that the elevation of the Andes was one of the
latest of these great disturbances, has been verified hy
304 A TREATISE ON GEOLOGY. CHAP. X.
the researches of Mr. Charles Darwin in Patagonia and
Chili. (Geol. Proceedings.)
Modern Period of Ordinary Action.
The value of such an arrangement as that here pre-
sented is not in its minute accuracy, but its general
application ; and in this respect it is, apparently, worthy
of considerable confidence. It is however impossible to
assert, or to believe, that the intervals of disturbance
were very short, or that a mountain range rose in a
moment, to divide an ocean and change the relations of
organic life. The alternation of great periods of repose
and disturbance, in every district yet examined, is cer-
tain ; the correspondence of these periods in remote
regions, though not completely proved, is rendered pro-
bable ; and it only remains to see what is the bearing of
this discussion upon geological theory.
Such alternations of repose and violence appear a
necessary consequence of the gradual refrigeration of
the globe ; the duration of repose and the violence of the
disturbance being dependent on the resistance to pressure
offered by the consolidated crust of the earth. However
hot a planet may have been, it is conceivable that in
time sufficiently long the radiation of its heat into the
cold ethereal spaces must continually reduce its internal
temperature. The solidified crust, when cooled to the
temperature derived from the joint influence of the hot
sun and the cold regions around the globe, suffers no
further loss of heat ; but the internal parts may still
grow cooler through immense periods of time; they
may thus contract more than the outer parts, and fail to
sustain them ; fractures follow, and the equilibrium of
pressure is restored, till a long period of cooling revives
the irregularity of forces, and the crust breaks again.
Periods of ordinary, and intervals of critical, action are
direct consequences of the Leibnitzian doctrine.
This however does not prevent the favourers of the
contrary hypothesis from adding to their speculation of
the constancy of natural forces the further assumption
CHAP. X. STATE OF GEOLOGICAL THEORY. 305
that they are subject to a cycle of large variations, such
as those " perturbations" which affect even the regular
orbits of the planets. Such cycles of variation have been
suggested, but unless a cause be assigned (as is done for
the planetary perturbations), this gratuitous addition of
one hypothesis to another weakens the probability of
both. This appears to us an impartial view of the
subject.
Climate.
That during early geological periods, the northern
zones of the earth enjoyed a climate approaching to that
which is now confined to the equatorial regions, is
admitted among the established inferences of geology,
upon the evidence of the remains of plants and animals
found imbedded in the strata. For reasoning on this
subject which we deem satisfactory, the reader may
consult a former chapter of this work. (Vol. I. ch. v.)
A true geological theory must be capable of fully ac-
counting for the change of temperature which has thus
affected large regions of the globe.
Besides the general speculation of a refrigerating
globe, we have on this subject three others to examine.
The hypothesis advanced by Mr. Lyell is founded on
the acknowledged fact that the mean temperature of
any point on the earth's surface is liable to considerable
variation, according to the position of land and sea. By
supposing a peculiar distribution of masses of land,
equal in area and elevation to the present continents and
islands, this eminent author endeavours to account for
the facts regarding ancient climate, without calling in
aid any external or internal sources of a change of heat.
There are, however, two external sources of change of
the mean temperature of the whole globe. The calorific
influence of the sun may increase or diminish, because
the mean distance of the earth from that luminary is sub-
ject to variation : the temperature of the ethereal spaces
in which suns and planets move may not be the same
in every part ; and., if the whole solar system has a move-
VOL. ii. X
306 A TREATISE ON GEOLOGY. CHAP. X.
ment of translation in space, it is possible that in some
former period the earth may have passed through
regions of the universe which communicated heat
instead of abstracting it.
We shall first notice the speculations which relate to
external sources of heat and cold.
The variability of solar heat, as bearing on geological
problems, has been investigated by Sir John Herschel.
It is known that the major axis of the earth's orbit is
invariable, but that the minor axis is subject to con-
siderable change in a long period of time, though the
limits of the variation of excentricity which this pro-
duces in the earth's orbit are unascertained. This ex-
centricity is at present, and has been for ages beyond
the reach of history, on the decrease, because the minor
axis of the earth's elliptic orbit is continually lengthening.
The limit of this elongation is now nearly reached, for
the orbit has become nearly circular.
It must be very obvious that the amount of solar
heat received on the earth (the major axis of the orbit
being constant) diminishes as the minor axis is elon-
gated, and, therefore, the earth's heat derived from the
sun has been through all historic time, and is at this
moment, on the decrease. The quantity of solar heat
received on the earth, is, in fact, inversely proportional
to the length of the minor axis of the orbit ; and were
the limits of the variation of this axis calculated (which
would be excessively laborious), the extreme change of
climate from this cause might be known. Taking,
however, the extreme measures of excentricity, which
occur in our planetary system (Juno and Pallas for
example), as possible in the case of the earth, Sir
J. Herschel deduces from calculation that the utmost
difference of mean solar radiation might amount to
about three per cent., a quantity certainly very small,
and altogether inadequate, except by a peculiar com-
bination of favourable circumstances, to account for the
changes of climates established by geological observations.
Until the calculation alluded to be actually made, it
CHAP. X. STATE OP GEOLOGICAL THEOBY. 3C'7
appears unreasonable to attach much weight to this
source of variation in climate.* The solar heat an-
nually poured upon the earth is stated by Pouillet to
be sufficient to melt a coat of ice 14 metres thick, en-
crusting the whole globe of the earth.
2. The heat of the planetary spaces is a subject on
which, Mr. Whewell justly observes, the scientific
world has hardly yet had time to form a sage and stable
opinion. Fourier has asserted the existence of a definite
temperature in these spaces, and ascribes it to the
radiation of the fixed stars in every part of the universe.
He assumed this temperature at about 50° centigrade
below the freezing point, and Swanberg has been led,
by a -wholly different line of reasoning, to nearly the
same result, as to the degree of temperature of the void
spaces of our system.
This view of the state of the ethereal spaces is im-
portant in the application of the mathematical theory of
heat to the present and former conditions of the earth.
But M. Poisson, while fully admiiting the existence of
considerable heat below the surface of the earth, and
the comparative cold of the spaces which now surround
our globe, assigns the following reason for the high
temperature below the surface. The cosmical regions in
which the solar system moves have a proper temperature
of their own, and this temperature may be different in
different parts of the universe. The earth, in whatever
part of these spaces it be placed, must be some time in
acquiring the temperature of that region, and this tem-
perature will be propagated gradually from the surface
to the interior parts. Hence, if the solar system moves
out of a hotter into a colder region of space, the part of
the earth below the surface will exhibit traces of that
higher temperature, which it had before acquired.
Thus, without supposing great heat in the whole mass
of the interior parts of the earth, the phenomenon of
» See Geol. Trans., 2nd seriei, ToL iii. ; and GeoL Proceedings, voL L
p. 245.
3C8
A TREATISE ON GEOLOGY. CHAP. X.
augmenting temperature below the surface would be
explained.*
Geologists will probably be pardoned for not attach-
ing importance to this remarkable speculation, except
for the proof it affords that men of enlarged conceptions,
and the highest mathematical endowments,, regard the
facts already known by observation of the heat now
present within, and the climate which anciently over-
spread the earth, as inexplicable, except by general
variation of heat through a considerable part of the
mass of the earth, or even a great range of the cosmical
regions. Local sources of heat are deemed inadequate,
and left unnoticed by Poisson, Fourier, Arago, and
Herschel.
We have therefore finally to compare the account of
the changes of ancient climate, proposed by the distin-
guished advocate of " modern causes," for comparison
with that furnished by " refrigeration of the globe."
The principle of Mr. Lyell's hypothesis of changes
of climate, in different geological periods, is the change
of position of the land. We have already stated as a
main cause of the differences of the mean annual heat
at places which lie in the same zone of latitude, and
consequently receive the same quantity of solar radia-
tion, the influence of oceanic currents. The tides raised
in the equatorial seas circulate round the globe, and,
by spreading up the North Atlantic and North Pacific
communicate warmth to the western shores of Europe
and America. Oceanic currents, arising from other
causes, mix the temperature of different latitudes, and
moderate the extremes of heat and cold. Nor is this all.
The higher that land is raised into the atmosphere the
colder does it become, and the larger the mass of this
elevated land the more powerful is its cooling influence
on fhe vicinity. For this reason, the mean tempera-
ture of North America and Northern Asia is generally
much lower than that of Europe in the same latitudes.
* See Mr. Whewell's Report and Communications to the British Associa-
tion, 183J.
CHAP. X. STATE OF GEOLOGICAL THEORY. 309
The nearly meridional band, which has the highest
mean temperatures on given latitudes, passes up the
Atlantic, along the west coast of Europe. In latitudes
below 30', the difference between the temperatures on
this line of greatest heat, and those of America and
Asia, though perhaps always sensible, is slight ; but
on arriving in high latitudes, the contrast is somewhat
startling. Upsal, in latitude 60° N., has about the
same mean temperature (4-2°) as Quebec, in lat. 4-7°.
The isothermal line of 32° crosses the North Cape in
lat. 70°, and from this vertex of curvature descends
southward by the south side of Iceland, and the south
part of Greenland, to the north point of Labrador,
almost to lat. 60°. This is the most southerly part of
the curve, which then bends to the north, and reaches
65° at Great Bear Lake, beyond which its course has
not been completely traced. In the other direction,
from the North Cape, this line deviates to the south,
till it crosses the Lena below lat. 65°. Thus on the
line of 32° it rises in the meridian of Norway 10° of
lat. further north than in America, and 5° further
north than in Asia. Nearly similar results follow from
tracing the other isothermal lines determined by Hum-
boldt in high northern latitudes, but the difference above
stated is more than the average. In the same latitudes,
Europe is warmer than North America by 5° Fahr. or
more, but in particular situations this difference is much
greater, amounting, in extreme cases, to 11°, or even
to 17°. Such uncommon differences, however, are un-
important in a general argument.
Some portion of the great difference of the Atlantic
and the continental climates may safely be ascribed to
the gulf stream, which carries the warmth of Guinea
even to Spitzbergen (according to Sooresby) ; but with-
out this aid, a deep polar ocean communicating to
equatorial seas must always mitigate the cold of the
Arctic zone along the main channel of connexion, as a
mass of Arctic land lowers the mean annual heat of the
temperate zones, by collecting an eternal covering of
x 3
310 A TREATISE ON GEOLOGY. CHAP. X.
snow and ice. On the contrary, in both respects, land in
the equatorial regions may absorb more heat than water ;
and thus we have, as general conclusions, the greatest
uniformity of climate, with the greatest expansion of
sea ; the greatest mean annual heat toward the poles,
with equatorial land and polar oceans ; and the least
mean annual heat with polar land and broad equatorial
sea.
If, therefore, during one long geological period, land
of the same extent as that now above the waves, and
rising to the same height, were situated round the poles,
while the zones of the earth, which received most solar
rays, were occupied by sea, there can be no doubt that
the mean annual heat of the whole terraqueous surface
might fall considerably, the greatest depression being in
the polar regions. Such a state of things is fancifully
called by Mr. Lyell the winter of the " great year" On
the contrary, with continents equal to the present placed
on the equator, and wide oceans overflowing either pole,
there would be an augmentation of mean annual heat,
and the " summer " of the great year would have re-
turned !
Several questions, however, remain to be answered,
before this elegant hypothesis can be embraced as a
sufficient cause of the changes of climate, which appears
to have come over the northern zones.
The Collecting of land around the poles, or on the
equatorial line, or in any other position, is not positively
contradicted by known geological facts, but neither is any
decided support given to the assumption by those facts :
it cannot even be declared to be probable or improbable, on
the ground of observations ; for though these certainly
teach us that the position of land and sea is indefinitely
variable, they have determined little or nothing concern-
ing their actual distribution in former geological periods.
This speculation is then purely hypothetical and
framed ta suit the phenomena, as others may be,, and
have been ; but it involves no physical improbability
oil a great scale, and its details are based on real causes.
CHAP. X. STATE OP GEOLOGICAL THEORV. 31 1
We may, therefore, inquire farther, whether it is suf-
ficient to explain the facts admitted concerning ancient
climate. If we take the oceanic polyparia, which
*abound in reefs among primary and carboniferous
strata, as a mark of climate not inferior to that of the
coolest regions where now coral reefs are formed, the
mean temperature of the sea in the latitude of Christiania,
situated on what is now the warmest band passing across
the isothermal lines (now about 43°), must have been
about 20° F. higher, which, added to the Already exist-
ing excess of temperature on this line above the average,
makes nearly 30° F. for the necessary augmentation of
marine temperature toward the north pole.
On the land, a very similar augmentation of temper-
ature must be supposed : for the evidence of the arbor-
escent ferns and fluviatile reptilia goes very much to
establish the necessity of a mean temperature of above
60°, wherever the coal deposits spread in great abund-
ance. Taking the coalfield of Edinburgh as an exam,
pie, the mean temperature of the ancient land which
supplied the plants there buried and changed to coal,
may have been about 15° hotter than now occurs on
this warm meridional band. It may, indeed, be sup-
posed that these plants were drifted from southern lands ;
but what is the inference from observation ? It is ex-
actly the contrary, according to the evidence furnished
in the Illustrations of 'the Geology of Yorkshire ; where
both for the oolitic and the earlier coal strata, it is
proved that the drifting was/rom the north.
Surely these are serious obstacles to the reception of
the hypothesis of change of ancient climate, by altered
position of land and sea, on the ground of its being suf"
ficient to meet the phenomena. In general, perhaps,
we may venture to remark that it is unsafe to push the
opinion of the possible average change of temperature in
extra-tropical regions, beyond the EXTREMES now ob-
served therein. America, with little north tropical and
wide north polar land, gives us a case of extreme refri-
geration from the pole toward the equator; Africa and
312 A TREATISE ON GEOLOGY. CHAP. X,
the west of Europe compose a surface of wide and hot
north tropical land, with free channels ta a polar sea.
The extreme difference of these extreme climates does
not, we believe, in any two points of like elevation
reach 20°, the half of which is, perhaps, more than the
extreme excess or defect of heat beyond the average of
the latitude at any one point upon the surface of the
earth.
If an average excess of 10° of temperature be allow-
able according to this hypothesis, the extreme excesses
may have been somewhat greater ; but from the con-
ditions of the hypothesis they cannot be taken to be so
great as the extreme excesses now observed on the globe,
but must be supposed comparatively small.
We have, therefore, only further to inquire in what
manner the doctrine of progressive refrigeration of the
globe from the earliest periods meets this case of the
change of climate in regions far from the equator. Some
geologists appear to have adopted, on the subject of the
earth's interior heat, a singularly erroneous opinion •
viz. that a cold solid crust and an incandescent nucleus
are incompatible. The doctrine of f( central heat " (as
the Leibnitzian speculation is sometimes inaccurately
termed,) is, upon this false notion of the conduction of
heat, declared to be a physical mistake. Yet it can be
easily shown, both by experiment and mathematical cal.
culations, to be a necessary truth) in a body circum-
stanced as the earth really is. If one end of a bar of
metal, a few feet long, be plunged in the fire, while the
other end is wrapped in a wet cloth, the one end may
be ignited to any desired degree, while the other can
be kept at any required temperature above a certain
point, depending on the heating and cooling powers ap-
plied to the ends of the bar, its length, and the conduct-
ing and radiating powers of the metal. Instead of the
metal bar, submit to the same heat a bar of stone, or a
rod of glass j in these cases, unless the har be very short,
no cooling power at all is needed further than that of
conduction and radiation from the surface of the bai,
CHAP. X. STATE OF GEOLOGICAL THEOBT. 313
because of the. extreme feebleness with which heat
passes through its interior parts. What is the difficulty
of applying this reasoning to the stony crust of the
earth ?
Fourier has done this in a manner which mathe-
maticians deem admirable and satisfactory, in his masterly
' Treatise on Heat,' now become the standard book of
reference in the highest department of this subject. We
shall use the words of one who has examined the
arguments of Fourier.* ff Some of the results of this
theory are fitted to make less formidable the idea of
having a vast abyss of incandescent matter within the
comparatively thin crust of earth on which man and his
works are supported. It results from Fourier's analysis,
that at 20,000, or 30,000 metres deep (12 to 18 miles)
the earth may be actually incandescent, and yet that the
effect of this fervid mass upon the temperature at the
surface may be a scarcely perceptible fraction of a degree.
The slowness with which any heating or cooling effect
would take place through a solid crust is much greater
than might be supposed. If the earth below 12 leagues
depth were replaced by a globe of a temperature 500
times greater than that of boiling water, 200,000 years
would be required to increase the temperature of the
surface 1°. A much smaller depth would make the
effect on the superficial temperature insensible for 2000
years. It is calculated, moreover, that from the rate of
increase of temperature in descending, the quantity of
central heat which escapes in a century through a square
metre of the earth's surface would melt a column of ice
having this metre for a base and 3 metres for its height."
Now it follows as a necessary consequence of the
progressive refrigeration of the globe, that whatever be
at this time the influence of interior heat upon the
temperature of the surface, it was in early geological
periods far greater than at present, and has been slowly
diminishing, till, in Leibnitz's words, a consistent state
» Wheweil's Report to British Association, 1835.
314? A TREATISE ON GEOLOGY. CHAP. X.
of things is reached*: for both theory and observation
agree in showing that internal heat is almost insensible
among the other elements of climate. During the last
2000 years it is calculated that the cooling of the globe
has not lowered its surface temperature -^J^th of a
centigrade degree ; for had this been the case some
change in the length of the day would have become
perceptible since the era of Hipparchus. This fact
has sometimes been urged as an objection to Fourier's
conclusions, though it is really a corollary from the
theory, and its agreement with observation might have
been, with equal justice, mentioned in corroboration of
its truth.
It is very conceivable that, in the earlier stages of
the cooling of the globe, a moderate general warmth of
30°, 20°, 10°, &c. might be successively communicated
from the interior to the surface; and it has been already
seen that this uniform addition to the effects of the solar
radiation would supply in northern zones as far as 70°,
60°, 50°, 40°, &c. of latitude successively, the temper-
ature requisite to allow of coral reefs in the sea, palms
and tree ferns upon the land, and crocodiles and other
huge reptiles in the rivers and estuaries.
On the whole, until the sufficiency of a peculiar po-
sition of land and sea, to meet the phenomena of a change
of climate is proved, and some independent ground of
definite probability is assigned for the occurrence of
such a position, it would be premature to recognise in
the present aspect of the hypothesis which proceeds
upon that assumption the features of a true theory.
But it would be equally unjust to condemn it as false,
for it is not disproved, and no one has shown that such
positions of land and sea as Mr. Lyell has contemplated,
may not acquire a determinate probability among other
consequences of a general theory. In the mean time
that admirable writer has conferred no small benefit on
* " Donee quiescentibus causis, atque aequilibratis, consistentior emer-
geret reruin status." (See Conybeare, Report on Geology, to Britisk
Association, 1832.
CHAP. X. STATE OF GEOLOGICAL THEORY.
geological theory by introducing for consideration this
elegant and consistent speculation.
CONCLUSION.
That the doctrine of progressive cooling of the globe
is to be now received as an established theory, those
who desire the real progress of geology will prevent
themselves from affirming ; and perhaps few who have
attended to the inferences contained in these volumes
will hesitate to believe that it will one day become so.
