518 Proceedings of the Royal Society 
there are now forming vast accumulations of Glohigerina and other 
pelagic Foraminifera, coccoliths, rhabdoliths, shells of pelagic Mol- 
luscs, and remains of other organisms. These deposits may perhaps 
he called the sediments of median depths and of warmer zones, be- 
cause they diminish in great depths and tend to disappear towards 
the poles. This fact is evidently in relation with the surface 
temperature of the ocean, and shows that pelagic Foraminifera and 
Molluscs live in the superficial waters of the sea, whence their dead 
shells fall to the bottom. Globigerina ooze is not found in 
enclosed ^eas nor in polar latitudes. In the Southern Hemisphere 
it has not been met with beyond the 50th parallel. In the 
Atlantic it is deposited upon the bottom at a very high latitude 
belov/ the warm waters of the Gulf Stream, and is not observed 
under the cold descending polar current which runs south in the 
same latitude. These facts are readily explained, if we admit that 
this ooze is formed chiefly by the shells of surface organisms, which 
require an elevated temperature and a wide expanse of sea. But 
as long as the conditions of the surface are the same we would 
expect the deposits at the bottom also to remain the same. In 
showing that such is not the case, we are led to take into account 
an agent which is in direct correlation with the depth. We may 
regard it as established that the majority of the calcareous organ- 
isms, which make up the Globigerina and Pteropod oozes, live in 
the surface waters, and we may also take for granted that there is 
always a specific identity between the calcareous organisms which 
live at the surface, and the shells of these pelagic creatures found at 
the bottom. This observation will permit us to place in relation 
the organic deposits and those which are directly or indirectly the 
result of the chemical activity of the ocean. Globigerina ooze is 
found in the tropical ^one at depths which do not exceed 2400 
fathoms, but when depths of 3000 fathoms are explored in this 
zone of the Atlantic and Pacific, there is found an argillaceous 
deposit without, in many instances, any trace of calcareous organisms. 
When we descend from the “ submarine plateaux ” to depths which 
exceed 2250 fathoms the Globigerina ooze gradually disappears, 
passing into a greyish marl, and finally is wholly replaced by an 
argillaceous material which covers the bottom at all depths greater 
than 2900 fathoms. 
