GEOLOGY OF LAKE PLEASANT QUADRANGLE 55 



The Mount Orrey-Dunham ridge terminates abruptly on the 

 south due to a fault scarp. Considering its height (looo feet) and 

 steepness, this is one of the finest fault scarps of the quadrangle. 



Two miles south-southeast of Wells there is a small fault, with 

 practically vertical scarp, which rises between 300 and 400 feet 

 in homogeneous granite. 



The minor cross-faults on the south sides of Mounts Rouge, 

 Orrey, and Dunham respectively, and either side of the summit of 

 Hamilton mountain also have very steep scarps in homogeneous 

 rock. 



Along Ninemile creek, between the Moose Creek and Whitehouse 

 faults, there are many crushed rock zones with strike north 10° to 

 20° east, thus proving that the creek has here carved out its channel 

 along a fault. Its topographic influence is not great but the upthrow 

 side appears to be on the east. 



The topography suggests a prominent cross-fault with nearly 

 east-west strike along the northern base of Speculator mountain. 

 The southward tilt of the great Speculator mountain mass away 

 from the escarpment harmonizes with the idea of this being a fault 

 block. No positive evidence for a fault could, however, be found. 

 Also the topographic evidence for a fault here is not so strong 

 because the large comparatively depressed area, just north of Specu- 

 lator, Indian Head and Fish mountains and in part occupied by 

 the large lakes, lies parallel to the foliation and in a region from 

 which much weak Grenville (including limestone) has been re- 

 moved by erosion. Such removal of a large body of comparatively 

 weak Grenville would in itself account for the existing topography 

 of this region. 



Fault ridges and troughs 



A glance at the geologic map will show numerous excellent ex- 

 amples of fault ridges and troughs. The largest and best defined 

 fault ridge lies between the Jimmy Creek-Sugarloaf and Elbow- 

 Three Ponds Mountain faults. Some of the highest points on this 

 ridge, which is 12 or 14 miles long and from i^^ to 3 miles wide 

 are : Elbow mountain, Mount Orrey, Finch mountain. Three Ponds 

 mountain, and Blue Ridge mountain. The ridgelike form is best 

 shown just west of the Wells valley, while the highest portion is 

 the Three Ponds mountain mass. Only two streams — Elbow 

 creek and West Branch Sacandaga river — cut across this ridge. 



The fault block lying between the Jimmy Creek and Hamilton 

 Lake faults is also a fault ridge notable for width and height. It 



