152 PROCEEDINGS OF THE BOSTON MEETING 



tops of all belong to the same former baselevel of erosion. There are now 

 ample evidences indicating that these two highland plains are not separated 

 parts of a once continuous peneplain. 



It appears that the terre pleins of the high plateaux and of the Mesa de 

 Maya, on the other side of the Cordillera, are widely removed tracts of the 

 same Miocene peneplain which once doubtless extended completely over the 

 Rocky Mountain region. The summit plain of the Rockies, however, seems 

 to be much older — Comanchean in date. It is continually made fresh, because 

 it is being rapidly exhumed by the peeling off of the Dakotan sandstone which 

 everywhere reposes upon it. 



Presented by title in the absence of the author. 



MOUNTAIN PEDIMENTS: A DISCUSSION OF THE EROSION OF DESERT RANGES 



BY KIRK BRYAN ^ 



(Abstract) 



Many of the mountains in the Papago country of southwestern Arizona are 

 bordered by plains cut in rock which superficially resemble alluvial slopes. 

 These plains are eroded by weathering in place and by corrasion of running 

 water. An analysis of the processes of erosion of mountain slopes and of the 

 rock plains at their bases is presented. The term pediment, with a series 

 of qualifying adjectives, is proposed for the rock plains. The present state 

 of dissection of most of the pediment areas is described and present condi- 

 tions of erosion compared to those of the past. Criteria are suggested for 

 interpretation of the history of desert valleys characterized by pediments on 

 the borders. 



Presented without notes. 



Discussed by Prof. W. M. Davis and Dr. J. L. Eich, with reply by 

 author. • 



• SOME FEATURES OF STREAM DEVELOPMENT AND OF GLACIATION IN THE 



CAT SKILL MOUNTAINS 



BY H. E. MERWIN 



(Abstract) 



The capture by the Schoharie of upper branches of the Delaware which 

 drained the unsymmetrical valleys of the northeastern Catskills was con- 

 sidered. An explanation of the "cloves" and deep notches was offered. Ob- 

 servations concerning the height of glaciation were given, and certain glacial 

 deposits were described with reference to local glaciation. 



Discussed by Dr. J. L. Kich and Prof. W. M. Davis, with reply by the. 

 author. 



Introduced by H. E. Gregory. 



