Page:The Journal of geology (IA journalofgeology11893univers).pdf/227
careous oozes and muds, we have a vast formation greatly exceeding in bulk and extent the coral reefs of tropical seas; they are most widely distributed in equatorial regions, but some patches of Globigerina ooze are to be found even within the Arctic circle in the course of the gulf stream."[1]
The percentage of carbonate of lime contained in deposits accumulating at different depths, as obtained from 231 samples collected by the Challenger, is shown in the following tabulation:
| 14 | cases | under | 500 | fathoms, | m. p. c. | 86.04 | |
| 7 | " | " | 500 | to 1000 | " | " | 66.86 |
| 24 | " | " | 1000 | to 1500 | " | " | 70.87 |
| 42 | " | " | 1500 | to 2000 | " | " | 69.55 |
| 68 | " | " | 2000 | to 2500 | " | " | 46.73 |
| 65 | " | " | 2500 | to 3000 | " | " | 17.36 |
| 8 | " | " | 3000 | to 3500 | " | " | 0.88 |
| 2 | " | " | 3500 | to 4000 | " | " | 0.00 |
| 1 | " | " | 4000 | " | " | trace. |
The fourteen samples under 500 fathons are chiefly coral muds and sands, and the seven samples from 500 to 1000 fathoms contain a considerable quantity of mineral particles from continents or volcanic islands. In all the depths greater than 1000 fathoms the carbonate of lime is mostly derived from the shells of pelagic organisms that have fallen from the surface waters, and it will be noticed that these wholly disappear from the greater depths.[2]
By a series of experiments Messrs. Murray and Irvine found: "That although sea water under certain conditions may take up a considerable quantity of carbonate of lime in solution, yet it is unable permanently to retain in solution more than is usually found to be present in sea water, and it is owing to this that the amount of carbonate of lime is so constantly low. The reaction between organic matter and the sulphates present in sea water (to which we have referred) tends also to keep the amount of carbonate of lime in solution at about one-half (0.12 grms.) of what it might contain (0.28 grms. per litre). This peculiarity of sea water, in taking up a large amount of amorphous carbon-