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WH THREE CRUISES OF THE BLAKE, VOL. 1.

BULLETIN

OF THE

ee - ' j
Hal ae | /

‘MUSEUM OF COMPARATIVE ZOOLOGY

HARVARD COLLEGE, IN CAMBRIDGE.

VOL. XIV.

[Published by permission of CARLILE P, PaTTERson and Jutius E. Hircarp
Superintendents U. S. Coast and Geodetic Survey.|

CAMBRIDGE, MASS., U. S. A. _
1888.

613755
fas

SCOAST AND GEODETIC SURVEY
LE Rigert Sup
WESTERN PART OF
ATLANTIC OCEAN
INCLUDING
PART OF GULF OF MEXICO

AND

|

peers

A Contribution to American Thalassography.

THREE CRUISES

OF THE

UNITED STATES COAST AND GEODETIC SURVEY

STEAMER “BLAKE”

IN THE GULF OF MEXICO, IN THE CARIBBEAN SEA, AND ALONG
THE ATLANTIC COAST OF THE UNITED STATES,
FROM 1877 TO 1880.

BY

ALEXANDER AGASSIZ.

IN TWO VOLUMES.
VOL. I.

BOSTON AND NEW YORK:
HOUGHTON, MIFFLIN AND COMPANY.
Che Riversive JOress, Cambridge.
1888.

Copyright, 1888,
By ALEXANDER AGASSIZ.

All rights reserved.

[Published by permission of CaRLite P. Patterson and JuLius E. HILeaRD,
Superintendents U. S. Coast and Geodetic Survey.]

The Riverside Press, Cambridge :
Electrotyped and Printed by H. 0. Houghton & Oo.

DEDICATED

TO

The Slemorp of
ig FF POURTALES,

A PIONEER IN DEEP-SEA DREDGING,
BY

ALEXANDER AGASSIZ.

wil

CONTENTS OF VOLUME I.

Bemwnnuerion. + (FiesA-Bo). 0-72. fs Bk ee ee ke
i Eqourmenr or tHe “Biane.” (Hos. 1-33.) - . 2 se ew ee we «6
7), HMisroricAn Sxerca or Deep-Sea Work - . .... +s « . 3
ii an Frerma Beers. « (Wigs. 34-54.) 2. 2 ee fie ck ee 8 we
IV. TorpoGrRapHy OF THE: EASTERN COAST OF THE NorTH AMERICAN
DONEENEN ES (Ham bo-Gl iw. 26S ape ss, Beau) wy = 15) 9S
V. RELATIONS OF THE AMERICAN AND West INDIAN FAUNA AND FiLorA 109
VI. THe PERMANENCE OF CONTINENTS AND OF OcEANIC Basins. (Fig.
LD) SOE me er em me? = MY ke iy Vente Dn ee ire a 175
ePrice PORMATIONS:.* . Gas. je 5 > w eee aes <4
Peeeieds: Derr oeA WAUNA; 7 go GS) 26. 6S) . eee 2, 27S
IX. Tue Peracic Fauna anv Fuora. (Figs. 63-139.). . . . . . . 171
X. TEMPERATURES OF THE CARIBBEAN, GULF OF Mexico, AND WEST-
wen Arnanric. (Figs. 140-167.) .-. ... 5... - DMT
a GULS STREAM. (Vigs. 168-176.) 02... 2 6 ss ape SAE
XI. Sopmarme Deposits. (Figs. 177-192.) . . . .. .... + « 260
XII. Toe Puysiotocy or Deep-Sea Lire. (Figs. 193,194.) . . . . . 294

Nore. — A List of the Figures will be found at the end of Volume II.

cA “ahha. vi
~

ae

INTRODUCTION.

—————__

My connection with the thalassographic work of the Coast
Survey dates back to 1849, when, as a boy, I accompanied Pro-
fessor Agassiz in his cruise on the “ Bibb ” off Nantucket, and
afterward, in 1851, served as aid on his survey of the Florida
Reef. More than twenty years later I returned to this line of
study, in a report on a part of the collections made by Pourtalés
in the “ Bibb ” in deep water in 1867-68, and since that time I
have been engaged, with little interruption, more or less directly
in deep-sea work. It was therefore natural that I should accept
the invitation given me in 1877, by Mr. Patterson, the Superin-
tendent of the Coast Survey, to continue, under its auspices, the
work in which I had begun my biological studies. If at times
the physical difficulties encountered were somewhat discour-
aging, it was a great pleasure to find that my professional train-
ing as an engineer not only contributed in no small measure to
the success of the expedition, but also increased my interest
in the many problems of deep-sea explorations.

The field of work opened to naturalists by thalassographic
surveys is of the greatest importance. The materials collected
throw a flood of light on our knowledge of the conditions of
animal life in deep water, and promise the most important gen-
eral conclusions on terrestrial physics and on geology. Fasci-
nating as has always been the study of marine life, this interest
has greatly increased since we have found the means of reach-
ing the abyssal fauna. Light has suddenly been shed on many
vexed problems concerning the geographical distribution of
animals and plants and their succession in time from former
geological periods to the present day. New notions of geologi-

Vill INTRODUCTION.

eal horizons and periods loom up before us, and the problems
concerning the formation of continents and oceanic basins now
present themselves from a very different standpoimt. Our ideas
regarding the formation of many marine deposits have been
greatly modified, and we are now able to look back into the
past history of the world with more confidence than heretofore.

The plans of the equipment of our expeditions were naturally
discussed with the Superintendent of the Coast Survey, with the
commanding officers, Lieut.-Commander Sigsbee and Commander
Bartlett, and during the cruise the criticisms and suggestions of
the commanders, of Lieutenants Ackley, Sharrer, Mentz, and of
the other officers of the ship, Messrs. Jacoby, Reynolds, and Pe-
ters, constantly modified our methods of work, and gradually
changed our apparatus to such an extent that it would have
been difficult to recognize the original dredging implements as
first devised. The exact share of each in these changes it is
impossible to state."

During the season of 1877-78 the dredging operations carried
on from December to March by the “ Blake,” in command of
Lieut.-Commander C. D. Sigsbee, U. 8. N., extended from Key
West to Havana, from Havana westward along the north coast
of Cuba, from Key West to the Tortugas, thence to the north-
ern extremity of the Yucatan Bank, to Alacran Reef, back to
Cape Catoche, and across to Cape San Antonio, returning to Key
West, and from Key West to the Tortugas, and northward to
the mouth of the Mississippi River. See track of “ Blake,”
Fig. A. After I left the “ Blake” that year, Sigsbee occupied
a number of stations off Havana in search of Pentacrinus, of
which we had obtained a quantity of fragments in the early part
of the cruise. He succeeded in discovering their haunts, and
was the first to dredge a number of specimens from a locality not
far from the Morro Light, which has become known as Sigbee’s
Pentacrinus ground.

Notwithstanding the delays incidental to bad weather and to
the unfortunate grounding of the “ Blake” at Bahia Honda
while in charge of a Spanish pilot, so that nearly three weeks

1 A detailed description of the “ Blake’’ moir on deep-sea sounding and dredging,
equipment is given by Sigsbee in his me- published by the U. S. Coast Survey.

INTRODUCTION. 1X

were lost before the ship could be floated and again in condition
to resume work, the following lines were run during the season
of 1877-78 : —

1. One lme from Havana to Sand Key, in depths of from 320
fathoms to 951 fathoms.

2. A second line along the coast of Cuba, from Havana to
a short distance west of Bahia Honda, from 292 fathoms to 850
fathoms.

3. A short line of about 40 miles northerly from the Tortu-
gas, from 111 fathoms to 37 fathoms, to examine the character
of the fauna of the Florida Bank to the westward of the main-
land as far as the hundred-fathom curve.

4, A line from the hundred-fathom curve on the west side of
the Florida Bank about 30 miles north of the Tortugas, across
to the hundred-fathom curve on the northeastern side of the
Yucatan Bank, from 110 fathoms to'1,920 fathoms, and back
to 95 fathoms.

5. A line from 1,568 fathoms north of the Alacran Reef,
from the deep basin extending from the northern slope of the
Yucatan Bank toward Vera Cruz up to 84 fathoms on the north-
ern edge of the Yucatan Bank.

6. A line from the hundred-fathom curve on the north side of
the Yucatan Bank to Alacran Reef, and from there in a south-
east direction into 20 fathoms off the Joblos Islands, diagonally
across the Yucatan Bank.

7. A line in the trough of the Gulf Stream from north of
Cape San Antonio to Sand Key, Florida, from 1,323 fathoms to
0309 fathoms.

In all, about 1,100 miles of lines, taking the shortest distances
from point to point.

Tn this first season the number of casts made with dredge and
trawl were over fifty, from 300 fathoms to 1,920 fathoms; of
these forty-three were successful hauls. In making 'them we
lost only 200 fathoms of steel rope.

8. Our operations were confined to dredging along a line to
the northward of the Tortugas, running, in a general way, par-
allel to the hundred-fathom curve of the western edge of the
Florida Bank. This line was extended northward to about.
the latitude of Tampa Bay, a distance of some 200 miles.

x INTRODUCTION.

9. A line was run from that point directly for the mouth of
the Mississippi, a distance somewhat less than 200 miles.

The weather during the greater part of our trip from the
Tortugas to New Orleans was very bad, as is usually the case
during March in the Gulf of Mexico. We could do but little’
beyond ascertaining, in the most general way, the faunal char-
acteristics of the lines run between Key West and New Orleans.
At New Orleans Mr. Garman and I left the ‘‘ Blake,” an event
which must have been a relief to the officers, more particularly
to the executive officer, Lieutenant Ackley, who was once more
free to put the ship in an orderly condition. The work of
dredging is not conducive to cleanliness, and during the whole
time I was on board no routine was ever allowed to interfere
with our work, Lieutenant Ackley himself always being the first
to see that everything was in readiness for our dredging opera-
tions at all times. That the interest shown in the work by the
other officers of the “ Blake,’ Messrs. Sharrer, Jacoby, Moore,
Sigsbee, and Dr. Nourse, did not flag after my departure is
amply demonstrated by the collections made off Havana, con-
taining as they do some of the most valuable specimens of the
expedition, all in an excellent state of preservation. The
“ Blake ” subsequently returned to Key West to continue her
regular work of sounding between the Tortugas, the coast of
Cuba, and the Yucatan Bank. On the way to Key West, a few
casts were made by Lieut.-Commander Sigsbee on the Florida
Bank, in Lat. 26° 31’, Lon. 89° 3’, in a depth of 119 fathoms,
at a point where a good notion of the fauna of the Florida Bank
could be obtained.

As connected with the work of oceanic exploration carried
on under the auspices of the U. S. Coast Survey, I may also
mention a visit to the Tortugas during 1881. I left Key West
for the Tortugas in the middle of March on the “ Laurel,” which
Lieut.-Commander Wright, in accordance with the permission of
the Lighthouse Board, had kindly ordered to transport me and
my assistant, Dr. Fewkes, to the Tortugas, with the necessary
coal for the steam launch which had been placed at my disposal
by Mr. Patterson. The launch I found ready at Key West,
fully equipped, manned, and provisioned, thanks to the care of
Lieut.-Commander Winn.

INTRODUCTION. Xi

While at the Tortugas we were allowed by the Secretary of
War to occupy such quarters at Fort Jefferson as were not oth-
erwise needed, and we selected as a laboratory a large room,
with excellent light, on the ground flocr of the barracks. On
days when the weather was not suitable for surface work out-
side in the Gulf Stream, I employed the launch in cruising
inside the reef, and thus examined carefully the topography of
the different groups of corals characteristic of the Florida reefs.
The results of this visit, as well as those made on previous occa-
sions, have enabled me to give a somewhat extended account of
the Florida reefs in a special chapter of this book. We re-
mained at the Tortugas five weeks, and returned to Key West
in the revenue steamer “ Dix,’ Captain Scammon, whom the
Secretary of the Treasury had authorized to assist us as far as
practicable. At Key West we occupied as a work-room the
loft of the Navy Depot building, and continued our studies of
the pelagic fauna of the Gulf Stream.

During the second dredging season (1878-79), the “ Blake”
was in charge of Commander J. R. Bartlett, U.S. N. The cruise
extended from Washington to Key West, from Key West to Ha-
vana, from Havana to Jamaica through the Old Bahama Chan-
nel and Windward Passage, from Jamaica to St. Thomas along
the south coast of Hayti and Porto Rico. From St. Thomas
the “Blake” visited Santa Cruz, Saba Bank, Montserrat, St.
Kitts, Guadeloupe, Dominica, Martinique, St. Lucia, St. Vin-
cent, the Grenadines, and Grenada ; she also carried the dredg-
ings south as far as the hundred-fathom line off Trinidad,
returned to St. Vincent, and finished the dredging operations
at Barbados.

On November 27, 1878, I joined the “ Blake” at Washing-
ton for a second dredging cruise. We intended to proceed to
Nassau, and there devote a few days to dredging and sounding,
in order to trace the connection between the fauna of the north-
ern extremity of the Bahama Banks and that of the Straits of
Florida. On account of rough weather this was not deemed
prudent, and we were compelled to put into St. Helena Sound ;
and, for the same reason, when off Jupiter Inlet, instead of
crossing the Gulf Stream to make Nassau, it was thought best

xl INTRODUCTION.

to put into Key West. From there, when the weather moder-
ated, we started for Kingston, Jamaica, calling at Havana for
the purpose of making a couple of hauls on the Pentacrinus

ground discovered by Sigsbee off the Morro Light. (Fig. B.)

Fig. B. — Morro Castle (Havana), with modern limestone terrace in foreground.

We made two casts of the dredge, passing from 175 to 400
fathoms, and obtamed a few specimens of Pentacrinus. We
kept on along the northern shore of Cuba, through the Old
Bahama Channel, without stopping to sound or dredge, Pour-
talés having in former years dredged and sounded from the
“ Bibb,” Acting Master Platt, U. S. N., over the greater part of
this line.

In the dredgings taken off the southeastern end of Jamaica
we did not bring up anything of great importance. From Ja-
maica we were obliged, owing to the strong trades, to keep on
toward St. Thomas, without either sounding or trawling till off
Porto Rico. During the winter months the trades blow suffi-
ciently hard to make dredging and sounding quite uncomfortable
on a vessel of the size of the “ Blake.” We therefore had no
opportunity of adding anything to the hydrography of that
part of the Caribbean Sea.

The region over which we chiefly worked this year reached
from St. Thomas to Trinidad. Over a limited area like this, it
was possible to cover the ground very satisfactorily. The work
done off the principal islands began usually at the hundred-
fathom line, and extended into. the deepest water off the lee side
of the Caribbean Islands. But little could be done in the way
of dredging in the passages between the islands or to the wind-
ward of them, owing to the strong trades. While working off -

INTRODUCTION. Xl

Barbados we undoubtedly obtained a fair representation of the
fauna to the windward of the Caribbean Islands, which does not
seem to differ from that of the lee side.

Tempting as it would have been to devote more time to a
prolonged study of the islands within sight of which we worked
for a whole winter, it was only natural “that our interest in the

land should give way to our work at sea.

~~ Our acquaintance with the Caribbean Islands was limited to
such examination as we could make from the deck of the
“ Blake,” as.we steamed from our night’s anchorage out into
deep water, or steamed and trawled slowly for days within sight
of the same island. Under these circumstances, we could not
fail to obtain a familiarity with their topography which few of
the inhabitants, or of even the more enthusiastic and energetic
foreign travellers, could have. The few excursions we were able
to make in the interior, while coaling or cleaning: boilers prepar-
atory to getting under way again, gave us charming glimpses
into regions rarely visited as yet. he traveller in these islands
is dependent almost entirely upon private hospitality, which,
however delightful it may be, is a great bar to independent ac-
tion and exploration. But the time is not distant when the-in-
creased facilities of communication will call into existence the
hotels which alone are needed to make the West India Islands
the winter resort of innumerable tourists, who now go to Florida
or to the south of Kurope. They will find in this new resort
the most lovely scenery imaginable, the perfection of winter cli-
mate, and unbounded hospitality ; and the lover of nature will
have endless occupation in the ever-varied rambles which each
island affords.

As seen from the sea, the contrasts offered by the different
islands is most striking. I will not here speak of Cuba, Jamaica,
Hayti, or Porto Rico, small continents as it were, although with
each of these the “ Blake” has some special association. Dur-
ing the first dredging cruise, the northern shore of Cuba from
Havana westward was partly explored by the “ Blake,’ and
while Bahia Honda will always remain to the commander a most
unpleasant landmark in the history of the cruise, because our
Spanish pilot ran us ashore as we entered the harbor, it is

XIV INTRODUCTION.

marked with a red letter in my journal as the spot where the
wonderful young Holopus was dredged.

The difficulty of dredging in ‘the region of the trade winds
with a small vessel like the “Blake” is very great. No ex-
tended explorations to windward were possible, but fortunately
we were able to reach deep water under the lee of the Lesser
Antilles. In the channels between the islands the sea was
usually too rough to allow us to sound even, and when steam-
ing to windward, as durmg the passage from Jamaica to St.
Thomas, all deep-sea work was out of the question, as we could
scarcely forge ahead, and we rejoiced to reach at last the shelter
of St. Thomas.

The appearance of the islands as seen from the deck of the
vessel is most interesting, each one having a physiognomy of its
own, yet all modifications of one type. If the physical features
are well marked, the national characteristics of the different
groups are no less so. Where Englishmen, Frenchmen, and
Spaniards once fought for the supremacy of the sea and the
possession of the New World, they are now content to live
in friendly rivalry with the Danish and Swedish West Indian
colonies.

The island of St. Thomas, with its land-locked harbor, near
the junction of the Lesser and Greater Antilles, is the central
West Indian station. It is a long, low, undulating island, with
summits reaching perhaps 800 feet in height, continuations of
the crests of the extensive submarine bank which forms the Vir-
gin Islands, one of which, Virgin Gorda, rises to nearly 1,800
feet. These islands are almost bare, and the larger ones, cov-
ered with wrecks of plantations and remaining uncultivated, are
gradually beg abandoned. The opposite island, Santa Cruz,
is, like the Virgin Islands, low, but its slopes are covered from
base to summit with brilliant fields of sugar-cane, and dotted
here and there with factories and thriving towns.

In the channel separating St. Thomas from Santa Cruz we
find the deepest water in which the “Blake” dredged, and
near Frederichsteed, at the western extremity of the island, we
come upon one of those rich localities characterized by an
extraordinary abundance of deep-sea animals in comparatively
shallow water.

INTRODUCTION. XV

From Santa Cruz we steam across the Saba Bank, dredg-
ing occasionally as the sea permits, and pass under the lee of
Saba, an old volcanic cone, which rises 1,500 feet sheer out of
the water. Steps lead up from the water’s edge, for a height
of 800 feet, to the bottom of an ancient crater, where a large
settlement exists. At Saba the greater part of the former rim
of the crater has disappeared, while at St. Eustatius the cone
is broken only at one point.

We next come to St. Kitts, perhaps one of the most eda
of the West India Islands, in its exhibition of their typical struc-
ture, —a single peak, rising to about 3,700 feet, but with gentle
slopes (Fig. C.), formed by old lava streams washed down by

Fig. C.— Western Slope of St. Kitts.

torrential tropical floods during the rainy season, and deeply
furrowed by diminutive caions. The whole outline of the
island is composed of graceful slopes, which become less steep
as they approach the sea, and covered nearly to the highest
point with flourishing sugar plantations, the steeper grades to-
wards the top of the crater becoming more and more barren as
they near the summit.

Such are in general the features of nearly all the Windward
Islands; the scenery varies as we pass from islands with one
summit to others with two or more peaks, and with slopes more
or less chiselled by the rains. Such islands as Saba, Montserrat,
St. Kitts, or St. Vincent, with a single central peak, present a
marked contrast to larger islands, like Guadeloupe, Martinique,
and Dominica, or to islands like the Grenadines, forming dis-
connected ridges rising from deep water, and differ still more

XVl1 INTRODUCTION.

from geologically recent islands like Sombrero, Barbuda, An-
tigua, and Barbados. St. Kitts may be said to form a twin
island with the adjoiming Nevis, which has a soufriére of its
own rising to 2,000 feet.

Montserrat comes next, another small volcanic island, well
known now for the large amount of lime-juice it exports. We
then pass by the lonely island of Redonda, with its cloud-
capped summit. Nearly all the higher peaks of the Windward
Islands are usually hidden from view by a cap of clouds, massed
against the windward sides, where the trade winds, saturated
with moisture, strike the cold fanks of the summit.

The huge central mass of Guadeloupe, perhaps the most mm-
posing of the West Indian volcanoes, rises to a height of at
least 5,000 feet. The larger island is separated by a swamp
from the Grande Terre, a low bank of recent limestone at the
base of the central voleano of Guadeloupe. The steep slopes
near the summit are covered with forests, but pass gradually
into the long, gentle cultivated slopes, which in thew turn fade
imperceptibly into the arid tracts of Grande Terre itself.

On the south, Guadeloupe is flanked by outlying islands, the
Saintes and Marie-Galante, where we dredge in vain for some of
the treasures of the deep, supposed to have been fished up in
the intervening channels by French naturalists at the beginning
of this century.

As we approach Martinique, it seems to consist of three sep-
arate mountain masses, not smoothly rounded, as in the more
northern islands, but with deeply furrowed flanks, cut out by
rains and torrents, and innumerable winding valleys, cultivated
from the water’s edge almost to the highest summits. The
island is crossed in all directions by excellent roads, and dotted
over with villages and plantations. The slopes of the deeper
valleys and the more inaccessible bottom lands are covered with
forests and with groves of tree ferns. Near the plantations,
avenues of royal palms rear their heads high above the dark
mango, orange, and lime trees. On the lee side of the island
is St. Pierre, the commercial centre of the French West Indies,
where at every step one is reminded of a French provincial
town. ‘T’o the south is the naval station of Port de France,

INTRODUCTION. XVI

separated by an inlet from the hamlet where the Empress Jose-
phine was born.

Nowhere else among the West India Islands are the slopes
so deeply furrowed as on the flanks of Dominica, a long com-
paratively low ridge, without prominent peaks, but with many
signs of active volcanic action. The island is as yet but little
cultivated, and on all sides one meets indications of its former
French dependency. But here, as in many of the islands
which have passed into English hands, and have been left
to shift for themselves, the results have not been satisfactory.
While at anchor in Petite Baie d’Arlet, we could not but be
pained at the wholesale destruction of humming-birds going
on. Ten thousand skins are annually exported from that single
settlement.

In St. Lucia, the most fertile of the West India Islands, there
is a handful of English settled at Castries, a deserted town,

Fig. D. — Pitons, St. Lucia.

neglected, like the island itself, and nearly abandoned. The
island is thickly wooded in parts; at the south end on the
lee side are two remarkable peaks, the Pitons, rising 2,700
feet perpendicularly out of the sea. (Fig. D.) Between them

XVill INTRODUCTION.

extends a lovely bay, where we anchored one evening, almost
touching the little beach, close to which stands a small collec-
tion of negro huts.

Coming to St. Vincent, we find it fairly cultivated on the
southern side. (Fig. E.) Its greater prosperity is undoubtedly

Fig. E. — Kingstown, St. Vincent.

due to its more varied agricultural interests, and the fall in
the price of sugar has not proved so disastrous there as in those
islands where the sugar crop forms the sole support of the pop-
ulation. From the southern extremity of the highest peak, the
soufriére in 1812 sent out vast sheets of lava during an eruption
which lasted for three days. It was heard eighty miles off, at
Barbados, which was enveloped in darkness and covered with
volcanic dust, while a heavy tidal wave swept its shores.

From St. Vincent we pass by the Grenadines, small, low, unin-
teresting islands, with names more romantic than their scenery ;
they are formed by the summits of a volcanic ridge rising ab-
ruptly out of deep water.

We come finally to Grenada, the last of. the Lesser Antilles.
Its excellent though small harbor reminds one of Malta on a
small scale, and the resemblance is not lessened as one goes
climbing the steep streets from the docks to the more level
region where Government House is located. At the entrance
of the harbor is Fort Richmond, and behind it rises the rim of

INTRODUCTION. X1x

an extinct crater, leadmg up to Mount Maitland, the highest
summit of Grenada.

There yet remain Tobago and Trinidad, but they are bits
of the South American continent, left stranded on the conti-
nental shelf.

Isolated from all the other islands, perhaps the least attractive
of them, stands Barbados, a volcanic cone, entirely surrounded
by coral terraces, which completely hide the cone. (See Figs.
39, 46.) In this the most flourishing of the English aelahde
the negro population is very dense. Pen is comparatively
as thickly populated as Belgium, and every inch of the soil is
cultivated. It is a huge sugar plantation, dotted over with
windmills and sugar-houses. Bridgetown has somewhat the
appearance of an Italian town. Its streets are crowded with
negroes, who, like their West Indian brethren, are noted neither
for morality nor cleanliness. Only about one tenth of the
population is white. There is a large garrison, so that Bridge-
town has its parade, cricket-ground, clubs, and all that renders
a British colony dear to an Englishman in exile.

The northeastern islands, Antigua, Barbuda, and Sombrero,
we did not visit. They are geologically more recent, and are
placed upon the eastern edge of the shallow plateau forming
the northern extremity of the submarine bank upon which the
Windward Islands rise. Of course they held out no imduce-
ment to the “Blake” expedition, which was in search of the
deep water on the lee side of this plateau.

For the third cruise I joined the “ Blake,” commanded by
Bartlett, at Newport, late in June, 1880. According to instruc-
tions, we proceeded to the northeastern edge of George’s Shoal,
where we ran our first line of dredgings from the hundred-
fathom line to a depth of nearly 1,250 fathoms. Our second
line was run to the southeast, off Montauk Poimt. This was
interrupted by bad weather. We were compelled to put into
Newport, and completed the line on our return from the South.
This line extended to about 1,400 fathoms.

On leaving Newport for the second time, we steamed directly
for Charleston, S. C. A line of dredgings was run from. the
hundred-fathom line normal to the coast, directly across the

xX INTRODUCTION.

Gulf Stream, to a distance of about 120 miles to the eastward
of Charleston. Finding that our depth did not increase at that
distance, — our greatest depth not bemg much more than 350
fathoms, — Commander Bartlett thought it prudent to return
towards shore, to the so-called axis of the Gulf Stream, and to
run a line in a northeastern direction parallel to the coast in the
trough of the Gulf Stream. To our great astonishment the
depth still did not increase, and we carried from 250 to less than
300 fathoms until we reached nearly the latitude of Cape Hat-.
teras, when in a short distance there was a very rapid drop from
352 fathoms to 1,386 fathoms. A fifth line was run normal to
this northern slope of the Gulf Stream plateau, to a depth of
1,632 fathoms. A sixth line was run to the northward of Cape
Hatteras, to a depth of 1,047 fathoms. A seventh line was run
east, off Cape May, from the hundred-fathom line to 1,200
fathoms.

In accordance with an arrangement made with the late Sir
Wyville Thomson, by which the collections made by American
and English deep-sea expeditions were to be sent to the same
specialists, the collections of the “ Blake ’’ were worked up
under the most favorable conditions. But as the greater part
of the collections made during the third cruise of the “ Blake ”
cover the extension into deep water of the ground already in
part occupied by the United States Fish Commission, the col-
lections made north of Cape Hatteras were sent to the natural-
ists to whom the collections of the Fish Commission had been
intrusted.

In the preparation of the final Reports published upon the
“ Blake ” collections, the special knowledge of those who have
carefully followed the development of a limited group of inver-
tebrates, their paleontological and geographical distribution,
their migrations, and the causes which have probably led to the
existing condition of things from a former geological period,
has been indispensable. I cannot adequately express my thanks
to the gentlemen who have so kindly undertaken the laborious
task of preparing the Reports of the “ Blake” collections.
Without their assistance, the work would have been neither
prompt nor satisfactory.

INTRODUCTION. Wr

The Report on the Hydroids was written by Prof. George J.
Allman ; on the Crinoids, by Dr. P. H. Carpenter ; on the Hy-
‘droids of the first expedition, by Prof. 8. F. Clarke; on the
Crustacea, by Prof. Alphonse Milne-Edwards; on the Annelids,
by Prof. Ehlers ; on the Myzostomide, by Prof. L. von Graff ; on
_ the Isopods, by Mr. Harger; on the Ophiurans, by Mr. Lyman;
on the Starfishes, by Prof. Perrier ; on the Corals, by Pourtalés;
on the Sponges, by Prof. Oscar Schmidt ; on the Bryozoa, by
Prof. Smitt ; on the Holothurians, by Dr. H. Théel; on the An-
thozoa, by Prof. Verrill; and on the Pygnogonide, by Prof. E.
B. Wilson. Mr. Garman, who accompanied me as assistant dur-
ing the first cruises of the “ Blake,” was indefatigable in caring
for the collections brought together, and he also wrote the
Report on the Selachians.

In addition to the preparation of the special Reports in their
departments, | am also indebted to Prof. Goode and Dr. Bean,
for additional notes on the Fishes ; to Mr. Dall, for the greater
part of the account of the Mollusks; to Mr. Lyman, for that of
the Ophiurans; to Mr. Fewkes, for that of the Acalephs; and
to Prof. S. I. Smith, for that of the Crustacea. To Mr. John
Murray I owe special thanks for his suggestions and assistance
in writing the chapter on Submarine Deposits. Commander
Sigsbee was kind enough to look over the chapter relating to
the equipment of the “ Blake.” Commander Bartlett of the
Hydrographic Office has read the chapters on the Gulf Stream
and on the hydrography of the Caribbean region; he has also
supervised for this volume the drawing of several of the accom-
panying maps.

I have myself prepared the Reports on the Coral Reefs, the
Surface Fauna of the Gulf Stream, the Sea-Urchins, and a few
minor papers relating to the cruises of the “ Blake.”

To the U. 8. Coast Survey Office I am of course under the
greatest obligation for copies of the many reports, maps, and
sections contained in that office to illustrate the hydrography of
the West Indian region and of the Gulf of Mexico, and that
of the Atlantic coast of the United States. Prof. James D.
Dana has kindly read some of the chapters relating to the geo-
logical problems discussed, and to Mr. Winsor I am indebted

XX INTRODUCTION.

for many suggestions relating to the history of the discovery of
the Gulf Stream.

The commanders of the “ Blake,” Lieut.-Commander Sigsbee
and Commander Bartlett, were ever ready to promote the special
interests of the cruise during my connection with the vessel, and
they were most cordially supported by the officers and crew in
this novel work, so foreign to their usual routine.

In arranging the following sketch of the work of the “ Blake”
expeditions, I have collected in different chapters what I had to
say regarding the special subjects of which they treat, based
upon the experience gained during the voyages with which I
have been associated. The greater part of these chapters has
been in type for more than two years; this will account for
some anachronisms, and for some omissions of reference to pub-
lications which would otherwise have been noticed. While of
course dealing with the subject of Thalassography as a whole,
I have avoided as far as possible all unimportant comparative
work.

ALEXANDER AGASSIZ.

5
MusEuM oF CoMPARATIVE ZOOLOGY,
CAMBRIDGE, December, 1887.

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THREE CRUISES OF THE “BLAKE.”

—_——~————_—.

I.
EQUIPMENT OF THE “BLAKE.”

THE principal object of the hydrographer is to ascertain the
depth of the sea at any given point, and this seems at first
glance a very simple process. Sounding in a few fathoms with
an ordinary lead-line and a heavy sinker presents no difficulties,
and even in one hundred fathoms the hand lead-line can be used
with a moderate degree of accuracy. Beyond this, the problem
is very different. I well remember my own first experience of
sounding, in Lake Titicaca, in not more than one hundred and
fifty-four fathoms, — when more than five hundred fathoms of
_ line were payed out and “no bottom” reported. This unsatis-
factory result was due simply to the insufficiency of weight of
the sinker. The experience of those who with the ordinary ap-
paratus have attempted to sound at still greater depths in the
oceanic basins has been the same. As the sinker descends, the
weight of the rope to which it is attached becomes, of course,
greater and greater ; the friction also increases to an alarming
extent ; and the action of the currents, where there are any, on
the immense surface presented to them by say one thousand or
fifteen hundred fathoms of two-inch rope, is sufficient not only
to counteract the very moderate weights used as sinkers, but to
exert a lateral force so strong in many cases that the depth
seems to increase in proportion to the amount of line payed out,
as if it were indeed fathomless.

It is not astonishing, therefore, to find recorded such extraor-
dinary depths in some parts of the Atlantic as eight thousand

2 THREE CRUISES OF THE “ BLAKE.”

fathoms and “no bottom,” or .to find, as was found by the
“ Blake” in the Old Bahama Channel, where the current was
running at the rate of four knots an hour, a depth of only four
hundred and fifty fathoms when sounding with wire, on the very
spot where previous rope soundings indicated eight hundred
fathoms and “ no bottom.”

This problem of deep-sea sounding was attacked from many

sides by American, English, and French naval officers, and the
most successful results were obtained by increasing the weight
of the sinker in proportion to the size of the line. The line was
thus gradually diminished in size in order to reduce both its
weight and the friction, and comparatively accurate soundings
were made with a stout cod-line and a heavy sinker (one hun-
dred pounds). This method of sounding had, however, its own
objections, for it involved the loss of the line, which was not
strong enough to bring back the sinker, and thus also no speci-
men of the bottom could be obtained.

Unsuccessful attempts to sound with wire as a substitute for
rope were made as far back as 1849, both by English and Amer-
ican naval officers. Their failures led to ever-renewed efforts to
improve the methods of sounding with line, and all the recent
more accurate deep-sea soundings taken with rope or line have
been made with comparatively small lines weighted with heavy
sinkers, which caused the line to run out with great velocity.
This velocity, of course, decreased as the depth increased, and
the time of reaching the bottom was indicated theoretically by
an abrupt change, — one practically, however, very difficult to
observe with great accuracy. Consequently, a good deal of line
would run out before the certainty of having reached bottom
became apparent.

It is to the need of submarine cables that Thalassography *
owes its great development. While a knowledge of the depth
of the sea is one of the first requisites for the laying of cables,
the character of the bottom is also an important element, and
an instrument which would bring up a good sample of the bot-
tom became therefore an absolute necessity. Professor John

1 The need of some single word to ex- basins has led to the construction of this
press the science which treats of oceanic term.

EQUIPMENT. 3

M. Brooke, then passed midshipman, devised a very ingenious
apparatus (Fig. 1), so contrived as to disconnect, on touching
bottom, the heavy smker — an old cannon-ball
with a hole bored through it — required for
running out the sounding-line to great depths.
This made it possible to use a very heavy sinker
compared to the size of the line, because the
latter, being instantly freed from the weight
on reaching the bottom, need only be strong
enough to bring back the light iron rod with
the collecting cup attached to it which passed
through the sinker. While going down, the
cannon-ball was suspended by slings from mov-
able cranks ; on reaching bottom the end of
the line became slack, the weight pulled down ee ee
the arms, and the slings slipped off, leaving the she a
shot behind, and the line free to bring back the small sample
of the bottom attached to the armature of the rod. This arma-
ture has since been greatly modified and the rod changed to
a cylinder by Commander Belknap, so that in the deep-sea
sounding-machine as used on the “ Blake” quite a large sam-
ple of the bottom can now be brought up. The apparatus
used by Brooke for detaching has also been greatly improved
by Lieutenant-Commander Sigsbee ; his detacher is now at-
tached to the Belknap cylinder when deep soundings are made.
The principle upon which it works is that of a bell - crank
suspended excentrically ; so long as the weight of the shot
is suspended from the crank, it cannot be detached, but the
moment the extremity of the sounding-cylinder touches bottom,
the pressure is relieved and the bell-crank is tripped, the shot
slips off, and the sounding-cylinder and detacher alone, weigh-
ing together about fourteen pounds, are drawn up to the sur-
face, with a small quantity of the bottom which has forced its
way into the collecting cylinder.

The examination of the specimens of the bottom collected by
the United States Coast Survey was intrusted at first to Pro-
fessor Bailey, and in later years to Mr. Pourtalés. The results
showed at once how large a part in the economy of the life of

4 THREE CRUISES OF THE “ BLAKE.”

the ocean is played by the pelagic forms which, after death,
slowly find their way to the bottom and form at the pre-
sent day deposits in every way similar to those of the chalk.
Mr. Murray has, however, from the more extended explorations
of the “ Challenger,’ clearly proved that the deposits going on
beyond the continental platforms, at great depths in the oceanic
basins, find no analogue among the stratified rocks with which
we are acquainted. Professor Agassiz and Sir Wyville Thom-
son also soon became convinced, as a result of their experience
in deep-sea explorations, that the oceanic basins were of great
antiquity and have always existed, and that the animals found
at great depths existed under conditions which have remained
unchanged from a remote period of time.

Sir William Thomson, who became interested in deep-sea
soundings from his connection with the laying of submarine

Fig. 2. — Sir William Thomson's Sounding Machine. (Thomson.)

cables, made a trial in 1872 of a machine he had devised
for sounding with a piano-wire line. This machine (Fig.
2), and his first use of it in sounding, is thus described by
him : “TI sounded from the ‘ Lalla Rookh,’ with a lead weight
of thirty pounds, hung by nineteen fathoms of cod-line from
another lead weight of four pounds, attached to one end of a
three-mile coil, made up of ends of piano-wire spliced together
and wound on a light wheel about a fathom in circumference,
made of tinned-iron plate. The weight was allowed to run
directly from the sounding-wheel into the sea, and a resist-
ance exceeding the weight in water of the length of the wire

EQUIPMENT. 5

actually submerged at each instant was applied tangentially
to the circumference of the wheel by the friction of a cord
wound round a groove in the circumference and kept suitably
tightened by a weight.”

He says further: “ When from two thousand to twenty-five
hundred fathoms were running off the wheel, I began to have
some misgivings of my estimations of weight and application
of resistance to the sounding-wheel. But after a minute or
two more, during which I was feeling more and more anxious,
the wheel suddenly stopped revolving, as I had expected it to
do a good deal sooner. The impression on the men engaged
was that something had broken, and nobody on board, except
myself, had, I believe, the slightest faith that the bottom had
been reached . . . until the brass tube with valve was unscrewed
from the sinker and showed an abundant specimen of soft gray
ooze. ... That one trial was quite enough to show that the
difficulties which had seemed to make the idea of sounding by
wire a mere impracticable piece of theory have been altogether
got over.”

The first experiment was made in the Bay of Biscay, near a
point where the charts showed a depth of twenty-six hundred
fathoms. It was entirely successful so far as determining the
depth was concerned ; and although the machinery for reeling
in the wire was defective, the problem had been solved, and the
machine only needed very slight modifications to become avail-
able for general use. These modifications have since been
effected, and many ocean steamers in the English service are
now provided with the new machine of Sir Wiliam Thomson.’
All the steamers of the submarine telegraph companies are also

1 Sir William Thomson has also an-
other sounding-machine, with which it
is possible to take soundings in from
twenty to one hundred fathoms in a
sailing yacht, without once rounding to
or reducing speed. He accomplishes
this by the use of a long galvanized-
iron sinker, provided with tubes lined
with chromate of silver. The compres-
sion of the air in the tubes, indicated
by the line of white lining of the chlo-

rate of silver, measures the height of
the column of water’ to the pressure of
which the sinker has been subjected.
Soundings of one hundred and twenty
fathoms have been made by steamers
of the Anchor Line while running at the
rate of twelve knots. The “ Britannic”
has made a sounding of one hundred
and thirty fathoms over the Banks of
Newfoundland while steaming at the
rate of sixteen knots.

6 THREE CRUISES OF THE “ BLAKE.”

provided with them, and for them as well as for the “Blake ”
sounding with wire to any depth has become a matter of daily
routine.*

Commander George E. Belknap, U. S. Navy, while com-
manding the U.S. 8. “Tuscarora,” during her operations in the
Pacific Ocean, in 1873, was the first to test thoroughly the
Thomson machine by constant use. While it was evident that
the machine for sounding by means of wire gave remarkable
results as compared with rope-soundings, its success was appa-
rently due in a great degree to the intelligence, patience, and
skill of Commander Belknap and the officers who assisted him.
Commander Belknap had always been forced to reel in the
wire by hand. Among the plans that presented themselves to
Lieutenant-Commander Sigsbee for the improvement of the ma-
chine, in order that it might be worked with fewer demands on
the watchfulness and mgenuity of those having charge of it,
was the interposition of an accumulator on the wire, between
the reel and the sinker, which, by showing the strain on the
wire at all times during the reeling in, and by easing the sud-
den jerks on the wire caused by the motion of the ship, would
allow of reeling in by steam. A machine for experimental pur-
poses was made in the winter of 1874-5, and the new machine
(Fig. 3) was used for three years on board the Coast Survey
Steamer “ Blake,’ when that vessel was under the command of
Lieutenant-Commander Sigsbee, and engaged in deep-sea work.

The following account of the main points of the Sigsbee ma-
chine is taken from the inventor’s detailed description of the
apparatus in the Bulletin of the Museum of Comparative Zodl-
ogy, and its improvements in “ Deep-Sea Dredging : —

The reel (A, Figs. 4, 5) should be, for convenience, one
fathom in circumference of drum, and should have a friction-
score which is V-shaped in cross-section. When the sinker
strikes the bottom, the momentum of the reel and its remaining
wire requires to be quickly overcome by the resistance of the

1 But even this excellent sounding the ocean with as great accuracy as we
machine may soon be superseded by can ascertain the height of mountains
Siemens’s bathometer, which will en- by a barometer.
able us to read on deck the depth of

Fig. 3.—SIGSBEE SOUNDING MACHINE. (SIGSBEE.)

-

cetera i

EQUIPMENT. 7

friction-line, in order that any undue slacking and consequent
kinking of the wire may be avoided. To secure this quick stop-

Ya
ia

Fig. 4.—Sigsbee Sounding Machine, profile view. (Sigsbee.) "

page, the reel should be made as light as
the very considerable strength required
for reeling in, will permit. In reeling in
without the reeling-in or strain pulley, it
is necessary that the reel should be of
sufficient strength to resist the accumu-
lated strain of successive convolutions of
the wire under strong tension (the difficulty encountered by
Thomson in his first sounding). It is rigidly attached to its axle
by a key, and the easy removal of the key would be a conve-
nience, since the reel, without its axle, could be stowed into a

(=> o
2

8 THREE CRUISES OF THE “ BLAKE.”

much smaller tank than is necessary when the axle is retained.
When a reel containing wire is out of use it is generally kept
in a tank of oil. A crank is provided for each end of the

axle.

The register (B, Fig. 4) is the same as that used by Sir
William Thomson, and is worked by a screw-thread attached to

= 1
7 EO ES OE 73)
7, pag
t/

»
Hens Tink aes
= va rae

Fig. 5. — Sigsbee Sounding Machine, end
view. (Sigsbee.)

the axle of the reel. The reg-
ister evidently does not record
fathoms, an interpolation being
necessary in determining, from
the reading of the register, the
length of wire payed out. It is
very handy, however, for keep-
ing an approximate account of
the wire payed off, so that the
correct amount of resistance can
be applied to the reel. The cor-
rection of the register is easily
found by the method used on
board the “Blake.” See p. 14.

The reeling-in or strain pul-
ley (C, D, H, Fig. 4) is com-
posed of three separate pulleys,
C,, D, and F,— the score # for
the wire ; the score C for a con-
necting rubber or rope band
with the friction score of the
reel, if desired; and the score
D for an endless rope-band
connecting with the hoisting-
engine.

The accumulator is composed
of the tubes F, F, F, and C
(Figs. 4, 5), containing spiral

springs (thirty-one inches long, two and a half inches outside
diameter, four feet movement for one hundred and fifty pounds
strain directly applied), connected with movable cross-head
(Fig. 5) by means of the chain (or wire rope) J, I (Figs. 4, 5),

EQUIPMENT. 9

which pass over the pulleys J, J (Figs. 4,5). The tubes are
hinged at K, K (Figs. 4, 5), so that the upper sections may be
lowered for convenient stowage. They are graduated for the
number of pounds pull on the wire, the upper arm of the cross-
head being the index. The cross-head H, containing the pulley
LI (Fig. 4), moves on the guides WM, MW (Fig. 5), which are
screwed to the tubes. The pulley Z is rigidly attached to its
axle byakey. To the axle is attached an odometer, JV (Fig. 5).
The pulley is exactly one yard (half-fathom) in circumference
on the face, less the allowance for thickness of wire. One
half the number of revolutions shown by the odometer will
therefore give the number of fathoms of wire payed out or
reeled in.

The object of the swivel pulley, S (Figs. 4, 5), is to allow
for the reeling in of the wire while the vessel is steaming
ahead.

The scales W, X (Fig. 4), should be of the kind that have a
long movement of the poimter for a slight extension of the
springs in the scales. In paying out the wire the difference
between the readings of the scales X and W will be the num-
ber of pounds of resistance applied to the reel by the friction-
rope. The wire to be used is the same as that recommended
by Sir William Thomson, namely, steel piano-forte wire, No.
22, Birmingham gauge, weighing fourteen and a half pounds
to the nautical mile. The friction-line should be a quarter of
an inch or slightly less in diameter, and should be oiled or
kept wet with water where it comes in contact with the fric-
tion-score of the reel. The weight is attached to a stray line,
to prevent kinking when it reaches the bottom. In taking a
sounding with the machine, allow the reel at first to revolve
slowly until assured that everything is working well, then ease
up the friction-line and follow out as nearly as practicable the
rule governing the amount of resistance to be applied to the
reel, which should be, as is stated by Thomson, always more
than enough to balance the weight of wire out. It is impossible
to say how fast the wire may be allowed to pay out, since the
limit of safety varies with circumstances, and depends on the
state of the sea and the extent and rapidity of the ship’s rolling
and pitching motions.

10 THREE CRUISES OF THE “ BLAKE.”

As soon as the sinker strikes bottom, which is made apparent
by the stopping of. the reel, read the register and the odometer,
and at the same time ship the crank on the axles of the reel,
and, to insure the detachment of the sinker, pay out a few turns

®

eA P

4d @ |

A TAA A

ig) EA 4
Fo "Zar |
ZZ Ay
4 A 2

“A H 6& H

abd

E 4

4

Fig. 6.—Sigsbee’s Detacher, and Fig. 7.— Section of Fig. 6. Fig. 8. — Belknap’s Cylin-
Belknap’s Sounding Cylinder. (Sigsbee. ) der detached from Shot.
(Sigsbee.) (Sigsbee.)

of the wire by hand, until it feels slack. Then reel in a few
turns, and the distance that the cross-head travels down its
guides will indicate if the sinker has been detached. Gener-
ally, with a good form of detacher, it drops off on striking bot-
tom. In place of the Stellwagen cup, rod, and detacher, used
in Fig. 4, we may use for deeper soundings the sounding-rod,
composed of Sigsbee’s detacher in connection with a modification
of Commander Belknap’s cylinder No. 2. During the descent
the cone / is kept up by the shot, as shown in Figs. 6 and 7,

_ EQUIPMENT. 11

and on striking bottom the bail is prevented from getting over
the top of the detacher by the bearing which the sinker has
against the under part of the cone.

When the sinker strikes bottom the slacking of the sounding-
line or wire trips the tumbler, and the sinker is free to slide off
the cylinder. This tumbler is kept back by the spring JV, and
the bail cannot be rehooked when the line is hauled taut to reel
in. The resistance of the bottom soil raises the poppet-valve /,
and the specimen of the bottom enters the cylinder, the water
within the cylinder being free to escape through the various
perforations P, P, etc. On hauling back the poppet-valve falls,
or is forced by its spring, HZ, to the valve-seat, and the cone J
falls, closing the water apertures. When the rod has been got
on deck the lower part of the cylinder is unscrewed, when the
specimen of soil may be extracted. To prevent the wire from
coiling on the bottom, a piece of rope somewhat less than quar-
ter of an inch in diameter, and from nine to twelve fathoms long
(the stray line), is spliced to the wire, and to this is attached the
sinker, detacher, and any instrument sent down while making a
sounding.

The great advantage of sounding with wire is in the very
ereat strength of the wire as compared with that of stout cod-
line; also in the smoothness of its surface, by which the friction
is reduced to a minimum; so that a wire weighing, say, twelve
pounds in water to the mile, can readily take down a hundred-
pound shot, and not only bring up the fourteen pounds weight
of the sinker and collecting cylinder, but carry besides the
thermometers needed to ascertain the temperature both of the
bottom, and of intermediate depths as well. It would, however,
in practice be more convenient to use a separate reel, and wire
slightly heavier for making the temperature observations, and
for having the water-cups attached.

The weight of the wire payed out in the deepest soundings yet
made, 4,655 fathoms, will, in water, be less than sixty pounds, so
that the weight of the sinker (one hundred pounds or more) can
always be made to exceed that of the wire, an impossibility in
the case of soundings made with hemp-lines. So far as accuracy
is concerned, everything also is in favor of the wire method.
The time of striking bottom is determined, not as in the case of

12 THREE CRUISES OF THE “ BLAKE.”

the hemp-line soundings by the great diminution of speed in the
running out of the rope after the sinker has struck,
yf but by the instantaneous action of the sinker on the
wire when striking bottom; the wire stops, and in
xd less than a second the momentum of the reel is
\B; checked by the friction-rope attached to it. The
AG dropping of the shot is detected on deck with as
bad great certainty as if it had been followed by the eye
to the very bottom; indeed, the percentage of error
in soundings made with piano-wire is probably not
more than one fourth of one per cent. The error in
soundings made by the old methods can only be de-
termined after the rope-soundings have been corrected
by wire-soundings. To those who are not familiar
with the practical working of deep-sea soundings as
formerly carried on, a few figures enabling them to
compare the old with the new methods may be inter-
esting. In the “Challenger” the

deep-sea soundings were made with (ee °
a rope of eight tenths of an inch », 9 — Comparative
in circumference, nearly as large as ize of Hemp and

the steel-wire rope which we used _ ing. (Sigsbee.)
| in dredging, and having a breaking weight of 1,200
pounds. The time occupied in lowering the sound-
ing machine and its weights, often more than 300
pounds, was three to four times as great as on the
“ Blake.” We employed a steel wire (No. 20, Amer-
| |, || ican gauge), with breaking weight of 240 pounds,
, i weighted for the deepest soundings only, with a sixty-
=~ pound shot. The time required to reel in with Cap-
tain Sigsbee’s wire machine was generally below one
minute and a half per one hundred fathoms, some-
times not more than fifty seconds, while the time re-
quired to strike bottom averaged from fifty to seventy-
Fig. 10. five seconds per one hundred fathoms in the deepest
“pagers * soundings up to two thousand fathoms. In depths
et ae less than one thousand fathoms or so, an ordinary
bee.) thirty-four pound lead with a Stellwagen cup for ob-
taining bottom specimens was used. The lead was reeled in

EQUIPMENT. 13

again and not detached ; the speed of the reel was not quite so
rapid, as will be seen on making a comparison of the following
records, the one showing a sounding with a thirty-four pound
lead, the other with a cannon-ball detached on striking bottom.

U. S. Coast Survey Steamer “ Blake.’ Locality, twenty miles N.W. of Sombrero Island.
Date, April 23, 1879. Sounding, No. 25. Line PP. Sinker used, shot ; weight,
60 lbs. Steel wire used, 0.028” im diameter ; weighs 14.5 lbs. to the nautical mile ;
breaking strain, 240 lbs.

Turns of Reel Reeling out. Reeling in.

as per
Register. Tien. Intervals. Times. Intervals.
He MM, 8. M. 8. H. M. 8. M. 8.
000 11 21 32 00 12 30 20 DD
100 22 34 2 29 35 47
200 23 25 51 28 38 47
300 24 15 50 27 51 49
400 25 6 51 PA 54
500 25 58 52 26 8 54
600 26 52 54 25 14 59
700 27 46 54 24 15 i pal
800 28 43 57 23 14 1 4
900 29 43 1 00 22 10 ae
1000 30 41 58 2 7 ity te
1100 31 43 1 (2 20 00 1 10
1200 32 46 1 3 18 50 1 10
1300 33 48 12, 17 40 1 13
1400 34 54 LG 16 27 1 18
1500 36 1 I 15 9 1 18
1600 37 9 i 38 13 51 1 21
1700 38 15 1 36 12 30 1 23
1800 39 26 111 tl ae 1 24
1900 40 35 i 9 43 1 25
2000 41 48 113 8 18 1 25
2100 43 2 1 14 6 53 1 37
2200 44 11 a9 5 16 1 34
2300 45 24 1 13 3 42 1 38
2400 46 38 1 14 2 4 1 31
2500 47 53 1 15 12 00 33 1 56
2600 7 Se 115 58 37 1 53
2700 50 24 1 16 56 44 59
2765 VOT LT 53 11 55 45
2900 |
3000
Metals 5. eee a 29 451 | 34 351
Reeaiinre or Meristere 50h...) cpu. s wits) @) afm epoe 2,765 turns.
Sgcrecuiol tOrisitay line, .—.))- «ow 3 se, we os 6
Correcmonior turns of wire. . 2%... ..2 » . » 158
Dirrecidemie ents s) os 3) we i ks be Seems od) > a! 2,929 fathoms.

1 The time intervals are slower than one of the deepest soundings made with
the average, but this record is given as_ wire at the time it was taken.

14 THREE CRUISES OF THE “ BLAKE.”

U.S. Coast Survey Steamer “ Blake.” Locality, off Grenada. Date, March 2, 1879.
Sounding No. 37. Line K. Sinker used, lead ; weight, 34 lbs.

asna chic Reeling out. | Reeling in.
as per
Register. Times. Intervals. Times. Intervals.
H. M. S. M. 8. H. M.S M. 8.
000 4 20 45 00 4 43 30 1 00
100 21 42 57 42 30 46
£00 | 22 35 53 41 44 43
300 O35 35 1 00 41 1 49
400 24 30 55 40 12 50
500 95°32 | iby ' 39) 22 BAP ye |
600 26 40 Liss 38 18 ey
700 250 110 37 15 Pas
800 29 25 i 35 Some 1 33
875 4 30 35 1 10 4 34 59
Totals - | 9 50 8 31
Readme of Repister: 2 csi) lsc vase (spe mu) aly «ee
Paerrectisndor shtaysae a Sway es, ee we tes Ae ee 6
Correetign: for turmsiof wire: 2 « ss 6 5 se ee
Worreetidepth 0 feo st' 201 “5, 5 es) ess! Ga a

The time occupied in taking one of the most recent deep-
sea soundings by the old methods (those of the “Challenger ’’)
is here given to show the comparative advantage of the two.

Hydra machine, weight 336 lbs. Weight of line, 12 lbs. 8 oz. per 100 fms. ; breaking
strain, 1,200 lbs. ; circumference, 0.8”.

Fathoms. Time. | Intervals. | Fathoms. Time. Intervals.

H. M. 8. | M8. H. M. S§. M. 8.
000 2 44 20 00 1300 258 5 1 23
100 245 5 45 ~ 1400 2 59 37 1 32
200 2 45 45 40 1500 23, 1 1 32
300 © 2 46 30 45 1600 3.2 42 1 33
400 2 47 25 55 1700 3 419 1 37
500 | 2 48 15 50 1800 os 6 6 1 47
600 2 49 15 1 00 1800 3. 7 53 1 47
700 2 50 24 ‘Le t9 2000 3 9 40 1 47
800 2 51 23 59 2100 Fit B43) 1 49
900 2 52 45 i 22 2500 3 13 24 1 55
1000 2 54 00 1 15 2800 3.15 23 1 59
1100 2 55 21 i Wier bee: 2400 3.17 15 1 52
1200 2 56 42 1 40

21 2435 3.17 55

The whole time occupied in descent was thirty-three minutes,
thirty-five seconds; and in heaving up, two hours, two minutes!

EQUIPMENT. 15

Sir Wiliam Thomson would find it difficult indeed to recog-
nize his original machine as now used on board the “ Blake,”
with the modifications introduced by Lieutenant-Commander
Sigsbee. During the four years of his command, the latter
ran no less than 12,766 nautical miles of sounding-lines, with
the necessary serial lites of temperatures. As the result of his
magnificent work, the Coast Survey is publishing a hydro-
graphic chart of the Gulf of Mexico, not merely unequalled
for its accuracy, but unique as the first chart of any extent
which carries the littoral hydrography to great depths.

The depth having been obtained, the thermometer attached
to the stray line will, if allowed to remain long enough before it
is drawn up, record the bottom tem- 7 my TIN iy
_ perature. The deep-sea thermometer ae (i tt

used is known as the Miller-Casella. : it Ni "h \

(Fig. 11.) It is a maximum and mini-_ | i fils -

Ve

mum thermometer. Its modified form
was suggested by Professor Muller,
and constructed by Casella. It con-
sists of a U-shaped tube, the lower
part of which is filled with mercury, the U ter- I =
minating on the one side in a large bulb filled |);
with a mixture of creosote and water, while the
small bulb of the other branch is filled only in |
part with the same liquid. A steel index, kept

iil
mag "eS p

Tg NT

i—] 2

SSS

i=)

in place by a horse-hair spring, is placed in each | | d
limb. The indications are given by the expan- Ey iilz
sion and contraction of the mixture in the large | ET
bulb, which allows the mercury either to recede |, 2 Ed
from the large bulb or to flow towards it; the |l=|f Ed
index is carried on either side by the movement || EJ
of the mercury, and on the retreat of the mer- || = ) NE EY
cury the index remains at the highest OSH ll ii

I

point reached. To prevent the effects | g

of the enormous pressures to which | sid (
these thermometers are subject, the Aan
mner large bulb is protected by an
outer bulb nearly filled with alcohol, oe io a sta Ts

LU

Wt

|

16

THREE CRUISES OF THE “ BLAKE.”

space enough being left for the compression of the outer bulb.
The correction of each thermometer for pressure is ascertained

by experiment.’

A great objection to the use of the Miller-Casella for obtain-
ing deep-sea temperatures is found in the fact that they will

aL
|
L

Fig. 12. — Negretti-Zambra
Thermometer, Italian
rnodel.

register only the lowest temperature ob-
tamed. ‘The most common form of deep-
sea thermometer now in use is a modifica-
tion of Negretti and Zambra’s instrument,
of which a figure is here given; the propel-
ler is constructed on the same principle as
that of the Sigsbee water-cup, and holds the
thermometer with the bulb (b) downward
till the line is drawn up. On being freed
from the stopper (/) the thermometer as-
sumes the position given in the figure, and
the column of mercury which has become
freed from the bulb by the tilting on the
axis (p) indicates the temperature at the
poimt where it was turned over. When tem-
peratures are taken in a district where they
diminish gradually from the surface to the
bottom, as is generally the case in the trop-
ics, this defect is not of great consequence.
When, however, we seek to ascertain the
temperatures of the Gulf Stream, or to
work in the Arctic regions; where the cold-
est water may be nearest the surface, we
are unable, of course, to determine the posi-
tion of the coldest or warmest intermediate
layers of water. The only perfect method
of taking serial temperatures is one which
records them continuously on deck during

1 Professor Tait, who has made an ex-
haustive investigation of the corrections
to be applied to the deep-sea thermom-
eters of the “Challenger,” came to the
conclusion that the only cause which is
active in affecting them when let down

into the sea is pressure, and that the
correction to be applied to them is that
given by Captain Davis and Professor
Miller, of somewhat less than half a de-
gree Fahrenheit for every mile under
the sea.

EQUIPMENT. 17

the descent of the thermometer. Such an apparatus has been
devised by Sir Wilham Siemens. In the Bakerian Lecture
for 1871, he showed that the principle of the variation with
the temperature of the electrical resistance of a conductor
might be applied to the construction of a thermometer, which
would be of use in cases where a mercurial thermometer was
not available. The instrument he described has since been
largely used as a pyrometer for determining the temperatures
of hot blasts and smelting furnaces; and it has been found
that its indications agree very closely with those of an air-ther-
mometer. He devised a similar instrument for measuring tem-
peratures where a much greater degree of
accuracy is required, as in the case of deep-
sea observations; and during the autumn of
1881, this deep-sea electric thermometer was
subjected to a series of tests on board the
“ Blake,” by Commander Bartlett.

The apparatus consists essentially of a coil
of silk-covered iron-wire (Fig. 13), fifteen mil-
limetres diameter, and about four hundred
and thirty-two ohms resistance, attached to
an insulated cable by which it can be low-
ered to the required depth, and connected so
as to form one arm of a Wheatstone bridge.
The corresponding arm of the bridge is
formed by a second coil, made precisely
similar to the former one and of equal re-
sistance. This coil is immersed in a copper
vessel filled with water, and the temperature
of the water is adjusted by adding iced eet ,
or hot water until the bridge is balanced. ‘Sinker and Resistance
The temperature of the water in the vessel (24, foe Ge.
is then read by a mercurial thermometer,
and corresponds with the temperature of the resistance-coil.

To avoid the error which would otherwise be introduced by
the leads of the resistance-coil, the cable is constructed of a
double core of insulated copper-wire, protected by twisted gal-
vanized steel-wire. One of the copper cores is connected with

Carle

18 THREE CRUISES OF THE ‘“ BLAKE.”

each arm of the bridge, and the steel-wire serves as the return
earth connection for both. Sir William Thomson’s marine gal-
vanometer, with a mirror and scale, is employed to determine
the balance of the bridge. (Fig. 14.)

The apparatus was set up on board the “Blake” in April, ~
1881, and experiments were made off the east coast during

Fig. 14. — Wheatstone’s Bridge. (Bartlett, U. S. Coast Survey.)

August. In each series of experiments the temperatures at dif-
ferent depths were first taken by Miller-Casella thermometers
attached to a sounding-wire. A sinker was then fastened to
the resistance-coil, and it was lowered by the cable to the same
depths, when the temperature was read by means of the mer-
curial thermometer attached to the comparison-coil. The depths
at which readings were taken ranged from the surface down
to eight hundred fathoms, and experiments were made in both
rough and still water. The temperatures recorded varied from
38.5° to 81.5° F. In every case the readings of the electrical

EQUIPMENT. 19

instrument were precisely the same as those of the Miller-Casella
thermometers for the surface and the maximum depth; but for
intermediate positions, it was observed that the electrical ther-
mometer in almost every case gave a slightly higher reading.
This discrepancy may be accounted for, Sir William Siemens
thinks, by the fact that the electrical thermometer gives the

OOOO);
BATTERY.
iG ZZ aay ECL

N

WV

a.
A\\ WW

QQ

\=

ANN

YEE

4
:
:
:
\

i

|
!

i

li

7

=
s

Fig. iC. W. Siemens’s Deep-Sea Thermometer. (Bartlett, U.S. Coast Survey.)

Wty

temperature of the water actually surrounding the coil at the
moment of observation, whereas the Miller-Casella instrument
brings to the surface, or at least its readings are affected by,
the maximum or minimum temperatures encountered in its as-
cent or descent, which may not coincide with that at the point
of stoppage. This furnishes a very strong argument in favor
of the superior accuracy of the electrical instrument. (Fig. 15.)

It was found that about five minutes must be allowed at each
observation for the resistance-coil to assume the temperature of

20 THREE CRUISES OF THE “ BLAKE.”

the water surrounding it, and a second period of five minutes
for adjusting the temperature of the comparison-coil on deck.
Allowing five minutes more for lowering the cable, fifteen min-
utes sufficed to complete a deep-sea observation.

The instrument was sufficiently tested by Commander Bart-
lett, during the season of 1881, to show its entire practicability.
The accompanying table is taken from his Report to Pro-
fessor J. E. Hilgard, the superintendent of the United States
Coast Survey : —

Depth in Fathoms. Siemens. Miller-Casella.

eis ie i ee See a ee ee ST 77s
So talngms S, Se ac pare e re a oon Gale eee 75}

Bg TS br Dar gg ten cae ee ge oo, Ns, gn 69
ls ie eae Le eee es aise te eee cy
20 CE rene Roster en > Le apis oes 57
30 « 514 51}
50 544 52
is. * 53h 53h
100 51 49h
125 48}
150 « 461 46
200 « 431 431
SOD) bs Ga sors Re RA Sc eS coe ee 403
LOIN Ae nN ME AD a tone: Ve ee 39%
EOS Ft can ec cae at ons, ee 39
eat ee eee eo eee SPR oe. fe 38}
(ln tae ee ee Tes ee ae Wey ea 38}
BOOR Wee. ck eo yite. or eh: Go~ a sok ns Cen cneae 38h

Much yet remains to be done before we can ascertain accu-
rately not only the force, but also the direction of the currents,
at different depths, from the surface to the bottom; the floats
usually employed to make these observations are rather primi-
tive instruments. Here also we must look to electricity for the
means of making simultaneous or continuous observations.

The specific gravity of the sea-water was determined on’ the
“ Blake ” by means of an apparatus devised by Professor J. E.
Hilgard (Fig. 16) of the Coast Survey. As the differences of
density are very small, the instrument must be one of great
delicacy ; it is constructed upon the same principle as that of

1 According to Commander Bartlett, 30 fathoms, which was not detected by
the Siemens apparatus recorded the the Miller-Casella, indicating only max-
presence of a warm belt between 10 and ima and minima.

EQUIPMENT. 2]

an ordinary aerometer. The specific gravity could also be de-
termined, as has been suggested by Professor Wolcott Gibbs, by
observing the index of refraction of the dif-
ferent samples of sea-water.
Some of the most interesting’ problems
of biology are dependent for their solution
upon an accurate knowledge of the physics
of the salt water at the great depths from
which animal life has been brought up.
In order to analyze with accuracy the water
brought from the bottom, the cup in which
it is conveyed to the surface must be so
hermetically closed as not to allow any ad-
mixture of water from intermediate depths,
or any escape of the gases during the up-
ward passage of the water-cup. The water-
cups thus far employed for this purpose are Fig. 16.— Hilgard Salino-
< meter. (Sigsbee. )
rather rude instruments, and do not guard
positively against these sources of error. Those in use on the
“ Blake ” seem to be the simplest, and superior in efficiency and
accuracy to any cups employed in the deep-sea explorations
preceding ours; when once closed there is no danger of their
opening again from the pitching of the vessel or the stopping of
the upward motion. The propeller, which screws down the
valves, from the time the regular upward movement of the
bottle begins is, as it were, thrown out of gear, and cannot
undo the work it has once performed. As the cup descends,
the resistance of the water raises the valves, and also screws
up the propeller until the lower thread in the hub clears the
upper thread on the shaft, when the propeller uncouples and
revolves freely on it; the blades of the propeller are bent on
their upper edge. It has been found, experimentally, that
with the blades thus bent, by rising and falling equal distances
through the water the propeller will screw up instead of down.
Without this bending it is evident that the propeller would
gradually screw down by a rising and falling motion. At any
stoppage each cup has within its cylinder a specimen of the
water from the place where it stops. (Figs. 17, 18.)

22 THREE CRUISES OF THE “ BLAKE.”

On hauling in, the propeller of the cup screws down, by the
resistance of the water, until the upper thread of the hub clears
the lower thread of the corresponding screw on the shaft, when
the propeller drops on the screw-cap ; the lugs A, f, clutch into
the slots U, U, and the screw-cap is screwed down until it
touches the upper valve, which keeps both valves closed. The
screw-cap is found screwed down so tight in coming out of the
water that it can be set no tighter without endangering the
thread.

The tests to which the water-cup has been submitted show
that it closes in a depth of about ten to fifteen fathoms, and then
remains hermetically sealed. For serial lines the water-bottles
and thermometers were not sent down on the sounding-line, but
a stronger steel cord, three eighths of an inch in circumfer-
ence, was used, to which the thermometers and bottles were
attached.

The annexed sketches of Sigsbee’s water-bottle (Figs. 17, 18)
will interest those who have used the older apparatus for ob-
taining water from great depth. The method of closing the
valves is entirely different from that employed by other hydro-
graphers.

Fig. 17 gives a view of Sigsbee’s water-bottle, seen facing
the frame of the propeller (p), by which the valves are
closed.

Fig. 18 shows a section of the same bottle, and Fig. 19 the
mode of attaching it to the steel rope by means of a spring
devised by Lieutenant-Commander Sigsbee. This is done in
an instant, and the bottles are firmly held in place by the
double spring holding the rope at two points. The same mode
of attachment has been adopted for securing the thermometers
(Fig. 20) to the line or wire with the least possible delay, and
for their easy detachment in place of the clumsy and tedious
process of tying and untying them hen a serial line of temper-
atures is to be made. 3

There was no attempt on our trips to make any chemical ex-
amination of the water brought up from different depths. The
small size of the vessel made a chemical laboratory out of the
question, and it seems more feasible for this purpose to establish

EQUIPMENT. 93

a laboratory on shore at some point near deep water, carrying
the bottles to the laboratory for analysis.

_ A small chemical laboratory was fitted up on board the
“Challenger,” where the elements of the chemistry and physics

Fig. 17.—Sigsbee’s Fig. 18.— Section of Fig. 19.—Mode of Fig. 20.— Miller-
Water-Cup. (Sigs- Sigsbee’s Water-Cup. Attachment of Casella Thermom-
bee.) (Sigsbee.) Thermometer and eter in Protecting

Cups. (Sigsbee.) Case, with Sigs-
bee’s Attach-
ment. (Sigsbee.)

of the water at the bottom of the oceans were worked out by
Mr. Buchanan, the chemist of that expedition. From his an-
alyses it appears that the amount of carbonic acid present in
water taken from the bottom is much greater than in surface
water, and that the amount of oxygen gas may be somewhat
larger than at the surface.

The apparatus used for bringing up the animals living at
great depths is very simple. Until recently, the dredge first
used by a Danish naturalist, O. F. Miiller in the last century,

24 THREE CRUISES OF THE “ BLAKE.”

had undergone but slight modifications. It consists of a rec-
tangular frame with flattened sides, to which a bag of net-
ting is attached, this again being protected by a canvas bag.

Fig. 21.— Miiller’s Dredze, (Thomson. )

The dredging-rope is attached
to one of the wire arms fas-
tened to the short side of the
dredge-frame ; the other arm
is made fast to the first by pa eae Wee
a stout marline, so that in case

the dredge fouls, the marline will give way, trip
the dredge, and not part the rope, which would
involve the loss of the dredge. The dredges
used in deep water are generally much larger and

heavier than those used from small sail-boats. «p)4/%: Dat
To prevent the crushing of delicate specimens

by the dragging of the bag over rough bottoms, a frame-work
(Fig. 22) has been added to the ordinary dredge; this is cov-
ered with heavy canvas (Fig. 25), so that the bag with its con-
tents is relieved of the wear and tear which comes of dragemg
it over the bottom; the most delicate specimens are thus secured
uninjured.

EQUIPMENT. 95

While using, especially on muddy bottom, the dredge as for-
merly made, with a frame having a bevelled edge, we experi-
enced great annoyance at first from the amount of mud brought
up by it. When the dredge was dropped in soft ooze, it evi-
dently sank deeply in it and filled at once; and since the viscid
mud did not wash out easily, it was even difficult to sift it on
deck. To obviate this defect, we stopped a piece of two-and-a-
half-inch rope below the dredge-frame to raise the lips and _pre-
vent it from cutting mto the mud. This worked admirably,
and after that our dredges always came up bringing less mud
and a larger supply of specimens. We subsequently made our
dredges with a flat frame, obviating completely the defects in
the old-fashioned dredges."

Attached to the end of the dredge-frame is a long iron bar
to which are fastened
large swabs. These
huge rope tails trail be-
hind the dredge, and in
them become entangled
all sorts of starfish, sea-
urchins, crabs, corals,
sea-fans, sponges, and
even fishes which do
not readily find their
way into the dredge.
When the bottom is
very rough or rocky,
or it is of uneven coral,
the bar and tangles
alone are frequently
used. (Fig. 24.) For this
sort of bottom, where
there is always danger
; that either a dredge or
Fig. 24.— Bar and Tangles. a trawl may be carried

1 A dredge is used among natives of in action in one of his lectures on Deep-
the Philippines and Japan. Mr. Mose- Sea Dredging.
ley has given a sketch of such a dredge

26 THREE CRUISES OF THE “ BLAKE.”’

away, the bar and tangles, which may be composed of a dozen
to fifteen bundles, afford perhaps
the most effective apparatus for
collecting. The amount of ma-
terial sometimes brought up baffles
description, and it is no easy task to
separate the specimens from the tan-
gled mass in which they have been
caught.’ The trawl is by far the most
useful instrument in deeper water,
where the bottom generally consists
of ooze or fine mud, — the finer in
proportion to the distance from land.
The trawl first used in deep water
was the ordinary beam-trawl of fish-
ermen. When this form of trawl is
used in shallow water, it is easy to
guide it or to weight it so that it will
always fall on its runners and drag
successfully. At great depths, how-
ever, this form of trawl becomes ob-
jectionable, from the impossibility,
owing to currents or the drift of the
vessel, of guiding it, no. matter how
well-balanced it may be, so that it
shall not land on the beam, a mis-
hap that involves great waste of time,
sometimes a whole day, from unsuc-
cessful hauls. On the “Blake,” a
modification of the trawl was used

(Figs. 25, 26), which worked admira-

oi

Oa id,
LEE
cies

Wee 5
easy
> <j
aes,
f

Fig. 26. — “‘ Blake”’ Trawl.

1 A tangle-bar of great efficiency, con- The members of the United States

sisting of two poles tied in the form of
the letter A, with cross-bar and lines
with fishing-hooks, has been used with
great success by Mr. Marshall, to collect
haleyonoids. A very similar apparatus is
also used by the natives of the Philip-
pines to collect euplectella.

Fish Commission have also introduced a
number of admirable modifications of
dredges, trawls, tangles, and sieves ; and,
in fact, every part of the dredging appa-
ratus now necessary for deep-sea work
has been greatly improved by the ex-
perience obtained during more than ten

eet oe ne rae an

Fic. 25.— ‘‘ BLAKE” TRAWL.

