330 THE SUPPOSED PERMANENCE [CHAP. XT. 



Take, for instance, the analysis of an ooze from the 

 depth of 450 fathoms, which contained 84.27 of carbonate 

 of lime, 2.60 of silica, and 4 per cent, of material lost on 

 ignition ; deducting the two latter from the total, we find 

 that 84.27 of 93.40 is equivalent to a fraction over 90 per 

 cent. ; and the analysis of this ooze is really much more 

 like Chalk than appears at first sight. Another sample of 

 ooze taken from 1,420 fathoms, and containing only 80.69 

 of carbonate of lime, really possesses a proportion of 87.70 

 to the material remaining after the abstraction of the silica 

 and loss on ignition (which amount to 7.94 per cent.). It 

 would, however, be much more satisfactory to compare the 

 ooze with analyses of those portions of the Chalk which 

 still retain a certain amount of the disseminated soluble 

 silica, and are not largely made up of the detritus of Ino- 

 ceramus shells. Such beds are known to occur in the 

 Lower Chalk, but very few analyses have yet been made of 

 them ; that, however, of a hard bed in the Lower Chalk of 

 Farnham yielded to Professor Way 2.11 per cent, of soluble 

 silica, and only 85.95 per cent, of carbonate of lime, pro- 

 portions which approximate closely to those of the same 

 minerals in the ooze from 450 fathoms. It may, therefore, 

 be concluded that the composition of the material which we 

 call chalk was originally analogous to, though not identical 

 with, that of modern oceanic ooze, and consequently that it 

 was formed under similar conditions. 



5. The truth of Dr. Wallace's last argument depends 

 much on the definition of an oceanic island, and, moreover, 

 our knowledge is not yet sufficient to justify so sweeping a 

 statement. Many oceanic islands have not yet been geo- 

 logically examined, but rocks of pre-Tertiary age have 

 certainly been found on some islands which fairly come 

 under this category. Thus New Zealand and the Seychelles 

 Islands are admitted by Dr. Wallace to be exceptions to 

 his assumed rule, but he minimizes the value of New Zea- 



