r46 NEW YORK STATE MUSEUM 



position of the Potsdam sandstone, quite likely considerably more. 

 Its duration was certainly several, quite likely many million years. 

 Few parts of the earth's surface have been continuously above sea 

 level for so long an interval. 



During this enormous length of time this surface has been sub- 

 jected to continuous wear. Its history is to be read in the re- 

 moval, not in the deposition of rocks. From this standpoint a 

 sharp contrast is to be noted between the Champlain valley on 

 the one hand and the Adirondack highlands on the other. The 

 Trenton limestone and the Utica slate are still found here and 

 there in the valley. In such places no great amount of erosion 

 can have taken place. Compared with the other rocks of the 

 region these are the least resistant of all, and their presence forces 

 the conclusion that the Champlain valley was early outlined as 

 a valley and must have remained pretty persistently at a com- 

 paratively low altitude. The Paleozoic rocks have suffered more 

 or less considerable erosion on the upthrown side of fault blocks, 

 but the loss has been very small from the downthrow blocks. 



On the Adirondack highlands, on the other hand, the entire 

 cover of Paleozoic rocks has been worn away from the surface, 

 except for an occasional insignificant patch on the outskirts. This 

 implies the removal of not less than 2000 feet thickness of such 

 rocks from the whole surface, and more likely double that amount. 

 An unknown amount, probably not excessive, has also been worn 

 away from the surface of the underlying rocks. 



It must not be supposed that this necessarily implies that the 

 district ever had an altitude much greater than the present. It 

 seems to have been an uneasy region with frequent small move- 

 ments of uplift. If long periods of quiescence had intervened, 

 they would have assuredly left their mark in the shape of well 

 defined old base levels of erosion, but such are not to be dis- 

 covered. Comparatively recent uplift is, furthermore, indicated 

 by the plainly marked character of the north and south axis of 

 uplift along the west edge of Clinton county, and thence south- 

 ward, as a topographic feature. The faults have served as lines 

 along which frequent displacement has taken place. 



