GEOLOGY OF LAKE PLEASANT QUADRANGLE 7I 



ages of weathering and frost action during the long Preglacial 

 period of erosion. 



An examination of the topograj)hic maps shows no possible Pre- 

 glacial channel of the West Branch Sacandaga river to the south, 

 west or north. Thus we are obliged to look for an eastward chan- 

 nel. Such a Preglacial channel is thought to be just north of The 

 Gorge. A small eastward flowing stream ^ occupies a wide, deep 

 channel really much more commensurate with a large stream such 

 as the river. The narrowest part of the channel is just at the map 

 edge, but since it is there heavily drift filled, the Preglacial rock 

 channel was certainly wider and somewhat deeper. At this place 

 the altitude of the present stream is less than 1680 feet, while west- 

 southwestward at Mud lake and the Piseco outlet the altitude is 

 nearly 1660 feet. The low, intervening divide is clearly due to 

 drift accumulation and, by allowing for comparatively little depth 

 of drift, there is no difficulty in considering the Preglacial river 

 channel to have been here. The Gorge has been cut as a notch by 

 the Postglacial river where it entered by steep gradient into the 

 Preglacial valley. 



STONE QUARRIES 



In Precambric rocks 



Granville marble. Of the few small masses of Grenville crystal- 

 line limestone or marble within the quadrangle, the only one ever 

 commercially used lies i^ miles a little south of east of Lake Pleas- 

 ant village, where are located an old quarry and a limekiln. The 

 rock is a medium-grained, greenish-gray, serpentine marble with 

 occasional green patches or blotches of serpentine. Many years 

 ago some of the rock was burned in the kiln for the production of 

 quicklime, while some is said to have been quarried and shipped for 

 building and decorative purposes. 



Road metal and building stone. During 191 2 the only quarry 

 in the syenitic or granitic rocks was alongside the state road i}i 

 miles northeast of Lake Pleasant village. This rock was crushed 

 for use in building the state road. Other quarries have doubtless 

 since been opened for state road work between Hope and Wells. 



The best road material of the quadrangle is the diabase, which 

 is a fine quality of so-called " trap-rock," but the only one of these 

 dikes known to be really accessible for road work is the one east 



1 This stream, instead of emptying into Hamilton Lake stream as shown 

 on the map, really enters the river nearly a mile above the mouth of Hamilton 

 Lake stream. 