It is no small argument in favour of this hypothesis (as
it must still be called), that it appears to include, easily
and obviously, so many of the leading and general truths
established by geological observation. The figure of the
earth, its density, the actual temperature of its surface
and interior parts; the general floor of igneous rocks
below the strata ; the repeated formation and uplifting
of such rocks ; the great and systematic fractures of the
earth's crust ; are all capable of explanation by this one
consideration. Moreover, it assigns a reason for the
remarkable uniformity and extent of the earliest as
compared with the latest deposits of water; and ac-
counts for the characteristic induration of the ancient
rocks, the rarity and even total absence of organic re-
mains in them, the changes of climate, and the periods
of ordinary and critical action, which observation has
established, by one and the same principle. The proximity
of heated masses to the surface in the early ages of the
world, to which these phenomena are easily referred, is
indeed hardly doubtful, since it is equally indicated by
a full investigation of the sources and distribution of
terrestrial heat at this day.
What then is wanted to turn this apparently for-
tunate speculation into an established general theory ?
It is the same process which has given stability to the
idea of gravitation, and is now employed to sustain the
undulatory theory of light. It is the deduction of cAo-
Sl6 A TREATISE ON GEOLOGY. CHAP. X.
racteristic phenomena in the real order of their succes-
sion.
To this taslc geologists, as such, are quite unequal.
The preliminary investigations in mechanical and che-
mical philosophy are yet incomplete ; we do not know
to what extent the earth, in its interior parts, is solid or
liquid ; we cannot affirm in what state of combination
the substances there occur ; the rate of increase of heat
below the surface is only approximately determined in
particular regions; the depths of the sea have not been
measured ; the geological surveyor has not visited above
half the globe ; the true relations of the existing crea-
tion of life to those which have passed away are yet the
subjects of discussion; the times which have elapsed
during the accomplishment of geological revolutions a;e
not even reduced to conjecture !
Yet in spite of these disadvantages, the conviction is
spreading that some good will result from even an un-
successful attempt to deduce mathematically the main
consequences of the Leibnitzian speculation. To this
task Mr. Conybeare invited attention in 1831; and since
that time Mr. Hopkins has given proof, in more than
one Memoir, that the subject is in able hands. The
mist is gradually disappearing ; and if we see not
clearly the high point of truth which we desire to reach,
and which may yet be far distant, at least the direction
of our march is found ; and though the paths may be
devious and hazardous, they are full of beauty and de-
light.
317
CHAP. XI.
POPULAR VIEWS AND ECONOMICAL APPLICATIONS OP
GEOLOGY.
THE favour with which geology has been received
into the circle of modern science, is mainly attributable
to its all-pervading and expanded harmony with other
branches of study, with popular sources of intellectual
enjoyment, and important commercial and agricultural
applications. Public taste changes from time to time
its objects of special attention, but not capriciously nor
unjustly; and geology has been advanced rapidly
during the last 10, 20, and 30 years, because its march
had been previously retarded, and because in its pro-
gress all other parts of the great contemplation of
nature were deeply interested. The preceding pages
have given illustration of the real and mutual depend-
ence of geology, and the parts of human study which
relate to the living forms, habits, and history of plants
and animals, — the energies resident in and acting
among the atoms of matter — the forces which operate
in the air and water above, and in the rocky depths
below the surface of the earth — the constitution and
phenomena of the planets, and the state of the ethereal
spaces in which suns and planets move, at distances
which are beyond expression and conception. Con-
sidered in these aspects, geology is a boundless study ;
and yet only the indolent will turn away from its
allurements, since every part of its truths is full of
rare and profitable results.
It is sometimes, not very fairly, objected to modern
geology, that the superior accuracy and power of re-
search which it has turned on the ancient mysteries of
S18 A TREATISE ON GEOLOGY, CHAP. XI.
nature, has been purchased at the cost of the plainness
and accessibility which it is imagined should attend the
interpretation of phenomena so obvious as those in the
crust of the earth : but in reality no branch of the
study of external nature is less loaded with technical
impediments. The thousands of organic remains which
have been cited as witnesses of the ancient character of
land and sea, are called by the names which have been
assigned them by zoology and botany ; the mineralogist
lias given the titles of rocks and individual minerals ;
chemists and mechanicians supply the laws of corpus-
cular actions and movements among the larger masses
of matter ; and all these parts of knowledge must enter
into the consideration of any one who may think
himself equal to propose a general geological theory.
But equal difficulties and not greater facilities belong
to the highest paths in every other branch of know-
ledge ; while in the collecting of facts for the foundation
and confirmation of such a theory, men of ordinary
mental power and application can hardly fail to be use-
fully and mcst agreeably occupied ; nor do they need,
for this valuable purpose, to become profoundly versed
in any other art or science than that of observation.
At the same time it is to be stated, that observations
of most value in every field of human inquiry, have
been made by those whose minds, previously directed
to the true bearings of the questions in progress, have
been ready to perceive and embrace the occasion of
adding new and appropriate truths to the stock already
gathered. It is therefore most important that as much
of the interpretation of geological phenomena as can be
correctly advanced, should be openly and frequently
communicated to the public at large ; since by this
means the mass of ignorance and prejudice, which it is
the function of science to remove, will be attacked at
all points, and thousands of valuable facts disclosed in
railways and canals, in wells, collieries, and mines, will
be saved from that oblivion hito which all the merely
experimental acquirements of practical men too easily
and quickly fall.
CHAP. XI. VIEWS AND APPLICATIONS. 31 9
There is, besides, another class of persons to whom
these remarks may be useful. The body of mere tra-
vellers who now hurry over the globe on the wings of
steam, would be converted into valuable pioneers for the
yet unexplored wastes of geology, could they be made
to see and feel the power which is possessed by every
voyager to contribute, though not so abundantly as the
prince of travellers, Humboldt, to the stores of natural
science. In meteorology, magnetism, zoology, and
botany, as well as geology, the officers of the army and
navy have begun to distinguish themselves ; and it is
with a view to extend this honourable love of knowledge,
by showing some of the popular and economical appli-
cations of geology, that the following remarks and sug-
gestions are written.
Aspect of the Earth's Surface.
Most unjustly has Natural History been accused of
favouring merely minute and curious inquiries into the
small, parts of creation, and of neglecting the larger
views and contemplations which delight the man of taste
and refined feeling. Whoever reads the works of Pallas,
Humboldt, White, or, to come more nearly to our sub-
ject, converses with Sedgwick or examines the pages of
Lyell, will acknowledge the error of this misrepresent-
ation. Mr. Murchison in his work now published*, has
vindicated geology from this aspersion, and, while ex-
ploring with extraordinary zeal and minuteness the
recesses of the border of Wales, has stopped to admire
the feudal ruins and trace the smiling landscapes of
that interesting region. Often has it occurred to our-
selves, while traversing other districts not less rich in
curious geological truth, to rejoice in the new knowledge
and deeper love of nature which an investigation into
the ancient causes of the present aspect of the land and
sea had imparted ; the puny hammer has dropped from
* The Silurian System, in two volumes 4to.
320 A TREATISE OX GEOLOGY. CHAP. XI
our hands while contemplating the mighty waste pro-
duced by atmospheric variations on rocks which in our
monumental buildings have stood the injuries of a
thousand years ; and we have turned from the perishing
granite of Arran, or the bleached and weathered lime-
stones of the Wye or the Meuse, to compare these
proofs of partial and slow decay with the deep chasms
and wide valleys which now diversify the surface of the
land, and to inquire whether the same causes long con-
tinued, or other causes operating with greater intensity,
have given to the earth this
" Pleasure situate in hill and dale."
The intellectual enjoyment of contrasted scenes, far
from being diminished by the application of scientific
methods of research into the causes of their differences,
is, in fact, very incomplete without such addition ; and
few persons really do feel gratification in contemplating
the beauties of nature, or the miracles of art, who have
not learned to associate with the mere perceptions of
form and colour, circumstances of higher and deeper
interest for the mind.
Outline of Land and Sea.
One of the circumstances most obvious to a geologist,
but most unintelligible to an ordinary observer, is the
real and necessary dependence of the form and aspect
of the earth's surface on the quality and arrangement of
the rocky materials beneath. If the reader will place
before him a coloured geological map of the British
Islands*, he will easily perceive the truth of this state-
ment, by comparing the outline of the coast with the
geological structure. There is a remarkable tendency in
the English and Scottish coasts to run out into long
points and retire into bays in lines more or less directed
from south-west to north-east, as the long projections
of Cornwall, Cardiganshire, Carnarvonshire, the Isle of
* One recently published by the author of this volume, at a moderate
price, may be used for this and other purposes of reference.
CHAP. XI. VIEWS AND APPLICATIONS.
Man, Galloway, Isla, the Hebrides, Orkneys, Aberdeen-
shire,, Norfolk, plainly denote. The direction from N.E.
to S.W. is the most prevalent one in England, Wales,
and Scotland; in Ireland, several directions of strata
appear, and the tendency to form promontories and
bays is correspondingly varied.
Passing to more precise inquiry, we find that the posi-
tion of the rocks in anticlinal and synclinal axes is a
fertile source of local and general irregularity of outline.
The Hebrides may be viewed as the tops of one long
anticlinal range of gneiss mountains ; nearly parallel to
these are the loftier chains of the North-western High-
lands, from Mull to Caithness, and the broader band of
the Grampians, both running out into vast projections ;
while between these severally, in synclinal lines and
newer strata, are a parallel channel of the sea, and a
parallel vale which unites the opposite bays of the
Moray Frith and Loch Linnhe. Another anticlinal
ridge in a north-east and south-west direction forms
the Lammermuir and other mountains from St. Abb's
Head to the Mull of Galloway, and between these and
the Grampians sinks the synclinal axis of the retiring
coasts of the Forth and Clyde. In all there cases, the
outline of land and sea is obviously the necessary result
of the intersection of parallel ridges and hollows by the
general sea line.
Farther south we find, on the eastern coast, the
influence of unequal hardness in the rocks which front
the sea. The straight line of the Northumberland
coast presents a series of carboniferous rocks which
waste slightly and equally ; the hollow at the mouth of
the Tees is in soft and perishing red sandstones and
clays ; the prominent points of Whitby Abbey, Scarbo-
rough Castle, and Flamborough Head are feebly guarded
by oolitic limestones and sandstones, and hard chalk ; while
the bays of Filey and Bridlington are excavated prin-
cipally in diluvial clays and sands. Vast areas of clays
underlay the wide levels of the Fens of Lincolnshire
and Cambridgeshire, which mark the ancient indraught
VOL. II. Y
322 A TREATISE ON GEOLOGY CHAP. XI.
of the North Sea; while the chalk of Norfolk and Kent
makes hold projections on each side of the tertiary clays
and sands of the Basin of London. Here, however, we
have again to notice the influence of the position of the
strata; for the Thames passes to the sea in a synclinal
trough, and thus its deep indentation is readily explained.
The Straits of Dover and Boulogne depend for their nar-
rowness on the anticlinal ridge of the Weal den ; parallel
to this is the anticlinal fault of the Isle of Wight and
Purbeck, by which these districts are extended east and
west ; and between the two runs the Hampshire trough,
which is now filled in the deepest parts by the channel
of the Solent.
It appears unnecessary to extend these remarks on
the outline of the land and sea, since every where the
same principles give equally certain explanations both
on a large and small scale. We may therefore turn to
consider the interior of a country like England.
Undulations of the Interior.
Geographers have noticed, as a fact of frequent
occurrence, the prevalence of bold coasts and high land
on the western sides of continents and islands, and of
sandy shores and low countries on their eastern bound-
aries. This is true with regard to a large part of the
American continent, England, Norway, Hindostan, and
other districts ; and it may hereafter be found of im-
portance in geological theory. In England, the exist-
ing information on the distribution of strata, and lines
of subterranean movement, is quite sufficient to give the
clue to this peculiarity of structure, and at the same
time to explain the exceptions to the general rule.
With the exception of the anticlinal ridges of the
Isle of Wight and the Wealden, a swelling under the
Yorkshire oolites, and the great faults of the valley of
the Tyne, no subterranean disturbance of great impor-
tance breaks the easy slope of the secondary strata in
the eastern parts of England. But on the western
CHAP. XI. VIEWS AND APPLICATIONS.
boundary of the island, a very different scene appears.
Bold anticlinal axes, and other dislocations without
number, undulate the stratification of Cornwall and
Devon, South and North Wales, the western sides of
Derbyshire, Yorkshire, and the almost insulated group
of the Cumbrian mountains ; and these include the points
of greatest elevation, and the ridges of boldest rocks,
both inland and on the sea coast, which England has to
boast.
Most of the great dislocations here noticed occurred
in early geological periods, and besides the local eleva-
tions which they have imparted to the western districts
of England, they had the effect of entirely changing
the bed of the sea, in such a manner as to cause general
slopes to the eastward, which were not reversed during
the whole subsequent periods of geology. Hence arises
another peculiarity in physical geography, which has
been long known to inquirers and surveyors, viz. the
alternation of ridges and hollows, on lines directed
north-eastward and south-westward through a large
portion of the secondary as well as primary districts of
England.
To describe instances of so well known a truth would
be very unnecessary; but we may remark in North
Wales the alternation of the Menai Straits, the Snow-
donian Chain, the Bala Vale, and the Berwyn Moun-
tains, all ranging north-east and south-west, as very
illustrative of the fact and the explanation. In South
Wales Mr. Murchison has traced the same connection
of anticlinal axes and hilly ground ; the great hollow
which crosses Devonshire from west to east, is formed
in a trough of the strata between the Dartmoor and
Exmoor ridges ; Mendip is an anticlinal rock ranging
east and west ; Malvern, a narrow chain passing north
and south ; Charnwood Forest runs west north-west.
The effect of these various elevations on the ancient
strata in the western parts of England, is sensible in the
very general declivity to the east or south-east which
belongs to the carboniferous, oolitic, and cretaceous
Y 2
324> A TREATISE ON GEOLOGY. CHAP. XI.
strata. And as among these the materials present un-
equal resistance to the atmospheric agents of destruction,
and waste unequally, long chains of limestone hills
alternate with wide parallel vales of clay, and render a
journey from London to Bath, Worcester, or Newark, a
succession of similar vales and hills. One tertiary vale,
one cretaceous ridge, one or more vales in clay, alter-
nating with as many ridges of oolite, are crossed on each
of these roads in the same order of succession. These
parallel vales are frequently, though not always, filled
for parts of their length by great rivers, like the Isis or
the Thames ; and investigation easily shows that the
hollows are not the result of fluviatile action, but of some
earlier and greater force of nature, which excavated the
wide vale in which the river now finds a narrow channel.
There can be little room for doubt that the currents and
tides of the sea, in action at the time of the elevation
of the land from its ancient level, were the instruments
by which the softer strata were worn away, and thus,
with a considerable approach to accuracy, we may assert,
in general terms, that by direct and indirect effects, the
leading features of the earthy surface are distinctly re-
ferrible to the force of interior heat.
Scenery.
The charm of rural landscapes, the romantic pleasure
of mountain prospects, and sequestered dells and water-
falls, is but feebly appreciated by those who, unacquainted
with the principles of art, have not learned to perceive
in all the works of nature the operation of law, and to
trace in all the diurnal aspect of creation the effect of
many preceding revolutions. The greater features of
physical geography are explained by subterranean move-
ments and their consequences ; the minuter proportions,
which are the proper province of pictorial art, are partly
due to other circumstances. The richness or desolation
of countries, besides the obvious influence of elevation
and climate, proximity to the sea, or snowy mountains,
CHAP. XI. VIEWS AND APPLICATIONS. 325
is not a little dependent on the chemical quality, and
texture of the subjacent rocks, for these, by their de-
composition, have furnished, in general, the soil ; which
does not indeed feed, but is a channel of nutrition for
the vegetable world.
Let any one compare, for example, the glorious trees
and rich pastures of the vales of Severn and Avon,
situated on lias and red marl, with the stunted oaks
and poor herbage of a great part of the broad vale of
York, which is filled by gravel drifted upon the same
red marls and lias ; or, in the vale cf York itself,
contrast the finely wooded and fertile region about
Thirsk, where these strata come to the day, with the
naked plains between North Allerton and the Tees,
and he will see the importance of attending to geology
in estimating the agricultural condition of a country.
Through a great part of England, the various ranges
of secondary limestones have characters of outline and
surface by which they may be fully represented in a
painting. Whoever has admired the Sussex Downs, or
Yorkshire Wolds, will seldom fail to recognise, in other
situations, those broad, rounded, and gracefully swelling
hills melting into gentle hollows, that smooth short
herbage, and that pleasing though dry and treeless
surface, which belongs to the chalk of most parts of
England. Different from these, in many respects, are
the tracts of the Gloucestershire and Oxfordshire oo-
lites, with their tabular summits and intervening woody
vales of clay, and the older limestones below the coal
wear other and bolder aspects, and all are different
from the intersecting outlines and rugged surfaces of
the primary strata of slate, mica schist, and gneiss.*
But besides these general characters of district sce-
nery, it is a familiar truth that every different kind of
rock has peculiar forms in the mass, particular ar-
rangements of the stiuctural lines, and even modes of
wasting, and vegetable accompaniments, which are often
* See on this subject the remarks which accompany each system of strata
in Vol. L
Y 3
S2() A TREATISE ON GEOLOGY. CHAP. XI.
attended to as pictorial effects, but which furnish to
the geologist the further enjoyment which arises from
inquiry into the cause. By a knowledge of the divi-
sional structures of rocks*, a geologist can very fre-
quently determine at a distance the nature of a rock,
distinguish basalt from slate, limestone from sandstone ;
and thus his sphere of gratification from scenery is
enlarged, his perception of the minuter shades and
lights of the landscape become more vivid, and his
memory of pa&t combinations more enduring.
It is needless to pursue this subject. Who has ever
imagined that the ruins of a rich monastic edifice are
less admired by the architect who strives to discover
the principles of its construction and the theory of its
decoration, or the antiquarian who searches the records
of its overthrow, than by those who merely gaze on
these masterpieces of the building art, without striving
to penetrate the mystery which time and the ravages of
man have gathered round the ancient aisles and turrets ?
Geologists are, as Cuvier felt and said, " antiquaries of
a new order," and their enjoyment of the fair scenes
of the earth which typify the will of their Creator,
partakes of the same high and solemn character which
belongs to the intelligent contemplation of the noblest
monuments of ancient art.
ECONOMICAL APPLICATIONS OF GEOLOGY.
Agriculture.
Agriculture, which, of all branches of human in
dustry, seems most directly dependent on the qualities
of soil and substrata, has been hitherto very little
benefited by the progress of geological science. Perhaps
the expectations of those speculative farmers who desire
to turn to good account the discoveries of botanical
* See VoL I. p. 62,
CHAP. XI. VIEWS AND APPLICATIONS. 327
physiology, vegetable chemistry, and geology, require
some better direction to attainable objects, than bo-
tanists, chemists, or geologists, are likely to furnish.
That plants, by growing frequently on the same spot,
poison the soil for themselves, though not for other
plants, appears a reasonable generalization of well-
known facts : that certain successions of crops are best
fitted for particular soils, is incompletely known by
experience, and may be turned to a profitable account
by the union of botanical and chemical research.
The chemical quality of soils, to judge from a super-
ficial examination, appears to be of real importance.