(SIGSBEE. )

+ dokme

“ay

EQUIPMENT. 27

bly, obviating all fouling, and doing away with the frequent
delays so annoying when the ordinary single-beam trawl is used
in deep water. It was practically a double trawl, bearing the
same relation to the old beam-trawl which the ordinary dredges
bear to the old oyster dredge, and sure to do its duty, on what-
ever side it might happen to fall; the runners were made ellip-
tical, high enough to give fair scope to the lead line of the
trawl, and thus it became a matter of indifference on which
side of the runners the trawl landed. Under these conditions
the hauls were always successful.

At great depths, where a light ooze covers the bottom, the
trawl soon becomes completely filled with the mass of sticky
mud which finds its way into it; and when brought to the
surface it is found that but little has been washed out through
the meshes of the trawl-bag. The labor of sifting this large
mass of mud (often as much as a ton) is very considerable.
It is done by washing off the mud in sieves provided with
handles, and shaken in tubs of water. The United States
Fish Commission use a table-sieve upon which plays a hose;
this quickly disposes of a large amount of mud. It became im-
portant to do the sifting as far as practicable while trawling.
To accomplish this, the bag of the trawl was greatly shortened
(reduced to fifteen feet), and the meshes of the outer net made
coarse, while only a very small part of the bag was fine enough
to allow the accumulation of mud. The result proved the wis-
dom of this change. We were now rarely overwhelmed with the
masses of mud which had rendered so much additional work of
sifting necessary during the first cruises. After this change it
also became possible to drag the trawl with considerable rapidity
over the bottom (sometimes as fast as three and one-half miles
an hour), and thus to catch the more active fishes and crus-
tacea, which keep out of the way of the trawl when it moves
slowly. We also tried dragging a heavy tow-net rapidly over
the ground at great depths, in hopes of accomplishing the same
object ; but we found that, after all, no deep-sea machine worked
_ years of dredging and sounding off the count of the apparatus will be found in

coast of the United States in the “Fish the Annual Reports of the United States
Hawk” and “ Albatross.” A full ac- Fish Commission.

28 THREE CRUISES OF THE ‘“ BLAKE.”

- better than a trawl, which, when moved rapidly over the ground,
at the rate sometimes of two to two and a half miles an hour,
invariably brought up a fine harvest of fishes and crustacea, in
addition to the usual contents of the sedentary and more slug-
gish forms. Although the deep-sea tow-net was used several
times, we never brought up any of the so-called deep-sea sipho-
nophores of Studer, even in localities where they came up on
the wire rope.

All dredging expeditions previous to the first cruise of the
“Blake” had used best selected hemp rope for dredging.’
The objections, already mentioned, to the use of hemp rope,
speaking of sounding, apply with even greater force to its use
in dredging. The necessity of loading down the trawl with
weights, or of making the trawl itself enormously heavy, in

Fig. 27. — Comparative Size of Dredging-Ropes. (Sigsbee.)

order to sink a heavy rope strong enough to bring back not
only its own weight, but that of the trawl and its contents and
of the weights usually sent down with the dredge, —all this
increased the danger that the rope might part at great depths.
The rope also, after short use in deep water, becomes very brit-
tle from the great pressure to which it has been subjected, and
unfit to bear any considerable strain. My familiarity with the
successful use of very long steel ropes for mining purposes nat-
urally suggested their adaptation to the new purpose of deep-
sea work. The results anticipated have been fully realized,
and the gains in space (Fig. 27), in time,’ in safety and facility

1 The rope used for deep dredging is made by the “Blake,” in fifteen hun-
usually two and one half inches in cir- dred fathoms, in less than two hours
cumference. It weighs two pounds to and three quarters, dragging on the bot-
the fathom, breaking strain about two tom twenty-five minutes. The trawl can
tons; so that the weight of rope, trawl, safely be lowered at the rate of one hun-
and contents is often more than half the dred fathoms in four minutes, and be
breaking strain. reeled in at the same or even a more

2 A haul of the trawl was frequently rapid rate.

EQUIPMENT. 29

of work, and finally in expense, have made deep-sea dredging a
possibility on comparatively small vessels. It would have been
difficult, if not impossible, on a small vessel of the size of the
“Blake” (of only three hundred and fifty tons burthen) to
make provision for the equipment of hemp rope necessary for
a season of dredging at the depths in which we usually worked
in the Gulf of Mexico. Our stock of steel rope was only six
thousand fathoms. The loss of rope was triflmg, and much of
the original steel rope, after three years of constant use dur-
ing two previous cruises, was still available during the third
cruise.

The wire rope we used was of galvanized steel with a hemp
core ; it measured one and one eighth inches in circumference,
weighing one pound to the fathom, with a breaking strain of
over eighty-six hundred pounds, as tested by the Roebling &
Sons’ Company, the manufacturers. We took with us only two
coils, each of three thousand fathoms. One coil was on deck,
wound to an iron reel and frame provided with a friction-brake
for lowering the dredge or trawl, the whole space occupied by
this length of rope on the reel being only five feet long, four
feet wide, and five feet high. In addition to the economy of
space thus gained, we were enabled to dispense with sending
down heavy weights to drag in front of the dredge at a dis-
tance from the frame, as was invariably done by the “ Chal-
lenger,” the weight of the steel rope in water rendering this
unnecessary. Our greatest gain from the use of steel-wire rope
came from the rapidity with which we could lower and hoist
the dredge. In fact, this was done as rapidly as is customary
in lowering or hoisting skips on the slope of a mine. Our
usual speed in lowering the dredge, until it came within a few
fathoms of the bottom, was between two and a half and three
minutes for a hundred fathoms, when we lowered more care-
fully, and then payed out the slack very gradually, the dredge
dragging on the bottom all the time. In bringing it up after
the dredge was clear of the bottom, we hoisted again at the
same speed, and as far as I could perceive the specimens were
none the worse for their rapid upward journey. This gave us
a chance to make several hauls a day, and by not leaving the

30 THREE CRUISES OF THE “ BLAKE.”

dredge or trawl to drag too long on the bottom we obviated
the great loss of time due to fouling, reversing, or any other
accident out of sight. In the “Challenger” the best part of
the day was generally consumed in making a haul at a depth
of fifteen hundred fathoms. We experienced no inconvenience
from the kinking of the rope, if it was kept well stretched,
and not allowed to lie slack on the bottom. The uniform suc-
cess attending the use of this rope during our dredging seasons
enables me to recommend it to any future deep-sea dredging
expedition, as insuring an economy of space, time, and money ;
for the rope occupied about one ninth of the space required
by a hemp rope, and was, at the end of the cruise, as good as
when we first left Key West.

Not the least superiority of the steel rope over the hemp
rope is its power of telephoning, as it were, from the bottom.
By keeping hold of the wire rope on deck, the least movement
of the dredge or trawl on the bottom is transmitted with ab-
solute certainty, and it soon becomes an easy matter for the
officer in charge of the dredging not only to tell whether the
trawl is dragging well, but also the kind of bottom over which
it is passing. The vibrations of the rope when the trawl passes
over a gravelly, or a sandy, or a smooth, muddy bottom are all
characteristic and in strong contrast with those produced by the
quick jumps of the trawl over a rough and slightly rocky bot-
tom. The movements of the dredge are repeated by the vibra-
tions of the steel rope so promptly that the moment it pulls or
passes over rough bottom the speed of the vessel can at once
be checked, or its direction altered, before the tension is great
enough to affect the accumulator.

Heavy strains on the line can be detected in the same man-
ner, and for greater safety an accumulator is connected with
the pulley over which the wire rope leads to the bow of the
vessel at the end of the dredging-boom. This accumulator (Fig.
28) is made up of a series i adenomas car-springs, suspended
along the foremast and kept in place by iron guides. These
are compressed by a strain, and expand again into their natural
position when the pressure is taken off. The amount of com-
pression indicates the care to be taken in handling the trawl

Fie. 29.— DECK OF “BLAKE,” WINDING REEL AND WINDING ENGINE, FACING Bow,
DREDGING BOOM, READY FOR DREDGING. (SI@sBEE. )

Fag Mort 1

EQUIPMENT.

ol

when there is a great weight in it, or when the vessel is pitching.
The curve made by the wire rope, as it leads from the vessel

to the trawl, is of itself the best accumulator, as a com-
paratively slight strain will constantly tend to change
the form of the catenary. It is only while hoisting
the dredge that the accumulator is useful, and long
before it works to its full power the changes of form
of the catenary of the wire rope, from an easy winding
in of the dredge to the fouling of the same, will pro-
duce a greater or less strain, entirely unnoticed, on the
accumulator, if (as in our case) the strain is less than
two thousand pounds. The friction of the steel rope
against the wire, even when two or three thousand
fathoms of wire are out, is far less than the breaking
weight (eighty-six hundred pounds) of the steel-wire
rope (one and one eighth inches circumference) used
on the “ Blake.”

The steel rope was hoisted by a small double-cylin-
der winding-engine, with a surging-drum, from which
the rope then passed to the reel, where it was coiled
as closely as practicable. The reel was managed by
a pair of small engines used to wind the line, and by
a friction-brake when the rope was lowered.

In dredging, the dredge or trawl was invariably
lowered independently of the winding-engine, from
a reel built especially for the work. This reel, built
of iron, consisted of a hollow axle two feet in diam-
eter, four feet long, flanked by flanges extending
eighteen inches above it, capable of winding about
four thousand fathoms of one and one eighth inches
steel-wire rope. The axle upon which the reel ran
was supported upon bearings carried upon a strong

Sooo oo
= a a |

ito

iT

Fig. 28.—Ac-
cumulator.
(Sigsbee.)

iron frame securely bolted to the deck; the reel was checked
by a band friction-brake, by which one man could readily con-
trol the velocity of the steel rope as it was unwound and could

accurately regulate the speed. The brake was of

sufficient

strensth to stop the dredge even at a depth of nearly two
thousand fathoms; and while dredging or trawling, the brake

32 THREE CRUISES OF THE “ BLAKE.”

was securely held in place, and the dredging carried on from
it. To wind up, the wire rope was stopped and sufficient slack
taken from the reel to make the necessary turns round the
surging-drum of the hoisting-engine. When this was done the
reel was made taut, the stops were unfastened, and the wire
rope was wound up by the winding-engine until the dredge
came in sight.

During the whole time the dredge or trawl was lowered or
hoisted, the recorders kept an accurate record of the time spent
in paying out or reeling in the rope, so that at any moment we
knew the precise position of the dredge and the quantity of
rope still out.

The uniform success which attended all our hauls was un-
doubtedly due not only to the improvements suggested in the
apparatus by Lieutenant-Commander Sigsbee, by Lieutenant-
Commanding Ackley, by Lieutenant Sharrer, and by Messrs.
Jacoby and Moore, but also to the great care taken by the
officer of the deck in handling the “Blake” during the pro-
gress of a haul.’’ With a vessel of the size of the “Blake,”
excellent judgment was necessary while working in a seaway,
and that we incurred so few accidents is entirely due to the
interest taken in the expedition by the officers, and the de-
vices constantly suggested by them for overcoming the diffi-
culties we encountered in this novel work.

The strain of the trawl is taken up directly by the reeling-
engine; this has a surging-drum round which the wire rope
passes eight or ten times, the wire reel becoming a mere spool
relieved of all pressure, either in winding or in dredging, by the
surging-drum of the winding-engine. This drum is a fathom
in circumference, and, being connected with an indicator, the
amount of rope out can always be accurately read on the dial.
A similar arrangement exists for measuring the sounding-wire ;
but as the wire piles on the reel, a slight correction must be ap-
plied in that case to determine the exact length of wire payed
out.

1 The other officers of the “ Blake’? gineer during the other dredging cruises
were Lieutenants Wallis and Mentz, of the ‘“‘Blake;” Dr. Nourse, Dr. Per-

Master McCrea, and Ensigns Peters and sons, and Mr. L. P. Sigsbee served as re-
Reynolds. Mr. Pemberton was the en- corders.

Fie. 29¢.—‘* BLAKE” DECK LOOKING AFT, READY FOR DREDGING, REELING ENGINE, DRUM, LEADING BLOCK. (Siesver.)

ia

ry

ay

“i

EQUIPMENT.

33

Between the reeling-engine and the drum the wire rope is led
on deck through heavy iron sheaves, and is guided in the same

way over the bow. The dredging-boom (Fig.
29) moves on a swivel, and can be raised or
swung sideways to facilitate the bringing of the
trawl on deck after a haul has been completed.

The small size of the “ Blake”’* (one hun-
dred and forty feet on the water line, twenty-
six feet and six inches beam, with a draught of
only eleven feet) rendered many devices neces-
sary for the easy handling of the wire rope.
As it was not considered best to bring the
strain of hoisting directly upon the winding-
reel, and as considerable room was required to
handle the slack of the wire rope as it passed
from the surging-drum to the reel, we sent the
rope by means of blocks round the deck almost
back again to the surging-drum. (Figs. 29a,
30.) The close proximity of the reel and drum
enabled the men at the brakes to watch either
engine readily and act accordingly.

The plan of the flush upper deck of the
“Blake” (Fig. 30) gives the position of the
large iron reel B, on which the steel-wire dredg-
ing-rope was coiled, the position of the snatch-
blocks C, leading the rope to the winding-en-
gine with surging-drum A, to C, and then to
the large block C, at the end of the swinging
dredging-boom D,—this last block, C, being
connected with the accumulator hung along
the foremast; the position of the sounding-
machine, G', on the port side is also shown,
and that of the small winding-engine to reel in
the sounding-wire.

Fig. 30.— Plan of
Deck of ‘‘ Blake.’’
(Sigsbee. )

B. Dredging-reel for wire
rope.

C. Snatch-blocks.

A. Hoisting-engine.

D. Swinging-boom.

K. Pilot-house.

G. Sounding-machine.

H. Reeling-engine.

In paying out the wire rope for a haul after the trawl or

1 The “ Blake ” is schooner-rigged, her knots.

She can carry coal at that rate of

speed but moderate, and with a consump- consumption for thirty-eight days’ steam-

tion of four tons, steams about eight ing.

34 THREE CRUISES OF THE “ BLAKE.”

dredge was over the side, and everything ready for lowering,
the reeling-engine was reversed slowly until the trawl was well
started, when the lowering could be done somewhat more rap-
idly; and as soon as sufficient wire had been payed out, so
that its weight and that of the trawl were great enough to
overcome the resistance to the descent of the rope, then steam
was shut off and the wire was managed. entirely by the fric-
tion-brake. During the lowering, the steamer was very slowly
backed, and as soon as the trawl was well planted she was
backed more rapidly, until, according to the soundings, an ad-
ditional amount of rope equal to from a third to twice the
depth had been payed out. Then, when the wire rope was
well fast, the steamer was backed at the rate of a mile and a
half to three miles an hour, according to the nature of the
bottom, dragging the trawl for a length of time varymg from
ten to twenty minutes. In hauling up, the winding-engine was
again brought into requisition, great care being taken, when
the trawl or dredge broke ground, that the movement should
be slow at first when the strain of the trawl and its load came
upon the wire rope.

A new crew requires a little practice to become familiar with
the working of the machinery, and in our first attempt off Ha-
vana we came to grief by paying out the dredge-rope too fast.
This produced a tangle of about two hundred fathoms of steel
wire, the cause of which was easily explamed when we saw the
hopeless result; but it also taught us the speed at which we
should lower and the proper manner of handling the vessel dur-
ing the operation, so that the accident was altogether a most
fortunate one for the future progress of the work.

Intimately connected with the fauna- of great depths is the
pelagic fauna. The innumerable marine animals which always
live at or near the surface, either during thei whole life or
merely during their earlier stages of existence, play an impor-
tant part in the economy of the deep-water fauna. The surface
of the ocean on calm days swarms with pelagic mollusks, crus-
tacea, echinoderms, jelly-fish, and the like, either adults or em-
bryos, associated with foraminifera and sponges. The surface
animals are collected by means of a hand-net (Fig. 31) made of

EQUIPMENT. 35

fine gauze, or of a net of similar material (Fig. 32), towed be-
hind a boat moving quite slowly. At the least ripple of wind
they retreat out of reach of the disturbance, and occupy a belt
of water probably one hundred, or at the outside one hundred
and fifty fathoms in depth. When they die their shells or hard
parts slowly find their way to the bottom, to serve, before they
are completely decomposed, as food for the deep-water forms.
The shells of many foraminifera and the like
being found apparently in such a fresh state at
the bottom, it was supposed that many of these
pelagic forms only came up accidentally, and
really lived at or near the bottom. This seemed
the more probable because there are undoubt-
edly many types of foraminifera which are
inhabitants of deep water. Still, the investiga-
tions of Miiller, Pourtalés, Schultze, Haeckel,
and of all the naturalists accustomed to the
study of pelagic forms plainly showed that a
great number of the types of which the dead
remains were found on the bottom really passed
their existence as pelagic forms near the sur-
face, within a comparatively narrow belt, where
they could find the greatest abundance of food. "** —Scvop Net

The naturalists of the “Challenger” attempted to prove
during her cruise that some of these forms lived at great depths,
and that there was practically no belt of ocean entirely barren

of animal life. The means adopted on the “Challenger” to
solve the problem did not, however, settle the point definitely.
The old practice was employed of dragging for animal forms at
intermediate depths by means of a tow-net, which, during the

36 THREE CRUISES OF THE “ BLAKE.”

several operations of lowering, dragging, and hauling back re-
mained open; this cannot be regarded as affording acceptable
evidence of the habitat of such specimens as were obtained. It
became an interesting problem on the “ Blake” to determine
accurately how far these pelagic forms really extend. Lieu-
tenant-Commander Sigsbee contrived a machine intended to
furnish means for solving this problem.’ It consisted of a cop-
per cylinder to be sent down closed on a collecting expedition
to any depth desired, when it was opened by a messenger ; being

1 Sigsbee’s apparatus consists of a cylinder, covered with
gauze at the upper end, and having a flap-valve at the lower
end. The cylinder is heavy enough to acquire a rapid vertical
descent between any two depths, — the valve during the descent
keeps open, but remains closed during the processes of lowering
and hauling back with the rope. An idea of what it is intended
to effect may thus be stated briefly : specimens are to be ob-
tained between the intermediate depths a and 6, the former
being the uppermost. With the apparatus in position, there is
at a the cylinder suspended from a friction-clamp in such a way
that the weight of the cylinder and its frame keeps the valve
closed ; at b there is a friction-buffer. Everything being ready,
a small weight or messenger is sent down, which on striking the
clamp disengages the latter and also the cylinder, when mes-
senger, clamp, and cylinder descend by their
own weight to 6, with the valve open dur-
ing the passage. When the cylinder-frame
strikes the buffer at b, the valve is thereupon
closed, and it is kept closed thereafter by the
weight of the messenger, clamp, and cylinder.
The friction-buffer, which is four inches long,
may be regulated on board to give as many feet
of cushioning as desired. The accompanying
sketch of the trap (Fig. 33) explains itself. The
copper cylinder A is retained in place by screw-
bolts. It is riveted to a wrought-iron frame
B, has a flap-valve C, fastened to a long lever
D, pivoting at E. The top of the cylinder is
covered by a wire sieve, and in addition there
is a wire-gauze funnel or trap H, inside the
cylinder. The cylinder is hung to the friction-
clamp K, by an excentric tumbler P, which is
released whenever the messenger X strikes it,
allowing the messenger, cylinder, and clamp to
travel with the valve open till it strikes at the
requisite depth the buffer Q. The valve is then
closed, the cylinder drawn up, and the contents _ Fig. 33. — Sigsbee’s Gravitating
of the sieves carefully examined on deck. Trap. (Sigsbee. )

EQUIPMENT. 37

opened, it was allowed to run on say from five to fifty fathoms
on the wire rope, and on reaching the lower point it closed
again. The cylinder was then brought up with great care and the
contents examined. In a similar way it was sent to collect the
pelagic forms between fifty and one hundred fathoms in depth,
and finally those of the intermediate belt between one hundred
and one hundred and fifty fathoms. As was anticipated, the
cylinder contained in the first experiment —from five to fifty
fathoms — about the same pelagic forms as were found on the
surface at the locality where the cylinder was sent down. In
the second experiment, — from fifty to one hundred fathoms, —
the same forms were found again, though greatly diminished in
number, and the water of the third trial was found to be entirely
barren of animal life. This collecting-cylinder was tried once
off the eastern extremity of George’s Bank, and a second time
in the axis of the Gulf Stream, in localities where the surface
fauna was very abundant, and could be followed with the eye
down to a moderate depth. These experiments serve to prove
that the pelagic fauna does not extend to considerable depths,
and that there is at sea an immense intermediate belt in which
no living animals are found, nothing but the dead bodies which
are on their way to the bottom. The collecting-cylinder should
also be modified so as to drag at intermediate depths horizon-
tally. Whenever this is done, the question can be definitely
settled.’

The “ Blake” has now been on three dredging cruises, and
has been employed every winter since 1874 in deep-sea sound-
ings. During the first dredging season in the Gulf of Mexico
in the winter of 1877-78, the “Blake” was commanded by
Lieutenant-Commander C. D. Sigsbee. To his inventive genius is
due the efficient equipment of the “ Blake,” and his suggestions
have greatly modified all the apparatus originally in use on the
vessel.

The officers spared neither pains nor work to accomplish the

1 It is stated in “Nature” of August Pisani,” is invariably sent down with the
4, 1884, that a tow-net which opens and thermometer-wire, and that it has worked
closes automatically, invented by Captain successfully.

Palumbo of the Italian corvette “ Vettor

38 THREE CRUISES OF THE “ BLAKE.”

best possible results. Their interest in the work never flagged,
and they have now attained a proficiency in deep-sea work
hardly deemed possible ten years ago. By the old methods a
single dredging at depths of from twelve hundred to eighteen
hundred fathoms occupied nearly twenty-four hours. It was
not an uncommon occurrence for the “‘ Blake” to make six, or
even seven hauls a day in depths varying from seven hundred
to eighteen hundred fathoms. The deepest sounding made by
the “ Blake” was in 5,428 fathoms; the deepest haul of the
trawl in 2,412 fathoms.

During the second cruise among the West India Islands and
the third cruise along the eastern coast of the United States,
the “ Blake” was commanded by Commander J. R. Bartlett,
whose interest in the work was not less than that of his prede-
cessor in command. It is pleasant to notice that the harmony
between the naturalists and the officers of the “ Blake” was
not for an instant disturbed during the time they were working
in common. LEKverything in the way of naval routine was sacri-
ficed for the time to the objects of the cruise, and the appear-
ance of the deck and bow of the “‘ Blake” was often more that
of a mud-scow than of a vessel in the service of the United
States.

Lf.
HISTORICAL SKETCH OF DEEP-SEA WORK.

Our knowledge of the depths of the sea was only incidentally
increased by the work of the great French, English, and Russian
exploring expeditions, sent on voyages of circumnavigation.
They collected interesting isolated facts regarding the distribu-
tion of temperature, the density of the sea-water, and the exist-
ence of animal life at great depths. Boyle and Hooke in the
seventeenth century both speculated and experimented as to the
saltness of the sea; Ellis, in the middle of the eighteenth cen-
tury, observed the temperature of the water from a depth of
neatly 900 fathoms. This observation, like many of the early
deep-sea temperature observations, was made by bringing up the
sea-water in a closed vessel and observing the temperature when
it was brought on deck. To Sir Joseph Hooker, when naturalist
of the Ross Antarctic expedition, we owe the interesting obser-
vation regarding the occurrence of surface desmids in the bot-
tom specimens of the dredgings of Sir James Ross. It was
principally from observations made in the Arctic and Antarctic
exploring expeditions that our first accurate knowledge was ob-
tained of the distribution of the temperature of the deep sea, of
the nature of the bottom, and of animal life at very great depths.
The observations of temperature, however, were not sufficiently
accurate for the requirements of modern physics, the thermom-
eters used not being protected from the great pressure to which
they frequently were exposed.

Within the last twenty years the investigations of the depths
of the sea have taken an immense development. Previous to
1866 several important exploring expeditions had made it a part
of their programme to sound at great depths and examine, as far
as was possible with the instruments then in use, the physical

40 THREE CRUISES OF THE “ BLAKE.”

conditions of the strata of water below the surface. But no ex-
pedition had been fitted out for that purpose alone. In fact, the
opinion was current among naturalists that beyond the 300
fathom line the field of the zodlogist was a barren one, notwith-
standing the many facts to the contrary which had been accumu-
lating! little by little since the beginning of the century. The
true bearing and full importance of these discoveries were
appreciated only by a few naturalists, who attempted in vain to
counterbalance the authority of Edward Forbes, the most bril-
lant naturalist perhaps of his time.

The deep-sea work of Forbes in the Augean Sea (1841) led
to the general acceptance of his theory that animal life was lim-
ited to a comparatively shallow depth (300 fathoms). The
peculiar physical condition of the region studied by Forbes may
perhaps account for the results he obtamed. For a time they
overshadowed later contradictory facts, as when in 1861, for in-
stance, living creatures were brought up by a telegraph cable
from a depth of over 2,000 fathoms in the Mediterranean. Yet
in spite of this, the poor success which attended the cruises of
the “ Porcupine” and “ Shearwater” in the Mediterranean led
Dr. Carpenter to assume that in that sea, below a few hundred
fathoms, life became practically extinct. It was reserved for the
French exploring expedition of the “Travailleur” and of the
“Talisman,” * in charge of Alphonse Milne-Edwards, to show
that while the great depths of the Mediterranean are not so full
of animal life as the corresponding depths of the Atlantic, they
yet contain favorable localities in which many of the Atlantie
deep-sea species may be found and were actually collected by
the French expedition. The great depths of the Mediterranean
are mainly covered by a thick bed of gray mud little favorable
to the development of animal life; and this fact, taken in con-
nection with the comparatively high temperature of that sea at
the bottom, would fuily account for the paucity of animal life.

1 Umbellula was brought up off the
coast of Greenland by Adrians in the
middle of the last century from a depth
of 1,406 feet in 70° N. L., and the speci-
mens were described by Eliis. In 1871
the same species was found again and

described by Lindahl from specimens col-
lected by the “ Ingegerd ”’ and “ Gladan.”

2 The eruise of the ‘‘ Talisman” to
the westward of the Atlantic coast of
Africa, 1882, led to some most important
results.

HISTORICAL SKETCH OF DEEP-SEA WORK. 41

These results were abundantly confirmed subsequently by the
rich collections made by Professor Giglioli in the “ Washington”
(Captain Magnaghi), sent out by the Italian Government to ex-
plore the depths of the Mediterranean. While the deep-water
species of the Mediterranean are, without exception, also found
in the abyssal region of the Atlantic, it is also true that the
Mediterranean contains only such deep-water species as can bear
a somewhat high temperature. We may consider that all en-
closed seas like the Sulu Sea, or inland seas like the Mediter-
ranean, the Red Sea, the Caribbean, and Gulf of Mexico, have
received their fauna from the adjoiming oceans. When from
some cause or other the colder water of the great depths was
shut out from a free circulation, only such species as were capa-
ble of living in a comparatively high temperature survived.
The fact that in the Mediterranean we find fossil Arctic forms,
such as occur in the glacial deposits of England and Sweden,
and are still found in the Italian pliocene deposits, shows plainly
that the temperature of the Mediterranean must have been dif-
ferent in former geological times from what it is now.

While naturalists were discussing the absence of animal life
below three hundred fathoms, Portuguese fishermen were taking
deep-sea sharks from nearly five hundred fathoms, and bringing
up occasionally a glass sponge (Holtenia) on their lines. Japan-
ese fishermen had also been catching a very similar shark in
three hundred fathoms, often drawing up with it a Hyalonema
which found its way to Europe as a great curiosity of Japanese
art. . No attention was paid to the existence of the many ant-
mals which from the end of the last century were shown to live
at great depths. Indeed, the occurrence of animal life in the
deeper waters of the ocean seemed to produce no impression on
scientific men, although in deep water on the two sides of the
northern part of the Atlantic, a number of species of fishes,
which could only subsist on animal life, were constantly caught,
thus plainly proving the existence of a varied animal fauna at
those depths. No attention was paid to the early observations
of Sir John Ross (1818) in Baffin’s Bay where, at the depth of
between 800 and 1,000 fathoms, a fine Astrophyton was brought
up on the sounding line. The extensive collections made by

42 THREE CRUISES OF THE ‘“ BLAKE.”

Torell at depths of over 1,000 fathoms, during his first expe-
dition to Spitzbergen, were only noticed by Keferstein * in 1846,
Similar observations by Sir James Clark Ross (1841) in the
Antarctic Ocean, at a depth of 400 fathoms, passed equally
without notice.

Yet as early as 1863 Professor Lovén”’ at the Meeting of
Scandinavian Naturalists held in Stockholm, gave a Report on
the expeditions of Torell to Greenland and Spitzbergen, in 1859
and 1861. These had demonstrated beyond doubt (with the
dredge) the existence at the deepest point reached (250 to 300
fathoms) of a fauna belonging to all the classes of marine in-
vertebrates. With the “ Bulldog” machine Torell brought up
from the great depth of 1,000 and 1,400 fathoms foraminifera,
molluseca, annelids, crustacea, echinoderms, and sponges. In
1868 Sars * published a long list of animals dredged to a depth
of 450 fathoms by his son G. O. Sars, off the coast of Norway,
since 1862. These belonged to all groups of marine inverte-
brates and seemed to show without doubt, as was well put by
Lovén, that off the Norwegian coast, at least, the zero point of
animal life had not yet been discovered; he further threw out
hints in regard to the existence of a uniform abyssal fauna over
the bottom of the Oceans which have formed the basis of all
subsequent speculations on this subject. From that time the
Swedes and Norwegians have been most zealous in their explora-
tions of the physics and natural history of the Arctic regions.
They have sent expeditions to Iceland, to Spitzbergen, and
Greenland, with Smitt, Goés, Ljungman, and Malmgren as
zodlogists, and although dredging had not then been developed
to its full extent, a few hauls were made by the “ Bulldog” ma-
chine to a depth of 2,600 fathoms, which showed the existence
at those depths of a large number of invertebrates. Their last
expeditions were those of Nordenskidld and of the “ Josephine”
(which ran a section across the Atlantic) with Captain Von Otter
as Commander. He had been the successful chief of the earlier
expedition of the “Sofia” to the Arctic region. .

1 Nachricht. d. K. Gesell. d. Wiss. z. 3 In 1850 Sars gave a preliminary ac-
Gottingen, 1846. count of a dredging trip to the Lofoten
2 See also Rept. Brit. Ass. Ady. Se. Islands in 1849.
York Meeting, 1844.

HISTORICAL SKETCH OF DEEP-SEA WORK. 43

In Great Britain, ever since the time of Forbes, dredging ex-
peditions have been undertaken, limited, however, to the more
shallow regions accessible by private means. The reports of the
dredging committee of the British Association have made the
names of Gwyn Jeffreys, of Norman, of Barrett, and Andrews,
familiar to students of marine zodlogy, while in this country the
shore dredgings of Stimpson, Dr. Ayres, Lieutenant Kurtz, and
of expeditions sent out by the Cambridge Museum form the
beginning of American investigations.

The successful deep dredgings of the Norwegian, Swedish,
and American expeditions were followed by the English expedi-
tions with which the name of Wyville Thomson will forever be
associated.

Sir Wyville Thomson, who visited Norway to examine the
collection of deep-sea animals made by the elder and younger
Sars, from depths varying between 350 and 500 fathoms, could
not fail to be struck with the variety of the fauna they had col-
lected. The discovery of Rhizocrinus, a small stalked crinoid,
the representative of a family of fossil sea-lilies, which had be-
come extinct with the chalk, opened to him a vista of what
might be accomplished by a systematic exploration of the great
ocean abysses. He had the great satisfaction, in connection
with Dr. Carpenter and Mr. Gwyn Jeffreys, to see in succession
the “ Lightning,’=“ Porcupine,” “ Valorous,” and “ Shear-
water ” placed at their disposal. These explorations culminated
in the “Challenger” expedition, one of the most remarkable
scientific explorations sent out by any government.

In 1868, the “ Lightning”? with Thomson and Carpenter ex-
plored the regions between the Ferées and Scotland, and made
successful hauls to a depth of 680 fathoms. The two following
years the “ Porcupine” was placed at the disposal of Messrs.
Carpenter, Jeffreys, and Thomson, and more extended explora-
tions were made off the coast of Ireland, the Bay of Biscay, in
the Atlantic, off Spain, and in the Mediterranean. The ship
was provided with the improved Miller-Casella thermometer for
taking the temperatures. These expeditions may be said to
have awakened in European naturalists general interest in the
importance of such investigations, and to have settled once for

44 THREE CRUISES OF THE “ BLAKE.”

all the question of the existence of animal life at the bottom of
the sea at all depths, — a varied fauna having been discovered
by the many casts in deep water at which the expedition dredged,
the greatest depth being 2,400 fathoms, then considered an
enormous one for the dredges.

But the crowning work of the English in this direction was
the “ Challenger” expedition. A man-of-war of 2,300 tons was
dispatched in 1873, commanded by Sir George Nares, with Sir
Wyville Thomson as scientific chief. The “Challenger” * was
gone three and a half years. She sailed or steamed over 69,000
miles, and crossed and recrossed the great oceanic basins,
dredging and sounding, and making physical observations at
no less than 360 stations. Indeed, the work of the “ Chal-
lenger”’ extended over the whole globe. Previous investigations
had been undertaken on a more limited scale along the coast of
North America, and in the North Atlantic and Arctic regions,
by the Norwegian,’ Swedish, Danish, American, and English
nations.

Any account of the work of the English would be incom-
plete without a mention of the important results, published im
1862, obtained by Dr. Wallich on the “Bulldog” in 1860.
These results, however, received from naturalists but little at-
tention. Dr. Wallich advocated the view that the condition of
the bottom of the sea was favorable to the existence of animal
life at the greatest depths ; unfortunately, the animals collected
by him, as well as by Sir James C. Ross, belonged to groups
which might live (and do, as we now know) at the surface, or to
the starfishes, which we could suppose might have floated out
far from the sea-shore, and finally have sunk. An Astrophyton
can swim to a certain extent, and starfishes can float for a long
time on the surface of the water, with their suckers uppermost.
Had, however, naturalists paid sufficient attention to the Re-
ports of Alph. Milne-Edwards, and Professor Fleeming Jenkin,
concerning the animals found growing attached to the cable laid
at a depth of 2,000 fathoms between Sardinia and Africa, the

1 Additional deep-sea work was also 2 Voringen expeditions, 1876 - 1878
undertaken by the “ Triton ” and “ Knight (Mohn, Danielssen, and G. O. Sars).
Errant” (Murray and Tizard).

HISTORICAL SKETCH OF DEEP-SEA WORK. 45

arguments of Dr. Wallich would not have waited so many years
for the recognition to which they were so justly entitled, and the
bearing of which the French naturalist fully perceived.

Of the more important of the early publications which have
little by little called attention to the presence of animal life at
great depths, we may mention, in addition to those of the Rosses,
the later (1853) papers of Professor Bailey of West Point, who
examined the soundings submitted to him in 1850 by Professor
Bache, the superintendent of the United States Coast Survey.
Professor Bailey was among the first to perceive the great im-
portance of the results for biology and geology. These sound-
ings extended to a depth of nearly 2,000 fathoms, and we find
here the first discussion of the mode of existence of the forami-
nifera. Professor Bailey considered that they did not live on
the bottom ; he further compared the nature of a part of the
Atlantic ooze to the chalk of England, and that of another to
our green sand. Bailey’s views were not supported by Ehren-
berg, who argued that the foraminifera lived on the bottom
where they were dredged. A very guarded report on the same
subject was written by Huxley on the soundings of Captain
Dayman of the “Cyclops” in 1857 (from a depth of 2,400
fathoms). He inclined to the opimion that the foraminifera
lived at the bottom, and called attention also, as Bailey had
done, to the great extension of globigerinz, and to the exist-
ence of genera dating back even earlier than to the time of the
chalk.

Maffitt and Craven investigated (1852) Gulf Stream globi-
gerne: chalk formed of globigerine. Ehrenberg began in
1850 his researches on the living and fossil marine organisms
of great depths. Then came the important memoir of Wallich,
the naturalist of the “ Bulldog,’ commanded by Sir Leopold
McClintock (1860). He confirmed the results of Bailey and
Huxley in regard to globigerine, and described ophiurans,
crustaceans, serpule, from a depth of 465 fathoms. Then fol-
low the explorations of Pourtalés, from 1867 to 1869, in con-
nection with the United States Coast Survey, in the “Corwin”
and “ Bibb.” !

1 Bull. M. C. Z., No. 6, Dec. 1867, and No. 7, Dec. 1868.

46 THREE CRUISES OF THE ‘“ BLAKE.”

As early as in Cook’s second voyage, Foster attempted to ob-
tain the temperature of the ocean below the surface. As one
of the results obtained by Krusenstern’s circumnavigating voy-
age, it was supposed that the temperature of the oceans at great
depths was uniform. But all the earlier observations were de-
fective from inaccurate soundings, and from the absence of
attempt to correct the temperature observations for pressure.
Among these we may mention those of the Arctic expeditions
of the Rosses, the Scoresbys, the Parrys, Franklin, and others.
As early as 1773, in Phipps’s Arctic expedition, temperature
observations were taken at considerable depths.

Lenz, on Kotzebue’s second voyage, corrected his observations
for pressure, and obtained a temperature of 3.05° C. at a depth
of about 960 fathoms. He was the first to establish the fact
that at the equator the cold water (bathymetrical isotherms) was
much nearer the surface than in the more temperate zones either
to the north or south of it. Yet, until a comparatively recent
time the idea was prevalent that below a certain depth the ocean
preserved a uniform temperature of 4° C., aithough we possessed
the very definite observations taken by the United States Coast
Survey officers, which annually recorded lower temperatures,
taken with instruments improved for each year’s work. It was
not until the Miller-Casella thermometer came into general use,
after being employed by the “Lightning” and “ Porcupine,”
that extensive thermometric observations were made sufficiently
accurate to serve as the foundation of oceanic temperature sec-
tions. We now have the broad outlines of ocean tempera-
tures, thanks mainly to the observations made under the direc-
tion of the United States Coast Survey, and by the “ Lightning,”
“Porcupine,” + the “Tuscarora,” the “Challenger,” and the
“ Gazelle,” with a number of other vessels of the Swedish,
Danish, Italian, Norwegian, English, French, and American
navies.

1 Pouillet and Humboldt seem both to hypothesis of an interchange of water
have been struck with the importance of between the poles and equatorial regions,
some of the early observations on deep- depending on a difference of tempera-
sea temperature, and Pouillet distinctly ture ; but this seems to have made no

states that the phenomena of ocean tem- impression on geographers.
peratures could be best explained by the

HISTORICAL SKETCH OF DEEP-SEA WORK. 47

The earlier deep-sea soundings were made with the usual
lines and leads, only somewhat heavier of course ; as the depths
increased, the difficulty of ascertaining when bottom had been
reached became greater and greater. Attempts were made to
sound with wire as early as 1849, by Lieutenant Walsh, U. 8.
N., and Captain Barnet, R. N., neither of which were successful.
An earlier attempt to sound with copper wire, also unsuccessful,
was made in 1842 by the United States exploring expedition
under Wilkes.

In 1850 Captain Platt of the U. S. schooner “ Albany,” with
cod-line and a heavy sinker, applied the method of determining
the depth by time-intervals as first suggested by Rear Admiral
W.R. Rogers. In doing this the line sent out was left behind
and the amount of twine lost was considerable, small vessels
going out fitted up with 40,000 fathoms of line. In 1854
Passed-Midshipman Brooke invented his detacher, so that the
line could be hauled in again, and Commander Sands perfected
in 1857 a cup which could bring back specimens of the bottom.
In 1868 the Hydra machine was invented ; it was in general use
by the English navy for deep-sea work till comparatively lately.
In 1872 Sir William Thomson invented his machine for sounding
with wire, and a new era for accurate deep-sea work commenced.

Commander Belknap devised a number of improvements in
this machine, and thus modified, it was in constant use during
the first season of the “ Blake’s” work. To Belknap belongs
the credit, not only of having first demonstrated the possibility
of using Sir Wiliam Thomson’s machine for taking accurate
soundings in great depths, but also of having made the deep-
est soundings yet taken (off the coast of Japan in 4,655 fath-
oms.' The result has taught us that there are in the ocean,
generally not very far from the shore lines, immense depressions
of the sea-bottom, which, in their relations to the topography

1 The accuracy of the deepest sounding
made by Commander Belknap has re-
peatedly been questioned by naval au-
thorities, because the wire broke while
reeling in. Any one experienced in deep-
sea sounding with wire must know that
the depth is accurately recorded on deck

the moment the wire stops running out,
and that it is not necessary to bring up a
specimen of the bottom to make an ac-
curate sounding. Lieutenant-Commander
Brownson brought up a bottom specimen
from a depth only 94 fathoms less than
that obtained by Commander Belknap.

48 THREE CRUISES OF THE “ BLAKE.”

of the ocean beds, can only be compared to the highest peaks
in the Andes and in the Himalaya chai. Similar gigantic pre-
cipices or depressions have been subsequently discovered by the
“ Challenger,” and by Commander Bartlett of the “Blake,” in
the Western Caribbean, and by Lieutenant-Commander Brown-
son, off Porto Rico (4,561 fathoms).

Although replaced in part by the trawl which was first used
in very deep water by the “ Challenger,” the dredge has played
a most important part in all except the latest explorations.
Tt dates back to O. F. Miiller (1779) ; it was used by Forbes
as modified by Ball in 1838, and with slight modifications by
all the more recent expeditions. It was, however, little in use
on the great expeditions before 1860, though in 1801, Péron
is said to have made casts with it. The Wilkes exploring
expedition in 1841 also used the dredge. Dr. Stimpson (1853)
seems to have been the first naturalist to handle it systemati-
cally within moderate depths in oceanic basins, during the North
Pacific exploring expedition under Ringgold and Rodgers.

Now, however, the United States Fish Commission use the
trawl almost exclusively in deep water. The same practice was
also observed on the “Blake” expedition, and on the “ Talis-
man.” The United States Fish Commission and the French
deep-sea expeditions have adopted for dredging the steel-wire
rope first introduced for that purpose on board the “ Blake,”
and it was found greatly to accelerate the trawling operations.

The publications of the “ Depths of the Sea,” of the “ Voy-
age of the Challenger,” by Sir Wyville Thomson, of the “ Nar-
rative” since his death, of “Notes” of the expedition, by
Professor Moseley, and of “ Thalassa,” by Dr. Wild, have
made the public familiar with the work of the English in the
exploration of the depths of the ocean. But little is known
even in America of the important part taken by the United
States Coast Survey in the solution of the problems of the phy-
sical geography of the sea, or Thalassography.

The Coast Survey, during the superintendence of Professor
Bache, instituted a series of investigations (begun as early as
1846) on the physical problems of the deep-sea, connected with
the Gulf Stream, which, little by little, were expanded by his

HISTORICAL SKETCH OF DEEP-SEA WORK. 49

successors, Professor Benjamin Peirce, Carlile P. Patterson, and
Julius EK. Hilgard, nto the most important hydrographic coast
exploration yet undertaken by any government. With a wise
liberality, secondary hydrographic scientific problems, mainly of
interest to the biologist and geologist, have been connected with
the work of the United States Coast Survey, while sections
were carried on across the Gulf Stream under the direction of
Lieutenant Craven in 1855, and subsequently under that of
Lieutenants Maffitt, Murray, Sands, Bache, Davis, and others.
In 1850 the extended biological survey of the Florida reefs by
Professor L. Agassiz was undertaken at the request of the U. S.
Coast Survey. The beginning of a more systematic deep-sea
exploration was made by Pourtalés and Mitchell, assistants of
the U. 8. Coast Survey, m 1867. During the explorations
of Pourtalés of that year, and of 1868 in the “Corwin” and
“Bibb,” dredging operations were carried on between Florida
and Cuba, and a depth of 850 fathoms was reached. The
collections were most interesting, and the first publications
of the results of the corals and echinoderms by L. F. Pour-
talés and A. Agassiz showed as clearly as possible the antique
character of the fauna then discovered, and the relationship
which it indicated to the cretaceous period, rather than to the
animals living upon the adjoining shores. An immense number
of new types were also discovered, and it became very plain that
the fauna living on the bottom along the course of the Gulf
Stream was one of the most interesting known to science.

The character of the bottom samples also first showed to
Agassiz that the deposits going on at the bottom of the ocean,
at great depths, were very different from the shore deposits
which as a general rule characterize all geological formations ; *
and that the modern chalk was not very different probably from
the old chalk of the cretaceous period. The expedition of the
United States Coast Survey steamer “ Hassler,’ Commander
Johnson (1871), which sailed with Professor L. Agassiz from
Boston to San Francisco, did not fulfil the expectations of its
projectors.

1 Among the earlier publications re- France et des Mers principales du Globe.

lating to the nature of the off-shore bot- Paris, 1871.
tom, see Delesse, Lithologie des Mers de

50 THREE CRUISES OF THE “ BLAKE.”

A systematic exploration of the Gulf of Mexico was begun in
1872 by Commander Howell, U.S. N., on the West Coast of
Florida, in comparatively shallow water, and was continued and
brought to a successful conclusion by Lieutenant-Commander
Sigsbee (1875-78) in the United States Coast Survey steamer
“Blake.” The deep-sea hydrographic work of the “ Blake”
was preceded by a number of soundings taken by the old meth-
ods, across the Straits of Florida, along the Florida Reefs,
and across the Gulf Stream beyond the Straits of Bemini.
Wire soundings were begun on the “ Blake” in August, 1874,
while she was in charge of Commander John A. Howell, U.S.
N., the apparatus employed being Sir William Thomson’s ma-
chine for sounding with piano-wire, as modified by Commander
George E. Belknap, U.S. N.

The expeditions of Pourtalés were followed in 1877-80 by the
dredging cruises of the “Blake,” a vessel built especially for
the hydrographic work of the Coast Survey, and thoroughly
fitted out for deep-sea dredging and sounding-work in 1877.
The “Blake” explorations extended through the Caribbean
(Bartlett commanding), the Gulf of Mexico (Sigsbee command-
ing), the Straits of Florida, and the east coast of the United
States as far north as George’s Bank. To these expeditions I
was attached in charge of the dredging operations. The deepest
trawling of the “ Blake” was in 2,423 fathoms, and the deepest
sounding taken by the “ Blake,” in 1882, by Lieutenant-Com-
mander Brownson, off Porto Rico, was in a depth of 4,561 fath-
oms. Finally, we must mention the extended operations of the
United States Fish Commission, directed by Professor 8. F.
Baird, assisted by a large staff of specialists. These commenced
in 1871 with naval tugs, and were carried on at first in moder-
ate depths. With the building of the “ Fish-Hawk” in 1882,
the operations were extended into somewhat deeper waters off
the east coast of the United States; the equipment of the “ Al-
batross” in 1883 supplied the Fish Commission with the best
equipped dredger for deep-sea work in existence ; and the work
of the Commission is now extended to the deepest water along
the American coast.

After the close of the Civil War the Coast Survey resumed

HISTORICAL SKETCH OF DEEP-SEA WORK. ol

its former activity ; and since 1866, the use of the dredge, the
trawl, the tangles, and all the apparatus necessary for a thorough
exploration of the fauna of the depths of the sea, has become as
familiar to some of the navy officers attached to the Coast Sur-
vey as the use of the sextant or the lead, and the Coast Survey
steamers, “ Bibb, “ Hassler,” and “ Blake” have acquired a
unique reputation as deep-sea dredgers. Not only naturalists,
but also hydrographers must be interested in Sigsbee’s volume
on deep-sea work, published by the Coast Survey, with its de-
tailed account of the equipment of the “ Blake,’ —a small
steamer of only three hundred and fifty tons burden, which,
under the skilful command of Lieutenant-Commander Sigsbee
and Commander Bartlett, has done not only more rapid, but
also far more accurate work than has been accomplished with
the old methods and appliances by the large men-of-war usually
detailed for similar work by European governments. The work
of the “ Bibb” and “ Hassler” is known to naturalists mainly
from the memoirs of Pourtalés. Only a part of the results of
the work done on the “Blake” under my direction has as yet
been published in the Bulletins and Memoirs of the Museum of
Comparative Zodlogy.

But we are only at the beginning of these investigations, and
we have much to learn as yet of the physiology of the ocean.
We have merely skimmed the surface thus far, and have only
traced a few thin lines with the dredge and trawl over the bot-
tom of the oceans.

The work of the Scandinavians has been supplemented by
that of the Americans, and the general agreement of the results
is most satisfactory. These results have, in their turn, been
greatly extended by the English, and subsequently by the Amer-
icans. Italians and French again have added to the stock of
common knowledge which formed the basis for the great
“ Challenger” expedition.

If.

THE FLORIDA REEFS.

FLoripa projects between the Gulf of Mexico and the Atlan-
tic as a broad, low peninsula, not strictly limited to the land
which rises above the level of the sea. Extensive shoals on its
southern extremity reach between the mainland and the line of
keys, and stretch nearly as far west as the Tortugas. Taken in
connection with the immense bank to the westward of the pe-
ninsula, they form the continuation of the mainland, below the
surface, to about the hundred-fathom line,—the mass of the
Florida plateau proper. To this must be added the narrower
coast-shelf of the eastern face of the peninsula. This shelf has,
however, a very different character ; for on the eastern side of
the peninsula, the calcareous or coral sand gives way to the
siliceous sand characteristic of the eastern Atlantic coast south
of Cape Hatteras.

The shore line of the southern extremity of the peninsula is
ill-defined, and, with the exception of the short stretch between
Cape Sable and Cape Florida, marked by bluffs of coral lime-
stone, is similar to that of the Everglades. It consists mainly
of innumerable low islands separated by narrow channels from
the mainland, to which it becomes united by flats, often bare
at low water. Similar flats, but far more extensive, stretch west-
ward from the mainland, back of the keys as far as to the
northward of Key West and the Marquesas. (Fig. 34.)

Portions of these flats are dry at low tide, and are separated
by occasional patches, more or less extensive, of deep water.
The water which covers these flats gradually deepens as one
passes westward from the mainland. The flats, as well as the
whole of the tract of surface between the mainland and the
Tortugas, dip slightly to the westward. These shoals are liter-

Fie. 34.—STRAITS OF FLORIDA, FROM COAST SURVEY CHARTS,

THE FLORIDA REEFS. 53

ally studded with mangrove islands, often-arranged without any
apparent regularity, either forming continuous ranges or small
archipelagos, broken by narrow and shallow channels. The
vegetation of these low islands is most luxuriant, and consists
mainly of mangroves.

Upon the flats which have reached the surface of the sea the
young mangrove plants drift in immense quantities. They are
fusiform bodies of about six inches in length, resembling a
cigar ; they float vertically, and when once stranded soon work
their way into the soft mud of the flats, and take root, sending
out shoots in all directions. The new stem rises rapidly, send-
ing down new shoots to the ground from higher points, forming
thus an arch of roots from which spread the branches of the
mangrove trees. Around sucha nucleus additional sand and mud
soon collect, and gradually build up extensive islands, covered
with a thick tangle of mangroves and other plants. The man-
grove islands on the flats to the north of Key West are specially
noteworthy. (Fig. 35.) The keys proper are all similar in struc-
ture, and form an extensive chain of low islands, rising nowhere
more than about twelve feet above the level of the sea. Start-
ing from north of Cape Florida, they form an immense crescent
extending as far west as the Tortugas. The keys usually con-
sist of the accumulation of dead corals, or of coral rock or coral
sand cemented into a greater or less degree of compactness.
The principal ones are long, narrow islands, varying in width
from a mile to less than a quarter of a mile, and in length from
mere patches to such islands as Key Largo, Indian Key, or Key
West, the longest of which extends about fifteen miles. The
keys are separated by shallow channels; they all slope very
gradually to the north into the mud flats, and present their
steepest face to the south on the shores which skirt the ship
channel that separates them from the reef proper.

The reef proper forms a curve similar to that of the keys,
never receding from them more than from three to fifteen miles.
The channel thus formed, which separates the reef from the
keys, is navigable for small vessels the whole length of the reef
as far as Cape Florida. The reef reaches the surface of the sea
at only a few points, as at Carysfort, Alligator Reef, and Ten-

54 THREE CRUISES OF THE “ BLAKE.”

nessee Reef. At other points it forms extensive shoals, which
are covered with a few feet of water. In other localities again,
the pounding of the breakers on the edges of the reefs has ac-
cumulated dead corals which form small keys along the line of
the main reef, as at Sand Key, Sombrero, and the Samboes.
There are passages of greater or less depth across several parts
of the reef, giving access from the Gulf Stream to the interior
ship channel. The main entrances to Key West Harbor are
formed by such channels. The depth of water on the reef, like
that of the mud flats, increases as one passes from Cape Florida
towards Sand Key and the Marquesas.

The small keys of the reef proper are built of accumulations
of larger coral boulders forming the foundation pieces of corals,
and fragments of shell and coral sand arranged according to
their size in the interstices, and heaped up by the action of the
waves, the tides, and the winds. Similar agencies must have
formed the keys proper, for they consist of the same coral rock
and sand, acted upon for a much greater length of time by the
storms.

A walk along the sea-face of any one of the keys will show
its coast line to be in incessant movement. In exposed places

Fig. 36. — Coral Breccia. Fig. 87. — Coral Odlite.

the larger fragments broken off by the breakers from the
coral rock of the shores are split into smaller fragments, which '
in their turn are changed to pebbles, and then finally become
cemented into coarser or finer sand or impalpable powder. The
cementation of these fragments at different stages gives us the

Fic, 35. — DISTANT MANGROVE ISLANDS SEEN FROM MANGROVE BEACH NORTH OF SLAUGHTER HOUSE, KEY WEST,

THE FLORIDA REEFS. 5S

so-called coral breccia (Fig. 36), and the different grades of
odlitic (Fig. 37) or compact limestone characteristic of the recent
reef formation.

The coral boulders are the remnants of huge masses of as-
treans and mezandrinas, and similar species of corals. The
broken fragments of corals come from the different species of
branching madrepores and porites or the smaller masses, such as
Manicina, Agaricia, and the like ; while the fragments of shells,
etc., are derived from the limestone carcasses of the hosts of in-
vertebrates which once lived on the active coral reef. The bor-
ing mollusks, annelids, and sponges have little by little riddled
masses of corals with their burrows, weakening them to such an
extent that the breakers pounding upon the exposed sea-faces
of the reef break off larger or smaller masses ; these are then
heaped up and ground together to form either the top of the
reef proper or the inner keys, as just described.

Of course it can hardly be expected that, with all this pound-
ing and grinding and constant rehandling of the material which
goes to make the limestone rock of the keys, many animal re-
mains should be preserved intact. In fact, with the exception
of fragments of the stouter shells of some of the mollusks or
tubes of annelids and the like, there are but few organic remains
to be found.

Corallines, or limestone alg, also play a most important part
in the formation of keys. They grow in great abundance upon
flats and upon the dead fields of corals which have reached the
surface of the sea; their joints are easily recognized in the com-
ponents of the coral sand of manya Florida key. Nowhere else
along the reef or the line of the keys do we find indications that
the highest elevation of the land is due to any causes except
those now acting in the formation of the keys. There is not
a single point so high that it cannot be reached by the waves in
severe storms, or the elevation of which cannot be traced to the
action of the tides and winds upon the material of the shore lines.

All naturalists who have visited the Florida reefs have felt the
difficulty of applying Darwin’s theory of reef formation to the
peculiar conditions existing along the Straits of Florida. Agas-
siz, Le Conte, and E. B. Hunt have each in succession attempted

56 THREE CRUISES OF THE ‘ BLAKE.”

to explain, from a different standpoint, the mode of formation
of the Florida reefs. Agassiz stated, and his statement was af-
terward confirmed by Le Conte, that the Florida reefs had a
distinctive character, and could not be explained by subsidence,
to which cause Darwin had ascribed the formation of barrier
reefs in general. In his report’ on this subject, Agassiz has
shown, not only that the southern extremity of Florida is of
comparatively recent growth, but that the causes by which it has
for the greater part been built up are still going on, and that
we have a specimen, as it were, of the past action in the mode
of growth of the present reef, keys, and mud flats. He shows
that the whole southern portion of Florida is built of concentric
barrier reefs, which have been gradually cemented into a con-
tinuous sheet of land by the accumulation and consolidation of
mud flats between them,—a process which is now going on
between the Florida keys and reefs from Cape Florida to the
Tortugas, and must end in transforming them, in like manner,
into a continuous tract, to be connected erent with the
mainland.

In Agassiz’s report no attempt is made to explain the sub-
structure of the peninsula upon which the reef-corals grow.
Le Conte, however, attributed this substratum to the mass of
material brought along by the Gulf Stream. He believed that
the Gulf Stream once ran parallel with the line of the present
peninsula, and that the substratum was formed by the heaping
up of these loose materials along that line. All the later in-
vestigations show, however, that the Gulf Stream never fol-
lowed this course. Then, as now, it swept across, and not par-
allel with, the line of the peninsula, and though it undoubtedly
assisted in the building up of Florida, it simply brought then,
as it does to-day, the food, or the greater part of the food, con-
sumed by the animals ving on the Bank of Florida. These
animals supply, by their growth and decay, the building mate-—
rial for. the great Florida Bank. No doubt, the floating ani-
mals brought by the Gulf Stream add something besides to the
mass of the bank itself; but they are chiefly consumed by the
animals living upon it.

1 Mem. Mus. Comp. Zool. VII. No. I. 1880.

THE FLORIDA REEFS. 57

The curve of the Florida Reef (Fig. 54) along the Gulf
Stream is due in great measure, as Hunt shows, to a counter
current along the reef, running westward. This current is
known to all navigators, and though ill-defined at Cape Flo-
rida, becomes stronger and wider as it goes west. It has a
width of at least ten miles at Key West, and of twenty miles
at the Tortugas. This is clearly shown by the mass of surface
animals driven along upon this westerly counter current by the
south-easterly winds.

The tides set strongly across the reefs, and through the chan-
nels between the keys, the flood running north and the ebb
south. When storms occur, the fine silt of the bank, made up
of coral sand from the reefs, is taken into the bay back of the
keys and deposited there. The counter current then carries this
to the westward, and thus material has gradually been added to
the flats. As Hunt has already noticed, tides and currents have
undoubtedly been the principal agents here. That this material
has not been brought by the Gulf Stream from the mouth of
the Mississippi, is shown by the fact that no trace of Mississippi
mud has ever been found in any of the innumerable soundings
taken to the eastward of the Mississippi, or more than a hundred
miles from its mouth. It is also probable that the action of the
waves from the southeast, in forming a talus of coarser material,
does not penetrate below one hundred fathoms, and everything
once fixed below that depth has its final character. The line
of keys seems to be formed by the waste of the exterior present
reef, rather than by the remains of an older anterior reef. At
the Tortugas, the contrary seems to be the case; but this per-
haps is due to the fact that the strong currents which sweep
over the reefs, and have excavated the Southwest Channel,
have also established conditions favorable to the growth of
corals on both sides of this channel, and that the two lines of
keys are due to this cause. Had the currents run only from the
southeast through the Northwest Passage, larger keys, separated
by channels running north and south, would then have been
formed.

I shall first show by an examination of the Tortugas’ how

1 A. Agassiz, The Florida Reefs; Mem. Am. Acad. xi. 1883.

538 THREE CRUISES OF THE “ BLAKE.”

far the explanations given by Agassiz, Le Conte, and Hunt are
satisfactory as regards the formation of the group of islands
making the extremity of the reef, and shall then attempt, by
the help of the dredging operations of the “ Blake” along the
Florida Bank, to reconstruct the past history of the peninsula
in its southern portion. Beginning with an account of the for-
mation of the present reef, based upon the knowledge obtained
by a careful survey of the Tortugas, I shall then proceed to the
elucidation of the structure of the peninsula itself.

The Tortugas (Fig. 38) are situated at the very extremity of

TORTUGAS.

Fig. 38. — The Tortugas from Coast Survey Charts.

the slope upon which the line of the Florida reefs has been built
up. They form the most recent of the cluster of Florida reefs,
and have not as yet been transformed into the normal coral reef
characteristic of the whole line extending from the Rebecca
Shoal and Marquesas to Cape Florida. There is as yet nothing
at the Tortugas corresponding to the extensive mud flat stretch-

THE FLORIDA REEFS. 59

ing uninterruptedly, a few feet below the surface of the water,
to the northward of the line of keys. (Fig. 34.) The northern
part of this flat, from Cape Sable to Key Biscayne, is fringed on
the southeast face by the line of narrow keys reaching from
Cape Florida to Bahia Honda. (Fig. 34.) In the oldest part of
the reef, the bay to the north of the keys, the waters of which
once undoubtedly covered the whole space between Pine Keys
and Cape Sable, has little by little been filled up and transformed
for the greater part into the wide, shallow mud flats now ex-
tending over that area. Next comes, from the Pine Keys to
Rebecca Shoal, a comparatively more recent portion of the reef,
in which the northern extremities of the keys rise somewhat
higher above the general level of the mud flats.

These two adjoining regions of flats and keys run parallel to
the main reef, at a distance of from one to nine miles from the
outer line of reefs, —the reef, that is, par excellence, over the
whole surface of which the living corals still prosper. Farther
yet to the westward, at a distance of fifteen miles from the west-
ern extremity of the outer parts of the reef, rise the Tortugas.
In this group a condition of things prevails at the present day
which must have been repeated over and over again, from the
time when the Florida Reef formed but an insignificant point
south of the line extending from Cape Sable to Key Biscayne,
until it reached the extremity of the present continuous mud flat,
about ten miles to the west of the Marquesas. As is well shown
on the Coast Survey maps, the mud flats, keys, and reef, dip as
a whole to the southwest, as does also the Florida plateau which
extends to the westward of the Marquesas. It is only upon
such parts of this plateau as from some cause or other have at-
tained a sufficient elevation to allow corals to flourish that the
reef may be expected to extend. Such an area is the knoll ris-
ing above the general level upon which the Tortugas have little
by little been built up ; and such also is the patch to the west-
ward of the Tortugas, upon which, as I shall show hereafter, an
incipient coral reef is already forming, at a depth of a little less
than twenty fathoms. (Fig. 38.)

It is not difficult to go back to a time when the great mud
flats of Florida did not exist. In their place was a steep slope,

60 THREE CRUISES OF THE “ BLAKE.”

such as we now find to the west of the Tortugas. Continumg
the parallel, it is easy to imagine how, little by little, since east-
erly winds and currents prevailed, materials coming from the
small outside reefs and held in suspension were gradually driven
to the westward, and accumulated finally upon what was then
the extremity of the great Florida Bank. There they gave rise
to knolls similar to those upon which the Tortugas have been
built. From the moment these knolls attained a sufficiently
favorable elevation for the growth of corals, a western reef was
formed, holding to the small Florida Reef then existing very
much the same relations as the Tortugas at the present day hold
to the great Florida Reef. Again, by the same agencies, the
channels which once undoubtedly ran back into the mud flats
to the north of the oldest keys were gradually closed, since such
channels as are still open, in part or wholly, im the more recent
and westerly portions of the reef, as, for instance, the entrance
to Key West Harbor, run from the south to the north across
from the reef to the mud flats. In like manner these channels,
and those which form an extensive strait in the most recent part
of the reef between Rebecca Shoal and the Tortugas, will in time
disappear, and become, in consequence of the extension of the
mud flats beyond Rebecca Shoal, narrow channels, like those of
Key West, of the Pine Keys, and of the Marquesas. By this time
there will also have been formed an extension of the outer reefs
along the twenty-fathom line, connecting the Tortugas with the
present reef, and only broken here and there by passages simi-
lar to those already existing along the reef, by which vessels
find free access to the middle passage between the reef and
keys. These channels are kept open by the same tidal agen-
cies as are now more powerfully at work at the Tortugas, but
which have gradually diminished in force from the Pine Key
Channel to the northward. The depth of the passage between
the Tortugas and Rebecca Shoal allows a larger and stronger
body of water to pass through that channel than through any
other.

It has been clearly proved by Hunt that the extensive flats to
the northward of the keys have been formed by the agency of
the tides, the whole triangular space between the Rebecca Shoal

THE FLORIDA REEFS. 61

and Cape Sable being filled up with silt. Since the flood runs
in a northerly and the ebb in a southerly direction, the tides in
their alternation hold in suspension the silt which they wear away
from the reef or from the shores of the keys. During storms
this floating silt is driven either on to the flats to the north of
the keys, or on to the slope of the reef toward the Gulf Stream.
An examination of the present condition of the Tortugas, and
of the mud flats beyond the Marquesas, gives us a very simple
explanation of the formation, and gradual extension westward
to its present limits, of the small reef originally existing only
as a diminutive spit, but gradually spreading to the southwest
from Cape Florida until it has reached its present gigantic pro-
portions.

The Tortugas show us, as will be seen, how the reef was
actually formed, while the extension of the mud flats beyond
the Marquesas explains how the bottom is prepared and grad-
ually raised to a level at which corals will flourish. One other
condition was, however, essential to the development of the
coral reef, — that of the existence of a powerful current, such
as the Gulf Stream, bringing an immense quantity of pelagic
animals to serve as food for the corals found along its path.
There is practically no evidence that the Florida Reef, or any
part of the southern peninsula of Florida which has been
formed by corals, owes its existence to the effect of elevation ;
or that the atolls of this district, such as those of the Marque-
sas or of the great Alacran Reef, owe their peculiar structure
to subsidence.

It cannot be denied that the backbone of the Florida penin-
sula was first produced by a fold of the earth crust in an earlier
geological period. Smith and Hilgard have also shown that
such a fold or folds formed the axis which has raised a part of
the northern base of the peninsula to a height of something less
than two hundred feet ; and that this axis, which has still, at
the latitude of Lake Okeechobee, an elevation of about forty
feet, but sinks gradually as we go south, was formed before the
Vicksburg limestone age, while on either side of it are deposited
the more recent limestones which have given Florida its present
width. They have pointed out, moreover, as a secondary result

62 THREE CRUISES OF THE ‘“ BLAKE.”

of this folding, the formation of an immense submarine plateau,
directly in the track of the Gulf Stream, by the accretions of
the solid parts of mollusks, echinoderms, corals, haleyonoids,
annelids, crustacea, and the like, which have lived and died
upon it; these solid parts have furnished the limestone for the
gradual completion of the peninsula. No one who has not
dredged near the hundred-fathom line on the west coast of
the great Florida plateau can form any idea of the amount of
animal life which can be sustained upon a small area under
suitable conditions of existence. It was no uncommon thing
for us to bring up in the trawl or dredge large fragments of
the modern limestone now in process of formation, consisting
of the dead carcasses of the very species now living on the
top of this recent limestone. To the westward of the western
shore line, Florida now stretches out as an immense submarine
plateau, forming, as the sections show, a huge tongue coated or
veneered only by coral limestone over its very top. The whole
of the peninsula of Florida south of St. Augustine, as far as
Tampa Bay, has probably in this way been built up from north
to south, of limestone somewhat older than the reef limestone.
The plateau, judging from the inclination of the axis, has but a
slight southward dip until one reaches the southern extremity of
the peninsula, where the fall is more rapid toward the outer reef.

The whole of the eastern and western edges of Florida con-
sist of recent limestones, the immediate predecessors of that
which is now forming on the western and southern slopes of
the great Florida plateau. The early dredgings of Mr. Pour-
talés, in 1867 and 1868, developed on the Gulf Stream slope
off the Florida reefs an extensive rocky plateau (Pourtaleés
Plateau) from a depth of about ninety fathoms to about two
hundred and fifty fathoms. The rock of which this plateau is
built (see Fig. 192) consists of the same species of corals and
shells as those now living upon it, to which it owes its forma-
tion.! A similar sea-bottom is found on the north side of Cuba,

1 Mr. S. P. Sharples, who examined of lime, the balance being organie matter
specimens of rock from the Pourtalés and phosphate of lime.
Plateau, found the corals made up of The recent limestone found on the
about ninety-five per cent. of carbonate Pourtalés Plateau contained from thirty-

THE FLORIDA REEFS. 63

but with a much steeper slope. These fringing limestones also
formed the southern extremity of Florida at a time when the
northern part of the Everglades had perhaps been built up to a
level favorable for the growth of coral reefs.

In the northern portion of the Everglades alone can we con-
fidently speak of the first concentric reefs, which have little by
httle built up Florida toward the south. It seems highly
probable that on the remainder of the peninsula north of the
Everglades, both the newer and older limestones were built up
by the same agencies now at work on the Florida Bank. There
are to-day other submarine banks which undoubtedly owe their
origin to similar agencies. The great bank to the east of the
Mosquito coast, which practicaliy extends to Jamaica, has prob-
ably been formed in the same way as the Yucatan and Florida
banks ; that is, by the gradual decay of the animals subsisting
in great abundance upon its slope, and fed by the pelagic
materials which the currents and the prevailing winds bring to
the bank, and which have been pouring upon the top of the
plateau for ages past. All the reefs on the south coast of
Cuba between the Isle of Pines and the shore of the east and
west may have had a similar origin. Among the West India
Islands the barrier reefs of the windward side are built upon
plateaux of a similar structure. The Grande Terre of Guade-
loupe is a fine example of such a plateau, which has been ele-
vated slightly above the level of the sea. At Barbados the
whole shell of the island consists of a series of terraces, which
have been successively lifted by the trachytic centre that forms
the nucleus of the island. These terraces are entirely com-
posed of limestone formed of the species of mollusks and radi-
ates now living in the West India seas.

six to forty-seven per cent. of carbonate
of lime and from thirty to thirty-five per
cent. of phosphate of lime, with ten to
twelve per cent. of carbonate of magne-
sia, and from ten to twelve per cent. of
oxide of iron. This large amount of iron
is probably brought down by the rivers,
and, coming in contact with the decompos-
ing organic matter, is deposited as a car-
bonate, and then slowly changed to a ses-
quioxide.

The most recent limestone contains,
like the corals of which it is almost en-
tirely made up, ninety-six per cent. of car-
bonate of lime and a little silica. In the
ooze the amount of carbonate of lime was
eighty-five per cent., there being also over
four per cent. of carbonate of magnesia,
and eight per cent. of organic matter, with
about one and one half per cent. cf silica,
and only a trace of phosphoric acid, which
distinguishes this ooze from Atlantic ooze.

64 THREE CRUISES OF THE ‘“ BLAKE.”

While there is thus undoubted evidence that a great part of
the shore line of the northeast extremity of South America has
been washed away, there is also evidence that the lines of the
bank connecting the lesser West India Islands have been built
up by agencies similar to those which have formed the Yucatan
and Florida banks, except that these latter have been formed
around the volcanic islands or folds which extend along the east-
ern edge of the Caribbean Sea. In some cases these banks have
been elevated since the existing condition of things came about ;
in others their elevation dates back to the period when the
separation of the Caribbean from the Pacific took place, at the
time of the closing of the Isthmus of Panama. Evidence of
this action is found in the elevated coral reefs and the raised
earlier tertiary and later cretaceous deposits of the West Indies
and Central America.

Nowhere do we find better examples than in the West India
Islands of the formation of submarine banks in connection with
volcanic peaks. A great number of peaks of volcanic origin
have risen nearly to the surface of the sea, or above it, and
serve as the foundation of great submarine or littoral banks.
It is well known, also, that the “ Challenger” and “ Tuscarora ”
soundings have developed a number of submarine elevations,
covered by deposits of pteropod and globigerina ooze, and these
deposits form extensive banks which serve as foundations for
barrier reefs and atolls, while the volcanic substratum has been
completely hidden. In the West Indies, as at Martinique, there
are volcanic peaks rising to a height of over four thousand
feet ; on their windward side are extensive submarine plateaux,
formed, I imagine, by agencies similar to those to which we
ascribe the formation of the Yucatan and Florida plateaux.
Whenever such plateaux have reached on their windward side
the level at which corals prosper, there coral reefs spring up
and flourish. Side by side with such conditions we find pla-
teaux at lower levels, under a greater depth of water, covered
only by the invertebrates living upon their surface, —as is the
case, for instance, in the northern extremity of the plateau of
the Grenadines. These plateaux have probably never risen to
the surface. We have also the still older phenomenon of such

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THE FLORIDA REEFS. 65

islands as Barbados (Fig. 39), where the terraces formed by
the raised coral reefs mark the successive elevation of the vol-
canic cone; or we may have still another combination, like that
of Guadeloupe, where a high volcanic peak forms the main
island, and an elevated plateau forms the Grande Terre with a
growing coral reef to the windward.

The fact that these great submarine banks of modern lime-
stone lie in the very track of the great oceanic currents sufli-
ciently shows that these currents hold the immense quantity of
carbonate of lime needed in the growth of the bank. Its
amount has, besides, been actually measured by Murray. He

Fig. 39. — Barbados Terraces.

has shown that, if the pelagic fauna and flora extend, as the
experiments carried on by the “ Challenger” and the “ Blake”
seem conclusively to prove, to a depth of one hundred fathoms,
we should have sixteen tons of carbonate of lime for every
square mile one hundred fathoms deep. But the greater the
depth at which these plateaux begin to form, the less rapid
must be their formation. The fact that the deeper part of the
ocean, below three thousand fathoms, does not contain any of
the larger shells of pelagic type can be readily explained on the
supposition that these, being very thin, like pteropod shells,
present a large surface to the action of the carbonic acid, which
is most abundant in deep water. Attacked as soon as they
reach deep water by this action, these shells of thinnest surface
are reduced to a bicarbonate, and are carried off in solution.
They do not, therefore, appear at these greater depths, and are

66 THREE CRUISES OF THE “ BLAKE.”

indeed rarely to be found below two thousand fathoms. The
thicker-shelled foraminifera reach a greater depth, not because
they are of different chemical composition, but because their
greater amount of substance yields less easily to the solvent
action of the acid or sea-water. At shallower depths the solvent
action of carbonic acid must be far less efficient, since there is a
rapid accumulation of dead siliceous and calcareous shells of
foraminifera, sponges, hydroids, corals, haleyonoids, mollusks,
polyzoa, echinoderms, etc., which must have lived upon the
bank long before they had by their accumulation brought it to
a level at which coral reefs could begin to grow.

