PEN N SYLVAN I AN -PERM I AN GLACIATION 483 



this force was obviously directed by an agency which moved down 

 the valley. 



It may be assumed for the present that if glaciation was the 

 cause of the extensive deposition of conglomerates, and of the various 

 striated and grooved rocks just described, it was a type of valley 

 glaciation developed on mountainous areas which probably stood 

 as islands in the Pennsylvanian-Permian seas. There is no evidence 

 from the conglomerates themselves to indicate anything other than 

 their local origin, either within the Arbuckle Mountain area, or 

 within the Wichita Mountain area. Perhaps in some places within 

 the area between these mountains, there may have been a comming- 

 ling of materials derived from the two mountain sources, but these 

 places are now deeply buried by the later Pennsylvanian and Per- 

 mian sediments. The present data therefore indicate that the gla- 

 cial source was in the mountains adjacent to where the boulder con- 

 glomerates and the striated and grooved rocks are found. 



Under this hypothesis the glaciers having their sources in the 

 mountains descended the valleys and coalesced on the low lands, 

 or in the seas that surrounded the mountainous islands. The pres- 

 ent valleys occupy the lines of ancient drainage, and ancient valley 

 glaciers, in moving down the valleys, would be in a position to develop 

 such features as the grooved granite of Figures 12 and 13, which 

 closely resemble the features of ''crag and tail" of glacial origin. 

 In the phenomena of " crag and tail"^ isolated stacks and bastions of 

 rock which faced the direction of ice flow are rounded and beveled 

 off and frequently a hollow is dug out in front, while debris has been 

 heaped up behind to form the so-called " tail" of the hill. 



In the valley which contains the grooved granite stack are coarse 

 boulder deposits in contact with the grooved granites which indicate 

 some adequate means for the transportation of coarse debris from 

 farther up the valley. In Devil's Canyon Valley, which lies adja- 

 cent to the east, there are grooved granite walls at various places 

 along the valley which appear to indicate a marked descent of the 

 grooves down the valley. While there is some rather steeply inclined 

 grooving of the granite in this region (see Fig. 14), the grooves 

 and flutings are in general approximately horizontal. Furthermore 



^ J. Geikie, Earth Sculpture, p. 242. 



