66 NEW YORK STATE MUSEUM 



brian elevation into a land area with its long protracted erosion 

 and its igneous action, the Paleozoic submergence and deposition, 

 and the ensuing and still continuing elevation above sea level, 

 with its erosion, its oscillations of level and its disturbance by 

 faulting, all have their share in the present topography; and, 

 lastly, the recent Glacial period with its advancing and eroding, 

 and its retreating and depositing ice sheets, is entitled to a very 

 large share of responsibility for present conditions. 



Pre-Cambrian surface 



Evidence as to the character of the pre-Cambrian surface at the 

 close of the long period of pre-Cambrian erosion, has already 

 been presented, and it has also been shown that it is here more 

 nearly a plaiie surface than is usual in the Adirondack region. 

 The writer is disposed to regard the more even surface here as 

 representing a plain of marine erosion, more even than on the 

 north, because subsidence was less rapid and of a more inter- 

 mittent character here, so that the action of the waves was 

 longer continued at a given level. 



As the district emerged from the sea after the deposition of 

 the Paleozoic rocks, it appeared in all probability as a coastal 

 plain, with gently sloping, quite even surface. The present pre- 

 Cambrian surface exposures are such because the Paleozoic cover 

 has been removed by later erosion. Along the contact line of 

 today we see the pre-Cambrian surface as it was when originally 

 covered by the later rocks. As we recede from that line, the pre- 

 Cambrian rocks have been exposed to progressively longer wear, 

 during which the less durable rocks have lost more than those 

 of greater durability, and more material has been removed from 

 along the stream courses than from the interstream areas; hence 

 the surface is now one of hill and valley. In r"egard to this 

 present surface two things seem quite clear, first, that the hill- 

 tops rise to quite concordant altitudes, with a general increase in 

 elevation to the northward, and second, that the comparatively 

 plane surface which w r ould be produced by filling up the valleys 

 to the level of the hilltops, does not correspond in inclination with 



