82 Proceedings of Royal Society of Edinburgh. [sess. 
summer months than during winter months. Indeed, a high tempera- 
ture of the sea water is more favourable to abundant secretion of 
carbonate of lime than high salinity. 
An examination of the deep-sea deposits collected by the 
“Challenger” and other expeditions in all oceans shows that, after the 
death of the pelagic organisms above referred to, their calcareous 
shells are rained down on the ocean’s bed, and there make up the 
larger part of the deposits known as Pteropod and Globigerina 
oozes, as well as a very considerable part of nearly all other marine 
deposits. If we take the samples of deep-sea deposits collected by 
the “Challenger” as a guide, the average percentage of carbonate of 
lime in the whole of the deposits covering the floor of the ocean is 
36 ‘83, and of this carbonate of lime, it is estimated that folly 90 per 
cent, is derived from the remains of pelagic organisms that have fallen 
from the surface waters, the remainder of the carbonate of lime 
having been secreted by organisms that live on or attached to the 
bottom. If coral muds and sands, together with Pteropod and 
Globigerina oozes, be considered, it is estimated that these contain 
an average percentage of 7 6 *44 of carbonate of lime, and cover 
about 51,859,400 square miles of the sea bottom. We have 
little knowledge as to the thickness of these deposits, still such as 
we have goes to show that in these organic calcareous oozes and 
muds, we have a vast formation greatly exceeding in bulk and 
extent the coral reefs of tropical seas ; they are most widely distri- 
Table showing the Estimated Area , Mean Depth, and Mean Per- 
centage of CaC0 3 , of the different Deposits. 
Deposit. 
Area, square 
miles. 
Mean Depth Mean per 
in | cent, of 
fathoms. | CaC0 3 . 
f Red clay, 
■ r\ Radiolarian ooze, 
Oceanic Oozes J Diatom 00z6; 
an a - v ’ | Globigerina ooze, 
l Pteropod ooze, 
f Coral sands and 
Terrigenous De- j otdT terrigenous 
P« s,ts ' | deposits, blue 
l muds, &c., 
50.289.600 
2,790,400 
10.420.600 
47,752,500 
887,100 
3,219,800 
27,899,300 
2727 
2894 
1477 
1996 
1118 
710 
1016 
6*70 
4-01 
22-96 
64*53 
79-26 
86-41 
19-20 
