Aug. 17, 1871] 
NATURE 
315 

Hutton, Playfair, and Hall. The chief features of geolo- 
gical interest examined were :— First, the manner in which, 
at Siccar Point, the vertical and highly-inclined Lower 
Silurian strata are covered unconformably by the gently- 
inclined Upper Old Red sandstone. It was this section 
which furnished Hutton with one of the most telling argu- 
ments for his “ ‘Il heory of the Earth,” and his search and 
discovery of which have been so graphically described by 
Playfair. The sections presented indeed a magnificent 
example of uncomformable stratification; the Old Red 
strata lying almost horizontally on the vertical Silu- 
rians, a phenomenon expressed by the local papers by 
the phrase, not devoid of a certain dry humour, that “the 
Old Red rested uncomfortably onthe Silurian!” We are 
bound however to state that on the whole the Edinburgh 
press was well up to the occasion; the Reports of the 
Addresses, Lectures, and Sectional Proceedings were good 
and full, and no pains were spared to make them really 
first-rate. The reports in the Scotsman should be men- 
tioned in particular as unusually excellent. 
The second point examined was the plicition of the 
Lower Silurian rocks. Along this wild coast-line the 
greywacke and shale are thrown into many anticlinal 
and synclinal curves, extending from top to bottom of the 
cliffs, which are here in some places more than 500 feet 
high. Along the part of the coast to be examined by the 
excursionists the best folds occur at Fast Castle. It was 
the curving of these rocks which attracted the attent.on 
of Sir James Hall, and led him to investigate the subject 
in his well-known paper on “ The Vertical Position and 
Convolutions of certain Strata,” some of the illustrations 
from which may now be found copied into almost every 
text-book of geology. 
A purty of naturalists, numbering about sixty, joined in 
the Dredging Expedition off the Bass Rok. Amongst 
the gentlhmen present were :—Prof. Wyville Thomson, 
Admiral Sir Edward Belcher, Sir Walter Elliott, Prof. 
Crum brown, Prof. Margo, of Pesth; Prof. Purser, of 
Belfast ; Dr Colding, of Copenhagen; Dr. Lii‘ken; Dr. 
Copeland, of Parsonstown, Ireland; Dr. Lindeman, of 
Bremen ; Mr. Shapter, Mr. G Barclay, Mr. Ray Lan- 
kester, Mr. Shepberd, and Mr, Davis. There were aiso 
a number of ladies in the party. 
About a hundred members and associates of the Asso- 
ciation took part in a botanical excursion to the top of 
Ben Ledi, under the leadership of the veteran Prof. 
Balfour 
The Conversazione held on Tuesday evening was a very 
good one; over 1,400 ladies and gentiemen attended. In 
addition to the varicd conrenis of the Museum of Science 
and Art where the Conversazione was held, and which 
are themselves of no ordinary interest, the following were 
the most interesting objects exhibited :—Mr. Fowler’s 
flint implements of the drift, Spencer’s local heliostat, Dr. 
Gladstone’s experiments in the crysta'lisation of metals by 
electricity under the microscope ; flint implements from 
Patestine. 
I: only remains to be added, that, thanks to the admir- 
able arrangements of the energetic local secretaries, Dr. 
Crum Brown and Mr, Rollo. everything went off well 
during the meeting ; and the third Edinburgh meeting of 
the British Association will be looked back upon as one 
of the most enjoyable of a long series, as it certainly has 
been the most important for many years. 
SECTION A. 
THE greater part ot the first day’s session in this Section was 
occupied by a paper Ox the Thermodynamics of the General 
Oceanic Circulation, by Dr. W. B, Carpenter, and the interest- 
ing « iscussion which followed. 
The inquiries in which the author, with his colleague, Prof, 
Wyville Thomsun, has recently been engaged, into the physical 
condition of the deep sea, have furnished a new set of facts in 

regard to its thermal condition, which seem to point to conclu- 
sions very different from the doctrines usually received in regard 
to the movements of oceanic waters and their influence on climate. 
