514 THE DEPTHS OF THE SEA. [CHAP. x. 



APPENDIX C. 



Notes on Specimens of the Bottom collected during the First 

 Cruise of the 'Porcupine 1 in 1869. By DAVID FORBES, F.R.S. 



ATLANTIC MUD contained in a small bottle marked ' Soundings 

 No. 20, 1,443 fathoms/ 



A complete analysis of this sample shows its chemical com- 

 position to be as follows : 



Carbonate of lime 5012 



Alumina * (* soluble in acids ') 1 "33 



Sesquioxide of iron (' soluble in acids ') ... 2'17 



Silica (in a soluble condition) 5 '04 



Fine insoluble gritty sand (rock debris) . . . 2677 



Water 2'90 



Organic matter 4'19 



Chloride of sodium and other soluble salts , 7 '48 



100-00 



If we compare the chemical composition as above with that 

 of ordinary chalk, which consists all but entirely of carbonate 

 of lime, and seldom contains more than from 2 to 4 per cent, 

 of foreign matter (clay, silica, &c.), it will be seen that it differs 

 chiefly in containing so very large an amount of rock-matter 

 in a fine state of division. If we subtract the water, organic 

 matter, and marine salts, which would probably in greatest 

 part be removed before such mud could in process of ages be 

 converted into solid rock, even then the amount of carbonate 

 of lime or pure chalk would not be more than at highest some 

 60 per cent, of the mass. 



As such deposits must naturally be expected to vary greatly 

 in mechanical character and chemical composition, it would be 



1 With phosphoric acid. 



