GEOLOGIC TIME. 



317 



Table showing the estimated area, mean depth, and mean percentage of CaCOi of the dif- 

 ferent deposits. * 



Deposit. 



Area, square 

 miles. 



Mean depth 

 iu fathoms. 



Mean per 

 cent of 

 CaCOg. 



Oceanic oozes and clays. ■ 



' Red clay 



Radiolarian ooze 



Diatom ooze 



I Globigeriua ooze 



[ Pteropod 



f Coral sands and muds 



Terrigenous deposits .. .{ Other terrigenous deposits, blue 

 I muds, etc 



50, 289, 600 

 2, 790, 4C0 

 10, 420, 600 

 47, 752, 500 

 887, 100 

 3, 219, 800 



27. 899, 300 



2,727 

 2,894 

 1,477 

 1,996 

 1,118 

 710 



1,010 



6-70 



4-01 



22-96 



64-53 



79-26 

 86-4 



" We have little knowledge as to the tliiekness of these deposits; still 

 such as we liave 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 distributed iu 

 equatorial regions, but some patches of Globigeriua ooze are to be 

 found even within the Arctic circle, in the courseof the Gulf Stream."f 



The percentage of carbonate of lime contained iu dei)Osits accumu- 

 lating at different depths, as obtained from 231 samples collected by 

 the Challefiger, is shown in the following tabulation: 



14 cases under 500 fathoms, m. p. c 86-04 



7 cases under 500 to 1000 fathoms, m. p. c 66-86 



24 cases under 1000 to 1500 fathoms, m. p. c 70-87 



42 cases under 1500 to 2000 fathoms, m. p. c 69-55 



68 cases under 2000 to 2500 fathoms, m. p. c 46-73 



65 cases under 2500 to 3000 fathoms, m. p. c 17-36 



8 cases under 3000 to 3500 fathoms, m. p. c -88 



2 cases under 3.500 to 4000 fathoms, m. p. c 0-00 



1 case under 4000 fathoms, m. p. c Trace. 



The 14 samples under 500 fathoms are chiefly coral muds and sands, 

 and the 7 samj)les from 500 to 1,000 fathoms contain a considerable 

 quantity of mineral particles from continents or volcanic islands. In 

 all the depths greater than 1,000 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 disap- 

 pear from the greater depths. | 



By a series of experiments Messrs. Murray and Irvine found, "that 

 although sea water under certain conditions may take up a consider- 

 able quantity of carbonate of lime in solution, yet it is unable perma- 

 nently 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 sul- 

 phates 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 grams) of what it might contain (0*28 grams per liter). This pecu- 



^Loc.cii.y p. 82. \ Loc. cit., pp. 82, 83. t Loc. cit., p. 84. 