Why else, amidst the heather which covers thousands
of acres in the moorlands of the north of England,
should there appear not one plant of Dutch clover,
though upon the removal of the heath, and the appli-
cation of quick lime, this plant springs up in abun-
dance ? Why else does Cistus belianthemum love the
calcareous soil, the oak delight in stiff clay, the birch
and larch flourish on barren sand ? Yet, to all the
conclusions drawn from facts of this nature, exceptions
arise, and the relation of the soil to moisture appears
quite as fertile and general a source of difference of
vegetation and productiveness, as any peculiarity of
chemical constitution. We once took the pains to
notice every species of plant growing on a purely cal-
careous soil 2000 feet above the sea, on Cam fell in
Yorkshire, and among them all, it appeared that not
one was commonly supposed peculiar to limestone.
It appears to us that it is chiefly by their various
power of conducting moisture from the surface that
rocks of different kinds influence the soil above them ;
and this is a circumstance which is sometimes interesting
to the farmer, for another reason. It is. not doubtful
that in many cases there is a possibility of draining
land which is underlaid at some small depth by a
jointed calcareous rock, just as by sinking a few feet in
a mining country, through clay to limestone, the whole
Y 4
328 A TREATISE ON GEOLOGY. CHAP. XI.
drainage of a mine may often be passed downwards,
through the natural channels of the rocks.
One of the most obvious sources of advantage to
the farmer from an acquaintance with the distribution
of mineral masses, is the facility with which in many
instances the injurious effect of small springs coming
to the surface may be obviated. The theory of the
earth's internal drainage is so simple, that every man
of common sense would be able to drain his lands upon
sure principles, or else to know precisely why it cannot
be drained, if he were to become so much of a geo-
logist, as to learn what rocks existed under his land, at
what depth, and in what positions. Springs never
issue from stratified masses, except from reservoirs
some how produced in jointed rocks — and at the level
of the overflow of these subterranean cavities. Faults
in the strata very frequently limit these reservoirs, and
determine the points of efflux of the water. Let those
faults be ascertained, or the edge of the jointed rock
be found, the cure of the evil is immediate. But some
geological information is needed here ; and landed pro-
prietors, who think it less troublesome to employ an
agent than to direct such a simple operation, may at
least profit by this hint, and choose an agent who knows
something of the rocks he is to drain.
The same knowledge which guides to a right general
method of draining, conducts to a clear and almost
certain method of finding water by wells, and enables
an engineer to predict with much probability, whether,
at what depth, in what quantity, and even of what
quality, water will be found. Why is water so gene-
rally found by deep wells at London and Paris ? Why
is it often so abundant in these wells ? Why is it
often of pure quality, though in the descent small
quantities of impure water are frequently penetrated ?
Because under both these capitals, the open, jointed,
purely calcareous chalk strata, in great thickness, con-
verge with opposite dips, and collect the water, which,
upon the perforation of the superincumbent masses of
CHAP. XI. VIEWS AND APPLICATIONS. 329
clay, &c., rises with much force, and continues to flow,
unless drained by other of these "Artesian " wells. This
method of obtaining water is now commonly known,
but deserves to be far more extensively practised in
agricultural districts, where natural springs of pure
water are rare blessings.
Another thing, probably of importance to agricul-
turists, is the discovery of substances at small depths
which, if brought to the surface, would enrich, by a
suitable mixture, the soil of their fields. This is very
strongly insisted on by sir H. Davy in his Essays, and
considering how easy a thing it is for a landowner to
ascertain positively the series of strata in his estate,
it is somewhat marvellous that so few cases can be
quoted, except that of sir John Johnstone, hart, of
Hackness, near Scarborough, in which this easy work
has been performed.
Finally, in experiments for the introduction of new
systems and modes of management, with respect to
cattle and crops, it will be of great consequence to take
notice of the qualities of the soil, substrata and water,
for these undoubtedly exercise a real and perhaps deci-
sive influence over the result.
Construction of Roads, Railways, Canals, $c.
In planning and executing public works, such as
canals, railroads, and common roads, a knowledge of the
rocky structure of a country ought to be considered
indispensable, and the boring rod is in continual requi-
sition. But the engineer, who is also a geologist, will
find it a surer method of research, to trace the systems
of strata across miles of country, than to merely feel by
the chisel at so many points of a line. To fix the line
of a road is the problem, and a knowledge of the geo-
logical structure of the country on a large scale is one
of the grand data for a true solution of it. When the
line is fixed, the practical man will need minuter in-
330 A TREATISE ON GEOLOGY. CHAP. XI.
formation than geology can give, but there will be
many occasions for the exercise of this science where
tunnels, and deep cuttings often show loose sands and
other formidable things unexplored by the boring-rod,
though not beyond the expectation of a geologist.
The choice of a line of country for canals may often
be rightly governed, by attending to the series of strata,
and the dislocations to which they are subjected. For
thus the summit levels may often be conducted in argil-
laceous tracts, or in synclinal hollows, where not only
no waste of water need be dreaded, but by suitable trials
fresh supplies may be had at moderate depths from the
surface.
Building Materials.
The assistance which Geology can render to the
architect in the choice of building materials is consider-
able, but not easily defined. Indeed, it is rather because
a geologist of experience has necessarily directed his
attention to the various degrees of resistance to decay,
which rocks of different kinds present, than by any
deductions from pure geology, that he can .materially aid
researches in this respect. There is no doubt that very
great benefit would result to the building art, if the
whole kingdom were surveyed by geologists and archi-
tects, for the purpose of determining generally the oc-
currence and qualities of stone suited for great and
costly edifices. In such a survey it would be proper to
inquire how far the indications of durability presented
in natural sections were corroborated by the evidence of
ancient buildings ; and a complete investigation would
require further the examination of the chemical quality,
mechanical strength, thickness, and other circumstances
of the several beds of a rock.
The importance of this caution will be evident when
we state that Roman sculptures remain at Bath and
York, executed in oolite, magnesian limestone, and mill-
stone grit, which yet retain all their characteristic per-
fection, while other Bath oolite, magnesian limestone,
CHAP. XT. VIEWS AND APPLICATIONS. 531
and gritstone have perished in churches and houses in
less than 100 years. The reason is, that the different
beds of a rock are of very unequal value, and here the
geologist or scientific mason will have their claim to at-
tention.
As certain trees will bear the ocean air even in our
unfavourable climate and others not, so with stone ; it
is not equally durable in all situations, but yields
variously and unequally to carbonic acid, smoke, damp-
ness, and salt vapours. Most wisely, therefore, has. a
commission been issued to determine, in the case of the
new houses of parliament, the best material for this
national work, and we trust that this symptom of re-
viving attention to the importance of scientific advice
in guiding the skill of our workmen, may be the har-
binger of a more frequent reference of questions unsuited
for the decision of statesmen, to those persons who have,
by a life of study, qualified themselves to give opinions
useful to their country.
Coal and other Mineral Products.
Two things have been established by geological re-
search in opposition to the contracted " experience " of
colliers, and it is difficult to say which is most im-
portant. First, it is perfectly ascertained that coal is
limited in Europe and America, almost absolutely, to
one portion of the series of strata. Secondly, it is de-
monstrated, that coal occurs in abundance and of excel-
lent quality beneath large tracts of country where few
or no indications of its existence appear at the surface.
In the practical working of coal which has been dis-
covered, geological principles may often be useful in
determining its probable extent, but their main value is
in the discovery of coal in new situations, and the arrest-
ing of costly and fruitless trials for coal, where it cannot
be found.
In both of these points of view, geology appears in
that favourable light when, compared with mere " prac-
332 A TREATISE ON GEOLOGY. CHAP. XI.
deal knowledge," that science always occupies when com-
pared to those branches of experience which it includes.
A landowner in one of the midland counties, as North-
amptonshire or Oxfordshire, where fuel is dear, is natu-
rally anxious to " discover " coal, and being completely
ignorant of geology, or blindly credulous in what is
called " practical " knowledge, sends for a workman, or
ff borer, " from some coal district, to " find " the coal.
A workman from some distant establishment is often
preferred, and great alarm is felt lest the opinion of
this oracle should be unfairly biassed by the influence
of the nearest coal proprietors. Such a workman might
be able to give in his own country a right opinion as to
the cheapest mode of working a bed of coal, the best
mode of walling a pit, and, perhaps, even the proper
position for a bore-hole. But when he is carried to the
oolites and Has of Northamptonshire and Oxfordshire, he
is expected to decide on a question of even national im-
portance, and to influence a landowner, perhaps already
impoverished, in the desperate venture of searching for
coal at the cost of many thousand pounds, merely because
the ditches yield blue clay (which the collier calls " me-
tal") or a bit of jet ! At the same time the youth of
Oxford and Cambridge receive accurate and admirable
instructions from the lips of gifted men ; lectures are
given in every philosophical institution ; geological maps
and books are offered in every window ; and all these
various modes of scientific caution are urged in vain: the
pit is sunk, and the landowner is ruined, merely by the
honest error of a workman set to a task beyond his ex-
perience. Is this a harsh picture ? Let the recollection of
old trials at Bruton in Somerset, and Bagley Wood near
Oxford, the more recent folly at Northampton, and the
failures of Kirkham and many other localities in the
north of England, serve as a warning to inconsiderate
persons in other districts. There may not always be
found a geologist, willing to turn away from his
delightful studies, to avert the ruin which can only fall
on those who disregard the plainest truths of geology.
CHAP. XI. VIEWS AXD APPLICATIONS.
In countries wnere coal has long been worked, almost
every district is explored at least nearly to its boundaries.
This is at present the case in England — indeed, generally
in Europe ; and, consequently, it may be thought that
the time has gone by for the geologist to be of service,
and the future is to be intrusted to coal viewers and
workmen. When coal viewers become geologists, (and
this is now very generally the case with men of emi-
nence in that profession), the question of the future
extension of our coalfields will be in safe hands ; but in
all cases, and at all times, this is a geological question.
Only sixteen years ago, (it is in our own memory,) a
valuable estate in Durham was pronounced to be devoid
of coal, " because it was situated on the magnesian lime-
stone," and might have been sold under this opinion, but
that a geologist of celebrity, Dr. William Smith, showed
the falsity of the reasoning, reported favourably of the
probability of finding good coal in abundance beneath
the property, and advised the proprietor to work it.
That estate is now the centre of a rich and well explored
mining tract, all situated beneath the magnesian limestone,
and this result was the fruit of scientific geology, not
"practical" coal- viewing, though the professional mine-
agents of the North of England are DOW employed in
extending its benefits.
This fact is one of a large claps; and it more particu-
larly deserves attention, because the magnesian limestone
overlying the coal of Durham is united in one system
of rocks with the red sandstones of Cheshire and Staf-
fordshire, beneath which, as beneath the magnesian lime-
stone of Durham, the coal appears to dip, and the red
marls of Somersetshire, under which it is largely
worked. Is there a coalfield below the great Cheshire
plain ?
If this question is to be answered without the boring-
rod, none but geologists can venture to speak ; nor of these,
any but those who have studied the peculiar character
and relations of the coalfields which border the red
sandstone plain in Lancashire, Shropshire, Staffordshire,
334 A TREATISE ON GEOLOGY. CHAF. XI.
and Flintshire ; or have ascertained the truth in ana-
logous situations, such as the district bordering the
coalfields of Leicestershire and Warwickshire.
Perhaps there is a coalfield beneath parts of the
Cheshire plain. This may be plausibly argued, from
the fact that all the bordering coalfields dip beneath
that plain ; and the probability of the inference is greatly
strengthened by the circumstance (first ascertained by
the author of this volume) that the limestone beds
which lie in the upper part of the Lancashire coal
tract are identical with those previously described by
Mr. Murchison from the coalfield of Lebotwood, near
Shrewsbury. This limestone is of a peculiar quality,
yields peculiar fossils, and lies in connection with coal-
beds yielding peculiar plants, at both these distant
points ; circumstances which go far to prove, not perhaps
the entire contiguity of the rock from point to point, but
its contemporaneous deposition in one and the same
coal basin. It is, therefore, probable that that coal basin
is really continuous under parts of the Cheshire plain of
red sandstone. Whether it will be worth while to sink
for this coal is not a question for geology to answer ;
but if the attempt is to be made, geological investigation
alone can indicate the proper situation for the trial.
Geologists must not be deterred, by the neglect which
too frequently has attended their recommendations,
from calling on " practical men " to consider and make
profitable use of their discoveries and reasonings. Few
of their important announcements have really been un-
productive; the seed which they have sown, though
favoured with little cultivation, has, in the end, grown
up to be fruitful of good.
• If any one should say geology makes no such pro-
phetic announcements — our collieries are extended
without the aid of science, our iron works are supplied
with the raw material by the experience of the work-
men, and our gold comes by accidental discovery — let
him be reminded of the well-known fact that, had
geology been believed, the date of the opening of our
CHAP. XI. VIEWS AND APPLICATIONS. 335
greatest northern collieries would have been earlier by
several years; let him be assured, that had practical
application kept equal pace with geological theory, we
should not have been startled, in 1851, by the discovery
of immense bands of ironstone which were measured
and described more than twenty years before ; and let
it be added, that because geology has of late years made
itself heard, even from a distance, and because the prin-
ciples of this science have been kept in view in the
field, gold will in future be looked for in the places
where it is likely to be found. A few words respecting
the ironstone and the gold.
The lias shales of the Yorkshire coast are of a greater
thickness, and contain a greater variety of valuable
substances, than those of the south of England. Be-
sides the jet, cement stone, and alum shale, there are
bands of ironstone, sometimes amounting to sixteen feet
in thickness, of quality equal to the average of the car-
bonates of a coal district. They lie toward the upper
part of the lias deposits, above a certain series of sandy
beds with peculiar and characteristic fossils, and below
certain other beds extensively worked for alum. The
stone can be obtained at so small a cost, that about
2.9. 6d. a ton is a remunerating price to the adventurer.
It is in such, immense quantity that an acre will yield
from 20,000 to 50,000 tons, and it may be opened in a
line of coast and aline of inland cliffs, at many points,
and for very many miles of outcrop. Railways are
now laid to it, furnaces are built near it, and hundreds
of thousands of tons of it are set in motion annually
from the hills of Cleveland. This great activity is ot
sudden growth, one of the wonders of 1851. It was
said, what was geology doing, that this vast treasure of
iron has been left for the practical man to discover ?
We reply, this ironstone was measured, its exact geolo-
gical place marked, and its prominent localities de-
signated, in printed type and coloured sections, more
than twenty years previously ! *
* Illustrations of the Geology of the Yorkshire Coast (1829.). See
336 A TREATISE ON GEOLOGY. CHAP. XI.
And, in regard to gold, the case is stronger. Con-
stantly brilliant in its natural aspect, occurring in many
river beds, easily fusible, remarkably ductile, and ex-
empt from rust, it was known and valued from the
earliest ages, and was probably the very first of all
metals tried in the fire and moulded by the hammer.
Gold has been gathered in every quarter of the globe,
in every age known to history and tradition. Scythia
and India — the Tagus and the Po — the Hebrus, the
Pactolus, and the Ganges — gave their gold to Rome,
as they had given to earlier masters. Yet not all this
immense experience, sharpened by the " auri sacra
fames," produced philosophical views of those co-ordi-
nate phenomena by which the presence of gold could be
predicated in new situations. It was simply a matter
of trial and error. At last it came under the domain of
geology, and was treated as a geological problem. The
usual consequence followed — experience became science,
and further discoveries were anticipated by theory.
For not only were observations having the character
of scientific generalization published many years before
the late discoveries, but public attention was distinctly
called to their practical application, and a certain country
was definitely indicated as likely to be highly produc-
tive of gold, and worthy to be explored for that metal.
This was done by Sir Roderick Murchison — one who
might well be excused, by the variety and importance
of his explorations, if he had left wholly to others the
care of pointing out the economical application of them.
But, after surveying the Ural, and publishing, in
1844, his critical observations on the old mines of that
" hyperborean " district, he took several occasions pub-
licly to declare the general views to which they had con-
ducted him ; made a special comparison of the Ural
with the eastern chain of Australia (1844) ; invited the
Cornish miners to emigrate to New South Wales and
dig for gold on the flanks of the " Australian Cordillera,"
also an earlier description of these ironstones in Young and Bird's Survey
(1822).
CHAP. XI. VIEWS AND APPLICATIONS. 337
where gold had been found in small quantity, and in
which, from its similarity to the Ural, he anticipated
that it would certainly be found in abundance (1846) ;
and presented a note on the subject to the British
Colonial Minister (1848).*
Facts like these are unanswerable ; but do they not
teach us that it is of the utmost importance to connect
more closely the theory and the practice, the intellect
and the hand ; to place the treasures of science within
the grasp of experience ; to bring together the Murchi-
sons and the Hargraves, the men of thought and the
men of action, so that right ideas may become fruitful
deeds, and patient labour be encouraged to under-
take enterprises which science shows to be of good
omen. The lectures which are now in course of de-
livery on Australian gold at the Museum of Practical
Geology, are a step in this direction. A Mining School
is established there. If it produce the fruits which are
expected from such an institution, many benefits will
accrue to humanity ; knowledge will be diffused among
classes who know how to value it ; industry will be
better guided and better rewarded ; our miners will
not breathe the slow poison of mephitic air, nor perish
by hundreds through the explosion of inflammable gas.
It appears unnecessary to extend these proofs of the
value of geological principles to the agricultural and
mercantile interests of a nation. One of the most ob-
viously useful applications of science is in the colonies
sent forth by a commercial people; and perhaps no
more important service could be rendered to Australia
or Canada, than by accurate geological surveys, such as
are now proceeding steadily in several of the United
States of America.t
This is, however, not the place to advocate plans
* See Trans. Roy. Geog. Soc., xiv. p. xcix. Trans. Roy. Geol. Soc.
of Cornwall (1845.), p. 324., and Rep. of Brit. Assoc. 1S49.
t This passase is left as it was written some years ago, for the purpose
of remarking that the appointments which it suggested are now made —
Mr. Logan is surveying Canada, and Mr. Stutchbury is engaged in
Australia.
VOL. II. Z
338 A TREATISE ON GEOLOGY. CHAP. XI.
of this nature ; nor can it be expected that recommend-
ations for colonial advantage will be much regarded
in times when even the laborious surveys of the geology
of England have been, tilfr lately, left entirely to the
generous self-devotion of individuals. It cannot be
expected that costly works, like that on the " Silurian
System " and some others we could name, produced at
private expense, should be numerous ; yet, except on
the scale of illustration adopted in these volumes, they
are inadequate for their object, and unsatisfactory even
to their authors. One step has, however, at length been
taken : the Ordnance Survey has been rendered in some
degree serviceable to geology, both in England and Ire-
land ; and the officers who conduct this noble work are
both able and desirous to make it a geological as well
as geographical monument.
Let this truly national labour be completed ; let the
Mining Districts be illustrated by maps on a larger scale ;
let a system be introduced by which invaluable mining
records, now perishing in the unsafe custody of indivi-
duals, shall be preserved for the benefit of this and
future times : the public will reap incalculable advantage,
and geologists will advance nearer to completeness the
bases of their speculations. This is all, or nearly all,
the encouragement which Geology needs from a govern-
ment; or rather, these are the most obvious modes of
giving to the community a foretaste of the benefits
which this science is destined to bestow. Strong in its
fundamental facts, corroborated in its inferences by the
progress of all collateral branches of the study of Crea-
tion, linked in union with the highest forms of scientific
truth, and grasping at objects full of the noblest interest
for man, and the most reverential thoughts toward the
Maker and Preserver of the Universe, nothing but
the general decay of the human intellect will permit
Geology to languish, till the Natural History of the
ANCIENT EARTH be known to its MODERN occupier MAN.
INDEX.
