44 NEW YORK STATE MUSEUM 



basin. Regarding the disposal of the early Paleozoic sediments, 

 however, our knowledge is much more certain. Both early and 

 late Cambrian strata are abundantly represented in western New 

 England and to some extent along the central-eastern border of 

 New York, while only late Cambrian strata rest upon the pre- 

 Paleozoic rocks around the borders of the Adirondacks. Also, the 

 late Cambrian strata of northern New York are nearly a thousand 

 feet thick on the northeastern side of the Adirondacks (in Clinton 

 county) and they become thinner southward and westward through 

 the Champlain, Mohawk and St Lawrence valleys, being entirely 

 absent from the southwestern border of the Adirondacks (in the 

 Black River valley). These facts show that the earlier Cambrian 

 sea did not reach into northern New York, but that the later Cam- 

 brian sea did extend most, or all, of the way around the Adiron- 

 dack region, the encroaching waters having come from the north- 

 east as proved by the older and much thicker Cambrian deposits 

 there. 



The first deposit to form in this late Cambrian sea is known as the 

 Potsdam sandstone which is well represented in the St Lawrence, 

 Champlain and lower Mohawk valleys. These regions were sub- 

 merged under the Potsdam sea. Not only is the Potsdam sand- 

 stone absent from the southwestern border of the Adirondacks, but 

 there is no evidence that it ever was deposited there, hence it appears 

 that that region was dry land during the Potsdam time. In the 

 southeastern Adirondacks the Potsdam sea certainly extended in 

 as far as Wells (in southern Hamilton county) and North River 

 (northwestern Warren county) because small outlying masses of 

 typical Potsdam sandstone occur at those places. These outlying 

 masses were formerly connected with the larger areas but they 

 have become completely isolated by extensive erosion since they 

 were deposited. There is no evidence whatever that the Potsdam 

 sea covered the interior of the Adirondack region. In short, we 

 may say that the ocean of Potsdam time covered all the borders 

 of the Adirondack area except on the southwest and extended well 

 over the southeastern portion. 



What do we know about the character of the topography of the 

 land over which that ancient Potsdam sea spread? As a result of 

 the profound erosion, thousands of feet in thickness of material were 

 removed and the whole region must have been well worn down. 

 Was the region worn down to the condition of a peneplain, that is 

 to say, to an area of very low rehef near sea level? Recent detailed 

 studies on all sides of the Adirondacks furnish a very satisfactory 



