﻿274 NEW YORK STATE MUSEUM 



zation so that they are now as sound as any other portion of the 

 rock. A good deal depends upon the type of rock and the conditions 

 under which the movement took place. In some of the more open 

 ones, circulating water has seriously affected the rock and in places 

 there is extensive decay even in the harder crystalline formations. 



Age of the faulting. The chief epochs of folding and faulting 

 are those of the mountain-making movements — one Precambric, 

 another Postordovicic, and still another Postcarbonic. All of these 

 date very far back in geologic history, and since the last of these, 

 nothing akin to them in importance has been felt in the region. 



In Posttriassic times however there was small faulting south of 

 the Highlands, that affected the areas of Triassic rocks of New 

 Jersey and Connecticut. 



Whether or not there continued to be slight movement along some 

 of the older lines it is now impossible to say. It is at least clear that 

 all of the great movements belong to very ancient time, and that the 

 last period of geologic time as we know it for this region, has been 

 one of comparative stability. The chief exception is evidently con- 

 nected with the continental elevations and depressions of the 

 glacial epoch. 



Recent movements. The effects of glaciation make it possible 

 to determine whether or not there has been further movement in 

 postglacial time. Conditions are not everywhere favorable enough 

 to detect minute changes, but where they do obtain, the evidence is 

 capable of very definite interpretation. The essential features of 

 these conditions are 



i A bed rock ledge that has been left well smoothed by glacial 

 scouring. 



2 Protection from postglacial destruction- so that the original 

 unevenness as left by the glacial smoothing can not be mistaken. 



If on such a ledge, as now exposed, there are steplike offsets or 

 minute escarpments that could not have remained had they been 

 present during the ice action, then there must have been displace- 

 ment to this extent, since the original smoothing took place. 



A few such evidences have been found in New York and New 

 England, and have been noted in geologic reports. W. W. Mather 

 in his report on ,the First District of New York ( 1843) pages 156-57, 

 was the first. The data as now known may be found in 'the last 

 bulletin of Geologic Papers of the New York State Survey [see 

 N. Y. Stxte Mus. Bui. 107 (1907) p. 5-28]. The following para- 



