PENNSYLVANIAN-PERMIAN GLACIATION 479 



to coarse boulder deposits that occupy the lower slopes of the moun- 

 tains. The boulder conglomerates are much eroded by the present 

 surface drainage, and on the lower slopes they appear as remnants 

 of a more continuous formation that once filled the intermontane 

 valleys. 



Above the general level of the zone of the grooved granites 

 and the boulder conglomerates, the granite walls of the mountains 

 rise to heights of 200 to 800 feet from the surrounding plains of the 

 Permian Red Beds, and on these higher slopes are developed (see 

 Fig. 16) the characteristic jagged or rounded exfoliation features, 

 developed by granite under the stress of wind and weather. 



Fig. 8. — View of grooved granite 



The character of some of the grooved granite surfaces is shown in 

 Figures 8, 9, and 10, which are examples occurring near the base 

 of a granite mound that rises about 200 or 300 feet above the Per- 

 mian Red Beds plain in the N.E. part of Sec. 7, T.5 N., R. 18 W. 



Figure 8 shows deeply grooved granite near the base of the 

 mound with the border of the plain sloping down to the right and 

 with the top of the mound rising up on the left. The grooves are 

 seen to extend around the outcurving heads of the projections and, 

 though they disappear beneath the talus in the re-entrants in this 

 particular place, they are believed to continue across as is indicated 

 in Figure 1 1 . The system of nearly, but not exactly, parallel grooves 

 is approximately horizontal in this example. The grooved surface 

 is roughened by spalling and other weathering processes, and the 



