﻿20 NEW YORK STATE MUSEUM 



and whose present northern margin of outcrop is distant but 15 

 miles from the map limits, may also have been somewhat deposited 

 within it. Certainly the sandstone extended orginally farther 

 north than now, but just how far no one can say. 



The deposit of these sands indicates a shallowing of the waters 

 over the region, following which it was uplifted above sea level. 

 Thenceforth in the main, throughout the millions of years which 

 have since elapsed, the district has remained a land area. It is 

 quite possible that the succeeding Siluric and Devonic seas, whose 

 waters covered central and western New York, may have washed 

 over this district, and laid down thin deposits. But if so, every 

 trace of such deposits hereabouts has disappeared through erosion, 

 so that no certainty can be arrived at in the matter. 



As a result of the various oscillations of level which the region 

 has undergone the rocks described have been changed from their 

 original nearly horizontal position, into a series of low folds. This 

 folding seems to have commenced early and to have been continued 

 on various occasions, since there is some evidence that the Pots- 

 dam and Theresa formations were somewhat folded before Pa- 

 melia deposition began. Subsequently more folding took place, in- 

 volving the entire series, and though the folding is gentle its topo- 

 graphic expression is plain. 



The principal folds have axes which trend northeast-southwest, 

 but there is also present another set with northwest-southwest trend, 

 or at right angles to the first set, whose arches and troughs are 

 thus folded up and down, producing gently elevated domes and de- 

 pressed basins, the former where the arches of the two sets cross, 

 and the latter at trough intersections. Many of the outliers shown 

 on the accompanying geologic maps owe their existence and pres- 

 ervation to this folding. 



Subsequent history of the region 



But little that is definite can be said of the history of the district 

 during its long existence as a land area following the deposition 

 of the rocks previously described. It seems quite certain that the 

 amount of rock worn away from the surface during this time is 

 slight, considering the length of the time interval, and that there- 

 fore the land has seldom had any considerable altitude. Where 

 the entire thickness of overlying rocks has been worn away and 

 the Precambric exposed at the surface, as is the case on parts of 

 the Theresa and Alexandria sheets, it seems quite certain that not 



