422 Darwin, and after Darwin. 



formed at all. We have already noticed in the text that it is 

 only the more or less hard parts of organisms which under 

 any circumstances can be fossilized; and even the hardest 

 parts quickly disintegrate if not protected from the weather 

 on land, or from the water on the sea-bottom. Moreover, as 

 Darwin says, "we probably take a quite erroneous view 

 when we assume that sediment is being deposited over 

 nearly the whole bed of the sea, at a rate sufficiently quick 

 to embed and preserve fossil remains. Throughout an 

 enormously large proportion of the ocean, the bright blue 

 tint of the water bespeaks its purity. The many cases on 

 record of a formation conformably covered, after an immense 

 interval of time, by another and a later formation, without the 

 underlying bed having suffered in the interval any wear and 

 tear, seem explicable only on the view of the bottom of the 

 sea not rarely lying for ages in an unaltered condition." 

 Next, as regards littoral animals, he shows the difficulty 

 which they must have in becoming fossils, and gives a 

 striking example in several of the existing species of a sub- 

 family of cirripedes (Chthamalince), " which coat the rocks all 

 over the world in infinite numbers," yet, with the exception of 

 one species which inhabits deep water, no vestige of any of 

 them has been found in any tertiary formation, although it is 

 known that the genus Chthamalus existed through the Chalk 

 period. Lastly, " with respect to the terrestrial productions 

 which lived through the secondary and palaeozoic periods, it 

 is superfluous to state our evidence is fragmentary in an 

 extreme degree. For instance, until recently not a land 

 shell was known belonging to either of these vast periods," 

 with one exception ; while, " in regard to mammiferous 

 remains, a glance at the historical table in Lyell's Manual 

 will bring home the truth, how accidental and rare has been 

 their preservation, far better than pages of detail. Nor is their 

 rarity surprising, when we remember how large a proportion 

 of the bones of tertiary mammals have been discovered either 