The bathymetrical sections (Figs. 40, 41) of the peninsula
of Florida to the eastward into the trough of the Gulf Stream
are very different from those taken on the western side of the
peninsula. Proceeding northward from Cape Florida, we pass
out of the action of the current from the Straits of Bemini,
where the velocity of the Gulf Stream is the greatest. As soon
as we reach a latitude at which the trade winds do not blow, we
come gradually upon the usual comparatively gentle slope off
shore, which shows little trace of disturbance either from currents
or from the action of the prevailing winds. Judging from what
I have seen of the east coast of the peninsula of Florida, the
shore line deposits, such as the coquina of St. Augustine and the
shelly beaches of Indian River, indicate the presence in deep
water of a limestone deposit formed of the detritus of mollusks,
annelids, starfishes, and sea-urchins. There are a few corals
only, and occasional patches of reef-builders, but no extensive
reefs ; but this is a difficult point to decide even at Key West.
Indeed, all along the line of the reefs it would be hard to deter-
mine to-day whether the reefs have been formed, like the Mar-
quesas Keys, merely by the accumulation of detrital matter
driven to the westward and northward, or whether the Mangrove
Keys and the reefs really indicate the old lines of a reef similar
to the one now in full activity on the northern edge of the Gulf
Stream, parallel to the main line of keys. The absence of the
more delicate shells from limestone, in the formation of which
they must nevertheless have shared, may be explained by the
solvent action of carbonic acid upon them, and by the deposition

Ut

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Fig. 41.—SECTIONS ACROSS THE FLORIDA REEF. Sze Fic. 34.

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THE FLORIDA REEFS. 67

of carbonate of lime as a cement. A comparison of the struc-
ture of Loggerhead Key at the Tortugas with that of the Man-
grove Islands and the main keys shows us the difficulty of
deciding these points. At Loggerhead Key we have a shore
line made up of brecciated and odlitic coral limestone, fuily as
characteristic as any similar shore line on the older keys like
Key West (Fig. 42.) Yet we still find on the southern, east-
ern, and northern sides of Loggerhead an active growth of
reef-building coral, while other parts of the island and some
of the flats, if covered by mangroves, cannot be distinguished
by their structure from the genuine mangrove islands on the
flats to the north of the inner line of keys along the main
reef. (Fig. 43.)

We must be careful to distinguish the line of islands running
from the mouth of the St. John’s to Cape Florida, and parallel
with the coast of Florida, from the line of islands forming the
Florida Keys. The latter seem at first glance to be the con-
tinuation of the former; but this is not the case, their mode of
formation, as well as their geological structure, being radically
different. As was long since pointed out by H. D. Rogers, the
line of narrow islands to the eastward of Florida belongs to the
series of coast islands lying parallel to the coast from Long
Island to Florida, and extending around the whole Gulf of
Mexico. They all seem to have been formed by the same cause ;
the action of currents along the continental shores has formed
lines of deposit of but little width, and separated from the main-
land by a shallow channel. Some of these islands have been
slightly elevated at a comparatively recent period. This is es-
pecially the case with the islands along the east coast of Florida,
Anastasia Island, and those running south to Cape Florida, sep-
arating Indian River from the Atlantic Ocean. In all these we
find the so-called coquina of St. Augustine raised from ten to
twenty feet above the level of the sea at such points as Anas-
tasia, Merritt’s, and Worth Islands, showing all along the east
shore of Florida a very recent formation of shell débris or brec-
cia, very similar to the formation now going on in the lagoons
near Venice. This bed of shell breccia was probably deposited
after the low backbone of the peninsula, extending perhaps from

68 THREE CRUISES OF THE “ BLAKE.”

southern Georgia and Alabama to the northern part of Lake
Okeechobee and the Everglades, had been raised, and when the
peninsula of Florida from the St. John’s to the eastward was below
the level of the sea at a shallow depth. At any rate, it seems
plain from recent evidence that no trace of reef-building corals
exists on the east coast north of Cape Florida. Mr. Dietz is
inclined to look upon the formation of these islands as due to
the action of the waves. But there seems to be nowhere, as is
well stated by Rogers, any deposit of the kind going on now;
and when such masses of shells are thrown up on beaches, the
tendency is strong to consolidate from fragments to the concrete
form known as coquina.’ The mode of formation does not,
however, seem adequately accounted for by the action of cur-
rents moving along the coasts. These currents must have
flowed over a wide plateau, and have supplied the large amount
of food needed for the development of a thriving bank of mol-
lusks and other invertebrates. As soon as these growing colo-
nies had risen high enough to form banks parallel to the shores,
they were in their turn cut off and isolated from the shore by
the action of the tides and currents, which must then have be-
gun to deepen the channels intervening between the bars and
the mainland. They must also have forced their way across the
banks to form the shifting inlets, such as Mosquito Inlet, etc.,
so characteristic of the channels leading into the inland waters
along our whole Southern Atlantic coast. The dip of the co-
quina bed to the westward is well shown by the borings of arte-
sian wells at Palatka. I was informed ‘by the contractor that he
met the coquina beds at a depth of about forty feet, when he
reached a mass of clay, which in its turn was underlaid by pebbles
resembling the small pebbles found on flats off a rocky shore.
Possibly this mass of clay was formed by the silt of the Gulf
Stream at a time when it flowed over the low ridge of central
Florida, before that ridge had risen to form a dividing lne
between the two plateaux, one of which must have extended to
the westward much as at present, while the other undoubtedly
extended in some localities north of Cape Cafiaveral somewhat
to the eastward of the present shore line of Florida.
1 Fourth Report British Association, for 1834-1838, p. 11.

—

Fig. 42,—CORAL ROCK BEACH, NORTH OF FORT TA

YLOR, EXPOSED TO ACTION OF WAVES OF CHANNEL BETWEEN OUTER
REEF AND KEY WEST.

THE FLORIDA REEFS. 69

All this evidence tends to show that the coral reefs had little,
if anything, to do with the building up of the peninsula of
Florida north of Cape Florida. The existing line of reef is in-
deed probably the only one which has played any important part
in the formation of land south of the line of the present south-
ern extremity of the peninsula of Florida. There seems, how-
ever, some reason to believe that a line of reefs, or perhaps two
lines not very distant from each other, once stretched along the
southeastern end of the Everglades before the present reef began
to extend westward. Judging from the sections shown by the
maps, the growth of the present reef, as fast,as the mud flats
were formed to the south of it, has been altogether in that di-
rection. (Figs. 40, 41.)

The Bahamas, the San Pedro, and Yucatan banks have pro-
bably all been formed by a similar process, — by the accumula-
tion of limestone either upon an early fold of the earth’s crust,
or upon a volcanic plateau, or upon a foundation of slower
growth from great depths. In Yucatan we can actually descend
into the bank itself through any one of the aguadas, or caverns,
found everywhere in the northern part of that country. Many
of these caverns extend to a considerable depth; one of them,

that of Bolonchen, has a depth of seventy fathoms, the whole
formation consisting of recent limestone entirely composed of
species of invertebrates now living on the Yucatan Bank. In
Yucatan, as in Florida, we find a low ridge of limestone, some-
what older than that of the coast, extending across the peninsula.
The uplifting of this ridge has caused the slight undulations of
the surface traceable throughout Yucatan, at a distance of from
twenty to thirty miles from the coast, and running nearly at
right angles to it. Judging from its fossils and lithological
characters, the limestone of which this ridge is formed is iden-
tical with the so-called Vicksburg limestone of the central
backbone of Florida. The fauna of the Yucatan Bank is iden-
tical with that of the Florida Bank, being characterized by the
same species of echinoderms, mollusks, crustaceans, corals, and
fishes, so well known already from shallow water on the Florida
side.
While on the Yucatan Bank I had the opportunity of exam-

70 THREE CRUISES OF THE “ BLAKE.”

ining the great Alacran Reef,’ an excellent plan (Fig. 44) of
which is given on one of the British Hydrographic maps of the
Gulf of Mexico, from the surveys of Commander Barrett, R. N.
It is one of the circular reefs resembling atolls, and I was the
more desirous to get an idea of its mode of formation because,
according to Darwin’s theory of coral reefs, such atolls should
not occur in areas of elevation like those in which the Florida
reefs, the coast reefs of Cuba, the Bahamas, and the Central
American reefs are found.

The examination of Alacran Reef showed it to be in full ac-
tivity. The greatest length of the reef is about fourteen miles;
its width, eight miles. It consists of a steep semicircular wall
rising abruptly on the eastern side, which is also that of the
prevailing winds, from a depth of thirty fathoms to ten fathoms,
where the corals begin to grow, and the slope becomes much
more gradual. The eastern edge of the reef presents a singu-
larly regular section, where the huge masses of heads of Madre-
pora palmata form a nearly compact level wall, with its top flush
with the level of the sea. This wall is constantly beaten by the
sea, and the breakers, pounding upon the coral heads exposed to
their action, detach large pieces or break off the dead masses,
which are again triturated into smaller fragments until they form
a fine sand swept by the wind in a westerly direction ; this sand
little by little fills up the channels left between the masses of
coral which form the outer wall and extend towards the centre
of the reef. The detritus from the outer reef diminishes gradu-
ally in quantity, and leaves a channel varying from three to nine
fathoms in depth on the eastern edge of the low islands to which
the reef dwindles at its western extremity. This channel de-
scribes deep indentations in the western edge of that section of
the plateau which extends from the eastern edge of the reef. On
the eastern edge of the islands the reef is completely choked with
sand, while on the gentle western sea-slope of their outer side
the corals are thriving, but creep out very gradually seaward in-
stead of building a steep, abrupt wall like that of the outer edge
of the reef.

It is probable that, in the case of an atoll of this sort formed

1 Letter No. 1, Bull. M. C. Z., V. No. 1, April, 1878.

Hig. 43, — LAGOON FORMED BY PROMONTORIES AND LOW ISLANDS COVERED WITH MANGROVES, NORTHEAST SHORE OF
KEY WEST ISLAND.

N . ’ ua z i : i)
= eee ee ee eee eee ee eee ee ae age Ss) eer ee Ae ae Te.

THE FLORIDA REEFS. 71.

on a flat plateau, the low islands now constituting the western
edge of the reef were at one time exposed to the full action of
the sea. As their sea-slope became little by little surrounded
by the wall now encircling the outer edge of the reef, the
growth of the corals was checked, the interstices and spaces
between the coral masses were gradually choked by sand and
coral fragments, until the low islands now known as Perez,
Chica Pajaros, and the great sand-bars of the western edge of
the reef were slowly built up a few feet above the level of the
sea, — mere strips of sand gradually cemented together by the
accumulation of the loose materials held in suspension by the
water. ,

The outer eastern edge of the reef or wall is from one to two
hundred yards in width, and inside of this extends for a max-
imum distance of seven to eight miles an extensive section which
is more or less filled with masses of astreans, of mzandrinas, of
gorgonians, and madrepores in more or less irregular patches,
with a general westerly trend. They reach nearly to the water’s
edge, where it is quiet, and are separated by deep gullies of clear
water varying from one to seven fathoms in depth. Through
these gullies a regular current sets to the westward, and has de-
posited on its path the coral sand held in suspension, thus keep-
ing these gullies clear of coral and gorgonian growth. These
heads are gradually but steadily approaching the western strip
of islands, and will in time completely fill the whole space in the
interior of the reef, or will leave only a narrow channel of vari-
ous depth between the outer broad bank to the east and the
narrow islands to the west.

The whole structure of this reef shows its identity of forma-
tion with that of the main Florida Reef, and with that of the
reefs on the northern coast of Cuba, where the line of distinct
and powerful elevation can still be plainly traced by old coral
slopes and by the ancient coral reefs in the hills surrounding
Havana and extending to Matanzas. These hills attain a height
of over 1,200 feet, and are entirely composed of species of corals
identical with those now found on the living reefs. Alacran
Reef thus gives us an easy explanation of atolls, apparently
formed in areas of elevation; I look upon the structure of this

72 THREE CRUISES OF THE “ BLAKE.”

interesting reef as a sort of epitome of the mode of formation
of the great Florida Reef and of the Bahamas Bank. Taken
in connection with its position on the Yucatan Bank, it will
perhaps explain the mode of formation of the greater part of
the Florida peninsula as connected with the bank lying to the
westward of the mainland and to the northward of the Florida
reefs.

The specimens thus far obtained from the rock composing the
Yucatan plateau consist of the same limestone as those of the
great Florida Bank; and there are forming upon it, though to
a much more limited extert, patches of reefs near the thirty and
twenty fathom curve, such as the Shoals, the Triangles, Cay Are-
nas, the Arcas, the Madagascar, English, Alacran, and the
fringing reefs of the eastern edge of Yucatan, that extend along
the Mosquito coast to the central part of Central America.

It is evident from the above that we need not refer the atoll-
shaped form of this reef (Fig. 44) to the subsidence of the Yu-
catan Bank as a whole, since the action of the prevailing winds
and currents would account for all the existing phenomena.
The decay of the animals living upon the great plateau, added
to the deposition of all the animal life brought to it by the cur-
rents, would explain a gradually increasing elevation of the sur-
face till the level was reached at which reef-building corals
could flourish, and at which a reef would naturally be formed.
Darwin has noted the close resemblance between encircling bar-
rier reefs and atolls. It seems to me that the structure of the
Marquesas (Fig. 44) and of Alacran proves conclusively that
not one point of difference exists between a barrier reef and an
atoll. Darwin has also called attention to the fact that in
shallow seas, such as the Persian Gulf and parts of the East
Indian Archipelago, the reefs lose their fringing character and
appear as irregularly scattered patches, often covering a con-
siderable area; and he also observes that many reefs of the
West Indies have been formed in like manner upon large and
level banks lying a little beneath the surface, — banks which
he believes to have been caused by the accumulation of sedi-
ment. Such patches of reef-building corals would seem, from
their analogy with the Tortugas, to be the beginning of more
extensive reefs.

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THE FLORIDA REEFS. 73

While on the way from Key West to the Tortugas we stopped
at the Marquesas,‘ which are grouped as a paeaine ring of
islands. Their formation has undoubtedly been identical sae
that of the great Alacran Reef; and from the fact that no corals
are now found living on their weather side, these islands must
have assumed their present shape at the time when their weather
side made a part of the outer reef in connection with the islands
of Key West and the other keys, previous to the formation of
the present growing reef, or while the latter existed only in the
shape of a submerged reef several fathoms below the surface.
The plan and section of the Marquesas Keys (Fig. 44) show
the formation of the keys on a knoll rising from the general
platform of the surrounding reef plateau. This knoll has un-
doubtedly been built up, as were the Tortugas, from the remains
of the corals which once lived upon its face and surface until
the formation of the outer reef shut out the prevailing easterly
winds, and the corals were killed through the accumulation of
silt upon them.

The filling of a lagoon like that of the Marquesas must be a
slow process, for we find the water of the inner lagoon deeper
than that of any part of the reef immediately surrounding the
outer slope. We can imagine that when the outer ring of the
reef surrounding the inside lagoon is once completed, or nearly
so, the enclosed calm area is so placed as to be subject to but few
disturbing agencies, and is practically excluded from receiving
any appreciable amount of sediment from the water of the outer
reef, since the lagoon connects with the surrounding waters only
by the narrow passages which form the channels between the
lagoon and the main channel. Whether the removal of the
dead coral rock from the interior of the lagoon of an atoll, by
the action of the current through the narrow connecting chan-
nels, and by the solvent action of the carbonic acid, will suffi-
ciently explain the great depth of the interior lagoon seems
somewhat doubtful. The mud of the interior of the Marquesas
atoll was found to be calcareous, as is practically all the mud
which forms the extensive mud flats to the northward of the
keys. This mud is, however, generally covered by a thin dark-

1 See Bull. M. C. Z., V. No. 6. Letter No. 2, July, 1878.

74 THREE CRUISES OF THE “ BLAKE.”

colored layer of decomposed vegetable and animal matter. The
Marquesas are covered by a thick growth of mangroves.

Judging from my examination of the Tortugas reefs, it would
seem that corals do not thrive below a depth of from six to seven
fathoms. It is, of course, impossible to determine whether that
is their bathymetrical limit, or whether they are killed by the
accumulation of ooze in the channels and adjacent slopes. We
find them confined, however, to the same shallow depths, along
the whole of the main reef to the northward (Agassiz). Captain
Moresby also has shown that at a depth of ten fathoms in the
Maldive and Chagos archipelagoes the masses of living coral are
scattered at greater distances with intervening patches of smooth
white sand, and that at a slightly lower depth even these patches
merge into a smooth steep slope wholly bare of coral. All the
evidence accumulated by Dana, Darwin, Ehrenberg, Quoy, and
Gaimard tends to show that the limit of reef-building corals is
found at about twenty fathoms. On the Yucatan, as on the Flo-
rida Bank, the conditions favorable for coral-reef growth have
been produced, not by the uplifting of the continent, but by the
gradual rising of the bank itself in consequence of the accu-
mulation of animal débris upon it. The requisite level once
attained, reef-building corals (Fig. 45) would first establish

s «themselves on such spots as were most favorably
situated with reference to currents and prevailing
winds, both of which are essential to their healthy
growth, and thus the reef would be begun.

How far the growth of corals is affected by
such local conditions is perhaps nowhere better
ead seen than in the smaller West Indian Islands.
Fig. 45. Page On the eastern side exposed to the prevailing

Porites Embr ryO,

magnified. trade winds and washed by the great equatorial
currents, the corals flourish, while on the lee side they do not
exist at all. The whole eastern coast of Honduras, of Yucatan,
and of Venezuela, exposed to the same action and washed beside
by the Gulf Stream, is studded with coral reefs. To the action
of the Gulf Stream on the south coast of Jamaica and of Cuba
we must ascribe the presence of extensive coral reefs, and to the
same cause is undoubtedly due the great San Pedro Bank. The

THE FLORIDA REEFS. T5

fringing reef which skirts nearly the whole northern coast of
Cuba is in a less flourishing condition than the Florida Reef on
the opposite shore, which is reached not only by the main cur-
rent of the Gulf Stream, but also by the prevailing winds. The
circular outline of the main reef is readily explained by the action
of the Gulf Stream, which sweeping along the steep edge of the
southern extremity of the great Florida plateau carries with it a
superabundance of animal life, and gives the general direction
along which the conditions most favorable to the luxuriant growth
of corals exist when once the proper depth has been reached.

For a similar reason, corals are found alive only on the edges
of the Great Bahama Bank, where they are subjected to the be-
neficent action either of currents or of winds, that drive the silt
clear of the growing corals, and bring an abundant supply of
food. The same causes which have formed the great mud banks
to the northward and westward of the Florida Reef have, in the
case of the Bahama Banks, formed the immense-sand flats and
shallows which are fringed by living corals on the east and
west. They owe their existence, on the one side, to the wash
of the northerly trend of the great equatorial current, and to
the action of the trades ; on the other, to the clearing action of
the Gulf Stream. It must also be remembered that the Bahama
plateau was originally joined to Florida, as part of the great
fold which built up the framework of that peninsula, and that
it was also connected at one time with the island of Cuba. It
was also united with the reefs, now elevated to eleven hundred
feet, which joimed the eastern and western islands in more recent
geological times, and formed, before the tertiary, the two ex-
tremities of Cuba. On the southern side the reefs are still in
full activity, while on parts of the northern coast, in the vicinity
of Havana, they have been elevated to a height of no less than
one thousand or eleven hundred feet, while the present barrier
reef of the north shore of Cuba forms an immense reef, extend-
ing with scarcely a break from Cape San Antonio to the eastern
edge of the old Bahama Channel.

The Bahama plateau we may also fairly assume to have been
built up, little by little, from its original level, by the accumu-
lation of limestone formed in great part from the bodies of the

76 THREE CRUISES OF THE “ BLAKE.”

mass of animals which undoubtedly flourished upon the great
submarine plateau at a time when the Gulf Stream found its
way out of the Gulf of Mexico with less velocity than it now
has as it passes through the narrow Straits of Bemini. At that
time it spread itself fan-shaped over the southern part of Florida
and the Bahama Bank, and flowed more gently northerly and
easterly along the coast, with the additional remforcement of the
westerly equatorial, flowing north of the Great Antilles to the
eastward of Cuba. The Bahama Bank then probably consisted
of a series of banks like Salt Key Bank, separated by channels
like the Santarem and St. Nicholas, which were undoubtedly
kept open by the same currents as now form the Old Bahama
Channel. These channels, like those between the keys on the
Florida side, have gradually become filled with the detritus
driven into them by the trade winds, until the bank has been
formed in its present state of consolidation. Yet it must not
be forgotten that, while in the western part of the Caribbean,
the Gulf of Mexico, and Florida a dead level prevails, at
Havana, Hayti, and Barbados we have reefs elevated to a great
height, and others at considerable elevation on certain of the
Greater and Lesser Antilles.

The somewhat capricious distribution of coral reefs may per-
haps be explained by the action of the great equatorial currents.
The larger reefs occur in regions to which these currents bring
in the track of their course abundant supplies of food for the
reef-building animals. On the eastern coast of Africa, of Cen-
tral America, or of Australia, for instance, extensive colonies of
coral reefs flourish, while on the western coast of the same con-
tinents, in similar latitudes, but not bathed by such powerful
equatorial currents, the supply of food seems insufficient for
more than the isolated patches of corals existing there.

Other naturalists, as Semper’ and Murray,’ and later, Studer,
have already attempted to explain the formation of coral reefs,
in part at least, on grounds differing essentially from those to
which Darwin ascribed them, and similar in the main to those

1 Semper, C. Zeits. f. Wiss. Zool., No. 107, 1880, X. p. 505, On the Struc-
1863, XIII. p. 558. ture and Origin of Coral Reefs and
2 Murray, John. Proc. R. S. Edinb., Islands.

THE FLORIDA REEFS. 16

here brought forward. Mr. Murray’s “ observations of the reefs
at Tahiti’ support the view that they have been built from the
shore seawards, and that the lagoons have been and are still
being formed by the removal of the inner and dead portions
of the coral reef by the solvent action of sea-water. . . . The
food supply for the masses of living coral on the outer slope
of the reef is brought by the oceanic currents sweeping past
the islands, — a fact which explains the more vigorous growth
of the reef on the windward sides. It is maintained by Mr.
Murray that the whole of the phenomena of the Tahiti reefs
may be fully explained by reference to the processes at present
in action, and without calling in the aid of subsidence, as is
done by Darwin and Dana; and it is further argued that the
form of atoll and barrier reefs generally can be explained on
the same principles.”

Undoubtedly, Darwin’s theory of reef formation presents a
sound and admirable exposition of the grander causes which
have brought about the elevation or subsidence of large tracts
to a level favorable for coral growth ; but at the time he wrote
upon this subject, the formation of extensive limestone banks,
built up by the animals living on the bottom, and constantly
strengthened and increased by the attendant phenomena of
winds and currents, was little understood. These facts have
been brought into notice and emphasized by recent deep-sea
explorations. Darwin, however, when examining maps of the
West Indies, had been struck by the probable connection be-
tween the areas of deposition of the great banks marked upon
the charts and the course of the sea-currents. He naturally ex-
plained the steep slopes, abruptly dropping from comparatively
shallow plateaux to great depths, by what is known to occur
wherever great masses of sediment are found, and he therefore
considered these plateaux to be submerged mountains. Such
they are, in a certain sense ; not wholly built, however, as Dar-
win supposes, of sediment, but in great part also of the remains
of the innumerable animals living and dying upon them. The
nucleus of these banks has probably been formed around the
shores of promontories subjected to the most active play of the
great oceanic currents.

1 Voyage of the “ Challenger,” Narrative of the Cruise, p. 781. 1885.

78 THREE CRUISES OF THE “ BLAKE.”

At the time when Darwin wrote, and when we knew little of
- the limestone deposits formed by the accumulation of the débris
of mollusks, echinoderms, polyps, and the like, upon folds of
the earth’s crust, the formation of the basal parts of barrier
reefs was difficult of explanation. The evidence gathered by
Murray, Semper, and myself, partly in districts which Darwin
had already examined, and partly in regions where his theory of
reef formation never seemed to find its proper application, has
in a measure removed this difficulty. It all tends to prove that
we must look to many other causes than those of elevation and
subsidence for a satisfactory explanation of coral-reef formation.
All-important among these causes are the prevailing winds and
currents, the latter charged with sediment which helps to build
extensive plateaux from lower depths to levels at which corals
can prosper. This explanation, tested as it has been by pene-
trating the thickness of the beds underlying the coral reefs,
seems a more natural one, for many of the phenomena at least,
than that of the subsidence of the foundation to which the
great vertical thickness of barrier reefs has been hitherto re-
ferred. Still, it is difficult to account for the great depth of
some of the lagoons— forty fathoms—on any other theory
than that of subsidence.

If, however, we have succeeded in showing that great sub-
marine plateaux have gradually been built up in the Gulf of
Mexico and the Caribbean by the decay of animal life, we shall
find no difficulty in accounting for the formation of great piles
of sediment on the floors of the Pacific and Indian Oceans,
provided these banks lie in the track of a great oceanic current.
Certainly the coral reefs of the Caribbean and the Gulf of
Mexico, of Florida and the Bahamas, are distributed upon banks
which lie directly in the path of the great Atlantic equatorial
currents and of the Gulf Stream, — banks which we know to
have been formed by the agency of these currents.

The fact that the coral reef at the extremity of Florida is the
most recent of the coral formations found on the Florida shores
plainly shows that these reefs, as well as those of Yucatan,
Cuba, the Bahamas, and the Caribbean Sea, though not all of
the same age, were yet of modern origin, since we find them

THE FLORIDA REEFS. 79

still in an active state of formation. Even the elevated reefs of
Cuba and of the other West India Islands, though older, prob-
ably belong, nevertheless, to the most recent deposits of the
kind we know. The difficulty of explaining the constant re-
newal of the coral faces of the atolls of the Pacific, and their
present condition, on the supposition of their having existed
from the time of the early tertiaries, was one of the main
causes which led Darwin to seek for some other agency, like
subsidence, to explain the renovating process of the original
structure. In some instances coral reefs have unquestionably
been uplifted. Ihave seen the elevated reefs of Cuba, of San
Domingo, and other West India Islands, and of Barbados '
(Figs. 39, 46), which are perhaps the most striking examples of

Fig. 46.— Terraces near Fort Charles Light House, Barbados.

elevated reefs. They are too well known to need more than a
passing notice here. The terraces they form show plainly the
successive stages of arrest in the agency of elevation, and there
is no difficulty in accounting for their existence especially in a
voleanic region like the West Indies; but that there should
have been an extensive area of subsidence, in which the rate of
subsidence was so evenly balanced with the rate of coral growth
as to create and maintain the necessary conditions for reef for-
mation, is less easy of explanation.

The cap of rhizopod earth for which Barbados is noted dates
back to a time when the volcanic centre round which the coral
reefs have grown in more recent times was still at a considerable
depth below the level of the sea. This large accumulation of
rhizopodial earth is an excellent example in favor of the theory

1 The trachytie cone forming the base crop out on the surface in the northeast-
npon which the successive terraces of ern part of the island.
Barbados have been elevated is seen to

80 THREE CRUISES OF THE “ BLAKE.”

of Mr. Murray, that the inorganic material held in suspension
in the sea became precipitated on the sides of volcanic peaks or
slopes, and thus forms little by little the base or plateau upon
which coral reefs eventually grew. If this be true, it is not
necessary to resort to Darwin’s theory of extensive areas of ele-
vation or of subsidence in order to explain the formation of
atolls or of fringing reefs. In the tropics and in regions situ-
ated in the path of great oceanic currents which carry along
their course an immense amount of pelagic life, serving as food
for the animals living upon the bottom, we have all the elements
of the gradual accumulation of submerged land, which, when it
rises to a certain level, becomes the foundation upon which reefs
are formed. In fact, as has been well pointed out by Mr.
Murray, we should have in an area of elevation as well as one
of subsidence all the elements necessary for the construction of
atolls.

In a very interesting article on the Bermudas, Rein’ has
taken very much the same view of their gradual building up,
and explains the present condition of things by causes greatly
differing from those adduced by Darwin to account for the
apparent atoll shape of the groups.

The islands composing the Tortugas (Fig. 38) are Logger-
head, Bird, Garden, Long, Sand, Middle, and East Keys. These
are always above the level of the sea, while Southwest Key and
Bush Key are exposed only at low water, and North Key and
Northeast Key have disappeared. These insignificant islands
are the outcrops of extensive submarine banks. Loggerhead
Key, not more than three fourths of a mile in length, is the top
of a bank about five miles in length, extending to the three-
fathom line, with an average width of three fourths of a mile,
and has extensive coral sand flats running in prolongation of
the northern and southern extremities of the key. Between this
and the Garden Key and Long Key Bank, there are a few
shoals running more or less parallel with Loggerhead Bank, the
largest of which are Brilliant and White Shoals. Garden Key
and Long Key Bank form a rectangular shoal of nearly the

1 Rein, J. J. Beitrage zur Physika- Bericht. Senckenb. Naturf. Gesell., 1869-
lischen Geographie der Bermuda Inseln. 70 (Mai, 1870), pp. 140-158.

Fig. 47. —MADREPORA PROLIFERA. (Aaassiz.)

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THE FLORIDA REEFS. 81

same length as that of Loggerhead, with an average width of
nearly two miles, the great sand flats of this shoal being those
of the Long and Bush Key tract. The Southwest Channel,
with a depth varying from ten to twelve fathoms, separates
Loggerhead Bank from the Bird, Garden, and Long Key Bank.
This, in its turn, is separated from the still greater North,
Northeast, East, and Middle Key Bank by the Southeast Chan-
nel, with a depth of about nine fathoms, while the Northwest
Channel separates Loggerhead Bank from the North Key Bank,
with an average depth of from seven to ten fathoms. The
Eastern Bank is irregularly horseshoe-shaped, convex to the
east, and partly surrounds a great interior bay, which has an
average depth of about seven fathoms. The flood tides run
from the south through the Southwest and South channels in
a northeasterly direction, the ebb tide flowing in the opposite
direction. The strongest tidal current passes through the South-
west Channel.

An examination of sections of the Tortugas from the west to
the east shows the gradual rise of the mound forming the Tor-
tugas, as we pass from the west side of the Loggerhead Bank to
a line extending through the southwest slope of the same bank,
and across to the main bank of the group; the mound falls
slowly on the eastern slope as we cut across the east end of East
Key Bank, till we finally come to the low elevation forming the
southeast slope of Hast Key Bank. The action of the tides
through the Southeast and Northwest channels is well shown
in the fact that they keep open the passages between Long Key
and Loggerhead banks, and between the former and North
Key Bank, and also the secondary channels separating Bird
Key, Garden Key, and Long Key. These are undoubtedly the
last traces of the deeper and wider channels, probably once run-
ning parallel to the Southeast Channel. They have gradually
been filled up since the sand flats of Bush Key began to form,
so that the free circulation of the tides through them has been
prevented. The presence of a few large heads of mzandrinas
and astrzans, as well as the luxuriant growth of Madrepora
prolifera (Fig. 47) near low-water mark, on the two sides of
these channels, now changed into sand flats, seems to indicate a

82 THREE CRUISES OF THE “ BLAKE.”

more active tidal circulation through them formerly than is now
taking place. An examination of the cross-sections in the direc-
tion of the prevailing winds, and in the direction of the tides,
shows at a glance the mound-shaped mass which forms the base,
rising from the general level of twenty-five to thirty fathoms,
with its abrupt side facing the east. There are also seen the
deep furrows, more or less broad, which have been scooped out
of this mass by the action of the currents, such as those passing
through the Southwest Channel.

The corals which give to the reefs their peculiar physiognomy
are the extensive patches of Madrepora (principally M. cervi-
cornis), the clusters of the two common species of Porites (P.

. furcata and P. clavaria) (Fig.

48) covering more or less the
shallow tracts of coarse sand,
and Meandrina areolata grow-
ing between the patches of ma-
rine lawns formed by a species
of Thalassia, with occasional
patches of Anadyomene. In other
parts of the reefs large holothu-
rians (Miilleria) lie scattered on
the bottom, while im somewhat
i deeper regions are pockets filled
Fig. 48.— Porites clavaria. (Agassiz.) wth large Diadematidze. Im-
mense masses of nullipores (Udotea and Halimeda, Figs. 49, 50)
and corallines grow on the shallowest flats, on the tops of the
branches of madrepores which have died from exposure to the
air, either because they have grown up to the surface and so
have become exposed by extreme low tides, or because strong
winds have blown the water from the flats. The destructive
effect which an extremely low tide has on a growing reef is well
shown on the flats to the southward of Fort Jefferson, where
the upper part of the branches of a certain size reaching up to
a given level are frequently killed off by low tides. Exposure
to the action of the sun even for a very short time is sufficient
to kill them. ‘Fhe extreme sensitiveness of all corals to atmos-
pheric action is well known, so that it becomes plain, as has been

Fic. 49. —UDOTEA FLABELLATA. (Aqassiz)

(AGAssIz.)

HALIMEDA TRIDENS.

50. —

Fig.

=

3 ; Ye D ; ia a = ‘
T ar ; A} ' May. She 7

\ rat , , + te wy Tudpd' ee) ws or

hf ta? vy ls j as sige’
) : . hg

i
“i
i
.. i
Tt
i a
‘
——
j
i ®
A
é
‘
m
v
‘ ,
bi
‘
. “

THE FLORIDA REEFS. 83

stated already by Darwin, Dana, and others, that no coral reef can
grow above the level of the lowest tides, and that all subsequent
additions of material must be due to accumulation of sediment
transported by the action of the tides and prevailing winds.

Next come the clusters of coral heads, huge masses of astreeans
and of mzandrina, very limited in their distribution at the Tor-
tugas, as well as the more or less extensive patches of Madrepora
palmata (Fig. 51), and finally what is known as broken ground,
namely, the outer edge of the reef occupied mainly by clusters
of gorgoniz (Fig. 52), which also reach upward into the shal-
lower region. Occasional patches may be seen of astrzeans, ma-
drepores, and other reef-builders, which have extended below the
depths at which they generally flourish, where they are soon
killed or choked by the accumulation of fine coral sand and cor-
alline sand or ooze of the deeper waters. This sediment fills
the broad and narrow flat channels dividing the three great
banks which compose the Tortugas, or separate the inner shoals,
banks, and islands. Finally come the lines of broken coral heads
and branches, mixed with dead corallines, shells of mollusks, old
serpule tubes,’ gorgoniz stalks, and the like. These form a
low dike, as it were, to be little by little pounded up by the
breakers into smaller fragments, and carried, either by the winds,
or waves, or currents, into the interior of the reefs, there to form
sand flats of more or less coarse materials, until on the western
faces of the banks the finest detritus is deposited in very steep
slopes, constantly shifting like those of sand dunes, and, like
them, running forward and backward at the will of the winds
and waves. This continues until the particles have become ce-
mented together by the action of the carbonic acid contained in
excess in the salt water surrounding the reefs, and by the gluing
of the slight amount of animal matter which holds these parti-
cles together. Some of the slopes (according to General Wright,
of the Engineers) are as great as thirty-three degrees.

All this fine material, composed of fragments of every animal

1 Serpule often form incrusting masses and dead corals from being too rapidly
of considerable extent, acting,as has been broken to pieces by the action of the
noticed by Darwin, much as the patches waves.
of nullipores do in protecting decayed

84 THREE CRUISES OF THE “ BLAKE.”

and plant with a calcareous skeleton, of course prevents the
growth of corals in positions which are not well scoured, either
by the action of the tides or by that of the prevailing winds.
The corals when alive are gradually buried under this mass
of material constantly passing over them, and held in suspen-
sion. They flourish, therefore, only where the disturbing ele-
ments are reduced to a minimum; namely, on steep banks, or
on the slopes which are scoured by tides, or on flats at con-
siderable depths, over which a large body of water can freely
pass, whether brought by the tides or driven by the winds. In
such cases the corals can grow gradually towards the surface as
fast as the sediment deposited has closed up the circulation of
the lower levels. The quantity of calcareous matter held in
suspension in the water in the vicinity of a reef, and on the reef
itself, is very great. The breakers pounding upon the exposed
slopes of the reefs destroy, even on calm days, large quantities
of corals which have been weakened by the borings of mollusks,
annelids, echinoderms, and sponges. On windy or stormy days
the powdered fragments are driven far and wide, turning the
surrounding water to chalk color for a considerable distance
from the reef. It is not an uncommon thing, after a blow, to
come upon this water discolored by the fine calcareous silt, to a
distance of six to ten miles from the outer reef. After a pro-
longed storm I have seen between two and three inches of fine
silt deposited in the interval between two tides. The limitation
of coral-reef growth to shallow depths may be due to the fact
that the ooze held in suspension rapidly smks towards the bot-
tom, the surface water remaining clear. The rapidity with
which the corals are choked readily explains why they must of
necessity have a limited vertical distribution depending upon
local causes. This is well shown along the sections of the Tor-
tugas. Off the Marquesas, and along the line of the main reef,
we find corals living and flourishing at a much greater depth, and
there seems to be no simpler explanation of the limited bathy-
metrical range than that of the baneful action of the silt near
all reefs. That the silt is carried on the bottom by currents and
waves is well known, and on the bottom of the Gulf Stream, to
the north of the Straits of Bemini, we have a huge muddy bot-

Fic. 51. — MADREPORA PALMATA. (AGassiIz.)

: ) os ae ‘

. i ‘

’ = P i | . : | | | | ;
ce rons ou) rath Wis v's Br

>. ~ ia , vy

“i | ewe | athe ig

es ; - hy Tee 4) eee |

= | | |

it ‘ r “ Nhs fart

iP) ; .

- ; 7

% ‘ | aay fa! i

< * + ‘ |

= :

*

th syn

en

uit

3 it MD Le? i i : \ na AR os - ied te
ne cee Fal aT SE wh gh eM ark: \ilidaie Keer
3 , Mera. i

THE FLORIDA REEFS. 85
tom river carrying its silt to the steep slope south of Hatteras,
depositing occasionally a few patches of green sand along the
sides of its course, while the upper waters are perfectly clear and
of the deepest blue.

Corals alone cannot supply all the sand we know to be carried
by the Gulf Stream. We must add to this the mass of silt, mud,
and sand which come from pelagic animals, and which is dis-
tributed by the winds and waves, to be spread uniformly over
large areas, as is well shown from the distribution of the immense
mass of calcareous ooze over the whole of the bottom between
Florida and Cuba. This mass undoubtedly owes its existence
in part to the silt which the Gulf Stream brings from the south-
eastern edge and slope of the Yucatan Bank, in part to the ac-
cumulation of the pelagic fauna which the same great current
sweeps along its course. She amount of work done by the ani-
mals living upon the reef in preparation for the grinding process
of the breakers is very great. All writers upon the reefs have
referred to the destructive agency of boring mollusks, annelids,
and echinoderms, that riddle the coral branches and heads with
holes, and prepare the way for their fracture into larger or
smaller fragments.

The echinoderms found upon the flats seem to live almost
exclusively upon the organic matter and foraminifera they find
mixed with the coral sand, upon which they feed, and which
fills their digestive cavity. Their action, however, while an
important one, in that they reduce the sand to a smaller size, is
yet very slight as compared to the action of the breakers upon
the sea-face of the reef. Darwin and others have referred to
this agency of the echinoderms as one among those at work in
triturating the corals. By some observers, these animals are
supposed to be browsing on the living coral. This is not the
case either with holothurians and Diadematide or with clypeas-
teroids: living on flats, they swallow the sand as they find it.
But with Cidaris and Echinometra, which dig out holes in the
coral rock, the case is different. H. H. Guppy has also ob-
served the holothurians full of sand on the flats of the reefs of
the Solomon Islands.

The Loggerhead, Bird, and Bush Key banks, which protect

86 THREE CRUISES OF THE ‘“ BLAKE.”

each other to a certain extent from the action of the strong
winds opposed to the prevailing trade-winds, present a more
normal growth than that of the North Key Bank, which is par-
ticularly exposed to the full fury of the northers; they must
counteract to a great extent the action of the trade-winds. The
distribution of the broken ground, the position of the masses of
Madrepora cervicornis, and the trend of the sand flats, all alike
show the conflicting action to which the two slopes of this great
bank have been subjected. This counterbalancing action of
the northers and of the trade-winds is also well shown by its
effect on the position of the islands themselves. During the
prevalence of southeasterly winds, East Key, Sand Key, and
Middle Key extend bodily to the westward, the materials for
their growth being washed from the eastern shores. The op-
posite takes place during the prevalence of northers. The out-
line of Loggerhead Key is also constantly shifting, and according
to the officers of the Lighthouse Board, none of the landmarks
furnished by these islands can be relied upon in the location of
buoys.

What takes place upon the shores of the islands also takes
place, of course, upon the flats. Owing to the action of the
winds and waves, the whole mass of the surface of the reef is
kept in more or less active movement, according to the depth
of water on the flats and to their position. The coarser mate-
rials covering the flats and shore lines, and made up of large-
sized fragments, are gradually changing to the coarse sand
which forms the flats nearer the outer edge of the reefs; and
this, in its turn, is changed into the fine silt which fills the
channels, and eventually limits the growth of the corals to re-
gions where they can find permanent lodging, and are not im-
mediately under the influence of this shifting sand and silt.
The quality of the sand forming the beaches at different points
on the keys and flats depends entirely on its position. It will
be coarser or finer, according to the exposure of the beach, and
the finest sand is found in the most sheltered places, where the
silt has free chance to settle. (See Fig. 53 for a view of a char-
acteristic coral sand beach at Key West.) The scarcity of
fossils in the coral limestones of the reef has already been dwelt

Fig. 52.— RHIPIDIGORGIA FLABELLUM. (Aeassiz.)

7%
Pr trod
‘ ~ =
Ae! cat)
vy
7
i)
_ net.
~ py

“i
Lip?
¢

‘- ar
; i]
1 =
(Gea
H,
‘. co,
~—
iQ
=
a -
q ‘
mt ;
} y
-
J
. i
}
+) f
_
5
,
rt
seu! n
He)
a
j
fe 5 |
wy
- she bh a
Bi
au ) -

mi

-

ba RIN 8
ee aoa Loe
i: ae is
AM Ga alla
TP Mien) ih is ie ideo
* a he as ah

‘THE FLORIDA REEFS. ST

upon, and their absence is readily accounted for by the con-
stant disturbance of the shore-line deposits, which reduce little
by little the larger fragments of shells and corals, or echino-
derms, to a breccia, or again to odlite or fine sand. This is
nowhere so well seen as on the shore line of Key West to the
north of Fort Taylor. (Fig. 53.) There the outer reef is suffi-
ciently distant to allow waves of considerable size to break upon
this coast, and then strike to a low line of shore rocks. These
rocks are completely riddled by larger or smaller cavities made
by boring mollusks, annelids, sea-urchins, etc., or left by fossils
or fragments of corals which have fallen out. Thus weakened,
large masses are easily undermined by the water, which washes
around them with considerable force. They fall off, become
then broken into smaller and finer pieces, which are again re-
ground in their turn, and are finally either re-soldered into finer
breccia or coarse obdlite, or into the finest odlite or sand, accord-
ing to the composition of the rock. This is then cemented
again to the shore line, forming a new line, more or less
regularly stratified, dipping towards the sea, and, when ex-
posed to the action of the air, soon coated with a thin film of
hard limestone. This hardens, and forms the ringing crust of
the rocks found everywhere on the keys. This coating is
formed with great rapidity. An exposure between two tides is
sufficient to form such a thin coating, as I have repeatedly had
occasion to observe in the deposition of finer odlitic sands which
fill the rock-pockets just within reach of the waves at high tide.
A process of undermining simijar to what has been observed at
Key West takes place along all the coral-rock shores which
happen to be exposed to the action of the sea. From the de-
scription of Rein and others, this undermining action, operat-
ing on a very much larger scale on zolian deposits of consider-
shies altitudes, must be dig principal agent in the formation of
some of the peculiarly characteristic features of the Bermuda
Islands. On the east and west shore of Loggerhead, near the
northern extremity, we can trace admirably the successive layers
of the coral limestone which have been deposited and have had
an opportunity to harden between the tides, forming what ap-
pear to be stratified beds, with their outcrops running as a gen-

88 THREE CRUISES OF THE “ BLAKE.”

eral thing parallel to the bend of the shore or at a slight angle
from it, and dipping on the one side to the eastward and on the
other to the westward.

The bank to the west of the Tortugas has large heads of
astreans (Fig. 54) and madrepores growing up on it at a depth

Fig. 54.— Orbicella annularis. (Agassiz. )

of from six to seven fathoms. Gorgoniz are still found at a
somewhat greater depth. This bank is an excellent specimen
of an isolated coral patch, such as must have formed the basis
of all the keys and reefs. In time it will undoubtedly form a
new reef, flush with the surface, to the westward of the Tortu-
gas. The greatest depth at which reef-building corals have
been observed to grow is in the Southwest Channel on the steep
banks of White Shoal, and in the channel to the southwest
of Bird Key, where madrepores grow to a depth of about ten
fathoms.’ As a general rule, however, the corals are choked

1 Murray found off the slope of the covered with a most luxuriant growth of
reef at Tahiti that “the whole of the corals, with the exception of one or two
space from the edge of the reef to a small spaces where there was white coral
depth of about thirty-five fathoms was sand.”

= * p “é at inf
ssc pam Eat 8 ce SSR

Fie. 53, -CORAL SAND BEACH SOUTH OF NAVY DEPOT, KEY WEST

a ; . ‘i
} o : . |
y a 7
| Os ee
in : ; ii
2 Watt oe, a 1
5 7 bie . 4
Z ¥ i ool sw, = a
3 ; . A Lane y i rit,
7 : i |
. hs tie A. ‘
i j a

ie Pir Va i, Te
av A ye es

init #8 iv et ‘ 7
ee ee cae
nt 4 ?

THE FLORIDA REEFS. 89

below six fathoms by the ooze, and their place is taken by gor-
gonians.

All estimates of the age of the southern extremity of Florida,
or of the reef alone, must necessarily be very defective. The
great age assigned by Professor Agassiz to the northern part of
the peninsula may not be exaggerated, if it be understood as
including the time at which the Vicksburg limestone forming
its backbone was deposited. But the extension of the coral
reefs proper so far north in Florida has never been proved.
The rate of growth of the reef-builders is very rapid, and it is
quite possible that the reef-builders of the Florida Reef began
at once all along the line extending from Key West to Cape
Florida, and quickly reached the surface, forming at first a
barrier somewhat less compact than the present line of reef.
Uncertain as we are respecting the time at which the various
parts of the reef reached the surface, we can only say that in
Florida, limiting the estimate strictly to the depth at which
corals grow, it would probably take from one thousand to twelve
hundred years for corals to rise from the seven-fathom line to
the surface. This would give us no clue whatever to the actual
age of the reef, because it is difficult to determine how far the
width of any coral reef is due to the growth of coral. But sup-
posing the reef to have an average width of half a mile, and its
lateral growth to be say four or five times more rapid than its
vertical increase, we should get at least twenty thousand years
as the age of the outer reef. It is quite possible for a great
width of reef to be forming at one time, and to spread laterally
with rapidity if the plateau upon which it grows is of the right
depth. Take, for instance, the width of flats upon which madre-
pores flourish. A plateau at favorable depth would very soon
be covered by them; they would spread rapidly until they
reached the edge beyond which no corals could thrive, on ac-
count of the depth.

Thus we see, from the sections and a study of the distribution
of the corals, that at the present day material is constantly
added to the knoll forming the Tortugas ; that this material is
derived either from the animals and plants living upon the reef,
or from the pelagic animals which die while passing through

90 THREE CRUISES OF THE “ BLAKE.”

the channels; and that we can find nowhere any trace of eleva-
tion. Here the calcareous material has evidently been heaped
up to its highest point by the influence of the waves or winds.
Furthermore, we see growing to the westward of the Tortugas
a knoll similar to that which has formed the Tortugas them-
selves, and which will form, in the course of time, an island or
a series of islands like them to the westward. It is further
evident, also, that the Alacran Reef has been built up in the
same way, and that its peculiar atoll shape is due to the action
of the prevailing winds and currents, and not to any subsidence
of the great Yucatan plateau.

The character of the fauna and flora of the Tortugas is inter-
esting as corroborating the comparatively recent age at which
the reef has been formed. We find, as we go north along the
keys, that the nearer we come to the mainland of Florida, the
greater the number of plants characteristic of the mainland.
As we reach islands more or less inaccessible, or islands merely
formed by flats which have reached low-water mark, the vege-
tation consists almost wholly of mangroves. Yet at the Tor-
tugas, in spite of the narrow channel which separates them
from the Marquesas, I saw but a single diminutive mangrove
plant, while a few bay-cedars, as they are called, a vine with a
thick white flower, and Bermuda grass have alone found their
way there, although the Tortugas are in the direct line of the
prevailing winds from the Marquesas. One of the species of
land shells common at Key West has already found its way
to the Tortugas. The group is visited by pelicans, cranes,
humming-birds, plovers, and a few land birds. It bemg the
winter season when I visited the place, the insects were few in
number. No terrestrial reptiles have been found on the Tor-
tugas, while at Key West there are many of the frogs, toads,
lizards, and snakes characteristic of the southern spit of the
mainland, — all this showing that the Tortugas reefs have not
been above the level of the sea long enough to have received
as yet the fauna or flora characteristic of the more northern line
of keys.

The explanation given here of the formation of huge deposits
of limestone from the limestone carcasses of invertebrates takes

THE FLORIDA REEFS. 9]

for granted that the most favorable conditions for their support
exist ; and this condition we assume to be an abundance of food,
brought to them by the great oceanic currents passing over the
regions where these submarine plateaux are forming. We know
as yet too little of the fauna of the oceanic basins to be able to
affirm how far the population of the bottom depends upon the
food it receives from oceanic currents. We can only judge by
analogy. No marine fauna has been explored which equals
in variety or in the number of its individuals that of the Ca-
ribbean and of the Gulf of Mexico, from the depth of two
hundred and fifty to about one thousand fathoms. It has
proved richest in the districts most favorably situated with re-
gard to the currents and the food supply they bring in ther
track. It is but natural to extend this effect to other oce-
anic currents, and in their track we may therefore expect to
find the most favorable conditions for the support of an im-
mense fauna. In fact, the question of food is of the utmost
importance to the distribution, not only of marine, but of ter-
restrial animals; and the absence or presence of an abundant
supply of suitable nourishment must of necessity be an all-
important factor in the character and variety of the fauna of
any place or period, — far more influential, perhaps, than the
many obscure physical causes upon which we are so apt to
explain the distribution of animal life. On the continental
ledges, where the shore detritus is gradually accumulated, bring-
ing with it a large amount of animal and vegetable food, we
find the most populous fauna near the hundred-fathom line.
When, in addition to the action of the influences which have
accumulated the shore detritus, we have a continental shore or
plateau bathed by a great and powerful current, bringing with
it an abundance of pelagic life, we may expect a superabundant
supply of food, and consequently a fauna of unusual richness
aad variety. The fauna of the Pourtalés Plateau, of the hun-
dred-fathom slope to the westward of the Tortugas, of the
northeastern slope of the Yucatan plateau, of the windward side
of the Lesser Antilles, and of the continental slope of the eastern
coast of the United States below the hundred-fathom line, are
all examples of such districts supporting a marine fauna of sur-

92 THREE CRUISES OF THE “ BLAKE.”

passing richness. In a similar way, we may expect to find in
the track of the Pacific equatorial current the most favorable
conditions for the support of a rich and varied marine fauna.
The “Challenger”? found, perhaps, no richer dredging fields
than off the coast of Japan, which lie directly in the track of
the Japanese stream ; the fauna of the Kuro Siwo may be con-
sidered as the Pacific equivalent of the Florida and Caribbean
fauna.

In past geological times the effect of the currents in deter-
mining the distribution of the marine invertebrates must have
been as marked as it is at the present day. As long as we had
a great equatorial current running practically unbroken round
the world, and only slightly deflected by the continental islands
of Central America and of the East Indies, which stood in
the path of this equatorial belt, it was natural that we should
have a very extensive geographical range for all the tropical
marine forms. It was only after the complete shutting off
or comparative isolation of the Atlantic from the Pacific that
different physical conditions began to exist simultaneously,
which were of the greatest importance in reducing the supply
of food to the animals on the west coast of the continental bar-
riers, and in extending towards the north, as far as the tempera-
ture would allow, a supply of food far more abundant than that
with which the fauna of the eastern coast was supplied before
such a break of continuity existed. As this separation of the
Atlantic and Pacific probably took place late in the cretaceous
period, and was perhaps not completed till the middle tertiary,
we shall naturally expect to find the marine fauna of the earlier
geological periods of the Old and the New World to be very
similar, and consisting of many identical species. These older
faunz flourished on the shores and continental shelyes which
were washed either by the equatorial currents, or by branches
extending both north and south along the then existing con-
tinents and continental islands; and where we now find rich
fossiliferous deposits we may feel assured that the beds at the
time of their formation were either formed along a continental
shelf, or lay in the track of a primary or a secondary marine
current, which supplied an abundance of pelagic food indirectly
necessary for the support of any rich marine fauna.

IV.

TOPOGRAPHY OF THE EASTERN COAST OF THE NORTH AMERICAN
CONTINENT.

Onty the most general features of the topography of the
Western Atlantic, including the Gulf of Mexico and the Ca-
ribbean, were known before the explorations of the “ Blake.”
The course of the hundred-fathom line from George’s Bank to
Cape Hatteras, the Straits of Florida and the Gulf of Mexico,
was accurately laid down from the work of the hydrographic
parties of the United States Coast Survey. (Fig. 55.) The
hundred-fathom line indicates in a general way the true conti-
nental outline of the eastern coast of the United States. The
continental slope connecting this submarine shelf with the bed
of the Atlantic, and with the basins of the Gulf of Mexico and
of the Caribbean, was traced in its details by the successive ex-
peditions of the “Blake.” We must except the oceanic lines
run by the “ Challenger,’ connecting Nova Scotia and New
York with the Bermudas, and the Bermudas with St. Thomas.’

1 “Similar investigations,” says Pro-
fessor Hilgard in an account of the work

Coast Survey in developing the configu-
ration of the ocean-bed between the Ber-

of the “ Blake,” “have since been pros-
ecuted by Commanders Bartlett and
Brownson, U.S. N., under the direction
of the Superintendents of the Coast Sur-
vey, in the western part of the North At-
lantic,— that great embayment, which,
limited by Newfoundland on the north
and by the Windward Islands on the
south, might be not inaptly named the
Gulf of North America. The depths and
temperatures obtained by these officers,
upon lines run across the course of the
Gulf Stream, and connecting with those
tun by H. M.S. ‘Challenger’ in 1873,
will make apparent the part taken by the

mudas and the West India Islands, and
northward to the Banks of Newfound-
land, and in defining the limits of the
continental plateau, which, extending
from the coast to the hundred-fathom
line, may be described as the western rim
of this great basin of the North Atlantic.
. . . During the winter of 1881 to 1882
the ‘Blake’ was engaged in developing
the limit and general character of the
great Atlantic basin between the Bermu-
das and the Bahamas, and along the out-
side of the West India Islands as far to
the eastward as St. Thomas. This cruise
has been of great interest. The bed of

94 THREE CRUISES OF THE “ BLAKE.”’

A great number of soundings, mainly along the continental
slope of the New England States, were also taken by the
vessels of the United States Fish Commission. Important
soundings were made by the United States Fish Commission

ATLANTICBASIN &
EASTERN UNITED STATES §

(FROM MODELS CONSTRUCTED BY ‘
U.S Coast SURVEY AxD
Exprocrapuic Orrick.

Fig. 55.— Model of part of the Western North Atlantie.

steamer “ Albatross” in the Caribbean, during the winter of

1885-1884.

Along the Atlantic coast of the United States (Fig. 56) from
Cape Hatteras north to the extremity of George’s Bank, the

the Atlantic is shown to have a general
depth of two thousand seven hundred or
two thousand eight hundred fathoms ; and
depths of over two thousand fathoms are

found almost if not quite in sight of most
of the islands along the outside of the
Bahamas, and even in the narrow passages
between them.”

HOIBO RL WANT LOS}OIN

‘TOW O OIUdvVuUo OUadAH

anv

HAMAS LSVOYST
‘NVIOQ JILNVILY HLYON

HL AO LV NULLS AAA

WESTERN PART OF THE
NORTH ATLANTIC OCEAN.

U.S.COAST SURVEY

AND

HyDROGRAPHIC OFFICE.

BD. Meisel, Lith, Bowton

TOPOGRAPHY OF THE EASTERN COAST. 95

continental shelf increases gradually in width from fifteen miles
at Cape Hatteras to about one hundred miles off the southern
coast of New England; opposite the Gulf of Maine the south-
ern edge of George’s Bank is nearly two hundred miles from the
coast of Maine. In the latitude of Cape Cod and nearly south
of Cape Sable there is a wide break in the hundred-fathom line,
giving access to a tongue of the ocean which, in some places,
extends to within fifteen or twenty miles of the coast of Massa-
chusetts and Maine. A similar break, the opening into the
Gulf of St. Lawrence, occurs between Sable Island Bank and
the Newfoundland banks.

Between Cape Hatteras and the Bahamas there extends a
huge triangular plateau, sloping gradually from the shore to
about the six-hundred-fathom line, where a steeper slope con-
nects it with the floor of the ocean. As will be seen from the
map, the thousand-fathom line runs parallel to the hundred-
fathom line from the eastern extremity of George’s Bank to
Cape Hatteras, and is nowhere more than fifteen miles dis-
tant from the former. The slope to the two-thousand-fathom
line, however, is by no means so abrupt, except a little south
of Hatteras, where it is only about fifteen miles distant. It
varies from forty miles off the extremity of George’s Bank to
over a hundred miles in the normal to the Jersey coast.

On the southern New England coast the continental shelf

1 Another break in the coast line is this hole to have a most remarkable char-

thus described by Professor J. E. Hilgard :
« During the summer of 1882 the ‘ Blake,’
under command of Lieutenant - Com-
mander W. H. Brownson, was engaged
in sounding off the entrance of New York
harbor. The charts have hitherto shown
a spot about a hundred miles south-east
of Sandy Hook known as the ‘hundred
and forty-five fathom hole.’ [Mr. Lin-
denkohl (American Journal of Science,
June, 1885, p. 475) has suggested that
this so-called hole is one of a series of
mud holes, showing the existence of an
ancient river channel, and that these holes
were once apart of a deep ravine, form-
ing the outlet of the river to the ocean. |
In her soundings, the ‘ Blake ’’ discovered

acter. Its depth varies from one hundred
and fifty to over four hundred and fifty
fathoms, the bottom being of mud ; and
in about the centre a knoll of mud, gra-
vel, and shell rises up to within sixty-four
fathoms of the surface. The dividing
ridge between the hole at its deepest
point and the deep water outside has a
least depth of one hundred and twenty-
nine fathoms. There seems to be a con-
tinuation of bottom of irregular character,
which extends from Sandy Hook about
south-east ; for about two hundred miles
farther the depth is over three thousand
fathoms, surrounded by very much shoaler
depths.”

96 THREE CRUISES OF THE “ BLAKE.”

slopes very gradually seaward, forming a broad, slightly inclined
submarine plateau. The edge of the plateau beyond the hun-
dred-fathom line falls rapidly to the thousand-fathom line, form-
ing a steep slope, the Gulf Stream Slope, so named by the
Fish Commission, because it extends under the inner edge of
the Gulf Stream along our coast, from Cape Hatteras to Nova
Scotia.

South of Hatteras the hundred-fathom line runs parallel to
the coast at a distance of about sixty miles till off Jacksonville.
From this point it gradually closes up towards the Florida shore,
and is not more than ten miles distant from Jupiter Inlet. It
then makes a gigantic sweep and runs parallel to the general
trend of the Florida reefs, until it turns abruptly northward
about a hundred miles to the westward of the Tortugas. South
of Hatteras the thousand- fathom line does not follow the line
of the hundred-fathom curve; it extends almost in a straight
line from the Cape to the northern extremity of the Bahamas,
and is connected with the sloping Carolina- Florida plateau
(the “ Blake Plateau”) by a sharp slope, reaching, however,
only about to the six-hundred-fathom line, which in some parts
of the plateau off Florida and Georgia is over two hundred
miles from the coast line. The two-thousand-fathom line is
about ten miles distant from the thousand-fathom line all the
way from north of Cape Caiiaveral to Sombrero Island, and
along the greater part of the east face of the plateau of the
Windward West India Islands.

North of Cape Cafiaveral as far as Cape Hatteras, the two-
thousand-fathom line is from twenty to sixty miles distant from
the thousand-fathom line, which forms as it were the bottom of
the steep slope of the continental shelf. From this line to the
deepest water between the Bermudas and the Atlantic States
the slope is hardly perceptible, —a general fall of say twelve
thousand feet in a distance of over two hundred and fifty miles,
or a slope of about fifty feet to the mile.

The eastern slope of the great Bahama Bank is very much
steeper than that of the Atlantic Coast of the United States.
In no case is the two-thousand-fathom line more than fourteen
miles from land, and in one case Lieutenant-Commander Brown-

TOPOGRAPHY OF THE EASTERN COAST. 97

son found nineteen hundred and seventy-six fathoms only two
and a half miles from land, — a declivity of thirty-eight degrees.
The thousand, two-thousand, and twenty-five-hundred fathom
lines run parallel to the general line of the eastern row of
islands which form the Bahama Bank, from Navidad Bank to
Great Abaco Island. Between Navidad Bank and San Do-
mingo, a deep and narrow tongue of the ocean, averaging over
two thousand fathoms in depth, extends to opposite the centre
of the Windward Passage. The same steep slope is continued
north of San Domingo, Porto Rico, the Virgin Islands, along the
eastern edge of the Windward Islands, till about off St. Lucia,
where the slope is somewhat less abrupt. The thousand-fathom
line follows closely the trend of the Windward Islands; but the
two-thousand-fathom line begins to diverge off Anguilla and St.
Barthelemy, and by running at a considerable distance outside
of the Barbados forms a gentler slope than to the north. From
off the Caicos Islands the slope is still steeper, a depth of nearly
three thousand fathoms being found from there to the Virgin
Islands, at a distance of generally less than fifty miles, and often
within twenty miles of the hundred-fathom line. The greatest
depth reached by the “ Blake” has been found off Porto Rico.
Lieutenant-Commander Brownson sounded there in four thou-
sand five hundred and sixty-one fathoms,’ the deepest sounding
but one yet made, and traced the extension of the deep water
which fills the basin of the Western Atlantic to the west of the
Bermudas, and is separated from the deep basin of the tropical
Atlantic by a spur of the Dolphin Rise, to the north of St. Paul’s
Rocks. The temperature, thirty-six and a quarter degrees,
clearly indicates that this deep hole, as well as the body of cold
water of which it is a part, is also separated by a ridge, which
probably rises to a depth .of about seventeen hundred fathoms,
from the colder water of the South Atlantic; there the tem-
perature is less than freezing, and the water is directly con-
nected with the Antarctic on the eastern part of the South
Atlantic. (See Fig. 61.)

1 Fifteen miles from the deepest point with brown ooze on the top and an under-
the “Blake” sounded, in four thousand stratum of gray ; temperature, 36° F.
two hundred and twenty-three fathoms,

98 THREE CRUISES OF THE “ BLAKE.”

Passing now from the Atlantic to the Caribbean (Fie. 57),
we find that a very different topography characterizes the west-
ern and eastern parts of this sea. The natural division between
them is an immerse submarine bank, — the extension of the
Honduras and Mosquito coast plateau (which is less than a hun-
dred fathoms) towards Jamaica, — this plateau being, as far as
is known, nowhere at greater depth than five hundred fathoms,
and forming a number of smaller banks, such as the Rosalind,
the Pedro, Serranilla banks, which are less than a hundred
fathoms in depth. The Mosquito plateau shelves very gently
towards the east, and forms an wregular triangular plateau
uniting Jamaica at the five-hundred-fathom line with Hondu-
ras. The channel between Jamaica and San Domingo slopes
gradually to the thousand-fathom line from both sides. The
island of Jamaica forms the western extremity of a chain of
mountains extending along the southern coast of San Domingo,
but with a tongue to the northward of Navassa between it and
Formigas Bank and another between Formigas and Jamaica.
These banks, with Porto Rico and the Virgin Islands, constitute
the northern boundary of the Eastern Caribbean, and separate
it from the Atlantic, leaving only the comparatively shallow
Mona Passage with two hundred and sixty fathoms at its great-
est depth between San Domingo and Porto Rico, and the still
shallower passages running between the Virgin Islands across
the plateau, which unites them all and is formed by the hun-
dred-fathom line.

There is a comparatively deep caiion of about eleven hundred
fathoms, leading from Sombrero into a small basin of twenty-
four hundred fathoms in depth between Santa Cruz and St.
Thomas. This cavion, separating the Lesser from the Greater
Antilles, has a bottom temperature of thirty-eight degrees,
plainly showing that it connects with the Atlantic, and indicat-
ing the existence of a ridge running between Santa Cruz and
Porto Rico. The “ Albatross” (as reported by Commander
Bartlett) discovered this ridge, with nine hundred fathoms as
its greatest depth. The soundings of the “ Albatross” further
developed the presence of an elevation running north and south
nearly parallel with the chain of the Windward Islands, reach-

CONTOUR MAP

CARIBBEAN SEA.
1885

Prepared trom data furnished by the
U.S Hydrographic Office,
based on the deep-sea soundings of the
USCSStrBlake and the USF CStr Albatross.

Ks dear arn)
SP Sree ee tecesnent

tanh

Hee alee
FE
HHT

Is

\ SEX
SS SY .

\
\ WS XY
\ \ S

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B. Meisel, lith

aie

an

estas

pat

ut
qeseeseigsthet

a

lees

CONTOUR MAP

OF THE
CARIBBEAN SEA

1885

Prepared trom data tarnished. by the
US Hydrographic Office,
based on the deep-sea soundings of the
OSCSStr Blake and the USF CStr Albatross.

~ SA
SO?
[ES SAS SAS

B Meisel, lth

TOPOGRAPHY OF THE EASTERN COAST. 99

ing from St. Christopher to Bird Island and about to the lati-
tude of the Grenadines, showing considerably less than a thou-
sand fathoms, with fifteen hundred to two thousand fathoms on
each side.

The eastern boundary of the Eastern Caribbean is formed by
the dumb-bell shaped plateau, from which rise the Windward
Islands. (Fig. 58.) These extend in a gigantic arc from Som-
brero and Santa Cruz to Grenada, Tobago, and Trinidad, leay-
ing broad, shallow passages between the islands to the north
of Dominica, with the three comparatively deeper straits sepa-
rating Dominica, Martinique, St. Lucia, St. Vincent. We next
come to the still shallower passages over the Grenadines Bank,
and the deeper passage between that bank and Tobago. This
island, as well as Trinidad, and all the Leeward Islands to the
north of Venezuela, lie within the hundred-fathom line." They
are all only outposts of the South American continent. From
the Gulf of Venezuela to the mouth of the Orinoco the hun-
dred-fathom line is about ninety to one hundred and twenty
miles from the South American coast.

The thousand-fathom line, which extends diagonally across
the Eastern Caribbean from the south-western extremity of San
Domingo to a point about one hundred miles north-west of
Aspinwall, runs towards the Venezuelan coast, and follows the
line of the hundred-fathom curve, with the exception of an
indentation from the deep water, extending to the southward
and eastward, between Curacgoa and the mainland. It also
follows closely the general trend of the south coast of San
Domingo, Porto Rico, and bears to the west of the Windward
Islands, being nowhere more than about forty miles from the
coast-line, and usually from ten to fifteen miles on the lee side
of the Windward Islands to the south of Guadeloupe.

Little is yet known of the depth of the main basin of the
Eastern Caribbean ; but from the absence of islands and banks,
it is probable that it is, like the Gulf of Mexico, a huge oval

1 The “ Albatross,’’ in 1884, ran a line from ten to forty miles. “ Albatross,”
from Curagoa to the mainland in a south- Hydrographic Report, 1884, J. R. Bart-
erly direction, the greatest depth found lett.
being 738 fathoms at a distance ranging

100 THREE CRUISES OF THE “ BLAKE.”

basin, in the north-eastern parts of which a depth of over 2,500
fathoms has been obtained. The only line yet run directly
across the main basin of the Eastern Caribbean has been
sounded by the “ Albatross” from Curacoa to Alta Vela, a
small island on the south coast of San Domingo. The deepest
water found was 2,694 fathoms, — the average depth nearer
the South American side of the basin being about 2,300 fathoms
until within a short distance of the land.

The topography of the Western Caribbean is strikingly dif-
ferent from that of the eastern basin. The soundings of Com-
mander Bartlett have developed an immense submarine valley,
extending nearly due east for about seven hundred miles, from
the southern extremity of Cuba towards the Chinchorro Bank,
off the coast of Honduras. This valley has an average breadth
of about eighty miles, and an average depth of over two thou-
sand fathoms. Towards its eastern extremity it attains the
depth of nearly 3,200 fathoms, and its greatest depth is 3,428
fathoms twenty miles south of Grand Cayman. So that the
highest peaks of the chain of mountains skirting the southern
shore of Cuba, which rise to 8,400 feet, are really 28,000 feet
above the bottom of this great submarine valley, distant only
fifty miles in a straight line. As Commander Bartlett has said,
the little Cayman, Grand Cayman, and Misteriosa banks are
the summits, just appearing above tide-mark, of a submarine
range of an average height of nearly twenty thousand feet.
This deep valley, which has most appropriately been called
“Bartlett Deep,’ forms a loop to the eastward of Cozumel
Island, south of Pine Island towards the Pickle Bank. To-
wards the Yucatan Channel, which connects the Western Carib-
bean with the Gulf of Mexico, the bottom shelves gradually,
rising to a height of 1,164 fathoms, —the deepest part of the
channel between Yucatan and Cape San Antonio. The West-
ern Caribbean connects with the deep tongue of the Atlantic,
reaching north of San Domingo through the Windward Passage,
the deepest part of which is 873 fathoms.

We could have no better example than the Gulf of Mexico
affords of the deceptive character of the shore-line for obtain-
ing a correct idea of a hydrographic basin. (Fig. 59.) This is

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Windward Islands

LTS. Qoast ard Geodetic Survey.
Reduced from latesd Charts. corrected
By soundings taken in Steamer Blake.
Commander J R.Bartlett, U. S N, 2879.

Heights in Feet. Soundings in Fathorns
i. incaiitas 100 Fathorns

Fig. 58. —SKETCH MAP OF THE WINDWARD ISLANDS.

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TOPOGRAPHY OF THE EASTERN COAST. 101

admirably shown in the account given by Professor J. E. Hil-
gard, the Superintendent of the United States Coast Survey, at
a meeting of the National Academy of Sciences : —

“We perceive that the basin of the Gulf of Mexico is an oval con-
nected with the general ocean circulation by two outlets, the Yucatan
Channel and the Florida Straits. The area of the entire Gulf, cutting
off by a line from Cape Florida to Havana, is 595,000 square miles.
Supposing the depth of the Gulf to be reduced by one hundred fathoms,
a surface would be laid bare amounting to 208,000 square miles, or
rather more than one third of the whole area. The distance of the
hundred-fathom line from the coast is about six miles near Cape Flor-
ida; one hundred and twenty miles along the west coast of Florida;
at the South Pass of the Mississippi it is only ten miles ; opposite the
Louisiana and Texas boundary it increases to one hundred and thirty
miles; at Vera Cruz it is fifteen miles, and the Yucatan Bank has
about the same width as the Florida Bank.

“ The following table shows the areas covered by the trough of the
Gulf to the depths stated : —

Depth. Area. Difference.
2,000 fathoms. 59,000 square miles. 132,000
1,500 ea 187,000 <« “ 73,000
1,000 < 260,000 « = 66,000

500 =e 326,000 “ = 61,000
100 = 387,000 <« * 208,000
Coast line 595,000“ ‘

“ This table shows that the greatest slopes occur between the depths
of one hundred and fifteen hundred fathoms. The maximum depth
reached is at the foot of the Yucatan Bank, — 2,119 fathoms. From
the fifteen-hundred-fathom line on the northern side of the Gulf to the
deepest water close to Yucatan Bank, — say to the depth of two thou-
sand fathoms, — the distance is two hundred miles, which gives a slope
of five-ninths to two hundred, and may be considered practically as a
plane surface. The large submarine plateau below the depth of twelve
thousand feet has received the name of the ‘ Sigsbee Deep,’ in honor of
its discoverer.

“The Yucatan Channel, with a greatest depth of 1,164 fathoms, has
a cross-section of one hundred and ten square miles, while the Strait of
Florida, in its shallowest part opposite Jupiter Inlet, with a depth of
344 fathoms, has a cross-section of only eleven square miles.

“ A view of the maps reveals at once some important facts, which
were unsuspected before this great exploration was completed. Thus,
the distance between the visible coast-lines of the north-eastern point

102 THREE CRUISES OF THE “ BLAKE.”

of Yucatan and the west coast of the Florida peninsula is four hundred
and sixty miles, while the distance between the submerged contours of
five hundred fathoms is only one hundred and ninety miles; between
the contours of one thousand fathoms only ninety miles. These facts
at once characterize the Gulf of Mexico as a Mediterranean Sea.

