BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 23, pp. 333-348, PLS. 15-18 JULY 15, 1912 



DIFFERENTIAL EROSION AND EQUIPLANATION IN 

 PORTIONS OF YUKON AND ALASKA ' 



BY DE LORME D. CAIRNES " 



(Presented extemporaneously December 30, 1911) 



CONTENTS 



Page 



Introduction 333 



Area 334 



Geological formations 334 



Differential erosion 337 



Yukon plateau 337 



Eroding and disintegrating processes 339 



Summary and deductions 343 



Equiplanation 344 



General 344 



Definition 345 



Equiplanating processes 345 



Introduction 



A study of the physiography of any district involves not only a con- 

 sideration of the surface phenomena, but an examination of the ma- 

 terials composing that portion of the earth^s crust and an investigation 

 of the subterranean forces to which they have been subjected. A steeply 

 inclined valley wall may merely indicate a youthful period in the topo- 

 graphic cycle; may be the result of glaciation; may be due to some in- 

 herent bedrock structure or the inclination of certain strata, or may even 

 have been caused by recent faulting. 



In investigating any physiographic problem, therefore, all the avail- 

 able evidence which tends to elucidate the physiography should be con- 

 sidered, no matter how superficial or deep seated may be the materials 

 or forces involved. It is thus that the domains of physiography and 

 general geology encroach and overlap — but always to their mutual ad- 



1 Published by permission of the Director of the Geological Survey, Department of 

 Mines, Canada. 



Manuscript received by the Secretary of the Society December 30, 1911. 



2 Introduced by Percy E. Raymond. 



XXIV— Bull. Geol. Soc. Am., Vol. 23, 1911 (333) 