A.1
AAR, glacier of the, its extent, ii.
13.
Abberley Hills, position of strata
in the, i. 39. Fossils of, 142.
Silurian strata of, 149.
Aberystwith, cleavage of rocks in,
i. 68.
Acosta, M., on waves, ii. 242.
Acunha, Tristan d', extinct vol-
cano of, ii. 231.
Adriatic, accession of new land on
the coasts of, ii. 28. 34.
JEgean Sea, its depth, divided into
eight zones, i. 337. Various spe-
cies of mollusca found in, 338, et
seq,
Africa, volcanos of, ii. 231.
Agassiz, M., his discoveries in fossil
zoology, i. 86, 87, 88. 90, 91. 96.
157. 176. 208. 233. 270. ii. 47.
Agnano, Lago, once a volcanic
crater, ii. 220.
Agriculture, successful pursuit of,
dependent on a knowledge of
f geology, ii. 326.
Aix, freshwater deposits of, ii. 43.
Insects found in, 44.
Aix-la-Chapelle, analysis of its mi-
neral waters, ii. 256.
Albano, Mount, extinct volcano of,
ii. 226.
Aldstone Moor, " flats" of, ii. 166.
Lead mines of, 176. Change of
the " hade " of the veins of, 191.
Aleutian Isles, reference to vol-
canic; phenomena in connection
with the, ii. 229.
Alhama, freshwater beds of, animal
deposits of the, ii. 44.
Alluvium. See Post -tertiary
Strata.
Alps, dip of stratified rocks in, i.
37. Position of strata in, 39.
Hypozoic strata predominant in,
58. Chalk little seen about or
beyond, 58. Of Savoy, alteration
of lias clays of, 68. An example
of the granitic basis of the
earth's crust, 108.
Altai Mountains, ii. 228.
Alte Hoffnung Gottes, temperature
of the mine of, ii. 271.
Alum Bay, I. of Wight, sand rocks
of, i. 250. 254.
Alumina, proportion of oxygen in,
Ambleside, mottled clay slate
found at, 1. 126.
America, North, fossils of, i. 143.
Hall's subdivision of rocks of,
143. Cretaceous system, how
developed in, 242. Volcanos of,
ii. 229.
America, South, volcanos of, ii.
229. Internal sea of melted rock
below a large part of, 247.
Ammonites, table of subgenera of,
Amorphous masses under strata,
ii. 108.
Amphitherium, new name for fossil
remains of marsupials, i. 96.
Andes, their elevation attributed
to volcanic action, ii. 208. Vol-
canos of the, 230.
Animal life, zero of, i. 339.
Animals, organic remains of, i. 69.
Articulated, 84. Tables of, found
in post-tertiary strata, 304. See
Organic Remains.
"Anticlinal, the Great Merio-
neth," of Sedgwick, i. 130.
Anticlinal Lines, their direction,
ii. 292. See Strata.
Antrim, basaltic formation of, ii.
96. 128.
Apennines, dip of stratified rocks
in, i. 37.
Arachnida not common as fossils,
i. 85.
Arago, M., his experiments on
heat, ii. 267, et seq. 308. On the
temperature of Artesian wells,
276.
Ararat, Mount, volcanic character
of, ii. 227.
z 2
340
INDEX.
Arbroath, Scotland, fossil remains
offish found at. i. 86.
Archipelago, the Dangerous, coral
islands of the, i. 331.
Archipelago, Greek, volcanos of
the, ii. 222.
Arctic regions, once covered by
plants of tropical lands, i. 226.
Various theories explanatory of
the origin of erratic blocks, ice-
bergs, glaciers, &c. of, 281—298.
Their influence on temperature
of the earth, ii. 310/
Ardennes, dip of stratified rocks
from, i. 37.
Argillaceous beds, three types of,
i. 246
Argillaceous slaty rocks of Corn-
wall altered by their proximity
to granite, ii. 142.
Arno, Val d', animal remains found
in, ii. 48.
Arran, granitic veins in the clay
slates of, i. 109. 134. Granite
found in gneiss of, 121. Remark-
able section of carboniferous sys-
tem in, 167. Igneous rocks of,
184. ii. 145.
Artesian wells, experiments on
their temperature, ii. 276.
Articulated animals, their re-
mains, i. 85. See Organic He-
mains.
Asaphi, where found, i. 147.
Ascension Isle, volcanic nature of,
ii. 231.
Ashby-de-la-Zouch, coal district
of, "i. 181.
Ashes of volcanos, dispersion of,
ii. 213. 235.
Ashgill Force, i. 177.
Asia, volcanos of, ii. 227.
Asphaltum, in Trinidad, ii. 230.
Atlantic Ocean, tertianes border-
ing on, i. 262. Its depth, how
ascertained, ii. 288.
Atlas, Mount, basaltic eruptions
of, ii. 231 .
Atmosphere, temperature of the,
its influence on the earth, ii.
264.
Augite, how found, ii. 84.
Australia, volcanic action formerly
exhibited in. ii. 232. Its survey
recommended, 337. Sir R. Mur-
chison's notes of its gold regions,
337, et seq.
Auvergne, dip of stratified rocks
from, i. 37. Bones in, covered by
volcanic scoria?, 47. Allusions
to its extinct volcanos, 278. ii.
206,207.216.
Avalanche, its origin and descent
explained, ii. 13.
Avernus, Lake, once a volcanic
crater, ii. 220.
Axis, anticlinal, the term ex-
plained, i. 39. See Anticlinal
Lines.
Axis, synclinal, its explanation, i.
39.
Aymestry, abundance of zoophyta
in bands of, i. 75,76. Limestones
of, 136. Corals found in rocks
of, 138.
Azores, rise of islands in the, ii.
222. 237.
B.
Bagshot sands, i. 255.
Bakewell waters, analysis of, ii. 255.
Bakur, its celebrated "'field of fire,"
ii. 227.
Bala, limestone of, i. 124. Fossils
of, 130.
Balachulish, quartz rock of, its
stratification, i. 115.
Bald, Mr., his experiments on the
temperature of coal mines, ii. 273.
Bal&na, fossil remains of, i. 98.
Baltic and Black Seas, sandy de-
posits which lie between, i. 262.
Relation of phenomena of raised
beaches to the gradual subsidence
of the level of, 324.
Bangor, black shales of, i. 130.
Banks of sand, clay, &c., their
origin accounted for, i. 341.
Banwell cave, i. 311. 315.
Barmouth sandstones, i. 130.
Barrande, M., reference to his geo-
logical researches, i. 143. 147.
Barrowdale, clay slate of, i. 129.
Bath waters, their analysis, ii. 255.
Barton clay, composition of, i. 254.
Basalt, proportion of oxygen, i. 25.
Divided prisms of, in Stafta and
the Giant's Causeway, 63. Mr.
Watt's experiments on the amor-
phous, of Rowley, i. 185. ii.73.
Analyses of, 84. 95- Of Hasen-
berg, 95. Of Staffa, 95.
Basin of Paris, convergence of stra-
tified rocks at, i. 37.
Batavia, coal fields of, i. 183i
Beaches, raised, phenomena of, i.
321. Theories of Messrs. Brong-
niart and Prestwich accounting
for, 321,322.
Beaumont, Elie de, on primary
strata, i. 150. His observations
on changes of the earth's crust,
153. 248. His name for the upper
term of the tertiary strata, 258.
Attributes elevation of Corsica
and Sardinia to disturbances
INDEX.
341
during tertiary period, 277. On
the oolitic strata of Tarentaise,
144. On volcanos, 205. On
direction of anticlinal lines, ii.
292. On ordinary and critical
action of the earth, 301 . On dis-
locations of molasse, 295.
Beche, Sir H. de la, on the fissures
of rocks of Cornwall, i. 65. Ord-
nance maps of, 129. On the fos-
sils of Bala, 130. His analysis of
minerals found in igneous pro-
ducts, ii. 91, etseq. His survey
of Devon and Cornwall, 105. On
the altered rock of Dartmoor,
143. On mineral springs, 259.
Beddgelert, valley of, i. 134.
Bellevue, M. de, his designation of
the phenomena of raised beaches,
i. 324. On temperature of Arte-
sian wells, ii. 276.
Ben Cruachan, an example of the
granitic basis of the crust of the
earth, i. 108. Porphyritic dykes
at, 121.
Ben Nevis, porphyry discovered in,
i. 121. Us height, i"i.26o. Not per-
petually covered with snow, 265.
Bengal, Bay of, amount of annual
discharge of sediment into, ii.
34.
Bermudas. Islands of, their origin
compared with that of limestone
corals of Dudley and \Venlock, i.
148. Coral reefs of, 330. Thought
to resemble leithakalk of Tran-
sylvania, i. 253.
Berwyn Mountains, dip of strata at
the, i. 38.
Bex salt mines, their temperature,
ii. 272.
Bielbecks, excavations at, and dis-
covery of animal remains by Mr.
W. V. Harcourt, ii. 50.
Bies Bosch, encroachments of the
sea on, ii. 33.
Binstead quarries, animal remains
found in, ii. 42.
Birds, fossil remains of, i. 95. See
Organic Remains.
Bize, bone caves of, remains of
Man supposed to be found in,
i. 100.
Black Forest, abundance of sali-
ferous deposits in, i. 207.
Black Hill, Jamaica, its origin vol-
canic, ii. 230.
Blainville, De, his researches in
fossil zoology, i. 96.
Blumenbach, his theory accounting
for animal remains found in caves,
i.312.
Boase, Dr., on the vegetable de-
posits of Mount's Bay, ii. 61. On
the mineral veins of Cornwall,
177. 189.
Bognor beds, their composition, i.
255.
Bogs of Ireland, their situation and
thickness, ii. 63, 64.
Bohl, valley of the, ii. 214.
Bolca, Monte, fossil deposits of, i.
87«
Borelli, his account of the destruc-
tion of Catania, ii. 211.
Bornholm, organic remains of cy-
cadece and equiseta in the rocks
of, i. 72. De Luc's account of,
ii. 62.
Borset, mineral waters of, their
analysis, ii. 256.
Boulder formation, i. 281. Specu-
lations concerning the origin of,
281—294.
Bourbon; Isle of, ii. 231.
Brachiopoda, shells of, in the
Welsh mountains, i. 72.
Bracklesham sands, their composi-
tion, i. 255.
Brahmaputra, amount of its annual
discharge of sediment, ii. 34.
Bredon Hill, i. 230.
Breislac, M., his computation of
the lava current of Vesuvius, ii.
211.
Brewster, Sir D., on temperature,
ii. 264.
Bridgenorth, remarkable row of
terraces at, ii. 7.
" Bridgwater Treatise," Dr. Buck-
land's, reference to, i.89.
Brine springs, analysis of, i. 205.
Brinham Rocks, ii. 10.
Bristol Hot Wells,1, analysis of the
waters of, ii. 255.
Brittany, stratified rocks of, their
dip, i. 37. Mines of, ii. 161.
Temperature of the mines of,
271.
Britishlsles, once submerged by the
sea, i. 148. Thermal springs of,
ii. 255. Scenery of, 325.
Broderip, Mr., reference to, i. 96.
Brongniart,M.Adolphe, his table of
living and extinct plants, i. 73.
His theory accounting for the
earth's early productiveness, 187.
His theory of the origin of coal,
188. His theory accounting for
fresh water interpolations in ma-
rine strata of Paris, 261. His
synopsis of tertiary plants, 265.
His views as to the origin of
raised beaches, 321, et seq.
Buch, Von, his table of Ammonites,
i.84. His speculation concern*-
ing Alpine dolomites, 210. On
the transformations of limestone,
z3
342
INDEX.
ii. 134. On the Sienite of Chris-
tiania, 143. His hypothesis on the
"craters of volcanos,"203, etseq.,
231. On direction of anticlinal
lines, 292, et seq.
Buckland, Dr., references to his
geological researches, passim.
His account of Kirkdale Cave,i.
315.
Buddie, Mr., notice of his sections
of the coal of Newcastle, i. 169.
His experiments on temperature
of coal mines, ii. 273.
Building materials, geology neces-
sary for proper choice of, ii. 330.
Bunter of the Mesozoic strata, i. 203.
Buprestidae of Stonesfield, i. 223.
Burdiehouse, fossil remains of fish
at, i. 87.
Buxton. analysis of the waters of,
255.
C.
Cader Idris, ancient strata of, i.
129, 130.
Cainozoic or Tertiary strata,table of
its deposits, i. 54. 249. Compo-
sition of, 250. Structure and
stratification of, 251 . Divisional
planes of, 252. Succession and
; thickness of, 252. Freshwater
formations above, 254. Geogra-
phical extent and physical geo-
graphy of, 260. Organic remains
of, 264. Disturbances during
and after, 276.
Calabria, lava of, its analysis, ii. 95.
Caldcleuph, Mr., his account of the
second great earthquake of Chili,
ii. 241.
California, volcanos of, ii. 229.
Cam Fell, plants on, ii. 327.
Cambrian system, i. 57. 124, et seq.
Canada, its survey recommended,
ii. 337.
Canals, a knowledge of geology ne-
cessary for the construction of,
ii. 329.
Canary Islands, volcanic in their
origin, ii. 231.
Cantal, Plomb du, ii. 205. Deposits
found in beds of, 44.
Caradoc, gritstone of, i. 136. For-
mation, table of, 139.
Carbonic acid, amount of, in ther-
mal springs of Germany, ii. 256.
Carbonic acid gas, its effect on
granite, ii. 9. Found in calca-
reous strata, 129.
Carboniferous system, table of de-
posits of, i. 56. Its prevalence in
England and Ireland, 58. Strata
of, 162. Its composition, 162.
Its structure, 163. Its succession
and thickness, 166. Its organic
remains, 170. Its physical geo-
graphy, 176. Its geographical
extent, 177. Igneous rocks of,
184. General view of the cir-
cumstances under which the sys-
tem was deposited, 186. Distur-
bances of the system, 193.
Cardona, salt mines of, i. 211.
Carguairazo, peak of, volcanic
eruption of the, ii. 215.
Carmeaux, mines of, their tem-
perature, ii. 274.
Carne, Mr., his description of the
vein systems of Cornwall, ii. 171,
et seq.
Carnivora, in marine deposits, i.
272. See Organic Remains.
Carpathians, dip of stratified rocks
in the, i. 37. Green sand plen-
tiful in, 58.
Carrara, marble of, ii. 130.
Catania, destruction of, by currents
of lava, ii. 211.
Caucasus, volcanic accumulations
of the, ii. 227.
Cautley, Captain, his discovery
of remains of quadrumana, i.
100.
Caves, Caverns, ossiferous, i. 303.
Their origin obscure, 310. Va-
rious kinds of, 310. Almost ex-
clusively found in limestone, 310.
Theories accounting for animal
remains found in, 311.
Cement, Roman, how derived, and
where found, i. 256.
Cephalopoda, amount of, found
fossil, i. 80. Table of, 83.
Cervus megaceros, recent exist-
ence of, i. 320.
Cetacea in marine deposits, i. 272.
See Organic Eemains.
Chahorra, Mount, its eruption of
stones, ii. 235.
Chalk, its extent of range in Eng-
land and France, i. 36. Little
seen about or beyond the Alps,
58. Its composition, &c., see
Cretaceous System. Its rise from
the sea accounted for, ii. 5.
Chambers.iMr., notice of his work,
" Ancient Sea Margins," ii. 2.
Chamouni, Vale of, position of
strata in, i. 39. Cleavage of
strata in, 128.
Channel, English, tertiaries de-
pendent on the, i. 262. Peculiar
shells of the, 269.
Chaos, mis-application of the term,
107.
Charlesworth, Mr., his researches
INDEX.
343
on the super-cretaceous deposits
of the eastern counties, ii. 52.
Charnwood Forest, i. 68. Clay
slate of, 126. 132.
Chat Moss, oak tree stumps found
in, ii. 58.
Chert, how and where found, i.
234.
Cheshire, salt district of, i. 212.
Chili, volcanos of, ii. 230. Earth-
quakes of, 221. 241. 249. Coast
of, raised by convulsive move-
ments, 241. 291.
Chloride of sodium, chemical name
for common salt, i. 210.
Chlorite schist, difference between
it and mica schist, i. 113.
Christiania, sienite of, ii. 143.
Cirripeda, not common as fossils,
i.96.
Cistus helianthemum, soil peculiar
for, ii. 327.
Clar, argillaceous, three kinds of,
i/246.
Clav, Kimmeridge, where found,
i/227.
Clay banks, their composition and
origin, i. 341.
Clay-slate, different colours of, i.
15*6.
Clay-slate system,!. 124. Regarded
by Sedgw'ick as the Cambrian,
124. Its composition, 125. Struc-
ture of. 126. Cleavage of, 127.
Succession of its strata, 128.
Organic remains found in, 131 .
Geographical extent of the sys-
tem, 132. Its physical geography,
133. Its igneous rocks, 134.
Clay-stone, proportion of oxygen
in, i. 25.
Cleavage of rocks, i. 67. 115. 128.
137. ii. 117. A result of pressure,
117. 120. Mr. Sharpe's views of,
117. 120, etseq.
Clee Hills, position of strata in
the, i. 39. The series of, how
expressed, 179.
Clift, Mr., identifies teeth of hip-
popotamus and ox in animal re-
mains of Georges Gmiind, ii. 47.
Climate of the earth, during early
geological periods, ii. 305. Mr.
1 Lyell's hypothesis on, 305. Spe-
culations on heat and cold as
affecting, 306. Hypotheses of Sir
J. Herschel and M. Poisson, ac-
counting for varieties, 306, et
seq. Difference of Atlantic and
Continental climates, to what
ascribed, 309.
Clwvdd, Vale of, its faults, i. 44.
Coal, dip of, in Gloucestershire and
Somersetshire, i. 49. In York-
shire and Durham, 50. Always
found in beds. 163. Its compo-
sition, 163. Ironstone found in
its districts, 165. Structure of
beds of, at Swansea."16o. Succes-
sion and thickness of strata of, 166.
Organic remains found in, 177.
Its inexhaustibility considered,
181. Theories accounting for the
origin of, 188. Its extent under
superior strata, 193. A know-
ledge of geology necessary for
its discovery and successful ex-
traction, ii. 331.
Coalfield, Newcastle, fault in the,
L42.
Coal mines, experiments on their
temperature, ii. 273.
Coalfield Dyke, account of, ii. 132.
Colchester, 'Mr., his discovery of
fossil quadrumana at Kyson, i.
100.
Coley Hill, igneous rocks of, i. 68.
Cleavage in, 128. 135.
Conception, destruction of, by an
earthquake, ii. 221. Elevation of
the strata of clav in the bav of,
241.
Conchifera, amount of, found fossil,
i. 80. Table of, 83.
Coniston, slate of, i. 133.
Connemara, serpentine found in, i.
121.
Conrad, Mr., his classification of
North American tertiaries, i. 264.
270.
Conybeare, Mr., his geological in-
vestigations, i. 154. 203. Refer-
ence to his " Geology of England
and Wales," 183. Onthe " killas"
of Cornwall, ii. 142.
Copper ore, the richest, at what
depth found, ii. 170. Lodes, an-
cient and more recent, 172, 173.
Coral, in rocks of Dudley, Wen-
lock, &c. i. 138. Reels and islands
of, their origin, 329. Labours of
zoophyta in forming, 331 . Pecu-
liarity of their form, 331, et seq.
See Organic Remains.
Cordier, M., his experiments on
temperature of the mines of Car-
meaux, ii. 274.
