GEOLOGY OF THE NORTHERN ADIRONDACK REGION 



421 



Consequently each would tend to be stripped away somewhat 

 more rapidly than what lay beneath ; thus a terrace would be 

 produced on the bared surface of each more resistant layer as the 

 weaker material above was removed [fig. 6]. This is the general 

 character of topography which is everywhere produced in dis- 

 tricts where the rocks lie nearly flat, are of unequal hardness and 

 are undergoing wear. How much progress was made in its pro- 

 duction, and how great an area was stripped of its Paleozoic cover 

 during this special interval, it is impossible to say. With the 

 passage of time, and with the increased possibility of wear 

 brought about by later uplifting, the fronts, or infaces, of these 



Fig. 6 Diagram to illustrate the condition of the Adirondack region after the 

 Postutica uplift, and the production of ten-aces by later wear. Vertical scale and 

 dip much exaggerated. P, B, T and IT indicate the Potsdam, Beekmantown, Trenton 

 and TJtica formations respectively, resting on the Precambric erosion surface. Erosion 

 has not yet cut to sufficient depth to expose the Potsdam, so that its terrace is lack- 

 ing, and the condition shown is quite like that which is found on the south and west 

 sides of the region today, though in a somewhat modified form on the south. Obviously 

 the depression produced by the opposing slopes of the Precambric floor and the 

 Beekmantown inface, would influence the location of a stream, and the Black river 

 on the west, and certain creeks on the south side of the region, such as Spruce creek 

 in the Little Falls region, are found today occupying precisely that situation. 



terraces would steadily retreat away from the center of the region, 

 without however changing their general character. They are 

 today prominent on the south and west sides of the district, 

 where they are accompanied and influenced by the infaces and 

 terraces of the later Paleozoic rocks which there overlie them. On 

 the east and north they are not conspicuous, owing to a variety 

 of causes. 



Appalachian uplift 



The long period of Paleozoic erosion was terminated by uplift 

 of the region, the movement being merely the local manifestation 

 of the widespread movement of uplift and of dislocation which 

 terminated the Paleozoic era in eastern North America. The 

 forces which folded the region to the eastward, affected the 

 Adirondack district but slightly, and the rocks are not folded. 



