CHAPTEE X. 
SOME AMERICAN MONSTERS. 
Geology, in the magnitude and sublimity of the objects of which it treats, 
ranks next to Astronomy in the scale of the Sciences,” — Sir John F. W. 
Herschel. 
With the advent of the Cainozoic or Tertiary era, we enter 
upon the “ Age of Mammals,” when great quadrupeds suddenly 
came upon the scene. The place of the reptile was now taken 
by the mammal. In the long previous era this higher type of 
life was not altogether wanting, but as far as the geological record 
is yet known, it appears only to have been represented by a few 
primitive little creatures, probably Marsupials, whose jaw-bones 
have been discovered in the New Red Sandstone, and the Stones- 
field Oolite.^ 
Geology tells of a great gap between the highest rocks of the 
Cretaceous period and the lowest group of the succeeding Eocene 
period (see Table of Strata, Appendix L). This gap, or break, 
testifies to a very long interval of time during which important geo- 
graphical and other changes took place; and consequently we find 
in Eocene rocks (at the base of the Cainozoic series) a very different 
fauna and flora to that which is preserved in the Chalk formation. 
The researches of Cuvier among the fossils collected from 
Eocene rocks in the neighbourhood of Paris, especially the 
^ The English Cretaceous rocks, previously thought to be destitute of 
mammalian remains, have quite recently yielded teeth belonging to some 
small mammal. These were found in Wealden strata. 
