NEW YORK STATE MUSEUM 



:fte retreat of the great ice sheet the valleys were partially filled 

 ■with drift deposits. Decomposed rock material of preglacial age 

 can now be seen at very few localities and those in specially shel- 

 tered places on steep south slopes where ice erosion was very 

 ineffective. One such place is along the road i mile east-northeast 

 of Wevertown at the south base of the mountain where the granite 

 is decomposed, and another is just west of Crane mountain where 

 the south side of a ridge of hornblende gneiss is badly decomposed 

 ito a reddish brown color. 



Where favorably situated with reference to the direction of 

 ice flow, the fault scarps were freshened up chiefly by the removal 

 of the heavy talus slopes. An especially noteworthy example is 

 the steep scarp ly^ miles north of Valentine pond where, on the 

 nearly vertical wall of rock, good glacial striae may be seen. Heavy 

 talus deposits which were not favorably situated for removal by 

 ice erosion occur at the base of the Loon lake mountain scarp on 

 >lhe south side, and also at the base of the scarp next to the south. 



There is good evidence for vigorous ice erosion in the valleys 

 in the southeastern portion of the quadrangle, some of the facts 

 favoring this view being: (i) the abundance of scratched, polished, 

 and rounded rock surfaces; (2) the comparative freshness of the 

 Tocks, even in the case of the weak Grenville ; (3) the unusual 

 weakness of much of the rock, especially limestone, which occupies 

 the valleys ; (4) the fact that these belts of weak rock must have 

 "been deeply decomposed during the long preglacial time, thus favor- 

 ing extensive removal of material; and (5) the north-south move- 

 ment of the ice being parallel to the Grenville valleys and hence 

 being favorable for ice erosion because of easy flowage of the deep 

 ice through the valleys. Other Grenville valleys were doubtlessly 

 ..also similarly lowered by ice erosion. 



GLACIAL DEPOSITS 



Glacial boulders or erratics are very common over the entire 

 area and, as usual, most of them are of local origin. This fact 

 of local origin was successfully employed to locate certain import- 

 ant outcrops, especially of gabbro or diabase, by tracing the line 

 of boulders to the parent ledge. All sorts of Precambric rocks of 

 the region are represented among the boulders, the granite and 

 syenite naturally being the most common. A type of boulder 