“The most striking features displayed by the map are: —

“The great distance to which the general slope of the continent
extends below the present sea-level before steeper slopes are reached.
The hundred-fathom curve represents very closely the general conti-
nental line; the massifs of the peninsulas of Florida and Yucatan
have more than twice their present apparent width.

“Very steep slopes lead from this submerged plateau to an area of
fifty-five thousand square miles, — as great as that of the State of
Georgia, — at the great depth of over twelve thousand feet. There
are three ranges on the Florida and Yucatan slopes, extending in the
aggregate to more than six hundred miles, along which the descent
between five hundred to fifteen hundred fathoms, or six thousand feet,
is within a breadth of from six to fifteen miles. No such steep slopes
and correspondingly elevated plateaux appear to exist on the unsub-
merged surface of the earth. With the exception of the deep sub-
marine valleys, caiions, and steep slopes found in the proximity of
volcanic islands, continental slopes are small, except beyond the conti-
nental shelf, as off the Yucatan and Florida plateaux at the Bermudas,
Bahamas, and off Hatteras.

“The protrusion of the Mississippi delta toward the deep water of
the Gulf seems to give evidence to the engineer of the probably per-
manent success of the Mississippi jetties, as delivering the silt of the
river into water of so great depth, that but few extensions will ever
become necessary.”

The principal topographical features of the Gulf of Mexico
are the great banks which lie within the hundred-fathom line,
and occupy no less than one-third of the surface. While the
shore line of Texas and Louisiana slopes very gradually towards
the deepest part of the Gulf (Sigsbee Deep), the Mexican coast-
line north of Vera Cruz is somewhat steeper. The west slope
of the great Florida Bank as well as the north-west slope of the
Yucatan Bank are characterized by their steep inclinations. In
two places along the Yucatan Bank the horizontal distance be-
tween the hundred-fathom line and the fifteen-hundred-fathom
curve is only from fifteen to twenty miles.

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TOPOGRAPHY OF THE EASTERN COAST. 103

landscape of the districts we have described, we cannot fail to
observe how strikingly it differs from terrestrial landscapes.
They present no proper parallel to the immense stretches of
hundreds of miles of gently sloping surfaces, such as form the
deepest part of the basin of the Gulf of Mexico, and of the
Eastern Caribbean, and the similar expanse of bottom which
extends along the whole Atlantic coast of the United States.
Aerial denudation is so powerful a factor that the least differ-
ence in the hardness of the material of adjoining tracts is

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Fig. 60. —Gulf of Maine.

sufficient to effect very striking changes in level. These find
their ultimate expression, in connection with the geological
structure, in such characteristic regions as the cafions of the
far West, the Mauvaises Terres, the summits of the Rocky
Mountains and of the Sierra Nevada, the Appalachian sys-
tem, the prairies of the West and the system of the Great
Lakes, the hydrographic basins of the Mississippi and of the

St. Lawrence.

104 THREE CRUISES OF THE “BLAKE.”

The effect of strong currents and tides, at moderate depths, is
well shown in the topography of the Gulf of Maine, as mapped
on the Coast Survey charts. (Fig. 60.) Here the tides are high,
the currents powerful, and the effect on the bottom in pro-
ducing ledges, banks, etc., is in striking contrast to the bottom
in the tideless sea of the Gulf of Mexico. But no influence of
this kind is at work at a great depth in the ocean. The action
of currents is probably not limited by depth, as we see in the
exceptional case of the Gulf Stream; but the action of the
winds and waves is felt at only very moderate depths; and it is
only in volcanic regions, like those of the West Indies and of
Japan, that soundings have revealed thus far any striking topo-_
graphical features. The very absence of modifying and dis-
turbing conditions, such as chemical and aerial denudation, tends
to keep the original features due to submarine disturbances of
the earth’s crust more or less intact; and it is to the absence
of those conditions that we undoubtedly owe the existence of
such gigantic plateaux as the Yucatan Bank, and the great
Florida Bank, with its eastern extension of the Bahama Bank,
which reaches out till it nearly meets the comparatively nar-
row South American bank, that extends from the mainland to
Sombrero.

What can be more impressive than the stupendous slope of
over twelve thousand feet that forms the eastern edge of the
Bahama Bank, stretching from the Great Abaco nearly unbro-
ken as far as the Virgin Islands, with high passes between Porto
Rico and San Domingo, and a deep caiion between San Do-
mingo and the southern end of the Bahama Bank? The north-
ern extremity of this cliff, over seven hundred miles long, forms
the edge of a huge triangular plateau, five hundred miles by
two hundred and fifty, scarcely rismg above the level of the sea,
and flanked on its western side by the high chains of Cuba. Its
eastern extremity falls into the edge of a sink, of a depth of over
four thousand fathoms, and culminates at a horizontal distance
of less than eighty miles in a summit on the island of Porto
Rico, no less than thirty thousand feet above the lowest point
of that depression. What can be more graceful than the com-
paratively narrow chain of the curve formed by the Windward

TOPOGRAPHY OF THE EASTERN COAST. 105

Islands, rismg from twelve to sixteen thousand feet above the
bottom of the Eastern Caribbean, with the many passes between
them, —the sieve through which the warm surface water of
a great part of the equatorial current is forced by the trade-
winds ?

We may imagine for a moment that we are taking a bird’s-eye
view of this whole district, and look down upon the compara-
tively level plains of the Atlantic to the eastward of the Barba-
dos. These plains rise from a depth of three thousand fathoms
to the hundred-fathom line in a distance varying from three
hundred and fifty to two hundred miles on the eastward of the
Windward Islands; the highest summits of these islands (five
thousand feet) are only separated by narrow passages, and thus
form a more or less continuous chain of voleanic peaks. On
the westward, toward the Caribbean, the slope is more rapid;
a depth of one thousand to fifteen hundred fathoms is reached
at a comparatively short distance to the leeward of the Lesser
Antilles. The chain is narrowest between Martinique and Do-
minica, widening gradually towards Grenada and Tobago to the
south, and somewhat faster towards the Virgin Islands, which
are separated from the Santa Cruz, Saba and Sombrero banks
by a deep basin opening into a narrow cation of about one
thousand fathoms, with a shallow connecting ridge between
Santa Cruz and Porto Rico.

The mountain chain, of which San Domingo, Porto Rico, and
the Virgin Islands form the summit, has a steep slope to the
north, dropping at the eastern extremity, at a distance of less
than one hundred miles, to a depth of three thousand fathoms.
The two-thousand-fathom line runs along the eastern edge of
the Bahama Bank, a distance of less than fifteen miles, and
forms a steep edge to that face of the bank, while the thousand-
fathom line cuts off a few isolated outside patches, and extend-
ing far to .the westward, beyond the Windward Passage, forms
the mouth of the funnel of the old Bahama Channel.

The southern slope of this part of the West India Islands
chain is fully as steep as the northern. At the western ex-
tremity of San Domingo, the southern line of mountains extends
- toward Jamaica, and that part of the chain is deflected to the

106 THREE CRUISES OF THE “ BLAKE.”

southward, having also a much gentler slope, and forming the
edge of the Pedro Rosalind Bank, the extension of the Hon-
flaeas Mosquito coast, which divides the Caribbean into an east-
ern and western basin. After passing the Pedro Rosalind
Bank, — the divide between the Western and Eastern Carib-
bean, — one comes into the valley of the Grand Cayman, the
eastern extremity of which is flanked on the one side by the
Blue Mountains of Jamaica, on the other by the coast range
of Southern Cuba, the highest summits of which rise fully
twenty-seven thousand feet above the deepest point of “ Bart-
lett Deep,” — the extension of the Cuban side of the valley
being formed by peaks, often rising to over twenty thousand feet
from the bottom of the valley. Compared to such panoramas
the finest views of the range of the Alps sink into insignifi-
cance; it is only when we can get a view of portions of the
Andes from the sea-coast, or such a panorama as one has from
Darjiling, facing the Kinchinjinga range, which towers fully
twenty-six flare feet above the level of the valley at its base,
that we get anything approximating to it in grandeur.

As it has been the practice with geographers to name the
highest peaks of our mountain chains after distinguished ex-
plarers, so it has become the custom of hydrographers to name
the deepest parts of the oceans after distinguished hydrogra-
phers. Sigsbee Deep in the Gulf of Meee Bartlett Deep
in the Western Caribbean, Thomson Deep and those of Nares,
the “Challenger,” Pourtalés, Patterson, Hilgard, and others,
have been named in connection with recent deep-sea hydro-
graphy.

The monotony, dreariness, oa desolation of the deeper parts
of this submarine scenery can scarcely be realized. The most
barren terrestrial districts must seem diversified when compared
with the vast expanse of ooze which covers the deeper parts of
the ocean, — a. monotony only relieved by the fall of the dead
carcasses of pelagic animals and plants, which slowly find their
way from the surface to the bottom, and supply the principal
food for the scanty fauna found living there.

Nearer to the continental masses we find the slopes mhab-
ited by a more abundant and more varied fauna, increasing m

TOPOGRAPHY OF THE EASTERN COAST. 107

variety and numbers according to the amount of food available.
But no matter how varied or how abundant life may be, the
general aspect of the slopes must be dreary in the extreme, and
can only be compared in character to those higher mountain
regions where we find occasional fields of wild-flowers and low
shrubs, or to those zones lymg beyond the limits of forests,
where vegetation is scanty and poor, and forms but a slight
covering to the earth’s surface.

It is true that along the continental slopes, where there is an
ample supply of food, we find animal life in great abundance,
and there are undoubtedly long stretches of bottom carpeted by
the most brilliantly colored animals, packed quite as closely as
they are on banks in shallower waters, or near low-water mark.
But the scene is much less varied than on land; the absence
of plants in deep water makes great diversity of scenery impos-
sible. The place of luxuriant forests with the accompanying
underbrush and their inhabitants is only indifferently supplied
by large anthozoa and huge cuttle-fishes, or nearer in shore,
within moderate depths, a sea-weed and the pelagic forests of
giant kelp.

It requires but little imagination to notice the contrasts, as we
pass from the shallow littoral regions of the sea, — full of sun-
light and movement, and teeming with animal and vegetable
life, —into the dimly lighted, but richly populated continental
zone; and further to imagine the gradual decrease of the conti-
nental fauna, as it fades into the calm, cold, dark, and nearly
deserted abyssal regions of the oceanic floors at a distance from
the continents. It is like going from the luxuriant vegetation
of the tropical shore line — the region of palms, bananas, and
mango — into the cooler zone of oaks and pines, until we pass
out into the higher levels, with their stunted vegetation and
scanty fauna, and finally into the colder climate of the bleak
regions of perpetual snow.

"The soundings thus far taken by the “ Bulldog ” and other
vessels to ascertain the general topography of the North Atlan-
tic (Fig. 61), the extensive lines of soundings across the North
Pacific by the “Tuscarora,” the “Challenger,” and the “ Ga-
zelle,” show that the topography of the ocean basins is far less

108 THREE CRUISES OF THE ‘“ BLAKE.”

varied than that of continental areas. As a general rule we
find that the continental masses form platforms sinking quite
rapidly into the adjoming oceanic basins. The hundged
fathom line may extend far out to sea in some cases, as, for
instance, in the northwestern extremity of France, where it unites
Great Britam and France. On the east coast of the United
States an extensive plateau — the continuation, in other words,
of the continent below the surface — follows the hundred-fathom
line along our southern coast to the extremity of George’s
Bank, expanding again farther north, off the coasts of Nova
Scotia and of Newfoundland, so as to include Sable Island Bank
and the Great Banks of Newfoundland within the true conti-
nental line. In the case of the West India Islands, this line
discloses a connection between adjoining islands which the mere
study of the land map would fail to show. But the hundred-
fathom line is simply the edge of the continental plateau along
which the detritus brought from the continents by its rivers is
deposited. Upon its slope the fauna characteristic of any
region extends into deep water, gradually becoming modified
in its character by the temperature of the region into which it
finds its way. Beyond this hundred-fathom line there is usually
a very rapid descent into deep water. This line may indeed be
considered as the true continental outline, the edge of the shelf
which forms the continuation of the continental masses, below
the surface and beyond those shore lines which we are accus-
tomed to consider as the true boundary between land and water.

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RELATIONS OF THE AMERICAN AND WEST INDIAN FAUNA AND
FLORA.

A GREAT number of animals and plants date back to a time
anterior to the present configuration of land and sea. In cer-
tain regions we are therefore justified in looking for traces of
ancient terrestrial or oceanic connections to explain the presence
of identical types at isolated points.*

The explorations of the “Blake,” though primarily turned
toward the investigation of the ocean floor, had an incidental
bearing also upon these and similar problems. The work of .
the “ Blake” has added much to our knowledge of the former
connection between South America and the West India Islands,
and has taught us something also of the agencies which have
helped to determine their peculiar fauna and flora. Indeed,
hydrographic researches have given us the only acceptable
theory of the mode in which many oceanic islands have received
their present fauna and flora.

According to Cleve,” the oldest fossiliferous rocks of the West
Indies belong to the cretaceous, and were probably deposited in
a time of powerful volcanic action. Upon the highly disturbed
and metamorphosed cretaceous rocks are found almost hori-
zontal and undisturbed miocene beds. The eocene beds are
also to a certain extent metamorphosed, while the miocene
period must have been a period of long volcanic calm. The
position of the most recent pliocene and postpliocene beds seems
to indicate that some of the volcanoes now active in the West
Indies date back to the pliocene period, others to the postpli-
ocene.

1 See Wallace’s “ Geographical Distri- 2 Kongl. Svensk. Vetensk. Akad.
bution of Animals,’’ and his “Island Handl. Bdt. 9, No. 12. 1871.
Life.”

110 THREE CRUISES OF THE “ BLAKE.”

The islands to the north of Guadeloupe form two parallel
chains, the western consisting of Saba, St. Eustatius, St. Kitts,
Nevis, Redonda, and Montserrat, all of which are volcanoes of
postpliocene date; while to the eastward is a chain of volcanoes
of tertiary age,— Sombrero, Anguilla, St. Martin, St. Barthe-
lemy, Barbuda, and Antigua. At Guadeloupe the recent islands
are directly united with the volcanic chain, and the still more
modern limestones are found on its western shores.

The miocene rocks of the greater West India Islands* have
been, as far as observed, but little disturbed. The cretaceous
beds, however, are found greatly modified.

The geological history of Florida is in striking contrast with
that of the greater and lesser West India Islands. The share
which modern limestones have had m building up a portion of
the peninsula during the most recent geological period has been
described in the chapter on the Florida Reefs. From the obser-
vations of Conrad, of E. A. Smith, and of E. Hilgard, it would
appear, as is stated by Smith,’ that up to the end of the eocene,
the great Florida limestone plateau was still submerged; that
during the time of the upper eocene, Florida was elevated
nearly to its present height. The axis of elevation did not
coincide with the present dividing ridge of the penisula, but
occupied probably a position to the westward. From the sub-
sequent deposition of sand, clay, and pebbles over Florida and
parts of the adjacent States, they must have been slightly sub-
merged again, and subsequently elevated (during the Champlain
period) to about their present configuration.

In attempting to reconstruct, from the soundings,’ the state

1 The most striking feature of the
West India Islands as a whole is the axis
of eruptive rocks, flanked by sedimentary
formations and terraces of elevated coral
reefs and recent limestones. On the
northern coast of Cuba the mode of for-
mation of the harbors within the fringing
reef, inside of the great outside barrier
reef, seems to prove that the rivers cut
their way out as fast as the land was ele-
vated and the successive terraces formed.
It must be remembered that coral reefs
have no such thickness as is seen on the
terraces, but that the greater part of this

limestone was probably deposited much
as was the limestone that forms the back-
bone of the Yucatan and Florida penin-
sulas. This limestone was subsequently
capped by reef-building corals during
periods of rest, followed by the elevations
to which the successive terraces are due.

2 Smith, E. A. American Journal of
Science, April, 1881, p. 292.

3 See the accompanying maps (Figs.
57, 58), for which I am indebted to the
Hon. Carlile P. Patterson, Superintendent
U.S. Coast Survey.

AMERICAN AND WEST INDIAN FAUNA AND FLORA. Ett

of things existing along the Lesser and Greater Antilles in a
former period, we are at once struck by the fact that the Virgin
Islands are the outcropping of an extensive bank. The great-
est depth between these islands is less than forty fathoms, a
depth which is found on the bank to the east of Porto Rico, —
the hundred-fathom line forming, in fact, the outline of a large
island, which would include the whole of the Virgin Islands,
the whole of Porto Rico, and extend some way into the Mona
Passage. The hundred-fathom line similarly forms a large
plateau, uniting Anguilla, St. Martin, and St. Barthelemy. It
also unites, as separate banks, Barbuda and Antigua, forms the
Saba Bank, and unites St. Eustatius, St. Christopher, and Nevis.
It unites Redonda with Montserrat. It forms an elongated
plateau, from Bequia to the southwest of Grenada, and runs
more or less parallel to the South American coast from Mar-
garita Island, leaving a comparatively narrow channel between
it and the hundred-fathom line south of Grenada, so as to
enclose Trinidad and Tobago within its limits, and runs off to
the southeast in a direction also about parallel to the shore
line. At the western end of the Caribbean Sea the hundred-
fathom line forms a gigantic bank off the Mosquito coast,
extending over one third the distance from the mainland to
the island of Jamaica. The Rosalind, Pedro, and a few other
smaller banks, limited by the same line, denote the position of
more or less important islands which may have once existed
between the Mosquito coast and Jamaica. On examining the
five-hundred-fathom line, we thus find that Jamaica is only the
northern spit of a gigantic promontory, which perhaps once
stretched toward Hayti from the mainland, reaching from Costa
Rica to the northern part of the Mosquito coast. There is left
but a comparatively narrow passage between this promontory
and the five-hundred-fathom line which encircles Hayti, Porto
Rico, and the Virgin Islands, in one gigantic island.

The passage between Cuba and Jamaica has a depth of over
three thousand fathoms, and that between Hayti and Cuba is
not less than eight hundred and seventy-three fathoms in depth.
The five - hundred-fathom line connects the bank uniting
Anguilla to St. Barthelemy, the Saba Bank, the one which joins

2 THREE CRUISES OF THE “ BLAKE.”

St. Eustatius to Nevis, and Barbuda to Antigua, and thence
extends south so as to include Guadeloupe, Marie-Galante, and
Dominica.' The five-hundred-fathom line thus forms one
bank of the, northern islands, and leaves but a narrow channel
_ between it and the eastern end of the five-hundred-fathom line
running round Sauta Cruz. Santa Cruz is separated from St.
Thomas by a channel of forty miles, which thus forms a basin
with a maximum depth of over twenty-four hundred fathoms.
It is united with Porto Rico by a submarine ridge with a depth
of about nine hundred fathoms. This plainly shows its con-
nection with the northern islands of the Caribbean group,
rather than with St. Thomas; yet, as is also well shown by the
geographical relations of its mollusca, their affinities are rather
with Porto Rico and that group of islands than with the Carib-
bean Islands. This may be explained by the existence of an
easterly current setting along the shore, or of a former land
connection with Porto Rico, still indicated by a ridge discovered
by the “ Albatross,” running from Santa Cruz to Porto Rico,
having a maximum depth of nine hundred fathoms. The five-
hundred-fathom line again unites, in one huge spit extending
northerly from the mouth of the Orinoco, all the islands to the
south of Martinique, leaving Barbados to the east, and a narrow
passage between Martinique and the islands of Dominica and
St. Lucia. ?

At the time of this connection, if it existed, the Caribbean
Sea was connected with the Atlantic only by a narrow passage
of a few miles in width between St. Lucia and Martinique, by
one somewhat wider and slightly deeper between Martinique
and Dominica, by another between Sombrero and the Virgin
Islands, and by a comparatively narrow passage between Jamaica
and Hayti. The hundred-fathom line connects the Bahamas
with the north-eastern end of Cuba; the five-hundred-fathom
line unites them not only with Cuba, but also with Florida.
The Caribbean Sea, therefore, must have been a gulf of the
Pacific, or have been connected with it by wide passages, of
which we find the traces in the tertiary and cretaceous deposits

1 Between Martinique and Dominica a peak in mid-channel was found within
eighty-five fathoms of the surface.

AMERICAN AND WEST INDIAN FAUNA AND FLORA. 113

of the Isthmus of Darien, of Panama, and of Nicaragua. Cen-
tral America and northern South America at that time must
have been a series of large islands, with passages leading
between them from the Pacific into the Caribbean.*

It is further interesting to speculate on what must have
become of the equatorial current, or rather of the current pro-
duced by the northeast trades. The water banking up against
the two large islands, then forming the Caribbean Islands,
must, of course, have been deflected north, have swept round
the northern shores of the Virgin Islands, Porto Rico, and
Hayti, and poured into the western basin of the Caribbean
Sea, through the passage between Hayti and Cuba. This water
was forced into a sort of funnel, by the five-hundred-fathom
line, which constituted the southern line of the great Bahama
Island, and connected nearly the whole of the Bahamas with
Cuba, forming thus a barrier to the western flow of the equa-
torial current; this current must, therefore, for the greater
part, have been deflected north, and either swept in a north-
easterly direction, as the Gulf Stream now does, or round the
north end of the Bahamas across Florida, which did not then
exist, across the Gulf of Mexico, and into the Pacific over the
Isthmus of Tehuantepec.

While undoubtedly the soundings indicate clearly the nature
of the submarine topography, it by no means follows that this
ancient land connection did exist as has been sketched above.
At the time when the larger West India Islands were formed
and elevated above the level of the sea, they may have been
raised as one gigantic submarine plateau of irregular shape, in
which were included the Bahamas, Florida, Cuba, San Domingo,
Porto Rico, and the Virgin Islands. © Exactly what portions
rose above the level of the sea at that time it is difficult to
determine, and it may be that at that period the islands, while
larger perhaps than they are now, may still have been the same
in number, having since been reduced in size by denudation,
while the channels between them have been widened.

1 We should bear in mind that the India Islands existed, thus leaving a free

Windward Islands were probably raised access to the Pacific up to that time.
long after the range of the greater West

114 THREE CRUISES OF THE “ BLAKE.”

As is well known, Cuba, the Bahamas, Hayti, and Porto Rico,
instead of having, as we might naturally assume from their prox-
imity to Florida, a decided affinity in their fauna and flora with
that of the southern United States, show, on the contrary, unmis-
takable association with that of Mexico, Honduras, and Central
America; the Caribbean Islands indicate in part the same rela-
tionship, though the affinity to the Venezuelan and Brazilian
fauna and flora is‘much more marked. The most characteristic
feature of the West Indian fauna is the immense development
of the land mollusks; the birds are South American; and ter-
restrial mammals are almost wanting, with the excepticn of
three genera peculiar to the larger islands.

One of the most remarkable of the mammalian types of the
greater West India Islands is the insectivore Solenodon,’ be-
longing to a family of which representatives are known only
from Madagascar. The rodents are all members of groups
characteristic of South America. The agouti, which once ex-
tended to the large islands, is now said to be found mainly in
the Windward Islands. The islands of Trinidad, Tobago, and
the Leeward Islands, are all on the great continental plateau
of South America, detached parts of the mainland itself, and
have its characteristic fauna and flora.

In view of the short distances between the West India Islands
it is not astonishing that the birds should partake somewhat of
the character of North, Central, and South America. There
are a number of North American birds which spend the winter
on these islands, or migrate farther south. The fact that the
majority of them only visit Cuba and Jamaica may be explained
by the direction of the tradewinds, which would prevent them
from reaching Hayti, Porto Rico, or the more eastern Wind-
ward Islands. Many of the birds formerly found in some of
the smaller islands have become exterminated by the increase of
population and the clearing of the forests. It is most probable
that in these islands, so favored in their climate and their flora,

1 But as the insectivores are now dying 2 In the caves of Anguilla are found
out, we may consider this genus a rem- fossil mammals belonging to South Amer-
nant of a group formerly having a much ican types.
wider distribution.

AMERICAN AND WEST INDIAN FAUNA AND FLORA. 115

special conditions more or less favorable to certain genera would
be produced, and thus tend to the remarkable specialization of
many of the birds in individual islands. This, as suggested by
Wallace, would show that the islands were not peopled by
immigration from surrounding countries while in the condition
we now see them.

The reptiles show likewise a general relation to the Central
American and Mexican types. One of the most interesting is a
gigantic land tortoise, found at Porto Rico, differing only in
size from the land turtle still found on Trinidad and adjoining
parts of South America. It is closely allied to the gigantic
turtles of the Galapagos and Mascarene Islands, and to the
fossil land turtles, of which fragments have been described by
the late Professor Wyman. These were collected by Mr. A. A.
Julien at Sombrero, in the phosphate beds of the island.

The species of iguana characteristic of the small island of
Navassa and of Hayti presents a case of specialization very sim-
ilar to that of the Amblyrhynchus of the Galapagos, and of an
allied species occurring at the Fiji Islands. The aquatic habits
of these large saurians make a migration to a distant point quite
feasible.

It is from the study of the land shells, however, which have
been so carefully observed by Bland and others, that we may
get a better idea of the great specialization which has taken
place in the development of the molluscan fauna characteristic
of the different islands. If, as we may assume, the islands have
received their molluscan fauna from the adjoining mainland, we
might naturally expect that those islands which were more re-
cently connected with the mainland, or to which access, owing
to the direction of the winds and currents, was most easy, would
show a greater preponderance of continental forms than those
which have been longer separated from the main coast, or to
which the winds and currents do not lead so directly. In addi-
tidn, the more or less favorable physical features of the different
islands have undeniably had their influence in the increase of
the land shells.

The greater West India Islands, according to Bland, are nearly
equally rich in land shells. The eastern islands, Porto Rico and

116 THREE CRUISES OF THE “ BLAKE.”

the Virgin Islands, are somewhat poorer, and as we come to the
Windward Islands the West Indian types disappear and are re-
placed by continental forms. In the Bahamas we find no con-
tinental types, the species being most clearly allied to those of
Cuba, with which geologically and physically they are in closer
connection.

While the flora of Florida undoubtedly has many of the char-
acteristic features of that of the Southern States, it has also a
decided West Indian tinge. Its mangroves, limes, and _pal-
mettos connect it with the vegetation found on the other side
of the Straits of Florida, and along its southern extremity are
found West Indian, Mexican, and Central American birds,
which rarely find their way farther north than the Everglades.

Our imperfect knowledge of the geology of Central America
tends to show that South America must have remained isolated
from North America before the tertiary period; that during
palzozoic times it formed a huge archipelago, and that its con-
nection with North America was never a very close one. Hence
the migration during tertiary times of many of the American
forms has produced in the West Indies and the Central Amer-
ican districts a strange mixture of ancient and recent types.
Many of these are now extinct both in North and South America.
This want of close connection between the Americas has prob-
ably affected the fauna of South America much as it has that
of the West Indies, and produced conditions highly favorable to
the extraordinary development of specific forms, which charac-
terizes the fauna of tropical America beyond. all other faunal
districts.

The deep soundings (over three thousand fathoms) developed
by the “ Blake” south of Cuba, between that island and Yuca-
tan and Jamaica, do not lend much support to the theory of an
Antillean continent as mapped out by Wallace, nor is it prob-
able that this continent had a much greater extension in former
times than now, judging from the depths found on both sides of
the West India Islands. This would all tend to prove the want
of close connection between the West India Islands and the ad-
joining continent. It leads us to look, for the origin of the
fauna and flora of those islands, to causes similar to those which

AMERICAN AND WEST INDIAN FAUNA AND FLORA. 117

have acted upon oceanic islands. The proximity of these islands
to a great continent has, however, intensified the efficiency of
these causes.

Among the oceanic islands which show most clearly the effects
of ocean currents and of winds on the distribution both of ma-
rine and of terrestrial animals and plants, the Bermudas are
the most interesting. Situated in the very track of the Gulf
Stream, we readily trace to their origin a host of littoral marine
animals and many plants, known to us from the investigations
of the older naturalists, in the West Indies and the northern
shores of South America; while the more recent investigations
have shown the community of origin of a number of rarer Ber-
mudan types with forms found in the deeper waters of the Ca-
ribbean Sea, the young of which are carried northward during
their pelagic embryonic stages, with the seeds of many of the
plants which have become acclimated in the Bermudas.

The fact that the Bermudas are of comparatively recent ori-
gin shows how varied the fauna and flora of a group may
become when placed in the path of a current or of prevailing
winds, and how comparatively little time is required for the
acquisition of faunistic characters which may closely link the
group to distant shores. Were the conditions of winds and
‘currents changed, we might be tempted to explain these charac-
ters upon the theory of former land connections, which perhaps
never existed.

The vegetation of the Bermudas is thoroughly Floridian and
West Indian, consisting of palmettos, mangroves, junipers, limes,
ete.; and we can easily see how the seeds or shoots of many
plants can have been brought by the Gulf Stream and settled on
the low shores of the islands when they once rose above the level
of the sea. There are no mammals except the rats and mice
imported with vessels. The birds are not numerous; they are
common North American species, of which only a few breed
on the island, while there are other annual visitants. The
only land reptile known there is closely allied to, if not iden-
tical with, a species of skink inhabiting the Carolinas, and the
marine fauna and flora are West Indian. The large tuctles of
the coast of Florida, the fishes, mollusks, crustacea, polyps, and

118 THREE CRUISES OF THE “ BLAKE.”

echinoderms, all indicate the source from which they have been
derived.

It is interesting in connection with the currents to note that,
as far as we know, the Bermudas were never inhabited by Caribs
or North American Indians, their great distance from land and
the facility with which boats, carried northward by the Gulf
Stream, must have drifted towards the mainland rendering such
an immigration quite improbable.

In this special case it is not difficult to go back to the time
(and that in a comparatively recent geological period) when the
Gulf Stream did not run its present course, and when probably
also the Bermudas, if they existed at all, were merely the nu-
cleus on which the subsequently formed atoll has been raised.
We may safely assert that their existence as a coral reef dates
from the time of the closing of the passages through which the
equatorial currents flowed across the Isthmus of Tehuantepec
and the other passes of the Isthmus of Panama. The coral reef
of the Bermudas is probably, therefore, of very much more re-
cent origin than the reefs on the windward sides of the West
India Islands, the southern coast of Cuba, the Mosquito coast,
the Yucatan Bank, the north shore of Cuba, the Florida reefs,
and the Bahamas and their connecting islands. It is to these
older reefs that the more recent Bermuda reefs owe their ori-
gin. The embryos of the corals were floated northward by the
Gulf Stream, and finding suitable conditions of temperature, as
well as of depth, due to this very current, became attached, and
soon formed a gigantic atoll rivalling in size some of the more
prominent atolls of the Pacific. Thus we readily account for
the presence of coral reefs off the Atlantic coast of North
America, in latitudes which are rather more northerly than the
usual extension of coral reefs in other seas. The same causes
which have thus scattered as far north as the Bermudas the
fauna and flora of the West Indies, and of some parts of tro-
pical South America, have also been influential in extending
some of these types to their more distant habitats, such as the
Azores, the Canary Islands, Cape Verde Islands, Madeira, the
west coast of tropical Africa, as well as to other points on the
east coast of North America, where a few of the same animals
and plants occur.

AMERICAN AND WEST INDIAN FAUNA AND FLORA. 119

On the Atlantic shores of the United States we have on a
more extended scale a repetition of the phenomenon first ob-
served in the Ferde Channel by the “ Lightning,” of the dif-
ference produced on the character of the fauna by a change of
temperature. The “warm and the cold areas,” as they have
been termed there, find their parallel on our coast as seen in
the extension of the West Indian fauna along the line of the
continental slope bathed by the Gulf Stream, flanked on either
side by the arctic fauna living in the colder water of the bottom
of the Gulf Stream on the east, and in the cold arctic waters
which bathe the continental plateau within the sixty-fathom line
on the western edge of the area occupied by this more tropical
fauna. This shows in a remarkable way the powerful influence
exerted by the action of the heated water of the Gulf Stream
in extending to the northward, along the bottom, the range of
the fauna of a more southern latitude. This action is not
limited to the bottom, for on the surface also the character-
istic pelagic fauna is carried northward. The larve of many
of the Caribbean and Mexican animals which swim, find an
abode as far north as the conditions of the water and the
bottom will allow ; the adults may also, little by little, creep up
northwards.

This northern extension of the southern fauna has been care-
fully studied by the United States Fish Commission along the
southern coast of New England; their dredgings have proved
the existence in this region of many animals known before only
from Florida, and of others which were previously considered
as characteristic tropical types. In fact, we have a northern ex-
tension, off the southern coast of New England, of the West
Indian and Gulf Stream fauna. The warm belt extending
from sixty-five to one hundred and twenty fathoms has an
equable temperature during the whole year, due to the action of
the Gulf Stream, while on the inshore plateau arctic animals
are found identical with those occurring at similar depths
north of Cape Cod, which flourish only in a variable but cold
temperature. Below the warm belt the temperature is uni-
formly cold, and passes into that of the general abyssal region
beyond it. The warm belt is but the northern extension of

120 THREE CRUISES OF THE “ BLAKE.”

the warm waters of the Gulf Stream. The belt is quite
narrow at Cape Hatteras, owing to the steepness of the conti-
nental slope at that point, and gradually increases in width
and depth as we go south along the trough of the Gulf
Stream, its greatest width being off the Carolina and Georgia
coasts. The marked influence of the currents on the fauna
of the district through which they flow is well illustrated by
the wholesale destruction of the tile fish and of several species
of crustacea during the winter of 1881-82, as noted by Pro-
fessor Verrill, of the United States Fish Commission. This
was perhaps due, as he suggests, to the fact that a severe
storm forced the cold water of the shallow shore-belt out to sea,
and suddenly lowered the temperature of the narrow belt of
outlying warm water. This belt covers an area which is prob-
ably the northern limit of many species collected in abundance
during previous seasons.

We were greatly surprised at the meagreness of the fauna on
the lines off Charleston and in the Gulf Stream. Owing partly
to the very gradual slope of the continent towards deep water,
and partly to the strong current of the Gulf Stream, which sweeps
everything off the bottom along its course, there is but little
food for the deep-water animals, and it was only along the edges
of the Gulf Stream where mud and silt had accumulated that
we made satisfactory hauls on our southern lines. What was
obtained seemed to be a scanty northern extension of the fauna
of the Caribbean Sea and of the Gulf of Mexico occurring
between the hundred and the three-hundred-and-fifty fathom
lines. It was not until we trawled on the steep slope of the
Gulf Stream plateau south of Cape Hatteras, where the bottom
was fine mud and globigerina ooze, that we made a rich harvest
again, in striking contrast to the poor hauls along the well-
swept rocky or hard bottom of the Gulf Stream to the south-_
ward. Although pteropods were very common at the surface
all the way from Charleston to Cape Hatteras, they were only
rarely brought up dead from the bottom; but when the steep
slope south of Hatteras was reached, they again assumed a
prominent part in the composition of the bottom mud.

The effect of currents on the distribution of birds has been

’

AMERICAN AND WEST INDIAN FAUNA AND FLORA. 12]

admirably traced by Alph. Miine-Edwards, in an interesting
memoir on the fauna of the antarctic regions. He calls at-
tention to the effect upon the distribution of penguins of
icebergs carried by currents. These birds are excellent swim- |
mers, and fond of resting on floating ice; they are prepared
for long voyages, and thus may have been transplanted from a
single centre to the varied localities where they are now found.
In their search for food they must naturally migrate to great
distances during the long antarctic winters, when they cannot
carry on their usual fishing avocations. The path of the ice-
bergs, as dependent on currents, may even enable us to trace
the original penguin home. Milne-Edwards concludes that the
inhospitable country of Victoria was the origin of the most char-
acteristic animals of the antarctic region.

It will be quite possible, when sufficient material has been col-
lected, to map out the course of the pelagic fauna ; and from its
bottom distribution much light will be thrown on the course of
the currents. Thus the existence at Newport of Agalma, Clio,
and Pneumodermon, — inhabitants of arctic seas, Labrador,
Maine, and northern New England, —is direct evidence that
the cold arctic current finds its way round Cape Cod to the
opening of Narragansett Bay. In the same way we may trace
the northern course of the Gulf Stream by the presence of Sar-
gassum, Porpita, Leptocephali, and southern pteropods, etc.,
which are carried each year to the coast of southern New Eng-
land. The range of southern globigerine and pteropods will
fix the eastern limits of the Gulf Stream, as northern types
determine those of the cold current along the east coast of the
United States.

It is most hazardous, especially on insufficient data, to spec-
ulate upon former land connections; and yet, in many cases,
the presence of identical genera of mammals seems to leave us
no alternative. When, however, there are powerful currents
running through the narrow channels that separate adjoining
islands, or when these currents skirt the shores of island ranges
and of neighboring continents, it is not always necessary to
assume such an extinct continental connection. The careful
study of the distribution of mammals on the islands of the

122 THREE CRUISES OF THE “ BLAKE.”

Pacific, and of their fossil remains, if any are to be found, taken
in connection with the bathymetric knowledge we have lately
acquired, would go far towards solving these problems. The
flora alone can hardly give us the necessary facts.

The fossil marine fauna, while it can do something to help us
to reconstruct the probable route of the oceanic currents, gives
us no clue to land connections. Neither does the distribution
of the birds, nor that of the reptiles or of the land shells, if we
are to judge by the case of the West Indies, Galapagos, and
Bermudas. The simplest assumption we can make for these
islands is that the drift carried by the existing currents for a
long period of time is amply sufficient to account for the pre-
sence of their few reptiles, mollusks, and even their mammals,
and for the distribution of their flora, without the existence at
any time of a direct land connection.’

In the case of New Zealand — an island for a long period of
time disconnected from continental masses, except perhaps by
its northern extension toward Australia— we account for the
South American elements of its fauna by the action of the cur-
rents. As yet we know positively of no South American mam-
mal element, and the birds have undoubtedly, as has been
concluded by Captain Hutton, been derived from the north.
The same would hold good of the antarctic elements. This
seems a more natural explanation than the attempts made to
cite plateaux of not less than two thousand fathoms in depth as
proof of a former continental extension, when, for aught we
know, these plateaux may be forming and increasing at the
present day. No better example of the fallacy of such reason-
ing can be given than the phenomena of the growth of the
great limestone plateaux of Yucatan and Florida, which we

1 The changes constantly going on over
the continental shelf illustrate admira-
bly what is meant by a former land con-
nection of continental islands. In a
letter to Professor Benjamin Peirce,
Superintendent of the United States Coast
Survey, Professor Agassiz thus referred,
in 1867, to the shoals and islands lying
to the eastward and southward of Cape
Cod: “The drift of the coast of New

England formerly extended many miles
beyond the present shores, and is still
slowly. washed away by the action of
tides, winds, and currents. This sheet of
drift once extended in unbroken conti-
nuity from Cape Ann to Cape Cod, and
farther south; ... it is constantly di-
minishing, and, in centuries to come, the
whole peninsula of Cape Cod may disap-
pear.” (See Fig. 60.)

AMERICAN AND WEST INDIAN FAUNA AND FLORA. 123

know to be even now growing and increasing in thickness. Yet
they have been mentioned by some writers as examples of a
former continental extension ; and archzologists have attempted
to find, on the Dolphin and Challenger ridges, the bridges, at
depths of nearly two thousand fathoms, of the former land con-
nections of Africa and Western Europe with Central and South
America. There seems to be no necessity for these supposed
Pacific and Atlantic continents, so long as we can explain by
more simple causes the distribution of the present fauna and
flora.

The marked difference between the fauna of the Red Sea and
of the Mediterranean’ clearly points to a distinct separation
between these seas — greater perhaps than that once existing
between the Bay of Panama and the Caribbean — previous to
the time when land masses united Malta and Sicily with Africa ;
when Crete and Rhodes were united with Asia Minor, and there
was no Eastern Mediterranean to reach the shores of Egypt and
Palestine. All this shows a comparatively recent connection
of Mediterranean with Atlantic waters, fully supported by the
similarity, if not identity, of their marine fauna. We certainly
find in the Eastern Mediterranean proof of the great changes
which have taken place in the distribution of land and water
during the tertiary and diluvial period. These changes, while
they may in part be traced to such agencies as denudation both
aerial and chemical, must also be referred to terrestrial changes,
—to such volcanic or telluric agencies as slowly raise or lower
definite tracts of country, when acting undisturbed through
long periods of time. We have in the Eastern Mediterranean
a district subject to volcanic action, the force of which is
marked by the number of active and extinct volcanoes which
have produced in the past and are still producing very marked
changes. The zodgeographical conditions existing between the
northern and southern shores of the Mediterranean do not of

1 The rapidity with which even slight way to the Mediterranean, much to the
water communications affect the distribu- detriment of the fisheries ; and a species
tion of species is admirably shown in the of sea-urchin, quite common in the Red
case of the Suez Canal. Since its com- Sea, has lately been found in the Medi-

pletion, several species of sharks charac- terranean, near Port Said.
teristic of the Red Sea have found their

124 THREE CRUISES OF THE “ BLAKE.”

themselves indicate a former land connection any more than the
presence of the remains of African mammals at Pikermi indi-
cates a direct communication between Greece and Africa. At
the time of their greatest development, with a geographical dis-
tribution extending over Spain, Germany, Asia Minor, Persia,
_and India, the connections between the lands bordering on the

Mediterranean may not have been materially different from
what they now are.

VI.
THE PERMANENCE OF CONTINENTS AND OF OCEANIC BASINS.

THE outlines of our continents as they are defined on geo-
graphical maps give us but an imperfect idea of their true
shape. An examination of the relief of the globe as developed
by soundings leads to very different conclusions concerning the
connection of continents and of islands from those obtained by
geographical data. The soundings have developed the great
terrestrial folds, of which the continents are merely such por-
tions as are elevated above the level of the sea.t. The latter
have been modified by the action of atmospheric agencies ; their
height has been reduced; and the material thus worked over
from the earliest times has built up the sedimentary formations
which have little by little been deposited on the flanks of these
ancient continental masses, extending their outlines so as to
cover larger and larger portions of the original folds in succes-
sive geological periods.

As the early soundings showed the existence of a former con-
nection between Great Britain and the Continent, so more recent
explorations have enabled us to understand the true relation of
Tasmania and New Zealand to the Australian continent, with
its adjacent archipelago, as it probably existed in the early part
of the mesozoic period. Similarly, the soundings give us some
idea of the relations of the East Indian Archipelago to the
Asiatic continent. We have a very different conception of the
relations of the insular groups of the Pacific to each other and
to the tertiary Pacific continent, so often called upon to explain
difficulties in the geographical distribution of the fauna and
flora of these islands. We may now speculate with some de-
gree of certainty on the former connections of Madagascar and

1 Such folds are probably the Challenger and Dolphin ridges of the Atlantic.

126 THREE CRUISES OF THE “ BLAKE.”

of the Mascarene Islands with Africa. The history of the
lesser and greater West India Islands and of the Bahamas as-
sumes a new interest from the explorations of the “ Blake.”
Even the fate of Lemuria and of Atlantis can now be settled
by the deep-sea soundings of the last ten years. These ex-
plorations mark a striking contrast between the continental
masses, or areas of elevation, and the oceanic basins, or areas
of depression,’ both of which must always have held to each
other the same approximate general relation and proportion.
In other words, the continental masses and the oceanic basins,
as at present defined, must be of great antiquity. The original
continental masses have formed a nucleus, around the old out-
lines of which the principal changes in configuration have taken
place.

The main outlines of the nucleus are fairly indicated by what
has been called the continental shelf. Its limits in a general
way are about the hundred-fathom line. Between this and the
shore, and on the sea face of the continental slope beyond it,
accumulations of materials, brought by the tides, currents, rivers,
and winds, are constantly deposited, thus modifying the shore
shelf. Within this area, or in close proximity to it, are found
deposits strictly characteristic of the present epoch, and corre-
sponding to similar deposits which must have been laid down
along more ancient continental shelves from the earliest geolog-
ical periods; the later deposits being in direct succession to the
more ancient ones. The amount of material which still remains
to be carried out to sea beyond the continental shelf, for the
farther extension of our continent, is comparatively small. Our
continental lands need to be twenty times their present height
before they could furnish waste enough to fill the present oceanic
basins. Their present elevation could hardly serve to raise the
ocean depths by more than one hundred fathoms.

That there have been important oscillations in the level of
large tracts of the earth from the earliest geological times, espe-

1 Kriimmel computes that the conti- (Kriimmel, O. Versuch einer verglei-
nental masses (their mean elevation above chenden Morphologie der Meeresriiume,
the level of the sea) and the oceanic p.108. Leipzig, 1879.)
masses are very nearly in equilibrium.

PERMANENCE OF CONTINENTS AND OCEANIC BASINS. 127

cially during the cainozoic period, is well known; but even if
the surface of the oceans were to sink from one thousand to
eighteen hundred fathoms, it would still be possible to recognize
in the-rough the present outline of our continents. Hence it
would seem as if that outline were intimately connected with
their earliest appearance and the subsequent evolution of the
continent, and that these masses are not merely due to acciden-
tal denudation.

The view of the great age of our continents and oceanic
basins was probably first suggested by Guyot; it was mdepen-
dently taken up by Dana, and Agassiz was perhaps the first to
show that the results of the earlier deep-sea dredging expedi-
tions added materially to the correctness of this view. Subse-
quently Thomson, Geikie, and Carpenter elaborated this theory,
which of late has gained ground among geologists, and has
found its most recent advocate in Wallace.

The geological structure of the different islands of the world
enables us to judge whether they are mere volcanic peaks, the
highest points of districts subject to cataclysmic local elevations,
or whether they are parts of larger masses of land first built up
by sedimentary deposits,’ and gradually reduced by denudation
to their present size, — the remains, in fact, of great submarine
banks, indicating in a certain measure the former outlines of
the land. The extent of this denudation has been calculated
in some cases; and so powerful is its agency, that, if carried on
during long periods of time, it may transform oceanic regions
into continental masses, and the reverse. This may have been
the case in the earliest periods of the formation of the earth’s
crust, when the precipitation was much greater than now; but
we have as yet no evidence of any such transposition of conti-
nental masses and of oceanic basins since the mesozoic period.
If such pre-archzan continents existed, they, like the continents
from which the materials for the mesozoic and tertiary deposits
were derived, have left no traces.

1 The careful examination of St. Paul’s having, as shown by Geikie, nothing what-
rocks by the Abbé Renard, for instance, ever to do with the remains of a former
: clearly proves this island to be of volcanic continent, the long lost Atlantis.
- origin, like many other oceanic islands,

128 THREE CRUISES OF THE “ BLAKE.”

We may go back to the time when all the water of our oceans,
rivers, and lakes existed only as vapor suspended round the
heated earth, — forming, as has been said by Mallet, an atmos-
phere of steam, producing greater extremes of light and heat
than are known to-day, enormous differences between summer
and winter, and very striking contrasts between the polar and
equatorial regions. When water was first deposited, on the
cooling of the crust, ice may have existed at the poles, while the
equatorial-seas may still have been too hot to sustain life. Such
contrasts in temperature must have occasioned oceanic currents
unparalleled in the present state of the globe. Consequently
the disintegration of the rocks forming the crust of the globe,
subjected as they were to the torrential rains, the powerful cur-
rents, and the extreme solvent powers of water at the high tem-
peratures then existing, must have been far greater and more
rapid than now. It is not surprising, therefore, if we find the
earlier stratified rocks deposited through agencies similar to
those now acting, and yet formed under conditions having no
exact parallel in our times.

The material brought down to the sea from the basin of the
Mississippi has been accurately measured by Humphreys and
Abbott, and their report states that it would require five millions
of years, at the present rate of denudation, to carry off a thick-
ness of one hundred feet. As far as we can judge from the
deposits off the mouth of the Mississippi, the mud brought down,
while it has made an extensive submarine deposit, projecting far
beyond the general continental line, has not been detected be-
yond a distance of about one hundred miles from the passes.
To this must be added the matter held in solution by rain-water,
the amount of which depends principally upon the nature of the
rocks forming a hydrographic basin. Frankland has calculated
that for every 100,000 tons of water there were 39 tons of car-
bonate of lime and magnesia, and 1,018 tons of sulphates; so
that, according to Reade, it would take twenty-five millions
of years to accumulate the sulphates now in the sea, and only
480,000 years to renew the carbonates ; but that it would take
about two hundred millions of years to replace the existing sup-
ply of chlorides. The carbonates have, of course, been con-

GEOLOGICAL MAP
OF THE
EASTERN UNITED STATES,

AFTER
C.H. HITCHCOCK.

<
=
Z
oO
(oo)
bh]
io)
&

C.H. HITCHCOCK.

ie)
(ae)
CZ

Quaternary

Tertiary

Cretaceous

Triassic

Carboniferous

MA

Devonian

Silurian

=
eS

Cambrian.

Huronian

(ey

Laurentian

PERMANENCE OF CONTINENTS AND OCEANIC BASINS. 129

-stantly used up by the formation of the immense beds of lime-
stone which have been deposited from the mesozoic to the pre-
sent time.

Professor Dittmar, in a lecture delivered before the Glasgow
Philosophical Society, formed an estimate based upon data
given by Boguslawski regarding the solids introduced into the
ocean by rivers ; from which he calculated that it would require
nearly twelve hundred years to increase the percentage of car-
bonate of lime in the ocean by one per cent of its present value,
supposing no part of what is added were precipitated by animal
life.

We know that a portion of the Spitzbergen coast is rising,
and that some points of the Scandinavian peninsula must have
been raised one hundred and fifty metres. Holland, on the
contrary, shows a sinking of its shores. Darwin’s observations
on the elevation of parts of the west coast of South America
are well known. I have myself visited. the principal localities
about Coquimbo, and have found evidence that the maximum
elevation probably took place near the latitude of Pisagua,
gradually diminishing farther south. We may perhaps regard
as remnants of a sea bottom the sloping plains extending from
the nitrate beds of Pisagua to the southern parts of Chih, par-
allel with the Coast Range, until it passes into the Chiloe Archi-
pelago. The terraces all along the coast, such as have been
noted by Darwin, plainly show the extent of the elevation, or
may have been a part of the movement resulting in the separa-
tion of the Gulf of Mexico and of the Caribbean Sea from
the Pacific.

Let us examine a geological map of North America. We
see that, during the earliest geological times, (Fig. 62) the
North American continent was’ indicated in its broad outlines
by a great telluric fold, —an immense V-shaped archzan con-
tinent, situated mainly in British North America, one arm
reaching northeastward to Labrador, and the other northwest-
ward from Lake Superior. In addition to this continental nu-
cleus, smaller mountain ranges — the Rocky Mountains and
Appalachian and other isolated areas — existed, indicating the
presence of a submarine American plateau, upon which the

130 THREE CRUISES OF THE “* BLAKE.”

palzeozoic, mesozoic, and subsequent formations were depos-
ited.

All the evidence we have seems to show that up to the time
of the cretaceous, the sedimentary rocks, in spite of their enor-
mous thickness, were deposited in comparatively shallow seas.
We find in them abundance of animal remains, fossils, and even
tracks, as well as ripple-marks, indicating the proximity of land

Fig. 62. — Archzean Map of North America. (Dana.)

or of continental islands. Undoubtedly, in earlier geological
periods there have been invasions upon as well as withdrawals
of the sea from the low continental masses resting upon the
continental folds, and these invasions have left probably large
shallow inland seas upon these folds. Then, as now, there
must have been a considerable deposit of finer material upon
the outer edge of the continental masses then forming, which

PERMANENCE OF CONTINENTS AND OCEANIC BASINS. 131

has been buried under coarser material by the advance of the
continents as they became older. The conclusion seems inevi-
table, that the sedimentary rocks attamed thew great thick-
ness in areas of regular subsidence, the subsidence being due
to the deposition of material along the shore lines. We
know of no other cause to account for the deepening of the
seas, the action of the waves being restricted to a very limited
depth.

The effect of the deposition of such immense plateaux of lime-
stone as the Florida peninsula, the Yucatan Bank, the Pedro
Bank, and the smaller plateau along the West India Islands,
should be to cause a gradual depression over the whole of the
area of the Caribbean and of the Gulf of Mexico. But all the
indications we have from the deposits of recent formations in
Florida, in the West India Islands, and at the Isthmus of Pan-
ama, show, on the contrary, that they are in an area of elevation
due to volcanic agencies, still more or less active at the present
day. In lke manner, the transfer of such huge masses of silt
as we have at the mouth of the Mississippi and near Cape Hat-
teras should theoretically be accompanied by a corresponding
subsidence. We can only assert, however, that the mud of the
Mississippi is slowly filling the deep basin off its mouth, and
that it has been doing this for some time past.

The distance to which the Mississippi mud is carried from the
shore shows us how far such deposits, representing immense
areas of denudation, may share in forming additions to conti-
nental masses, and determining their relations to the formations
immediately preceding them. According to the soundings oz
the “ Blake,” the presence of Mississippi mud cannot be de-
tected more than one hundred miles from its mouth; beyond
that we find the usual deep-sea specimens characteristic of the
bottom of the Gulf of Mexico. Off Cape Hatteras, also, an
immense slope of fine detritus has been formed by the wearing
action of the Gulf Stream. As far as agencies now at work are
concerned, the forces acting to-day are mainly efficient along
continental masses and along the shores of islands, and must of
necessity have left the basins separating the continental masses
practically intact, except along their margins.

132 THREE CRUISES OF THE “ BLAKE.”

If a pressure of two thousand tons to the square foot is suffi-
cient to render rock viscous, it would follow that, at a short
distance below the bottom of our oceanic basins, the rocks of
which are subject to a pressure of nearly seven thousand tons
to the square foot, we should soon come to a viscous layer pos-
sessing a very high temperature. Now as the upper layer of
the rocks of the ocean bottom has a temperature nearly ap-
proaching the freezing point, this alone would, according to Mr.
Gardner, cause the bottom of the ocean, being under a greater
weight than the rocks near the shores, to remain more perma-
nent. The tension of the viscous layer, however, would be
very great, and would find relief along lines of least pressure,
in ridges or along shores of land masses, as is the case with
volcanic outbursts or with lines of elevation. For this reason
we should naturally seek the lines of greatest elevation in the
later geological periods. As is well known, the highest moun-
tains are the most recent, and nowhere do we find such great
altitudes as in the vicinity of shore lines: as along the west
coast of South America, or near the coast of Japan, where the
depth is over 4,300 fathoms; or off Porto Rico where the eleva-
tion above and below the level of the sea is not less than thirty-
two thousand feet.

Many attempts have been made to reconstruct the geography
at different geological periods, and to trace the paths of the
oceanic currents. These attempts have been more or less suc-
cessful, and are probably, in our present state of knowledge,
as accurate as the maps of the world made by the ancients
compared with the results of modern geodesy. We need not
go back to the earlier geological periods, beyond stating in a
general way that, as far as we know, the outline only of the
continents existed at the time of the silurian, —the skeleton,
the framework, as it were, upon which have grown all subse-
quent additions. This skeleton allowed a free equatorial cr-
culation, broken by larger or smaller islands in the region of
the East Indian Archipelago, impeded in a similar way by huge
islands on the east and west coasts of equatorial Africa, and by
an archipelago occupying the whole northern extremity of South
and Central America. Europe was only a series of islands; the

PERMANENCE OF CONTINENTS AND OCEANIC BASINS. 1533

greater part of Northern Asia was swept by a westerly current ;
and we may imagine a North Atlantic equatorial current de-
flected so as to reach the arctic region, the main branch finding
its way into the Pacific to form a part of the Pacific equatorial
current; and asecond current from the equatorial Atlantic ram-
ifying along the eastern coast of the South American Archi-
pelago.
_ If we omit the intervening periods and pass over to an exami-
nation of the map of the world at the time of the chalk, we
shall find our continents greatly increased in size. The littoral
and shallow-water deposits, which ‘have formed the devonian,
the carboniferous, the lias, the jura, have united many of the
older islands. They had perhaps given to Africa much the out-
line which it now has, with the exception of the broad passage
which was still open to the Indian current, through Arabia and
North Africa, to the Atlantic. The European Archipelago
consisted of large islands. The northern part of Asia was still
disconnected from China, Siam, and India by a wide strait,
through which flowed a current joining that in the Indian
Ocean, and forming a large inland sea, connecting the Caspian,
Black, Aral, and Baikal Seas. The islands forming the south-
ern extremity of South America had become connected, but
there was probably little change in the outlines of the archi-
pelago forming the northern part of South and Central America. ©
But North America itself has greatly changed. There is a
deep bay extending from the Gulf of Mexico far up towards
the sources of the Missouri, while the shores of Mexico, of the
greater part of Texas, Louisiana, Mississippi, Alabama, Florida,
Georgia, North Carolina, parts of Virginia, and New Jersey are
still swept by the returning Atlantic equatorial stream, much as
the shores of the Gulf of Mexico are nowadays. Only a small
part of the North Atlantic equatorial current finds its way now
through the Central American and South American archipel-
agoes into the Pacific, the greater part of it raising the tem-
perature of the shores of North America as high as that of the
Gulf of Mexico at the present day. Undoubtedly the combined
influence of this equatorial drift in its eastern extension and of
the Gulf Stream was then far more powerful in raising the

134 THREE CRUISES OF THE ‘“‘ BLAKE.”

climate of the arctic regions than it is to-day, and was felt not
merely on the coast of Iceland, the Feerdes, Norway, Spitzber-
gen, and along the north shore of Siberia, but also in the tem-
perature of Greenland, making it possible for a flora similar to
that of the temperate zones to flourish there.

During the tertiary period, the inland sea of Western Asia
became greatly reduced in extent; and the connection between
the Indian Ocean and the China Seas, across the central part of
China and the northern part of India, Arabia, Asia Minor, and
Palestine, closed the free access of the Indian current from the
Mediterranean. South America, with the exception of the
pampas and Amazonian gulfs, had practically assumed its pre-
sent outline; while the shore line of the southern part of North
America had more nearly approached the existing line of the
Gulf of Mexico. There was thus a less amount of water heaped
up in a smaller Gulf of Mexico, and a corresponding decrease
in the influence of the Gulf Stream of the tertiary period over
the climate of the arctic region, till in our own epoch the effect
of this equatorial current is practically felt only on the eastern
part of the North Atlantic, reaching also toward Nova Zembla
and the northern shores of Siberia. With the cooling of the
arctic region a greater influence was exerted by the cold current
which found its way from the North Pole towards the equator
along the eastern coast of North America, thus driving the
warm water towards the eastern part of the North Atlantic
Ocean.

The soundings of the “Blake” during the dredging season
of 1880 developed some striking features in the profile of the
slope which extends eastward from the shore along the Atlantic
coast, south of Cape Hatteras as far as the northern extremity
of Florida. The few lines run in 1880 normal to the coast, and
the line run parallel to the so-called axis of the Gulf Stream,
showed the probable existence of an immense submarine pla-
teau, of which the eastern edge had not been reached, or else
the soundings indicated a very slight slope from the shore to
deep water along the whole coast line south of Cape Hatteras to
the latitude of the Bahamas.

Everywhere else along the Atlantic coast of the United States

135

north of Cape Hatteras, and in the Gulf of Mexico, the con-
tinental line of one hundred fathoms is most plainly marked,
forming the upper edge of the more or less abrupt descent lead-
ing into deep water with a regular inclination. Owing to the
absence of this hundred-fathom line south of Cape Hatteras, it
became an interesting problem to trace the exact profile of that
part of the coast, and to continue it into deep water. The sea-
son of 1881 was spent by Commander Bartlett in the “ Blake,”
under the direction of the Hon. Carlile P. Patterson, the late
Superintendent of the Coast Survey, in running a number of
lines normal to the coast, south of Cape Hatteras and north of
the Bahamas, and carrying them into deep water. The Super-
intendent of the Coast Survey has kindly allowed me to make
use of the results of Commander Bartlett in connection with
my report of the dredging expeditions of the “ Blake.” *

As was to a certain extent anticipated, the lines developed an
immense plateau, of a triangular shape, reaching from the Ba-
hamas to a point immediately south of Cape Hatteras, where this
plateau passes into the northern continental shelf, limited by
the hundred-fathom line.

The eastern edge of this plateau is from three hundred to
three hundred and fifty miles from the coast, and with an ab-
rupt slope passes into deep water. For the sake of brevity I
shall call it the “Blake Plateau.” (See Figs. 56, 176.) The
eastern edge of the slope of the Blake Plateau commences at an
average depth of at least four hundred fathoms, so that the
general profile of the lines carried normally across it shows a
gradual incline from the shore to a depth of about fifty fath-

PERMANENCE OF CONTINENTS AND OCEANIC BASINS.

oms, then a somewhat abrupt

1 These lines have, during the season
of 1882-83, been extended south of the
Bahamas as far as Porto Rico. Under
the direction of Professor Hilgard, the
“ Blaxe,” in command of Lieutenant-
Commander Brownson, U. 8. N., ran nor-
mals into deep water, showing that the
Blake Plateau developed by Commander
Bartlett commences slightly to the west-
ward of Great Abaco, and extends thence
northward. (See Figs. 56,176.) Lieuten-

slope to a depth of about four

ant-Commander Brownson proved further
that to the south the eastern edge of the
Bahama Bank ran but a short distance
seaward parallel to the general line of the
outer row of islands of the group, till it
united with the plateau upon which Porto
Rico and the Caribbean Islands crop out,
leaving probably one or two deep pas-
sages extending towards the old Bahama
Channel north of San Domingo and Cuba,
leading to the Windward Passage.

136 THREE CRUISES OF THE “ BLAKE.”

hundred fathoms, then a very gentle descent to the edge of the
sharp, steep slope forming the outer eastern edge of the Blake
Plateau, at a depth of nearly six hundred fifa:

It is interesting to speculate how this peculiar profile, so dif-
ferent from that of any other part of our coast, was formed.
The explanation to my mind is comparatively simple. The pre-
sent outer eastern edge of the Blake Plateau, which is now at a
depth of six hundred fathoms, was at one time at a much higher
level. In fact, I assume that this slope probably represents the
remnant of the slope formed at the time when it began at the
hundred-fathom line, and that this trough with unequal sides has
been worn away by the action of the Gulf Stream acting upon
the Blake Plateau from a geological time which we can trace
with a certain degree of accuracy.

We may also imagine the slope off the Carolinas and Georgia
to be due, not to the wearing action of the Gulf Stream along
the surface of the ancient continental plateau, but to the depo-
sition of a large amount of silt from the remains of pelagic ani-
mals, which has gradually formed the bank—the Blake Plateau
— occupying the angle between the northern extremity of the
Bahama Bank and (ane Hatteras.

In the one case, the hundred-fathom line aed formerly far
out to sea beyond its present position, along a line now repre-
sented by about the five-hundred-fathom line ; in the other case,
the hundred-fathom line was nearer the coast, perhaps even
within the present shore. The accumulated growth of caleare-
ous animals together with the deposition of pelagic material has
gradually enlarged the outer edge of the former continental pla-
teau, and thus the distinct line of demarcation usually formed
by the hundred-fathom line has been obliterated along that por-
tion of our coast. To this may be due the formation of the
Blake Plateau.

In other words, the old continental line extended at least two
hundred and fifty to three hundred miles farther to the east-
ward, forming a huge plateau, the hundred-fathom line of which
was found where the six-hundred-fathom line now runs, and
stretched so far south as to include the Bahamas and Cuba in
this great submarine plateau. The elevation of the Blake Pla-

PERMANENCE OF CONTINENTS AND OCEANIC’ BASINS. 137

teau probably dates back to the end of the cretaceous period,
the time when the plateau of Mexico was raised, by which what-
ever communication may have existed between the waters of the
Atlantic and those of the Pacific was cut off, and there were
formed a number of islands, more or less extensive, in the range
of the Greater or Lesser Antilles.

We may attempt from the topography of the bottom of the
Gulf of Mexico, of the Straits of Florida, and of the ocean off
the east coast of the Southern States, to reconstruct the ancient
course of the Gulf Stream from the time of the cretaceous, and
to speculate upon its action in modifying the topography of the
continental shelf which runs from the Bahamas to Cape Hat-
teras.

At that time the Gulf Stream, passing between Yucatan, then
a submarine plateau of comparatively moderate depth, and Cuba,
furrowed the deep channel, one thousand fathoms or more, which
now separates Yucatan from Cuba. The Gulf Stream then lost
itself northward in a Mississippi bay, and spread fan-shaned
partly over the submarine plateau of Florida. It brought, how-
ever, an accession of materials, by the deposition of which the
plateaux of Yucatan and of Florida were slowly built up, and
which also supplied food to the innumerable marine animals
whose former existence is proved by the structure of the very
plateau upon which they must have lived. The Gulf Stream
thus contracted its own boundaries, and was forced into the
narrower channel it had constructed between Yucatan and
Cuba. As a consequence, it cut an ever deepening trough, and
in proportion as Florida rose from the sea it was also compelled
to find an outlet for the mass of water by which the Florida
peninsula had been covered. It naturally followed the track
of least resistance, and forced its way up-hill over the lowest
part of the plateau, the southern point of Florida, through the
then comparatively shallow passage of the Straits of Bemini,
which it must have deepened by degrees as Florida was build-
ing up.

The mass of water which in the early part of the tertiary
period forced its way north, partly up the Mississippi, and partly
_ east over the peninsula of Florida, was litile by little confined to

138 THREE CRUISES OF THE “ BLAKE.”

the single channel of the Straits of Bemini, and then the whole
mass of the Gulf Stream flowed northward over the shallow
Blake Plateau extending north of the Bahamas to Cape Hat-
teras. It is this part of the Blake Plateau which, if I am night
in tracing its past history, has been worn away by the unceas-
ing flow of the Gulf Stream.

The Gulf Stream now flows north of the Straits of Bemini
upon this comparatively shallow submarine Blake Plateau,’ with
an average depth of about four hundred and fifty fathoms, and
finally pours into the deep water of the Atlantic over the edge
of the steep slope south of Cape Hatteras. At the same time it
precipitates on this slope all the silt it has carried on its bottom,
accumulated mainly through the decay of pelagic material and
the wearing action of the Gulf Stream in its course northward.
A similar action, but on a smaller scale, also takes place on the
steep western and northeastern slopes of the Yucatan Bank.
The shallow surface waters of a part of the Stream pour over
this bank, and deposit on its slopes the silt held in suspension,
and whatever materials are gathered along its course by its
action upon the smaller banks and reefs of the great bank
itself.

We have, unfortunately, no very definite data regarding the
wearing action of water so densely charged with silt as is shown
by the immense quantity deposited by the Gulf Stream on the
northeastern edge of the Blake Plateau, just south of Cape
Hatteras. The Mississippi, with a depth of say five fathoms,
and a velocity not much greater than that of the Gulf Stream,
has in a couple of years dug out a depth of at least eighty feet
a short distance back of its bar. What may be the wearing ac-
tion of a mighty river like the Gulf Stream, having an average
depth of three hundred and fifty fathoms, and a breadth of some
fifty to seventy-five miles, with a velocity of five miles, it 1s diffi-
cult to say. Supposing, however, that this wearmg action is
no greater than the wate denudation over the area of the Mis-
sissippi drainage basin, — that is, at the rate of one foot im six
thousand years, and it certainly is not too much to assume the

1 The different shades on the map (see Fig. 176) correspond with the respective
velocities of 1, 2, 3, 4, and 5 knots per hour.

PERMANENCE OF CONTINENTS AND OCEANIC BASINS. 139

same amount for the grinding action of the Gulf Stream, —
this would give us a period of about ten millions of years since
the termination of the cretaceous period. This estimate is pro-
bably far too high, judging by what we know of the wearing
action of water in hydraulic sluices ; we have a safer estimate
in a period of five millions of years as denoting the time which
has elapsed since the beginning of the tertiary. If we assume
with Ramsay that this represents about one tenth of the time
which may have elapsed since life appeared on the earth, we
should have a total of not more than fifty millions of years since
the first appearance of life upon this globe. To this must be
added, as indicating the age of the globe, whatever time mathe-
maticians think was necessary to reduce the globe from its
primitive state to a condition fit for animal life.

Va
DEEP-SEA FORMATIONS.

Tue study of oceanic deposits has materially modified many
of our notions regarding the mode of formation of the marine
deposits of former geological periods. These deposits consti-
tute a considerable portion of the crust of the earth, and we may
to-day, as has well been said by Saporta, study their mode of
formation, like that of the beds of the chalk, of the odlite, of
the miocene, and of the later tertiaries, as plainly as if we had
lived and witnessed the Rion which have left ge record
in the geolog ical time tables."

“Tt is to-day the privilege of the special student to decipher
the history of the past with a certain boldness, and from the
careful study of the present to picture to himself the most
ancient phenomena. Beds composed of globigerine, of ptero-
pods, of fine sand, or of ooze, have long been known to the
geologist; but their interpretation by the knowledge of to-day
calls up pictures of the past which his predecessors could never
have imagined.”

Granting the great age of our oceanic basins, it follows that
while there were in earlier geological periods deep-sea deposits
similar to those laid down to-day on the floors of our oceans,
yet they constitute but a small part of the beds which go to
make up the thickness of the earth’s crust. Abyssal deposits
must always have been formed near the sea-edge of the conti-
nental nuclei, or in the track of the principal currents of those
days ; while on the continental folds were deposited in succes-
sion the formations which have built up our continental areas.
Then, as to-day, the coarser materials were deposited within a
short distance of the existing shore line, while the coarser sands

1 Saporta, Gaston de, Revue de Deux Mondes.

DEEP-SEA FORMATIONS. 141

and finer clays were carried subsequently to longer distances,
and finally to depths of nearly six or seven hundred fathoms.
The finest shore deposits are not known to extend beyond four
hundred miles. Along the course of currents fine silt will be
deposited on the farther slope of ridges over which they pass,
as in the Windward Passage, or on the sea-face of the conti-
nental slope off Hatteras, at the foot of the falls of the Gulf
Stream, if I may so call that slope. Greensand appears to-day
to be deposited in the eddies of the Gulf Stream. Rounded
pebbles with conchoidal fractures are found in the West Indies
at considerable depths. Their shape is probably due to the
action of the comparatively warm water of those depths upon
the fragments of rocks disintegrated from their original layers.
Manganese nodules and incrustations are met only in deep
water. In the vicinity of coral islands extensive deposits of
comparatively coarse limestones often run to great depths, as
off the western Florida Bank; quite large pieces of such lime-
stone were brought up by the “Blake” from a depth of about
fifteen hundred fathoms. Nullipores extend to a depth of one
hundred and fifty-five fathoms. We find large forests of the
larger kinds of bryozoa at a depth of from one hundred to two
hundred fathoms. Deposits of sand, of groves of bryozoa, or
of nullipore limestone, can therefore be found within the limits
of the deep-sea fauna.

The plateaux of limestone which form the submarine base of
the Florida and Yucatan banks are examples of deep-water
limestone deposits, the like of which we know to have been
formed in the West Indies during cretaceous and tertiary times,
and to have been elevated to considerable heights, as, for in-
stance, in Cuba, Jamaica, San Domingo, Barbados, and other
West India Islands.

By deep-sea deposits of past ages we of course mean those
deposits in which animals now characteristic of the deep-sea
fauna have been found; that is, such deposits as do not in our
day seem to play any important part in modifying the outline
of our continents ; such deep-sea deposits consist exclusively of
globigerina, diatom, biloculina, and radiolarian ooze, and of the
abyssal red clay.

142 THREE CRUISES OF THE “ BLAKE.”

The littoral fauna of to-day occupies a somewhat narrow belt
within the hundred-fathom line, at no very great distance from
the shore; in fact, inside of what has been termed the continen-
tal line (one-hundred-fathom line), while the rest of the bottom
of the ocean is occupied by the continental and the strictly
deep-sea fauna.

Littoral deposits take place under constantly changing condi-
tions, and are subject to violent perturbations, which disturb
and modify the stratification. Deep-sea formations, on the
contrary, must of necessity be subject to less interference, and
therefore acquire a greater thickness. If this was really the
case with the older formations, those which — like some of the
limestones — are of deep-sea origin, will be found to be much
thicker than the contemporaneous littoral deposits. This we
may assert to be the case. Care must of course be taken, as
has been urged by Fuchs, to compare such deposits as are
comparable, and not to draw deductions from phenomena which
have nothing in common. A coral fauna, a brachiopod fauna,
and an ammonite fauna give us no terms of comparison. We
may even have marked contrasts, as between eocene mamma-
ha and cretaceous saurians, while a common factor is presented
by the flora of the two periods. Invertebrates pass from the
jura to the chalk without presenting striking contrasts, while
among fishes the transition from ganoids to teleosteans shows
the relationship in one case to be with the past, in the other
with the future. They are the young and the old generations.
The effect of surroundings is of course very different upon
organisms of various classes at successive periods of their geo-
logical and palzontological development. The attempt, made
by Fuchs, to identify the deep-sea formations of former geo-
logical periods from the facies of the fauna is subject to the
same difficulties that are found in determining the upper and
lower limits of ‘the abyssal fauna. These difficulties are due
to the enormous bathymetrical range of many species, which
were at first regarded as strictly abyssal, but have subsequently
been proved to extend almost into the confines of the littoral
zone.

By far the greater number of the marine forms characteristic

DEEP-SEA FORMATIONS. 143

of the oceanic fauna and flora of the present day are found
within the hundred-fathom line. In attempting either to define
or to contrast the fauna of the shores and of the deep, we find
a neutral region, characterized perhaps by no forms strictly its
own, but in which the stragglers from each zone flourish, and
nothing typical either of the littoral or of the deep-sea fauna
is any longer found.