Cordilleras, volcanos of the,ii. 221.
Cornwall, mica schist and gneiss
rarely found in, i. 58. Granitic
structure of the rocks of, 108,
109. ii. 104. Survey of, by Sir H.
De la Beche, 105. Alterations
produced on the slaty rocks of,
by proximity of granite, 108. 142.
Minerals of, 156, et seq. Tem-
perature of the mines of, 271.
Corygiils, Arran, the rocks of, i. 63.
344'
INDEX.
Cotidal lines, Whewell's Essays
on, ii. 288.
" Crag," marine Deposit, where
found, i. 255. 'Roman cement
made from, 2£6t]
Craven district of Yorkshire, posi-
tion of strata at, i. 39. Length
of faults in, 43. 135.
Cretaceous system, table of deposits
of the, i. 54. Its composition,
233. Its stratification, 235. Suc-
cession of its strata, 236. Or-
ganic remains found in, 2M7. Its
geographical extent, 240. Its
physical geography, 242. Its
igneous rocks, 243.
Crinan canal, i. 116.
Crocodiles, fossil remains of. i. 92.
Their instinctive habits alluded
to, 93, 94.
Crossfell, position of strata at, i.
39. The " Whin Sill," a ba.
saltic formation found at, ii. 96.
Crust of the earth, historical view
of the rocks of, i. 107. Granitic
base of, 10S. Disturbances of,
at close of Silurian period, 149.
At close of Secondary period,
244. During and after the Ter-
tiary period, 276.
Crustacea, table of fossil genera of,
85.
Cullercoats, fault at, i. 40. 193.
Cumberland, red sandstone of, i.
16. Cleavage of rocks in, 68.
Slate of, 133, 134. Lake district
of, 133.
Cumbrian mountains, dip of strati-
fied rocks in, i. 37. Granitic
structure of, 108. Porphyry abun-
dant in, 134. Detritus yielded
by, to diluvial currents, 283.
Cuvier, his opinion of "true" geo-
logy, i. 69. His discoveries in
fossil zoology, 88. 90. 96. 98. 116.
256.261.298.312.
Cycadeae found in oolitic strata, i.
222.
D.
Danube, organic remains found in
the, i. 269.
Dartmoor, altered rocks of, ii. 143.
Darwin, Mr., his ingenious theory
of the origin of boulders, i. 296.
His observations on corallige-
nous zoophyta and coral islands,
331, ft seq. On the volcanic ori-
gin of the islands of the Pacific,
ii. 232. On the dynamics of
earthquakes, 247. On the dis-
placements of stratified rock
accounting for continental ele-
vation, 289. 304.
Daubeny, Dr., references to his
work on volcanos, ii. 136. 210,
et seq. On mineral and thermal
springs, 254, et seq.
Daubuisson, M., extract from his
" Traite de Geologic," ii. 250.
His experiments on the heat of
mines, ii. 270.
Dauphine, organic remains found
in, i. 123.
Davy, Sir H., reference to, ii. 329.
Dechen, Von, his plans of granite
veins, ii. 104. On the alterations
produced on argillaceous slaty
rocks by granite, 108. 142. On
the changes effected by the gra-
nite of the Harz, 143.
Decise, mine of, its temperature,
ii. 275.
Deltas, how formed, ii. 25, et seq.
Demavend, Peak of, its height, ii.
228.
Denham, Captain, his survey of the
estuary of the Mersey, ii. 33.
Deposits, British, table of, i. 54.
Various kinds of, 58. Of the
various strata, see Hypozoic and
following Strata. Supracreta-
ceous, 249. 272, et seq. Modern,
278. Classification of, 281. De-
trital, 281. Tables of vertebral,
304. Ancient marine, 321. Ma-
rine, in progress. 329. Fluviatile,
ii. 1.8. {Lacustrine, 36. Metalli-
ferous, 155.
Derbyshire, coal formation of, i.
166. Difference in herbage of,
177.
Derwent, delta of the, how formed,
ii. 25.
Deshayes, M., his researches con-
cerning tertiary mollusca, i. 265.
His discoveries of animal re-
mains in lacustrine deposits, ii.
48.
Desnoyers, M. J., his comparison
of the English "crag" to the
epilimnic group of Paris basin,
i. 257. His report on ossiferous
caves, 303.
Detrital deposits, i. 281, et seq.
Devil's Arrows, Boroughbridge, ii.
10.
Devonian system, table of deposits
of, i. 56. Composition of the
strata of, 154. Organic remains
found in, 156. Its geographical
extent, ICO.
Didelphys, fossil remains of, i. 96.
Dillwyn, Mr., his notice of phe-
nomenon in coal formation of
Swansea, i. 163.
INDEX.
345
Diluvial period, theories account-
ing for the phenomena of the, i.
281, et seq- General considera-
tions of the phenomena of, 316,
et seq. Zoological and botanical
characters of the period, 319.
See Post-tertiary Strata. Lakes
of the, ii. 48.
Diluvium, i. 278. 281. See Post-
tertiary Strata.
Dislocations of strata, their direc-
tion considered, ii. 292, et seq.
See under heads of the various
Strata.
Disturbances of stratification in
British Islands, tables of, ii. 152.
Dolcoath Mine, depth of, ii. 170.
Its temperature, 271.
Dolgelly, valley of, i. 134.
Dolomitic limestone, description
and origin of, ii. 133.
Donati, M., his researches in the
Adriatic, i. 46. On deposits of
the Rhone, ii. 29.
Drainage, effects of, ii. 21.
Dream Cavern, skeleton of a rhi-
noceros found in, i. 311.
Drift in post-tertiary strata, i. 281.
Dudley, corals found in rocks of,
i. 138.
Dufrenoy, M., his remarks on the
strata of the Pyrenees, i. 244.
His memoir on the tertiaries of
France, 257. 259. On the metal-
liferous veins of the Pyrenees,
162. On volcanos, 205.
Diinolly, cubic pyrites found at, i.
126.
Durham, dislocation of coal and
limestone strata in, i. 50.
Dykes, another name for faults, i.
40. Their extent and frequency,
42. Their relation to disturbed
rocks, 44. See Strata.
Dykes in igneous rocks, ii. 98. Sin-
gular combination of, at Kaghlin,
128. Remarkable one at Cock-
field, 132.
E.
Earn, Loch, stratification in the
quartz rock of, i. 115, 116.
Earth, strata of the, its age, how as-
certained, i. 8. Physical changes
of the, how determined, 18. 20.
Chemical data for the exterior
parts of the, 23. Composition of
its mass, 23. Physical data of
its interior constitution, 26. Its
mass, whence derived, 28. Struc-
ture of its external parts, 33.
Historical view of stratified rocks
in the crust of, 107. Granitic
base of the crust of, 108. Dis-
turbances in the crust at the
close of the Silurian period, 149.
Disturbances at the close of the
Secondary period, 244. Disturb-
ances during and after the Ter-
tiarv period, 276. Waste of the,
ii. 9. Effects of rain, &c., as
agents of disintegration of, 10,
et seq. Unstratified rocks in
crust of, 71. Huttonian hypo-
thesis of its construction, 194.
Modern effects of heat in, 200.
See Heat, Volcanos. Experi-
mental inquiries into heat of, 262.
Its physical geography, 286. Its
distribution into land and sea,
286. Heights and depths of, 288.
Displacements of stratified rocks
of, 289. Direction of anticlinal
lines of, 292. Periods of ordinary
and critical action of, 301. Mo-
dern period of ordinary action
of, 304. Climate of, 305. Hy-
potheses advanced accounting for
climates of, 305, et seq. See
Heat. Aspect of the surface of,
319. Outline of the land and sea
portions of, 320. Undulations of
the interior of, 322. Scenery of,
324. Agriculture of, dependent
on a proper knowledge of its
geology, 326. Proper construc-
tion of roads, &c., dependent on
a knowledge of its strata, 329.
Knowledge of the various strata
of, and their qualities, necessary
for architectural and building
purposes, 330. This knowledge
requisite also for successful ac-
quisition of its mineral and other
products. 331.
Earths, proportions of oxygen con-
tained in various, i. 24.
Earthquakes premonitory of vol-
canic eruptions, ii. 208. 221.
Towns destroyed by, 221. Phe-
nomena attending, 234, et seq.
Account of various, 24 1 . Move-
ments of, described, 243. The-
ories accounting for, 243, et seq.
Wave movements of, 243, 244.
Egypt, Lower, the gift of the Nile,
ii.28.
Eifel, extinct volcanos of the, ii.
135. 202. 216. 220.
Electricity, currents of, their effects
on metallic bodies, ii. 114. 195.
Mr. Fox's theory accounting for,
114. 195, et seq.
Elevation of mountains, ii. 289.
290,
Elgin, fossil remains at, i. 92.
346
INDEX.
Elk, the Irish, fossil remains of, i.
99. ii. 56. 69.
Ellis, Mr., his description of the
crater of Kirauea, ii. 532.
Elster, valley of the, fossil remains
of Man found in, i. 100.
Ems, its mineral waters, their ana-
lysis, ii. 256.
Eocene period, deposits of the, ii.
41. See Strata.
Epilimnic formation, the, i. 257.
Eppelsheim, animal remains found
at, ii. 45.
Eribol, Loch, rorteoceratites dis-
covered at, i. 118. Quartz rock
of, 117.
Erratic block groups, i. 281. 283.
Theories accounting for their
formation, 281 — 298.
Estoary and shore deposits, de-
scription of, and their effects, ii.
31, et seq.
Etna, volcano of, i. 278. ii. 203. Phe-
nomena attending eruptions of,
204. Height and circumference
of, 21 1 . Various eruptions of,
217,218.
Euganean hills, extinct volcanos
of, i. 278. ii. 227.
Europe and British Isles, once co-
vered by the sea, i. 149.
Everest, Mr., his analysis of the
waters of the Ganges, ii. 34.
F.
Facts, geological, the means for
investigating, i. 18.
Falconer, Dr., his discovery of
fossil quadrumana, i. 100.
Faults, description of, i. 40. Local
names for, 40. Extent and fre-
quency of, 42. Their relation to
disturbed rocks, 44. Their
cause, ii. 301. See Strata.
Fauna of the magnesian lime-
stone, i. 200. Of the Permian
system, 201. Glacial marine,
327.
Felspar, proportion of oxygen in,
i. 25. Its composition, 31. How
and where found, ii. 84.
Felspathic rocks, how and where
found, ii. 84.
Ferrybridge, discovery of subma-
rine forest at, ii. 57.
Festiniog, valley of, i. 134.
Firs, remarkable heights of, ii. 67.
Fish, thrown out by volcanos, ac-
count of, ii. 215.
Fishes, fossil remains of, i 86.
Orders of, 89. Table of, 90. See
Organic Remains.
Fissures, in rocks, i. 303. In ig-
neous rocks, ii. 97. Vein, their
origin, 188. Filling of, 192.
Longitudinal, production of,
299. Transverse, their forma-
tion, 300. In conical elevation,
their formation, 300.
Fleming, Dr., on deposits of the
Frith of Tay, ii. 60.
Flinders, Captain, his account of
the coral reef of New Holland,
i. 332.
Flint. See Cretaceous System.
Flora, British. See Organic Re-
mains.
Fluviatile deposits, ii. \.S,et seq.
Forbes, Prof. E., on marine depo-
sits, i. 327. His researches in
the JEgean Sea, 337. His ob-
servations on the glacier of Mon-
tanvert, i. 14. 19. His work on
the lacustrine deposits of Pur-
beck, 40. On the volcanos of
Auvergne, 207. On mineral
springs, 257, et seq.
Forchammer, Dr., his suggestion
respecting the origin of pisolite,
i. 210. His view accounting for
the boulder formation of Den-
mark, 317. On deposits of lakes
of Denmark, ii. 54.
Ford, Mr., his account of Cock-
field Dyke, ii. 132.
Forest of Dean, i. 181.
Forests, subterranean and marine,
discoveries of, ii. 57. Their an-
tiquity, 64.
Formations, ancient valley, ii. 2.
Forster, Mr. Westgarth, his ar-
rangement of the Newcastle coal
beds, i. 168.
Forth, great valley of the, dip of
stratified rocks in the, i. 37.
Fossils, and fossil remains of ani-
mals, &c. See Organic Remains.
Fourier, M., his mathematical the-
ory of heat, ii. 264. 268. 308. 313.
Fox, Mr., on the changes of metal-
lic bodies by electrical currents,
i. 68. 135. ii. 114.195. On the
mineral veins of Cornwall, 160.
164, etseq. On fissures in mi-
neral veins, 195. His experi-
ments on heat and the tempera-
ture of mines, 271, et seq.
France, coalfields of, i. 183. Cre-
taceous rocks of, 241.
Freyberg, mines of, ii. 174. Pro-
portions of lead and silver found
in, 174. Temperature of, 270.
Friendly Isles, tabular form of the,
i. 332.
Friesland, lakes of, once woods, ii.
61.
INDEX.
347
Frost, effects of, as an agent of
disintegration, ii. 11.
G.
Gainard and Quoy, MM., their
observations on the labours of
coralligenous zoophyta, i.331.
Galena, sublimation of, by steam,
ii. 197.
Gallapagos Islands, volcanic origin
of, ii. 230.
Ganges, analysis of the waters of
the, ii. 34.
Garnets, where found, ii. 138.
Garonne, tertiary deposits of the
basin of the, i. 257.
Gas, carbonic acid, in calcareous
strata, ii. 129.
Gasteropoda, number of, found
fossil, i. 80. Table of genera of,
82.
Gautemala. volcanos of, ii. 229.
Geneva, lake of, reference to the
deposits of, as forming the delta
of the Rhone, ii. 25.
Gensanne, M., his experiments on
the temperature of the Vosges
mine, ii. 270.
Geography, physical, of the globe,
. the subject considered, ii. 286.
See Earth, Globe, Strata.
Geological Intersector, Professor
Phillips', i. 68.
Geological Map, Professor Phil-
lips', ii. 320.
Geological time, scale of, i. 8.
Lapse of, inferred from series of
rocks, 10. Nature of the scale
of, 12. Terms of the scale, 12.
14. Interruptions of the series
of, 16. Length of the scale, 17.
Geology, and Geological Theory,
objects of, i. 1. Means of inves-
tigating, 6. How distinguished
from Natural History, P. Its phe-
nomena, how interpreted, 20.
Analogy between the tertiary
and modern periods of, 99. State
of, ii. 277. Considered as one of
the inductive sciences, 279. Er-
rors to be guarded against in
study of, 280. Phenomena of the
earth, proper subjects for geolo-
gical observation, 281. Leibmt-
zian and Huttonian theories
considered, 285. Its physical
geography and phenomena exa-
mined, 286, et seg. See Strata.
Popular views and economical
applications of, 317, et seq. Be-
nefits conferred on mankind at
large, by its pursuit, 326, et seq.
See Earth.
" Geology of Yorkshire," refer-
ences to, i. 137. 172. 190. ii. 112.
162.311.335.
Georges Gmiind, ossiferous beds
of, i. 280. 3?0. Animal remains
of, ii. 46.
German Ocean, peculiar shells of
the, i. 269. An examination of
its organic contents recommend-
ed, ii. 36.
Germany, volcanos of, ii. 223.
Thermal springs of, 256.
Giant's Causeway, i. 63. 244.
Girogmagny, mines of, their tem-
perature, ii. 270.
Glaciers and their phenomena, i.
294—298. ii. 13, et seq. Then-
origin, ii. 12.
Gleichenberg, in Styria, trachytic
mountain of, ii. 225.
Glen Coc, porphyry discovered in,
i. 121.
Glen Tilt, granitic veins in, i.
109. Crystallised primary lime-
stones of, 116. Hornblende schist
of, 117.
Globe (see Earth), construction of
the, how ascertained, i. 7. Age
of its strata, how determined, 8,
et seq. Physical changes of, what
means to be taken for acquiring
a knowledge of, 18. 20. General
reasonings concerning the sub-
stances of, 23. Its mass, whence
derived, 28. Structure of its ex-
ternal parts, 33. Disturbances
in crust of, at close of Silurian
period, 149. Disturbances at
close of the Secondary period,
244. Disturbances during and
after Tertiary period, 276. Waste
of the surface of, ii. 9. Rain,
&c., las agents of disintegration
of, 10, et seq. Unstratified rocks
in crust of, 71. Heat of, 72.
Modern effects of heat in, 200.
Experimental inquiries into heat
of, 262. See Heat. Its physical
geography, 286. A knowledge
of its construction, &c. 'neces-
sary for all the purposes of life,
and benefits conferred by this
knowledge on mankind, 317, et
seq. 326, et seq.
Gneiss and Mica Schist systems, i.
111. Their composition, 111.
Lamination prevalent in, 114.
Stratification less easily trace-
able in, than in other systems,
115, Remains of organic life
seldom traced in, 1 18. Extent to
which they prevail, 119. Found
348
INDEX.
prevalent in Scotland and Ire-
land, 119. Physical geography
of, 120. Igneous rock of, 121.
General inferences to he deduced
from a consideration of the
whole subject, 122.
Gneiss, proportion of oxygen in,i.
25. Rare in the Harz, Coru-
• wall, and Wales, 58. Metamor-
phism of, how effected, ii. 143.
Golt, how and where found, i. 233,
et seq.
Gordian Medal, discovery of a, at
Groningen, ii. 65.
Graham, Mrs., her account of the
first Chilian earthquake, ii. 24 1 .
Graham's Island, its volcanic phe-
nomena, ii. 214.
Grampians, dip of stratified rocks
in the, i. 37. Hypozoic strata
predominant in, 58. Afford an
example of the granitic basis of
the earth's crust, 108. Pictu-
resque beauty of, 133, 134. Once
uplifted, 151. Gneiss mountains
of, ii. 321.
Granite, proportion of oxygen in,
i. 25. Its composition, 25. The
basis of the earth's crust, 10S.
Veins of, in Glen Tilt, Cornwall,
&c., 109. 121. Its rapid decom-
position by carbonic acid gas, ii.
9. May have been derived from
fusion of previously formed
strata, 72. Once a melted fluid,
79. Great protuberances of, in
the valley of theJValteline, 88.
Composition of, 92. Huttonian
theory of the crystallisation of,
101. Alterations produced by
the proximky of, to various
strata, 101 , et seq. Age of, how
determined, 148. Basis of the
trachytic masses of Mexico,
230.
Grauwacke system. See Pal&ozoic
Strata, Clay Slate System. Ori-
gin of the term and its applica-
cation, i. 126.
Gravel, various theories account-
ing for the origin of, i. 298. 302.
Not necessarily of diluvial ori-
gin, 301. Sir R. Murchison's ex-
amination of the Welsh border
accounting for deposits of, in
vales of the Dee and Severn, 301.
Geographical circumstances ac-
counting for distribution of, 301.
Local origin of some sorts of,
302. Problems suggested by
these theories, important for a
correct view of the origin of di-
luvial accumulations, &c., 302.
Banks of, 341.
Green sand, how and where found,
i. 234. See Cretaceous System.
Green stone, how and where found,
i. 121. 208.
Greenhow Hill, disturbed strata
of, i. 44.
Greystone, how found, ii. 84.
Griffith, Mr., on fissures, i. 65.
His map, 178. On colour of
slaty rocks of S. E. Ireland, ii.
143.
Grit, millstone, an important de-
posit in the north of England, i.
180.
Group, erratic block, i. 281. 283.
Guadaloupe, earthquake of, ii. 246.
