410 Li TLem O}GHIEV GEES 
Trenton entirely covered the Adirondacks, having since been 
removed except in the case of a few outliers. The pre-Cre- 
taceous erosion period reduced the soft rocks of the Appalachian 
region to almost absolute baselevel; in the Adirondacks the 
same period sufficed to clean out nearly all the softer rocks from 
the valleys, and to reduce the more resistant crystallines to a 
condition of moderate slopes and slight relief. The tilting of 
the plain in the Adirondacks is such as to bring its level into 
close relation to those further south as well as to the less cer- 
tainly Cretaceous peneplain of New England. If this correla- 
tion proves to be correct, the dome-shaped uplift of the 
Adirondacks marks the western and northern. corner of a great 
post-Cretaceous uplift. The lower Adirondack level would cor- 
respond to the Tertiary level elsewhere observed. 
The age of this lower level in the Adirondacks can be fixed 
with more certainty. The'valley floor on which the drift was 
deposited consisted of the level described, into which the 
streams had just begun to incise their channels, They must 
have been rejuvenated in Pliocene or post-Pliocene time, since 
they had just begun to lower their levels before the ice invasion. 
If the rejuvenation of them closed the Pliocene, the cutting of 
the level must have been in the period immediately preceding, 
or in the earlier Tertiary. 
When the ice invaded the region it encountered a drainage 
long established and well adjusted, but physiographically young 
in that the region had recently been uplifted and its streams 
rejuvenated. After its withdrawal it left the valleys completely 
drift-filled, and the courses of the rapidly cutting streams 
determined by the slope of the drift. The resulting drainage 
modifications are numerous. 
Rivers—The preglacial divides had been determined by 
two axes of uplift, a north-south and an east-west axis intersect- 
ing in the Marcy region. The postglacial divides are of drift, 
deposited in the old valleys, and although conforming in a gen- 
eral way to the old directions the streams are often in quite 
new channels. Often a few rods of drift is all that separates St. 
