310 LEWIS G. WESTGATE 



portions of the region which were not subject to glacier-erosion 

 during the Plejstocene, and have thus retained their preglacial form 

 essentially unchanged to the present. The character of this topog- 

 raphy was suggested in the opening pages of this paper. Briefly 

 it was as follows: the Arkansas was flowing in a broadly opened 

 graded valley between ranges which rose on either side to a height 

 of from 3,000 to 5,000 feet, but which were characterized by rela- 



Fig. 12. — Lost Canyon Mountain from the Arkansas Valley. 



tively gentle and graded slopes. The term most applicable to such 

 mountains is "massive." A view of Lost Canyon Mountain (Fig. 

 14) from the Arkansas valley is probably typical for the mountain 

 range in general in preglacial time. 



The study of mountain form about Twin Lake's is the question 

 how far in any particular locality this preglacial type of mountain 

 has been destroyed by glacial erosion; how far cliffs, arret es, and 

 peaks of glacial origin have replaced the more gentle and even slopes 

 of mature subaerial erosion. Back toward the divide of the Sawatch 



