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



APPENDIX C. 



Notes on Specimens of the Bottom collected during the First 

 Cruise of the 'Porcupine' in 1869. By DAVID FORBES, F.E.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 50'12 



Alumina 1 (' 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 



lOO'OO 



If we compare the chemical composition as above with tha 

 of ordinary chalk, which consists all but entirely of carbonat 

 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 differ 

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

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

 matter, and marine salts, which would probably in greates 

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

 converted into solid rock, even then the amount of carbonat 

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

 60 per cent, of the mass. 



As such deposits must naturally be expected to vary greath 

 in mechanical character and chemical composition, it would b 



1 With phosphoric acid. 



