50 NEW YORK STATE MUSEUM 



Section 2 



MAIN FEATURES OF THE GEOLOGY OF NEW YORK 



STATE 



The physical features of our State as they now appear have 

 their beginnings far back in the remote periods of geologic time. 

 Among the rock formations underlying its surface are some of the 

 oldest that are anywhere exposed on the American continent, pos- 

 sibly antedating the appearance of life, and at any rate so com- 

 pletely altered by the vicissitudes of the ages that they show no 

 recognizable organic remains and few of their original physical 

 structures. Tt is in those Precambric formations as represented in 

 the Adirondacks and the southeastern Highlands that the earliest 

 records of the physical development of our State are to be sought. 



There is naturally much doubt about the conditions which pre- 

 vailed in the remote periods of time included within the Precambric 

 era. It would appear, however, that the continental land surface 

 already existed in general outline in that era, although of course 

 the area was not confined by the present bounds. Most of the 

 Precambric formations now exposed are gathered in the north on 

 the Canadian side of the boundary; the southern line of this central 

 or nuclear area follows the St Lawrence river from the Gulf to 

 the Great Lakes. But there are important extensions of this old 

 land to the south of Lake Superior in Michigan, Wisconsin and 

 Minnesota and also one considerable area farther east in the 

 Adirondacks. The Hudson Highlands, a part of the Appalachian 

 highland, also have Precambric strata along their main axis. 



The lowest formations of this old land surface which are largely 

 of igneous character may be separately' classed in the Archean 

 system. Upon their exposed parts the agencies of construction 

 and destruction were operative probably in a similar manner and 

 with equal energy as now. From the erosional waste, extensive 

 deposits of limestone, shale and sandstone were accumulated at a 

 later period beneath the waters which encroached on the land. 

 These old sediments, aside from their highly metamorphosed states, 

 are not essentially different from those accumulated during succeed- 

 ing ages. Volcanic forces no doubt had their part in the develop- 

 ment of the structure, but all vestiges of the ancient lava flows 

 have been swept away and only the underlying channels are now in 

 evidejnce with their fillings of diabase and porphyry. 



