80 NEW YORK STATE MUSEUM 



new maps of Essex county are studied. These seem to show the 

 possibility of separating the hills into* two classes several hundred 

 tfeet apart in altitude, but the distinction i® not sharp, and all 

 sorts of intermediate elevations occur. It is quite certain that, 

 when this erosion period was terminated by an uplift, the uplifted 

 surface was a quite hilly one, though it was also a surface of 

 moderate slopes and subdued relief. 



The valley bottoms owe their present level character to glacial 

 deposits. Their present quite uniform altitude® indicate strongly 

 a corresponding rather uniform altitude for the rock surface 

 buried beneath the drift. Many of the valleys have resulted from 

 the erosion of the crystalline limestones and associated gneisses, 

 which are much the least resistant of all the Adirondack rocks. 

 Other valleys occupy lines of fracture or faulting. Still others, 

 however, are carved out of the same resistant rocks which consti- 

 tute the hills. 



The period of time during which the region rested at the new 

 base was far less prolonged than the earlier period of rest. Some 

 of the valleys are quite wide, others are narrow, but as a general 

 average considerably less than half of the region has been cut 

 down to the new level. 



The last period of uplift occurred in comparatively recent times 

 and must have been of considerable amount in order to give the 

 valleys their present elevation above tide. 



Tilting of base levels. Throughout most of St Lawrence county 

 the hills are low, only rising a few hundred feet above the valleys, 

 and their summits rise to approximately the same altitudes. 

 Passing eastward into and across Franklin county, the hilltops, 

 though of variable hight, reach progressively greater and greater 

 elevations, till a north and south line is reached whose course 

 coincide® approximately with the boundary line between Frank- 

 lin and Clinton counties and the prolongation of this line south- 

 ward. Along this line are situated the highest elevations in the 

 Adirondack region, culminating in the high peaks of the Marcy 

 group, of which Marcy and Mclntyre exceed 5O0O feet, and several 

 others nearly reach that elevation. To the north of these is. 