Guanaxiato, mines of, their tem-
perature, ii. 272.
" Guide to Geology," references
to, i. 128. 137.
Gypsum of the Triassic system,
where found, i. 204. Its origin,
210.
H.
Hall, Sir James, his experiments
on powdered limestone, ii. 79.
His examination of mountain of
Tornideon, 102. His examination
of the Huttonian doctrine of the
induration of rocks by heat, 129.
Quotation from his " Geology of
New York," i. 143.
Ham, Mr., his analysis of the
waters of the Severn, ii. 34.
Hamilton, Sir W., on the eruption
of Vesuvius, ii. 235.
Harcourt, Mr. W. V., his experi-
ments on the effects of long-con-
tinued heat,i. 126. His geological
investigations, ii. 42. 50.
Hardrow Force, i. 177.
Harlech sandstones, i. 130.
Harz Mountains, mica schist and
gneiss of rare occurrence in, i.
58. Elevation of the, 153.
Hasenberg, basalt of, ii. 95.
Hatfield Chase, extent and drain-
age of, ii. 65.
Hawaii or Owhyhee, volcanic cra-
ter at, ii. 232.
Headon Hill, limestones of, i. 251.
Heat, Mr. Harcourt's experiments
on effects of long-continued, i.
126. Its effects on rocks, ii. 72.
111. Its modern effects on the
globe, 200. Hot springs and
volcanos indicative of the pre-
sence and degree of, 200. See
Volcanos, Thermal Springs,
Earthquakes. Dependent on the
calorific influence radiated from
the sun, 263. 266. This influence
INDEX.
349
not cumulative in its effects, 263.
This influence modified by the
refrigerating action of the plane-
tary spaces, and the elevation of
places above the level of the sea,
263, 264. The peculiar distribu-
tion of land and water, another
cause productive of difference of
temperature, 265. Leslie's ex-
periments, 266. Experiments of
M. Quetelet and others, 267, et
seq. Daubuisson's experiments
on. in mines of various depths,
270. Experiments of Mr. Fox,
271. Experiments on, in stratified
rocks, by Saussure and others,
272. Experiments on, in Artesian
wells, 276. Sir J. Herschel's
theory of the variability of, 306.
Hypotheses of various geologists
accounting for changes of climate
produced by solar heat, 305, 306,
et seq.
Hebrides, composed of gneiss, i.
119. ii. 321.
Hecla, eruptions of, ii. 219.
Heights and depths of the earth,
how ascertained, ii. 288.
Heligoland, encroachments of the
sea on, ii. 3a
Kenwood, Mr., "on the shoots of
mineral veins.'ii. 168. 184, et seq.
On the temperature of mines,
275.
Herbage, difference of, In limestone
districts of England, i. 177.
Herculaneum, destruction of, ii.
213.
Herodotus, on the alluvial deposits
of the Nile, i. 11. ii. 23.
Herrenschneider, M., his experi-
ments on heat, ii. 2G7.
Herschel, Sir J., his speculations
on the planetary masses, i. 31.
Trilobites found by, 147. Views
geology as a science, ii. 279. On
the variability of solar heat, 306.
Hibbert, Dr., o'n the cervus mega-
ceros, i. 320.
High Force waterfall, ii. 112.
Himalaya, height of the, i. 18.
Deposits in the, 58. Application
of the theory of the divisional
strata of England to, 218.
Hindostan, undulations of the in-
terior of, ii. 322.
Hippopotamus, remains of, where
found, ii. 47. 68.
Hodgkinson, Mr., his experiments
on the temperature of salt mines,
ii. 273.
Hoffman, M., on coal of north-west
Germany, i. 168.
Holderness, operation of the sea
on the coast of, ii. 32. Deposits
of, 54. 5X.
Holland, Dr., his hypothesis re-
specting the Cheshire salt dis-
trict, i. 212, 213.
Holland, New, coral reefs of, i.
332.
Hopkins, Mr., his remarks on the
earth's solid crust, i. 28. On the
rock fissures of Derbyshire, 65.
On disturbances of the earth's
crust, 153. 195. His theory of
the formation of erratic blocks.
296. On glaciers, ii 18. On the
phenomenon of cleavage, 246.
On dislocations of strata and
their direction, 298.
Homer, Mr., his experiments on
the waters of the Rhine, ii. 33.
Hornblende, how found, ii. 84,
85. Slate, 140.
Hot springs, see Thermal Springs,
ii. 200.
Huelgoat, mine of, its temperature,
ii. 271.
Huel Peever mine, plan and sec-
tions of, ii. 180. et seq.
Hugi, M., his discovery of fossil
remains in the Jura mountains,
i. 223.
Humber, deposits at the mouth of
the, ii. 32.
Humboldt, on the age of granite,
ii. 148. On the nf-w mountain of
Jorulio, 204. Traces lava to
summit of Peak of Teneriffe, 209.
On volcanic rocks. 215, et seq.
On temperature of the mines of
Guanaxuato, 272. On direction
of anticlinal lines, ii. 292.
Hundsruck, fossil remains of fish in
the, i. 87. Elevation of, 153.
Hungary, extinct volcanos of, ii.
220'. 224. 227.
Button, Dr., his view of Geo-
logy as a science, i. 1 . 4, 5. His
study of stratified rocks in Scot-
land and Saxony, 38. His re-
marks on the various opinions
respecting the crust of the earth,
110. On the subterranean forests
of Lincolnshire and Yorkshire,
ii. 66. His doctrine of the crys-
tallisation of granite, 10J. Ob-
jections to his theory, that the
induration of rocks is attributable
to the action of heat, 129. His
hypothesis of the earth's con-
struction oppose;! to \Verner,
194. His theories considered,
284.
Hvpozoic system, strata of. i. 57.
Its predominance in Scandinavia,
the Alps, and Grampians, 58.
350
INDEX.
System considered, 111. Its com.
position, 111. Lamination in,
114. Stratification of, 115. Suc-
cession and thickness of, 117.
Organic life discovered in, 118.
Extent of, 119. Physical geo-
graphyof, 120. Igneous rocks of,
121. General inferences drawn
from the subject, 122.
Iceland, volcanos of, dates of their
eruptions, ii. 219. Names of its
volcanos, 219. 222.
Icebergs, how formed, i. 294. De-
tritus deposited by, 294.
Igneous rocks, i. 121. 134. 184. 208.
231. 243. ii. 71. See Rocks, Igne-
ous.
Imbaburu, volcano of, its ejection
ofprenadillas, ii.215.
Indian Ocean, submarine volcano
in the, ii. 232.
Indies, West, all volcanic in] their
origin, ii. 230.
Indus, basin of the, stratified de-
posits in. 58.
Ingleton, Yorkshire, cubic pyrites
found at, i. 126.
Interior of the earth, undulations
of, ii. 322. Of England, 322.
Intersector, the Geological, i. 68.
lona, primary limestone of, i. 117.
Serpentine found in, 121.
Ireland, scenery of limestone dis-
tricts of, i. 176. Bogs of, ii. 64.
Iron ore of the Pyrenees, ii. 162,
163. Carbonate of, how found in
coal, i. 163. Green silicate of,
where found abundant, 242.
Ironstone, singular structure of, in
coal districts, i. 165.
Ischia, volcanos of, distance of
time between their eruptions, ii.
216.
Islands, new, formed by volcanic
action, ii. 236
Isomeric or Isomerous, derivation
of the word, ii. 86.
J.
James, Captain, his contribution to
the zoology of the glacial sea, i.
327.
Jameson, Professor, on veins of ig-
neous rocks, ii. 100.
Java, volcanic mountains of, ii.
228.
Jelly, Rev. H., his notice of corals,
i.75.
Jersey, New, bleached shells found
in,ii.56.
Joints, meaning of .the term, i. 64.
Various kinds of, and their situ-
ation, 64, 65.
Jorullo, new mountain, its height,
ii. 204. 236.
Juan Fernandez, volcanic island of,
ii. 221. 230.
Jukes, Mr., his geological re-
searches, i. 129.
Jura, the Swiss and German, oolitic
rocks of the, 229. Limestone of,
disrupted by granite eminences,
ii, 292.
K.
Kaisarstuhl mountain, volcanic, ii.
223.
Kendal, mineral springs of, ii. 253.
Kennedy, Dr., his analysis of the
greystone lava of Calabria, ii.
95. His analysis of basalt of
Staffa, 95.
Kent's Hole, Torquay, animal re-
mains found in, i. 314.
Keuper, of the Triassic system, i.
203.
Keyserling, M., his geological la-
bours, i. 200.
Killas of the rocks of Cornwall, ii.
104.
Kimmeridge clay, fossil deposits in,
i.92. Where found, 227.
King, Mr., his tables of British
Fauna, i.201.
King's Bath spring, analysis of the
water of, ii. 255.
Kirauea, crater of, ii. 232.
Kirby Lonsdale, position of strata
near, i. 39.
Kirkdale cave, composition of the
rock in which it is situated, i.
310. How discovered, 314. Its
description, 314. Remains of hy-
asnas and other animals found
in, 315.
Kitzpuhl in the Tyrol, the deepest
mine in the world, i. 18.
Klaproth, M., his analysis of the
basalt of Hasenberg, ii. 95.
Knottingley, limestones of, i. 197.
Krabla, first eruption of, ii. 219.
Kupferberg, mineral veins of, ii.
170.
Kupffer, reference to his tables
of the temperature of mineral
springs, ii. 253.
Kyson, red crag at, remains of
quadrumana in, i. 1GO.
INDEX.
351
Lacustrine deposits in tertiary
strata, i. 273." In post-tertiary
strata, ii. 1. 36. Of the Eocene
. period, 41. Of the Middle Ter-
tiary period, 43. Of the Pleio-
cene period, 48. Modern, 53.
Ladrone Islands, volcanic chain of
the, ii. 232.
Lakes, on the course of rivers,
remarks on their influence in
changing the earth's surface, ii.
23—27. Deep. 24. Shallow, 27.
' Of the Ple'iocene period and
their deposits, 48.
Llanberis, purple slates of, i. 130.
Valley of, 134.
Llandeilo, rocks of, i. 124.136. Table
of their formation, 139.
Llandovery, metamorphic slates of,
i. 137.
Lamarck, M., reference to his
group of echinodermata, i. 76.
Lamination, prevalence of, among
schists, i. 114. In coal forma-
tions, 163.
Lammermuirs, dip of stratified
rocks from 'the chain of the, i.
37. Silurian strata of, 147.
Lancashire, coal deposits of, i.
180.
Lancaster, position of strata at,
i. 39.
Land and sea, distribution of the
globe into, ii. 286. Outline of,
320.
Lands, new, their formation at the
mouths of rivers, ii. 27. Dis-
placements of, from convulsive
movements of the earth, 240.
292.
Langdale, clay slate of, i. 126. 129.
Languedoc, plains of, rise of strata
from, i. 37.
Lartet, M.. his discovery of remains
of quadrumana, i. 100.
Laplace, his speculation on the
planetary masses, i. 31.
Lava, greystone, of Calabria,
analysis of, ii. 95. Diversified
appearance of, 209. Compo-
sition of, 209. Curious descrip-
tion of its effects when liquid,
210. See 1'clcanos.
Lead Hills, metallic deposits of
the, ii. 161.
Lead mine of Strontian, i. 122. Of
Nant y Moen, and the Shelve
district of Shropshire, 149.
Lead, ore, in what proportions
lound in the mines of Freyberg,
ii. 174. " Throw" of, in mines
of Aldstone Moor, 176. Lead
mines of Cornwall, 176.
Lee, Mr., his contributions to geo-
logy, ii. 56. 68.
Lehman, M., extract from his
work on " Mineralogy," ii. 193.
Leibnitzian theory. See Geology
and Geological Theory.
Leslie, his statement of the rela-
tive weights of water, mercury,
and air, at different depths below
the earth, i. 27. His experiments
on heat, ii, 266.
Lettry, coal mines of, their tem-
perature, ii.275.
Levant tin and copper mine, tem-
perature of, ii. 271.
Lewis, serpentine found in, 121.
Lias, where found, i. 226, et seq.
Life, organic, traces of, not dis-
coverable in gneiss and mica
schist, i. 118.
Lignitic deposits in Cainozoic
strata, i. 273.
Lime, proportion of oxygen in,
Limestone, proportion of oxygen
found in, i. 25. Oceanic types
of, 245. Changed by action of
igneous rocks, ii. 126. Experi-
ments in illustration of, 129, 130.
Powdered, converted into stone,
130. Dolomitic, 133.
Limestone, carboniferous. See
Carboniferous Limestone. Its
extent in England and on the
Continent, i. 58. Peculiarities of
the districts of, in England, 176,
177.
Limestone, magnesian, limited
range of, in the north of England,
i. 36. Peculiarities of districts
of, in England, and their extent,
176—178. See Magnesian Lime-
stone.
Lincolnshire, fen lands of. their
breadth, to what cause attributed,
ii. 32.
Lindley, Dr., result of his experi-
ments on land plants, i. 70. 104.
Linnaeus, his zoological researches,
i. 91.
Lipari Isles, volcanos of the, ii.
218.
Lisbon, earthquake of, ii. 241.
Logan, Mr., geological researches
of, i. 144. 188.
Lomond, Loch, stratification easily
found in the chloritic schists of,
i. 115. Succession of strata at,
117.
Lonsdale, Mr., geological re-
searches of, i. 155. 162.
352
INDEX.
Loss on the Rhine, deposit of,
ii. 3.
London clay, its composition and
position, i. 255.
London sand, i. 16. Dip of, 38.
Luc, De, quotation from, distin-
guishing the sciences of Geology
and Natural History, i. 6. His
opinion on the antiquity of the
earth's strata, 13. His theory of
the origin of coal, 188. His no-
tice of the boulder formations,
291 , 292. His discussions on ossi-
ferous gravel, 298. His theory
accounting for animal remains
in caves, 312. On rivers and
their deposits, ii. 22. 30. 33. On
the subterranean forests of the
Humber, 59, et seq.
Lucretius, reference to, ii. 217.
Ludlow, mudstone of,i. 136. Table
of the formation, 139. Extent of
the formation, 146.
Lyell, Mr., reference to his " Prin-
ciples of Geology," i. 109. His
speculations on the " crust " of
the earth, 110. 123. 249. His
views on the gradual rising of
the Weald, 249. 263. His theory
accounting for origin of Lon-
don tertiaries,263. His researches
among animal remains in various
deposits, ii. 3. 23. 39. 43. 56. His
speculations on the Adriatic, 28,
29. His estimate of the deposits
of British estuaries, 34. Extract
from, on the aboriginal forests of
Hercynia, &C..65. On metamor-
phic rocks, 125. On the Sienite
of Christiania, 144. On volcanos,
203, et sea. On the volcano of
Skaptaa Jokul, 211, 212. His
hypothesis on climate, 305, et seq.
If.
Macculloch, Dr., quotation from,
on lamination, i. 114. Disco-
vers Orteoceratites at Lake Eri-
bol, 118. His map of Scotland,
114.178. His theory accounting
for waste of the earth's surface,
ii. 9. On the limestone of Skye,
96. 126. His drawing of schist
rock, 146.
Madagascar, volcanic character of,
ii. 231.
Madeira, once volcanic, ii. 231 .
Maestricht, limestone district of,
i. 237.
Magnesia, proportion of oxygen in,
i.24.
Magnesian limestone series (the
Permian), limited range of rocks
of, in N. of England, i . 36. Table
of its deposits, 56. The system
considered, 195. Its composition,
196. Its structures of deposition,
197. Its divisional planes, 197.
Succession and thickness of its
strata, 197. Its organic remains,
198. Fauna of, 200, 201.
Mallet, Mr., on the dynamics of
earthquakes, ii. 243, 244.
Mallow Spa, analysis of the waters
of, ii. 255.
Malvern Hills, strata of, i. 39.
Echinida and stellerida, zoo-
phytes tound in, 76. Abundance
of fossils found in. 125. Volcanic
sandstones of, 136. Consist of
Silurian rocks, 148.
Mammalia, fossil remains of, i. 95.
98. Tables of, 99. In ma-
rine deposits, 272. In post-ter-
tiary accumulations, 306. See
Organic Remains.
Man, no fossil remains of, yet dis-
covered, i. 99. Discovery of a
man, in a turf pit, with tanned
skin, but bones consumed, ii. 67.
Man, Isle of, composed principally
of slaty rocks, i. 132.
Mantell, Dr., his researches in
fossil zoology, i. 92.
Map, Geological, ProfessorPhillips',
ii. 320. "
Maranon, forests of, i. 187. Col.
Sabine's observations on the sea
current of the, 343.
Marine deposits of tertiary period,
i. 272. See Organic Remains.
Marls, varieties of, found in Trias-
sic system, i.204.
Martins, Dr., his examples of the
glaciers of Spitsbergen, i. 297-
Masses, overlying, of igneous ronks,
ii. 97. Amorphous, of all strata,
108.
Mastodon, teeth of a, found at'Fort
M' Henry, ii. 69. Skeletons of,
where found, 69.
Maunsell, Archdeacon, obtains pos-
session of skeleton of Irish elk,
ii. 56.
Mauritius, volcanic character of,
the, ii. 231.
Mediterranean, tertiary deposits of
the, i. 262.
Melaphyre. ii.133.
Mendip Hills, i. 17.
Meridian of least land, ii. 286.
Mersey, Captain Denham's survey
of the estuary of, ii.33.
Mesozoic or Secondary strata, table
of deposits of, i. 54. The strata
considered, 203. See Triassic,
INDEX.
353
Oolitic, and Cretaceous Systems qf
Strata.
Metallic veins. See Mineral Veins.
Metalliferous deposits. See Mine-
ral reins.
Metals, bow and where found. See
Mineral Veins.
Metamorphic rocks, i. 123. ii. 125.
143.
Metamorphic slates, ii. 139.
Meteoric stones, their origin, i. 32.
Meuse, course of, compared to that
of the Wye, i. 176.
Mexico, volcanos of, ii. 230.
Meyer, M., reference to his u Pa-
laeologica," i. 272. On animal
remains in lacustrine deposits, ii.
46, 47 ; and in subterranean fo-
rests, 69.
Mica, proportion of oxygen in its
composition, i. 25. Its composi-
tion,31.111. Rarely found in the
Harz, Cornwall, or Wales, 58.
Metamorphism of mica schist,
ii. 143. See Gneiss and Mica
Schist Systems.
Michael, St., shells of, i. 324.
Middle tertiary period, deposits of
the,ii.43.
Mill Pond, N. Jersey," bleached
shells found at, ii. 56.
Mineral veins, relation of, to dis-
turbed rocks, i. 44. Found in
Silurian strata, 149. Remarks on,
ii. 155. Werner's distinction be-
tween " true veins " and false ap-
pearances of, 155. Their geo-
graphical distribution, 156. Their
occurrence near centres of igne-
ous action, 159. Relation of, to
the substance and structure of
neighbouring rocks, 163. Rela-
tion of, to one another, 171.
Theory of, 177. Are posterior to
the rocks which they traverse,
178. Origin of vein fissures, 1 88.
Tilling of the fissures, 192. Re-
capitulation of the phenomena of,
196. A study of Geology neces-
' sary for the proper working of 331.
Minerals, proportions of oxygen
contained in certain, i. 24. Crys-
tallised, found in sedimentary
strata, 123. In igneous products,
their analysis, ii. 91—95. Gene-
ration of new, by igneous action,
136. Their successful discovery
and extraction dependent on a
knowledge of geology, 331.
