328 THE SUPPOSED PERMANENCE [CHAP. XV. 



posits uniform in character and more than 150 or 200 

 miles wide were rarely, if ever, formed at the same time " 

 (" Island Life," p. 101), is rather surprising when on a 

 previous page (p. 91) he quotes Sir Charles Ly ell's estimate 

 of the range of the Chalk beds of nearly uniform aspect 

 and composition extending from the north of Ireland to 

 the Crimea, a distance of about 1,140 geographical miles, 

 and in an opposite direction from the south of Sweden to 

 the south of Bordeaux, a distance of about 840 geographical 

 miles. 



In point of fact, all that Dr. Wallace succeeds in proving 

 in Chapter VI. of his " Island Life " is that deep-sea de- 

 posits are of rare occurrence beneath the soil of modern 

 continents. This, however, is a very different thing from 

 proving a universal negative, which is what he sets himself 

 to do. It only amounts to this, that the conversion of even 

 a comparatively shallow ocean into continental land is a 

 stupendous operation, requiring many geological ages for 

 its accomplishment, and consequently that it has not 

 happened many times in the course of geological history. 



4. The argument derivable from the differences between 

 Chalk and oceanic ooze has already been partially refuted, 

 but may now be more fully discussed. In the first place, 

 it is unreasonable to assume that the constituents of deep- 

 sea ooze, and the proportions of these constituents, should 

 have been just the same in the Cretaceous period as they 

 are now ; and, in the second place, it has been shown that 

 the differences between the two kinds of material is not so 

 great as Dr. Wallace supposed. It would appear that the 

 relative abundance of pelagic Foraminifera is largely de- 

 pendent on the temperature of the water, and that they 

 only occur in great abundance where the water is compara- 

 tively warm. This was especially remarked by M. Pour- 

 tales 1 with regard to the character of the deep-sea deposits 

 1 See " Geol. Mag.," vol. viii. 1871, p. 425. 



