64 NEW YORK STATE MUSEUM 



prominent in this part of the Adirondacks. Among these factors 

 are: (i) character and distribution of the rocks whereby small to 

 large masses of hard, homogeneous, igneous rocks have broken 

 through the comparatively weak Grenville strata to produce a sort 

 of " patchwork " effect so that, as a result of long erosion, the hard, 

 igneous masses have stood out prominently above the Grenville; 

 (2) faulting, whereby the *' patchwork " eft"ect and steep scarps 

 have been either produced or sharply accentuated; (3) glaciation, 

 whereby the isolated mountains of igneous rock were swept clean 

 of decomposed surface rock and more or less smoothed or rounded 

 off, thus favoring postglacial exfoliation; and (4) temperature 

 changes, humidity etc., whereby the bare slopes of the isolated 

 elevations of crystalline rock, under the conditions of comparatively 

 rapid temperature changes in this the driest part of the State, are 

 favorable for exfoliation. 



PENEPLAINS 



It is well known, especially as a result of the work .of Professor 

 Kemp and, more recently, that of Professor Gushing on the Sara- 

 toga sheet and of the writer on the Broadalbin sheet, that the south- 

 eastern Adirondack region had been worn down to the condition 

 of a fairly good peneplain immediately prior to the advance of the 

 upper Cambric (Potsdam) sea. Altitudes above the general pene- 

 plain level were not over a few hundred feet at the most. This 

 conclusion has been reached through a study of those places along 

 the borders of the Adirondacks where the Paleozoic rocks directly 

 overlie the Precambrics. The position of the North Creek quad- 

 rangle renders it practically certain that this very ancient (Cam- 

 bric) peneplain extended over its area, but because of the exten- 

 sive faulting and erosion of the region, that old peneplain surface 

 is nowhere certainly recognizable. 



Again, it is well known that, by the close of the Mesozoic era, 

 a fairly well-developed peneplain condition had once more been 

 produced over this region in common with southern New England, 

 New York, and the northern Appalachians. Professor Davis has 

 shown ^ that the Berkshire hills area, during the late Mesozoic, had 

 been worn down to a fairly good peneplain with occasional low 

 mountains (monadnocks) rising above the general level. There is 

 strong reason to believe that a similar condition prevailed over 

 the southeastern Adirondack region, but with the monadnock 



1 Physical Geography of Southern New England in Physiography of the 

 United States. 