‘In many localities where deep-sea deposits are taking place at
the present day, the distance from the coast is often not very
great, especially in volcanic regions. Along the face of the
whole Atlantic coast from.the Bahamas to St. Thomas, the line
between the continental curve and the two-thousand-fathom line
is nowhere more than fifteen miles distant. We cannot there-
fore infer that because a formation has been deposited parallel
to a continental coast it must necessarily be a shallow-water
formation. What to-day would be called continental forma-
tions, from the character of their fauna, lie within the limits of
say three hundred and fifty to seven hundred and fifty, or per-
haps one thousand fathoms. But as the character of the fauna
in its turn depends mainly upon the constitution of the bottom,
this interdependence introduces many variable elements. There
is no greater contrast than that which exists between the fauna
living upon the recent limestones of the steep slopes of the
Florida plateau and that found at similar depths in the calea-
reous ooze of the trough of the Gulf Stream in localities not
many miles distant.

We are justified in considering deposits containing large
amounts of globigerina, radiolarian, and diatom mud as pelagic
deposits laid down at certain distances from land in considerable
depths ; but, as these animals are pelagic, the possibility exists
of their being found in shallow deposits. Pelagic foraminifera
are found in the muds which have been brought down by rivers
into the Gulf of Mexico. The modern greensand found off
the coast of the Carolinas on the edge of the Gulf Stream
occurs in depths of less than fifty fathoms. Arenaceous fora-
minifera are to-day only found in large quantities in deep.
water.

If, as Wallich suggests, flints are now formed only in deep-sea

144 THREE CRUISES OF THE “ BLAKE.”

deposits, this fact would go far towards settling the question of
the depths of the cretaceous sea. Along the coast range of
Chili, in the nitrate districts, the position of the flint beds shows
that they were deposited in estuaries. Judging by the analogy
of their recent representatives, the siliceous sponges so common
in many of the formations must have lived at considerable
depths. The presence of pentacrinoids and thei allies, which
were not attached to the bottom, but like those of to-day lived
imbedded in mud or ooze, denotes deep water; while fossil
types with a strong, powerful root may give evidence of shal-
lower waters.

Were we to decide by the size of the fossils, the smallness of
the mollusks and echinoderms collected from certain beds, like
those of the triassic beds of St. Cassian, would point to a deep-
sea fauna.

The liassic beds of Hierlatz near Hallstadt in Austria are said
by Fuchs to be analogous perhaps to massive calcareous de-
posits like the Pourtalés Plateau of Florida. Massive whitish,
subcrystalline limestone occurs in them, built up almost entirely
of small brachiopods; but deep-sea corals are wanting in these
beds.

Many of the cephalopods of to-day are like the argonaut, pe-
lagic, or else they are deep-sea types, like nautilus and spirula.
The Eryon-like crustacea brought up by the dredge are all in-
habitants of considerable depths, and the macruroids, Ophidude,
and the like, are deep-water fishes. We should constantly bear
in mind that the absence of certain types of invertebrates may
be very marked, owing to the disappearance of the more sol-
uble tests from beds in which the heavier and less soluble
remains are still to be found. So that in many formations
we probably find only a part of the fauna which, when in its
most flourishing condition must have characterized them. The
fauna of the deposits of the old red sandstone of the Connecti-
cut River indicates that it lived in shallow water, while de-
posits rich in remains of belemnites, etc., were formed in deep
waters.

The scarcity of vertebrate bones in dredgings is very marked.
Mr. Pourtalés, who seems to have been more fortunate than all

DEEP-SEA FORMATIONS. 145

others, dredged a few manatee ribs in the Straits of Florida.
Neither the Fish Commission nor the “Blake” has been equally
successful. The “Challenger,” however, dredged thousands
of sharks’ teeth and cetacean bones in 2,300 to 2,800 fathoms.
They were principally found in restricted areas, far removed
from land, in the abyssal red-clay regions, where the rate of ac-
cumulation is very slow, and where such bones are not likely to
be buried by detritus coming from the shores, or by the more
rapid deposition going on along continental shelves. These
deposits may be analogous to the bone beds of the corniferous,
or perhaps to the phosphate beds of South Carolina, or the
Cambridge coprolite beds. On the east coast of the United
States, and in the Gulf of Mexico and the Caribbean, sharks’
teeth have been dredged, but rarely. Either the sharks of
former times were much more numerous, or, as has been sug-
gested by Professor Verrill, their remains, as well as those of
fishes * and other vertebrates, were not immediately devoured
by other inhabitants of the deep sea. One would also expect
that the bones of porpoises would be common in localities
where they are often seen sporting by hundreds, as along the
Windward Islands. Yet none were dredged by the “ Blake.”

An examination of the fossils from many of the raised sea-
beaches reveals types which the late explorations have shown
to be deep-sea forms. Seguenza was the first, in studying the
pliocene deposits of southern Italy, to show that some of them
were deposited in deep water. He suggested that the forami-
niferous, bryozoan, coral, and radiolarian beds were deposits
which must have been laid down at considerable depths ; he was
led to this conclusion by a comparison of their fossils with the
animals of the present day found at great depths. Before the
recent deep-sea investigations, geologists were misled by the
strange forms contained in many of the foraminiferal deep-sea
deposits of the tertiary period, and looked upon these deposits
as much older than they were in reality.

Fuchs has also compared other beds of the tertiary, on account
of their characteristic fossils, with certain deep-sea deposits. The

1 Otoliths of fishes occur not unfrequently in the fine muds of the Gulf of
Mexico.

146 THREE CRUISES OF THE “ BLAKE.”

flysch, which forms so important a part in the geology of south-
ern Europe, he thinks must have been a deep water deposit.
The beds of the mesozoic period in which ammonites are found,
Fuchs looks upon as deep-water formations, because in all dis-
tinctly shallow-water beds of that time no ammonites have been
found.

From the time of the earliest examination of the globigerina
mud of the Atlantic, by Bailey and Ehrenberg, that deposit has
been compared to the chalk; and since the time of deep-sea
investigations, the white chalk, with its globigerinz, Hexactinel-
lid, and peculiar echinoderms, has always been regarded as an
antique type of deep-sea deposits. Jeffreys, on the contrary,
assumes it to be a shallow-water formation from the study of
the mollusks. His reasons are that the foramimifera of the
chalk are many of them pelagic, and might therefore be found
in littoral or shallow-water deposits; that globigerina ooze con-
tains a large percentage of silica, while the chalk is nearly pure
carbonate of lime; that the mollusca of the chalk are all litto-
ral types; and that the so-called deep-sea genera are wanting.
Yet we find in the chalk such genera as Terebratula, Lima,
Pecten, and Spondylus, all of which are found im very deep
water,—to a depth of fourteen hundred and fifty fathoms.
While admitting that pelagic foraminifera frequently occur in
littoral deposits, it seems impossible that some of the beds of
foraminifera of great thickness should have been deposited oth-
erwise than in deep water. Foraminifera ought to serve as
excellent guides in identifying deep-sea formations, since genera
like Cristellaria, Margimulina, Clavulina, Nodosaria, and others,
with arenaceous .and siliceous tests, occur in the seas of to-day,
principally in deeper waters.

The present chemical constitution of the chalk is also not the
one in which it was deposited, the siliceous particles having
probably been concentrated as flint. As regards the fauna,
the mollusks are not so good a guide as either the sponges or
the echini, the representatives of both of which — Hexactinel-
lidee, Ananchytide, Pourtalesiz, Saleniz, and Echinothurie —
are eminently deep-sea types. That many of the molluscan
forms which lived in the chalk have been dissolved as arago-

DEEP-SEA FORMATIONS. 147
nite there is no doubt,’ but the presence in the chalk of deep-
sea brachiopods, cephalopods, and crustacea, tends to prove the
deep-sea nature of the old white chalk. ;

We should, however, bear in mind that at the present day the
distinctions made to determine faunistic regions are often based
on the presence or absence of certain species, and not of genera.
Genera have a far wider range both geographically and bathy-
metrically, and can only be used for such comparisons with the
greatest care. It would certainly be impossible to find any-
where to-day a littoral fauna with the facies of the characteristic
chalk. .

Tt is difficult to institute a comparison of the globigerina
ooze with the chalk proper, as from the length of time the
latter has been exposed to the action of the atmosphere its com-
position must have changed materially either by solution or
metamorphosis.”

The difference in the analysis of the chalk and of the globi-
gerina ooze consists mainly in the fact that there is more car-
bonate of lime and less alumina in the former; while the flint
nodules in the chalk are replaced perhaps by the large amount
of silica in the globigerina ooze. Coccoliths and coccospheres,
sumilar to those detected by Wallich in the chalk, also occur in
the deep soundings.

Murray and Renard consider that “chalk must be regarded
as having been laid down rather along the border of a continent

1 This was discovered by Hébert. In
the seas of the present day the shells of
pteropods and globigerine are, as has
been discovered by the “ Challenger,”
dissolved beyond a certain depth. Pter-
opod ooze is not found in depths greater
than fifteen hundred fathoms, and glo-
bigerina ooze disappears in its turn at
about twenty-five hundred fathoms.

2 The solvent power of the ocean dur-
ing some of the earlier geological depos-
its seems to have been far less than in
later times. What the cause is which
has acted so much more vigorously in
later periods, and caused the disappear-
ance of aragonitic organisms in the mod-
ern limestones, is not known. “Silica

has been removed and segregated into
flints from the white chalk. Other chalks
have become cherty. Siliceous skeletons
of sponges are replaced by calcite, calcite
by silica, and aragénite has been entirely
dissolved away.” Professor Dittmar sug-
gests that the dissolving of shells may be
due to the action of sea-water itself, as
after a sufficient length of time it can take
up an amount of lime additional to what
it already contains. But the carbonic acid
present in sea-water undoubtedly plays
some part in this dissolving process. Pter-
opod shells, in all possible stages of
decay and solution, form an important
element in the deeper deposits of the Gulf
of Mexico.

148 THREE CRUISES OF THE “ BLAKE.”

than in a true oceanic area.” ' There is no proof that massive

formations are deposited anywhere except along continental
shelves, while at the greatest depth we may find the true red
clay, the result of chemical decomposition.

Mr. J.S. Gardner considers the blue ntud found around shores
and in partially closed seas, and passing into a deep-sea deposit
at a distance from land, as the equivalent of the gault. The
gault has among its mollusca, Leda, Limopsis, and Denta-
lium, all well-known deep-sea mollusca. Its foraminifera and
echinoderms likewise are deep-water types. The upper gault
represents a deeper sea ; blue muds are replaced by green muds;
from that we pass to chalk marl, which is apparently a sort of
globigerina ooze, and finally to the white chalk, with its great
extent and thickness, which proclaim it to be an oceanic or a
deep-water deposit ; and there seems to be nothing with which
it can be compared except globigerina ooze.

Professor Liversidge describes a chalk formation from New
Zealand, consisting of eighty-one per cent of carbonate of lime
and seven per cent of silica. This contains, as is stated by
Brady, species of foraminifera now found in deep-sea specimens
of globigerina ooze from fifteen hundred to two thousand fath-
oms in depth in the South Pacific. The origin of the New
Britain chalk is not known, but it is probably recent; the speci-
mens are thrown up on beaches after storms. White chalk con-
tains ninety-eight per cent of carbonate of lime, and gray chalk
ninety-four per cent. The “Blake” also dredged off Nuevitas,
in 994 fathoms, recent chalk which Murray says is more like
white chalk than anything he has seen.

Chalk is certainly not derived from the disintegration of coral
reefs, although we frequently find patches of rock associated
with coral reefs closely resembling true chalk, both in texture
and composition, —as, for instance, in the so-called modern
chalk of Oahu. The percentage of carbonate of lime com-
posing reef corals* varies from ninety-five to ninety-eight ; this

1 Chalk may be forming at very great * Sharples gives the following per-
depths close to a continent. See the an- centages of carbonate of lime: Ocu-
alysis of the modern chalk collected off lina, 95.37 ; Manicina, 96 54 ; Madrepora,

Nuevitas in 994 fathoms. (Murray, Bull. 97.19; Siderastrea, 97.30; Millepora,
M. C. Z. XII., No. 2.) 97.46 ; Agaricia, 97.73. Madrepora pal-

DEEP-SEA FORMATIONS. 149

is larger than the percentage of lime characteristic of true
chalk.

On the western edge of the Florida Bank, northward of the
Tortugas, sponges occur in abundance, and the trawl would
constantly come up from a depth of one hundred fathoms
filled with masses of sponges, both siliceous and calcareous,
from a modern limestone bottom. Masses of fossil sponges
occur in the jurassic beds of southern Germany and Switzer-
land, made up of calcified skeletons of Hexactinellide and
of Lithistide. Siliceous sponges are also common in the
white chalk of England and France. Calcareous sponges are
very abundant in some of the shallow-water beds of the creta-
ceous.

Judging from my own experience, we must unquestionably
refer this supply of silica to the large fields of deep-sea siliceous
sponges, which when dead and decomposed supply the spicules
found scattered all through the calcareous mass of the deep-sea
globigerina ooze. These siliceous sponges are often found in
great numbers, as in the globigerina ooze off Santa Cruz for in-
stance, where numerous specimens of an interesting new Phe-
ronema were dredged, as many as ten to fifteen in a single haul.
The whole mass of the mud was so thoroughly impregnated with
spicules and with sponge sarcode as to be sticky and viscid.
More than once the dredge “ must have plunged headlong into
one of the ubiquitous sponge-beds, — the glairy mass like white
of egg, with a multitude of spicules distributed lke hair in
mortar throughout the mud.” This, as well as the analyses of
the bottoms, plainly shows that the amorphous substance, giving
to the mud its viscidity, is not produced by sulphate of lime in
a flocculent state, but is due to the presence of a mass of decom-
posed protoplasm, — the remnants of all the animal life which
has accumulated for ages upon the bed of the ocean. This is
slowly used again by living animals, and kept from putrefac-
tion and decay, by being preserved, in the excess of carbonic
mata contained over 98, and Porites only The remaining one to two per cent is
95.8 per cent of carbonate of lime. made up of silica, magnesia, fluorine,
These corals have about two per cent of phosphoric acid, and alumina and iron

organic matter, which when fresh gives oxide.
a strong reaction for phosphoric acid.

150 THREE CRUISES OF THE “ BLAKE.”

acid, in regions where no rapid oxidation takes place, either
from currents, or waves, or from other atmospheric influences.

An immense amount of silica must find its way into the sea,
and be immediately dissolved by the excess of carbonic acid
found near the bottom, while only a portion of the calcareous
mud can be taken up in solution. Hence, this silica is at once
placed under the most favorable conditions for resorption by
organisms living upon the layer of protoplasmic substance
which covers the bottom of the ocean, into which the silica has
been received. As Wallich and others have most distinctly
proved, this protoplasmic layer, where it exists, is the product
of the organic life, and not its source.

Wallich gives some most excellent reasons for supposing that
the silex nodules found in the chalk owe their origin to sponges.
This is additional evidence in favor of the opinion, which is
gradually gainmg ground, that the deep-sea calcareous mud is
but a chalk deposited in the present epoch, and in every way
to be compared with the chalks of the cretaceous period ; and
further still, that this deposition of chalk has been going on
uninterruptedly from cretaceous times, and that we may be said,
as far as that special deposit is concerned, to be living in the
period of the chalk, for no lithological distinction of any value
has been established between the chalk proper and the ealea-
reous mud of the Atlantic.

The Atlantic ooze is mainly made up of the calcareous casts
of globigerine, and their sarcode must have contributed in no
small degree to the protoplasmic mass of the bottom. It must
have been an important addition to the silica supplied by
sponges in the seas where siliceous foraminifera are abundant.’
As an additional source of supply of silica we have the exten-
sive deposits of diatoms, which fall to the bottom after death.
A similar condition of things probably existed during creta-
ceous times, and the chalk flints were derived from the same
groups of animals which now supply the silica and the globi-
gerina ooze of the Atlantic.

1 Sir Henry De la Beche states, that ter, but if allowed to remain too long in

siliceous particles are generally dissemi- suspension the silex will become aggre-
nated in water if mixed with clayey mat- gated into small lumps.

DEEP-SEA FORMATIONS. 151

The absence of typical cretaceous belemnites, baculites, and
ammonites does not in the least prove that a process similar
to that which deposited the chalk of the cretaceous period may
not be going on at the present day on the floor of the Atlantic.
But owme to the variable nature of the bottom, it does not
follow by any means that the same process is going on syn-
chronously all over the Atlantic bed. Deep-sea muds, such as
we find on the steep slopes like those of Hatteras, the Wind-
ward Passage, and the continental slopes of the Gulf of Mexico
and the Caribbean, can be compared to fossiliferous shales.

How far the presence of deep-water types can be traced to
paleozoic times is very uncertain. All the evidence thus far
tends to show that the deep-sea fauna originated at the close of
the palzozoic times, for many of the genera which we have been
* led to consider as deep-sea types in the mesozoic period lived
in comparatively shallow water. The Lingula of to-day is a
shallow-water dweller; it may have been one then. The pre-
sence of pteropods and thin-shelled cystideans, and of many
blind trilobites, would seem, however, to indicate the existence
of invertebrates at considerable depths along the continental
slopes even in these early days. Deep-sea faune, like all marine
faune, are essentially dependent upon the nature of the bottom;
in former times, globigerine and siliceous sponges must have
- flourished on calcareous ooze; mollusca and annelids character-
ized muddy bottoms, while polyps, gorgoniz, and corals throve
on rocky ground. It is to be noticed that those of the older
formations which were probably deposited in deep water,
always appear to be of far greater thickness than the so-called
littoral beds. This would show that there was in past times
as great a variety of conditions in which marine animals lived
as we find at the present day, and that the limits of tempera-
ture were fully as great; while the existence of equatorial cur-
rents tended to give the marine animals a wider unbroken
range than they now have. There were then striking contrasts
of temperature between eastern and western continental shores,
and variations of a few degrees were quite sufficient to produce
very different climates. There are many of the same types in
the deep waters of the Atlantic, the Pacific, and the Southern

152

THREE CRUISES OF THE “ BLAKE.”

Oceans, — the survivors perhaps of an abyssal fauna, which,
thanks to the distributing agency of the equatorial currents,
extended, in mesozoic times, over the whole floor of the equa-
torial and a part of the temperate zones.’

1 Under favorable conditions, animals
having a wide geographical and geolog-
ical distribution have been found in prox-
imity to continental masses. The “ Al-
batross ” has dredged in deep water off
Chesapeake Bay many deep-sea types

first known from the European tertiaries,
from the arctic and antarctic, from the
shores of Europe and of South America,
from the West Indies, and even from In-
dia and the Pacific Ocean.

WELL

THE DEEP-SEA FAUNA.

Ir is vain to inquire what animals and plants could have
lived in the primordial ocean. We can only conjecture, if we
adopt the speculations of Mallet regarding the conditions of
the ocean, that they must have been capable of bearing an
intense degree of heat, and probably inhabited a mass of boil-
ing mud.

Whole classes of animals and plants live only in the water,
and cannot subsist elsewhere : water penetrates all their tissues,
and from it they take the elements needed for their growth.
Animals living in salt water, with very few exceptions, die in
fresh water, probably from the lack of soluble salts." There
are vast numbers of animals whose function seems to be the
distribution of the soluble salts which have from time imme-
morial been swept into the sea. Globigerine, pteropods, mol-
lusks, echinoderms, corals, and sponges, all distribute over the
floor of the ocean, in the form of shells or solid calcareous skel-
etons, the lime and silica which they have derived from the sea-
water.

Tn an atmosphere saturated with moisture, crustacea could live
under moist stones and bark. Lichens as well as many infuso-
ria, which when dry remain inert, but are resuscitated by moist-
ure again, may have formed the principal elements of the fauna,
and have survived during the transition from the older marine
to a very moist climate, or one resembling the climates of the
present day. Similar adaptations may have led to the gradual
change of marine shells into terrestrial types. In fishes proper

1 Sharks are known to inhabit Lake on the shores of northern Brazil extend
Nicaragua and the fresh waters of some far up the Amazons, and some hydroids

of the larger rivers of India ; many marine flourish in fresh water.
fishes, selachians, and cetaceans common

154 THREE CRUISES OF THE “ BLAKE.”

the swimming-bladder precedes in time the lung, which first de-
veloped among reptiles. The development is from aquatic ba-
trachians to saurians, and finally to warm-blooded vertebrates,
adapted mainly to a terrestrial existence.

If, as has been suggested by Moseley, the condition of life
of the earliest littoral types was pelagic, we may find in this
an explanation of the reversion of the larval forms of so large
a number of our littoral species to a pelagic free-swimming
stage. ;

‘Che believer in cataclysms and the man who seeks in natural
causes an explanation of the phenomena around him will each
put his own reading on all attempts to explain the causes of the
apparent revolutions of earlier geological periods. As those rev-
olutions were undoubtedly limited to well defined areas, species
living within narrow boundaries in the depths of the ocean may
have continued to exist till from local disturbances they in their
turn disappeared.

We are justified in explaining the difference between adjoin-
ing deposits, the one barren of animal life, the other crowded
with animal remains, by supposing conditions similar to those we
find in contiguous areas in the depths of the sea. These differ-
ences imply variations in the physical conditions of adjoining
areas; they are not climatic or necessarily due to geological
changes. One area will be teeming with animal life, while the
other, either from want of food, from the constant deposition of
sediment, or from the sudden changes of temperature affecting
it, may be a desert on the surface of which no animal life can
maintain itself.

At the time when the greater part of the surface of the earth
was covered by water, during the laurentian, huronian, and
cambrian periods, the seas contained annelid tracks, sponges,
polyps, some echinoderms, and brachiopods, with few marine
plants. From these low types, whether they are the earliest
or not, must have descended the present population of the seas
and land, both animal and vegetable. The study of the cur-
rents of early geological periods can to a certain extent give
us a clue to the regions from which subsequent marine faune
have descended, radiating thence little by little over the globe.

THE DEEP-SEA FAUNA. 155

On comparing the marine fauna of some of the older forma-
tions with that of recent ones, we are struck with the similarity
of the types. In the silurian we find crinoids, echini, starfishes,
crustacea, mollusea, and fishes, an association of types like those
of our epoch. Some groups, however, attained at that early
day a preponderance such as none of the types of the present
epoch have ever reached.

There is nothing in our living fauna, for instance, analogous
to the immense development of the crinoids or of the trilobites,
the most prominent crustacea of the silurian period, which dis-
appeared abruptly at the time of the coal period, and are rep-
resented to-day only by our horseshoe crabs. The ammonites
— which, like their distant allies of to-day, the nautilus, argo-
naut, and spirula, must have swept over the surface of the seas,
or sunk to its greatest depths — have had a most remarkable
history. From straight gigantic shells, nearly rivalling in size
the huge squid of to-day, they have passed through a series
of transformations, including types of the most complicated
combinations, and finally seem to have succumbed to the ex-
quisite perfection of their type, and to have been killed in the
struggle for life. ‘They were slowly relegated to interior seas,
and, ceasing to advance, gradually died out.

The depths of the seas seem at first glance the safest of all
retreats, — the secret abysses where the survivors of former geo-
logical periods would be sure to be found. Yet oceanic dredg-
ings have not brought to light as many of the ancient types as
the more enthusiastic dredgers had led us to expect. They have,
however, given us a large number of animals living in deep
water, where they have been subjected to no violent changes, to
which no revolutions of the surface of the earth can extend, and
where the only changes are probably those of temperature, —
animals living now in the depths of the sea, under much the
same conditions as those which prevailed during the last days of
the jurassic period.

The conclusion drawn from these facts by Lovén, Moseley,
Perrier, and others is that the abyssal fauna has descended
from the littoral and other shallow regions, to be acclimatized
at great depths. The conditions of existence becoming more

156 THREE CRUISES OF THE “ BLAKE.”

and more constant, or even in the deeper regions perfectly
uniform, species of the most varied derivations, when they had
once attained a certain zone, could spread everywhere. This
explains at once how the deep-water fauna presents a very unt-
form composition in all regions of the globe, but at the same
time includes various species the analogues of which live in the
sublittoral regions of both cold and hot climates, and may have
sent an occasional wanderer into deeper waters.

While the little dredging thus far done in deep water has
added to our knowledge a large number of antique types which
strongly remind us of tertiary, cretaceous, and even of jurassic
forms, we should not forget that such antique types occur
everywhere, in limited numbers, it is true, both in the shallower
regions of the sea and in fresh water. We can only say that
in the deep-water fauna a relatively larger number of such
antique forms has been found than elsewhere. In contrasting
the littoral with the continental and the abyssal faune, the
last shows a closer affinity to types of a former period than
does the fauna living at higher levels, where the descendants
of antique types are also met, but have become familiar from
their common occurrence. There are in deep waters no ga-
noids ; to-day their representatives are found in the fresh waters
of Australia (Ceratodus) and of North America (Lepidosteus).
Neither are there any deep-sea graptolites or belemnites.

Old-fashioned animals lke Trigonia, Limulus, and Lingula are
all from shallow water, as are also Amphioxus and Cestracion.
No species of characteristic palzeozoic corals have been dredged,
and nothing resembling the remarkable crinoids, so abundant in
former times. The affinities of the deep-sea types recall to us
mesozoic and cainozoic types, such as we find in the chalk and
tertiaries. No such old-fashioned animals have been discovered
as throw new light on our zodlogical knowledge, although, as
Moseley well says, in our deep-sea explorations we obtain for
the first time a glimpse of the fauna and flora of nearly three
quarters of the earth’s surface. Our whole knowledge of the
sea bottom has been created within a few years; before that
time we knew little of its fauna and flora beyond what is found
on a comparatively narrow belt of the coast line.

THE DEEP-SEA FAUNA. 157

That none of the palzeozoic forms are found in the deep sea
seems to indicate, as has been suggested by Moseley, that its
first inhabitants date back no farther than the cretaceous period.
Of course, there must have been pelagic animals, and foramini-
fera may have lived at great depths in the track of the currents,
but probably no invertebrates of a period older than the jura
and chalk existed, or if they did exist they did not wander far
from the continental shelf. Their distribution was then, as to-
day, mainly a question of food. The animals of those times
lived upon the coast shelf, and while they and their predecessors
remained as fossils in the littoral beds of the earlier formations,
their successors, belonging either to the same or to allied genera,
passed over into the following period.

The littoral belt is perhaps the most important portion of the
sea floor, since within its limits the greatest changes of light,
heat, and motion occur. To the modifications which under
such influences have taken place durig past ages, and are still
going on, in this limited area, we may attribute the gradual
migration of the littoral fauna into the deeper waters, and into
the less favored portions of the continental belt and the abyssal
region. This succession we see going on around our shores,
and in some groups of animals it has been traced with consid-
erable detail. I may take as an example the history of the
origin of the West Indian echinid fauna.

The resemblance of the fauna of the Gulf of Mexico and of
the Caribbean to that of the Pacific was noticed by writers, even
at a time when the materials available for comparison included
but little beyond the littoral fauna. From the results of the
deep-sea dredgings we have become quite familiar with the ex-
tent of this resemblance. In fact, the deep-sea fauna of the
Caribbean and of the Gulf of Mexico is far more closely related
to that of the Pacific than to that of the Atlantic. Before the
cretaceous period the Gulf of Mexico and the Caribbean were
undoubtedly in freer communication with the Pacific than with
the Atlantic Ocean ; so that, notwithstanding the presence of a
number of Atlantic types, the characteristic genera were com-
mon to the Pacific. Many of the genera have remained un-
changed, since the separation of the Atlantic from the Pacific

158 THREE CRUISES OF THE “ BLAKE.”

by the elevation of the Isthmus of Panama and the Mexican
Plateau. To these have been added, especially in the West
Indian fauna, a number of Atlantic types, which, as long as the
Gulf of Mexico and the Caribbean were practically a part of the
Pacific, perhaps did not find conditions as suitable to their de-
velopment as those which have existed ever since they became
merely extensions of the equatorial Atlantic district.

In short, to the successive changes brought about in the
physical conditions of the Gulf of Mexico and of the Carib-
bean, we may ascribe in the main the present state of the West
Indian fauna, as compared with that of other geographical dis-
tricts.

This explanation gives us an apparently good reason for the
mixed character of the fauna of the West Indian seas, showing
us at the same time that, however long a period may have
elapsed since this separation took place, it has not been sufficient
to effect any radical change in the echinid fauna of the two
sides of the Isthmus. The principal differences are due to the
immigration of true Atlantic types into the West Indian faunal
region during the tertiary and post-tertiary period. But as the
physical conditions of the sea in the tropical regions of the
Isthmus are so nearly identical, we could not expect from phy-
sical causes alone any great differences to arise between the
Panamic and West Indian faune.

To ascertain the former distribution of the genera of the
West Indian echinid fauna, we should trace back as far as pos-
sible the origin of these genera. We find a few genera, like
Cidaris, Dorocidaris, Porocidaris, and Salenia, which date back
to the jurassic period, and in the tertiary had as wide a geo-
graphical distribution as at the present day.

Hemipedina, as old as the jura, is found fossil in the tertiary
of North America, and has thus far not been dredged outside
of the Caribbean fauna. There are no less than ten genera
which date from the cretaceous period, and some of them had
during the tertiary as extensive a geographical range as they
have to-day.

The genera of the earlier tertiary period characterize largely
the West Indian fauna. Of these a few extend into the equa-

THE DEEP-SEA FAUNA. 159

torial belt of the Atlantic and Indo-Pacific region. Others have
an Atlantic and Pacific range; others again only a more or less
limited range in the Caribbean, Indian Ocean, and East Indian
Archipelago, and with nearly the same distribution as in the
tertiary, having died out from the eastern North Atlantic region
where they once flourished. A few genera are strictly tropical
American, occurring both on the Pacific and Atlantic sides of
the continent ; but they formerly had a much wider geograph-
ical distribution, having once lived in the tertiary of Egypt and
Australia.

Some of the clypeastroids date back to the later tertiary, and
they are eminently tropical American, occurring on both sides
of the continent.

This leaves a number of genera belonging to the families of
the Diadematide, Ananchytide, and Pourtalesiz, with an ex-
tended geographical range in the tropical belt of both the
Atlantic and the Pacific oceans, no representatives of which
have yet been found fossil. The nearest allies of the Diade-
matidz date from the cretaceous, and the others are to-day the
representatives of the types of old-fashioned spatangoids which
characterized the cretaceous seas.

This analysis shows that the echinid fauna of the West In-
dian seas of to-day is made up,— (1) of five jurassic genera ;
(2) of ten genera which go back to the cretaceous period ; (3)
of twenty-four genera dating from the earlier tertiary period ;
(4) of only four genera characteristic of the later tertiaries ;
(5) of seven genera which we may look upon as the repre-
sentatives of the Ananchytide and Infulasteride, and of the
Pseudodiadematide, of the cretaceous period. In all these
old-fashioned genera there are species having a cosmopolitan
range.

Of the so-called American genera, containing all most closely
allied representative species (Agassizia, Moira, Meoma, Macro-
pneustes, Encope, Mellita, Arbacia) which probably flourished
in the Central American seas soon after the closing of the
Isthmus of Panama, the three spatangoids date back to the cre-
taceous, the two clypeastroids and two Echinide to the later
. tertiary. The nearest allies of the clypeastroids are found in

160 THREE CRUISES OF THE “ BLAKE.”

the tertiaries of Western France and of Egypt; the above-named
West Indian spatangoids and clypeastroids, as well as Ccelo-
pleurus and Macropneustes, disappeared first from the Eastern
Atlantic. The past history of the ten West Indian genera al-
ready found in the cretaceous, and of the twenty-four genera
descending from the earlier tertiary, gives us but slight assist-
ance in determining the mode of their origin in the Caribbean
fauna.

It would be most interesting to be able to make a compari-
son of the deep-sea Panamic fauna with that of the Caribbean,
and to ascertain if, in the continental and abyssal regions, at
the depths beyond which the effects of motion, of light, and
of heat cease to be prominent factors, there is as marked a dif-
ference in the representative species as in those of the littoral
fauna.

Soon after the end of the cretaceous period the specialization
of the Atlantic and Indo-Pacific marine realms began. Before
that time the equatorial currents swept nearly uninterruptedly
round the globe, and maintained across the Indo-Pacific and
Atlantic the conditions which existed in the Western Atlantic
before the equatorial currents became deflected by the West
India Islands and the northern extremity of South America.
If the physical causes we now see at work have, as they have
become altered, also modified the fauna of the equatorial belt
district then existing, we should naturally expect to notice after
along period of time the changes thus brought about. We
are perhaps justified in ascribing to the subdivision of this
equatorial belt, into an Indo-Pacific and an Atlantic district,
the marked changes perceptible in the character of the fauna
as regards the genera which date back to the late cretaceous,
and the changes still more marked in the genera which date
from the tertiary period.

How far it is possible for us directly to follow these modifica-
tions, and to trace the transition of the older fauna into the
characteristic West Indian fauna of to-day, is another question.
It involves the necessity of tracing back from the triassic and
jurassic periods the genera which have appeared in succes-
sion ; how far this is practicable I have attempted to show on

THE DEEP-SEA FAUNA. 161

a former occasion.!. The present comparison does not extend
so far.

Thanks to the researches of Professor Duncan on the fossil
corals of the West Indies, we can carry our comparison of the
living corals into the tertiary.

The earlier tertiary fossil corals of the West Indies have but
little specific affinity with existing species, and there is some
difficulty in comparing the two, owing to the varying condi-
tions of preservation in which the fossils are found. This 1s
especially the case in the raised coral beds, which follow the old
shore lines, as indicated by the terraces seen at Barbados and
many other islands of the Caribbean. These contain a limited
number of species of corals generically and specifically identical
with the present West Indian coral fauna. According to Dun-
ean the fossil West Indian corals are related on the one side to
the coral fauna which flourished in the odlite, and on the other
to a fauna, the first appearance of which is uncertain, but which
attained its greatest development in the miocene, and is now
represented in the Pacific Ocean and its associated seas. In
deep water some of the species with Pacific affinities still live.

From the oldest periods the faunz of successive reefs had few
species in common, but genera were most constant and persis-
tent ; and it seems clear that physical conditions which are now
absolutely essential to the formation of coral reefs existed dur-
ing the mesozoic and cainozoic periods. The presence of these
conditions enables us to rebuild the geography of the past, and
to imagine in the time of the trias a succession of larger and
smaller islands far from continents or large rivers, but having
deep and shallow seas, such as we now find in coral areas. The
simplicity of the physical conditions and their continuance
from one age to another seem a natural explanation of the unt-
formity which has evidently prevailed in all coral regions from
the earliest times to the present day.

These conditions offer a ready explanation of the more north-
ern extension of the areas of coral reefs, of their disappearance

1 « Paleontological and Embryological Association for the Advancement of Sci-
Development,” Address at the Boston ence.
Meeting (for 1880) of the American

162 THREE CRUISES OF THE “ BLAKE.”

from the European seas, and of their limitation to those regions
of the African, Indian, Australian, Pacific, and West Indian
seas which most faithfully represent at the present day the con-
ditions which formerly made it possible for coral reefs to thrive
so far to the north as the British Islands. At the same time,
they give a natural explanation of the cosmopolitan nature of
many of the species of older geological periods. I have already
referred to this when speaking of the Echini of the two sides
of Panama. The history of coral reefs forms one of the most
suggestive aids in tracing the persistency of species and types
from the earlier geological times. The identity of some of the
cainozoic deep-sea corals with those now living at great depths
shows us that, with advancing knowledge, the distinctions be-
tween the marine fauna of the miocene and pliocene and the
fauna of to-day are constantly narrowed.

It becomes evident that a large number of the species now
living must have flourished before the important changes in the
physical geography which distinguish the present period from
the later tertiaries had taken place. We recognize the main
outlines of the bathymetrical faunal divisions as clearly as we
trace a tropical, a temperate, and an aretic fauna and flora along
a mountain slope within the limits of the tropics. They con-
sist of a littoral fauna, all light, motion, and heat; a continental
fauna, with superabundance of food and an equable tempera-
ture; and a deep-sea fauna, having a cold, unvaried temperature,
deriving its food largely from pelagic animals and plants. It
is however impossible to determine zones of depths except in
the most general way, because representatives of nearly all the
principal groups characteristic of the deep sea find their way up
to higher levels, and vice versa.

The fauna found at great depths in the ocean is peculiar, and
appears to contain many species of extensive geographical range,
and to be made up of a smaller number of representative species
than is common in areas of lesser depth. We lose the geo-
graphical limits we are accustomed to find in lesser depths, and

1 Oersted was perhaps the first to at- he recognized extended but little beyond
tempt a subdivision of the littoral range low-water mark.
of marine animals and plants. The belts

THE DEEP-SEA FAUNA. 163

meet something analogous to an alpine or arctic fauna and flora
spreading over wide oceanic areas below the continental regions,
without the breaks of continuity caused in similar land faune
by isolated mountain chains.

Hexactinellidz, brachiopods, Pleurotomariz, Spirule, crinoids,
deep-sea corals, Echmothuriz, Ananchytide, Pourtalesiz, Bri-
singe, Elasopodiz, Macruroids, Ophidiude, Willemoesiz, ete.,
are among the most characteristic deep-sea types.’

There is a gradual transition and disappearance of deep-sea
types in the continental and littoral zones, just as vegetation
at the level of the sea passes to that of mountains, and finally
dies out at varying heights at the snow line.

An attempt has been made by Fuchs to prove that the dis-
tribution into littoral, continental, and abyssal zones is not a
natural one, and that there are but two zones, the littoral and
abyssal, the limits of which are well defined, bemg determined
by the depth to which light penetrates. He bases his conclu-
sions on the facts that marine vegetation, which is impossible
without light, and on which so large a number of marine animals
depend, is limited to a shallow depth ; that the coral reefs and
banks of mollusca on which another set of animals depend for
shelter are also confined to a very moderate depth; and, lastly,
that in the tropics the upper limit of the deep-sea fauna is found
in depths of ninety to one hundred fathoms. While I do not
deny that many ancient types to which attention has not yet
been called do occur in shallow depths, and that the upper limit
of many of the deep-sea genera extends into the littoral region
across the continental zone, yet from my own experiences in
dredging at Barbados, along the slope of the Florida Bank, and
in the Gulf of Mexico, I may state that a more abundant fauna
of sponges, gorgonians, echinoderms, crustacea, mollusks, anne-

1 Dr. Norman has given a detailed list
of the species dredged in the Northern
Atlantic on bottom covered by red clay,
and another of the fauna known to live
at greater depths than one thousand fath-
oms. (Presidential Address, Tyneside
Naturalists’ Field Club, May, 1881, Trans.
Nat. Hist. Soe. Northumb., Durham, and

Neweastle-on-Tyne, VIII., Part I.) In
the description of the characteristic deep-
sea animals from the West Indies, the
Gulf of Mexico, and the east coast of the
United States will be found references to
the principal types of the Atlantic abys-
sal fauna.

164 THREE CRUISES OF THE “ BLAKE.”

lids, ete., can hardly be found anywhere, — comprising genera
and species which do not seem to have an extreme bathymetrical
range, but are limited to a somewhat narrow continental belt,
as I have ealied it.

We should remember that, while temperature and light are
important factors in the tropics, the temperature adapted for
deep-sea animals comes nearer to the surface than in the tem-
perate zone. It begins at from three hundred to four hundred
fathoms. In the temperate zone the same temperature is not
found till we reach a depth of six hundred fathoms. In the
polar regions we find the deep-sea forms cropping out far nearer
the surface than either in the tropics or in the temperate zone.
We are not justified in disregarding the effect of temperature
because many species can withstand a considerable range, or be-
cause the same or a similar fauna occurs in distant localities
under different conditions of temperature.

Other causes acting for a long period may have led to the
isolation of the fauna, as in the case of enclosed seas, like the
Mediterranean, the Red Sea, the Sulu Sea, the Caribbean, and
the Gulf of Mexico. Deep-sea forms may gradually have become
accustomed to varying temperatures and thus have acquired a
greater bathymetrical distribution.

Since the temperature of the sea is nearly the same everywhere
in deep water, we have a uniform cosmopolitan fauna, of consid-
erable antiquity, at great depths, corresponding to that of high
isolated peaks or mountain chains. They have preserved down
to our own time the remnants of a former fauna, which may
once have been connected with a fauna at lower levels during
an epoch of ice or of lower temperature.

Wallich speaks of the unchecked migrations along the homo-
thermal sea, and, as subsequent explorations show, the great
submarine folds, like the Dolphin and Challenger ridges, form
no barrier to migration. Except in the case of the Mediter-
ranean and some of the enclosed seas, they do not rise high
enough to reach the belts of higher temperature. In the Gulf
of Mexico and in the Caribbean (the American Mediterranean),
deep-sea forms are found in abundance, extending to upper lim-
its as high as any occurring in the great oceanic basins ; this is

THE DEEP-SEA FAUNA. . 165

owing to the fact that the temperature of the bottom continues
upward along the face of the ridges which separate the Carib-
bean from the Atlantic.

While it cannot be denied that the littoral fauna is largely
influenced by the fact that its inhabitants live within the limits
of the action of the sun, — that is, in the variable limits of
temperature (150 fathoms),—it does not follow that light
alone, which perhaps does not penetrate even to one hundred
fathoms, is the all-important factor regulating distribution.
The action of the waves, of the shore currents, and of the
tides, is only felt in that belt, and must exert a powerful influ-
ence in modifying the habits of many of the littoral animals and
plants.

Species living beyond one hundred fathoms may dwell in total
darkness, and be illuminated at times merely by the movements of
abyssal fishes through the forests of phosphorescent alcyonarians,
and by the feeble light which many of the deep-sea acalephs,
echinoderms, and mollusks emit. Perhaps at those depths as
beautiful effects may take place as attend the phosphorescence
so common in shallow water along a coral reef. The structure
of the organs of vision of the deep-water echinoderms, crus-
tacea, polyps, mollusks, and annelids, differs only in a few cases
from that of their congeners in shallower regions, to which the
direct light of the sun penetrates. Were it not for the phos-
phorescence, we might almost imagine the deep-sea animals
devouring each other without ever having seen their food, and
living for ages under conditions subject to but trifling changes,
while during the same length of time terrestrial modifications of
great importance were taking place.

Many of the deep-sea gasteropods, as well as some of the
fishes and crustacea, are blind. They belong generally to the
more antique types, and the absence of eyes and the presence
of rudimentary organs of sense are compensated by the de-
velopment both in fishes and crustacea of tactile organs of
gigantic size which serve as special organs of sense.’

1 Grimm, in studying the deep-water oped organs of sight, at the same depths
fauna of the Caspian, noticed that, while there were genera in which the eyes are
several of the crustacea have well-devel- atrophied, and other organs of sense re-

166 THREE CRUISES OF THE “ BLAKE.”

A number of the deep-water species have retained habits of
their congeners from shallower waters, which can be of little
use to them. Far beyond the limits to which light is supposed
to reach, we find sea-urchins and ophiurans buried in the mud,
like many of the littoral species. There are quite as many cases
of mimicry among the ophiurans, polyps, crustacea, and annelids
which cling to corals or polyps, and imitate their coloring, as in
the littoral zone, under very dissimilar conditions of existence.

As has been stated before, the deep-sea flora is most limited ;
the more highly organized marine plants cannot, owing to ab-
sence of light, flourish at any considerable depths. Dr. Car-
penter dredged corallines in the Mediterranean at a depth of one
hundred fathoms, and Dr. Duncan has noticed a parasitic fungus
in corals from a depth of one thousand fathoms. He has also
found a lowly organized substance, probably a plant, which bores
into siliceous spicules.

The American land has occupied from the remote huronian
period to the tertiary the same position as at present, the changes
being merely those of relative level between land and sea. Dur-
ing all these changes, there never has been a time when the land
was not a fit resort for the leading forms of life, and the same
is true of the ocean. We may imagine the distribution of land
animals to have taken place from the arctic regions, and that
they reached Australia, Africa, and South America, and there
remained separated. The physical conditions of these regions
were perhaps better adapted to the preservation of the types
now characterizing them than to the production of new types.
So may we imagine that from the Southern Ocean have little
by little been sent forth the deep-sea forms which tend con-
stantly to mix with the modified types farther north. :

That animal life could have been disseminated from the arctic
regions as a centre can readily be conceived if we bear in mind,

ceive a greater development ; as in Ni-
phargus, which has well-developed organs
of smell and of touch on its antenne,
while in Onesimus, with only rudimen-
tary eyes, organs of touch are developed
in its jaws. In Amblyopsis, from the
Mammoth Cave, we note the absence of

eyes, and the extraordinary development
of tactile organs as special organs of
sense. In Chologaster, another cave fish,
frequenting external waters of a subter-
ranean origin, eyes are present, and tac-
tile organs are also developed.

THE DEEP-SEA FAUNA. 167

as has been suggested by Dawson, that there was a time when
the arctic regions had a climate similar to that of some of our
Southern States, like North and South Carolina, and during six
months were subject to the active iyht and heat of an arctic
summer. We may perhaps thus form an idea of the immense
growth and development which animal life must then have
known.

The deep-sea fauna in the track of oceanic currents was
remarkably uniform, and when they changed, new types must
have driven out the old ones. To the action of an equatorial
current flowing without interruption where the Isthmus of Pan-
ama now intervenes, we ascribe the marked generic affinities
found to-day in the deep-sea fauna of both sides of that isth-
mus ; this resemblance of the deep-sea types carries us back to
the cretaceous period when the equatorial current found its way
between the islands of the huge archipelago occupying northern
South America, and a part of Central America and southern
Mexico.

We cannot fail to be struck with the narrow limits of temper-
ature which characterize most distinct faunal regions, nor can
we fail, while speculating on the course of oceanic currents in
former geological periods, to note the simple causes which ex-
plain satisfactorily the migration of an ancient flora and fauna to
totally different realms. We need not seek for cosmic changes,
when such a simple cause as the formation of a barrier to deflect
an oceanic current explains the disappearance of climatic con-
ditions at any given point, and their reappearance in some other
region of the globe.

Since geologists have begun to compare the deposits of past
periods with those of the depths of the sea, as we now know
them, they have seen how impossible it is to establish from fossils
alone the synchronisms of distant beds. The nature of the de-
posits, the distance from shore, in fact, the geographical and
physical conditions of former times, influenced the marine fauna
of past ages as much as that of to-day. There is nothing im-
probable in the synchronism of foraminiferous beds with clay
and shale deposits in which lived faune having nothing in
common, while these beds themselves had a radically different
facies.

168 THREE CRUISES OF THE “ BLAKE.”

A careful study of the facies, of the mode of occurrence of
deep-sea faunee, and of the nature of the bottom as developed
by recent explorations, will assist us in obtaining a clearer idea
of the conditions under which the continental and abyssal de-
posits of past ages, dependent not only on the depth, but on
the character of the bottom, have been made. The existence
of the same species at points remote from one another appear
to indicate a somewhat uniform fauna in deep water, extend-
ing perhaps, with slight modifications, over extensive areas, from
the arctic to the antarctic in both the Atlantic and Pacific
oceans. Yet the localization of certain species was one of the
most characteristic results of the earlier dredging explorations,
and extremely rare animals came up in the dredge by hundreds
in certain localities.

The thousands of specimens of some of the species of echino-
derms, crustacea, polyps, and other invertebrates, which have
been dredged from favorable localities, give us an example of
the localization of species identical with that found in many fos-
siliferous beds of former geological periods. The wide geo-
graphical distribution of other species has been equally well
proved from their occurrence both in the shallow waters of the
arctic region and in deep water in more southern latitudes, but
of course this distribution is dependent to a great degree upon
the character of the bottom.

Some fishes only extend to a depth of five hundred fathoms ;
others take their greatest development below that belt, and many
of them are blind. Below five hundred fathoms we have a large
number of Gadoids, Macruroids, Ophidiide, and fishes with
large eyes, slender bodies, and rudimentary skeletons. Echino-
derms live in masses at considerable depths, and form huge
banks, containing a great variety of forms, similar to those
found in some of the favored localities for fossils in New York
and Towa. |

Species of Echinus, of Brissopsis, of Periaster, of Ophi-
oglypha, of Ophiomusium, and of Ophiozona have been brought
up in countless numbers in the dredge. Pentacrinus forms to-
day, as it did in the jurassic seas, forests of specimens at a depth
of one hundred to one hundred and fifty fathoms. Deep-sea

THE DEEP-SEA FAUNA. 169

corals, solitary forms usually, are often dredged in great num-
bers, and are in striking contrast to the extensive coral reefs of
former geological periods, which resemble those of recent times,
and must have flourished in shallow water under conditions of
temperature analogous to those of the districts in which coral
reefs are found to-day. |

The Echini characteristic of the shallower littoral districts
were formerly, as now, mainly Clypeastridee, while the Echinide,
Cidaridz, Diadematide, and Ccelopleuridz characterized the con-
tinental areas, and the Ananchytide, Pourtalesie, Phormosome,
and Galeritide probably flourished best in deep water.

Lingula may have been from the earliest times a littoral
species, while Terebratula and other brachiopods belonged to
the continental and abyssal regions. Gasteropods are found in
deep water, but are usually of small size. The larger species
seem to have lived, as to-day, in comparatively shallow areas,
though a few, such as Voluta, Dentalium, and Pleurotomaria,
lived in deep water. Of the cephalopods many are pelagic,
others littoral, while Nautilus and Spirula are deep-sea types,
though Verrill has dredged shells of the pelagic argonaut in
deep water. In the older formations the huge cephalopods of
these times were abundant in the littoral regions.

Among the crustacea Eryon-like forms predominate in deep
waters, and gigantic isopods and Pygnogonidz are also found at
great depths. Accumulations of terrestrial animals and plants
driven out to sea by the winds and currents may likewise find
their way to deep-sea deposits.

The remains of pelagic animals, often occurring in great
numbers, do not always indicate an oceanic deposit, as they may
after their death be taken by the winds and currents far from
their habitat, and be carried considerable distances by fishes.
The shell of Spirula is found on all tropical beaches. We find
immense accumulations of pelagic animals, as well as of the
dead carcasses of squids, driven ashore in quantities by storms
or caught by the tides. The mortality among fishes is often
very great; large shoals are hunted to the shore by predatory
species and sharks, and our beaches are not unfrequently lined
for long distances with fishes which have perished from sudden
unknown causes.

170 THREE CRUISES OF THE “ BLAKE.”

On the character of the bottom upon which these animals die
will depend the chance of their being preserved, and while the
accumulations of dead limestone carcasses may go on indefi-
nitely at a depth of one hundred to one hundred and fifty fath-
oms, the same mollusks, when thrown upon rocks, or upon a
gravelly or sandy beach which is exposed to a greater or less
action of the sea, would soon be reduced to an impalpable
powder, and be unrecognizable.

The fine muds and ooze deposited at considerable distances
from shore form beds admirably adapted for the preservation
of the most delicate pelagic or deep-sea types which may hap-
pen to become imbedded in them. ‘The coarser sands and
pebbles may form a conglomerate, in which the firmer kinds of
invertebrates will occasionally be partially preserved.

When the deposition of a deep-sea mud is rapid, the form of
the body of fishes and the soft part of mollusks is often re-
tained, but in littoral flats, where large quantities of gas are
evolved, and the decomposition of animal matter takes place
rapidly, few well-preserved fossils will be found.

IX.

THE PELAGIC FAUNA AND FLORA.

Tue pelagic fauna is made up of very distinct factors. It
contains many animals which pass their whole life as wanderers
on or near the surface, — probably within a couple of hundred
fathoms, — where they drift helplessly at the mercy of the
winds and waves and currents. While there are stretches
of the sea along the line ‘of currents, as, for instance, the
course of the Gulf Stream, where the pelagic fauna is more
abundant than in other marine regions, there seems to be
no portion of the sea from which it is totally absent. The
pelagic fauna proper includes representatives of all classes of
the animal kingdom, though usually these are of smaller size
than their allies on or near the continental shores and beaches.
The majority of them are noted for the greater or less trans-
parency of their bodies, while their coloring is generally har-
monious with that of the surrounding sea. Pale, bluish, and
translucent colors characterize the majority of the pelagic ani-
mals that live during the day upon the surface of the water.
Such are, for instance, the violet or blue tints of the transpar-
ent acalephs and siphonophores; those of the Janthina, which
its name describes, of the glassy heteropods and pteropods, and
of the iridescent ctenophores, which seem, when touched by the
sun, like rambow fragments floating in the water.

The brilliant Sapphirina, the red Daphnia and globigerina,
the pinkish or bluish Salpa, are often seen in such masses that
they discolor the water for miles, and make the ocean like a sea
of milk. By daylight, only the practised eye detects the sep-
arate forms which, from their number and delicate texture, melt
into each other. But at night the scene changes. The greater
number of the pelagic animals are brilliantly phosphorescent ;

172 THREE CRUISES OF THE ““BLAKE.”

and when the sea is calm and the circumstances are favorable,
these animals are individualized by the greenish, golden, or sil-

Fig. 63.— Arach-
nactis, Embryo of
Edwardsia. 1).

F ig. 64 a. — Strongylocentro-
tus Pluteus. Greatly mag-
nified.

Fig. 64. — Asteracanthion Pluteus.
Greatly magnified.

Fig. 66. —- Littorina Embryo.
16

iv

Hii —= sai)

Fig. 65. — Cyphonautes, Embryo of
Bryozodn. Greatly magnified.

a

Fig. 67. — Embryo of Loligo. 22.

very light which betrays their presence, and defines their out-
lines, while it illuminates the sea itself. On tempestuous nights,
the phosphorescence, intensified by the motion of the water, adds

THE PELAGIC FAUNA AND FLORA. 173

singularly to the wildness of the scene. Each wave rises like
a mass of molten iron, and seems to threaten the vessel with

Fig. 68. — Tornaria.
Greatly magnified.

. Fig. 69.— Pilidium. Greatly
magnified.

\ i
Fig. 72. — Dactylopus Larva. Greatly magnified.

Spelt ‘

["y
Her
va reo

way
bbb

i

‘ : SRS
Fig. 70. — Leucodora Larva. Fig. 71. — Polygordius
Greatly magnified. Larva. 22.

destruction ; it breaks, then passes off in her trail, and adds new
beauty to her brilliant wake. In this general illumination,

174 THREE CRUISES OF THE “ BLAKE.”

however, it is easy to distinguish the different forms. The
huge ctenophores float by, like luminous balls, among the
myriad lesser lights caused by the smaller jelly-fish, while the

ow

~

(Rares es Ss
| a If
f Sf) o\\ :
af)
|
Fig. 73. — Balanus Larva. Greatly
magnified.

Fig. 74. —Squilla Embryo. 1.

Fig. 75. — Pagurus Larva. Fig. 76. — Peneus Embryo.
Greatly magnified. Greatly magnified.

Physalia resemble fire-balloons on the surface, and spread the
phosphorescence in all directions.

THE PELAGIC FAUNA AND FLORA. 175

Near the continental lines the pelagic fauna is reinforced by
numberless pelagic embryos, representing nearly every type of
marine animal. The polyps (Fig. 63), acalephs, echinoderms
(Figs. 64, 64a), mollusks (Figs. 65, 66, 67), and articulates (Figs.
63, 69, 70, 71, 72, 73, 74, 75, 76), of our coasts, although living
upon the bottom and on the shores when adult, yet pass a por-
tion of their earlier life as pelagic forms. The larve and young
of many of these types swarm during the breeding season, and
often find their way to a considerable distance from the shore.
With them are associated the eggs (Fig. 77) and embryos of
a number of our migratory and shore fishes. The
study of all this pelagic life is very recent. There
are many types of which the Life history is un-
known, so that it is often difficult to determine
whether an animal is merely the young of some | ~~

: : Fig. 77. — Pe-
well-known littoral form or a true pelagic type. _ lagic Fish Egg.
Indeed, many of these free-swimming animals, de- si)
scribed at first as strictly pelagic, have subsequently proved to
be only embryonic stages of well-known species.

ees
MNO OIE
S KNAAD

i f

INI
WANA AN EYY
S

ne ow
es ==

N : AO

NASA

ea
| ne

Fig. 78. — Plagusia. #4.

It is probable that among the larval forms of many pelagic
animals there is, under certain conditions, a retardation of de-
velopment similar to that known among batrachians. The
larval stage continues in Plagusia (Fig. 78) and Phyllosoma
long after the time when the embryo should have passed into
Rhombodichthys (Fig. 79) and Palinurus. Leptocephalus is

176 THREE CRUISES OF THE “ BLAKE.”

undoubtedly the larval form of some littoral or deep-sea genus,
which, like Amblystoma, has
not reached its adult condi-
tion, and, if subject to unfa-
vorable influences, continues
to increase in size as long as
it remains pelagic.

The great development of
the organs of sense and of lo-
comotion is a striking feature, which pelagic types share in com-
mon with the embryonic stages of many littoral marine animals.
It is true not only of the pelagic crustacea and annelids, but even
of certain vertebrate embryos, in which the organs of sense are
developed out of all proportion to the size of the embryo.
Compare, for instance, the size of the eyes, of the brain, and of
the dorsal chord, in the young stages (Fig. 80), with their ulti-

: =) Ssiss SS
YL
qu

Fig. 79. — Rhombodichthys (Plagusia). ° 4.

Fig. 80.— Embryo Fish, with Lateral Organs. 49.

‘mate proportions in the full-grown fish. Or, as another in-
stance, take the Phronima (Fig. 81), which, not satisfied with a
set of eyes enabling it to see both laterally and downward, has

Fig. 81.— Phronima. #.

also an immense pair facing dorsally, so that the animal has a
free field of vision in all directions.
The lateral or cephalic sense-organs of some pelagic fishes

THE PELAGIC FAUNA AND FLORA. et

are also sometimes brilliantly phosphorescent. The lateral or-
gans, though they are prominent in the young, disappear or be-
come atrophied in the adult. We can indeed say, with truth,
that many of the young fishes, soon after they escape from
the egg, are only bundles of nerves, ready to be acted upon by
every influence of light, heat, or motion.

< GG Ss
SSCL EES

Fig. 82.—Leptocephalus. 32.

The range of vision of a Plagusia, a thin, transparent pelagic
flounder, or of Leptocephalus (Fig. 82), a long, narrow, trans-
parent tape-like fish, is very great. In the case of the former,
it is really comical to see either eye winking at you through the
transparent head. The same disproportion exists between the
gigantic eyes of zoez and other embryo crustaceans, and those
of the adult ; nor is the difference less between the size of the
organs of sense in embryo acalephs, echinoderms, mollusks, or
annelids, and that of the same organs in the adult.

The pelagic animals do not come to the surface at all times.
The day fauna is seen at its best only when the sea is smooth
and the sun bright. The least ripple on the surface, or the
retreat of the sun, is enough to send the more delicate animals
into deeper water, beyond the reach of such disturbances. At
night again, calm, smooth weather is essential to the many noc-
turnal animals which come to the surface only in the hours of
darkness and disappear with the dawn. It is true, that occa-
sionally a tempestuous night brings out the phosphorescence,
but this is rare.

Many of the pelagic animals undoubtedly smk during the
day some distance below the surface, in order to escape the
intense sunlight. The young of some discophores come to
the surface only early in the morning, soon after sunrise.

Some acalephs, like Tima, Zygodactyla, and Staurophora, are
very abundant before ten in the morning, while the Polyclonia,
(Fig. 83), both old and young, swim about either early in the
morning, or late in the afternoon, or during the night; they

178 THREE CRUISES OF THE “ BLAKE.”

generally pass the day resting upon the bottom, with their ten-
tacles turned upwards, the disc pulsating slowly while at rest.
The young are far more active than the adult, which, when thus
half buried in coral mud, resemble huge actinie with fringed
tentacular lobes (Phytactis) fully expanded.

Fig. 83. — Polyclonia frondosa. 4. (Agassiz.)

How far down the pelagic fauna sinks during the day or night
to get out of reach of disturbances is not yet accurately known ;
we can only form a rough guess from the few experiments made
on the “ Blake,” to be found farther on. The lowest point is
probably not far from one hundred and fifty fathoms, which is

\\ \ tat -
WAG AW \\\ ANH

{

Fig. 84.— Copepod. Greatly magnified.

perhaps the limit also of the greater superficial disturbances of
heat, ight, and motion within which we may imagine the pela-
gic fauna to oscillate.

THE PELAGIC FAUNA AND FLORA. 179

The customary method of collecting these pelagic animals
from the surface is by means of a tow-net, dragged behind a
boat as it moves slowly through the water, or hung from the
sides of the steamer in any weather which allows the handling
of a trawl or dredge. The contents of the net are emptied
into glass jars, and carefully examined. The larger speci-
mens of fishes, of annelids, of crustaceans, of mollusks, and
of ceelenterates, visible to the naked eye, are of course in
better condition when collected with a hand-net. The smaller
fry alone survive the
packing which they : \,
get at the bottom of \| AWWA
the tow-net. Fre- Sa
quent examination of ~~
the net is important in order to “|
obtain in proper condition the =
more delicate pelagic animals. In =
many cases the contents of the
tow-net consist chiefly of pelagic
crustacea, among which the pro-
minent types are the Calani and
other pelagic copepods. (Fig.
84.) The many species,of Mysis
(Fig. 85), regular tramps of the
sea, are with the Calani the great
marauders of the pelagic fauna,
attacking at once any of the
larger animals which show the Ay tt
least signs of decay.’ 3

UE ee

Fig. 85. — Mysis. 4.

1 Around our coasts and in the Gulf of Mexico and the Caribbean, sma}! Hemi-
ptera (Halobates) (Fig. 123) are not
unfrequently met, skimming over the
surface at a considerable distance from
the coast. The larva of a species of
fly (Chironomus) is quite common off
shore from our northern coasts. The
“Challenger” found the pelagic Ha-
lobates very abundant in certain regions -_ ——
of the Pacific. Fig. 123. — Halobates wiillerstorffi.

8. (Chall.)

wat

180 THREE CRUISES OF THE “ BLAKE.”

Eminently characteristic of the Gulf Stream, and wherever its
influence extends, Porpite (Fig. 86), Velelle, Physalie (Fig.
87), and floating barnacles (Fig. 88) have been found. In

Pieri

pry aiGy
me

Fig. 86.—Porpita. #.

fact, these surface animals are excellent guides to the course of
the current of the Gulf Stream, — natural current bottles, as it

were.!

1 During the voyage of the “Chal-
lenger,”’ observations were made addi-
tional to those mentioned by Lyell upon
the transportation of seeds by fruit-pi-
geons ; and in the Botany of the “Chal-
lenger ” Expedition (Chall. Ex., Bot.,
Part IIL., p. 277 et seq., 1885), there is
an interesting Appendix on the dispersal
of plants by oceanic currents and birds.

They are thrown up along the whole length of the

Robert Brown, Chamisso, Darwin, and the
French botanists attached to the “ Ura-
nie,” paid considerable attention to the
plants they found scattered on the shores
of many of the islands in the Pacific.
Moseley describes the masses of drift-
wood met with by the “Challenger” off
New Guinea, about seventy-five miles
northeast of Point d’Urville. I have my-

THE PELAGIC FAUNA AND FLORA.

Atlantic coast of the
United States, from the
Straits of Florida to the
south shores of Cape Cod
and Nantucket. Physa-
ha, Velella, and Porpita
are occasionally driven
into Narragansett Bay ;
the first is an annual vis-
itant, the last has only
been found once, in
1875, and Velella has
come into Newport har-
bor during three sum-
mers. It is undoubted-
ly also to the action of
the Gulf Stream that
we must ascribe the pre-
sence of the few species
of siphonophores which
appear on the southern
coast of New England
towards the middle and
last of September, such
as Eudoxia, Epibulia, and
Diplophysa, which are
found at the Tortugas.
Agalma (Fig. 89) and

Nanomya, on the con-

self seen on the weather shores
of Miui masses of huge Oregon
pine logs. On’some of the Sand-
wich Islands there are great ac-
cumulations of such masses of
drift-wood, probably brought
from the northwest coast of the
United States. Sloane, in 1696,
recognized as coming from Ja-
maica beans and fruits cast upon
the shores of the Orkneys.

|
a

. Fig. 87. — Physalia eae

1

3°

( Agassiz.)

182 THREE CRUISES OF THE ‘“ BLAKE.”

> > 6

EES
ee

of Sm)

cs

o>
Jess

Cm

SK
s

aA
~ oe
base)
Te

<<

rp

~ Ke)

Fig. 89. ear elegans. 3. (Fewkes.)

trary, are northern visitants at Newport, brought down by the
arctic shore current from the northern side of Cape Cod, Agalma
being common at Eastport. Other species of our southern New

THE PELAGIC FAUNA AND FLORA. 183

England meduse, such as Cunina (Fig. 90), Eutima, Trachy-
nema, Kucheilota, Liriope, Zanclea, and many other species
which have been described by McCrady from Charleston, 8. C.,
are also brought north every year along the course of the Gulf
Stream, and during the summer are blown to the westward
towards the New England coast and the Atlantic coast of the
Middle States by the prevailing southwesterly winds.

The common green turtle of Florida is caught every year in
Narragansett Bay, and the leather-back turtle (Sphargis) has
been caught as far north as Massachusetts Bay.

Fig. 91. — Velella mutica. 7.

Velella (Fig. 91) is found in large numbers in the Straits
of Florida, between Cuba and the Florida reefs. Thousands
of this animal are brought by favorable winds and tides into
Key West harbor, and are carried by the same agencies be-
tween the Tortugas channels. They are usually seen in large
schools, and, although capable in a smooth sea of independent
movement by means of their tentacles, are practically at the
mercy of the winds and currents. They are destroyed in im-
mense numbers by even moderate waves, which upset them,
-drive them ashore, or kill them, if kept below the surface for
any length of time. They apparently need a good deal of
movement, for when kept in confinement they do not thrive,
soon die, and are rapidly decomposed. The dead floats are
thrown upon the beach behind Fort Jefferson at the Tortugas

184 THREE CRUISES OF THE “ BLAKE.”

in great numbers, forming regular windrows, and, when dry, are
blown by the winds to the highest parts of
the beach.

Some of the structural features of the
Porpitidee indicate affinities with acalephian
corals like the Milleporide, which date back
to the cretaceous, but their general homo-
logies ally them most closely with the tu-
bularian hydroids of to-day. Among the
finest siphonophores is a large Stephanomia,
with its bells arranged in many vertical
rows.

One of the most interesting siphono-
\ phores is Pterophysa grandis. (Fig. 92.)
9 Of this species, which grows to a large
! size, huge specimens measuring no less than
=, thirty feet, often came up on our dredge-

‘\\ wire in the Gulf of Mexico and the Carib-

y¥ bean. It is closely allied to those which
| Studer, the naturalist
of the “ Gazelle,” re-
gards as strictly deep-
sea siphonophores. The
@ polypite of large speci-
Jmens often measured
two to three inches.

Pterophysa and other
siphonophores have the
power of sinking and
then swimming back to
the surface, but neither
Velella nor Porpita ap-
pears eapable of such
movements. A very
young Physalia, col
lected at the Tortugas,
was observed to swim at
different levels in the jar in which it was kept.

Fig. 92. —Pterophysa grandis. *z)y. (Fewkes.)

THE PELAGIC FAUNA AND FLORA. 185

Studer gives a list of the depths from which Rhizophysa came
up attached to the sounding-line ; but it is by no means certain
that these siphonophores belonged in the depths indicated by
the wire. They may have become caught on the wire while it
was reeling in at only a short distance from the surface." The
fact that Studer never succeeded in bringing up any of these
species in the tow-net, even when it was lowered to a consider-
able depth, is equally inconclusive, since, at any rate in the Ca-
ribbean Sea, their isolated parts and fragments are not infre-
quently found floating on the surface. It is probable that they
usually live at a constant depth below the surface, and some of
them may, like Polyclonia, prefer to dwell near the bottom.
But until we possess a net so constructed as to give some sure
indication of the intermediate depths at which the animals living
at various distances between the surface and bottom have been
gathered in, it seems hazardous to define the bathymetrical range
of a large number of pelagic animals, such as the acalephs,
siphonophores, heteropods, pteropods, numerous foraminifera,
radiolaria, and the like, the habits of which are scarcely
known.

In the case of fishes, dredged in deep water at a moderate
distance from the land, we ought not to take it for granted that
they invariaby live at the depth to which the trawl may have
been lowered. The young of many of the deep-water fishes are
undoubtedly pelagic, often till a late period of growth, and this
would account for the discovery of many of the deep-water
fishes, especially in the proximity of oceanic islands or around
coasts situated near deep water.

Of the acalephs, the greater number of the ctenophores, many
of the discophores and a few sertularians, are pelagic; the ma-
jority of the hydroids and some of the discophores are pelagic
only during a period of their existence, and remain the rest of
the time attached to the bottom; as fixed hydroids, they extend
into deep water. A number of families of discophores are

1 In one case, when we were dredging wire! On another occasion, the same
in one thousand fathoms, numerous frag- species came up after we had drawn in
ments of a Rhizophysa came up after we three hundred fathoms, while dredging in
had drawn in one hundred fathoms of five hundred fathoms.

186 THREE CRUISES OF THE ‘‘ BLAKE.”

characteristic inhabitants of deep water, though they come to
the surface occasionally.

Nearly all the ctenophores are found
in swarms, which cover the surface
for long distances. Schools of dis-
cophores are not uncommon. I have
frequently met Cyanee and Aureliz
in such quantities that they appeared
at a distance like huge sand-banks,
just rising to the surface of the water.
Occurring in windrows along the whole length of the Florida

Reef is a small yellowish brown discophore (Fig. 93) (Linerges

Fig. 93. — Linerges mercurius. 3.

Fig. 95. — Fourth Stage.
Glossocodon Larva.

Greatly magnified.

a ae Fig. 96. — Sixth Stage.
ae Nat Glossocodon Larva.
Fig. 94. — Glossocodon tenuirostris. Magnified. Greatly magnified.
mercurius), which looks like a thimble ; it is one of the most

common of the West Indian medusez, and is remarkable for the

Fig. 97. — Janthina.
Slightly reduced.

Fig. 98.— Glaucus. Enlarged.

THE PELAGIC FAUNA AND FLORA. 187

pouches, bag-like expansions of the lower floor of the bell, which
hang down into the bell cavity. Among the more interesting
hydroids may also be mentioned a species of Glossocodon (Fig. ;
94), noticeable for the changes it undergoes during growth.
(Figs. 95, 96.)

Of the surface mollusks of the Gulf Stream, Janthina (Fig.
97) is very common, and is often seen in large numbers,
helplessly carried along by the current with the dark blue
Glaucus. (Fig. 98.) Durimg the day an occasional pteropod
is seen; but at night no cast of the tow-net is made without

Fig. 99.
Hyalea. 2.

Fig. 100.— Atlanta. 1).

bringing them up in numbers. Characteristic of the Gulf
Stream are Hyalea (Fig. 99), which, like the more common
Atlanta (Fig. 100), Styliola (Fig. 101), Pleuropus (Fig. 102),
and Tiedemannia (Fig. 105), find their way far north to the
shores of Narragansett Bay and southern New England; while
among the more common types of the Straits of Florida and
of the Gulf of Mexico are Salpa, Doliolum (Figs. 104-106),
Pyrosoma (Fig. 107), and Appendicularia (Figs. 108, 109),
all belonging to types of which individuals collect frequently
in such numbers as to fill the ocean as far as the eye can
penetrate, reaching out for miles in all directions. Salpe, as
has been shown by Moseley, sink rapidly to the bottom (two
thousand fathoms in two days) where they die; and their dead
bodies, as well as the mass of dead pteropods, heteropods, crus-

188 THREE CRUISES OF THE “ BLAKE.”

tacea, and foraminifera, must form an important element in

roa

Fig. 102.— Pleuropus.

Fig. 101.—Styliola. ?- Fig. 103.— Tiedemannia. 4.

the food of the sedentary deep-sea species, as they must reach

the bottom long before they are decomposed

GE eS
Aaa ==

14
i
l

SSS ———

Fig. 105.—Doliolum. ?.

THE PELAGIC FAUNA AND FLORA. 189

Among the tunicates I may mention two new species of
Salpz, one of which is interesting, since its chain occupies an

Fig. 106.— Doliolum. 4.

intermediate position between that of Salpa pinnata and the
ordinary Salpa chain of S.-zonaria or S. Caboti of our coast.

Fig. 109. — Appen-
dicularia House.
Greatly magnified.

Fig. 107.— Pyrosoma. }-

Fig. 108. — Appendicularia. Greatly

magnified.
The solitary individuals are gigantic specimens, measuring no
less than twelve inches in length. This solitary form is closely
allied to S. maxima, but differs
from it in the number and ar-
rangement of the muscular
bands. The chains grow to a
great length, some of them mea~ gy. 110, —Salpa Cabot
suring more than ten feet and Forme, 7).
as much as nine inches in breadth. The zoéids are placed as

Solitary

190 ‘THREE CRUISES OF THE “ BLAKE.”

in S. pinnata, side by side in a single row, stretching vertically
across the whole width of the chain, and forming a thin ribbon,
which when floating is usually slightly coiled like
a tape. The zodids of the chain resemble S. Afri-
cana. This species was found from Cape Hatteras
as far north as the eastern extremity of George’s
Shoal.

The sudden arrival of innumerable Salpe on
our coast is most interesting. It is not unfrequent
for the northern species of Salpa (Figs. 110, 111),
so common along the eastern coast from Cape
Hatteras to Cape Cod, to make its appearance in a
single night in such masses as to discolor the sea
for miles near the entrance of Narragansett Bay,
and to remain swarming: for a couple of months,
when it disappears as quickly and mysteriously as
it came. The explanation of this sudden imroad
is probably due to the fact, that durimg the time
they are sterile the solitary individuals remain at
some distance below the surface, but when they
begin to bud and form the chains they come near
the surface. It is easy to explain their abundance
then by the rapid development of the young
chains, which are formed, thrown off, and increase
in size with extraordinary rapidity.