" Mineralogia Cornubiensis," re-
ference to, ii. 170.
Mines, heat in, experiments on,ii.
270. See Heat, Minerals, Mineral
Veins.
" Mining Record Office," origin of
the, ii. 177.
Mississippi, forests of the, i. 187.
Mitchell, Mr.,his theory that physi-
cal geography forms the basis of
laws of geological phenomena, i.
38. On earthquakes, and their
movements, 244.
Mitscherlich, geological researches
of, ii. 81.
Mixed rocks, ii. 86.
Modern deposits, i. 278. ii. 53.
Moel Siabod, i. 129, 130.
Moel Tryvaen, height of, i. 322.
Shells of, 322.
Molasse, dislocations of, their ex-
amination recommended by M.
Beaumont, ii. 295.
Mollusca, i. 77. Tables of, 80, 81 .
327. 339. See Organic Remains.
Molucca Isles, volcanic nature of
the, ii. 228.
Montabusard, animal remains found
at, ii. 45.
Montanvert, glacier of, ii. 14.
Monte Nuovo, its remarkable rise,
ii. 204.
Monte Rossi, double cone and its
height, ii. 204.
Monte Somma, ancient crater of
Vesuvius, ii. 216.
Montmartre, gypsum quarries of,
i.63.
Moray Frith, uplifting of, i. 322.
Morris, Mr., on the Permian sys-
tem of plants, i. 200. On de-
posits of the valley of the
Thames, ii. 57.
Mount's Bay, vegetable deposits
found at, ii. 61.
Mountains, new, formation of, by
volcanic action, ii. 236.
Mourne Mountains, granite of the,
i. 108.
Mudstone of Ludlow, i. 136.
Muncke, M., his experiments on
heat, ii. 267.
Munster, Von, his table of am-
monites, i. 84. His catalogue of
animal remains of Georges
Gmiind,ii.46.
Murchison,Sir R., His Silurian sys-
tem, i. 124. \36,etseq. Organicfos-
sils described by, 140,e/s^. His
description of trap rocks in coal
districts, 185. His British fauna,
200, 201. His opinion respecting
shelly marls of Gosau, 237. His
tertiary series, 258. His memoir
on the Alps and Carpathians,
259. On animal remains in la-
custrine deposits, ii. 47. His
survey of trap rocks of Silurian
system, 109. On volcanic erup-
VOL. II.
A A
354
INDEX.
tions, 214. His survey of the
Ural mountains, 336.
Muschelkalk of the Triassic sys-
tem, i. 203.
N.
Nant Francon, purple slates of, i.
130.
Nant-y-Moen, mineral veins of, i.
149.
Natural History, definition of, i. 6.
How distinguished from Geology,
6. Remarks on its study, ii.
319.
Natural sciences, their definition, i.
1. 6.
Nebulse, Lord Rosse's observations
respecting, i. 32.
Necker, M., his geological re-
searches, ii. 88. On mineral
veins, 159, et seq,
Neptunists and Plutonists, conflict-
ing hypotheses of the, ii. 283. See
Hutton.
Newcastle coalfield, its faults, i.
42. Cleavage of its igneous
rocks, 68. Order of its coal beds,
168.
Newhaven, fossil remains of fish
at, 87.
New York system, subdivisions of
the rocks of, i. 143.
Nile, alluvial land of, i. 11. Hero-
dotus's account of, 11. ii. 28. Its
delta, how formed, ii. 27. Ana-
lysis of its deposits, 29.
Nitrogen, amount of, yielded hy
warm springs of the British Is-
lands, ii. 255.
Nordstrand, history of? ii. 33.
North Sea, tertiary deposits in the,
i. 262.
Northumberland, dip of stratified
rocks in, i. 37.
Northwich, salt mines of, i. 63.
213.
Notre Dame des Ports, notice of,
ii. 28.
Oak, proper soil for, ii. 3'27.
Gats, Captain, his experiments on
the temperature of Tresavean
mine, ii. 272.
Obsidian, analysis of, ii. 94.
Ocean, Atlantic, depth of, how as-
certained, ii. 288.
Ocean, German, a survey of its
organic contents recommended,
ii. 36.
Ocean, Indian, submarine volcano
in, ii. 232.
Ocean, Northern, its division at
the commencement of the car-
boniferous era, i. 186.
Ocean, Pacific, its waters a theatre
of volcanic action, ii. 232. Its
islands of volcanic origin, 232.
Oeningen, fossil remains found in
the quarries of, i. 92. ii. 47.
Oeynhausen, M., on the alterations
effected by granite on argilla-
ceous slaty rocks of Cornwall,
ii. 108. 142.
Oolites of France and Germany,
their resemblance to same group
in England, i. 58. See Oolitic
System.
Oolitic system, tables of deposits
of, i. 55. 199. 204, et seq. Its com-
position, 214. Its structure, 217-
Its divisional planes, 217. Series
of strata of, 218. Its organic re-
mains, 222. Geographical extent
of the, 226. Its physical geogra-
phy, 230. Its igneous rocks, 231.
General review of the system,
23!.
Oppel, Von, on the " Working of
Veins," extract from, ii. 192.
Ordnance Survey of England and
Ireland, its services to geology,
ii. 338.
Organic remains in hypozoic strata,
i. 118. In Palaeozoic strata, 131.
In Silurian strata, 140. In De-
vonian system, 156. In Carboni-
ferous system, 170. In Permian
system, 198. In Triassic system,
205. In Oolitic system, 222. In
Cretaceous system. 237. In Caino-
zoic or Tertiary strata, 264. In
Post-'ertiary strata, 298, et seq.
ii.41, etseq.
Orleannois, animal remains found
in the freshwater beds of, ii. 45.
Oronoko, forests of, i. 187.
Orteoceratites, of Loch Eribol, i.
118.
Ossiferous caves, i. 281. 303—316.
Ossiferous gravel, i. 281. 298—302.
Ott, M., his experiments on heat,
ii. 267.
Ovid, his view of the earth's being
an animal breathing out flame,
ii. 219.
Owen, Professor, his discoveries in
fossil zoology, i. 92. 96. 98. 106.
ii. 42.
Oxygen, table of proportions of,
contained in certain earths, &c.,
i. 24. Expansion of, when li-
berated from its compounds, 31.
Oysters and their habits, i. 337.
INDEX,
355
p.
Pacliydermata, in marine 'eposits,
i. 272. See Organic Remains.
Pacific Ocean, a theatre of volcanic
action, ii. 232. Volcanic origin
of the islands of, 232.
Padua, volcanic hills of, ii. 225.
Palaeontology, classical term for
Organic geology, i. 2.
Pal&osaurus, discovery of the, i.94.
Pala»otherian formation, its com-
position, i. 257.
Palaeozoic! or Primary strata, table
of deposits of, i. 56. The system
considered, 124. Its composition,
125. Structures of, 126. Cleav-
age of, 128. Succession of the
strata, 128. Organic remains
found in, 131. Geographical ex-
tent of, 133. Its physical geo-
graphy, 133. Igneous rocks of,
134. See Devonian, Carbonife-
rous, and Permian Systems.
Paris, Basin of, convergence of
dips of stratified rocks towards
low ground of, i. 37. Epilimnic
group of, 257.
Patterson, Mr., his experiments on
the sublimation of galena, ii.
197.
Peak Cavern, i. 310.
Peak of Teneriffe. lava traced to
summit of, ii. 2C9.
Peat in lacustrine deposits, ii. 54.
Bogs of Ireland, 63, 64.
Pebbly clay and sand, theories ac-
counting for, i. 281. 298.
Penine chain, faults of the, i. 39.
44. Area uplifted by, il. 291.
Pentateuch, errors resulting from
a misunderstanding of the, i. 247.
Pentland, Mr., animal remains dis-
covered by, in the Val d'Arno,
ii.48.
Permian system, table of deposits
of the. i. 56. Long considered a
part of the Saliferous system
195. Its composition, 195, i9fi
Its structures of deposition. 197
Its divisional planes, 197. 'Sue-
cession and thickness of its strata
197. Its organic remains, 198
Fauna of, 201. Its geographical
extent, 202. Origin and aggre-
gation of the materials of the
system, 209.
Persian Gulf, volcanic phenomena
. of, ii. 228.
Peru, volcano in, ii. 230.
P/iascolot/ierium of Buckland, i.
97.
Phenomena, of the earth, how to
be interpreted, i. IS. 20. Consi-
derations drawn from diluvial,
316.
Phillips, Mr., his analysis of pu-
mice, ii. 95. On the copper and
tin ores of Cornwall, ii. 170. On
Tin Croft mine, 185.
Phillips, Professor, references to
his Geological Intersector and
Map, i. 68. ii. 320.
"Pipe " of ore, explanation of the
term, ii. 168.
Pitchstone of Newry, analysis of,
ii. 94, 95.
Plants, fossil remains of, i. 69. See
Organic Remains.
Plas^Newydd, crystallised minerals
found at, i. 123. Dyke of, ii. 1*7.
Plastic clay group, its composition,
i. 257.
Playfair, Dr., on the word stra-
tum, i. 60. . A supporter of the
Huttonian theory, ii. 101, 102.
Pleiocene period, lakes of the, and
their deposits, ii. 48.
Pleistocene deposits, i. 278.
Pliny the Younger, on the great
eruption of Vesuvius, ii. 216.
Plomb du Cantal. ii. 64. 205, 206.
Plutonic rocks and J olcanic pro-
ducts, distinctions to be drawn
between, ii. 80.
Poisson, M., on the effects of solar
heat, ii. 307.
Pompeii, destruction of, ii. 213.
Pompeiopolis, half destroyed by an
earthquake, ii. 242.
Pontypool, coal district of, i. 181.
Ponza Islands, extinct volcanos of,
ii. 226.
Porphyry, where found, i. 121. 134.
291. Igneous origin of, ii. 71.
Portland, Isle of, "dirt bed" of,
i.71.
Portsoy, serpentine found at,i. 121.
Post-tertiary strata, their origin
and romposition, i. 278. Detri-
tal and other deposits of the,
281. Organic remains of, 298.
Table of vertebral remains found
in, 304. General considerations
of diluvial phenomena of, 316.
Zoological and botanical charac-
ters of the diluvial period, 319.
Ancient marine deposits of, 321 .
Marine deposits of, in progress,
329. Fluviatile and lacustrine
deposits of, ii. 1, et seq.
Poullaouen, mine of, its tempera-
ture, ii. 271.
Prenadillas, ejection of, by volca-
nos, ii. 2 1 5.
Pressure and tension, a cause of
the cleavage of rocks, ii. 117. 123.
The subject examined,! 23, <r< seq.
A 2
356
INDEX.
Prestwich, Mr., his notice of trap
rocks, i. 85. His observations on
the London clay, 255. His theory
accounting for the uplifting of
Moray Frith, 322.
Primary system, table of deposits
in the, i. 56. See Hypozoic and
Silurian Systems.
Prony, M., his account of the
Adriatic coast, ii. 28.
Pryce, Mr., on copper ore, ii. 170.
Pryme, Rev. A. de la, his descrip-
tion of Hatfield Chase, ii. 65.
His account of remains of a man
found in a turf pit, 67. His con.
elusion that the Romans were
destroyers of the forests at the
bottom of moors, now adopted
by geologists, 68.
Psalmodi, account of, ii. 28.
Pterodactylus, fossil remains of, i.
98.226."
Pucklechurch, dislocation of strata
at, i. 49.
Pumice, analysis of, ii. 95.
Purbeck beds, fossil deposits in, i.
92. Lacustrine deposits of, ii.
40.
Puzzolana of Naples, its composi-
tion, ii. 214.
Pyrenees, dip of stratified rocks in
the, i. 37. Offer an example of
the granitic basis of the earth's
crust, 108. Three depositaries
of iron ore in, ii. 163. Its mineral
springs and their chemical ana-
lysis, '256.
Pyrogenous rocks, antiquity of, ii.
145.
Pythagoras, maxim of, ii. 125.
Quadersanstein of Weinbohla, i.
244.
Quadrumana, remains of, dis-
covered in the lacustrine deposit
of Sansan, &c., i. 100. See Or-
ganic Remains.
Quartz, proportion of oxygen in, i.
25. Its composition, 31. Ar-
rangement of, in cross courses of
Cornwall, ii. 167. Cross courses
of, 173.
Quetelet, M., his experiments on
heat, ii. 267.
Quito, volcanos of, ii. 230.
R.
Rabenstein, cavern of, animal re-
mains tound in, i. 311.
Raffles, Sir Stamford, his account
of the volcanic eruptions of Java,
ii. 228.
Raiatea, island of, its coral reefs, i.
332.
Railways, construction of, a know-
ledge of Geology necessary for,
Rain, its effects as an agent of dis-
integration, ii. 10.
Ramsay, Mr., ordnance maps of, i.
129.
Rasleigh, Mr. P., on the deposit of
Sandrycock, ii. 60, 61.
Red Sea, volcanic phenomena near
the, ii. 228.
Refrigeration and its effects, ii. 264.
305, et seq.
Reliquiae, organic, best method for
comprehending, i. 103.
Remains, organic, found in various
strata, i. 118. 131. 140. 156. 170.
198. 205. 222. 238. 264. 298—316.
ii. 4],etseq.
Reptiles (Reptilia), fossil remains
of, i. 91. See Organic Remains.
Rhine, fossil deposits in the, i. 92.
269. Amount of mud carried off
by its waters, ii. 33.
Rhinoceros, skeleton of a, found in
Dream Cavern, i. 311.
Rhine, delta of the, how formed,
ii. 25. Deposits from the, 29.
Ribblesdale, notice of sparry cracks
at, i. 64.
Richardson, Dr., his account of the
Giant's Causeway, i. 244.
" Rider," explanation of the term,
ii. 166.
Riley, Mr., his discoveries in fossil
zoology, i. 94.
" Rise," meaning of the term, i. 36.
Riobamba, destruction of, by an
earthquake, ii. 221.
Rivers, their effects in disinte-
grating the earth's surface, ii. 20.
Lakes formed in the course of,
23. New land formed at the
mouths of, 27.
Roads, their construction neces-
sarily involves a knowledge of
Geology, ii. 329.
Rock, ocean of melted, under South
America, ii. 247.
Rock salt, origin of, i. 210.
Rock sandstone, its composition,
i. 31.
Rock terraces in valleys, ii. 6.
Rocks of the New York system,
Mr. Hall's classification of, i.
143.
Rocks, proportions of oxygen con-
tained in certain, i. 24. Forms
of masses of, 35. Position of,
INDEX.
357
with respect to surface of the
earth, 36. Fissures in, 303. Par-
ticles of, re-arranged by action of
igneous rocks, ii. 126. Alteration
of chemical nature of, produced
by igneous action, 131. Argilla-
ceous slaty, altered by the prox-
imity of granite, 142.
Rocks, igneous, prevalence of, be-
neath gneiss and mica schist, i.
121. In Palaeozoic strata, 134.
In Silurian system, 148. In Car-
boniferous system, 184. In Tri-
assic system, 208. In Oolitic
system, 231. In Cretaceous sys-
tem, 243. Origin of unstrati-
fied, ii. 71. See Rocks, Unstra-
t'fied. Gradations among, 87.
Chemical composition of, 90.
Analysis of minerals found in,
91—95. Exterior forms of the
masses of, 95. Interposed beds
of, 95. Overlying masses of, 97.
Fissures in, 97. Dvkes in, 98.
Veins in, 99. Amorphous masses
tinder all the strata of, 108. In-
ternal divisions of, 108. Pheno-
mena of, when in contact with
stratified masses, 109. Alteration
of the structure of, by heat, 111.
Metamorphism of ro'cks, a phe-
nomenon of,125. Re-arrangement
of particles of limestone rocks, a
phenomenon of, 126. Alteration
of the chemical nature of rocks
a result of the action of, 131.
New minerals formed by the
action of, 136. Metamorphic
slates, another result of, 139.
Metamorphism of mica schist
and gneiss caused by action of,
143. Antiquity of, 145. Tables of
principal disturbances of stratifi-
cation in connection with, 152.
Rocks, metamorphic, ii. 125.
Rocks, mixed, ii. 86.
Rocks, pyrogenous, antiquity of,
ii« 145.
Rocks, series of stratified, i. 9. 53.
Lapse of time, how ascertained
from their nature, 10. Their dip
at various parts of England and
the Continent, 37. Local decli-
nations of, 39. Relation of faults
to disturbed, 44. Origin of strati-
fied and unstratified,45. Varieties
ofstratified,59. SecondaryofYork-
shire, 66. Cleavage of stratified,
67. Historical view of stratified,
in the earth's crust, 107. Phe-
nomena attending igneous rocks
when in contact with, ii. 109.
Induration of, 109. Temperature
of, 272. Displacements of, 289.
Rocks, unstratified, crystallisation
of, ii. 47. General remarks on,
71. Their igneous origin, 71.
Geological age of, 72. Composi-
tion of, 72. Mineral composition
of, 80. Gradations among ig-
neous, 87. Chemical composi-
tion of, 90. See Rocks, Igneous.
Rocks, volcanic, Scrope's synopsis
of, ii. 83. Classification of, 84
—87. See Volcanos.
Rodentia in marine deposits, i. 272.
See Organic Remains.
Rogers, Professor, reference to his
report on the succession of strata,
i. 237. Tertiaries of N ."America,
how classed by, 264. '270. On
extinct gigantic animals of North
America, ii. 69. On earthquakes,
244, et seq.
Romans, woods of England de-
stroyed by the, ii. 68.
Rose, Mr., researches of, on augite
and hornblende, ii. 81.
Rosenmuller, M., his discovery of
animal remains in caves of Ger-
many, i. 312.
Rossberg Fall, ii. 20.
Rosse, Lord, his observations on
Nebula, i. 32.
Rotheliegende, where found, i. 203.
Rowley Hills, basalt of. ii. 73. 109.
Rudberg, M., his experiments on
heat, ii. 267.
Ruminantia in marine deposits, i.
273. See Organic Remains.
Russia, coal districts of, i. 183.
Sabine, Colonel, on the sea current
of Maranon, i. 343.
Saddle, meaning of the word as
used in geology, i. 39.
Saliferous system. See Permian
and Triassic Systems.
Salisbury craigs, greenstone of, ii.
110.
Salt, origin of, i. 210. Rocks which
enclose, 211. Cheshire district,
212.
Salt mines, of Northwich, i. 63.
Their temperature, ii. 273. Of
Bex, their temperature, 272.
Sand banks, origin accounted for,
i.341.
Sands bf London, their composi-
sition, i. 16.
Sandstone, of Cumberland and
Westmoreland, i. 16. Proportion
of oxygen in, 25. Its analysis, 31 .
Table of deposits of new red, 55.
Table of deposits of old red, 56.
A A 3
358
INDEX.
Thickness in Scotland, 160. Its
change of character in South
Devon and on the Severn, 160.
Raised by Murchison to the rank
of a system, 162. Real littoral
types of, 245.
Sandrycock, deposit of, ii. 60.
Sansan, remains of quadrumana in
lacustrine deposits of, i. 100.
Santorini, Islands of, changes in the,
ii. 236.
Saurians, Professor Owen's divi-
sion of, i.92. Fossil remains of,
92, et seq. See Organic Re-
mains.
Saussure, M., on the mountains of
Switzerland, i. 38. On the strata
of Buet, ii. 145. On the tern-
perature of Bex mines, 272.