It may now be asserted as probable that the temperature of the bed 
of the ocean below 2,900 fathoms is everywhere, even under the 
equator, but little above 32° F., while it may be as low as 29°5° F. 
in particular channels of less depth, such as that which lies 
between the Shetland and the Faroe Islands. That this depres- 
sion of temperature has no dependence on depth Zev se, appears 
to be conclusively proved by the fact that it does not show itself 
in the Mediterrancan, for though depths of 1,600 fathoms have 
been sounded in its western basin, and 2,000 in its eastern basin, 
the temperature below the surface stratum of about fifty fat) oms, 
heated by direct sular radiation, remains at a uniform level of 
about 54° to the very bottom, being in fact the average winter 
temperature of this vast mass of water, which may be regarded, 
as to all but its surface, in the light of an inland lake. 
Now, if the condition of the Mediterranean be compared with 
that of the eastern border of the Atlantic under the same parallels, 
we find a most striking contrast in their thermal condirions. 
The superheating of the surface-stratum by direct solar radiation 
shows itself in the latter as in the former; below the surface- 
stratum there is a very gradual descent of the thermometer from 
about 53° to 49°, which-last is the temperature at 8co fathoms ; 
in the 200 fathoms below this there is a rapid loss of 9°, bringing 
the thermometer down to 40° at 1,000 fathoms ; whilst beneath 
that line there is a further gradual descent with increase of depth, 
36°°5 being the lowest temperature yet observed in this region. 
The author regarded this anomaly as due to the fact that the 
former was virtually cut off from the great oceanic circulation 
that diffuses over the latter the waters that have been chilled in 
the polar seas. The author found that the Arimeem mobile of 
this circulation was not in equatorial heat (which being applied 
to the surtace could exert no motor force beneath the thins ratum 
which it directly affects), but in polar coid, which by its action 
on the suriace-water would produce the same kind of movement 
from above downwards, as heat applied at the bottom does from 
below upwards, 
Suppo-ing the whole surface of a limited basin of sea-water to 
be exposed to intense cold, the surface flm, when rendered 
heavier by reduction of temperature, will sink, to be replaced 
fiom the warmer stvatum beneath. The new surface-straium will 
then be cooled ; and the same process would be rejeated unul 
| the temperature of the who-e basin comes to be reduced as low 
as the cooling action will carry it—it may bedo«n to 27° oreven 
25°. But suppose that only a portion of the :urface area of the 
basin be exposed to cold, the phenomena would be different. (1) 
As each surlace-film cools and sinks, its place will be supplied, 
not from below, but by a surface influx of the water around ; 
and (2) the bottom stratum will flow away over the deepest parts 
of the basin, while, since the total heat of the liquid is kept up, 
there will be an upper stratum which will be drawn towards the 
cold area, to be precipitated to the bottom and repeat the action. 
Applying this principle to the great oceanic area that str tches 
between the Equaror and the Poles, we should expect to find the 
upper stratum moving jrom the Equator towards the Poles, and 
its lower stratum from the Poles towards the Equator. That 
such a movement really takes place is indicated, as it seems to 
me, by various facts. 
(1.) ‘The general prevalence of a temperature not far above 32° 
over the deepest paits of the great ocean basin, which could 
scarcely be maintained if there were not a continual flow of cold 
water from the polar area. 
(2.) The distinction between the upper and lower strata of 
Atlantic waters is shown by the change of temperature between 
S00 and 1000 fathoms. 
(3.) The existence ofamovement of warm surface-water towards 
both polar areas. From a consideration of these facis in detail, 
the author was led to the hypothesis of a north-easterly movement 
of a vast stratum of oceanic water, having a depth of at least 600 
fathoms. In the remaining portion of his paper Dr. Carpenter 
discussed the different causes of horizontal and vertical currents. 
He was inclined to believe that the propulsive force of the trade 
winds produced only a horizontal motion. 
Sir W, Thomson said that Dr. Carpenter’s explanation had 
been so lucid and demonstrative that he thought litle remai: ed 
to be said. It seemed to him that Dr, Carpenter thoroughly 
established his case. The distinction drawn by him between 
horizontal and vertical circulation was important. When the 
jaih of least resistance was in a wide circuit along the surface, 
hen the chief return would be along the surface. In an 
