Geology and Natural History. 209 
sinking of the surface layer as it becomes more dense by evapora- 
tion, an effect not apparent in the Atlantic, because the difference 
of salinity above and below is so slight. 
(3.) The temperature of the North Atlantic waters near the mar- 
gin of the basin decreases downward toward 35°, but with an 
? 
perature at 81 fathoms was 53°°5; from which it gradually sunk 
to 51°-5 at 300 fath.; 50°-5 at 600; 49°3 at 800; and then fell off 
aters of the Mediterranean 
Very Nearly uniform, being between 54° and 56°°5, and nowhere 
lo . and . 
> 
e@ te 
at lot, 71°. ©. at 40 £, 5773; at 50 f, 
, at 20 £, 61°; at 30 £, 60°; at ade # 
“'T; at 100 £, ae 54° was found at a depth in one case of 