Sea Fell, height of, i. 133.
Scenery, of England, its character
dependent on strata of the dis-
trict, i. 176. ii. 325. Of the earth,
dependent on its geological for-
mations, ii. 324.
Sciacca, Island of, its transitory na-
ture, ii. 222. 237.
Scriptures, Jewish, their use, i. 10.
Scrope, Mr., on volcanic rocks, ii.83.
Sea and land, distribution of the
earth into, ii. 286.
Secondary system, table of its de-
posits, i. 54. Its rocks, 66. Dis-
turbances at its close, '244. See
Carboniferous and following Sys-
tems.
Sedgwick, Professor, Lower Cam-
brian system of, i. 124. His ar-
rangement of the clay-slate sys-
tem, 124, et seq. His investiga-
tion of the Silurian system, 146.
162. His opinion respecting shelly
marls of Gosau, 237. His section
of the tertiary series, 258. His
description of the granite veins
of Trewavas Head, ii. 105. His
account of the strata of the Cal-
dew, 140.
Selwyn, Mr., reference to, i. 129.
Serpentine, where found, i. 121. Its
composition, ii.94.
Severn, fossils of the, i. 140. De-
posits of gravel in valley of, 301 .
Its rock terraces, ii. 7. Analysis
of its waters, 34.
Sewalick Hills, Hindostan, re-
mains of quadrumana in, i. 100.
Shap, dip of stratified rocks at, i. 37.
Sharpe, Mr., his illustration of the
idea, that "pressure" is a cause
of cleavage, ii. 117. 120, et seq.
Shells, freshwater, found in I. of
fc Wight, i. 77. Found in raised sea-
beaches, 321, et seq. Beds of,
336. Classes of, at various depths
of the sea, 340. See Organic Re-
mains.
Sheppy, fossil remains of turtles
found in the clay of, i. 92.
"Shoot" of ore, meaning of the
term, ii. 168.
Siebengebirge, trachytic mountains
of, ii. 223.
Sienite, composition of, ii. 93. Of
Christiania, 143, 144.
Sienitic granite, occurrence of, in
Strontian and Ben Cruachan, i.
108.
Silica, proportion of oxygen in, i.
24. ii.73.
Silurian System, Sir R. Murchison 's
classification of, i. 124. 136. Ta-
bles of deposits of, 139. 157. Its
composition, 136. Its structure,
136. Succession and thickness
of its strata, 138. Organic re-
mains found in, 140. Its geogra-
phical extent, 146. Its physical
geography, 148. Igneous rocks
of, 148. Mineral veins found in,
149. Close of the Silurian period,
and ensuing disturbances of the
earth's crust, 149.
Silver ore, proportions of, found in
mines of Freyberg, ii. 174.
Silvertop, Colonel, his account of
the deposits of the Alhama beds,
ii. 44.
Skaptaa J^kul, preat eruptions of,
ii. 211. 219. Mr. Lyell's descrip-
tion of, 212.
Skiddaw, granitic veins of, i. 109-
Igneous rock of, 121 . Clay slate
of, 126. 129. Height of, 133.
Skye, Island of, Macculloch's ac-
count of, ii. 96. 126.
Slate system, i. 124. See Paleozoic
Strata and Clay-slate System.
Slates, metam orphic, how and
where found, ii. 139, 140.
Smith, Dr. W., reference to, i. 44.
His notice of disturbed strata at
Pucklechurch, 49. Signification
attached by him to the word
stratum, 60. His principles con-
firmed by Murchison, 140. His
opinion respecting the divisional
strata of England, 218.
Snow, the parent of glaciers, ii. 19.
Suowdon, Snowdonia, abundance
of zoophyta in summit of, i. 75.
Clay-slate of, 126. 129. Porphyry
and greenstone of, 134.
Society Islands, coral reefs of the,
i. 332.
Soil, or external investment of the
land, an object of interest to
geologists, i. 33. Its depth ex-
INDEX.
359
tremely irregular, 33. Its super-
ficial and local accumulations
considered, 34. A chemical
knowledge of, necessary for agri-
culture, ii. 326, et seq.
Solar heat, its influence on climate,
ii. 305, et seq. Its variability,
306.
Solfatara, extinct volcano of, ii.
220.
Somerville, Mrs., her quotation of
Leslie, i. 27.
South S^a Islands, their prigin dis-
similar to that of the Bahamas,
&c., i. 139.
Sowerby, Mr., fossils of S. Devon,
first figured by, i. 156.
Springs, effects of, as agents of dis-
integration, ii. 19. Thermal,
see Tfiermal Springs.
Sponges, see Organic Remains.
Spruce fir, remarkable height of
one at Fountain's Abbey, ii. 67.
Stabiae, destruction of, ii. 213.
Staffa, basalt of, its analysis, ii. 95,
96.
Staffordshire, ironstone how found
in, i. 165.
Stiperstones, disturbed strata at,
i. 44.
Stones, meteoric, their origin, i. 32.
Their ejection by volcanos, ii.
235.
Stonpsfield, fossil remains In the
oolite of, i. 92. 96, 97, 98. 106. 223.
ii. 39.
Stony Middleton, waters of, their
analysis, ii. 255.
Strabo, hi* account of the surface
of Asia Minor, i. 1.
Strata of the earth, its age, how
ascertained, i. 9. Declination of,
36. Unusual position of, 39. Sec-
tions of, 53.
Strata, Hypozoic, i. 111. Palaeo-
zoic, 124. Silurian, 136. Of the
Devonian system, 154. Of the
Carboniferous system, 162. Of
the Permian system, 195. Of
the Oolitic system, 199. Of the
Mesozoic system, 203. Of the
Tnassic system, 203. Of the Cre-
taceous system, 234. Of the
Cainoroic, or Tertiary, system,
249. Of the Post-tertiary sys-
tem, 278.
Stratification, faults in, i. 40. Sel-
dom produced in perfection, ex-
cept by water. 45. Relative pe-
riods of disturbed, 49. Varieties
of, 59. Less easily traceable in
gneiss and mica schists, 115.
Tables of principal disturbances
of, ii. lo'2,etseq.
Stratified rocks, meaning of the
term, i. 9. Their construction
explained, 9. Their antiquity,
9. Their dip at various parts of
England and the Continent, 37.
Their local declination and un-
usual position, 39. Faults in, 40.
Origin of, 45. Generally stored
with reliquiae of plants, &c., 47.
Affected by subterranean move-
ments, 48. Series of, 53. Varie-
ties of, 59. Divisional structures
in, 62. Cleavage of, 67. His-
torical view of, in the crust of
the earth, 107. Phenomena at-
tending igneous rocks, when in
contact with, ii. 109. Induration
of, 109. Experiments on tem-
perature of, 272. Displacements
of, 289.
Stratum, meaning attached to the
word by different geologists, i.
59,60.
Strickland, Mr., on the Silurian
system, i. 147.
Strike, meaning of the term, i. 36.
Stromboli, its volcano always ac-
tive, ii. 218.
Strontian, sienitic granite of, i. 108.
Stratification plain in the gneiss
of, 115. Lead mine of, 122.
Structures, divisional, explanation
of, i. 62. Superposed, 115. Of
rocks, altered by heat, ii. 111.
Stutchbury, Mr., his discoveries in
fossil zoology, i. 94. On the
growth of coral, 330, et seq.
Styiia, Lower, basin of, tertiary
series of, i. 258, 259.
Submarine and subterranean fo-
rests, ii. 57. Their antiquity, 64.
Subsidence, movements of, ii. 239.
Substances of the earth, analysis
of, i. 23. 54. Number of elemen-
tary, 23.
Succession of strata, the law of, ii.
282. See Strata.
Sulphurets, formation of, ii. 198.
Sulphuric acid, its combination
with the waters of Purace, ii.
215.
Superficial deponts, see Post-
tertiary Strata.
Superposed structures, i. 115.
Surace of the earth, its age how
ascertained, i. 11. Its waste, ii.
9. Aspect of, 318.
Sussex Weald, passim.
Sykes, Rev. C., his collection of
fossils, i. 96.
Systems of the various strata, see
Strata,Hypozoic, and other Strata.
Swinden, M. Van, his account of
the Friesland lakes, ii. 61.
360
INDEX
T.
Taafe's Well, Cardiff, analysis of
the waters of, ii. 255.
Tahaa, coral reef of, i. 332.
Tahiti, coral reefs of, i. 332. 333.
Extinct crater of, ii. 232.
Talcahuano, destruction of, by a
wave, ii. 241.
Tarentaise, oolitic strata of, ii. 144.
Tay, Frith of, deposits of, ii. 60.
Tees, river, waterfall of, ii. 112.
Teesdale, crystallised minerals
found in, i. 123.
Temperature, of the earth, see
Earth, Globe, Heat. Of mineral
springs, ii. 255, et seq. See Ther-
mal Springs. Of the atmosphere,
263. Of mines, 270, et seq. Of
stratified rocks, 272. Of coal
mines,274. Ot Artesian wells, 276.
Teneriffe, Peak of, ii. 209. 231.
Weight and velocity of stones
ejected from, 235.
Terraces in valleys, ii. 6.
Terrain tertiare, i. 249.
Tertiary period, table of deposits
of the, i. 43. 54. Composition of
the, 249, 250. Structure and stra-
tification of, 251. Divisional
planes of, 252. Succession and
thickness of, 252. Freshwater
formations of, 254. Geogra-
| phical extent and physical geo-
graphy of, 260. Organic remains
found in, 264. Disturbances
during and after, 276.
Testacea, comparative table of, i.
327. See Organic Remains.
Thames, valley of the, deposits of
mammalia in, ii. 51.
Theory of mineral veins, ii. 177.
Thermal springs, their origin, tem-
perature, and chemical pro-
perties, ii. 252, et seq. List of
British, yielding nitrogen, 255.
List of German, yielding carbonic
L acid, 256. Of the Pyrenees, 257.
Heat of, derived from volcanic
action, 257. ; and from depths of
the channels from the surface,
258. Numerous in volcanic re-
gions as well as in ancient lines
» of uplifted rocks, 258. State-
ment of degrees of temperature
of the various, 259, 260. Their
quantityand temperature affected
by earthquakes and volcanic vio-
lence, 261. Importance of gene-
ral conclusions to be derived from
a study of, 261.
Thecodontosaurus, discovery of the,
i. 94.
Thuringerwald, zechstein" 'of, .i.
202.
Thylacotherium, new name for
marsupials, i. 96.
Tierra del Fuego, volcano of, 'ii.
230.
Tignaux, tower of, ii. 28.
Time, geological, scale of, i. 8.
Lapse of, how ascertained, 10.
Nature of the scale of, 12. Terms
of the scale, 12. 14. Interruptions
of the series of, 16. Length of
thp scale of, 17.
Tin Croft mine, ii. 185.
Tin ore, drifted, ii. 60. At what
depth found, 170. Position of
oldest mines of, 171.
" Toadstone," volcanic rock, ii. 96.
Tornideon, mountain of, ii. 102.
Torre del Greco, lava of, its den-
sity, ii. 209. Destroyed by lava,
III.
Touraine, mammalia found in the
marine beds of, ii. 45.
Towey, vale of, i. 139.
Trachyte, how found combined,
ii. 83.
Transylvania, volcanic rocks of,
ii. -224.
Trap dykes, ii. 98.
Trap rocks, passim. See Igneous
Rocks, Carboniferous System.
Trebra, Mr., his experiments on
temperature of the Freyherg
mil es, ii. 270.
Trees buried in course of a river,
ii. 57.
Trenton limestones, organic re-
mains in. i. 144.
Tresavean copper mine, its tem-
perature, ii. 272.
Trewavas Head, phenomena of the
granite veins of, ii. 105.
Triassic system, considered a part
of the Saliferous system, i. 203.
Mr. Conybeare's union of, to the
magnesian limestone, 203. Its
composition, 203, et seq. Organic
remains of, 205. Its geographical
extent, 206. Its physical geogra-
phy, 208. Igneous rocks found
in, 208. Origin and aggregation
of the materials of, 209. Origin
of rock salt and gypsum of, 210.
Trilobites, where found, i. 147.
Trinidad, asphaltum of, ii. 230.
Trosachs, stratification in the mica
schist of, i. 115.
Trough, meaning of the geological
term, i. 39.
Turf moors, ii. 62.
Tunguragua, volcano of, ii. 215.
Discharge of " nioya " 1'rom the
foot of, ii. 215.
INDEX
361
Tynedale, great fattlt of, i. 41,42.
I Its length, 43.
U.
Uddevalla, vast quantities of shells
found at, and their use for the
making of footpaths, i. 324. Ex-
plored by Linnaeus, 327.
Ulverstone, dip of stratified rocks
at, i. 37.
Undulations of the interior of the
earth, ii. 322. Remarkable in-
stances of, 323.
Unstratified rocks, i. 45. Crystal-
lisation of, 47. See Rocks, Un-
stratified and Igneous.
Ural, survey of, by Sir R. Murchi-
son, ii. 336.
^ : v.
Val d' Arno, ossiferous beds of the,
i. 280. Animal remains found
in, ii. 48.
Val di Fassa (Alps), hypersthenic
granite of, i. 108.
Valenciennes, M., his application
of the name Thylacotherium to
marsupials, i. 96.
Valley formations, ancient, ii. 2.
Their origin suggestive of inter-
esting inquiries, 4. Rock ter-
races in, 6.
Valparaiso, raised by convulsive
movements, ii. 241.
Van Diemen's Land, corals and
sponges abundant in, i. 105. Coal
of, 183.
Vauquelin, M., his analysis of ob-
sidian from Hecla, ii.94.
Veins, mineral, in disturbed rocks,
i. 44. In igneous rocks, 72. ii.
99. Werner's distinction between
true and false, ii. 155. Their
geographical distribution, 156.
Their occurrence near centres of
igneous action, 159. Relation of,
to the substance and structure of
neighbouring rocks, 163. Rela-
tion of, to one another, 171-
Theory of, 177. Are posterior to
the rocks which they traverse,
178. Origin of vein fissures, 188.
Filling of the fissures, 192. Re-
capitulation of the subject, 196.
Verde, Cape de, volcanic iu cha-
racter, ii. 231.
Vermuiden, Sir Cornelius, drains
Hatfield Chase, ii. 65.
Verneuil, Dr., geological labours
Of, i. 200.
Verschoyle, Archdeacon, on the
trap dykes of Mayo and Sligo, ii.
98.
Vertebral remains, tables of, found
in post-tertiary accumulations,
304.
Vesuvius, incidental reference to,
i. 277. Deposition of specular
iron in lava of, ii. 160. Pheno-
mena attending its eruptions,
204. Minerals found in products
of, 210. Eruption of, destroys
Torre del Greco, 211. Various
eruptions of. 213. 217, et seq.
Discnarge of boiling water from,
215. Its history very instructive,
216. Its cone of modern date,
216. Pliny's narrative of the
great eruption, 216. Weight of
stones ejected from, 235.
Villarica, volcano of, 230.
Virgil, reference to .Eneid of, ii.
220.
Volcanic action, remarks on, ii.
201. Exhibition of the forces of,
234. See Volcanos.
Volcanic rocks, synopsis of, ii. 83.
Classification of, 84 — 87. See
Volcanos.
Volcanos, of Auvergne, and Eu-
ganean Hills and Hungary, phe-
nomena attending violence of, i,
278. Of Etna and Vesuvius,
277, 278. See Etna', Vesuvius.
Phenomena of, indicative of pre-
sence and degree of heat below
the earth's surface, ii. 200. Ac-
tion of, 201. Origin of, 202.
Phenomena attending those in
action, 208. Earthquakes pre-
monitory of eruptions of, 208.
Dispersion of ashes and stones
by, 213. 235. Extinction of, 216.
Account of extinct, 220. Geo-
graphical distribution of, 221.
Asiatic, 227. American, 229.
African, 231. Australian, 232.
Of the Indian Ocean, 232. Of
the Pacific Ocean, 232. Geolo-
gical age of, 233. Eruption
forces of earthquakes, 234. Hy-
pothesis of volcanic action, 248.
Vosges mines, temperature of the,
U. 270.
W.
Wales, principality of, dip of stra-
tified rocks in, i. 38. Mica.schist
and gneiss rarely occur in, 58.
Cleavage of rocks in, 68. Slate
of, 126, et seq. Surveyed by
Murchison, 136. Coal fields of,
181.
362
INDEX.
Wales, New South, coal of, i. 183.
Ware, Dr. H., on the Shetland
Isles, ii. 88.
Water, weight of, below the earth,
i. 27.
Watt, Mr. Gregory, his experi-
ments on the amorphous basalt
of Rowley, ii. 73. 109.
Waves, Acosta on, ii. 242. See
Earthquakes.
Weald of Sussex and Wealden
formation, freshwater shells of
the, i. 77. Deposits of the, ii. 2.
References to, passim.
Weaver, valley of the, speculation
respecting the, i. 212.
Weighten, ossiferous beds of, date
of, unfixed, i. 280.
Weinbohla, quadersandstein of, i.
244.
Wells, Artesian, their temperature,
ii. 276. A knowledge of geology
requisite for discovery of, 328.
Wenlock formation, zoophytes
and corals abundant in, i. 75.
138. Limestone of, 136. Table
of the formation, 139.
Werner, his view of geology as a
branch of mineralogy, i. 1. 4.
His study of the Scottish and
Saxon mountains, 38. On py-
rogenous rocks, ii. 146. His dis-
tinction between " true " and
; false veins, 155. His classifica-
tion of the veins of Freyberg,
171. 174. On the union between
a vein and a rock, 186. On fis-
sures in mineral veins, 194.
Westmoreland, red sandstone of,
i. 16. Clay slate of, 126. Lake
district of, 133.
Westphalia, organic remains of
plants in, i. 72.
Wharfdale, scar limestone of, i.
63.
Whewell, Mr., allusion to, i. 21. ii.
288. 307.
"Whin Sill," in Crossfell, basaltic
formation of the, ii. 96.
Whitehaven, dip of stratified rocks
at,i.37.
Wicklow Mountains, afiford an ex-
ample of the granitic basis of
the earth's crust, i. 108. 121. |
Wieliczka, salt mines of the, i. 212.
Wiesbaden, mineral waters of,
their analysis, ii. 256.
Wight. Isle of, freshwater shells
found in, i. 77. Marine tertiaries
principally exhibited in, '^54.
Williams, Mr., on mineral veins,
ii. 165. On Huel Peever Mine,
180.
Wittgendorf, diluvial deposits at,
ii. 69.
Wrekin, fissures in the, ii. 97, 98.
Wren's Nest, Dudley, i. 137.
Wurtemberg, salt mines of, i. 212.
Wye and the Meuse, similarity of
their course, i. 176.
Yoredale rocks, i. 176. ii. 6.
Yorkshire, dislocation of coal and
limestone strata in, i. 50. Table
of secondary rocks of, 66. Coal
formations of, 167. Amount of
molluscous reliquiae found in,
173.
" Yorkshire, Geology of," quoted
and referred to, i" 137. 172. 190.
ii. 112. 162.311.
Z.
Zechstein, where found, i. 202, et
scq.
Zetland, serpentine found in, i.
121.
Zircon sienites, their transporta-
tion, i. 291.
Zoology, its use in the pursuit of
geology exemplified, passim.
But see Organic Remains of va-
rious Strata.
Zoophyta, fossil, i. 73. Table of,
76. See Organic llemains, Co-
rals.
Zuyder Zee, its excavation by the
sea, ii. 33.
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