Fuly 28, 1870| 
NATURE 259 
de Pourtales dredging in the Gulf Stream in the Strait of 
Florida has found a true S«/enia, several representatives 
of the chalk forms of Casstdulid@ ; and M. de Pourtales 
on the American side, and we off 
the west coast of Ireland and off 
the Shetlands, have dredged a re- 
markable form, appropriately named 
by Lyman Povrtalesia miranda, 
which is most nearly related to the 
Jurassic and Cretaceous genus, Dy- 
saster, 
The Crustaceans of the chalk are, 
as yet, very imperfectly known, so 
that little can be founded upon them, 
The Mollusca have not yet been 
worked up, but the large number of 
smooth terebratule, and of species 
é of the genera Aporrhais, Dentalium, 
Between the Farée and a f 
Shetland Islands. 61° /ectew, Lima, &c., from the deeper 
ar’ N. Lat., 3° 44 W-L., water, are highly suggestive of older 
Gr: times. Mollusca are, of course, most 
abundant in comparatively shallow water, and we were 
prepared to hear from Mr. Gwyn Jeffreys that out of 
‘ about 120 species new to the British 
area, dredged in the Porcupine ex- 
pedition, alarge number date back to 
the newer Tertiaries. 
With these facts before us, it can 
scarcely be a matter of surprise that 
the point of view of those who are 
carrying on these investigations is 
insensibly changing, and that when 
the dredge comes up from a depth 
of one or two thousand fathoms the 
number of new species which it may 
contain is not now so much the ques- 
tion as the relation which these new 
forms may bear to their ancestors of 
an earlier epoch, and the light which 
they may be expected to throw upon 
types hitherto supposed to be entirely 
extinct, 
Although there is so striking a 
resemblance in general character be- 
tween the fauna of the European 
chalk and that of the deeper portion 
of the bed of the Atlantic, especially 
of a band extending from a depth of 
4oo fathoms to 900 fathoms in the 
Gulf Stream area, none of the animals, 
Between Rockall & N.w, With the possible exception of some 
Coast of Ireland. of the Foraminifera, are absolutely 
identical. The species of Syipagella, Holtenia, and 
Farrea approach the siphonias and ventriculites very 
nearly, but they form a distinct sub- 
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SURFACE 
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TCMPERATURE IN C* 
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— cold INDRAUCHT---- 
ARCTIC & ANTARCTIC 
we _sunrace section of the order. /hézocrinus 
a -s) | and its allies resemble Bovrgette- 
crinus, and undoubtedly represent it, 
but there are important differences. 
The Saleniz, the Cassidulidee, and 
the Dysasters, &c., of the chalk mud 
approach their Cretaceous antetypes 
more closely than they do any known 
living forms, but they are generally 
dwarfed, and otherwise diverge so 
far as to require in most cases the 
establishment of new genera for their 
accommodation. Now, if we admit 
the continuous accumulation of 
sediment of the same character, and 
STREAM 
8 HW 950 
Sree mas UNL: 
SCA-BOTTOM 
South-West of the Farde the persistence of the same general 
Islands. 59° 35/N. Lat., conditions over a large portion of the 
gf xr! W. L., Gr. area of the present ccean from Meso- 
zoic times, it seems at first sight more difficult to account 
for this great amount of modification than for the per- 
petual recurrence in deep dredgings of forms suggestive 
of close relationship to, and lineal descent from, extinct 
species. 
At the bottom of the ocean, where other conditions are 
comparatively uniform, we may probably regard succes- 
sive changes of temperature as the main cause of succes- 
sive alterations in the fauna of a region, by the modifica- 
tion, extinction, emigration, and immigration of species. 
It is my object, in the present lecture, to show that in the 
vertical oscillations which are known to have occurred 
since the close of the Mesozoic period, we have a vera 
causa of alternations of temperature fully adequate to the 
entire result. 
In order to understand this point 
thoroughly it will be necessary, in 
the first place, to pass in review the 
present conditions of distribution of 
temperature in the North Atlantic.* 
There seems to be little room for 
reasonable doubt that the present 
temperature of the basin of the North 
Atlantic depends, it may be said, 
entirely—for other modifying causes, 
such as the drift of the variable 
winds and the surface-heating and 
consequent expansion of equatorial 
water, are comparatively trifling— 
upon the Gulf Stream and the general 
indraught of cold water from the 
Arctic and Antarctic basins to supply 
the place of the constant warm cur- 
rent streaming north-eastwards from 
the Strait of Florida. Means of 
summer temperature which indicate 
roughly, not quite exactly, for higher 
temperatures, the mean amount of 
heat derived from the sun by direct 
radiation : the heat derived from all 
other sources, have been reduced 
from many thousands of isolated 
observations, and their results in- 
corporated in anadmirable and care- 
ful paper by Dr. A. Petermann (Geo- 
graphische Mittheilungen, 1870). 
The curves on the accompanying 
map, copied from Petermann, ex- 
plain at a glance the distribution 
of abnormal temperature along the 
coasts of Western Europe, and indi- 
cate unmistakeably the source and 
direction of the warm current. One 
point only remained in doubt,namely, 
the depth to which the temperature 
of the ocean is affected by the Gulf 
Stream water. Now that there has 
been time to correlate and compare 
the large series of invaluable obser- 
vations made with consummate skill 
and care by Captain Calver, R.N., 
during the Porcupine Expedition, 
this question may be considered solved over a consider- 
able area, and the depth of the Gulf Stream off the 
west coast of Great Britain and France determined at 
about S800 fathoms (4,800 feet). This is so very im- 
My colleague, Dr. Carpenter, in many interesting communications on 
the temperature results of the Porcupine expedition (NATURE, Voli 
p. 490, &c., &e.), denies that the Gulf Stream exercises any influence upon 
the temperature of the basin of the North Atlantic, and doubts whether it 
reaches the coast of Europe at all. He attributes the differences of tempe- 
rature between different zones of depth to ‘‘a great general movement of 
equatorial water towards the polar area, of which movement the Gulf Stream 
contributes a peculiar case, modified by local conditions.” And if I under- 
stand him aright, he supposes that this general movement 1s produced by 
some cause analogous to that which produces the general circulation in the 
atmosphere. Iam sorry to be obliged todissent so completely from his view 
on this point, 
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SEA-BOTTOM 
Bay of Biscay. 47° 38’ N 
Lat., 12° 8’ W. L., Gr. 
