THE GEOLOGICAL HISTORY OF NEW YORK STATE 67 
development. During this era the great dinosaur reptiles, the largest 
land animals that every lived, stalked the western plains. Some 
remains of smaller dinosaurs have been found in the Triassic beds 
of the Atlantic coast, one specimen lately having been discovered 
in the Newark beds along the lower Hudson. Reptilian tracks 
abound in the Newark strata. Mammals appeared in the early 
Mesozoic, but throughout the era they continued small and com- 
paratively insignificant. The first birds and true bony fishes 
(teleosts) appeared in the later Mesozoic, but they are either absent 
or not important in the Mesozoic of the middle Atlantic coast. The 
invertebrate life of the era was in general very different from that 
of the Paleozoic, few types from the latter era having persisted, 
and by the end of the Mesozoic the invertebrates took on a decidedly 
modern aspect. 
Among plants, those of the early era were still simple nonflower- 
ing kinds much like those of the Carbonic or “ Coal age,” while in 
the late Mesozoic flowering plants of very modern types, including 
many of our present forest trees, were prominently developed. The 
Cretacic beds of the Atlantic coast are rich in fossil plants. 
TAP CRETACIC PENEPLAIN AND ITS UPLIFT 
During all the Mesozoic era most of the eastern portion of the 
United States was above water and undergoing erosion, so that, 
as a result of this very long period of wear, the region was reduced 
to the condition of a more or less perfect peneplain. It is known 
as the Cretacic peneplain because of its best development during 
the Cretacic period. This vast plain extended over the areas of the 
Appalachian mountains, Piedmont plateau, all New York State, 
the Berkshire hills, and the Green mountains. Its most perfect 
development was in the northern Appalachians, for example, from 
east-central Pennsylvania to Virginia, where hard and soft rocks 
alike had been so thoroughly cut down that no masses projected 
notably above the level of the low-lying plain. 
Farther northward, however, over New York and western New 
England, its development was less perfect so that certain masses of 
harder rock stood out more or less prominently above the general 
level of the plain. In the central and eastern Adirondacks many 
low mountains of very resistant igneous rock rose above the pene- 
plain surface. In a similar manner an occasional low mountain 
stood out in the Berkshire Hills region, and it seems probable that 
the hard Devonic sandstones of the Catskills also rose notably above 
the peneplain, though in the latter case positive proof has not been 
3 
