GEOLOGY OF THE NORTH CREEK QUADRANGLE 5/ 



side of the south end of Schroon lake and thence southward to the 

 north end of Loon lake. At two places along Schroon lake the 

 fairly steep scarp rises fully 400 feet. The southern end of the 

 fault block is a mass of Grenville (chiefly quartzite) whose bold 

 scarp at one place rises 400 feet. The whole fault block, especially 

 the southern part, shows the usual downslope toward the east. 

 This scarp strikes at a high angle across the foliation bands and 

 hence it is difficult to account for except on the basis of faulting. 



A smaller fault along the western side of the southern end of 

 Schroon lake has a prominent scarp rising some 300 to 400 feet. 

 Where it cuts across the gabbro stock near the map edge the fault 

 scarp rises as a high vertical wall along which the rock is unusually 

 soft and weathered and evidently sheared. 



Loon Lake mountain fault. The short fault shown on the map 

 just east of the north end of Loon lake and at the base of Loon 

 Lake mountain is one of special interest. Here again the contours 

 are not close enough together since the fault scarp which rises to 

 a height of 700 feet is very steep, the upper 300 or 400 feet being 

 a sheer precipice. We have here at once the highest steep ledge 

 of Grenville and the finest example of a practically unaltered fault 

 cliff within tlie quadrangle (see plate 10). The upper portion of 

 the cliff consists of quartzite in thin to thick beds with low north- 

 easterly dip so that the truncated edges of the quartzite layers are 

 distinctly visible in the face of the cliff. The less steep scarp 

 forming the western face of this fault block as well as its down- 

 tilt toward the east are due to the Schroon lake fault already de- 

 scribed. Plate IT gives a good idea of the aj^pearance of this fault 

 block mountain. 



Other faults. The small fault north of Valentine pond strikes 

 due north and south and shows a prominent scarp near its north 

 end. The contours are not close enough together on the mountain 

 side since the wall of rock, w^hich rises fully 600 feet, is very steep 

 to actually vertical in places. Hard, distinctly banded Grenville 

 gneiss makes up the upper three-fourths of the wall and rests upon 

 granite. The fault has broken sharply across the strike of the 

 foliation of hotli the Grenvilk' and granite. 



As judged wholly by the topography, there appears to be a con- 

 siderable fault 1)lock just west of Loon lake. The fault and its 

 scarp lie from i to 1J/2 miles west of the lake and the downtilt 

 toward the lake is very noticeable. 



The shai)e of the lake basin and character of the topography 

 suggest the presence of a fault along the west side of Friends lake. 