The pteropods and heteropods are by
far the most common pelagic forms of the
“aN aN mollusca, the dead tests of the former be-

Ne ing literally heaped up in beds on the
es) \\ bottom of the sea in deep water. The

¥ \\)
BE dredge often came up completely choked
G i) with pteropod shells, showing what an

Az important part they play in building up
. the deep-sea deposits by the decomposi-
Fig. 111.—Salpa Caboti, “98 of their tests. In former geological
Chain, somewhat enlarged. periods, when there were gasteropods

allied to pteropods like Bellerophon, of gigantic size, their

effect in forming bottom accumulations must have been still

THE PELAGIC FAUNA AND FLORA. 191

greater. Indeed, if their habits were similar to those of like
animals at the present day, they must have supplied a large part
of the animal food of deep-sea forms. The heteropods are rep-
resented by abundant specimens of Firoloidea (Fig. 112), many
fully sixteen inches long, associated with Pterotrachea; Carina-
ria is also frequently seen.

We know only enough of the habits of our cephalopods to
be able to state that some of the species, like Stenoteuthis,

Fig. 112.— Firoloidea. 4.

Stauroteuthis, and the giant squids of Newfoundland, are un-
doubtedly pelagic at times, although the majority of the spe-
cies known to come from our coast have been dredged from
considerable depths. Many of the cephalopods have great

on
Fig. 114.—Spirula
Peroni. 1.

Sek
Fig. 115. — Argonauta.
2. (Verrill.)

Fig. 113. —Argonauta. %. (Verrill.)

freedom of locomotion, and equal fishes in their migrations,
often moving in schools. But it will always be difficult to fix

192 THREE CRUISES OF THE ‘“ BLAKE.”

the bathymetrical range of free-swimming animals like these.
Argonauta (Fig. 115) has been known for a long time to be

aS WER
Fig. 116.—Sagitta. <i Sa
pelagic, while nautilus, though seen at the surface occasionally,

is probably a deep-sea type. Spirula has been dredged from
deep water by the “Challenger” and “Blake,” while French

Fig. 117. = Tomopteris. 3.

collectors have observed it swimming in numbers at the sur-
face in the Indian Ocean. The shells of Spirula (Fig. 114) are

common on all tropical shores, while the shells of Argonauta

THE PELAGIC FAUNA AND FLORA. 193

(Fig. 115), though not uncommon in deep waters, are more
rarely thrown up on beaches. Professor Giglioli has dredged
them in the Mediterranean, and they have been dredged east of
Long Island by the United States Fish Commission.

One of the most characteristic of the Atlantic pelagic types 1s
Sagitta (Fig. 116); as its name implies, it darts through the
water in search of its minute prey, which it seizes with its
gigantic jaws. Other worms, like Autolytus and Nereis, are
at times pelagic, while the large-eyed Argyope and the trans-
parent Tomopteris (Fig. 117) are constant attendants of the
surface fauna. Of crustacea there are a host of minute pre-
datory forms, — Calanus, Mysis, Nebalia (Fig. 118), etc.,—
regular scavengers of the surface,
and thousands of copepods, the main
object of whose existence seems to
be to keep themselves on hand as
food for the larger pelagic types
of crustacea, like Kuphausia and its
allies. We have certain forms of
pelagic fishes, the transparent Plagu-
siz, Leptocephali, and the like, some
species of which are only the young
of deep-sea forms. Pelagic species
of fishes often attain a large size,
such as the thunny, horse-mackerel, sword-fish, Orthagoriscus,
Coryphzna, Histriophorus, and others. The group of flying-
fishes is a true pelagic type, to which we might add some of
the migratory fishes, as the clupeoids and scombroids. Many
of the large types of sharks like the thrasher, basking shark,
and mackerel shark, are pelagic, and are met with at great dis-
tances from the coast. The skates, on the contrary, are nearly
all deep-water types, though they are occasionally seen hunting
near the surface. Finally, of the mammals, the whales, dol-
phins, and porpoises, dancing attendance on ships far out at sea,
complete our general enumeration of the pelagic types.

Among the more minute types are the graceful globigerine,
with their delicate arms, appearing like scarlet dots on the sur-
face of the sea. These swarm on warm, calm days. I had an

Fig. 118.— Nebalia. 4.

194 THREE CRUISES OF THE “ BLAKE.”’

Fig. 119. — Globigerina bulloides. 13°. (Challenger-.)

excellent opportunity of seeing a number of Globigerine (Fig.
119) and Orbulinz’ alive on one occasion to the westward of

1 The genetic connection, if there be gether, is not known. It may be a case
any, between Orbulina and Globigerina, of dimorphism. See chapter on Rhizo-
which are always found associated to- pods, vol. ii.

THE PELAGIC FAUNA AND FLORA. 195
‘

the Tortugas, where numerous patches of them gave a reddish
color to the sea.

The siliceous types of Polycistine (Fig. 120), so common in
former geological times in the West Indies, form an extensive
deposit at the Barbados,’ near the highest part of the island,
are now found but rarely in the Atlantic. A few types of the

Fig. 120. — Pterocanium charvbdeum. Highly
magnified. (Miiller.) Fig. 122. —Spherozoum. 12.

Thalassicole (Fig. 121), and Acanthometride, as well as of
such forms as Collozoum and Spherozoum (Fig. 122), are, how-
ever, quite common in the Gulf of Mexico and Caribbean, and
during the summer come as far north as the larger pelagic
animals. Siliceous radiolarians are quite common in the tropi-
cal regions of the Pacific.

While many of the foraminifera, like Globigerina and Has-

1 Nummulitic beds occur in Thibet at a height of sixteen thousand feet.

196 THREE CRUISES OF THE “ BLAKE.”

tigerina (Fig. 124), are pelagic, there is a host of other are-
| naceous forms, perhaps
the majority of the fora-
minifera, which certainly
live at the bottom. Both
the pelagic and bottom spe-
cies form a most impor-
tant factor in the food sup-
ply of the abyssal fauna.
The modern greensand
found along the edge of
the Gulf Stream proves
that multitudes of dead
tests constantly drop
from the surface, and
when they reach bottom,
they still contain a suf-
Fig. 124. — Hastigerina pelagica. 35. ficient amount of sarcode
ceca, to make an excellent meal
for some abyssal echinoderms. The species that live on the
bottom, and in some localities must thickly cover its surface,
afford excellent feeding-grounds for the dwellers of these
depths. With the thousands of radiolarians and other pelagic
globigerinze occur minute protozoa, their capacity for floating
being increased by the huge spines or extensile pseudopodia
which they stretch out in every direction. The depth at which
so-called pelagic foraminifera have been found depends upon
the fact that, during rough weather or under unsuitable cir-
cumstances, they sink to a considerable depth, and, while they
would strictly come within the definition of pelagic animals,
they may thus frequently be found living apparently on the
bottom.

One of the most common of the pelagic protozoa is a spe-
cies of the genus Noctiluca. (Fig. 125.) On favorable nights
it forms a thin sheet of phosphorescence, as it were, spread
over the sea. The tow-net, when dragged during the night,
reveals the phosphorescent color characteristic of different
groups, and one who is accustomed to such nocturnal pelagic

THE PELAGIC FAUNA AND FLORA. 197

fishing soon learns to know what kind of harvest his night’s
Bias will give him from the coloring of the oa apes
cence he sees passing into his
net.

As we lift our net from the
water, heavy rills of molten metal
seem to flow down its sides, and
collect in a glowing mass at the
bottom. The jelly-fishes, spark-
ling and brilliant in the sunshine,
have a still lovelier hight of their
own at night. They send out a
greenish golden light, as lustrous
as that of the brightest glow-worm, and on a calm summer night
the water, if you but dip your hand into it, breaks into shining
drops beneath your touch. It would seem that the term “rills of
molten metal” could hardly apply to anything so impalpable as
a jelly-fish (Figs. 126, 127), but their gelatinous discs give them

Fig. 125. — Noctiluca. Magnified.

Fig. 126. — Eucope diaphana. $. Fig. 127.— Lizzia grata. Magnified.

weight and substance, and when their transparency is not per-
ceived, and their whole mass is aglow with phosphorescent
light, they have an appearance of solidity which is most strik-
ing when they are lifted out of the water and flow down
the sides of the net. The larger acalephs bring with them a
dim spreading halo of light, and look lke pale phantoms wan-
dering about far below the surface; the smaller ctenophores
become little shining spheres, while a thousand lesser creatures
add their tiny lamps to the illumination of the ocean.

All this phosphorescence is seen to greatest advantage on a

198 THREE CRUISES OF THE “ BLAKE.”

dark night, when the motion of the vessel sets the sea on fire
around one. At such times there is something wild and weird in
the whole scene, which at once fascinates and appalls the imagi-
nation ; one seems to be rocking above a volcano, for the sea
is intensely black, except where fitful flashes or broad waves
of light break from the water under the motion of the vessel.
The sea may be black as ink, with the crests of the waves
breaking heavily and surrounding one with walls of fire in all
directions.

To Professor Panceri we owe the fullest investigations as yet
made into the causes of marme phosphorescence. The phospho-
rescence is limited to portions of the exterior of the animal; or
is connected with special organs, — sometimes with the gener-
ative organs; or it may take place wherever tissues change rap-
idly. But as this power of emitting phosphorescence seems
to be always produced by an external irritation, it may be, as
has been suggested by Studer, that the phosphorescence serves
as a protection for the animal.

The Pyrosomz, which form so essential a feature in the phos-
phorescence of the Indian Ocean, are not common in the Carib-
bean or Gulf of Mexico. The specimens we saw in the track
of the “ Blake” were diminutive in comparison with those huge
fire cylinders, often more than a foot in length, described by
naturalists who have sailed through the Indian seas. On the
other hand, we found a Salpa colony far exceeding in size those
before known, —a huge band, several yards in length and a
foot in breadth, which at night, when seen from the deck,
seemed like a huge veil of bright greenish phosphorescence.
One of the smaller kinds of Salpe gives out generally a bluish
light.

The pelagic fauna of the Eastern Caribbean is, during the
winter season, rather scanty. Owing to the constant agitation
of the water, I had no opportunity, as in the Gulf of Mexico,
of making much use of the tow-net. From the number of
fragments constantly found, siphonophores must be very nu-
merous. In the roadstead under the lee of the islands there is
little pelagic life. Everything either remains at a short dis-
tance below the surface, or is blown away to seaward of the

THE PELAGIC FAUNA AND FLORA. 199

islands. The phosphorescence, in consequence, is far less bril-
liant than in the Gulf of Mexico, although occasionally masses of
ctenophores (a species of Mnemiopsis) (Fig. 128), swimming at
different depths, produce a very striking illumination; sudden
flashes of light appear, as if from great balls of fire floating
a short distance below the surface. :

The most surprising phosphorescent
phenomena were produced by a
small annelid allied to Syllis which
we found in Petite Baie d’Arlet.
Just after dark, the bay was cov-
ered for a time with hundreds of
phosphorescent spots gliding slowly
about, when suddenly a number of
them began to move actively, per-
forming the most remarkable gy-
rations. Soon the whole bay was
traversed by brilliant phosphorescent
trains, made up of small particles of ek
light, which remained refulgent for Fig. 128. — Mnemiopsis. Leidyi.
a while, so that the track, winding ho on cnnte
swiftly in and out, backwards and forwards, could be distinctly
made out till the light became exhausted. After a period of
rest the process was repeated. Several deep-water species of
Gorgonia and Antipathes (especially Riisea) showed a_ bright
bluish phosphorescence when coming up in the trawl. An
ophiuran also, like one of the Mediterranean species men-
tioned by Panceri, was exceedingly phosphorescent, emitting
at the joints along the whole length of its arms a bright bluish-
green light. Among the deep-sea fishes certain parts, either
lateral organs or specialized parts of the head, are highly phos-
phorescent.

It is interesting to note that Professor Forel, who has studied
the habits of the pelagic fauna of the large Swiss lakes, finds
that, like the marine pelagic fauna, the animals marked for
their transparency, especially the crustacea, sink to small depths
during the day and come up at night, to feed upon the pelagic
alow.

Thies itt
en!
ny pers Pe,

X
. BOT
tay
se
LO eee OT ; AA
TRYTSCCEAEACEERETT tea ‘i
—<—= eid|
oy

eseurrannccenmeneare

200 THREE CRUISES OF THE “ BLAKE.”

I made no attempts to use the tow-net to ascertain the pre-
sence of foraminifera, radiolaria, or other pelagic animals, at a
distance from the surface. All naturalists familiar with the use
of the dip-net, the tow-net, or with their modifications first em-
ployed below the surface by Baur, know that the pelagic ani-
mals are driven from the immediate surface by winds and rain,
or by some other cause, into moderate depths, where they may
always be procured, while at greater depths they fail to be found.
Such, at least, has been the experience of Johannes Miiller,
Claparéde, and others, who have followed their method of fish-
ing either at the surface or a little below it.

The evidence of specimens brought up by the “ Challenger”
nets from intermediate depths is inconclusive, since the ordi-
nary tow-nets were used. These were lowered open, kept open
while towing, and remained open while coming up. It is per-
fectly true, that, by differentiation of the contents of the several
nets at one locality, some approximate results might be obtained,
if the work were carried on for a long period; but an occasional
haul taken by itself means nothing. The important desideratum
is to devise a tow-net which will go down closed to any depth re-
quired, will then open and tow while the ship is in motion, and
close again within a reasonable distance as it comes up. The
collecting cylinder devised by Lieutenant-Commander Sigsbee
meets some of these requirements." He accompanied us on the
“ Blake,” to superintend in person its first trial. It was sent
down in thirty fathoms of water, from five to twenty-five fath-
oms, with quite a fresh breeze blowing, at about eleven in the
morning, in full sunlight, —a time when, with a smooth sea,
the pelagic animals would all have been on the surface. The
cylinder worked most satisfactorily, and brought up a few Calani,
hydroid medusz, such as usually occur at the surface. A few
slight changes were suggested by the designer, and Commander
Bartlett recommended the addition of a wire-gauze trap, to
facilitate the washing out of microscopic animals.

On the Ist of July the Sigsbee cylinder was tried for the
second time, in Lat. 39° 59’ 16” N., Lon. 70° 18’ 30” W., in

two hundred and sixty fathoms of water. The surface was
1 Described in the chapter on the Equipment of the “ Blake.”

THE PELAGIC FAUNA AND FLORA. 201

carefully explored with the tow-net, to see what pelagic animals
might be found there; they were Calanus, Sagitta, annelid lar-
ve, hydroid meduse, Squille embryos, Salpz, and a few radiola-
rians. The cylinder, filled with water which had been strained
through fine muslin, was then fastened to the dredging wire,
and lowered, so as to collect the animals between five and fifty
fathoms. The time taken by the cylinder in passing through
that space was twenty-eight seconds. It was then drawn up,
and the sieves and gauze trap washed with water, which had also
previously been strained through fine muslin. The water was
carefully examined; it contained the very same things which
had a short time before been brought together with the tow-net
and the scoop-net : nothing different was obtained by the cylin-
der. The radiolarians (two genera) were perhaps more numer-
ous. A slight breeze having sprung up after the surface collec-
tions had been examined, the cylinder was operated a second
time at this same station, adjusted for a depth of fifty to a hun-
dred fathoms. Not only in this experiment, but in all the sub-
sequent ones, the same precautions were taken in regard to
straining the water which filled the cylinder at the start, as well
as that used for washing out the sieve and the gauze trap.
The messenger sent to detach and open the machine occupied
twenty-one seconds in reaching the fifty-fathom point to which
the cylinder was attached, and the cylinder thirty seconds in
passing to the stop at one hundred fathoms. On examining the
sieves, the more common surface forms, Calanus, Sagitta, anne-
lid larvee, hydroid medusz, and Squille embryos, were wanting,
and only two radiolarians of the same species as those from
the upper levels were found. Nothing additional was brought
up. The cylinder was lowered a third time to a depth of one
hundred fathoms, the messenger occupied 45” to open it, and
the cylinder travelled from a hundred to a hundred and fifty
fathoms (time 45”), so as to gather the animal life to be obtained
between these limits. On drawing up the cylinder and wash-
ing out the sieve of the trap, not only did we find that the
water contained nothing different from what had been brought
together by the cylinder from the lesser depth, but it did not
- include even a single radiolarian.

———

202 THREE CRUISES OF THE ‘“ BLAKE.”

On the 15th of July, in Lat. 34° 28’ 25” N., Lon. 75° 22’ 50”
W., we tried the Sigsbee cylinder for a third time, in a depth
of 1,632 fathoms. With the same precautions before and
after using it, the cylinder was operated first between five and
fifty fathoms (time 30”). The water was somewhat ruffled, and
but little was found on the surface beyond a few crustacean
larve and heteropods. The cylinder contained hydroids, frag-
ments of siphonophores, pelagic alge, crustacean larve, and het-
eropod eggs; forms which differed from those gathered at the
surface, but were identical with the species obtained on previous
days under more favorable conditions of the sea. Next, the cyl-
inder was arranged for a depth of between fifty and a hundred
fathoms (time of messenger 21” from surface to fifty fathoms,
time of cylinder 40” to stopper from fifty to a hundred fath-
oms). The water was found to contain only a couple of
Squillz larvee, similar to those fished up at the surface. The
third time the cylinder went down at this station, it was lowered
to collect from a hundred to a hundred and fifty fathoms (time
of messenger from surface to a hundred fathoms 45”, time of
cylinder in passing from a hundred to a hundred and fifty fath-
oms 45”). The water when examined contained nothing. No
radiolarians were found at this station, either at the surface or
at any depth to which the cylinder was lowered (one hundred
and fifty fathoms).

The above experiments appear to prove conclusively that the
surface fauna of the sea is really limited to a comparatively
narrow belt in depth, and that there is no intermediate belt,
so to speak, of animal life, between those living on the bot-
tom, or close to it, and the surface pelagic fauna. It seems
natural to suppose that this surface fauna only sinks out of
reach of the disturbances of the top, and does not extend
downward to any depth. The dependence of all the pelagic
forms upon food which is most abundant at the surface, or near
it, would naturally keep them where they found it in quantity.

The experiments in using the tow-net at depths of five hun-
dred to one thousand fathoms, as was done by Mr. Murray
on the “ Challenger,’ were not conclusive, as has been already
pointed out on a former occasion, while the so-called deep-sea

THE PELAGIC FAUNA AND FLORA. 203

siphonophores, taken from the sounding-line by Dr. Studer on
the “ Gazelle,’ may have come, as I have so often observed in
the Caribbean, from any depth. I do not mean, of course, to
deny that there are deep-sea meduse. The habit common to
so many of our acalephs (Tima, Auquorea, Ptychogena, ete.) of
swimming near the bottom is well known; Dactylometra moves
near the bottom, and Polyclonia remains during the day turned
up with the disc downwards on the mud bottom. I only wish
to call attention to the uncertain methods adopted for deter-
mining at what depth they actually live.

One must have sailed through miles of Salpz, with the asso-
ciated crustacean, annelid, and mollusk larve, the acalephs,
especially the oceanic siphonophores, the pteropods and_heter-
opods, with the radiolarians, globigerinz, and alge, to form an
idea of how rich a field still remains to be explored. The
pelagic fauna in the course of the Gulf Stream is probably not
surpassed in variety by that of any other part of the ocean.

When they die and decompose, the pelagic forms, both ani-
mal and vegetable, sink to the bottom fast enough to form an
important part of the food supply of the es animals, as
can easily be ascertained by examining the intestines of the
deep-water echinoderms. We can thus account for the pre-
sence at great depths of much of the necessary plant-food
needed for the herbivorous types living in the continental and
abyssal regions. The variety and abundance of the pelagic’
fauna and flora, and their importance as food for marine ani-
mals, are as yet hardly realized.

According to the recent investigations of Regnard and Certes,
decay and decomposition do not progress rapidly in deep water,
the great pressure and the absence of light and heat bemg un-
favorable to such progress. This mass of slowly decomposing
material, which accumulates on the bottom of the ocean, mixing
with the ooze, forms the organic slime which all dredgers have
brought up, and which in early days of deep-sea investigations
was regarded as a special organism of the highest scientific
interest.

There seemed something providential, indeed, in the existence
of this primordial pap, laid out in the thinnest layers over the

204 THREE CRUISES OF THE “ BLAKE.”

whole floor of the oceanic basins, in which the lower forms only
needed to roll round to find all the food they could absorb. The
naturalists of the “Challenger,” who introduced Bathybius to
the scientific world, were the first also gracefully to recant before
the overwhelming proof of its non-existence which they them-
selves had collected.’ But it still figures in some quarters as a
prominent organism, which the Haeckelian theory of the views
of creation demand. The younger Sars and Alphonse Milne-
Edwards have also found this sheet of organic matter, the nature
of which is certainly not Bathybius in the sense in which it is
understood by Haeckel. .

A number of the marine animals ultimately depend for their
food upon the pelagic fauna. The fishes feed upon the hosts of
free-swimming’ crustacea, many of which develop with immense
rapidity ;* these in their turn depend for their food upon smaller
creatures floating in the water, and found everywhere in the
track of currents. There can be no better evidence of the mass
of food contained in the sea than is afforded by the examina-
tion of the contents of a tow-net any night. Pour the contents
into a glass jar, and note the edge of the vessel exposed to the
light, — it is covered with crustacea, annelids, and mollusks ;
and examine also the residue at the bottom, —a true broth, con-
sisting of the carcasses of all the minute shore and pelagic ani-
mals, and a mass of spores of all sorts of marine plants. This
broth is used in the Newport Laboratory to feed young fishes
and other embryos kept in confinement.

Nowhere do we see the struggle for existence going on so
visibly as among the pelagic animals. They all prey one upon
the other. The acalephs swallow hosts of minute crustacea,
which in their turn are filled with embryos of crustacea smaller
than themselves, or with spores of alge.

The crustacea, large and small, form the main food supply of
the young fishes which dart about in search of nourishment in

1 The naturalists of the “Challenger” 2 Of some copepods there are no less
showed that bathybius was only flocculent than thirty generations in three weeks ;
precipitate of a sulphate of lime, thrown so that, with ample food and in the ab-
down from salt water by organic matter sence of enemies, the progeny soon passes
in the presence of alcohol. beyond calculation.

THE PELAGIC FAUNA AND FLORA. 205

the smooth streaks of the surface formed by the currents and
winds. The mollusks in their turn, according to their size and
activity, are either eaten or are the eaters of some animals more
helpless than themselves. While the pelagic forms can move
about from place to place in search of more abundant food,
the more sedentary types must depend on the supply dropped
in their immediate vicinity, or brought to them by currents.

It is difficult, in this gigantic Seale for food going on
among the pelagic animals, to trace the ies of protective agen-
cles. “While undoubtedly we seem to be able to satisty eee
as to the efficiency of various causes, such as transparency, the
extraordinary development of locomotory organs, or coloration,
to take the pelagic types at certain stages out of reach of te
ger, yet there are in the course of the development of nearly all
these pelagic types long periods during which the embryos are
more than ever one to destruction, at the very time when
they would seem to have specially adapted themselves to sur-
rounding circumstances. Probably at no time during the life of
many crustaceans do they run so imminent a risk of destruction
as during their zoea stage. (Figs. 129, 130, 131.) Left at the
mercy of every current or ripple, they fall a prey to acalephs, to
polyps, to cephalopods, and especially to young fishes, in spite of
the huge appendages which seem at first sight to serve as pro-
tests against beg swallowed by their smaller enemies. It
would carry me too far to repeat in detail how many of our
fishes devour minute organisms ; how many mollusks and polyps
live upon the most diminutive denizens of the seas, both animal
and vegetable ; how the echinoderms find their food by swallow-
ing mud filled with living foraminifera or dead organic matter ;
and how the minute pelagic crustacea act as scavengers upon all
dead animals.

The quantity of food contained even in apparently clear sea-
water can readily be tested by leaving a shallow dish of it to
settle during the night, and examining the bottom on the fol-
lowing day, when it will be found to be covered by a consider-
able amount of. fine silt, made up of animal and vegetable
fragments. (Fig. 132.)

It can readily be seen that, as far as the deep-sea forms are

206 THREE CRUISES OF THE “BLAKE.”

concerned, they naturally procure their most abundant supply
of food within a comparatively short distance from land, where
all the detritus brought down by rivers, or formed by the action

Fig. 129. — Zoea of Carcinus. Fig. 130. — Panopus Embryo.
Greatly magnified. Greatly magnified.

Ril

Fig. 151. — Zoea of Porcellana.

of the sea on the coast line, settles on the bottom around the
slope of the continental areas. The larger materials are left
close to the shores, and with increasing distance the detrital mat-
ter becomes smaller, till finally reduced to an impalpable ma-
terial or solids in solution it finds its way to the most distant
parts of the continental slopes, or is carried still farther by
oceanic currents skirting the shores. As I have shown in the
chapter on the Florida Reefs, the distribution of the deep-sea
fauna is really a question of food; and we may expect to find it
most abundant upon the continental shelf,—along the lines to
which the greatest amount of detritus is carried by the incessant
action of the varied winds, tides, and currents to which the
sea-shore is exposed.

THE PELAGIC FAUNA AND FLORA. 207

The wide bathymetrical range of species belonging to the
principal groups of the animal kingdom shows that nearly all
littoral types can adapt themselves to the conditions of the deep
sea ; and there seems to be no reason why, in the oldest geolog-

ae \

Fig. 152. — Pelagic Refuse. Magnified.

ical periods, the same adaptation should not have taken place.
Yet, as we well know, no forms characteristic of the palzozoic
period have been dredged from the abyssal regions of the sea.
We are therefore warranted in assuming that such a migration
did not take place from the littoral regions to the deep sea in
palzozoic times, and that it was not before the end of the juras-
sic or commencement of the cretaceous that the littoral fauna
began to find its way into deep water along the lines of the con-
tinental slopes. This colonization may have taken place, either
through the gradual migration of the adults from their shal-
lower habitat towards deeper regions, or, as I suggested in the
report upon the sea-urchins collected by Pourtalés during the

208 THREE CRUISES OF THE “ BLAKE.”

first deep-sea expedition of the “ Bibb,” through the transpor-
tation of their pelagic larve by currents to more and more distant
regions ; much as we account for the extension of certain deep-
sea faunz, into adjoining geographical districts, as in the case of
the northern extension of many Florida species far towards the
coast of New England.

. It seems difficult for us to speculate on the origin of the
pelagic fauna. Going back to the earliest fossiliferous periods,
when the marine fauna was made up of pteropods, gasteropods,
sponges, crinoids, graptolites, brachiopods, and crustaceans, we
have animal types whose development in these early days must
have been similar to that of their recent allies. Their youngest
stages must already at that time, as are their representatives in
our day, have associated with true pelagic types as part of the
littoral pelagic fauna of the period. There is no reason why
the true pelagic types of those times should not hold to the
free-swimming embryo of the earlier marine faune the same
relations which they hold to those of our own. It seems, there-
fore, most natural to look upon the pelagic fauna of to-day and
that of former geological periods as made up of embryonic types
removed from the influences necessary for their full develop-
ment, and which have remained thus permanently in embryonic
stages, even after a time reproducing themselves, as other larval
forms are now capable of doing. But to consider that the lit-
toral forms were developed from pelagic types, as has been
suggested by Moseley, does not seem to be warranted by the
embryological history of marine invertebrates.

Associated with the pelagic animals we find in all latitudes
minute alow, covering immense stretches of sea, often in suffi-
cient quantities to discolor the water. The black and white
water of the arctic, the so-called feeding-ground of whales, is
mainly made up of diatoms, with which are also found pelagic
animals. The color of the Red-Sea is due to a minute alga,
forming huge patches of a blood-red tint. A similar phenome-
non is described by Darwin on the coasts of Chili and of Peru,
where I have frequently seen it myself. In the Gulf of Mexico
a pelagic alga, identical, probably, with that of the Red Sea (Z7i-
chodesmium erythreum) (Fig. 133), is seen on calm days, in

THE PELAGIC FAUNA AND FLORA. 209

long trains or patches of a dirty yellow color. Dr. Farlow has
identified as the same alga the pelagic plant found on one
occasion north of Cape Hatteras, tinting the surface of the sea
a dirty yellow for an area of about a quarter of a mile in length

=

Fig. 133. — Trichodesmium Fig. 154. — Coccosphere. Fig. 135. — Rhabdosphere.
erythreum. 8. 690. (Chall.) 13°. (Chall.)

1

by a hundred yards in width. This pelagic alga has been aptly
described as resembling minute sheaves and bundles of chopped
hay. Coccospheres (Fig. 134) and rhabdospheres (Fig. 135)
are calcareous pelagic surface organisms, of which the tests
and fragments, coccoliths and rhabdoliths, oceur in numbers in
globigerina ooze. They have been studied by the naturalists of
the “Challenger,” and Thomson regards them as calcareous
alow of a peculiar form. They are found in abundance in the
stomachs of Salpze.

In addition to these smaller algze, which are indeed the true
inhabitants of the surface, and flourish equally well in all parts
of the ocean, —in the central parts of the Gulf of Mexico, along
the Atlantic coast of the United States, or on the west coast of
South America, — we find some of the higher algz, but these
are confined to very much more limited areas. Si Joseph
Hooker has described the giant kelp in the floating condition
in which it ranges over a wide extent of the Southern Ocean.
A similar species of kelp occurs in the Gulf of Georgia, where
it serves as a refuge to a host of marine animals, which are
sheltered within the comparatively quiet area occupied by it.
Both in the Atlantic and Pacific, large tracts are covered by
a species of Sargassum (Fig. 136), which in the Atlantic has
given its name to the area known as the Sargasso Sea.’

1 The Sargasso Seais animmense body with a thickness of 300 fathoms, the sur-
of warm water of 1,000 miles in diameter, face temperature of 22° C., diminishing

9210 THREE CRUISES OF THE “ BLAKE.”

This weed is not only pelagic, but is also found growing
attached to rocks in the West Indies and along the Florida

Fig. 136.— Gulf-Weed. 3.

Reef,’ but no locality is known which could furnish the supply
of gulf-weed necessary to form the floating masses in the Atlan-
tic. How it has assumed its pelagic life is not known, but it
undoubtedly forms extensive narrow strips, long irregular trains
very slowly to 16° C. at that depth. It 1 A Pacific species of Sargassum, which
occupies in the central part of the south- is occasionally found floating near the
ern North Atlantic the position of the Sandwich Islands, grows quite abun-

area of greatest density of sea-water,— dantly on the coral reefs of Oahu and
over 1.027. Maui.

THE PELAGIC FAUNA AND FLORA. AM

of yellowish green or golden olive, reaching over the dark blue
water of the Atlantic.

The “Challenger” sailed round this so-called Sargasso Sea,
but nowhere encountered it im sufficient quantities to become
an impediment to navigation. We meet with this gulf-weed
everywhere in the Gulf of Mexico, but scattered and only in
small patches, and to the leeward of the Windward Islands.
It is very abundant in the old Bahama Channel, and mod-
erately common all along the course of the Gulf Stream from
off Charleston to Cape Hatteras. The largest mass of gulf-
weed I have encountered was in making the passage from
St. Thomas to Havana.’ While steaming within sight of the
northern shores of Porto Rico and of San Domingo, we were
never out of sight of immense accumulations of gulf-weed, parts
of which rose a few inches above the water, the whole forming
long trams which trailed with the winds and currents. The
weed became less and less common as we approached the old
Bahama Channel. But these masses of Sargassum were of
shght thickness, and were mere floating patches, more or less
entangled.

The numerous young and tender leaves found on every stem
show that the weed is in a most flourishing condition, and is
not merely dead weed floating about in the great vortex of oce-
anic circulation. It is not known what becomes of the gulf-
weed annually driven by the equatorial current through the
passages of the West India Islands into the Caribbean.’ The
bulk of the weed which passes through the Windward Passage
probably finds its way through the Yucatan Channel and the
Straits of Florida into the Gulf Stream proper, but its final fate
is not known. The amount of gulf-weed met with north of.
Cape Hatteras in the track of the Gulf Stream is small; it grad-
ually increases as one goes south.

One of the objects of the “Talisman” expedition was to
investigate the Sargasso Sea. The French explorers “ nowhere
met the enormous masses of floating Sargassum, which the old
navigators compared to floating prairies.” While sailing, the

1 Commander Bartlett found large masses of gulf-weed on the southern edge of
the Gulf Stream. .

212 THREE- CRUISES OF THE ‘“ BLAKE.”

“Talisman ” constantly crossed long bands of Sargassum trail-
-ing according to the direction of the winds and the currents,
and forming larger or smaller patches, which were, however,
rarely more than four or five yards square. Yet the “Talis-
man ”’ crossed the Sargasso Sea from north to south in the areas
indicated ‘in the charts as the most prolific in Sargassum.

The weed as described by the younger Milne-Edwards does
not differ from that which we have frequently examined. The
central stalk and the basal leaves are usually of a brownish tint,
the terminal leaves, on the contrary, of a greenish-yellow golden
tint. The same animals as those commonly found in the gulf-
weed of the West Indies were collected by the “ Talisman.” The
number of fishes alone, perhaps, is somewhat more varied. The
botanist attached to the expedition did not succeed in finding
any branches with reproductive organs, although the terminal
shoots were in most active states of development; and he came
to the conclusion, as Harvey and others had done before him,
that, while pelagic, the Sargassum increases ‘merely like a cut-
ting of extraordinary vitality. We were not fortunate enough
to find it in fructification, but Professor Moseley states that he
saw specimens covered with fructification in Harrington Sound,
Bermudas.

Only by placing a piece of the gulf-weed in a jar of sea-
water, with abundant space for it to expand, do we get an idea
of its beauty and its graceful form. The delicate fronds, of all
shades, from deep olive to golden yellow, are often crossed by a
delicate tracery of hydroids and of bryozoan reticulation, which
stands out in bold relief of white upon a dark background.

In the “ Narrative of the Challenger” is given a list of the
species of animals occurring on the Sargassum. Many ob-
servers have described the antics performed by the hosts of
crustacea when shaken out of thew hiding-places, and have
dwelt at length on the phenomena of mimicry noticed among
the crustacea, mollusks, annelids, and other animals which make
their abode among the fronds, stems, or air-vessels of the gulf-
weed. At first glance the bunch of weed seems deserted, but
shake it in a glass dish, and hundreds of many-colored deni-
zens are seen rushing about in all directions, eager to return to

THE PELAGIC FAUNA AND FLORA. O15

the particular spot best adapted to conceal them; and in a
few minutes only the practised eye of the naturalist can detect
their presence. Of course they do not all succeed in their first
attempt at finding the fittest sheltering-place, and an occasional
striking contrast formed by a white checkered crab upon a dark
background, or some other equally great opposition, will reveal
the presence of a straggler. But these stragglers quickly cor-
rect their error. |

The Sargasso Sea of the North Atlantic covers a rather in-
definite area between 22° and 36° of north latitude, and, accord-
ing to the statements of the older navigators, the amount of
Sargassum to be met with varies from occasional patches to
masses large enough to impede the progress of sailing-vessels.
The Sargasso Sea was seen by Columbus, and alarmed his com-
panions, who looked upon it as an insuperable obstacle to their
expedition. The Sargassum probably changes its position con-
stantly, according to the seasons, the currents, and the direc-
tion of the wind; but within the area bounded by the Gulf
Stream on the west, the equatorial current on the south, and
the return current from the Azores and Canaries, the Sargas-
sum has always been found in larger or smaller quantities.

We are perhaps justified in considering the great banks of
Sargassum in the Atlantic, Pacific, and Southern Oceans as
survivors of a single bank, which probably swept round the
globe in the great equatorial current of pre-tertiary times. The
origin of this ancient bank may be due to the littoral species
of Sargassum still living to-day in the track of its former
path. |
Some of the pelagic animals we have spoken of are specially
interesting from a physiological poimt of view, owing to their
association with vegetable organisms. As early as 1851 Max
Schultze noticed the presence of chlorophyll in planarians, in
some infusoria, in fresh-water sponges, and in a few worms and
crustacea.

Peculiar yellow cells were observed by Johannes Miiller in
radiolarians, and were at first supposed by him to be connected
with their reproduction, while Haeckel, who detected the pre-
sence of starch in these cells, considered them as digestive

wc

214 THREE CRUISES OF THE “ BLAKE:”

glands, and Vogt regarded the yellow cells of Velella (Figs.
137, co. and Porpita as liver cells.

In 1871 Cienkowsky expressed the
opinion that these yellow cells were para-
sitic alee, basing his view on the fact
that they survive the radiolarians, mul-
tiply, and become encysted, — pheno-
mena not in the least connected with
the life process of radiolarians. In 1879
Hertwig discovered similar cells in acti-
nize which he considered as. unicellular

Fig. 137. — Velella mutica.

Vascular canal filled with yel- glo,
low cells, magnified. zs -
In 1881 Dr. Brandt confirmed Cien-

kowsky’s discoveries, and strongly urged the para-
sitic nature of the cells. Geddes subsequently con-
firmed the views of Cienkowsky and Brandt, and
traced the presence of starch and of a cell wall
of true plant cellulose; he showed also that the
chemical composition and the mode of division of s eae
these yellow cells were those of unicellular alge, magnified.
for which he proposed the name of Philozodn. The exposure
of large quantities of radiolarians soon proved them to be stud-
ded with tiny gas globules, and a shoal of Velellz yielded a
large quantity of gas containing more than twenty-one per cent
of oxygen. Dr. Geza Entz seems to have anticipated, as early
as 1876, the observations and theoretical deductions of both
Brandt and Geddes. |

In the relationship of these animals and plants, — for which
the name of Symbiosis, given by De Bary to an association of
dissimilar organisms, has been adopted, — it cannot be doubted
that the animal cell must be benefited by the death of the
vegetable cells which are digested, and that the animal cell is
constantly producing carbonic acid and nitrogenous waste,
which are of the first importance to the vegetable cell; the
vegetable cell in its turn evolving oxygen under the action
of sunlight, which is taken up by the surrounding animal
tissues.

This association, as far as we know, must be very beneficial, for

THE PELAGIC FAUNA AND FLORA. 215

the radiolarians and Velellz (Fig. 138), in which the provision
of philozodn is most abundant, survive longer in confinement
than other pelagic animals. The common Polyclo-
nia of Florida can be kept for weeks in jars, un-
doubtedly owing to the mass of philozodn found
in its oral arms.

Similar associations which do not have the same
physiological value are found throughout the an-
=) imal kingdom. It is difficult to draw the line be-
Iella Medusa tween functional symbiosis and mere associations of
with yellow position, in such cases as that of the Vorticellide,
cells, magnified. :

which fix themselves anywhere; that of the Bry-
ozoa, growing on fronds of sea-weeds, or the tests of crabs or of
mollusks ; or that of many kinds of
alow and sponges, found growing on
the carapace of crustacea. A similar
association is that of the hermit crab
and its house, of Phronima and its Do-
holum quarters (Fig. 139), neither of
which differs greatly from the some-
what less passive relationship of the
oyster and its crab ; of Fierasfer and the
holothurians ; of ophiurans and crusta-
ceans living in the body of sponges ;
or of fishes swimming about in the fig. 139.—Phronima seden-
midst of the tentacles of meduse. taria. j.
~ More intimate still is the relationship existing between some
species of crabs living in the branches of coral, or of worms
or mollusks covered by gorgoniz and crabs, where the presence
of an associate modifies considerably the structure and mode
of growth of the abode. From this we pass gradually to
parasitism proper, where the organs of nutrition are specially
developed, and those of locomotion degenerate. Again, free
parasitism, we might almost call it, such as exists between in-
sects and plants, is readily traced in a sort of commensalism of
animals belonging to different classes of the animal kingdom,
living together in a relationship almost close enough to be con-
sidered as functional; such as exists, for instance, between an-

216 THREE CRUISES OF THE “ BLAKE.”

nelids and starfishes, or crabs and actinie. Finally, we come: to
those communities among invertebrates where the subdivision of
labor is carried out so far that the different individuals possess
special functions. These cases belong to the same phenomena :
they illustrate the interdependence of the animal and vegetable
kingdoms, and the influence of special conditions of existence
upon the development of the animal and vegetable life of our
shores, continental slopes, and deep-sea basins.

U.S HYDROGRAPHIC OFFICE.

9

BOTTOM TEMPERATURES
ERN NORTH ATLANTIC

WEST

U.S.HYDROGRAPHIC OFFICE.

B. Meisel Lith Boston:

a.

TEMPERATURES OF THE CARIBBEAN, GULF OF MEXICO, AND
. WESTERN ATLANTIC.

Havine given the reader a general sketch of the configu-
ration of the sea-bottom in the districts traversed by the
“Blake,” we may now pass to an examination of the tempera-
tures and currents of the sheet of water covering that region.
(Fig. 140.) The temperature sections of the Gulf of Mexico
- were obtained mainly by Lieutenant-Commander Sigsbee ; those
of the Caribbean and along the Gulf Stream, with the exception
of the few observations made by the “ Albatross,’ were taken
by Commander J. R. Bartlett on the “Blake.” They are here
reproduced as they have been kindly sent to me by Professor
J. E. Hilgard, Superintendent of the Coast Survey.’

Of course, during the cruises, sound-
ings were taken with Sigsbee’s modifica-

1 In addition to the graphic method of representing
each temperature section which has been adopted on
uw many of the maps of this volume, it has been found

? TL convenient to construct curves (Fig. 141), showing at a
glance the temperature at any depth. By su-
perposition the curves of separate observations
may be readily compared ; in the same way,

etal ch we may, by means of curves, bring

to the eye at once the thermal
AAKACEEEEEEtE |

as we wish to contrast. In at-

it ‘SESSURERE EEEEEE tempting thus to set forth the

5 - ut should not forget that at every

% a “% > %e Cy Ce “o., 7 £

*e 7%, moment they are changing in di-

the atmospheric currents ; and

their graphical representation merely gives us their most general features, leaving

conditions of such distant points

emai ee | temperature of currents, we

Fig. 141.—Temperature Sections. (Curves.) rection and intensity, much as are
the local disturbances to be more or less accurately defined.

218 THREE CRUISES OF THE “ BLAKE.”

tion of Sir William Thomson’s sounding-machine; the bottom
and the surface temperatures, taken with the Miller-Casella
thermometer, were compared from time to time with a standard.
We obtained in the Caribbean and in the Gulf of Mexico a uni-
form bottom temperature of 394° Fahrenheit, below six or seven
hundred fathoms. The cause of this uniform bottom temper-
ature is to be found in the depth of the passage between the
Windward Islands, through which the cold waters of the Atlan-
tic, from similar depths, force their way slowly northward, first
into the Caribbean Sea, and then into the Gulf of Mexico,
through the Straits of Yucatan. (Fig. 142.)

To Commander Bartlett I am indebted for information re-
specting the lines run between'the islands. His report remains
unpublished in the archives of the Coast Survey. The follow-
ing extract from one of his letters will show the extent of the
work done by the “ Blake : ” —

“T connected the islands by running traverses across the ridges.
From St. Vincent to St. Lucia the ridge was only from 150 to 170
fathoms below the surface, with a channel of 400 fathoms near St. Vin-
eent. The channel between St. Lucia and Martinique had 500 fath--
oms in mid-channel, sloping upward to each island. The channel
between Martinique and Dominica was a tough one, and I thought I
should never find a ridge. The soundings increased regularly on a
ridge to 300 fathoms in mid-channel, where I got a sounding of 883
fathoms, and then 1,000 fathoms; beyond this the ridge was some ten
miles to the westward, with an average depth of 400 fathoms, but I
found two peaks with only 40 fathoms. The deep water from the Ca-
ribbean Sea makes in between Guadeloupe and Montserrat, but I
found a ridge of about 300 fathoms connecting Antigua with Guade-
loupe. In this channel I also found a peak with only 40 fathoms. I
finished up the line connecting Saba Bank with St. Croix. I found the
connection perfect, but the ridge has 700 fathoms water on it near St.
Croix. There is 1,000 fathoms three miles north, and 1,800 fathoms
five miles south of the ridge. I ran a line from Dog Island to White
House Shoal, and back to Sombrero. Here JI found a channel about ten
miles wide, with 1,100 fathoms. The temperature was 38° at 1,100;
outside, 574° at 1,600, and 364° at 2,500. I shall run a number of
lines from St. Thomas to Sombrero, to be sure that this channel con-
nects with the deep water off St. Thomas. I ran a line of soundings
from the south end of Dominica to Avis Island. The soundings were
regular at 1,000 fathoms to within ten miles of Avis Island.”

‘TOIdHO OIHAVYDOUCGAH'S “1

Te a a ae

‘OMNVILY GHL JO SAMALVYAdNAL WOLLO

J

“HOT O OTMAV MO OW MAES

AAS

Sts OMNVILY FHL 10 SAUMALVEAd WL WOLLO

TEMPERATURES. 219

The soundings made by Commander Bartlett after I left the
“Blake,” and by the “Albatross,” to determine the ridges
which unite the various islands between Sombrero and Trinidad,
show plainly that the cold water of the bottom of the Caribbean
can only come in through the passage between Sombrero and
the Virgin Islands. This passage has a depth of about 1,100
fathoms, with a bottom temperature of 38°; the water which
passes over the ridge connecting Santa Cruz with Porto Rico
has a depth of about 900 fathoms and a temperature of 393°.
The five-hundred-fathom line, as I have stated, marks a large
bank formed of all the islands to the south of Sombrero, in-
cluding Dominica, with a narrow oceanic bay of 575 fathoms
between it and Martinique ; the five-hundred-fathom line again

iS s
s 8.
= 5
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~
Sa Et oe
f a o — 2
Fel - an ad * 3 =) 2 F
CampecheBank 3 & S Yess gs 8 2 2 & SS 2 Cape San Antonio Lich
ucatan.” p:) s_git-9 Br gar 3s aoe ‘West End of Cuba
oa aS et Yr. H 77> et ar
aes ee a a : eat We
W3e 7 t - . ~ i ! s ‘ 65?
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Fig. 143.

uniting all the islands to the south of it into one large spit, as a
part of South America. Thus the bulk of the water forced into
the Caribbean Sea has a comparatively high temperature, — an
average, probably, of the temperature of the three-hundred-
fathom line. The cold water of the Atlantic is, however, also
forced into the western basin of the Caribbean through the
Windward Passage, and this passes through the Yucatan Chan-
nel, between Cape San Antonio and the Yucatan Bank.

The greatest depth of the Yucatan Channel (Fig. 145) is

somewhat more than 1,100 fathoms, so that the temperature of

220 THREE CRUISES OF THE “ BLAKE.”

the water which finds its way into the Gulf of Mexico is neces-
sarily at its deepest point (2,119 fathoms) only that of the bot-
tom of the Straits of Yucatan (1,127 fathoms), namely, 393° F.
This can only have the temperature of the deepest ridge sepa-
rating the eastern Caribbean from the Atlantic (392° F.). The
depth of the channel through which the water of the Gulf ul-
timately finds its outlet is very much less (344 fathoms), and
the Straits of Bemini, with a cross-section of not more than
eleven square miles, are not half the width of the Straits of
Yucatan. The temperature of the water at the bottom of the
Gun Key Channel is much higher (see Fig. 158), with a far
greater surface velocity than that of the current flowing into the
Gulf of Mexico through the Straits of Yucatan.

It is therefore incredible that, with this huge mass of water
pouring into the Gulf of Mexico, there should be anything lke
a cold current forcing its way up-hill into the Straits of Florida,
as has been asserted on theoretical grounds. The channel at
Gun Key can only discharge the surplus water by having a great
velocity.

The soundings made by the “ Challenger” off Sombrero on
their line from Sombrero to Teneriffe, as well as the soundings
north of St. Thomas on the line from St. Thomas to Bermudas
(see Fig. 170), were fortunately both taken in March, at about
the same time with those of Commander Bartlett.

On comparing the soundings taken by the “ Blake” off Som-
brero (Fig. 144), twenty miles from shore, with those of the
“Challenger” (see Fig. 170), three hundred miles from shore,
we find the surface temperature observed by the “ Blake,” and
at a depth of fifty fathoms, slightly higher (2°), at 100 fathoms
2° less, at 200 fathoms 1° less. The temperature of 50° is
reached at a depth of 350 fathoms by the “Challenger;” at
300 by the “ Blake.” The “ Blake” observed 46° at 400 fath-
oms, the “Challenger” 45° at 425 fathoms, and at a depth of
700 fathoms both the “Challenger” and “ Blake” record a tem-
perature of 40°. The “Blake” serials show 40° to a depth of 900
fathoms, while the “Challenger” has at the same depth 39°.
At the deepest point on that line (2,558 fathoms) the “ Blake”
observed a temperature of 36°, while at the same depth the

TEMPERATURES. DA.

“Challenger” records 35.1°. These observations show, as we
approach the coast, an increase of temperature to a depth of
about 400 fathoms, and a diminution of temperature to a depth
‘of about 1,700 fathoms.

In the section from Sombrero to Virgin Gorda (Fig. 144)
across the Anegada Channel, the temperatures agree more closely
with those of the Atlantic sections taken by the “Challenger”
than with the more littoral one taken by the “Blake.” There
is a marked increase of temperature in the layers between
100 and 300 fathoms. Between 400 and 600 fathoms, how-

ever, the water is somewhat colder, and at the bottom the tem-

Sombrero 1.
ao

Marcie Bf LEZI:
J

perature is nearly that of the corresponding
depth three hundred miles at sea. The bot-
tom temperature of this channel does not in-
dicate that the cold water is thrown up along
the gentler slope of the channel, as in the temperature sections
across the Yucatan Channel (Fig. 143), and across the narrow
part of the Straits of Florida. (Fig. 158.) |The bottom temper-
ature, 38° and 383°, indicates that the basin and this channel are
an oceanic tongue of the Atlantic, and that there must be a ridge,
extending between Santa Cruz and Porto Rico, which separates
it from the Caribbean basin.’ Far inside of the Caribbean Sea,

1 The temperature of 383° also shows
that the Anegada Channel is divided by
a ridge from the deeper part of the oce-
anic basin of the western Atlantic to
the north of the West Indies, as in that
basin the temperature observed by the
“Challenger” and by Lieutenant-Com-

mander Brownson sinks to 36° in its deep-
est parts. Since this was written, the
U. S. Fish Commission steamer “ Alba-
tross,” Lieutenant-Commander Tanner,
has developed a ridge running between
Santa Cruz and Porto Rico, with a great-
est depth of about 900 fathoms and a

229 THREE CRUISES OF THE “ BLAKE.”

within the ridges separating it from the Atlantic, the deepest
soundings, such as those off Bequia, 1,591 fathoms, and off Mar-
tinique, 1,224 fathoms, indicate a bottom temperature of 394°.
From St. Thomas to Ham’s Bluff (Santa Cruz), on the con-
trary, the temperature section seems to indicate that the deep
water there (2,376 fathoms, with a bottom temperature of
384°) is connected by a deep channel extending between Som-
brero and Virgin Gorda with the cold Atlantic water. The
temperatures in the section across the passage between Domi-

Pt Rosalie
Dominica

nica and Martinique (Fig. 145) show an extraordinary fall
between 50 and 150 fathoms, — from 71° to 53°; then a much
colder layer between 150 and 300 fathoms, with a bottom tem-
perature of 423° at a depth of only 430 fathoms. The bottom

Salines Pt.

temperature in the northern part of the passage was 41° at a
depth of 575 fathoms.

In a section from Martinique to St. Lucia (Fig. 146), with a
somewhat larger area than that of the southern part of the pas-

bottom temperature of 393°. The “Al- perature of 39}° at the greatest depth
batross ” also ran a line across the east- recorded, — over 2,600 fathoms.
ern Caribbean, and found a bottom tem-

TEMPERATURES. 223

sage between Dominica and Martinique, the diminution of tem-
perature between the surface and 100 fathoms ranges from 79°
to 54°; a temperature of 46° is recorded at a depth of 300
fathoms, and a bottom temperature of 403° in 591 fathoms.

In the section of the passage between St. Lucia and St. Vin-
cent (Fig. 147), we find 56° at a depth of 100 fathoms, 452° at
300 fathoms, 40° at 600 fathoms, and a bottom temperature of
39}° at 1,082 fathoms.

Across the Mona Passage there is but a small passage for cold

z March 21'1879.
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Cape Moule aChique & 2 See ao Ae g Tarratce Pl.
St.Lucia ~ _ Bo 2 Se° gi? 82 ae St. Vincen
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Fig. 147.

water between Direcho Island and Porto Rico. (Fig. 148.) We
find there at a depth of 454 fathoms a bottom temperature of
44°, about what we have in the other passages. The larger
area of this section across this passage, with an average depth

of 300 fathoms, shows a much higher temperature, the decrease
being only 12° for the first 100 fathoms, and 9° for the second
100, with a bottom temperature of 51° at 337 fathoms. We
notice in this section a temperature of 54° at 260 fathoms near
Direcho Island, while it is 56° at a distance of about fifteen

924 THREE CRUISES OF THE “ BLAKE.”

miles in a depth of 56 fathoms. This cold water may come
from the colder water of the deeper channel on the east of the
island. The water is also colder near San Domingo, where we
find at 339 fathoms 49°, while seven miles to the eastward,
toward Porto Rico, it is 51° in 337 fathoms. This section is
very similar to that of the Anegada Channel.

The temperature sections of the passages between the Wind-
ward Islands on the eastern side of the Caribbean — Dominica,
Martinique, St. Lucia, and St. Vincent —are in striking con-
trast to those of the northern side, the Anegada, Mona, and
Windward Passages. Ata depth of 75 fathoms there is a dif-
ference of no less than 9° ; at 200 fathoms, one of 10°; and one
of 5° at 300 fathoms. The equilibrium is only restored at a
depth of 600 fathoms, where we have again the temperature of
40°. We find repeated here on a smaller scale the variations of
temperature at given depths near the equator and in the more
temperate zones. A temperature of 41° has been observed in
the Atlantic near the equator at a depth of only about 250
fathoms, while in the temperate latitudes both north and south
of the equator we must go to a depth of at least 600 fathoms
in one case, and of over 400 fathoms in the other, to obtain the
same temperature. In other words, there must be an active
lateral and upward flow of the cold water, and this establishes
one of the primary causes of the equatorial oceanic circulation.
It also shows that the temperature of the deepest point of the
ridge which separates an inland sea, and thereby forms a med-
iterranean, is not necessarily that of the bottom of the enclosed
sea. It is very evident that, supposing the ridge to have been
only 300 fathoms deep, we could have a bottom temperature of
50°, which would indicate an oceanic ridge of 350 fathoms, on
the same principles that have led Dr. Carpenter and others to
speak of the bottom temperature of enclosed seas as assuming
that minimum temperature.

The section across the Windward Passage (Fig. 149) bears a
close resemblance to the oceanic temperature section of that
region. The belt of water between 400 and 800 fathoms is,
however, considerably warmer. It also resembles the section
between Jamaica and San Domingo (Fig. 150), though the belt

TEMPERATURES. Da

of water between 200 and 500 fathoms is somewhat colder than
in the Windward Passage. This is perhaps due to a similar
cause to that which lowers the temperature of the water in the
shallower sections of passages between the islands of the eastern
edge of the Caribbean. As for instance in the Mona Passage,

oa a
z Feb.IL 1860.

o J
s in 2 Tortuea I.
A San Domingo

7200 __ 5

Fig. 149.

where a belt of water exists between 200 and 337 fathoms, colder
than in the adjoining deeper passage between Cuba and San
Domingo. Similarly the section between Jamaica and the Pedro
Bank (Fig. 151) shows a slight diminution of temperature be-
tween 300 and 600 fathoms, which we are inclined to refer to

‘May 111879. E
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Fig. 150.

the existence of a ridge to the eastward, over which the colder
water of the eastern Caribbean forces its way.

The section from Jamaica to San Domingo (Fig. 150) shows
in the deep channel extending northeast of Jamaica, which con-
nects the eastern basin of the Caribbean with the Honduras
basin, a larger amount of cold water between 150 fathoms and

226 THREE CRUISES OF THE “ BLAKE.”

800 fathoms than we find in the corresponding belt of the sec-
tion of the Windward Passage between Cuba and San Domingo.
This section has in fact at that depth more the character of an
oceanic section than has the section of the Windward Passage.
This may be due, perhaps, to the fact that the water in the
eastern part of the Caribbean is not so greatly superheated
as in the belt to the northward of the Greater Antilles, from
St. Thomas to San Domingo, which is forced into the funnel
ending in the Old Bahama Channel, and finds an outlet into
the Honduras basin of the Caribbean through the Windward

ann Lertiaa® Scele tithoms

ae

Fig. 151.

Passage. Or it may be that the colder water which flows into
the eastern Caribbean through the Anegada Channel passes
to the south of Porto Rico and San Domingo as far as the
cation which connects the eastern Caribbean with the Honduras
basin.

In the section from Santiago de Cuba to Jamaica (Fig. 152)
across the Formigas Bank, there are no marked departures from
the temperatures of the section across the Windward Passage.
This section goes across the eastern extremity of Bartlett’s Deep
(see also section, Fig. 153), and at a depth of 2,978 fathoms
has a temperature of 39°. This temperature may be due to the
cold water on the ridge of the Windward Passage (39° at 932

TEMPERATURES. Q27

fathoms), or to that of 39° at a depth of 1,297 fathoms in the
passage between Jamaica and San Domingo. Judging from
the few bottom temperatures obtained between the Formigas
Bank and Jamaica, the water of that section is slightly warmer,
a temperature of 39° being obtained at a depth of 1,140 fath-
oms. ;

The bottom temperatures taken off Barbados, from 56 to 713
fathoms, on the southern and western sides of the island, show
a remarkable diminution in temperature, as contrasted with the
same depths of the serial line off Sombrero. There we have at

» /Morant Pt. Jamaica

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Fig. 152.

a depth of 50 fathoms a temperature higher by 24° than off
Barbados ; at 100 fathoms it is 83° higher, at 150 fathoms 7°,
at 200 fathoms 82°, at 300 fathoms 4°, at 400 fathoms 14°;
and finally at 700 fathoms the temperatures become identical,
40°. The temperature lines off Sombrero were taken at the
end of March, and those off Barbados at the beginning of
March of the same year. These results agree with the tem-
peratures taken to the southward by the “ Challenger,” between
Pernambuco and Fernando Noronha. Near the last-named place
the temperature falls to 60° at a depth of 50 fathoms; off Bar-
bados the same temperature occurs at 82 fathoms. At 100
fathoms the temperature is 55° ; it is the same at 150 fathoms off

228 THREE CRUISES OF THE “ BLAKE.”

Barbados. The temperature is 45° at a depth of 225 fathoms,
at 347 fathoms off Barbados; it is 40° at 350 fathoms, while
the same temperature is found ata depth of 713 fathoms off
Barbados. That is, the layer of water below 150 fathoms be-
comes gradually warmer as we go north from Pernambuco, the
isothermal of 40° being at 350 fathoms off Pernambuco, while
it is at 700 fathoms off Barbados and Sombrero. The isother-
mal of 50° is at 150 fathoms off Pernambuco, at 225 fathoms
off Barbados, and at 350 fathoms off Sombrero.

A line of soundings southwest by south from Saline Point off
Grenada shows the water to be as a whole colder than at simi-
lar depths off Barbados. Off Grenada at 400 fathoms we find
41°, at Barbados 44°; at 350 fathoms, the temperature 1s only
about 1° colder off Grenada; at 300 fathoms, it is again 2°
colder; at 150 fathoms, about 3°; and at 100 fathoms, only I’.
A series of bottom temperatures on the lee side of Grenada
shows the water for depths between 100 and 400 fathoms to be
considerably warmer than that of the corresponding depths
standing in free communication with the Atlantic. Ata depth
of 92 fathoms, the water on the lee side is 33° warmer than that
of the same depth on the windward side. The same difference
exists at 300 fathoms, and at 400 fathoms the temperature on
the lee side is still 1° warmer.

The bottom temperatures on the lee side of St. Vincent show
a similar difference. The bottom temperatures off St. Lucia on
the lee side are slightly colder than those off St. Vincent and
Grenada, but they are warmer than the temperatures at iden-
tical depths in the passage between St. Lucia and St. Vincent,
and from St. Lucia to Martinique. The lower temperature is
probably due to the deeper passages admitting cold water on
each side of St. Lucia, as compared with the depths at which
water pours into the Caribbean south of Grenada, or across the
bank of the Grenadines and through the shallower passage be-
tween St. Vincent and Bequia. We must, however, call atten-
tion to the remarkably cold temperature occurring between 127
and 171 fathoms on the lee side of the Grenadines.

On the lee side of Martinique the bottom temperatures are
still lower, — fully as low as those of the same depths in the

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TEMPERATURES. 229

passage between Martinique and St. Lucia. They are actually
lower than the temperatures of the corresponding depths ob-
served in the passage between Martinique and Dominica.

On the Caribbean side of Dominica the series of bottom tem-
peratures shows a marked increase from the surface to a depth
of over 800 fathoms, and we must go to nearly 1,000 fath-
oms before we find the deep-sea isothermal of 39.7°. At 600
fathoms there is a temperature of over 40°; at 542 fathoms,
of 42°. Comparing this with the temperatures outside of the
Windward Islands, we find them considerably lower at a depth
of 250 fathoms, and only slightly lower from that point to 600
fathoms.

Off Guadeloupe on the western side, the bottom temperatures
between 62 fathoms and 300 fathoms are higher than at corre-
sponding depths off Martinique, Dominica, and St. Lucia, and
the same is the case off the islands of St. Kitts, Nevis, Mont-
serrat, and the Saba Bank. This increase in temperature of the
upper strata extends to a depth of over 250 fathoms. The broad
bank which the above-named islands form upon the inner edge
of the Caribbean seems to raise to an abnormal degree the tem-
perature of the water which covers it, while the narrow bank of
which the Grenadines form the crest appears to act more as a
dividing ridge, cold water bemg brought nearer the surface on
the Atlantic side of these islands, as is the case with the cold
water on the dividing ridges in passages between adjoining
islands.

The same high temperature is continued in the line of bot-
tom soundings observed off the western extremity of Santa
Cruz, where at a depth of 625 fathoms we still find 41°; at
450 fathoms, 422°; at 314 fathoms, 48°; and at 248 fath-
oms, 543°. These temperatures agree well with those found
outside, at similar depths, off Sombrero. That is, the strata
of water to the eastward of the northern Windward Islands
between 625 fathoms and 250 fathoms are much warmer than
the same belt to the south, while the belt on the lee side
between 250 and 100 fathoms is slightly colder. In the line
of bottom temperatures between St. Thomas and Santa Cruz,
we find at 218 fathoms only 51°, a temperature which corre-

230 THREE CRUISES OF THE “ BLAKE.”

sponds on the Atlantic side to a depth of but little less than
300 fathoms; but near the six-hundred-fathom line the tem-
peratures of the inside section again agree with those of the
oceanic section. .

Across the Yucatan Channel the temperature section shows
great smmilarity with the Atlantic section just outside of Som-
brero. The water which finds its way into the Gulf of Mexico
has nearly the same temperature as the water forced from the
Atlantic over the eastern edge of the Caribbean basin through
the passages between the Windward Islands. In the Gulf of
Mexico itself, the sections from the Tortugas to Yucatan show
a very decided increase of temperature below the one-hundred-
fathom lne. At 200 fathoms, the temperature is 65°; at 300
fathoms, it is 57° ; at 400 fathoms, 505°; at 500 fathoms, 41°;
with a bottom temperature of 39° at 1,685 fathoms. That is,
the temperature of the water between 150 and 600 fathoms is
from 13° to 4° warmer than the water which finds its way into
the Gulf of Mexico. Compared with the temperature section of
the Windward Passage (Cuba to San Domingo), the temperature
of the Yucatan Channel line between 150 and 500 fathoms is
from 1° to 2° warmer than that of a similar belt of water in
the Windward Passage. .

The temperature sections across the Gulf of Mexico show, on
the whole, that the temperature of the upper strata between the
surface and 150 fathoms diminishes much more rapidly than in
the Caribbean, and that already at the one-hundred-fathom line
it is lower than at the same depth in the Caribbean. From the
one-hundred-fathom line the temperature falls very rapidly, the
sectional lines across the Gulf showing a difference of 5° to 8°
between 150 and 600 fathoms from the temperatures of corre-
sponding depths in the Yucatan Channel. A comparison of
temperatures in the Gulf of Mexico on the two sides of the
Yucatan Bank brings out a striking contrast in temperature
between the eastern and western sides of the Gulf.

The lines from the Tortugas to Yucatan (Fig. 154) have
as a whole a warmer section than that of the Straits of Yucatan,
while the lines from the Yucatan Bank to the coast of Mexico
show at the same depth an increase of cold of more than 10° at

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TEMPERATURES. Oat

100 fathoms, of 14° to 17° at 200 fathoms, of 9° to 13° at 300
fathoms, of 7° to 8° at 400 fathoms, and of 2° to 4° at the five-
hundred-fathom line. The temperatures of the long lines from
Mexico to Florida bring out the same differences, with the ex-
ception that there is a marked rise of the cold-water belt along
the edge of the Florida Bank, which may be due to the general
rising of the cold water, as in other sections along the planes of
steep slopes. A comparison of the lines running north and
south shows that the line from Vera Cruz to Galveston (Fig.
155) is colder than that from the Yucatan Bank to Louisiana.
(Fig. 156.) The latter, in its turn, is colder than the line from

Port Muriel
(Cuba)

Se May 121878

GardenKey Licht
Dry Tortugas

P-% 39 fms,

Fathoms
§ 1
i

Yucatan to Santa Rosa, and that again colder than the line from
the Yucatan Bank to the Tortugas. The presence of this
thick layer of cold water between 150 fathoms and 600 fathoms
— water colder than we find at the same depths in the adjoin-
ing Caribbean, or at the same depths in the Atlantic — can per-
haps be explamed by the increased evaporation of the super-
heated upper stratum cooling the water below it.

The sections from the Tortugas to Cuba (Fig. 157), and from
Cape Florida across to Gun Key (Fig. 158), agree remarkably
in their general character with the Yucatan section. The de-
crease of temperature is nearly the same. The layer of warm
water is thicker close to the Cuban and Bahama side of the sec-

232 THREE CRUISES OF THE “ BLAKE.”

tions, showing that the temperature ' of the outflow of the Gulf
Stream across the Straits of Bemini is the same as that of the
mass of water which lies to the westward of it. As it was con-
clusively proved by Professor Mitchell in 1867 that the current

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Bight i B28 3 53 as : 232 riereds ( GreakBahama Bank)
saad 78° 788 7a 7a ast ech
<8 3? ok ‘6 ze } 738774
ee em g Oe 7 3s pete ms A
Tid fo” cex* ESS 69 i
so. —__----... = br aa" 62" St Ge 7 &
E 432° S3t Se es ez eta
E ACE 563 53* Got ie a
: oh me SE
Ce pase Se e sat 5, 5ér 6d ee
Ss E a Leb ee Ba 555
= < Ast a 56% 5
ce PR ees oe ee ee St 1a ee say
page ea At eR Box 4
net Le aS
406 oe a ca x Ls
Se ae ee
Te FES meena weew eee
Fig. 158

of the Gulf Stream extended to the bottom in the section be-
tween Havana and Key West, it is impossible any longer to
account for the cold water of the sections across the Straits of
Florida by an inflowing of cold water under the warmer water
across the Straits of Bemini. As a further confirmation of this,
we have the temperature of sections of the Gulf Stream taken
off Jacksonville (Fig. 159), north and south of Cape Cafiaveral

1 I copy from Commander Bartlett’s Report the cross-section taken by the

“Blake” between Jupiter Inlet and Memory Rock : —

“ At anchorage near Memory Rock, in four fathoms water. Surface, 78° ; bottom,
78°. ¥

5 miles Surface, 814° ‘ 294 fathoms, 564°
44 “ “ 814° SAT “ 52°
4, « « 814° 395 45°
44 “ “ 824° 439 “ 44°
eS « 83° 416 44°
5 “<c “ 83° 341 “ 44°
53 “ “ 824° 950 “ec 50°
Be ie « 80° 176 50°
3 «“ 80° 9 « Yh
a « “ 80° a) ae 71°
23 “ “ 80° 10 “ 782

21 miles from shore.
“ The area of this cross-section is 429,536,240 square feet, and, assuming the velo-
city at three knots, the delivery per hour would be 51,028,905,312,000 gallons.”

TEMPERATURES. 233

(Figs. 160, 161), and in 1853 oif Cape Caiiaveral (Fig. 162), off
St. Simon’s Island, Ga. (Fig. 163), and off Charleston, S. C., by

Lieutenant - Commanders Craven and Maffitt. These sections

\ 2431 fms.
$50 miles E.of
Jacksonville

a o
0 =)
Ss
= a
4
i

show that the temperatures of the line across the Gulf Stream
from Gun Key are, as a whole, colder than those at the above-

named points.
We seem here to have positive proof that the large body of

| g wf
ud o>
oF - a
& “S ae a Eg
‘a Sa eee e's
Qa & aS i) a £50
i = | ou ‘> } (oo
: & Hee aa Sf S55 Bos 2 Hee
ee = 4 aes) °o i g Sms
am ra 2 @ o aie
x o o ~ ac gy 3 9

¢# = one Bk i : i

as a H i :

A 3 | H

t ' '

§ tea eee :

‘ iS Lo le ————

gh” he

ees

Fig. 161.

warm water to the north of the straits adjoining the colder
water of the Gulf Stream must mainly derive its heat from the
equatorial current itself, and that it does not come wholly from
the superheated water of the Gulf of Mexico. Some of the

234 THREE CRUISES OF THE “ BLAKE.”

warmer water which joins the Florida Gulf Stream is driven
into it through the Old Bahama Channel, the temperature of
which seems to be very warm, being higher than we find it at
equal depths to the eastward nearer the Windward Passage.
The variable cold bands which have been traced in the course
of the Gulf Stream may also be due not wholly to cold water

= _—_,, Zstances from Cape Canaveral in Nautical Miles.
zi = Ao

|

war um Ix x x ao
! 1
ae ee eee
were I 1 1 '
, ha
i tee im
ee) aie Ue ee eae Bei 5
ims. : i H 4 i ! ‘ fms
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= Position

from an arctic current, but in part to the cold water of lower
and colder layers of the Florida Stream itself.

A comparison of the temperatures of the different sections
across the passages of the Windward Islands, the Straits of
Florida, and the Straits of Bemini is interesting as showing that
from the close agreement of the temperatures themselves across
these lines there is nothing to dicate that a powerful current
flows to the northward through the Straits of Bemini, or that
similar currents, though of less velocity, pass through the Straits

TEMPERATURES. 239

of Yucatan and the Windward Passage. Nothing but actual
observation has developed the fact that in the Straits of Bemini
this current extends across the whole width of the straits and
to the very bottom." In the Windward Passage the dredgings

Distances fiom the Coust in Nautical Miles.
fo is

eke mare
—] ar |
ee

Ems
50

200

300

400

600

Position.

Fig. 163.—Off St. Simon’s Island, Ga.

made on the dividing ridge and on each side of it indicate, from
the presence of a large amount of pteropod silt on the southern

1 Henry Mitchell looks upon the Nich-
olas and Santaren Channels, as well as
the Providence and Exuma, not as chan-
nels proper worn by currents, but as por-
tions of the ocean bed left undisturbed in
the upheaval of the Bahamas. These
channels are motionless masses of water,

in which the decline of temperature with
the depth is a little more rapid than in
the track of the Gulf Stream. Mitchell
also considers that the current of the Gulf
Stream has had no share in cutting out
the Straits of Florida.

236 THREE CRUISES OF THE “ BLAKE.”

face of the passage, and from the comparatively clean crest of
the plateau across which the Atlantic waters are driven into the
western Caribbean, that the current is flowing to the westward,
and extends to the very bottom of the passage. Our experience
in dredging between the Windward Islands was similar. We
found the floor of the passages generally swept clear of all ani-
mal life, while it was only to the leeward of the dividing ridges

So a)
A a i
2.4 ER
ES Sus
° om
2 $22 2 gon
2 na a
!

Fathoms

Fig. 164. ,

and of the islands, where the silt had a chance to accumulate,
that marine animals were found in great profusion.

A similar experience followed us along the course of the Gulf
Stream to the north of the Straits of Florida, while dredging
across the Blake Plateau, off the coasts of Georgia and the
Carolinas, and it was not until we reached the sea slope of the
Gulf Stream trough near Cape Hatteras that we again came
upon animal life in abundance; there we found it flourishing
in the silt which had been rolled by the Gulf Stream along its
bottom throughout its whole course from the Bahamas to Cape
Hatteras.

It was only on the shore edge of the Gulf Stream, or in por-

aes 237

tions where the current was of less velocity, that we found the
greensand deposits, and made an occasional successful haul of
the trawl or dredge. But the condition of the bottom speci-

a
an x
3
a
E€ Eos
|
Oo Wm in — —~
22h} so So 8 Se? ous 5 S Py E
SPS Ry UCI > o ~ > Ox 2 = es @
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‘ ; H | f r by Pe
H ' { H Hl i | { H i | H
; 7 H H 1 ! ' ! H
i rT 1 1 1 1 i I ' '
; ‘ ' ' | ! 1 ' '
; ‘ { i } i 1 H t H
H 1 1 ‘ 1 1 1 -
‘ ‘ 1 ' ! H i :
' 1 1 ' ' '
' ' ie} ; H :
fol BS ete ab eres ed ST
' ' 1 i 1 ; 1
' ‘ i 1 H
: ‘ a H 1
1 ‘ 1 '
H H H t 1
i) ‘ ' i

H
‘
'
!
‘
i
‘
!
‘
:
3 : :
g abt
BS pa Hr at H H
KR he
H ' 1
e400 ' H
Hes aie {
E See
2700; 36° | |
fe oe
L '
3000; =e Se ae :

Fig. 165.

mens and the absence of silt from our hauls gave us every in-
dication that the floor of the trough of the Gulf Stream was
bare and hard, and practically swept

ce S oe
Aw & Eo %
clear of all débris, and consequently a8 23% Sze
ee ae a2
!

could afford little foothold for the
development of animal life.

