386 NEW YORK STATE MUSEUM 



Cambric times, was checked and replaced by the contrary ten- 

 dency during Lorraine timies, a tendency which has, in the main, 

 persisted to the present. 



Helderberg submergence. On the south and west of the Adiron- 

 dack region the Lorraine rocks are successively overlain by the 

 Medina, Clinton, Niagara, Salina and Waterlime deposits. These 

 are more likely to have overlapped on the west side of the region 

 than elsewhere. On the south they thin and disappear in going 

 eastward, showing that they are approaching a shore line in that 

 direction, and that the lower Mohawk region was not receiving- 

 deposit during most of the interval. Then ensued a change at the 

 extreme east, a considerable depression being formed there, in 

 which marine limestones accumulated, whose fauna entered the 

 basin through some connecting channel with the eastern sea. 

 These rocks do not extend westward as far as the upper Mohawk 

 region, showing that that district did not participate ini the de- 

 pression, or else that a barrier was formed there, separating the 

 eastern basin from that to the west, waterlime conditions per- 

 sisting in the latter after they had been brought to an end in 

 the formei'. From Albany these rocks extend far south into the 

 Appalachian region, as deposits in a long, trough-shaped basin. 

 As to the northern limits of that basiiui, we are in ignorance, the 

 deposits having been* swept away by erosion ; but, since it is known 

 that the present line of the St Lawrence was also depressed dur- 

 ing that time, deposits of that age occurring on St Helen's island, 

 near Montreal, it is rendered quite likely that the Champlain and 

 upper Hudson valleys were also involved, forming a channel which 

 furnished a connection with the outer sea by way of Montreal. 

 If such wiere the case, the subsequent removal of the deposits 

 has obliterated all the evidence on which a demonstration might 

 be based. There was some connecting channel with the outer 

 sea; there may have been more than one ; the line suggested would 

 furnish a natural route. 



Summary of early Paleozoic oscillations of level. The evidence 

 which is given by the distribution, character and thickness of the 

 several Paleozoic formations which were deposited on, and around, 

 the Adirondack region, as to the oscillations of the land surface. 



