GEOLOGY OF THE BLUE MOUNTAIN QUADRANGLE 63 



Still exist in the southeastern Adirondack region, the nearest to 

 the Blue Mountain quadrangle being a small area of Potsdam sand- 

 stone near the village of North River about i6 miles a little south 

 of east of Indian Lake village. 



The best available evidence shows that the ancient peneplain 

 became sufficiently submerged during late Cambrian time to allow 

 the sea to cover all but a considerable part of the central Adiron- 

 dack region, and that the maximum submergence occurred during 

 mid-Ordovician (Trenton) time when only a comparatively small 

 portion of the central Adirondack area (including the Blue Moun- 

 tain quadrangle) remained as a small low island. During this 

 Trenton time the sea may have extended over some of the south- 

 eastern portion of the Blue Mountain quadrangle, though of course 

 any positive evidence is entirely lacking.^ 



At some time (or times) during the middle or late Paleozoic era 

 the whole Adirondack region, then largely mantled with Paleozoic 

 sediments, was raised well above sea level. Some of the upward 

 movement may have taken place at the time of the Taconic revolu- 

 tion (close of the Ordovician), though it is generally considered 

 that the major uplift occurred at the time of the Appalachian revo- 

 lution (toward the close of the Paleozoic). In northern New York 

 this upward movement was not accompanied by folding, but there 

 was a general tilting of the strata downward toward the south or 

 southwest. 



Mesozoic History 



The erosion cycle inaugurated by the Paleozoic elevation of 

 northern New York continued for a vast length of time or till the 

 close of the Cretaceous period when the Paleozoic strata were 

 largely removed from the Adirondack area and another eroded 

 surface approaching the condition of a peneplain was produced. 

 Apparently this peneplain was least perfectly developed in the cen- 

 tral and east-central Adirondacks where various hard rock masses 

 (monadnocks) stood out more or less prominently above the general 

 peneplain surface. This peneplain was upraised about the close of 

 the Cretaceous period so that remnants of it in northern New York 

 now lie at altitudes of from 2000 to 3000 feet or possibly more. 

 Within th€ quadrangle no very accurate idea of this peneplain or 



1 Certain oscillations of level between land and sea, which are clearly 

 recorded in the rocks around the Adirondacks, maj^ also have affected the 

 central Adirondack area, but the utter absence of all Paleozoic strata from 

 the central area renders any determination of this kind difficult if not 

 impossible. 