The soundings made by the YP a eee os |
“Blake” to the northward of San §
Domingo (Fig. 164) and to the east- £
ward of the Bahamas, as far as the
Bermudas (Fig. 165), and from the
Bermudas again along the triangle
bounded by the Bermudas, Cape Hat-
grag (Nic. 166), and the southern (7° =
coast of Massachusetts (Fig. 167),
have developed the following facts: namely, that there must
be a ridge which prevents water colder than 36° from finding

238 THREE CRUISES OF THE “ BLAKE.”

its way north between the Bahamas and the Bermudas, and
that there is a deep hole in which the enormous depth of
4.561 fathoms has been sounded by Lieutenant - Commander
Brownson, with a temperature of 36°. The same temperature
(between 36° and 37°) is found to be the bottom temperature in
the sections taken to the northward, the only exceptions being a
few colder soundings (a temperature of 35°) met within the lines
off Norfolk, off Cape May, and off Nantucket, at a distance of
about three hundred miles from the coast. Ata depth of 600

Bermuda Ids.

ag Uf£Montauk Pt,
=---% 12206
2900
~--y 2678
2675
..--| 2850
--| 2835
2600
---- 2520 fms,
w-----| 3175

Fathows

Fig. 167.

fathoms, off San Domingo, the temperature is 42°; at 500 fath-
oms, it is 45°. Off the northern extremity of the Bahamas it was
about the same. Owing to the abruptness of the slope and the
absence of serial soundings, we have no data regarding the thick-
ness of this body of cold water, with a temperature of about 36°,
which covers the bottom. Farther north this temperature begins
at a depth of about 1,500 fathoms. In the sections taken off
the Middle States, the temperature falls very rapidly, being 75°
at the surface, while at a depth of 1,000 fathoms it is not more
than 38°; and judging from the single section to the eastward

TEMPERATURES. 239

of the island of Eleuthera, the temperature appears to fall fully
as fast. This would indicate that the whole mass of water be-
tween the Bermudas and the eastern shore of the Atlantic coast
of the United States is moving northward under similar ther-
mic conditions, disturbed only by the cold stream which forces
itself southward from George’s Bank, along the edge of the
continental shelf, the exact limits of which are not yet ascer-
tained.

The presence of a large body of cold water close to the east
coast of New England * and the Middle States is shown by an
examination of the sections which extend from the vicinity of
Cape Hatteras to the northeastern end of George’s Bank. The
surface waters become gradually warmer as we pass to the east-
ward, rising, from temperatures of 55° at the surface and 42° at
a depth of 71 fathoms, to a surface temperature of 68° and
a bottom temperature of 38° at a depth of 980 fathoms. A
similar but somewhat less increase in surface temperatures is
traced in the lines run off Newport, of from 70° to 72°, and
off Montauk, of from 74° to 76°, in passing from 129 to 1,594
fathoms, with bottom temperatures of 51° and 38°. Off Cape
May the difference at the surface is still less, 77° to 78° while
falling from a depth of 89 to 1,200 fathoms, with bottom tem-
peratures of 56° and 39°. On the line immediately north of

1 The recent explorations of the United
States Fish Commission cover a belt about
160 miles long and from 10 to 25 miles
wide, along the coast of southern New
England, at a distance of 80 and 110
miles from the coast line, in depths be-
tween 65 and 700 fathoms. The sound-
ings and dredgings show the southern
continuation of the inshore cold belt, as
well as the warm belt outside of it, and
the cold deep-water belt. Professor Ver-
rill says, speaking of the Gulf Stream
slope: “The bottom along the upper
part of this slope and the outermost por-
tion of the adjacent plateau, in 65 to 150
fathoms, and sometimes to 200 fathoms
or more, is bathed by the waters of the
Gulf Stream. Consequently, the tem-
perature of the bottom water along this
belt is decidedly higher than it is along

the shallower part of the plateau nearer
the shore;in 30 to 60 fathoms. The Gulf
Stream itself is usually limited in depth
to about 150 fathoms, and often even less,
in this region ; below this, the temper-
ature steadily decreases to the bottom of
the ocean basin, becoming about 38°-37°
in 1,000 to 1,500 fathoms, and falling to
37°-35° in 1,500 to 2,500 fathoms. We
may, therefore, properly call the upper
part of the slope, in about 65 to 150 fath-
oms, the warm belt. According to our
observations, the bottom temperature of
the warmer part of this belt, in 65 to 125
fathoms, is usually between 47° and 53°
F. in summer and early autumn. Be-
tween 150 and 250 fathoms, the temper-
atures, though variable, are usually high
enough to show more or less influence
from the Gulf Stream.”

240 THREE CRUISES OF THE “ BLAKE.”

Hatteras, where the Gulf Stream and the northern current meet,
we find temperatures of 79° and 60° at the surface, in depths of 65 *
and 1,000 fathoms, and a bottom temperature of 38° near the
one-thousand-fathom line. South of Hatteras the surface tem-
perature is more uniform, like that of the stream itself, with a
far greater fall of temperature, 493° at 178 fathoms, 39° at 464
fathoms, and 37° at 1,632 fathoms, until we reach the lines
farther south, where, for the whole extent of the Gulf Stream,
in its northern extension along the Blake Plateau, we have a
bottom temperature of 44° at a depth of 400 fathoms, corre-
sponding to the temperature, at the same depth, of the Gulf
Stream when it passes through the Straits of Bemini.

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XI.
THE GULF STREAM.

Tue Gulf Stream is the best known and at the same time the
most remarkable example of the effect of oceanic circulation
upon the distribution of temperature in connection with the
currents of the North Atlantic. It has long been known to
geographers that a cold current coming from Greenland joins
the Labrador current, and extends in a southerly direction along
the eastern coast of the United States, while a warm current
pouring through the Straits of Florida flows in the opposite di-
rection * along the coast of the southern Atlantic States, and is
deflected from the Banks of Newfoundland, crossing the Atlan-
tic diagonally. This body of warm water makes itself felt along
the west coast of the British Islands, penetrating even as far as
the coast of Spitzbergen, and perhaps beyond, to Nova Zembla.
It is impossible to discuss the results of the more recent inves-
tigations of the Gulf Stream carried on by the “ Blake,” with-
out including the general questions of oceanic circulation, and
of the thermal conditions of the Atlantic in particular. I shall
therefore briefly state such points, derived from the explorations
of the “Challenger” and other expeditions, as will assist us in
understanding the history and physics of this great oceanic
current.

Sir Charles Lyell has called attention to the fact that in the

1 Along the American coast the sudden
transition from the green, cold, and more
or less turbid water found along the coast
and continental shelf, into the deep blue
waters of the warm Gulf Stream, is one
which has been noticed by all who have
passed from the shore seaward. This

cold green water, which has such a chill-
ing influence on the climate of the New
England States, follows the line of the
Atlantic coast of the United States far
towards the base of the peninsula of Flo-
rida.

942 THREE CRUISES OF THE “ BLAKE.”

present epoch the most marked physical feature of the surface
of the globe is its subdivision into a land and an oceanic hemi-
sphere. Thomson, like him, looks upon the oceans as contin-
uous, and has happily styled the Atlantic, the Pacific, and the
Indian oceans as great gulfs of the Southern Ocean.

The striking hydrographic character of the North Atlantic is
its comparative isolation from the Arctic Ocean; the South At-
lantic, on the contrary, is fully open to the circulation of cold
water coming from the Antarctic Ocean. (See Fig. 162.) The
South Atlantic is shut off from its northern area by the ridge ex-
tending from St. Paul’s Rocks to Ascension, at a depth of about
2,000 fathoms. The Challenger Ridge runs nearly north and
south, leaving a free communication between the Antarctic
Ocean and the eastern and western basins of the South Atlantic.
The North Atlantic is subdivided into an eastern and western
basin at a depth of about 1,500 fathoms by the Dolphin Rise,
which follows in a general way the course of the S-shaped At-
lantic basm. Ridges separating the Atlantic from the Arctic
Ocean extend across Denmark Straits, probably at a shallow
depth. From Greenland to Iceland the depth has an average of
500 fathoms ; from Iceland to the Fries, an average of about
300 fathoms; and from there to the Orkneys, of not more than
220 fathoms. From the configuration of the bottom (see Fig.
61), it is evident that a larger amount of cold water must reach
the tropics from the antarctic than from the arctic regions,'
which are shut off from the Atlantic by submarine ridges. Over
these, and through the channels of Baffin’s Bay, but a limited

1 The temperature line run diagonally
across the Atlantic from Madeira to
Tristan da Cunha by the “ Challenger ”
brings out the remarkably shallow stra-
tum of warm water of that part of the
equatorial regions which corresponds to
the regions of the tradewinds both north
and south of the equator. The tempera-
tures of the belts of water between 200
and 500 fathoms north and south of the
line plainly show that the colder water
found south of the equator cannot come
from the warmer northern belt of the
same depth, but must come from the

colder belt adjoining the equatorial re-
gion. In other words, the cold water
inay be said to rise towards the surface
near the equator ; and from the tempera-
ture of the two sides of the North Atlan-
tic it is also evident that the supply of
cold water flowing from the Antarctic
into the Atlantic is greater than that com-
ing from the arctic regions. This vertical
circulation, characteristic of the equato-
rial belt, is insignificant, however, when
compared with the great horizontal oce-
anic currents.

eae

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Pig. 169.

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pay

243

amount of cold water can find its way south. In the Eastern
Atlantic,’ the principal cooling agent must be the cold water
slowly flowing northward from the Antarctic between the Chal-
lenger Ridge and Africa.

The shape of the northern extremity of South America,
together with the action of the southerly trades, is such as to
split the southern equatorial current, and to drive a consider-
able part of this southern current northward to join the west-
erly drift which flows to the northward of the Greater Antilles
and Bahamas. The phenomena of oceanic circulation in their
simplest form are here seen to consist of westerly currents
impinging upon continental masses, deflected by them to the
northward and eastward, and gradually lost in their polar ex-
tension.

There is on the west side of the North Atlantic an immense
body of warm water, of which the Gulf Stream forms the west-
ern edge, flowing north over a large body of cold water that
comes from the poles and flows south. The limits of the line
of conflict between these masses are constantly changing, accord-
ing to the seasons: at one time the colder water from Davis’s
Straits spreads like a fan near the surface, driving the Gulf
Stream to the east ;* and at another, large masses of warm water
extend towards the Ferde Islands, with branches towards Ice-
land and the coast of Portugal.

An examination of an isothermal chart of the Atlantic (Figs.
168, 169) clearly shows the effect of the isolation of the North-
ern Atlantic; the area of maximum temperature (82°) extends
over a far greater space in the North than in the South Atlantic.
The Gulf of Mexico and the Caribbean become greatly super-
heated in September (to above 86°), the effect of this super-
heating in conjunction with the westerly equatorial drift being

THE GULF STREAM.

1 In the Pacific, the amount of cold
water flowing into it through the narrow
and shallow Behring’s Strait is infinitesi-
mal compared with the mass of cold
water creeping northward into the Paci-
fie gulf from the depths of the Southern
Ocean.

2 The direction from which the cur-
rents come is plainly shown by the nature

of the bottom specimens, made up in
part of globigerinz brought by the warmer
southerly surface currents, and in part
of northern foraminifera and of volcanic
sand derived from Jan Mayen and Spitz-
bergen. The dividing lines between these
deposits may be considered as the boun-
daries of the arctie current where it passes
under the Gulf Stream.

944 THREE CRUISES OF THE “ BLAKE.”

seen clearly in the northerly extension of the isothermal lines.
In the South Atlantic,’ owing in part to the greater regularity
in the shape of the basin, the difference in the extension of the
isothermal lines is but little marked.

The temperature sections of the “ Challenger,’ from Tene-
riffe to Sombrero, show remarkably well the great contrast mm
temperature between the eastern and western basins of the At-
lantic, which are separated by the Dolphin Rise. In the eastern
basin, the cold water on the bottom is supplied by the indraught
from the South Atlantic, while the warmer surface water of the
western basin is due to the westerly equatorial currents. We
seem, therefore, to have masses of water of different temper-
atures accumulated at certain points by surface or bottom cur-
rents, to be distributed again, either north or south, into the
general oceanic circulation, thus restoring the equilibrium dis-
turbed by the unequal distribution of heat and cold on the sur-
face of the ocean.

Another temperature section (Fig. 170) which I shall borrow
from the “ Challenger” soundings, to complement the work of
the “ Blake” in the same regions, is that which extends from
Halifax to the Bermudas, and thence to St. Thomas. The
temperatures observed by these vessels show plainly the path of
the warm surface-water, which flows outside of the West India
Islands, and joins the Gulf Stream proper, whose waters when
united are banked against the cold Labrador current in its course
along the American coast.

Undoubtedly, the early observations made upon the temper-
ature of the ocean were defective, owing to the somewhat im-
perfect instruments at the disposal of the early explorers. Yet
they determined the general position of the cold and warm cur-
rents of the ocean along our shores. The more systematic work
of the officers of the Coast Survey first proved the existence of
vast bodies of water, of considerable thickness, and of very dif-
ferent temperatures at corresponding depths, moving in opposite
directions. It is to the Coast Survey that we owe the demon-

1 The parallelism of the lines of tem- fluences. See J. J. Wild, “Thalassa,”
perature is also very marked inthe South Plate XV., and ‘Challenger Tempera-
Pacific, where there are no disturbing in- tures.”’

2900
3000
53100
3200
3300
3400
3500
3600
3700
3800
3900
4000

Sambro I.

b

1

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we Chet
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ro) e io} io) ° Fo02 8 ° ° °
wt ry nu ° 1» ve) oun = S ° 9 ”°
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A a ” u a mon om nu a a )
— - -ae—— 7° _- -___-___ _~34 =
0 = ae i
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: = =
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| ‘ i \ | {
H k igee; \ ' {
36°3 ! Bee \ H !
1B6°4

390 fms.

st Thomas

roe

et

THE GULF STREAM. 245

stration of the fact that the waters of the polar regions pour
into the tropics along the bottom, just as the warmer equatorial
waters flow across the temperate zones near the surface, and
make their influence felt in the polar regions.

The submarine ridges interrupt the flow of these cold polar
waters, and form the so-called closed basins, with a higher bot-
tom temperature than that of the adjoining oceanic basin. The
effect of such ridges upon the bottom temperature was first
traced by the soundings of the “ Porcupine” in the North
Atlantic and in the Mediterranean. Subsequently, the “ Chal-
lenger”’ discovered several such enclosed seas while sounding in
the Kast Indian Archipelago.

The correctness of these results has been confirmed by the
Coast Survey, from soundings in the Caribbean and in the Gulf
of Mexico; their bottom temperature (at a depth of over 2,000
fathoms) is exactly that (393°) of the deepest part of the ridge,
at about 800 fathoms, which separates them from the oceanic
Atlantic basin, with its temperature of 36° at the depth of 2,000
fathoms. |

The presence of thick layers of water having a higher bottom
temperature than that of adjoining areas would indicate the
presence of ridges isolating these warmer areas from the general
deep-sea oceanic circulation. A map of the Atlantic, made en-
tirely with reference to the temperatures, would correspond to a
remarkable degree with the topography of the bed of the ocean,
and show how and where the breaks in the continuity of the cir-
culation, both for the arctic and antarctic regions, occur in the
Atlantic. (See Figs. 140, 142.)

It was not, however, until the Miller-Casella thermometer
came into general use for deep-sea investigations that a degree
of accuracy before unattainable in oceanic temperature became
possible. It soon was a well-recognized fact that as we go
deeper the temperature diminishes, and that at great depths the
temperature of the ocean is nearly that of freezing. In 1868-
69, in the Ferées Channel, the “ Porcupine” found a tempera-
ture of —1.4° C. at a depth of 640 fathoms, and a temperature
of 0° C. at 300 fathoms, this being a southern extension, as was

subsequently found, of the deep basin of 1,800 fathoms lying

246 THREE CRUISES OF THE “ BLAKE.”

between Norway and Iceland. The same temperature, 0.9° C.,
occurs under the equator at a depth
of about 2,300 fathoms, while 5°
C. is found at a depth of 300
fathoms. As early as 1859 the
Coast Survey had recorded in the
Straits of Florida a temperature
of 40° F. (4.4° C.) at a depth of
300 fathoms, while at the surface
the temperature was 80° F. (26.7°
C.). Beyond 1,000 fathoms the
temperature diminishes very slowly.
The “Challenger” also found a
temperature somewhat below zero
off the Rio de la Plata, at a depth
of about 2,900 fathoms.

| The temperature of the oceanic
_ basin depends upon the depth, the
_ latitude, the currents, and the
seasons; that of mediterraneans
(land-locked seas) is controlled by
other causes, which will be more
fully discussed when we come to
treat of the temperature of the
Caribbean and of the Gulf of Mex-
ico. The constants are the depths
and latitude, while the disturbing
elements are represented by the
varying atmospheric and oceanic
currents and the seasons." The
effects of seasonal differences of
temperature do not extend to great
depths, yet act with sufficient
power greatly to modify the force

1 Dr. J. J. Wild has givenin “Thalassa”
an excellent diagram, showing at a glance the
general relations of the temperature in the
liquid envelopes to the earth’s crust. It is
Fig. 171. here reproduced (Fig. 171), slightly modified.

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THE GULF STREAM. 247

and volume of the oceanic currents. As a general rule, the tem-
perature diminishes from the surface towards the bottom, a belt
limited in depth (about 150 fathoms) alone being subject to
variations due to the action of the sun. Below that, the tem-
perature generally decreases with the depth, until we reach the
body of water of which the temperature may in general be
said to be uniform (about 35°)."

As explanations of the oceanic currents, we have, first, the
gravitation theory, which looks upon the differences of tempera-
ture and of specific gravity of the water at the equator and poles
as the prime cause of oceanic circulation ; next, Thomson’s the-
ory, according to which the difference in evaporation and preci-
pitation between the northern and southern hemispheres causes
a consequent heaping up of water in the southern hemisphere,
which south of latitude 50° is completely covered by water ;
thirdly, the theory which attempts to account for the circulation
by the vis nertie of the equatorial waters; and, lastly, the the-
ory which considers the tradewinds and other prevailing winds
as the principal causes by which oceanic currents are produced.
Franklin, Humboldt, Rennell, Sir John Herschel, and Croll have
supported this view of the origin of oceanic currents.

Of course, until the extension of the frictional effect of winds
to great depths has actually been measured, the last theory,
plausible as it may appear, lacks its final demonstration. It is
by no means proved, because there is an apparent connection in
time between the periodic variations of the currents and of the
tradewinds, that we must seek in the latter the only cause for the
existence of the former. The presence of the Guinea Stream,
the position of the region of calms in the northern and southern
hemispheres, the diminishing force of the tradewinds as we ap-
proach the equator, the rise of the colder strata of water to shal-
lower depths in the equatorial than in the temperate regions, are
phenomena which the action of the tradewinds alone does not
seem to explain. Why may not oceanic circulation, like the

1 As currents sink as soonas theirtem- well as from the equator to the pole, a
perature falls below that of adjoining combination of these varying elements
waters, and as the temperature diminishes may produce a somewhat complicated
from the surface towards the bottom, as_ circulation.

248 THREE CRUISES OF THE “ BLAKE.”

movements of our atmosphere, be dependent upon cosmic phe-
nomena, practically independent of any secondary causes, and
modified by them within very narrow limits ?

The difference in salinity of certain oceanic districts is in it-
self insufficient to explain oceanic circulation ; so that while the
secondary causes referred to above are undoubtedly active as
producing more or less extensive local circulation, we seem jus-
tified in looking upon the differences of temperature of the zones
of the ocean as the principal cause of the general oceanic cir-
culation. We may state, in the main, that the density of the
ocean water is least at the equator, gradually rises towards the
poles, and attains its maximum at 60° of latitude. For the sake
of convenience we may call the density of the ocean as one at a
depth of 500 fathoms, and consider the strata of water above
and below as having a less and a greater density,’ within very
narrow limits; thus the watery envelope is not in a state of
equilibrium.

The most important disturbing factors of a uniform distribu-
tion of oceanic temperature are the continental masses which lie
in the path of the equatorial currents.. A comparison of the
position of the oceanic isotherms of the North and South At-
lantic shows a striking contrast in their course north and south
of the equator. A similar comparison between the Atlantic
and Pacific brings out plainly the contrast in the course of the
isotherms of two oceans, in which the disturbing effect is due
in the one to continental masses, and in the other to large
groups of oceanic islands.

Perhaps the best example of the unstable equilibrium existing
between adjoining oceanic areas is furnished by the heaping up
of the waters driven by the tradewinds into the Gulf of Mexico
from the Caribbean. The amount of this accumulation has
actually been measured by officers of the United States Coast
Survey. It gives an additional force at work to keep up the
efficiency of the Gulf Stream. The Gulf of Mexico is consid-

1 Ocean water, at depths exceeding either colder or warmer, it must expand ;
1,000 fathoms, has a temperature of this it cannot do, on account of the pres-
nearly 35° F., the temperature of great- sure.
est density. Should the water become

THE GULF STREAM. P49

ered by Mr. Hilgard as an immense hydrostatic reservoir, rising
to the height of more than three feet * above the general oceanic
level, and from this supply comes the Gulf Stream, which passes
out through the Straits of Bemini, the only opening left for its
exit.

Avago, Lenz, and Leonardo da Vinci before them, maintained
that since the water of the equator was greatly heated and
lighter, and attained a higher level, there was a flow of the sur-
face waters towards the poles, a compensation being established
by the flow of lower strata from the poles to the equator. The
_ principal features of this thermic theory have of late found their
most efficient exponent in Dr. Carpenter. The results of his
experiments to prove this theory upon a small scale seemed to
show that the cooling of the waters at the pole, and their rapid
fall, were a more efficient force than the heating of the water at
the equator. Ferrell has called attention to the phenomenon
that cold water at the bottom will be swung more to the west-
ward than the water at the top, which will be turned in an east-
erly direction. As the particles of water ascend, they retain the
velocity they had in deeper parts of the ocean, and thus, when
reaching’ either the surface or lesser depths than their original
position, they must show themselves as producing a westerly
current. This current, deflected by the continental masses as
it strikes the east coast, would then be set in motion towards
either the north or sduth pole. At the equator, the water
which flows westward from the eastern shores of the continen-
tal masses can only be replaced by the compensating waters
flowing to it from the north and south. This circulation fairly
agrees with the phenomena observed in the South and North
Atlantic.

It is interesting to trace the gradual development of our
knowledge of the Gulf Stream, and to see how far-reaching
has been the influence of the oceanic currents upon the explora-
tions of maritime nations, and the effect these have had in their

1 By a most careful series of levels, first point is forty inches lower than the
run from Sandy Hook and the mouth of Gulf of Mexico at the mouth of the Mis-
the Mississippi River to St. Louis, it was _ sissippi.
discovered that the Atlantic Ocean at the

250 THREE CRUISES OF THE “ BLAKE.”

turn on the discovery of America and its settlement.! The
hardy Norse navigators, nearly five hundred years before Co-
lumbus, sailed along the eastern shores of Greenland and
America, and extended their voyages possibly as far south as
Narragansett Bay, following the Labrador current, which swept
them along our eastern shores. It was well known to naviga-
tors that upon the western shores of Norway and the northern
coast of Great Britain, driftwood of unknown fimber and seeds
of plants foreign to the temperate zone were occasionally
stranded, coming from shores where probably no European had
as yet set foot.

The Portuguese navigators, sailing west, came beyond the
Canaries to an ocean covered with seaweed (the gulf-weed of
the Sargasso Sea), through which none dared to push their way,
and the problem of the “Sea of Darkness” remained unsolved
until the time of Columbus. He possibly was familiar with the
traditions of the voyages of the Norsemen, and undoubtedly
had access to more or less accurate information regarding the
Atlantic, accumulated previous to his time im the archives of
Portugal and Spain, or circulated among the sea-folk of that
day, and this information included legends of lands to the west.
Columbus started under the full persuasion that he could reach
the lands from which the remarkable products brought by the
currents had originated. When he came into the region of the
northeast trades, and found himself swiftly carried westward,
not only by the winds, but also by a current moving in the
direction of the trades, his return seemed very hazardous, un-
less he could strike upon that opposite current, which had
borne the trees and seeds to the. northern coasts of Europe.
Obliged by the trades to take a northerly course on his way
home from Hispaniola in 1493, he came upon the region of
variable and westerly winds, with a current setting in the same
direction. Columbus was thus the first to mtroduce the circular
sailing course which, up to the present day, vessels sailing from
the West Indies to Europe are compelled to take. They come
before the wind with the trades, make the Windward Islands,
and, sailing northward, find their way through the Windward

1 See Kohl, J. G., Geschichte des Golfstroms und seiner Erforschung, 1868.

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THE GULF STREAM. 251

or the Mona Passage, until they reach the belt of variable and
westerly winds, when they steer toward the European shores
again.

After reaching the Mexican coast, Comes by one of his
broad generalizations, practically discovered the Straits of Flo-
rida ; arguing that it must have an outlet into the Atlantic, and
that i would thus escape the tedious voyage in the teeth of
the northeast trades, which would be his lot if he attempted to
find his way home by the usual route of the Windward or the
Mona Passage. In 1519, an expedition inspired by Alaminos
was despatched by aes Governor of Jamaica, to follow the
easterly current running along the northern shores of Cuba.
The expedition, however, did not succeed in passing to the east-
ward of Cape Florida.

An accurate knowledge of the currents and winds enabled
the freebooters of the sixteenth century to carry on their depre-
dations with impunity, and their successors, the wreckers of the
Florida reefs and Bahamas, made use of their intimate know-
ledge of the coasts, and of the winds and currents, to obtain
commercial advantages, not always by the most honest methods.
With the mapping of the reefs by the Coast Survey all this has
disappeared, and the lighting of the great highway of the
Straits of Florida has reduced to a minimum the dangers of
navigation, though the Tortugas are still a favorite resort, even
in broad daylight, for old ships properly insured. (Compare
Figs. 172 and 54.)

The captain of one of the Spanish vessels was carried south,
off the coast of South America, by the current which sweeps
from Cape St. Roque along the shores of Brazil, and involunta-
rily discovered the Brazilian shore current. Though these dif-
ferent currents were known to exist in the Atlantic, the most
crude notions of their origin and course prevailed. (Fig. 172.)
' According to Columbus, at the equator the waters of the ocean
moved westward with the heavens above, rolling over the fixed
earth as a centre. It was only in the seventeenth century that
physicists began to suspect a connection between the currents
and the rotation of the earth, a view afterwards maintained by

Arago and Humboldt.

252 THREE CRUISES OF THE “ BLAKE.”

The first scientific basis for the exploration of the Gulf
Stream was undoubtedly due to Franklin. At the time he was
Postmaster-General of the Colonies, his attention was called to
the fact that the royal mail packets made much longer passages
to and from Europe than the trading vessels of Massachusetts
and Rhode Island. On talking the matter over with Captain
Folger of Nantucket, he first learned the existence of a strong
easterly current, of which the New England captains took
advantage in going to Europe, and which they avoided by
sailing a northerly course on the home voyage. Folger also
called Franklin’s attention to the fact that this current was a
warm one.’ He and Dr. Blagden becoming interested in the
question, Franklin set out to ascertain the size of the current
and its temperature. Soon after, Franklin published the first
chart of the Gulf Stream (Fig. 173), for the benefit of navi-
gators, from information obtained from Nantucket whalemen,
who were extremely familiar with the Gulf Stream, its course,
strength, and extent.

From the time of Franklin until the problem of the Gulf
Stream was again attacked, in- 1845, by Franklin’s descendant,
Prof. A. D. Bache of the United States Coast Survey, many
ingenious theories were published, but nothing was added to our
knowledge of the origin and structure of the Gulf Stream.
Humboldt, Arago, and others attempted to trace in the Gulf
Stream a secondary effect of the tradewinds, and of the rota-
tion of the earth. The officers of arctic expeditions sent to
Spitzbergen did not fail to see the effect of a mass of warm
water passing northward, and Von Baer was among the first to
consider this body of water as an eastern extension of the Gulf
Stream. Meanwhile the arctic explorers of Baffin’s Bay and
western Greenland found themselves baffled in their efforts to
reach high latitudes by the powerful southerly current, carry-
ing with it fields of ice or huge icebergs, which had found their
way south below the southern limits of the Banks of Newfound-
land, and even beyond the latitude of Cape Cod and Nantucket
Shoals.

1 It was noticed by Lescarbot, in 1605, both north and south of it the water of
that far north there was a mass of warm the Atlantic was cooler.
water moving towards the east, and that

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GHART OF THE GULF STREAM

Showing: its axis and limits

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U.S.COAST SURVEY
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CHART OF THE GULF STREAM
from 1845-1860.

Showing its axis and limits

THE GULF STREAM. 253

The earlier work of the Coast Survey in its investigations
into the structure of the Gulf Stream (1845 to 1860) consisted
in making sections across the stream, from the Straits of Bemini
as far north as the latitude of Nantucket. From the studies of
Craven, Maffitt, Bache, and Davis were developed the so-called
cold and warm bands, believed at that time to be the principal
characteristic of the Gulf Stream. The accompanying map
(Fig. 174), published in 1860 by the Coast Survey, will serve
to illustrate the structure of the Gulf Stream as it was then
understood ; namely, as a succession of belts composed of warm
northerly currents flowing side by side with a cold southerly
eurrent, or of a cold southerly enrrent which had found its way
under the warmer northerly currents. These alternating belts
had no definite position, the size of the colder bands and warmer
belts being dependent, the one upon the force of the arctic cur-
rent, the other upon that of the tropical current, increased in
breadth and volume beyond the Bahamas by the whole of the
warm belt of surface equatorial water, which is deflected north-
ward by the Windward Islands, instead of forcing its way
through the passage between the Windward Islands, the Mona
and Windward Passages, and the Old Bahama Passage."

1 Great as is undoubtedly the effect of creasing the temperature of the water in
the Gulf Stream proper (Fig. 175) in in- northern latitudes subject to its influence,

3
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A

Futhoms

Fig. 175. (Challenger.) .

254. THREE CRUISES OF THE ‘“ BLAKE.”

Commander Bartlett found no warm or cold bands, no distinet
cold wall, and no bifurcations in the surface waters till he came
off Hatteras. Near the shore, the current was greatly influ-
enced by winds. The work of the “Blake” seems to show
that the cold bands so called, which figure so largely in all early
descriptions of the Gulf Stream, have no regularity, and only
represent at any given moment the unceasing conflict goimg on
between layers of water of different velocities and of different
temperatures. Such a conflict is perhaps the well-known rip we
encountered off Charleston, which may be caused by a struggle
between portions of the Labrador current passing under the
Gulf Stream. As the isotherms rise and fall with the irregu-
larities of the bottom, where water accumuiates or piles against
ridges, hot and cold bands may be flowing one above the other.
We need, however, more prolonged observations to show how
far below the surface these bands extend. Commander Bartlett
from the last Coast Survey investigations under his direction
is inclined to consider the cold bands of the Gulf Stream as
quite superficial.

A cold current striking against a warmer stream that is flow-
ing in the opposite direction may split. it into more or less
marked hot and cold bands. Bands similar to those of the
Gulf Stream were observed by the “Challenger” in the Agu-
lhas current off the Cape of Good Hope, and off Japan in the
Kuro-Siwo.

It is of course difficult to ascertain the part taken by the

we must not forget to add to it that of
the greater mass of heated water which
is forced north, and finds its way to the
northernmost shores of Siberia, losing in
its passage the heat it has accumulated
within the tropics. So that, while we
cannot say that the Gulf Stream has dis-
appeared, and has been replaced off the
Banks of Newfoundland by the equato-
rial drift, neither can we attribute to the
Atlantic drift alone the masses of warm
water found in the basin of the northern
part of the North Atlantic. (See Figs.
170 and 175.)

1 Tn sailing from Halifax to the Ber-

mudas, Sir Wyville Thomson speaks of
passing alternate belts of cold and warm
water. Early in the morning of the 22d
of May, the surface water was of a tem-
perature of 17° C.; at midnight it had
fallen to 12° C., to rise again half an
hour later to over 15° C. Thus, from
the time the “Challenger” left Hali-
fax with a surface temperature of 4°
C., gradually rising to 10° C. until she
encountered the Gulf Stream proper,
marked by a rapid rise of temperature,
she passed through alternate belts of
warm and cooler surface waters varying
between 18° C. and 23° C.

THE GULF STREAM. 255

tradewinds in originating the oceanic circulation of the Atlan-
tic. That winds blowing steadily from one quarter give rise to
powerful currents is well known, and it is not difficult to imagine
the prominent part the trades must play in setting in motion,
in a southwesterly and a northwesterly direction, the mass of
water over which they sweep so persistently on each side of the
equator.

The change of currents in the Indian Ocean due to the shift-
ing of the monsoons is well known. How far below the surface
this action of the winds reaches, is another question. Theo-
retically it has been calculated by Zoeppritz that one hundred
thousand years is ample time to allow the friction of the parti-
cles to extend from the surface to the bottom, say to two thou-
sand fathoms, were the winds to blow without intermission in
one direction during that time, with the average power they are
known to possess.”

We may imagine the whole of the mass of the Atlantic within
the belt of the tradewinds to be moving in a westerly direction,
and impinging upon the continental slope of South America *
and upon the Windward Islands; at which point it is deflected
either in a southerly or northerly direction, or forces its way
into the Caribbean. In our present state of knowledge it is
difficult to trace the path of the equatorial water as it is forced
into the eastern Caribbean. Commander Bartlett supposes that
it is warmed in the Caribbean by circulating round the whole
basm. The water which is swept into the Caribbean by the
tradewinds through the passages between the Windward Islands,
and being then driven into the Old Bahama Channel funnel,

1 The movement arising from the ac-
tion of the winds on the surface is trans-
mitted by friction from one layer to an-
other, and communicates the velocity of
the upper particles to the underlying
layers in succession. If this is continued
long enough, the velocity of the lowest
layers will equal within a fraction that of
the upper layer.

2 It is therefore possible that currents,
which owe their existence to causes that
have. been modified to a certain extent,
should still exist in the ocean long after

the conditions producing them (acting
from the surface) have ceased to be effec-
tive by any break of continuity due to the
interposition of islands or of banks in
the track of oceanic currents.

3 Did the Gulf Stream not meet conti-
nental masses, it would simply expand
north and south, losing its initial velocity,
and gradually cool down towards the
poles ; the cold penetrating all the deeper
portions of the ocean, just as we find it
reaching the higher summits that rise
above the line of perpetual snow.

256 THREE CRUISES OF THE “ BLAKE.”

flows through the Windward Passage, represents a far greater
mass than that which can find its way into the Gulf of Mexico
through the Straits of Yucatan, or that of the stream flowing
north through the Straits of Bemini. This is the actual Gulf
Stream, a body of superheated water filling the whole straits ; it
has an average depth of about three hundred and fifty fathoms,
and a velocity extending to the bottom of at least three and a
half miles an hour.’

The section of the Yucatan Channel is too small to allow for
an outflow equal to the inflow into the Caribbean,’ so that, after
the trades have ceased to force the equatorial water into the Car-
ibbean basins, it must remain there a considerable length of
time before it passes into the Gulf of Mexico, where, owing
to similar differences between the rate of inflow and outflow,
the water must become still more superheated.

We must therefore consider the Gulf Stream proper, as it
emerges from the Straits of Bemini, as an immense body of su-
perheated water, retaiming an initial velocity which originated in
lower latitudes ; then losing both its velocity and its heat on its
way north.’ (See Fig. 176.)

The Straits of Florida have a width of about forty-eight miles
between Jupiter Inlet and Memory Rock; the greatest depth is
439 fathoms, and the cross-section 430,000,000 square feet. At
three knots the delivery would be, as calculated by Commander
Bartlett, about 436,000,000,000,000 tons a day,—an amount
of warm water far less than that we find over the North Atlantic,

1 Current observations taken by Mit-
chell off the coast of Cuba, in the deep
part of the Gulf Stream, show that it has
a nearly uniform and constant velocity
for a depth of 600 fathoms, although the
temperature varies 40° F.

the section of the Gulf Stream observed
by the “Challenger” was cooled 1° C.,
as compared with that of the Bermudas
to New York. The Gulf Stream retains
its heat as a surface current as long as the
temperature is sufficiently high to make
it lighter than the surrounding water.
Its greater salinity at last causes it to
sink below the comparatively fresher wa-
ter of northern latitudes. Similarly, the
arctic current, when it reaches a cer-

* A part of this -water emerges again
at a higher temperature between Guade-
loupe and Hayti, and joins that portion
of the equatorial current which finds its
way into the Windward Passage. This

increased temperature may be due to its
passing over shoals and banks at the
northeastern end of the eastern basin of
the Caribbean.

® Between Halifax and the Bermudas

tain latitude along our eastern coast, smks
from its greater specific gravity below the
warmer surface currents, and continues
its way south as an undercurrent of cold
water.

257

which, as has been shown, is derived from the western set of the
equatorial current joming the Gulf Stream in its way towards
the European shores.’ . (See Figs. 170-175.)

Commander Bartlett thus describes the general course of the

Gulf Stream : —

“The Gulf Stream has for its western bank the one-hundred-fathom
curve as far as Cape Hatteras. It has a depth of 400 fathoms as far as
Charleston, where it is reduced to 300 fathoms; but the Arctic current
has for its western bank the one-thousand-fathom curve, which is quite
close to shoal water from the George’s Bank to Hatteras.

“The average surface temperature in the axis of the Stream rarely
exceeded 83° F. in June and July. On one or two occasions the ther-
mometer read as high as 86°, and once 89°; but it was at high noon in
adead calm. The temperature at five fathoms did not range above the
average of 813°.

“The increase of temperature of the surface was found as we entered
the current... .

“The surface temperatures did not indicate a cold wall inside of
the Stream, and the water inside of the one-hundred-fathom line to
the shore seemed to be an overflow of the Stream, as the temperatures
to five, ten, and fifteen fathoms were nearly as high as those found in
the Stream.

“The temperatures at the bottom in the Stream, at corresponding
depths, were the same as those found in the Windward Passage, and
in the course of the current to the Yucatan Passage. The average
bottom temperature at 400 fathoms was 45°, and, as off Charleston,? in
300 fathoms, 53°. The temperature at 300 fathoms, off the George’s

THE GULF STREAM.

1 It might, perhaps, be advisable to
distinguish between the eastern exten-
sion of the Gulf Stream combined with
the Atlantic drift, and the Gulf Stream
proper, understanding by the latter the
water which passes through the Florida
Straits. This has been called by Peter-
mann the Florida Stream ; and the name
of Gulf Stream he has applied to the im-
mense body of warm water which super-
heats the basin of the Eastern Atlantic

2 About eighty miles from Charleston
the axis of the Gulf Stream.

to the eastward of 45° W. Long. There
seems to be no reason for changing the
name of the Gulf Stream because so many
other liberties have been taken with it.
We should retain the original name, limit-
ing it to the Florida Stream coming from
the Gulf of Mexico, and apply to its east-
ern extension, in connection with the At-
lantic easterly drift, some new name,
such as the Equatorial Drift, or the Car-
ibbean Stream.

a line was run parallel to the coast, along

Depth in Surface Tem- Temperature Bottom Tem- Nature of

Pathoms. perature. at 2 fathoms. perature. Bottom.
257 83° 83° 50° No specimen.
291 83° 83.5° 45° Fine sand.
274 83.5° 83.5° 44.5° Coarse sand.
288 87.5° 83.5° 45° No specimen.
265 84° 83.5° 45° Coarse sand.

258 THREE CRUISES OF THE “ BLAKE.”

Bank, was found in July to be 40°; and this last was the temperature
that we found at the same depth just north of Hatteras and the Gulf
Stream.

“T have stated that the surface temperatures did not show a cold
wall inside the Stream; but the bottom temperatures give a narrow
cold section close to the one-hundred-fathom curve all along the course
of the Stream from Hatteras to Florida. Soon after leaving the Straits
of Florida there is a division of the Stream shown by the bottom tem-
peratures, part following the coast, and the remainder branching off to
the eastward. . . .

‘“* We found that three knots was a general average to allow for the
whole stream. This would give a greater velocity at some central point.
Between the Bahamas and Florida the average was exactly three miles
per hour; but for a distance of fifteen miles in the axis of the Stream
it was as high as 5.4 miles per hour. To the northward of the Bahama
Banks, and to the eastward of the Stream, there was a slight current
setting southeast. We found the direction of the current in the Stream
very much affected by the wind, — sometimes inclining it to the east,
then to the west.!

“ In the latter part of June, 1881, we were hove to, some fifty miles
east of the Gulf Stream, off Charleston, where we experienced a current
of three miles per hour, setting southeast; wind blowing a gale from
southwest.”

“The sudden rise of the plateau off Charleston, together probably
with the meeting of the arctic and warm currents, creates a remarkable
disturbance at ee point. .

“* We crossed the Beenie SIX Atinas in this locality, under conditions
of weather from a calm to a strong breeze, and always crossed, near the
centre of the Stream, bands of rippling water several miles in width.
It is very like the rip at the entrance to Long Island Sound.”

The Gulf Stream flows at the rate of about one fourth of a
mile an hour through the Yucatan Channel, which is ninety
miles wide, and over one thousand fathoms deep. Through the

1 Inshore of the Gulf Stream, thougha
southerly current was distinctly traced in-
side the one-hundred-fathom line, yet the
temperature of the water towards the
shore was but little cooler than that of
the Stream itself ; the same is found to
be the case if we examine the tempera-
ture sections of the eastern edge of the
Gulf Stream. The Stream itself seems

to be mainly characterized by its velocity
and by its color.

2 On the southern side of the Gulf
Stream Commander Bartlett observed im-
mense quantities of gulf-weed ; this is also
blown into Narragansett Bay in consider-
able quantities, covered with clusters of
floating barnacles.

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THE GULF STREAM. 259

Straits of Bemini it has a velocity of from four to five knots, a
width of fifty miles, and an average depth of three hundred and
fifty fathoms. This velocity rapidly decreases as we go north.
(Fig. 176.) Off St. Augustine it is rarely more than four miles ;
from there to New York it decreases to two and a half miles
per hour; off the Banks of Newfoundland it is reduced to one
and a half or two miles; and at a distance of three hundred
miles to the eastward the velocity of the Gulf Stream, which
has constantly been spreading out fan-shaped, is scarcely per-
ceptible.

As far as the current observations of the “Blake” may be
trusted, they indicate a greater speed in the axis of the Gulf
Stream than along its edges, —a velocity varying between two
miles an hour, or even less, and fully five miles. The width of
the Stream off the east coast south of Hatteras varies from fifty
to nearly one hundred miles.

The observations of the “‘ Blake ?” show that the bottom of the
Gulf Stream along the Blake Plateau is swept clean of slime and

* ooze, and is nearly barren of animal life.

Xl.
SUBMARINE DEPOSITS.

THE explorations of the “ Blake’ during my stay on board
did not extend to oceanic basins far from land, but were limited
to the investigation of enclosed seas like the Caribbean and Gulf
of Mexico, and of the continental edges of a part of the west-
ern basin of the North Atlantic. The “Blake” subsequently
sounded the oceanic basin to the west of the Bermudas and
north of the Windward Islands. I have myself had no oppor-
tunity of seeing on the spot the deposits characteristic of a true
oceanic area, and have supplemented the results of the “ Blake”
by those obtained by the “Challenger” and “Tuscarora” in
the great oceanic basins.

The character of the bottom specimens near shore differs very
materially from that of deposits brought from corresponding
depths in the open ocean. Along the Atlantic shores of the
United States, these deposits are primarily affected by the geo-
logical structure of the mainland, the width of the continental
shelf, the direction of the currents and of the prevailing winds,
and the presence or absence of rivers. Within the Caribbean
and on the oceanic face of the Greater and Lesser Antilles, the
presence of an equatorial current, of the tradewinds, of volcanic
rocks, and of extensive limestone plateaux, introduces conditions
which differ radically from those operating upon the Atlantic
coast. In the Gulf of Mexico, although the distance from shore
of the central part of the basin is often very considerable, still
the character of the bottom deposits is always somewhat affected
by its peculiar physical conditions. And nowhere in the Gulf
or the Caribbean, or around the Atlantic slope of the United
States, do we find any ooze strictly comparable to that of the
open oceanic basins.

261

SUBMARINE DEPOSITS.

The constant working over of the loose material by the waves
and currents along every part of the coast line is repeated on a
larger scale upon the continental shelf of our Atlantic coast.
There the results depend, not only on the nature of the materi-
als of the adjoining coast, but also upon the distance from shore,
the depth, the slope of the coast, and the character of the bot-
tom, and of the animals and plants living upon it and in the
surface waters.

Mr. Murray * of the “Challenger”’ has paid special attention
to the bottom deposits, and we draw freely from his papers
in the sketch which we give of the various kinds of bottoms he
has recognized, as well as of the interesting views he holds on
the nature and origin of oceanic deposits. The subject as a
whole was first treated by Mr. Murray, to whom in connection
with the Abbé Renard we owe a connected sketch of deep-sea
formations.

Our knowledge of marine deposits was formerly limited to
those of shallow waters. Attention was paid only to specimens
which could be collected by the Stellwagen cup, commonly used
for inshore hydrographic purposes. Our older charts contained
at best only meagre information regarding the most character-
istic shore deposits. From the study of these we were able to
obtain a general idea of the nature of deposits on the inshore
plateau of the continental shelf, derived from materials con-
stantly subjected under very special conditions to the action of
the tides, waves, and currents. We could of course find no clue
to the conditions under which deposits were taking place in the
immense abyssal basins, thousands of miles in extent, that occupy
certain areas both in the Pacific and Atlantic, far away from any
continental mass. As soon, however, as samples of the bottom
were obtained from these great depths, a new chapter was
opened in thalassography. An examination of these samples
has given us the first comprehensive sketch of deep-sea deposits.

1 Mr. John Murray, to whom the spe-
cimens of bottom deposits collected by
the “Blake” were sent for examination,
has described in detail some typical spe-
cimens from the coast between the Gulf
of Maine and Cape Hatteras; between
Cape Hatteras and Lat. 31° 48’ N. ; from

the shores of the Greater and Lesser An-
tilles ; and, finally, from the Gulf of
Mexico and Straits of Florida. Analyses
of the characteristic deposits will be found
in the Bulletin of the Museum, Vol. X.
No. 2.

262 THREE CRUISES OF THE ‘“ BLAKE.”

The specimens examined are procured by the collecting eylin-
ders of sounding-machines, and the results are corrected to a
certain degree by those obtained from the larger masses of ma-
terial brought up by the dredge or trawl. The bottom deposits
collected by the latter instruments may have had some of their
smaller particles washed out on their way to the surface, and
they are also exposed on their upward journey to different phy-
sical conditions. This may affect their relative chemical com-
position, so that in examining these larger masses care should
be taken to consider them merely as indicating the nature of
the bottom deposits. Our ultimate knowledge of these ‘de-
posits is derived from the most careful microscopical’ investi-
gation, supplemented by chemical
analyses of the organic and mor-
ganic substances which they con-
tain. The presence of amorphous
mineral matter, of calcareous shells
and other skeletons of inverte-
brates, and of minute organic par-
ticles, greatly complicates this ex-
amination. In addition, all these
particles have been subjected to
the action of many agencies, chem-
Fig. 177. —Spherule of Bronzite from ical and physical, the nature of

eee poten ane which is not well understood, and

(Chall.) 28, ee
have had their original characters
more or less modified by these agencies.

Marine deposits are composed of organic and imorganic par-
ticles, derived, on the one hand, from the rocks of the conti-
nental masses and oceanic islands, and, on the other, from the
remains of the animals and plants living in the surface waters
and on the floor of the ocean. There are, however, in some of
the deposits of very deep water far from continents certain mi-
nute metallic and magnetic spherules (Figs. 177, 178, 179), and
other small fragments, called chondres, which Mr. Murray has
shown to be of cosmic origin, —the dust of falling stars and
meteorites accumulating on the bed of the ocean in those places
where the rate of deposition is at the minimum.

SUBMARINE DEPOSITS. 263

The various kinds of deep-sea deposits are named after the
fragments or organisms predominating in each, or so numerous
as to be characteristic.

The deposits found in more or less close proximity to conti-
nental shores are chiefly made up of the débris brought down
by rivers or torn away from the adjoming coasts. These are

Fig. 178. — Black Spherule with metallic Fig. 179. — Spherule covered with a coating

nucleus. 7%. (Chall.) 3,150 fathoms, of black shining magnetite. The most
Atlantic. External coating removed to common shape showing the depression
show the metallic nucleus. (Chall.) found at the surface. 7°. 2,575 fath-

oms, Pacifie. (Chall.)

called generally terrigenous deposits, and consist of quartz sands,
marls, blue, red, and green muds, and greensands. Around the
shores of volcanic islands and coral islands, the deposits are vol-
canic muds and sands, and coral muds and sands.

Masses of rock, or huge boulders, but little altered, are found
close inshore, near the spot from which they originated. . Far-
ther out, these are replaced by coarse shingle and gravel,
merging gradually, in the progress seaward, into the finer mate-
rial on the bottom.

The fragments of quartz, feldspars, mica, together with frag-
ments of gneiss, granite, mica schist, and other ancient and
stratified rocks, which are very abundant in the deposits along
continental coasts, become gradually smaller in size and fewer
in number as we proceed towards the deeper and more distant
parts of the oceanic basins, when they become no longer re-
cognizable in the deposits, but form an impalpable ooze; the
case, however, is different with those regions of the ocean which
are affected by floating ice and icebergs,’ and certain other

1 Along our coasts, icebergs loaded northern regions drift south as far as lati-
with boulders and detritus brought from tude 36°, and distribute fereign material

264 THREE CRUISES OF THE “ BLAKE.”

regions where the dust from deserts is blown a long distance
to sea.

Where great rivers enter the ocean, the finer material is car-
ried out to a much longer distance than happens along coasts
where there are but small rivers. The greensands, which owe
their peculiar character to the presence of glauconitic grains
and glauconitic casts of foraminifera and other organisms, are -
generally found along continental coasts where the fine silt from
rivers is not very abundant, as, for instance, off the Shetland
Islands, off the Cape of Good Hope, and off Japan, Australia,
and some parts of the east coast of North America. It is
within the limited area in proximity to the continents, and oc-
cupied by terrigenous deposits that the varied physical condi-
tions are found upon which our zodgeographical divisions are
based.

The deposits now forming at the bottom of the great ocean

Fig. 180. — Pteropod ooze. 4. (Murray and Renard.)

basins far from land are made up of organic oozes or red clay.
The organic oozes derive their chief characteristic from the pre-
sence of immense numbers of dead shells, skeletons, and frus-
tules of pelagic organisms, which have fallen from the surface
waters. In the pteropod and globigerina oozes, the remains of
these organisms consist of carbonate of lime, which occasionally

upon the floor of the Northwestern At- shore rocks become mixed with oceanic
lantic. Thus boulders and fragments of deposits.

SUBMARINE DEPOSITS. 265

comprise over ninety per cent of the deposit. A pteropod ooze
(Fig. 180) is met with in depths of less than two thousand fath-
oms in the tropics, and is very largely made up of pteropod and

Fig. 181. — Globigerina ooze. 2°.

1

(Murray and Renard.)

heteropod shells, as Hyalea, Styliola, Spirialis, Atlanta, ete.
These shells also exist in considerable numbers in the deposits

around oceanic and other islands.
A globigerina ooze (Fig. 181) has
a much wider distribution in lati-
tude than a pteropod ooze, and
is met with in deeper water. It
consists of vast numbers of the
shells of various species of forami-
nifera.. Some of the species pre-
dominate in one locality, and some
in another. There are a large
number of other species of fora-.
minifera in the deposits, but those
named make up more than ninety

Fig. 182. — Globigerina slab, off Alliga-
tor Reef. 147 fathoms. 45.

per cent of those present. They live in the surface waters, and
their dead sheils accumulate on the bottom, while the other

species live on the bottom itself.

(Fig. 182.)

1 They are Pulvinulina Menardii, cana- Murrayi and pelagica ; Orbulina universa ;
riensis, crassa, Micheliniana, and tumida; Globigerina bulloides, cequilateralis, sac-
Pullenia obliquiloculata ; Spheeroidina de- culifera (hirsuta), dubia, rubra, conglobata,
hiscens ; Candeina nitida ; Hastigerina and inflata.

266 THREE CRUISES OF THE “ BLAKE.”

In radiolarian (Fig. 183) and diatom (Fig. 184) oozes the

deposits consist of siliceous skeletons and frustules of surface

BOs Bs Ze Rf ee: ha am
Fig. 183. — Radiolarian ooze (Murray). GB. Fig. 184. — Diatom ooze (Murray). 150,

organisms, which have likewise fallen from the surface waters.
A radiolarian ooze has hitherto been met with only in the deep-
est waters of the Western and Central Pacific, and diatom ooze
appears to be confined to the Southern Ocean, a little north of
the Antarctic Circle.

Thus it will be seen that the character of a marine deposit is
largely determined by its distance from land, and again by the
nature of the organisms living in the surface waters. The
dead shells of pteropods, of foraminifers, of radiolarians, and of
diatoms are heaped up on the bottom, some in one part of the
ocean, some in another; and as no other materials reach these
distant regions to cover them, they form characteristic deposits.
Depth is, however, an important factor in reference to the com-
position of a deposit in any locality. There seems to be now
no doubt that the whole of the carbonate of lime shells, such as
those of mollusks and foraminifers, are entirely removed by
solution in very deep water during their fall from the surface to
the bottom, or immediately after reaching the bottom. It is
found that, with increasing depth, the pteropod and heteropod
shells are the first to disappear from deposits, then the more
delicate surface foraminifera, and finally the larger and heavier
ones. It is likewise observed, that the more numerous these
shells are in the surface waters, the greater is the depth at
which they will accumulate at the bottom. As a rule, a ptero-

SUBMARINE DEPOSITS. 267

pod ooze or a globigerina ooze is found in deeper water in the
tropics than in temperate regions.

The red clay occupies those portions of the ocean’s bed in
the central parts of the ocean basins where the carbonate of
lime surface shells have been almost or completely removed.
The composition of this clay is rather varied. Mr. Murray has
shown that it is most largely composed of fragmental volcanic
material, which in very many cases has undergone profound
alteration. He also points out the important part played by
floatmg pumice-stone in the formation of oceanic deposits.
After volcanic eruptions, such as that of Krakatoa, the sea is
frequently covered for square miles in extent with floating pum-
ice. These fragments are carried far and wide by ocean cur-
rents, and are often arranged in long lines on the surface of
the ocean ; they are knocked against each other by the action
of the waves, and there results from this trituration a fine rain
of dust, which falls to the bottom of the sea.

The larger fragments themselves become water-logged after a
time, and also fall to the bottom. These pumice-stones have
been found in all the varieties of deposits, but they are espe-
cially abundant in the red clay areas. At the foot of Misti,
near Arequipa, Peru, the torrent which sweeps round its base
earries during floods quantities of pumice, which are drifted
out to sea and float for a time along the coast. Mr. Murray
has also shown that these pumice-stones are occasionally thrown
up on coral islets in immense numbers, and, there decomposing,
form the red clay and red earth of these islands, the source
of which was long a great mystery. During the “Challen-
ger” expedition, pumice was continually taken in the tow-nets
in all parts of the ocean’s surface. There is also abundant evi-
dence, in many deposits and fragments, of showers of volcanic
ashes, most probably derived from submarine eruptions. In
the red clay areas these volcanic matters have usually under-
gone decomposition into clay, and also have given rise to other
secondary products, such as manganese nodules (Fig. 185) and
zeolitic crystals.

It must be remembered that all the bottom deposits merge
into one another, and at times it is difficult to say whether a

268 THREE CRUISES OF THE “ BLAKE.”

deposit should be called a red clay, or a radiolarian ooze, or a
globigerina ooze, or a blue mud. A pteropod ooze frequently
contains many globigerine, a red clay many radiolarians or

Fig. 186. — Shark’s tooth (Oxyrhina), 2,350 fathoms.
(Chall.) .

Fig. 185. — Sealpellum Darwinii,
attached to manganese nodule.

(Chall.) 4. 7 i
Fig. 187. — Ear-bone (Zyphius), 2,375 fathoms.

(Chall.)

globigerme, and a blue mud may have a large proportion of
those organisms so characteristic of true deep-sea deposits.
From the slow rate of accumulation of the red clay in the
deep regions of the Pacific lying far from land, we may infer
that the remains of tertiary sharks and whales are buried on
the bottom. These are probably mingled with such bones of
their recent representatives, teeth (Fig. 186), ear-bones (Fig.

SUBMARINE DEPOSITS. 269

187), and the like, as have not been removed in solution; only
the densest bones remaiming, around which have formed de-
posits of manganese (Fig. 188) and iron. Here the rate of
deposition is at the mmimum. After this come radiolarian
ooze, diatom ooze, globigerina ooze,
and pteropod ooze, the terrige-
nous deposits upon the shores of
the continents accumulating at the
highest rate.

Near the shore, in proximity with
the hundred -fathom line, there is
undoubtedly held in suspension in
the water an immense amount of
decaying organic matter, both ani-
mal and vegetable, in connection Fig. 188.—Section of manganese
with the detritus swept into deeper ate. Cy Be
water from the shores of the con-
tinental masses; and this probably accounts for the presence
of glauconite and phosphatic nodules in these areas. At a
distance from shore, the supply is limited to the dead or-
ganic matter which finds its way to the bottom,—the re-
mains of the pelagic fauna and flora. In areas not in the
track of oceanic currents, or which do not underlie regions where
pelagic algze float with more or less regularity, this supply must
be infinitesimal.

We owe to Pourtalés the first general sketch of the bottom
deposits around the eastern shores of the United States. He
availed himself of the earlier results obtained by Professor
Bailey from the examination of the deep-sea soundings sub-
mitted to him by the Coast Survey, and, supplementing these
by his own observatiens, he published in Petermann’s Journal a
_ map of the bottom of the western Atlantic, adjoming the coast
of the United States. In that memoir he calls attention to the
main subdivisions of siliceous sand and calcareous deposits, the —
first extending along the eastern coast from New England as
far south as Cape Florida, and the second around the southern
extremity of Florida, the Bahamas, and a part of the coast of
Cuba. ®

270 THREE CRUISES OF THE “ BLAKE.”

The explorations of the “ Blake” have extended our know-
ledge of the bottom deposits of our coasts so as to include the
Gulf of Mexico and the Caribbean. Within the Caribbean, the
explorations of the “ Blake” have been supplemented by those
of the “ Albatross.” In addition to the soundings of the
“ Blake” on the eastern edge of the Gulf Stream, and in the
basin of the western Atlantic between the West India Islands,
Bermudas, and New York, we have a few observations made by
the “ Challenger.” The work of the “ Blake” on the south-
ern coast of New England has been materially advanced by the
continuous explorations of the United States Fish Commission
during the past years.

From these different sources we may obtain a moderately
complete sketch of the character of the bottom deposits of the
western Atlantic, and of the adjoining enclosed seas. For the
sake of convenience, we shall describe in order the deposits pro-
cured from the Gulf of Maine, and from the eastern coast as far
south as Cape Hatteras; next, the specimens from the coast
south of Hatteras, to latitude 31° 48’ N., off the northern ex-
tremity of the Bahamas; then those of the Gulf of Mexico,
of the Caribbean, and of the West India Islands, closmg with
the description of the deposits of the basin of the western At-
lantic. I shall transcribe descriptions from Mr. Murray’s report
on the deposits collected by the “ Blake,’ adding observations
of general interest from the soundings of Pourtalés and of
the Fish Commission, and from my own.

“The deposits procured in the Gulf of Maine, and along the east
coast of the United States as far south as Cape Hatteras, consist of
blue or gray colored muds and sands.1. The muds are darker-colored
when wet, earthy, plastic, more or less granular, and coherent, drying
into hard lumps. These deposits are chiefly made up of the débris of
the land of the North American continent.

“In 1,240 fathoms and Lat. 38° 34' N., off the coast of New Eng-
land, the ‘ Challenger’ dredged many rounded and angular pebbles of
milky and hyaline quartz, fine-grained quartzites, feldspathic quartz-

1 The sandy deposits are found only examined by the “ Blake ” along our east-
within 100 fathoms. They lie between ern coast are 1,394 and 1,186 fathoms,
the coast and the inner edge of the Gulf which are situated between thirty and
Stream. The greatest depths of the tract forty miles outside the 100-fathom line.

SUBMARINE DEPOSITS. 271

ites, mica schists, serpentine rocks, and compact limestones. These
fragments were not larger than six or seven centimetres in diameter.
The ‘ Blake,’ in 1,241 fathoms, and Lat. 39° 43’ N., dredged large frag-
ments of the same rocks, some of which were glaciated. In Lat. 41°
14’ N. and 1,340 fathoms the ‘ Challenger’ again dredged similar rock
fragments, and one block of syenite weighing five hundred-weight.
These deposits being all within the influence of the Labrador current,
these rocks may be regarded as chiefly ice-borne. The mineral par-
ticles* and clayey matter usually make up from eighty to eighty-five
per cent of the whole deposit.

“ The carbonate of lime in these deposits varies from about three to
eighteen per cent; it consists of coccoliths and coccospheres, of pelagic
and other foraminifera, and of fragments of echinoderms, polyzoa, ostra-
codes, and mollusks. The pelagic foraminifera shells and coccospheres
are more abundant in the deeper deposits far from the land than in
those from shallower water near the coast.

“The siliceous remains of diatoms, radiolarians, and sponges, to-
gether with arenaceous foraminifera and glauconitic casts of calca-
reous foraminifera, make up sometimes four or five per cent of the
deposit. Mixed with the mud are also found pinnules of crinoids and
otoliths of fishes.”

Mr. Pourtalés noticed, from his examination of the large col-
lection of foraminifera brought together in the soundings made
by officers of the Coast Survey, that off our Atlantic coasts cer-
tain forms of foraminifera characterized distinct regions.

“‘ The first, nearest the coast line, is marked by a great poverty of
forms. Excepting a few small Polystomellz, we find nothing in the
sand, which is kept in continual motion by the waves. This region
may be considered to extend to a depth of ten or twelve fathoms.
Farther seaward there are different species of Milioline, but not in
large numbers. They extend to about forty fathoms, and also beyond,
as it were sporadically. ...

“ From twenty-five to seventy fathoms Truncatulina advena D’Orb.
is the characteristic form. The next region, that of the larger Margi-
nuline and Cristellariz, encroaches on the first; it begins at a depth
of about thirty-five fathoms, and extends one hundred fathoms be-
a

“From a depth of sixty fathoms the sand begins to be mixed with
Globigerinz, their numbers increasing so much with the depth that at

1 The mineral particles consist of frag- hornblende, augite, mica, tourmaline, and

ments of ancient rocks, quartz, mono- occasionally glauconitic grains.
clinic and triclinic feldspars, magnetite,

272 THREE CRUISES OF THE “ BLAKE.”

one hundred fathoms they equal in bulk the grains of sand, and in
greater depths they become the chief constituents of the sea bottom,
thus gradually passing into and leading us to the true calcareous globi-
gerina ooze, and finally disappearing into the red clay formation, in the
deeper parts of the Atlantic basin.

* In the mud of the ‘ Block Island soundings,’ and of the ‘ mudholes’
off New York, we find very little besides a few Guttuline.

“The'same general distribution prevails all the way to Cape Florida,
with few exceptions. Interruptions are rare in this great sandy plain
of the continental shelf. We find only one or two small rocky patches
in the neighborhood of the entrance to New York Bay.”

A triangular area of clayey .bottom, of considerable extent,
within the hundred-fathom line, extends within the usual limits
of the siliceous sands south of Block Island. The northern
and southern extensions of this clay deposit, as it gradually
fades, or is covered by globigerina ooze, can be traced many
miles along the slope of the continental shelf.

Professor Bailey noticed in the soundings off Montauk Point,
in fifty-one fathoms, an extraordinary development of forami-
nifera, rivalling in abundance, as he says, the vast accumula-
tions of analogous forms constituting the marls under the city
of Charleston, 8. C. In the more southerly soundings of sim-
ilar depths, a greater number of globigerine are found, as well
as other genera known to occur in large numbers round the
shores of Florida and the West India Islands. Professor Bailey
also calls attention to the fact that these Mexican and Caribbean
types are not represented in the chalk, but are very common in
the tertiary deposits; their absence from deep-sea soundings
seems to afford additional evidence of the difference in depth
at which cretaceous and tertiary beds have been deposited. He
further suggests that the immense development of globigerine
and other pelagic foraminifera, forming a perfect milky way
along the course of the Gulf Stream, may be due to the high
temperature of its surface waters; and that the deposits under
Charleston may have been produced under the similar influence
of an ancient Gulf Stream. According to Bailey, the sound-
ings around the Atlantic shores and in the course of the Gulf
Stream present no analogy to the vast accumulations of infusoria
which occur in the miocene marls of Virginia and Maryland.

SUBMARINE DEPOSITS. 273

The soundings of the Fish Commission between southern
New England and the latitude of Chesapeake Bay were not
carried on at a sufficient distance from the continental shelf to
reach the limits of the red clay. Even in the deepest sound-
ings, the globigerina ooze was still quite impure, being always
more or less mixed with sand and clay mud. In a number of
localities, the bottom between 500 and 1,200 fathoms consisted
of ‘tough and compact clay, of which large angular masses,
weighing more than fifty pounds, were brought up in the trawl
by the “ Albatross.””* In other localities, in 1,000 to 1,600
fathoms, the bottom appeared to be covered with flattened crust-
like concretions of clay, containing iron and manganese oxides,
these masses affording a foothold to many mollusks which could
not exist on softer bottoms. Similar points of attachment are
provided by the scattered boulders and pebbles found by the
Fish Commission at many points on the inner edge of the Gulf
Stream. These have probably been transported off shore by
floating ice.

The explorations of the “ Blake” and of the Fish Commission
off the New England coast were not carried on much beyond
the foot of the continental slope, where it passes into the west-
ern Atlantic basin. Only a portion of this region hes outside
of the limits of the disturbing forces due to the action of waves,
currents, and tides, which, as is known, extend to a distance of
from two hundred to two hundred and fifty miles from shore,
and perhaps to a depth of nearly three hundred fathoms.

Off the southern coast of New England, concretions of vary-
ing sizes were dredged by the Fish Commission in 640 fathoms,
the largest weighing’ sixty pounds or more. They were com-
posed of grains of siliceous sand cemented by calcareous mat-
ter. In some cases the casts of foraminifera could be identi-
fied, or fossil shells distinguished that were identical with recent
species. Professor Verrill thinks these deposits may be of plio-
cene age, and that they probably form a part of the extensive

1 According to Professor Verrill, this age of the material. Similar deposits
clay was mixed with more or less sand, were found by the “ Blake ” somewhat
showing grains of quartz, feldspar, and farther north; they contained, however,
mica, tests of globigerinz and other fora- a larger proportion of foraminifera.
aminifera making up but a small percent-

274 THREE CRUISES OF THE “ BLAKE.”

submarine tertiary formation which extends for several hundred
miles along the outer banks, from Cape Cod to George’s Bank
and the Grand Banks off Newfoundland, constitutimg perhaps
the solid foundations of the banks themselves.

The bottom of the Gulf Stream slope, from 70 to 300 fath-
oms, and a belt varying from sixty to a hundred and twenty
miles, is composed in great part of siliceous sand, with grains
of feldspar, hornblende, mica, glauconite, etc., fragments of
sponge spicules, diatoms, and a very large percentage of calcare-
ous organisms. Arenaceous foraminifera are often dredged in
considerable quantities (from five to eighteen per cent). The
percentage of argillaceous matter increases rapidly with the
depth. Ata depth of about 400 fathoms, it is not more than
ten per cent; in 1,300 fathoms, nearly thirty-nine. The ab-
sence of argillaceous matter in the inner portion of the conti-
nental shelf (60 to 150 fathoms) is very marked.

Professor Verrill has called attention to the floating beach
sand met with at a distance from shore, the fine argillaceous
sediment being carried out to sea to sink in greater depths near
the foot of the continental slope, or to mix with the globigerina
ooze in the track of the Gulf Stream or in the deeper waters
of the Atlantic.

The conditions under which the shells of mollusks and the
hard parts of mvertebrates may become fossil depend greatly
upon the habits of many of the deep-sea denizens. Some of
the deep-sea fishes, judging from the contents of their stomachs,
must dig up the muddy bottoms in search of their food. Others
again, like many of our shore fishes, swallow shells, which are
disgorged subsequently unaffected by digestion. Starfishes de-
stroy large numbers of mollusks, bormg sponges and carnivo-
rous gasteropods many more, and the bottom of districts where
an abundant fauna exists must be covered with fragments of
remains of invertebrates in all possible stages of conservation,
ready to be imbedded in the muds, clays, or limestones forming
on the floor of the ocean. MHolothurians and sea-urchins work
over the infusorial animals and smaller invertebrates livmg on
the bottom, by throwing them out again after swallowing them
for the sake of the organic matter they contain. Under the

SUBMARINE DEPOSITS. 275
most favorable conditions for thei preservation, therefore, the
fossils would give very imperfect evidence in regard to the
variety of species which once constituted the fauna of any dis-
trict.

I quote from Murray and Pourtalés : —

“ Between Cape Hatteras and Lat. 31° 48’ N., the deposits are green
muds or sands. They are with two exceptions under 1,000 fathoms,
and are mostly under the waters of the Gulf Stream, or along its inner
margin. The mineral particles are much the same as those in the de-
posits north of Cape Hatteras, but are all very much smaller, and have
evidently not been transported by ice. The mineral particles, with the
exception of the concretions formed at the bottom, seldom exceed 0.4
mm. in diameter, and consist of quartz, feldspars, augite, hornblende,
magnetite, and a few fragments of glassy rocks. Glauconitic grains
and casts are frequently very abundant, as are also grains of manganese
peroxide.

**The carbonate of lime makes up usually over fifty per cent of the
whole deposit, and consists chiefly of the dead shells of pelagic and other
foraminifera, along with shells of pelagic mollusks, fragments of echino-
derms and polyzoa, ostracodes, and coccoliths. All the tropical species
of pelagic foraminifera are abundant in these deposits, while they
were relatively rare in the deposits along the coast to the north of Cape
Hatteras.

“The remains of siliceous organisms, as diatoms, radiolarians, sponge
spicules, and glauconitic casts of foraminifera and other organisms,
make up usually ten or twelve per cent of the deposit.

“The finer washings of these deposits are of a greenish color, which
seems to be chiefly due to the presence of some amorphous organic sub-
stance, the nature of which has not yet been determined. A similar
greenish matter was met with by the ‘Challenger’ im deposits from
the same depths off the coasts of Africa, Australia, Japan, and China.
These are the modern greensands and muds to which attention was first
ealled by the late Professor Bailey.

“Many of these deposits might equally well be called globigerina
ooze.

“Phosphate of lime and manganese concretions are present in all
the deposits, and one remarkable concretion is described in detail, from
Station 317, in a depth of 333 fathoms, immediately under the waters
of the Gulf Stream. The ground from which the concretion was pro-
cured was hard, and it appears to have been formed in the position
from which it was dredged. Its form was irregular,— the greatest
diameter being about nine inches, — and of a mottled black and brown

276 THREE CRUISES OF THE “ BLAKE.”

color. The surface was irregular, and presented many ovoid, smooth
projections, the largest of which were about one centimetre in diameter.
The whole mass was overgrown with sponges, corals, and annelids.
(Fig. 189.) Imbedded in the concretion were two shark’s teeth, re-
sembling Zamna, the larger being 2} inches in length and one inch

(Blake Station 317.) 2.

Fig. 189. — Concretion. 335 fathoms.
across the base. This tooth is the same as many found by the ‘ Chal-
lenger’ in great numbers in the greater depths of the central Pacific,
frequently forming the centres of manganese nodules. In the speci-
mens from the deep water of the Pacific, the interior of the tooth had
been in every instance completely removed, only the hard outer dentine
remaining. In the tooth imbedded in this concretion, on the contrary,
the vaso-dentine of the interior of the tooth is well preserved, in this re-
spect resembling the shark’s teeth of the same kind found in various
tertiary deposits, as for instance in South Carolina and in the island of
Malta. The vessels of the tooth are infiltrated with peroxide of iron
and manganese, and phosphate of lime. The whole mass has a breccia-
like appearance, the several fragments being cemented by deposits of
carbonate of lime and manganese peroxide.’

1 “When thin sections are prepared
and examined with the microscope, the
preparation has a variegated appearance.
All the grains are closely cemented to-
gether. There are numerous sections of
pelagic and other caleareous foramini-
fera, of pteropods, and fragments of
echinoderms. The interior of the forami-
nifera is sometimes completely filled with

calcite, and the same crystals are found
cementing many of the fragments of

which the rock is composed. Small frag-

ments of quartz, of feldspar, and of zoi-
ene are also seen in the sections. But the
most characteristic element is formed by
small rounded grains of a brownish or
yellow-green color, having much the as-
pect of glauconite, which is also present.

SUBMARINE DEPOSITS. ATT

“There are off the coasts of North and South Carolina small rocky
banks slightly raised above the general level of the sea bottom, consist-
ing of a calcareous material, which are probably the continuation of the
tertiary beds found inland along the adjoining shores. They are cov-
ered by corals (Oculina), gorgonians, and other invertebrates, and afford
better feeding-grounds for fishes than the sandy bottom. They are the
fishing-banks of the inhabitants. Similar banks are found off Cape
Fear, and, to judge from the nature of the corals and shells thrown up
on the beaches near Cape Hatteras and Cape Lookout, others probably
exist in their vicinity.”

