REPORT OF THE DIRECTOR I912 . 81 



CAMBRIC PHYSIOGRAPHY 



The Cambric peneplain. As is well known, the whole Adiron- 

 dack region was above water and undergoing erosion during the 

 early and middle Cambric. This is proved by the total absence 

 of the early and middle Cambric strata and also because there 

 is not the slightest evidence that any such strata ever were 

 deposited over the region. Furthermore there is every reason 

 to believe that this important erosion interval was inaugurated 

 long before the opening of the Paleozoic era. As a result of 

 this vast erosion the whole Adirondack region had, by the open- 

 ing of Potsdam (late Cambric) time, become worn down to the 

 condition of a more or less well-developed peneplain. 



As will be shown below, the distribution of the strata proves 

 that the northeastern and eastern borders of the Adirondacks 

 sank below sea level first in early Potsdam time ; then the south- 

 eastern and southern portions in late Potsdam, Theresa and 

 Little Falls times ; and last the southwestern border well along 

 in Ordovicic (Pamelia) time. 



The peneplain surface of the Precambric rock under the Paleo- 

 zoic strata has been carefully studied on all sides of the Adiron- 

 dacks and it has been fully demonstrated that it is roughest 

 along the northeastern and eastern sides ; less rough along the 

 southeastern and southern sides ; and very smooth along the 

 southwestern side. Even where roughest the differences of 

 elevation never amount to more than a few hundred feet, while 

 on the southern side Cushing^ and the writer^^ have each found 

 knobs or ridges of hard Precambric rock projecting upward from 

 fifty to eighty feet into the Cambric strata, though these appear 

 to be extreme cases of ruggedness of the surface of the pene- 

 plain. Along the southwestern border of the Adirondacks the 

 writer has shown by his mapping of the Port Leyden quad- 

 rangle^ that the surface of the peneplain is there remarkably 

 smooth. This increasing smoothness of the peneplain from 

 northeast to southwest is precisely what would be expected 

 because the southwestern side of the Adirondacks remained dry 

 land much the longest time. In the eastern Adirondacks Kemp^ 



2 Page 57-58. The footnote numbers refer to the numbered references 

 given in the list at the end of this paper. 

 10 Page 51. 

 9 Pages 40-41. 

 « Pages 408-12. 



