﻿Il8 NEW YORK STATE MUSEUM 



very likely source of such additional pressure is to be found in 

 the well known oscillations of level which the district has under- 

 gone preceding, during and since glaciation. The general dis- 

 trict has increased its altitude by some 400 feet since the ice dis- 

 appeared from the St Lawrence valley, and this change is simply 

 the last of a series of oscillations. Furthermore these move- 

 ments were of the nature of warps, the changes in level not being 

 everywhere the same, but of varying amount. Such warping 

 must bring about compression in some tracts and stretching in 

 others. The contraction produced in the rocks by the cooling of 

 the ice sheet would likely have manifested itself in mere slight 

 widening along the joint cracks, and side compression brought 

 about by warping may have sufficed locally to close up these 

 widened joints. In such case postglacial increase of tempera- 

 ture might well tend to cause buckling of the rocks. The warp- 

 ing is of such nature that it would tend to produce thrust from 

 the northeast, and it is to be noted that these folds trend north- 

 west, as should be the case on this hypothesis. 



There at once arises, however, the further question as to 

 whether the compression consequent upon warping may not 

 have been perfectly competent to cause the buckling, entirely 

 independently of any effect which the ice may have had, and 

 this seems to the writer very probable. Dr Reid, in correspond- 

 ence, states his belief that " we must fall back on the general 

 explanation that movements of the crust are in progress which 

 have produced these bucklings." Dr Branner expresses similar 

 views. In any case, until it has been shown that lateral spread- 

 ing may be produced in rocks of this resistant type by load no 

 greater than that of the ice sheet, some doubt must attach to the 

 competency of Gilbert's hypothesis as applied to these special cases. 



Faults 



Faults of. considerable magnitude and importance have not 

 been noted in the district, and the fairly accurate areal mapping 

 which the abundant rock exposures render possible, indicates 

 that no such are present, at least in the Paleozoic rocks. Small 

 faults appear, however, in considerable number in all the rocks 

 and are apparently of different age. 



In the Precambric rocks. Small faults, with dislocations of 

 from a fraction of an inch to a few feet occur in a great number 

 of localities in the Precambric rocks, as already pointed out by 