In the strength of the current of the Gulf Stream the bottom
was washed nearly bare, and we found little animal life in the
trough of the stream. The bottom was composed of a hard
limestone, the edges of the sounding-cylinder coming up much
defaced. Off Charleston the whole width of the Gulf Stream
was swept clean. From Jupiter Inlet to the latitude of the
northern Bahamas the bottom specimens resembled more the
ooze of the Gulf of Mexico and the Caribbean, containing a
proportionally larger percentage of pteropod remains than the
ooze farther north, where the globigerine increased in number.

The rapid changes in the character of the mud in proportion
to the distance from shore and the depth are well shown in the
nature of the deposits at different levels along the short, steep
line which forms the northern slope of the Blake Plateau to
the south of Cape Hatteras. There we pass quickly from the
comparatively coarse shore mud to finer and finer ooze, which
becomes an impalpable silt in the deeper water beyond one
or two thousand fathoms, assuming at the same time a lighter
color. The gradual decrease of color of the bottom deposits
with an increase in depth is very evident in the soundings
Chemical reactions show that these grains portion of this concretion by M. Klement,
are phosphatic. They are similar to see Bull. M. C. Z., XII. No. 2.
the grains found in phosphatic nodules “ The ‘Challenger’ dredged on several
dredged off the Cape of Good Hope and _ occasions, especially off the Cape of Good
elsewhere, and identical in their physical Hope, concretionary masses like that
and chemical properties with the phos- above described, but very much smaller.
phatie grains in cretaceous rocks. Phosphatie nodules were always found

“The manganese is infiltrated through in the deposits at less than 1,500 fath-
the whole mass of the concretion. The oms, near continental shores, but never

phosphatic grains are sometimes enclosed in the deeper deposits far removed from
in the manganese. For an analysis of a_ land.”

278 THREE CRUISES OF THE “ BLAKE.”

in the Gulf of Mexico, and during my first dredging trip I was
struck with the change of the light yellowish-gray ooze of the
trough of the Gulf Stream into the darker shades as we ap-
proached the coast of Cuba.

While running the line parallel to the coast from off Charles-
ton to Cape Hatteras, we came twice upon localities where
the sounding-cup brought up nothing but clean globigerine,
the bottom consisting entirely
of the modern greensand? to
which Bailey and Pourtalés had
already called attention as form-
ing off shore on the Atlantic coast
of the United States. From the
examination of a large number
of bottom specimens, Pourtalés
succeeded in determining the
position of a belt off the coast of
Georgia and of South Carolina
where the modern greensand was
well developed. The patches of
greensand occurred in depths
varying from fifty to a hundred fathoms on the boundary line
between the siliceous sand and calcareous bottoms on the inner
edge of the Gulf Stream. Now and then this modern greensand
(Fig. 190) is found also in deeper water under the Stream itself.
Pourtalés gives the following description of the formation of
our modern greensand : —

Fig. 190.— Greensand. 142 fathoms.
(Blake Station 314.) 19.

“Khrenberg made, as is well known, the interesting discovery that
the so-called greensand or glauconite consists of the casts of foramini-
fera.2 That this process is still going on at the bottom of the ocean,

1 Murray says, that fifty per cent of 2 Bailey confirmed the observations of
carbonate of lime, mainly made up of Ehrenberg, on the greensand of the Zeu-
pelagic and other foraminifera, and forty glodon limestone of Alabama, and detected
per cent of greensand residue, enter into the same structure in some of the creta-
the composition of one of the samples of ceous deposits of New Jersey and Texas,
modern greensand he examined. The and in the eocene of South and North
remainder consists of siliceous organisms Carolina.
and argillaceous and green amorphous
matter.

SUBMARINE DEPOSITS. 279

near our coasts, was discovered by Bailey, from the examination of our
bottom specimens. In some of them the whole process can be followed
in the most interesting way. Thus we find, side by side, the tests per-
fectly fresh, others still entire, but filled with a rusty-colored mass,
which permeates the finest canals of the shells like an injection. In
others, again, the shell is partly broken away, and the filling is turning
greenish ; and finally we find the casts without trace of shell, sometimes
perfectly reproducing the internal form of the chambers; sometimes,
particularly in the larger ones, cracks of the surface or conglomeration
with other grains obliterate all the characters. They even coalesce into
pebbles, in which the casts can. only be recognized after grinding and
polishing.

“Why this process of transformation should occur only in _partic-
ular localities is as yet unexplained.? It is easy to distinguish this
fresh formed greensand from the tertiary one off the coast of New
Jersey, by the greater number of perfect tests of foraminifera mixed
with it.”

As was pointed out by Pourtaleés, it is remarkable how closely
the limits of the siliceous sand bottom coincide with the bound-
aries of the cold current coming from the north, while the limits
of the calcareous deposits correspond with the course of the
warm waters of the Gulf Stream. We might almost trace its
course by a study of the bottom specimens. On each side, as
well as at the falls of the Gulf Stream south of Hatteras, ooze
of varying composition was invariably brought up. The distri-
bution of the foraminifera seems to throw considerable light on
the circulation, and to give additional support to Commander
Bartlett’s view, based upon thermometric sections, that the bulk
of the Arctic current does not extend south of Hatteras along
our coast, but that the colder and heavier waters of the northern
current plunge beneath the Gulf Stream off Hatteras, and flow
slowly on the outside edge of the Blake Plateau towards the
equator.

During the years 1875 and 1876, previous to my connection

1 Many of the foraminifera dredged by due to foraminifera, but also in part to
Pourtalés and myself in the Straits of other organisms, and he suggests that we
Florida were filled with a yellow mass, may safely infer that this matrix has in-
like that of the first stage of transforma- variably been formed in connection with

tion into greensand. decaying organic matter.
2 Bailey shows that the casts are not all

280 THREE CRUISES OF THE “ BLAKE.”

with the ‘ Blake,” very extensive series of bottom deposits
were obtained by the vessels of the Coast Survey, at all depths
and in all parts of the Gulf of Mexico. Of these deposits
Murray says in his Report : —

“ There is a very great variety in the shallow-water deposits under
one hundred fathoms. Near the coasts of the continent along the
shores of the Gulf, where rivers enter and where there are few coral
reefs, the deposits are either sands or fine clayey muds, formed of de-
trital matter brought down from the land. We find in these muds,
however, in the track of currents, a number of pelagic foraminifera as
well as other calcareous organisms. -Where the shores are lined by
coral reefs, the deposits are chiefly made up of coral débris, the shells
of pelagic foraminifera and mollusks, and other calcareous organisms.

“The character of the deposits in depths greater than one hundred
fathoms is likewise largely determined by the greater or less proximity
to coral reefs or the embouchure of rivers.

“Tn all the deeper deposits in the Gulf of Mexico and the Straits of
Florida, the crystalline mineral particles are very small, rarely exceed-
ing one tenth of a millimeter in diameter. They consist principally of
small rounded grains of quartz, with fragments of feldspar, mica,
hornblende, augite, magnetite, and rarely tourmaline. In a few places
there were fragments of pumice, and glauconitic particles were occa-
sionally noticed. The mineral particles and fine clayey matter appear
to be almost wholly derived from the rivers emptying into the Gulf of
Mexico.

“The carbonate of lime in the deposits of these regions is mostly
made up of the shells of pelagic foraminifera and mollusks, though we
also find coccoliths, rhabdoliths, and fragments of echinoderms. In
depths greater than 2,000 fathoms, the pteropod and heteropod shells
appear to be nearly, if not quite, absent, — the carbonate of lime then
consisting of the shells of pelagic foraminifera; in lesser depths the
pteropod and heteropod shells are present; and in depths of 200
to 500 fathoms they make up the bulk of the deposits in many places.
In several of the deposits, where the percentage of lime is very high,
the whole has a very chalk-like appearance ; it appears, indeed, as if it
were in the process of transformation to true chalk.”

According to Murray, in the deposits of the Gulf of Mexico
the carbonate of lime varies greatly. In muds brought down
by rivers, there is sometimes little more than two per cent of lime.
The percentage rises to ten or fifteen per cent in some of the
volcanic muds. In the coral muds it varies from sixty-seven to

SUBMARINE DEPOSITS. 281

over eighty per cent. The variation in the percentage of lime
in pteropod ooze is from sixty-eight to eighty-three. In the
coral muds and pteropod and globigerina ooze, the lime is re-
placed in part, in accordance with the locality, by a greater or
smaller amount of siliceous organisms or by argillaceous matter.
The variations of lime in globigerina ooze range from thirty-two
to seventy-two per cent, in proportion to the proximity of the
shore, the percentage of mineral residue varying from sixty-four
to twenty-seven, in addition to the changes due to a larger or
smaller proportion of siliceous organisms or argillaceous matter.

While sounding, it was easy to follow the depth and the dis-
tance from shore by the gradual decrease of bright tints in the
bottom specimens ; these were probably colored more intensely
by organic matter when close in shore, but became bleached
with increasing depth. Along the lines of soundings in the
Caribbean, we found the coral muds to be of a light greenish-
gray or yellowish tint. Pteropod ooze varied from a chalky
gray to white, while globigerina ooze passed from dark brown
to reddish, reddish brown, and light brown, or cream-color.
The river muds were usually gray or brown.

The globigerina and pteropod ooze of the central parts of the
basins of the Gulf of Mexico and the Caribbean, like those
found in proximity to the Greater and Lesser Antilles, differ ma-
terially from similar deposits in the great oceanic basins. The
siliceous organisms consist of radiolarians and sponge spicules,
with afew diatoms ; but these seldom make up more than three
or four per cent of the whole deposit. An unusual number of
otoliths of fishes were detected in the bottom specimens of the
Gulf of Mexico; they occurred at considerable depths, from 392
to 1,568 fathoms. Fish teeth were also found in some of the
mud deposits, from over 500 fathoms.

I take the following from Murray’s Report : —

“The phosphatic concretions in the dredgings in the Straits of Flo-
rida are very interesting. In a great many deep-sea deposits there is
usually a small percentage of phosphate of lime, but near the shore,
in some instances, the quantity is very considerable. Sharples, who
analyzed the ooze of the Gulf Stream, found over eighty-five per cent
of carbonate of lime, and only 0.18 per cent of phosphate of lime.

282 THREE CRUISES OF THE “ BLAKE.”

“Tn certain concretions found by the ‘ Blake’ in the Florida Straits,
and by the ‘Challenger’ in various parts of the world, near land, the
quantity of phosphate of lime is very much greater. These concre-
tions appear always to be associated in an intimate way with or-
ganisms.

“In 125 fathoms, southwest of Sand Key, a fragment of manatee
bone was obtained several centimetres in diameter. It was of a dirty
brown color, of great hardness, and had a conchoidal fracture. <A mi-
croscopic examination of thin sections showed that the bone structure
was perfectly preserved. It was found to contain over thirty-three per
cent of phosphoric acid, and nearly fifty-two per cent of lime.

“From the same place was obtained a concretion of a brown color,
consisting of an aggregation of calcareous organisms cemented by a
brownish yellow matter, often showing concentric rings after the man-
ner of agate.!

** At other stations small phosphatic concretions were also obtained
by the ‘ Blake,’ all more or less resembling those described above.
There are difficulties in understanding how phosphate of lime and car-
bonate of lime are deposited at the bottom of the sea, yet there is no
doubt that such a deposition does take place under some special cir-
cumstances. Their solution is, however, an almost universal phenome-
non in the ocean.”

When dredging off Cuba, Pourtalés procured, at the depth
of 270 fathoms, a number of nodules of a very porous lime-
stone, similar in color and texture to the limestone which forms
the range of low hills on the shore of Cuba, and is composed
of the remains of the same animals which are found living.

The globigerina ooze of the Gulf extends northward until
it strikes the Mississippi River slope. Here the fauna changes,
and with the presence of dark rich muds that of the deep
Gulf ooze disappears, and is replaced by a number of interest-
ing forms of annelids, mollusks, ophiurans, and sea-urchins,
characteristic of the continental Gulf slope, and typical of mud
deposits. Nowhere around the shores of the United States
can we so readily trace the denudation of the continent as
in the succession of formations which since the time of the

? “This yellowish brown matter is iso- attacking the brown or yellow parts un-
tropic ; between crossed nicols only the der the microscope with molybdate of
calcite and the shells of the foraminifera ammonium and nitric acid, there is an

brighten up ; the calcite lies crystallized abundant yellow precipitate characteristic
in the interior of the foraminifera. In of phosphoric acid.”

SUBMARINE DEPOSITS. 283

jurassic period have gradually filled the shallow sea formerly
existing to the west of the Mississippi basin and of the southern
portion of the Gulf States. In more recent times, the muds
brought down by the Mississippi and other rivers emptying into
the Gulf of Mexico have been deposited upon its shores, and
have formed the steep continental slope of the Gulf beyond the
hundred-fathom line.

The recent river muds now occupy a narrow strip of the Mis-
sissippi basin, between Louisiana and Mississippi, as far north as
the mouth of the Ohio. They have also built out the delta of
the river to within a short distance of the hundred-fathom line,
and extend along the shore of Texas, slowly filling up the Gulf
of Mexico.

I was very much struck, on first seeing the ooze of the deep
water of the Straits of Florida between Havana and Florida
Keys, with the immense number of dead pteropod and_hetero-
pod shells which it contained, in addition to the countless tests
of globigerinz and orbuline. These shells belonged mainly to
the genera Clio, Hyalea, Triptera, Atlanta, Styliola, etc., all of
which swarm on the surface, or a little below it, in all the parts
of the Gulf of Mexico which we had thus far passed over. I
could at once see how important a part these dead pteropod shells
must play in the formation of the sedimentary matter accumulat-
ing at the bottom. Globigerine and orbuline form, as we know,
the bulk of the ooze, but the remaining part of the mud is
made up mainly of the dead shells of pteropods in all stages of
disintegration, from perfect shells, still filled with the decaying
animals, to the most minute grains, in which we can just detect
the presence of the pteropod test. This composition of the
ooze is the rule in all specimens of the bottom which I have
thus far had time to examine. The decay and solution of the
test become more rapid with increasing depth, and may be due,
as suggested by Mr. Murray, to the excess of carbonic acid
present at great depths, or, as Professor Dittmar is inclined to
believe, to the solvent action of the sea-water itself. In a vol-
canic region like that of the West Indies, there is no difficulty
in accounting for the presence of a large supply of gas. To
show how far the dead pteropod shells make up the globigerina

284

THREE CRUISES OF THE ‘“ BLAKE.”

ooze, | took from the contents of the trawl drawn from 860
fathoms equal portions cf mud as it came up; one part was
left undisturbed and roughly measured, and the other was care-
fully sifted; the pteropod shells and their fragments were then
collected, and likewise measured, when their bulk was found to
be somewhat more than half the bulk of the sifted mud from
which they came.

Pourtalés, who first traced the extent of the region covered
by globigerina ooze in some parts of the Gulf of Mexico and
upon the Atlantic coast of the United States, thus speaks of
the foraminiferous calcareous bottom : —

‘“‘In great depths, as, for instance, in the Straits of Florida, at the
outward limit of the rocky bottom (Pourtalés Plateau), and, where
this does not exist, even in less depths, the bottom is covered by a
chalk-like layer, which resolves itself under the microscope into a mass
of foraminifera,’ and their fragments more or less comminuted. This
formation extends almost uninterruptedly in the whole bed of the Gulf
Stream, in the greater depths of the Gulf of Mexico, in the deep
channels which intersect the Bahama Banks, and then up the Atlantic
coast from about the hundred-fathom curve outward, or from the inner
limit of the Gulf Stream, which nearly coincides with it, and so over
the greater part of the Atlantic basin. The discovery of this forma-
tion belongs to the year 1855, when it was found almost simultaneously
by Lieutenants Craven and Maffit, then in the Coast Survey, and ex-
ploring the Gulf Stream. It became more extensively known some-
what later, by the soundings made for the Atlantic telegraph.

“The genus of foraminifera most abundantly represented in this bot-
tom is the Globigerina ; hence the term ‘ globigerina bottom’ (ooze) is
becoming generally used. Then comes in order of frequency Rotalina
cultrata ; then several Textularie, Marginuline, etc. It is now pretty
generally admitted that these rhizopods live and die in these great
depths,” although formerly false ideas of the effects of pressure, of the

1 The extent to which pteropod shells
enter into the composition of the ooze of
the Caribbean and Gulf of Mexico had
not then been noticed. 7

2 As far back as 1850, Pourtalés stated
that at depths of 257 fathoms globige-
rine are still living in immense num-
bers. As I have mentioned before, I
found an allied species of globigerina
swarming on the surface to the westward

of the Tortugas. While examining the
specimens of foraminifera collected by
Coast Survey expeditions, Pourtalés made
the interesting discovery that many spe-
cimens of Orbulina contained a young
Globigerina, more or less developed, and
that these two genera must be considered
as probably two stages of alternate gen-
eration.

SUBMARINE DEPOSITS. 285

want of light, ete., seemed to militate against this supposition. But
that animals living near the surface contribute also a not inconsider-
able proportion, is proved by the numerous shells of pteropods, occa-
sional teeth of fishes,” ete.

It was on this-bottom that Pourtalés dredged the interesting
little stalked ermoid Rhizocrinus, which he referred at first to
Bourgueticrinus. The importance attached to the subsequent
discovery of the identity of Bourgueticrinus with the Rhizo-
crinus dredged by Sars off the coast of Norway, as well as
by Pourtalés, Agassiz, Thomson, and Carpenter, undoubtedly
awakened the general interest of naturalists to the problems of
thalassography, and to the two successful hauls of the dredge
in the Straits of Florida and off the Lofoten Islands we owe in
great part our recent deep-sea explorations. As stated by Pour-
talés, —

“The sandy bottom ends exactly at Cape Florida. Key Biscayne, of
which the southern point is Cape Florida, consists in great part of
siliceous sand. The next island to the southward, only five miles dis-
tant, shows no trace of sand, but consists exclusively of coral lime-
stone, of which the whole range of the Florida Keys is also formed.

“¢ About Cape Sable siliceous sand reappears, and extends along the
western coast of Florida, though at first strongly mixed with lime.

“Tt is remarkable how the littoral fauna changes with the constitu-
tion of the bottom. Many forms of animals peculiar to the Caroli-
nian fauna disappear at Cape Florida, and reappear at Cape Sable and
on the west coast of the peninsula. Between these points they are en-
tirely crowded out by the interposition of the West Indian fauna of the
coral reefs. To take but one example, oysters are not found on the
coral bottom, though abundant to the east and west on the sandy
bottom.”

This shows that the nature of the bottom far more than the
depth is the cause of the abrupt changes of fauna which are
observed when we pass from one kind of bottom to another.

To the westward of the shores of the southern extremity of
Florida we gradually come upon the belt of mud, more or less
mixed with calcareous matter, which stretches from Florida
towards deep water and around the shores of the Gulf of Mex-
ico, until it strikes again the calcareous deposits of the Yucatan

2386 THREE CRUISES OF THE “ BLAKE.”

Bank. The structure of the limestone banks which form the
greater part of the peninsula of Florida, of Yucatan, of Hon-
duras, of the Bahamas, and of the extensive ancient and mod-
ern coral reefs of Cuba and the greater and lesser Antilles,
and extend along the northern coast of South America, has
been already described in the chapter on the Florida Reefs. I
merely allude to their general position to point out the connec-
tion of these immense deposits of limestone with the calcareous
bottom of the deeper parts of the floor of the Caribbean and of
the Gulf of Mexico.

The distribution of the recent coral reefs is shown on the
map. (Fig. 191.) The coral bottom, or coralline sand, which
owes its origin to their presence, extends but a short distance in
depth ; the coral reefs proper being sharply limited in depth, as
reef-building corals only, flourish within very moderate depths.
On the surface, the slope is made up of fragments of shells, of
the tests of invertebrates, and of similar material more or less
broken and worn, which reaches to a depth of about a hundred
fathoms or more. But nowhere in the West Indian area do we
meet with the steep slopes which have been described as charac
teristic of the coral islands of the Pacific.

Outside of the reefs we pass into a layer of soft, calcare-
ous ooze, whiter nearer the reefs, and becoming somewhat col-
ored at a greater distance. The whole deposit “is an im-
mense layer of chalk, to which the organic life developed on its
surface is constantly adding; while nearer shore the faune of
the littoral and deep-sea regions, with their numerous corals and
shells, contribute to the formation of limestone of various char-
acters, such as oblite, muschelkalk, coral rag, and conglomerates
from beds broken up and reconstructed.”

The explorations of Pourtalés along the Florida reefs devel-
oped an extensive limestone plateau, to which the name of Pour-
talés Plateau has been given. This rocky plateau, with a very
moderate slope, begins a little to the westward of Sand Key,
and stretches to the northward and eastward, until it reaches its
maximum breadth, of about eighteen nautical miles, to the east-
ward of Sombrero. It then diminishes in breadth, and finally
ends between Carysfort Reef and Cape Florida, at the same

SUBMARINE DEPOSITS. 287

time approaching the reef. The plateau begins at a depth of
about 90 fathoms, and ends at about 300.

The bottom, as described by Pourtalés, is rocky, rather rough,
and consists of a recent limestone (Fig. 192), continually though
slowly increasing
from the accumula-
tion of the caleare-
ous débris of the
numerous small
corals, echino-
derms, and mol-.
lusks living on its
surface. These
débris are consoli-
dated by tubes of

serpulz ; the inter-
stices are filled up Fig. 192. — Rock from Pourtalés Plateau.

by foraminifera, and further smoothed over by nullipores. The
region of this recent limestone’ ceases at a depth varymg from
250 to 350 fathoms, and beyond it comes the trough of the
straits. The bottom here forms a great bed of foraminifera,
and especially of globigerine, which so extensively covers
oceanic basins.

If uncovered, the Pourtalés Plateau would be found to be built
up of beds of limestone filled with fossils, the remains of the
animals now living on its bottom, with such pelagic forms as
have sunk after death, like the remains of fishes and of pelagic
mollusks, or which, like the bones of manatee, may have
been brought by currents from the littoral regions. The rich
fauna of the reef extends but slightly seaward, and until we
reach about the hundred-fathom line the coast shelf is singularly
barren; but beyond this, we find a region remarkably rich in
animal forms. The fauna found on the Pourtalés Plateau is
undoubtedly due to the action of the Gulf Stream, which sup-
plies the animals living upon it with an abundance of food, and,

1 Tt would be an interesting experi- compare, for instance, recent dolomite
ment to determine the specific gravity of and recent limestones with the specific
rocks taken from deep water, and to gravity of similar rocks.

288 THREE CRUISES OF THE ‘“‘ BLAKE.”

in addition, sweeps the floor of the plateau clear of all fine sedi-
mentary accumulations.’

“A similar sea-bottom, but with a very steep slope, is formed
on the north side of Cuba, to a depth of three or four hundred
fathoms, also inhabited by a rich fauna, which presents, how-
ever, considerable differences from the one just mentioned, not-
withstanding the short distance between the two coasts.” (Pour-
tales.)

Near the Bahama Banks, Pourtalés found the steep slope cov-
ered with calcareous sand. In his description of the fauna of
these plateaux he called attention to the resemblance of many of
the types described by him to tertiary and cretaceous forms, and

to their extended geographical distribution.
Mr. Murray thus describes the typical bottom deposits of the

Caribbean district : —

‘The specimens procured around the shores of the Greater and Lesser
Antilles are chiefly from depths between a hundred and one thousand
fathoms, although a few are in depths less than a hundred fathoms

and a few are over two thousand fathoms.
or less close proximity to the coasts.

1 The hard parts of the corals, mol-
lusks, sponges, and other invertebrates,
which build up the limestone of the Pour-
tales Plateau, are often riddled with ca-
nals made by vegetable parasites, or by
boring sponges. The former often form
beautiful networks. Their manner of
boring is not well understood. Wedl and
Kolliker suggest that the vegetable para-
sites may dissolve the carbonate of lime
by emitting an acid as they advance, at
their terminal extremity. In the case of
boring sponges, the penetration is proba-
bly mechanical. The canals, like the sur-
face of many of the concretions from

Rock Concretion.
Carbonate of lime . 36.50
Tricalcie phosphate . 35.54
TENCE © |e AP ire. Fad os A9

Ferric oxide . . 14.77
Carbonate of magnesia 10.56
Organic matter and water . 1.46

99.32

They are all in more
The mineral particles are chiefly

these regions, are frequently coated with
a glaze of manganese.

Sharples found traces of oxide of iron
in the ooze he analyzed from the Straits
of Florida, and a considerable quantity
in the concretions and specimens of rock
of the Pourtalés Plateau. The presence
of iron ina closed sea, like the Gulf of
Mexico, is readily accounted for by the
presence of large rivers carrying down
into it large quantities of iron. The
waters from the open ocean are nearly
free fromit. The following are Sharples’s
analyses : —

Rock and Corals. Limestone. Ooze.
47.11 96.96 85.62
13.15 1.20 18

1.92 2.12 1.52
20.23 — 1
12.39 oo 4.26

5.89 a 8.15

100.69 100.28 100.04

‘ SUBMARINE DEPOSITS. 289

fragments of volcanic rocks, or crystals derived from these! In the
deposits farthest from land the size of the mineral particles seldom
exceeded 0.1 mm. in diameter, but near shore they were very much
larger, and fragments of rocks and pebbles were frequently dredged.

“The percentage of carbonate of lime in these deposits was usually
very high, being frequently seventy or eighty per cent, and in the case
of a chalk rock 90.24 per cent. This lime consisted of fragments of shells
of pelagic and other mollusks, of calcareous algz, of echinoderms, of an-
nelid tubes, of corals, polyzoa, aleyonarian spicules, coccoliths and rhab-
doliths, and of pelagic and other foraminifera. Where the shores were
composed of volcanic or other rocks not calcareous, the débris of these
made up the larger part of the deposits, which might be called volcanic
muds. But the majority of the devosits should be’ termed pteropod or
globigerina ooze, owing to the large number of these organisms present
in them. The ooze varies greatly in color. The pteropod ooze is either
a white, a yellowish brown, or a dark brown; the globigerina ooze
ranges from a light gray to light brown, the coral muds are yellowish
and white, and the voleanic muds light brown. The darker-colored
ooze and mud usually occur nearer shore than the lighter ooze found in
the central parts of the basin of the Gulf of Mexico and in the Carib-
bean. It should be remembered, however, that, both in the size of the
mineral particles and the nature of a large number of the calcareous
particles, these deposits differ considerably from similar deposits found
far away from land in the open ocean, and called also pteropod and glo-
bigerina ooze.

** The siliceous organisms never make up more than four or five per
cent of the whole deposit, and consist of radiolaria, sponge spicules, and
a few diatoms.

“ From 994 fathoms, off Nuevitas, Cuba, there was obtained a frag-
ment of white chalk coated on the surface with streaks of peroxide of
manganese. This chalk contained 90.24 per cent of carbonate of lime.
The sections showed the rock to be composed of crystalline grains of
carbonate of lime, but not the result of precipitation. A few sections
of globigerina and textularia were observed, but no other organisms
could be recognized. After dissolving away a considerable quantity,
small fragments of quartz and hornblende, sponge spicules, and radi-
olarians were recognized in the residue. It is not possible to be certain
that this rock was formed in the position from which it was dredged,

1 Monoclinic and triclinic feldspars, these deposits, and phosphatic grains
hornblende, augite, olivine, magnetic iron, were likewise rare. Altered fragments
and pumice; fragments from ancient of plagioclase, basalts, and diabase were
rocks, as quartz, tourmaline, mica, epi- rather frequent.
dote. Glauconitie grains were rare in

290 THREE CRUISES OF THE “ BLAKE.”

though there are reasons for supposing it was. The ooze which came
up from the same place was of a reddish or brownish tinge, and con-
tained an immense number of pteropods, heteropods, and pelagic fora-
minifera; the percentage of lime was not so high as in the white chalk
rock, and the residue was much darker in color.

** Caleareous concretions and nodules of manganese were also dredged
in this district.” *

In the district around the shores of the Antilles there is a
gradual transition from the coarser volcanic bottom deposits of
shallow waters to the finer sands and muds, which at a distance
from the islands pass into ooze. While dredging in the passages
between the islands the trawl often came up well filled with
rounded pebbles of volcanic rocks. Their shape may be due
either to the action of the strong currents rushing between the
islands, or perhaps to the disintegrating action of the warm
water. This process may account for the abundance of the
coarse volcanic sands found in the West Indian waters. Below
six or seven hundred fathoms the bottom in the Caribbean is
composed of calcareous ooze, consisting in great part of ptero-

pod shells, and in a less degree of foraminiferous remains.

1 «Off the Barbados, in 221 fathoms,
a very hard calcareous concretion was
obtained, which showed perfectly how
the rock was formed by crystallization of
carbonate of lime around the shells of
foraminifera and other centres. A zone
is seen around the shells, composed of
fibro-radiate calcite ; the crystals of cal-
cite, coming from the various centres,
abut against each other, and frequently
leave an empty space between them.
When these spaces are filled by a further
deposition of lime, the whole becomes
very compact and massive.

“The centres of the foraminifera are
frequently filled with a gray or yellowish
substance, which does not, however, give
the reactions of phosphate of lime.

“The mineral particles were very few
in number, among them fragments of
quartz and plagioclase being observed.
This concretion was about two inches in
diameter, and had a rough areolar sur-

face on which serpule and polyzoa were
growing.

“A similar and somewhat larger con-
cretion from 200 fathoms (Station 291)
was also obtained off Barbados, which
was much more overgrown with organ-
isins, and on its upper surface had a large
cavity in which a hermit-crab, Polycheles
Agassizii, had lived. (See Bulletin M.
C. 2a, W Tl. No. 49

“Off the north coast of San Domingo,
in 772 fathoms (Station No. VI), were
obtained several small manganese nodules
and a few fragments of a Corallium
coated with manganese, precisely similar
to that dredged by the ‘Challenger’ in
1,525 fathoms near Cape Verde. (See
Narrative of the Challenger, p. 125.)
The nodules were of a light brownish
color inside, composed in all cases of a
mass of pelagic foraminifera. The largest
of these nodules had a diameter of about
two inches.”

SUBMARINE DEPOSITS. 291

While dredging to the leeward of the Caribbean Islands, we
could not fail to notice the large accumulations of vegetable
matter and of land. débris brought up from deep water many
miles from the shore. It was not an uncommon thing to find
at a depth of over one thousand fathoms, ten or fifteen miles
from land, masses of leaves, pieces of bamboo and of sugar-
cane, dead land shells, and other land débris, undoubtedly
blown out to sea by the prevailing tradewinds. We frequently
found floating on the surface masses of vegetation, more or less
water-logged, and ready to sink. The contents of some of our
trawls would certainly have puzzled a paleontologist ; between
the deep-water forms of crustacea, annelids, fishes, echinoderms,
sponges, etc., and the mango and orange leaves mingled with
branches of bamboo, nutmegs, and land shells, both animal and
vegetable forms being in great profusion, he would have found
it difficult to decide whether he had to deal with a marine or a
land fauna. Such a haul from some fossil deposit would natu-
rally be explained as representing a shallow estuary surrounded
by forests, and yet the depth might have been fifteen hundred
fathoms. This large amount of vegetable matter, thus carried
out to sea, seems to have a material effect in increasing, in cer-
tain localities, the number of marine forms.

We can thus see the method by which land shells, small sau-
rians, and insects of all sorts, may readily be transported from
island to island, and we might possibly trace the actual path
taken by the immigrants into the Lesser and Greater Antilles
from the northern parts of South America.

We made three casts off the coast of Cuba, between Nuevitas
and Cape Maysi. In Lat. 21° 2’ N., Long. 74° 44’ W., off Cayo
de Moa, in 1,554 fathoms, we found a patch of greensand, made
up of large globigerine, similar to that mentioned by Pour-
talés in his “ Deep-Sea Corals.” We also obtained, in 994
fathoms off Nuevitas, large blocks of genuine white chalk, com-
posed mainly of globigerine and pulvinuline. Large quanti-
ties of ooze and white clay, which proved to be only the white
chalk in different stages of compression, also came up in the
trawl. If the conditions now existing at that depth at all re-
semble those of the time of the white chalk, f can readily un-

292 THREE CRUISES OF THE “ BLAKE.”

derstand how perfectly sea-urchins or mollusks would be pre-
served in this homogeneous substance, and gradually compressed
into solid white chalk.

Commander Bartlett observed that the strong current passing
over the ridge of the Windward Passage between Cuba and
San Domingo swept it entirely clean, so that but little animal
life was found to live upon it. But immediately beyond this,
on the Caribbean side, the mud and silt are deposited in great
quantities, and animal life becomes plentiful again. This, as I
have already stated, was also our experience while dredging
along the so-called axis of the Gulf Stream. The bottom of
that region, swept clean by the Stream, forms a great contrast
to the slope off Hatteras, where the silt accumulates in such
masses as to make it often difficult to detach the shot of the
sounding-wire when it has sunk deep into it. These and similar
deposits, accumulating within restricted areas, may often guide
us in determining the direction of currents, and the distribution
of pelagic types may also assist us in defining the slower move-
ments of large masses of water.

The red clay deposit first discovered by the “ Challenger”? is
found at depths greater than two thousand fathoms, and is
probably in part the result of the decomposition of voleanic
products. The materials of the red clay are present in all de-
posits, but at lesser depths its presence is obscured by the
more rapid accumulation of calcareous matter. Near shore,
and upon our continental shelf or near its base, even at very
considerable depths,’ we do not find the characteristic red clay’
deposit of the deeper basins of the Atlantic. Its presence is
hidden by the larger mass of continental detritus, of voleanic
muds and sands, of globigerina ooze, and of other calcareous
deep-water deposits.

According to the “ Challenger,” red clay has not been found
in the western basin of the North Atlantic except at one locality
a little to the westward of the Bermudas. There seems to bea
triangular-shaped basin filled with red clay to the eastward of

1 This has been the experience of both which genuine red clay was brought up
the “ Blake” and of the U.S. Fish Com- by the “Challenger” in more favored
mission, when dredging at depths from localities.

SUBMARINE DEPOSITS. 293

the Bermudas, and extending to the north as far as latitude 38°.
Commencing at about longitude 50° W., it follows southward
and westward toward South America nearly the line between
two and three thousand fathoms. It has been found close to
Porto Rico in deep water, and covers the floor of the ocean be-
tween it and the Bermudas. The western boundary of the
red-clay basin is not yet clearly defined. A narrow strip of this
basin reaches southward towards the ridge which separates it
from the northern extremity of the red-clay basin of the west-
ern South Atlantic. The smaller red-clay basin of the eastern
Atlantic lies between the Cape Verde Islands and the Dolphin
Rise. The eastern red-clay basin of the South Atlantic, sepa-
rated by the Challenger Ridge from the western red-clay basin,
is situated to the westward of equatorial Africa. The western
red-clay basin of the South Atlantic probably stretches into the
Southern Ocean.

PAT.

THE PHYSIOLOGY OF DEEP-SEA ‘LIFE.

I HAVE no observations of my own to present in regard to
the composition of sea-water. For convenient reference, the
interesting results of the chemists of the “ Vorimgen” and
“Challenger” are here given in a condensed form.

As early as 1872, the chemist of the German expedition to
the North Sea and the Baltic, Dr. Jacobsen, successfully .ex-
tracted at sea the gaseous elements of sea-water. The appara-
tus which he used was subsequently adopted by other expedi-
tions, with but little modification.

On board the Norwegian vessel, the “ Véringen,” Dr. Tornée
employed a machine modified by Captain C. Wille, consisting of
a spiral tube nearly five feet in length, open at both ends,
through which water passes freely as the instrument is lowered.
When raised the ends are closed by conical valves worked by
screw fans, which, as in the case of the Sigsbee cup, revolve in
one direction while going down, and in the opposite while
ascending, the valves closing in a short distance.

The difficulty of making an analysis of gases on board a
small vessel is very great, though the separation of the gases
from the sea-water is not a hard process, and is accomplished
by an apparatus not materially different from that employed
by Bunsen. But the modification made in this apparatus by
Dr. Behrens (Fig. 193) is all-important, and renders the opera-
tion comparatively easy. The attempt made on the “Blake”
with Bunsen’s apparatus failed, partly from want of room, and
partly from my want of familiarity with the work.

The apparatus is made up of a flask for the reception of the
sea-water to be tested, and of a bulb-tube connecting with the

THE PHYSIOLOGY OF DEEP-SEA LIFE. 295

mouth of the flask by a close-fitting india-rubber stopper.
The tube of the bulb has a lateral opening from an ingenious
slide-valve between the bulb
and the flask. To the upper
part of the bulb is attached a
gas-tube with a double-ended
pipette, in which a vacuum is
formed by boiling out distilled
water from the bulb, closing the
upper end of the gas-tube, and
then making a connection with
the flask, which under the re-
lieved pressure will allow the
gas contained in the sea-water
to find its way into the gas-
tube. This is then sealed at
the other extremity, and the

contents analyzed on shore. 7

Dr. Jacobsen concluded from

his analyses that the percent-
age of oxygen in sea-water was
practically invariable, the low-
est and highest percentages be-
ing 33.64 and 34.14. While STR
this is undoubtedly true for lim- Fig. 193. — Bunsen’s apparatus, modified
Z by Jacobsen and Behrens.
ited areas, the analyses by Dr.
J. Y. Buchanan of the “Challenger” show that, under varied
conditions of temperature, there was a somewhat wider range,
— between 33 and 35 per cent, in round numbers. The pro-
portion of oxygen being greatest on the surface, it begins at
once to diminish rapidly till it reaches more slowly a minimum,
at a depth of 300 fathoms; and below this depth, its percent-
age remains constant. This does not quite agree with Dittmar’s
results stated further on.

The carbonic acid in the water was determined directly by dis-
tilling in a current of air conveying the gas, and collecting the
steam and carbonic acid in a vessel charged with baryta water.
- By adding to the water to be tested a measured quantity of acid

296 THREE CRUISES OF THE “ BLAKE.”

of known strength, and driving off the liberated carbonic acid
by boiling gently and collecting it in baryta water of known
strength, the amount of acid neutralized will give the carbonic
acid present as neutral carbonate; the quantity of baryta neu-
tralized will give the total amount of carbonic acid.

More than thirty elements are known in solution in ocean-
water, but in such minute quantities that no attempt can be
made to determine them from small samples. Forchhammer’s
memoir dealt with surface water only ; but he stated that the
percentage of the salts of the sea-water was the same in all
parts of the ocean. Dittmar extended this, and proved that in
depth also the composition was subject to but one exception:
the proportion of lime was larger in very deep water than near
the surface.

Professor Dittmar, in his admirable Report on the samples of
sea-water collected by Dr. Buchanan, the chemist of the “ Chal-
lenger,” gives the following analyses as the average composition
of ocean-water salts : —

“Chlorine. : : 3 4 : : 52.292
Bromine : : : : : ‘ . 0.1884
Sulphuric acid. } : : : ; 6.410
Carbonie acid ; : : : i i, aaae
Lime ? : ; : : we ise : 1.676
Magnesia : . : ; : ; . 6.209
Potash : : : : ; : , 1.332
Soda. 2 : : : : . 41.234
(Basic oxygen, equivalent to halogens) . (—12.493)

Total Salts : : . 100.000

“Giving the following as the average composition of sea-water : —

Chloride of sodium. : : : : 77.758
Chloride of magnesium . ; : : . 10.878
Sulphate of magnesium ‘ : : 4.737
Sulphate of lime . ; A : : . 3,600
Sulphate of potash .- . : : ; 2.465
Bromide of magnesium . : : ; ..) ee
Carbonate ‘of lime : ; : : : 0.345

Total Salts ; z . 100.000”

1 The amount of lime is as 10,000: 247 in the West India seas, and as
10,000 : 371 in the Baltic.

THE PHYSIOLOGY OF DEEP-SEA LIFE. 297

The quantity of carbonic acid in the water is not yet definitely
settled. Water kept for several years is of no use for analyses.
Dittmar found that free carbonic acid in sea-water is the excep-
tion: as a rule, carbonic acid is less than the proportion cor-
responding to bicarbonate. In surface water the carbonic acid
increases when the temperature falls, and vice versa. Within
equal ranges of temperature, it seems to be lower in the Pacifie
than in the Atlantic. The alkalinity of bottom waters was
found to be distinctly greater than that of surface water. There
is in sea-water salts a distinct preponderance of free over fixed
acid, the difference being probably due to carbonates. Dittmar
says that sea-water, even when aikaline, takes up additional car-
bonate of lime, if sufficient time is given.

The only source of oxygen and nitrogen present in sea-water
is in the atmosphere, their quantity being dependent on surface
conditions, and not on the depth. Thus, owing to the constant
oxidation which goes on, sea-water must continually be losing
its oxygen in proportion to the depth. Dittmar found that
there was nothing characteristic of bottom waters, as such, in
regard to their absorbed gases, — nothing to distinguish them
from waters of intermediate depths. With reference to the ab-
sorption of oxygen and of nitrogen by sea-water, the amount
of air which ought theoretically to be absorbed by sea-water
of the temperature and at the pressure at which samples were
collected was calculated ; from the quantity of nitrogen found,
the amount of oxygen which should be associated with it was
reached.

The quantity of air found is usually less than what is theo-
retically called for, — probably from the fact that the water in
the ocean is always in motion, the temperature and pressure
varying greatly with the locality. Air is not taken up in deep
water; it is absorbed elsewhere at the surface, and its presence
at any point is due to the constant movement of the waters.

There is no definite relation in the ratio of carbonic acid to
- oxygen present over any area. It seems to depend not so much

on the depth as on the abundance and character of the fauna
found at certain depths. From the action of the waves, oxygen
finds its way down from the surface, and is resorbed subse-

298 THREE CRUISES OF THE “ BLAKE.”’

quently ; while the carbonic acid, coming from the shores and
from the disintegration of the rocks, is held in solution. Were
it not for the constant movement of the sea, the stagnation of
life would soon become universal.

The specific gravity of ocean waters, free from the effects of
local disturbing influences due to proximity of land, is found to
vary within very narrow limits, — between 1.024 and 1.028,"
reduced to a standard temperature of 60° Fahrenheit, or 15.56°
Centigrade. Mr. Buchanan found that the concentration of
the waters of the Atlantic was greater than that of either the
Pacific or the Southern Ocean, and greater in the North Atlantie
than in the South Atlantic. Below the surface the specifie grav-
ity decreases gradually until a minimum is reached at about eight
hundred or one thousand fathoms,’ and then increases slightly
towards the bottom, where in the South Atlantic and Pacific
quite a uniform specific gravity prevails.’ In the equatorial re-
gions the specific gravity first increases to a depth of from fifty
to one hundred fathoms, and then follows the same course as in
other parts of the ocean.

In the North Atlantic, the bottom specific gravity is compar-
atively high. The principal causes for this concentration are
apparently the tradewinds, which, as has been suggested, in-
crease in their capacity for taking up moisture as they proceed
on their course from colder to warmer latitudes of the trade
regions in the Atlantic; in higher temperate latitudes the oppo-
site effect is produced by prevailing westerly winds, which soon
become saturated with moisture in the warmer latitudes from
which they rise. A similar concentration is also brought about
by the formation of ice. The accumulation of salt in the
northern Atlantic is naturally removed by the slow flow from
north to south which probably takes place in the North Atlantic
below the depth of about one thousand fathoms. Similar condi-
tions undoubtedly exist in the Pacific, but it is more difficult to
trace them.

* The differences in specific gravity due sea-water is approximately compressed
to differences of temperature are far in the ratio of 0.0009 for every hundred
greater than those arising from the per- fathoms of depth.

centage of salt. 3 Of 1.0257 to 1.0259.
2 Buchanan’s observations show that

THE PHYSIOLOGY OF DEEP-SEA LIFE. 299

The specific gravity of the surface water of the American
coast, as worked up by Mr. Buchanan from the observations of
the * Challenger” and other vessels, is as follows : —

In the Atlantic outside of the West India Islands (Fig. 194),
close to the American coast, on a line about at the end of the

&

|

|

Fig. 194.—Specific Gravity of Sea-Water. Western N. Atlantic. (Buchanan. )

Bahamas, it varies between 1.0270 and 1.0275. In the Carib-
bean and Gulf of Mexico, as well as waters parallel to the
Atlantic coast as far as Cape Hatteras, and after that along the
course of the hundred-fathom line, it is between 1.0265 and
1.0270. For the waters within a line drawn from Newfound-
land to Cape Cod, the specific gravity is below 1.0260.

The saltest water was found by the “ Challenger ” in the middle

300 THREE CRUISES OF THE “ BLAKE.”

North Atlantic, in the heart of the region of the tradewinds,
and in the South Atlantic in the corresponding regions to the
east of the coast of Brazil. To determine from its density the
salinity of the water, the water specimens were reduced to its
value at a standard temperature, from the tables prepared by
Professor Hubbard of Washington, and shghtly corrected by
the physicists of the “ Challenger.”

The salinity is affected by the fixing of the salts held in so-
lution, which, like lime and silica, are precipitated, as it were,
by organic substances.

In the regions of great rainfall near the equator, the surface
water is frequently quite fresh ; and in the temperate zone there
is nearly an equilibrium between the rain and evaporation. To
these subdivisions of concentration and precipitation Thomson
assigned an important part in the formation of oceanic currents,
for these result from the constant interchange of vapor and
water between the air and the sea.

It is interesting to compare the density of the Caribbean
and that of the Gulf of Mexico (below 1.0270), both enclosed
seas, but supplied with water from a region of low specific
gravity (between 1.0260 and 1.0270), with the high density of
seas, like the Red Sea and the Mediterranean (above 1.0280),
where evaporation goes on with immense activity, although they
are both in communication with oceanic basins. In connection
with this we might also compare the density of Hudson’s Bay
with that of the Baltic, and that of the Great Salt Lake with
that of the Dead Sea and the Caspian, representing climatic

conditions totally unlike.

As has been well said by Meee we live in the depths of
the atmosphere, just as deep-sea creatures live in those of the

ea; but our range, measured by the difference of temperature,
is far wider than that to which deep-sea animals, even when
subjected to the greatest extremes, are exposed. Terrestrial ani-
mals can withstand differences of heat and cold far better than
marine animals. The difference of temperature between an
arctic winter and a tropical summer, for instance, is from three
to four times as large as the widest range of temperature to
which any marine animal can be subjected. The lowest tem-

THE PHYSIOLOGY OF DEEP-SEA LIFE. 301

perature to which man is known to have been exposed is prob-
ably 78° F. below zero, while in the Colorado River desert a
maximum temperature of 120° is not uncommon. The highest
temperature of the surface of the sea is about 89°, and the
lowest only a couple of degrees below freezing.!

It is well known that many species of marine invertebrates
have a range in depth corresponding to the whole scale of this
difference of temperature, say 60°, while in the case of land
animals the extremes differ by nearly 200°. But the facts are
exactly opposite where pressure is concerned. At moderate
heights, when compared to the whole depth of the atmosphere,
the conditions of pressure are sufficiently changed to affect most
painfully all terrestrial animals; indeed, these animals are prac-
tically limited in their range to a small proportion of the total
depth of the atmosphere. With marine animals the conditions
are reversed. A difference in bathymetrical range, in which a
marine animal may pass from a pressure of a few pounds to the
square inch to as many hundred is not uncommon; while a
difference of twenty pounds to the square inch will represent
the maximum to which terrestrial animals can with safety be
subjected. |

Enormous as is the range of pressure which marine animals
can endure, it is not to this, but to the slight differences in the
temperature of the succeeding belts of the sea, that we must
look for an explanation of the principal causes of bathymetrical
distribution. The heat of the sun, judging from the tempera-
ture sections, does not extend farther than to a depth of one
hundred and fifty fathoms. This is the range within which at
different latitudes are limited the widest variations of tempera-
ture (to about 50° F.), and the range within which the oceanic
faunz, as formerly understood, are restricted. Below this belt
—of different depth, according to the latitude —we find a
second belt of from three to four hundred fathoms, within
which the temperature falls very rapidly (to about 38°), until
it reaches the depth at which the remaining mass of water may
practically be said to have a uniform temperature, varying only

1 The highest surface temperatures Gulf of Mexico, and along the Guate-
have been observed in the Red Sea, the mala coast.

302 THREE CRUISES OF THE “ BLAKE.”

between that of 38° and one near the freezing point. Of course,
the depth at which the belt reaches the surface will change ac-
cording to the latitude of the intermediate zones of cold and of
the coldest water. The belt of variable heat is deepest in the
tropics, while the belt of maximum cold reaches the surface in
high latitudes.

In these belts of temperature, we can most satisfactorily trace
the so-called faunal districts into which the shores of our conti-
nents have been subdivided. The recognized geographical pro-
vinces, circumscribed, as first pomted out by Dana, by the lowest
degree of cold to which they are subject, comprise, as a general
rule, animals living along the shores stretching north and south
within certain limits. The bathymetrical range of these lit-
toral species is small, 4nd with few exceptions they do not live
within the limits of either the continental or the abyssal areas,
where flourish the faunz of the other two belts. The tempera-
ture of the continental belt is sufficiently low to crop out in
high latitudes, and hence the large number of so-called arctic
species which have been found to be quite common in moderate
depths upon this so-called continental area; while the strictly
deep-sea or abyssal forms rarely occur within the range of the
continental, and still more rarely within that of the littoral belt.

In making a comparison between the atmospheric and watery
envelopes of the earth, it is interesting to compare the high
velocity of the atmospheric currents and their cataclysmic dis-
turbances with the slow movements of the strongest oceanic
currents, — the direction of the atmospheric currents being more
nearly what those of the ocean would be were it not for the
disturbing effects of continental masses; to the action of these
currents we undoubtedly owe the general drift of the surface
flow of the oceanic basins. This, in connection with the ther-
mal differences and variations in specific gravity, would produce
surface and under currents, modified in their turn by the rotation
of the earth.

The general conditions of temperature below five hundred
fathoms are very simple. From there an immense body of
cold water with a temperature of less than 40° (as lowas 33.36",
or near the freezing point), stretches to the bottom of the

303

oceanic basins. And this is the temperature of all seas which
are not, like inland seas, subjected to special conditions ; as, for
instance, the Mediterranean, the Red Sea, the Sulu Sea, the Car-
ibbean, and the Gulf of Mexico. These all depend for their
lowest bottom temperature on the height of the ridges separat-
ing them from the general circulation.

The differences of temperature observed over extensive areas
in the Atlantic are easily explained by the presence of ridges
rising to heights which isolate the western basin of the Atlantic
_ from the eastern, and that protect these basins again from the
indraught of cold water from the depths of the South Atlantic.
We may thus find enclosed seas or circumscribed oceanic areas
with higher bottom temperature than adjoming seas, due en-
tirely to their exclusion from oceanic circulation by elevations
of a portion of the bottom.

The great cold of the bottom water of the ocean, even in the
tropics, is best brought home to those who have examined the
contents of a haul of the trawl under the tropics. The bottom
ooze is intensely cold, and it is a strange sensation, while one’s
back is broilmg beneath a tropical sun, to have one’s hands
nearly frozen from the stiff, cold mud or ooze one is compelled
to handle while assorting the contents of the trawl."

The increase of temperature as one passes into the interior
of the earth does not affect the temperature of the bottom
of the ocean, for there the constant renewal of cold water sup-
plied from the poles keeps the temperature uniform even in the
equatorial regions. Were the body of water affected in a sim-
ilar manner as the solid crust of the earth, we should find about
350° F. at a depth of three thousand fathoms. But if the in-
creased heat of the interior of the earth’s crust is due to pres-
sure, and not to solar agency through the absorption of heat, we
can see some reason for a lower ocean temperature at correspond-
ing depths, even were there no oceanic circulation.

THE PHYSIOLOGY OF DEEP-SEA LIFE.

1 We followed the advice given by Com-
mander Belknap to dredgers and sound-
ers, to ice their wine in the common
refrigerator ; but the fate of a small bot-
tle of champagne, sent down to a depth
of twenty-four hundred fathoms, was only

encouraging to the friends of total absti-
nence. It came back to us cold, it is
true, but filled with muddy salt water,
which had been forced through the foil
and cork, and had replaced the more pala-
table contents of the bottle.

304 THREE CRUISES OF THE “ BLAKE.”

The oceans, through convection, are the great moderators of
climate, carrying north the heat of the tropics, while the cold
water of the arctics gradually finds its way to the tropics to be
heated, and start on its northward voyage again at a high tem-
perature. By this action in past geological periods, we may
seek to explain the remarkable climatic conditions which have
characterized the cretaceous and the tertiary. Atmospheric tem-
perature rapidly decreases as we rise to high altitudes, into
regions where the pressure is reduced, or pass from the tropics
to the north, where the conditions of pressure are nearly the
same. In the ocean, where the action of the sun is limited to a
comparatively shallow belt, the water having the greatest den-
sity is by no means that having the highest temperature. Oce-
anic circulation is very slow; and, as in the case of the atmos-
phere, there are no enormous changes of temperature affecting
the whole fluid envelope.

The pressure to which animals living in deep water are sub-
ject is enormous. At a thousand fathoms, it can be roughly
stated to be a ton to the square inch, — more than a hundred
and twenty times the pressure borne by terrestrial animals at
the level of the sea. Deep-sea animals are probably no more
conscious of the pressure acting upon them than animals living
on dry land; and they undoubtedly bear, within certain limits,
much greater extremes of pressure. A difference of pressure
due to a height of twenty thousand feet is perhaps the utmost
terrestrial animals can stand ; while some invertebrates with a
wide bathymetrical range may be subject either to the ordinary
pressure of shallow waters, or, if living near the three-thousand-
fathom line, to nearly four hundred atmospheres.

Marine animals readily adapt themselves to these immense
pressures. ‘Their tissues are permeated by fluids, and perfect
equilibrium is established between their circulation and the me-
dium in which they live. Hence pressure has scarcely any effect
upon them, as is proved by the wide bathymetrical range of
a number of invertebrates, and even of fishes belonging to
families in which the bony skeleton remains more or less carti-
laginous. Fishes and mollusks are apparently the only animals
which show very markedly the effect of a diminished pressure.

THE PHYSIOLOGY OF DEEP-SEA LIFE. 305

In fishes brought up from deep water, the swimming-bladder
often protrudes from the mouth, the eyes are forced out of their
sockets, the scales have fallen off, and they present a most dis-
reputable appearance.

Regnard’s experiments on the effects of pressure — experi-
ments producing a pressure fully as great as that to which they
are subject in deep water — indicate that algz, infusoria, mol-
lusks, worms, and even fishes, are thrown by pressure into a
torpid condition, from which they recover after a time when
placed again in normal conditions. If the pressure is very
_ powerful and long-continued, it proves fatal to fishes.

But few experiments have been made to ascertain the depth
to which light penetrates. They seem to show that a depth of
about two hundred fathoms is the lower limit. Forel proved
that in the Lake of Geneva photographic plates remained sensi-
tive to between thirty and fifty fathoms, a depth at least four
times that at which the presence of a white disk sunk below the
surface could be detected, according to the experiments tried
by Pourtales.

These experiments, however, do not determine the limits at
which very faint rays of various colors may reach considerable
depths. Secchi found that red, yellow, and green successively
disappeared, while blue, indigo, and violet remained quite bright
at a depth of about forty fathoms. This may explain why,
among so many of the deep-sea echinoderms and other animals,
violet pigments seem to be the most prominent ; yet it has been
assumed that the presence of red and carmine among abyssal
crustacea and the like proves that the red rays have the greatest
penetration. We may imagine a reddish yellow twilight at a
depth of about fifty fathoms, passing into a darker region
near the hundred-fathom line ; and finally, at two hundred
fathoms, a district where the light is possibly that of a bril-
lant starlight night."

M. Edouard Sarasin and Professor Fol recently made an inter-
esting report of the experiments conducted by the committee of
the Physical Society of Geneva to ascertain the transparency of

1 Professor Verrill has made the rather there may be a soft green light, not unlike
' startling suggestion, that in deep water a pale moonlight.

306 THREE CRUISES OF THE “ BLAKE.”

the water of the lake, and the depth to which light penetrates.
Three candles in a lantern —the flame being fed by a contin-
uous current of air — were visible at a depth of thirty metres,
in pure water. An electric light was distinctly seen at a depth
of thirty-three metres. A few centimetres more, and the clear
image disappeared. It was replaced by a diffuse light, faintly
perceptible at sixty-seven metres.

Messrs. Sarasin and Soret noticed a very characteristic absorp-
tion ray (in the red near B) in the spectrum light which had
traversed a certain layer of water. They further observed that
the distance of clear vision varied very little with the increase
of the brilliancy of the luminous body and its absolute dimen-
sions. Photographic experiments in the deep portions of the
lake showed the effect of light on the sensitive plates down to
two hundred and fifty metres. This depth seems to be, at least
for the plates now in use, the extreme limit of action of the
sun’s light. “ Below this point the lake is a vast dark cham-
ber.”

In March, 1885, Messrs. Fol and Sarasin concluded, from
their experiments at Villefranche, that in fine weather the last
rays of light were dissipated at a depth of about four hundred
metres below the surface of the sea.

Nowhere can the effect of light, heat, and motion be bet-
ter realized than on any beach in the tropics, or upon a coral
reef. There, exposed to the full glare of a tropical sun, a pro-
fusion of animal life flourishes, unknown in more temperate
latitudes. We meet its parallel again in the arctic regions,
where an immense number of specimens developed during the
long arctic days replace the diversity of forms of tropical
realms. The varying conditions of rocky coasts, of long sandy
stretches, of mud flats, of gravelly beaches, — whether ex-
posed to or sheltered from the action of the sea, — whether
situated in deep or shallow water, in the tropics, the temper-
ate, or the polar regions, — give us an almost endless variety .
of physical conditions under which our marine fauna and flora
flourish, in striking contrast with the conditions in the abyssal
and intermediate districts of the oceanic basins.

Pelagic animals, living as they probably do within a belt 150

THE PHYSIOLOGY OF DEEP-SEA LIFE. 307

fathoms in depth, must habitually move, when they come to the
surface, from regions of darkness through tracts gradually be-
coming lighter, until they strike the top of the water, which
they find flooded with white ight. The range of the nature
of sunlight which they pass through is far greater than any we
can experience in going from the level of the sea to the high-
est mountain summits. But the phenomenon of the green hight
of the sea, gradually replaced near the surface by white light,
must be similar to the one so well described by Langley, when
he ascended Mount Whitney to a height so much nearer the
upper limits of the atmosphere that the color of the sun ap-
peared blue, owing to the disproportionate amount of blue and
violet tints, which have been mainly resorbed selectively by the
upper layers of the atmosphere, allowimg only the white rays
to reach us.

In discussing the question of the penetration of hght to
great depths, we should not forget, on the one hand, that blind
crustacea and other marine invertebrates without eyes, or with
rudimentary organs of vision, have been dredged from a depth
of less than 200 fathoms, and, on the other, that the fauna,
as a whole, is not blind as in caves, but that by far the majority
of the animals living at a depth of about 2,000 fathoms have eyes
either like their allies in shallower water, or else rudimen-
tary, or sometimes very large, as in the huge eyes developed out
of all proportion in some of the abyssal crustacea and fishes,
and undoubtedly adapted to make the most of the little light
existing in deep water. These, as well as the appendages of
such deep-sea fishes as the Lophioids, intended to attract prey,
seem to tell us something of the exceedingly faint light, or of
the actinic rays which alone may reach them through the ap-
parently transparent water.’

The eyes of the deep-water fishes, crustacea, cephalopods,
gasteropods, annelids, echinoderms, and celenterates, are in
general identical in structure with those of the same classes liv-
ing upon the coasts in shallow water. We know little regard-

1 Ata distance from the shore, out of shelf by the action of the waves and cur-
reach of all the sediment brought down rents, sea-water is remarkably clear, and
by rivers, or washed from the continental free from impurities.

308 THREE CRUISES OF THE “ BLAKE.”

ing the vision of marine animals, and we should be careful in
drawing conclusions with reference to physical conditions de-
rived from the functions of organs of sense, which may serve
other purposes than those of vision alone. The sense organs
of ccelenterates and of annelids, varymg between mere pigment
spots and more complicated organs, may be of use, not only to
detect differences in the intensity of light, but also in receiving
other impressions, — of sound, motion, or heat.

The deep-water gasteropods, with rudimentary eyes, or to-
tally blind, live as do their littoral congeners, buried in mud.
The blind fishes belong to families with burrowing habits,
and living in the soft deep-sea mud. Their organs of vision
may gradually have become atrophied, and been replaced by
highly specialized tactile organs. The same thing occurs with
crustacea. Astacus zaleucus is blind, its claws are long and
delicate, and with similar tactile organs must be of assistance
to them in enabling them to feel thew way about. Dr.
Carpenter and Professor Thomson came to the conclusion
that phosphorescent animals play an important part in lighting
up the abyssal regions of the sea. The contents of the trawl
are frequently brilliantly phosphorescent, and among the deni-
zens of the deeper regions are a number of highly luminous
anthozoa, ophiurans, hydroids, crustacea, and even fishes.
Swimming or creeping between the forests of gorgonians,’
which become luminous by disturbances due to currents or other
movements, the deep-sea crustacea, fishes, cephalopods, echino-
derms, and others, must be able to see a considerable distance
during the emission of the phosphorescent light, and thus re-
ceive assistance in searching for their food. The light devel-
oped from such a source, and in such a manner, cannot be
very intense, and yet such areas may be, as has been stated
by Moseley, favorite spots where deep-sea animals congregate.
It has been suggested by Professor Verrill that this phos-
phorescence is protective, and may prevent fishes and other
animals from browsing on the luminous actinozoa, lest they

1 Such forests we find commonly on stance, where the masses of animals ac-
the shallower slopes of the continental cumulated within quite limited areas are
areas, as on the Florida plateau for in- really prodigious.

THE PHYSIOLOGY OF DEEP-SEA LIFE. 309

should be stung by large lasso-cells. According to fishermen,
fishes avoid nets when filled with phosphorescent animals; yet
on coral reefs fishes are constantly seen browsing upon the
corals and shoals of gorgonians. The commensalism of many
acalephs and quite delicate fishes living surrounded by the ten-
tacles of meduse, and especially by the intensely burning ten-
tacles of Physaliz, would seem to prove that they are not in
dread of lasso-cells.

During the voyage of the “Challenger,” Professor Moseley *
made a series of spectroscopic observations on the coloring-mat-
ters of various deep-sea invertebrates. Special attention was
paid to spectra presenting isolated bands, because they are read-
ily identified. He says :—

* Peculiar coloring-matters giving absorption spectra have now been
found to exist in members of all the seven groups of the animal king-
dom. Amongst Protozoa such coloring-matters occur in Infusoria and
Sponges ; amongst Celenterata they occur both in Anthozoa and Hy-
dromedusz, in Echinodermata, in both Crinoidea, Echinoidea, and
Holothuroidea, but not in the Asteroidea. In Vermes, in Annelids
and Gephyreans. In Arthropoda, in Crustacea and in Insecta. In
Mollusks, in Gasteropods only. In Vertebrata, in four fish, three spe-
cies of Odax and one Labrichthys, and twelve birds of two closely
allied genera. The Echinodermata and Celenterata appear to be the
groups which are most prolific of such coloring-matters. Pentacrinin
and Antedonin seem to be widely diffused in immense quantities
through the tissues of the crinoids in which they occur; and Echino-
derms generally seem to be characterized by the presence of evenly
diffused, abundant, and readily soluble pigments.

“Tt seems improbable that the eyes of other animals are more per-
fect as spectroscopes than our own, and hence we are at a loss for an
explanation, on grounds of direct benefit to the species, of the exist-
ence of the peculiar complex pigment in it. That the majority of spe-
cies of Antedon should have vivid coloring-matters of a simple charac-
ter, and that few or one only should be dyed by a very complex one, is
a remarkable fact, and it seems only possible to say in regard to such
facts, that the formation of the particular pigment in the animal is
accidental, 7. e., no more to be explained than such facts as that sul-
phate of copper is blue.”

Professor Moseley also observed that the phosphorescent light
1 Quart. Journ. Mic. Science, XVII., 1877, p. 1.

310). THREE CRUISES OF THE “ BLAKE.”

emitted by alcyonarians consisted of red, yellow, and green

rays only.

‘Hence, were the light in the deep sea derived from this source, in
the absence of blue and violet, only red, yellow, and green colors could
be effective... . / A brilliant green coloring-matter was found in some
deep-sea Annelids. No doubt in many cases the coloring of the deep-
sea animals, as in the case of the purple Holothurians, is useless, and
only a case of persistence. The madder coloring of some of the soft
parts of the Corals may be in like case, but possibly useful for at-
traction of prey, being visible by the phosphorescent light. .

“The same coloring-matters exist in deep-sea animals which are
found in shallow-water forms. In the case of deep-sea possessors
of these pigments, they perhaps never exercise their peculiar complex
action on light during the whole life of the animal, but remain in dark-
ness, never showing their color.”

Many of the deep-sea fishes collected by the “ Blake” are of
a grayish color, or a dull black, or have as it were lost their
color, and been bleached to a dirty white; they resemble in
this respect semi-transparent fish embryos, in which black is still
the most characteristic pigment. No blue animals have been
noticed among’ the deep-sea types 5 blue is, in spite of its appar-
ent protective color, rarely seen in marine animals, except in a
few pelagic forms.’ Deep-sea burrowing animals have fully as
marked a diversity of coloring as their shallower water con-
geners. There is apparently in the abysses of the sea the same
adaptation to the surroundings as upon the littoral zone. We
~ meet with highly colored ophiurans within masses of sponges,
themselves brilhantly colored, at a depth of more than 150
fathoms.

Again, other ophiurans, coming from the globigerina ooze,
could hardly be seen when stretched out on its surface. As in
shallower waters, they must live buried in this material, from
which they can scarcely be distinguished. It seems difficult to
believe that protective characters which are of use in waters of
moderate depths should have been retained in deep-sea types,

1 We must except a small incrusting line in the Gulf of Mexico, as well as blue
sponge of a blue color, not uncommon in eggs of a crustacean living buried in large
the dredgings near the hundred-fathom masses of sponge.

THE PHYSIOLOGY OF DEEP-SEA LIFE. 311

which have flourished for long periods of time in regions far
beyond those where protective coloration would be of ser-
vice. We have a strong argument in favor of the gradual
and comparatively recent migration of littoral forms into deep
water in the fact that oe. are still so many vividly colored
_ bathyssal animals belonging to all the classes of the animal
kingdom, and possessing nearly all the hues found in types
living in littoral waters.

While we recognize the predominance of tints of white, pink,
red, scarlet, orange, violet, purple, green, yellow, and allied col-
ors in deep-water types, the variety of coloring among them is
quite as striking as that of better-known marine animals. The
fishes belonging to the lophioids, to the labroids, to the wrasses,
and to the scorpenoids, remind us in their coloring of that of
their littoral allies. There is as great a diversity in color in the
reds, oranges, greens, yellows, and scarlets of the deep-water

_starfishes and ophiurans as there is in those of our rocky or
sandy shores.

Among the abyssal invertebrates living in commensalism, the

adaptation to surroundings is fully as marked as in shallow
water. J may mention specially the many species of ophiurans,
attached to variously colored gorgonians, branching corals, and

“stems of Pentacrinus, scarcely to be distinguished from the part
to which they cling, so completely has their pattern of color-
ation become identified with it. There is a similar agreement
in coloration in annelids when commensals upon starfishes,
-mollusea, actiniz, or sponges, and with crustacea, and actiniz
_parasitic upon corals, gorgonians, or mollusks. The habits of
the deep-sea hermit-crabs are not unlike those of their shallow-
water species, and there are deep-water pygnogonids associated
with hydroids. Deep-water cephalopods do not differ in their
type of coloration from those of the coast shelf.

The echinoids dredged beyond the hundred-fathom line are
many of them dark-colored, but generally present, as in the case
of the spatangoids, the neutral colors that are characteristic of
those living at higher levels on sandy beaches, or do not differ
in their tints from those of the littoral zone as in the case of

_the many species of Echinus proper.

~—

'

THREE CRUISES OF THE “ BLAKE.”’

312

Among the actinians brought up from deeper water, red,
orange, or rosy and flesh-colored tints and stripes are as abun-
dant as in the more common species of shallow water. The
dominant colors of gorgonians are orange, red, green, violet,
yellow, fully as varied an assortment as exists in the anthozoa
of a flourishing coral reef.

The number of species of crustacea (schizopods, peneids, cari-
dids) colored a brilliant scarlet is quite large, and it is somewhat
remarkable, as has already been noticed by Moseley, that a pig-
ment which is seen occasionally in some of the more minute
pelagic crustacea should be so abnormally developed in deep
water. In other deep-sea crustacea there is a predominance
of shades of yellow, pink, and pale greenish tints.

Large masses of sponges of a_ brilliant one ena or
brownish pink are constantly dredged from depths near the two-
hundred-fathom line, associated with species having the colors

of the littoral sponges.

is similar to that of the shore species.
reddish yellows, and browns, the prevailing tints.

In the deep-sea comatulz the coloring |

We have violet, green,

Among the

stalked crinoids the tints vary from cream-colored to dark green

or
in

grayish violet.

The coloring principle, pentacrinin, dissolved
alcohol, produces an intense purple red.

The distribution of marine plants’ plays an important part

1 The recent observations of Berthold
in regard to the bathymetrical range of
alge indicate clearly that the principal
features in their distribution are light
and the motion of the water. The species
characteristic of localities exposed to
violent action of the waves are differ-
ent from those found in more protected
places. There are alge which require
intense light, and others which flourish
best in sites sheltered from direct action
of the sun.

The green and brown alge need the
greatest amount of light and motion,
and flourish in those limits of the shores
which are closest to the high-water mark,
while on the contrary the red alge live
in deeper water, where the light is more
diffuse, and the motion somewhat les-
sened. The calcareous alge thrive in

quiet waters, though they are not, at
least in the tropics on reefs, affected un-
favorably by a flood of light. Berthold
states that they are still found in great
quantities in deep water, — sixty fath-
oms in the deepest parts of the Gulf
of Naples. The intense light and heat
of the tropical seas may perhaps be the
primary cause of the absence of an ex-
tended marine flora. Yet light and heat
are most important to the extensive pe-
lagic flora, and in the tropical regions in
the track of oceanic currents there are
vast fields of surface alge, often dis-
coloring the sea for miles. The fullest
development of our coast alge undoubt-
edly takes place in the temperate regions,
and the fact that some of the larger
fronds of Macrocystis have a length of
150 fathoms, and that some of the eal-

313

in the food supply of shore animals; vegetable life forms the
basis of all life; for while many animals are carnivorous, yet
those they feed upon depend in a measure for their sustenance
upon plants. It is therefore an interesting problem to ascer-
tain how far vegetable life extends into the depths of the sea.
Its disappearance in comparatively shallow regions is a remark-
able phenomenon, when we remember that all animal life is
ultimately dependent upon vegetable life for its own existence.

The discovery ef the carcasses of pelagic animals at the bot-
tom of the ocean, still fresh enough to supply a large amount
of food for the animals constituting the deep-sea fauna, solves
the problem at once. The pelagic animals derive a large part
of their food supply from the swarms of large and small pelagic
algze covering the surface of the sea in all oceans. On dying,
both surface animals and plants drop to the bottom, and still
retain an amount of nutritive matter sufficient to serve as food
for the carnivorous animals living on the bottom. The pelagic
fauna thus becomes the medium of transfer to the bottom of a
large quantity of vegetable matter living at the surface. This
transfer takes place rapidly. Moseley says Salpz will sink two
thousand fathoms in less than three days.

The larger carnivorous animals of course prey upon one an-
other, but foraminifera, sponges, and their allies, cannot feed
upon each other, as do the mollusks, annelids, polyps, and the
like. They need vegetable substances, or diluted organic mat-
ter, such as they find in abundance on the bottom.

A sort of “ broth,” as it has been called by Carpenter, collects
on the bottom of the ocean, from which the lower types may
possibly be able to obtain thei sustenance directly, and transfer
it for their uses, as they do the silex and lime which they get

THE PHYSIOLOGY OF DEEP-SEA LIFE.

eareous alge are found at that depth,
would prove conclusively that some kind
of light penetrates to this depth. Some
of the organisms which have been de-
seribed as single-chambered foraminifera
are in reality calcareous alge, allied to
the green spore-bearing alge, the Dasy-
clade of Harvey.

Boring alge have been dredged in deep
water (over 1,000 fathoms).

At a depth of 270 fathoms off Havana,
Pourtalés dredged a single specimen of
a minute alga, Centroceras clavulatum
Aghard, which Harvey says is common
at low-water mark at Key West. Di-
atoms were also brought up from the
same locality.

314 THREE CRUISES OF THE “ BLAKE.”

in solution in the sea. This broth probably remains serviceable
for quite a period of time; the decomposition of the organic
material which has found its way to the bottom takes place
gradually, and its putrefaction must be very slow.’ This broth
is derived not only from the pelagic fauna and flora, but also,
along the littoral and continental zones, from the decomposition
of animal and vegetable detritus washed from the shore belts, or
swept by the rivers into the sea, or carried into deeper water by
slowly moving currents. Though we are only beginning the
investigation of the physical conditions of the ocean, we have
learned enough to see how necessary to any exposition of the
evolution of the present condition of our earth is a knowledge
of the physics of the sea.

1 M. Certes (Acad. Royale de Belgique,
Bull. VIL, No. 6, 1884) has shown the
presence of microbes at considerable
depths, 250 to 2,500 fathoms, and of a
large number of tests he made, only four
have given no result. He submitted a
bacterium to a pressure of 600 atmos-
pheres, and found that this did not affect
it. He seems to think the effect of pres-
sure varies with each species, and that no

littoral species can resist an excessive or
prolonged pressure.

Regnard (Comptes Rendus, Mars 24,
1884, p. 745), who also experimented on
the effect of great pressure, found that
while under a pressure of six hundred at-
mospheres yeast mixed with a solution of
sugar showed no signs of fermentation.
This pressure is equal to a depth of nearly
4,000 fathoms.

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