﻿GEOLOGY OF THOUSAND ISLANDS REGION 1 7 



In the Champlain valley the Beekmantown rocks are overlaid 

 by the Chazy limestones. There is evidence there of a break 

 between the two formations and the Chazy has a basal sandstone. 

 The Champlain Chazy trough also had a westerly bay but it never 

 extended as far west as the district under discussion. During the 

 long time interval therefore during which Beekmantown and early 

 Chazy sedimentation was transpiring in the subsiding Champlain 

 trough, the district here was above sea level and experiencing wear 

 rather than receiving deposit. Considering the length of the interval 

 the amount of erosion which it suffered was but slight, arguing for 

 low altitude and gentle slopes for the land. Broad, shallow valleys 

 were cut in the surface of the Theresa limestone but the depth of 

 cutting seems never to reach the base of the formation. 



Pamelia (Stones River) limestone. The Chazy basin of the 

 Champlain, St Lawrence and Ottawa valleys was landlocked to 

 the south and west during lower and middle Chazy time. Dur- 

 ing this time interval, however, other and larger basins of sub- 

 sidence and deposit existed to the south and west but completely 

 separated from the Chazy basin. Both the rocks and the con- 

 tained fossils therefore differ from the Chazy and the formation 

 is known as the Stones River. Notwithstanding difference of 

 name the two formations represent substantially the same time 

 interval. 



As Chazy time passed on, the large Stones river basin to the 

 southward encroached northwardly and toward the latter part of 

 the interval had become sufficiently extended to submerge the 

 immediate district. The slow warping of the land which brought 

 about this subsidence gave the district a wholly different direc- 

 tion of slope. In Potsdam and Theresa times it had sloped to 

 the northeast and formed part of the extreme westerly end of the 

 subsiding trough. It now came to slope to the southwest, was in- 

 vaded by the sea from that direction, and to the northeast lay a 

 land area which separated it from the Chazy basin beyond. 

 Though the district was covered by the waters of both marine 

 invasions it was near the shore line in each case and received 

 only comparatively thin, marginal deposits, representing only a 

 small fraction of the entire thickness of the formations con- 

 cerned. Hence in a broad way it is true that what had been the 

 western shore of the earlier sea became now the eastern shore 

 of this later western sea, or that the general district formed an 

 axis or pivot from which the land tipped now in one direction 



