68 NEW YORK STATE MUSEUM 
given. Thus, toward the end of the Mesozoic era all the area of 
New York State had been reduced to a vast, monotonous, feature- 
less plain (peneplain) except for the mountain masses of very 
moderate elevation in the east-central Adirondack, and possibly 
also the Catskill, regions. As Professor Berkey says: “ The con- 
tinent stood much lower than now. Portions that are now moun- 
tain tops and the crests of ridges were then constituent parts of the 
rock floor of the peneplain not much above sea level. This rock 
floor was probably thickly covered with alluvial deposits (flood 
plain) not very different in character from the alluvial matter of 
portions of the lower Mississippi valley. of today. Upon such a 
surface the principal rivers of that time flowed, sluggishly 
meandering over alluvial sands and taking their courses toward 
the sea (the Atlantic) in large part free from influence by the 
underlying rock structure. The ridges and valleys, the hills, moun- 
tains and gorges of the present were not in existence, except poten- 
tially in the hidden differences of hardness of rock structure. Such 
conditions prevailed over a very large region, certainly all of the 
eastern portion of the United States.” ? 
In the western part of the United States the Mesozoic era was 
brought to a close by what must take rank as one of: the greatest 
mountain upheavals in the history of North America. This is 
known as the Rocky Mountain revolution because the great Rocky 
Mountain system was chiefly formed at this time. At the same 
time im the eastern part of the United States the Mesozoic was 
closed by an important physical disturbance though on a far less 
grand scale than that of the west. This disturbance produced an 
upwarp of the vast Cretacic peneplain with maximum uplift of from 
two to three thousand feet following the general trend of the 
Appalachians and thence through northern New York. This up- 
ward movement was unaccompanied by any renewed folding of 
the strata, and the effect was to produce a broad dome sloping 
eastward and westward, and northward to the Gulf of St Lawrence 
and southward to the Gulf of Mexico. 
A prominent effect of this great uplift was to revive the activity 
of the streams so that they once more became active agents of 
erosion. We are now prepared to make the important statement 
that the present major topographic features of New York State, as 
well as western New England and the whole Appalachian region, 
have largely been produced by the erosion or dissection of this up- 
1N. Y. State Mus. Bul. 146, p. 67. 
