BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 34. pp. 243-252 JUNE 30. 1923 



THE ASIATIC AECS ^ 



BY WILLIAM HEKBERT HOBBS 



{Read tefore the Society December 28, 1923 



CONTENTS 



Page 



Escher's definition of bilateral symmetry 24S 



Assymmetrical arrangement of ranges 243 



Views of Kober 244 



Suess' theory as to mountain arcs 245 



Author's views and conclusions 245 



Escher's Definition of bilateral Symmetry 



All earlier studies of folded mountain ranges ignored the relationship ' 

 -between plan and cross-section or profile. Largely in consequence of this 

 neglect, the forces to which they have been supposed to owe their struc- 

 ture have been assumed to possess a bilateral symmetry. For the clas- 

 sical area of the Alps, the folded region which has been studied for the 

 longest time and in the greatest detail, this idea of bilateral symmetry 

 was expressed in the words of Escher and his pupil Heim as zweiseitigen 

 Druch. 



Assymmetrical Arrangement of Eanges 



It was Eduard Suess who as early as 1875, in his Die Entstehung der- 

 Alpen, by focusing attention on the plan, rather than the profile, of 

 mountain ranges, showed that an asymmetrical arrangement of the ranges 

 within definite arcs called for an asymmetrical disposition of the forces 

 which had produced them. Very shortly thereafter James Dana, in 

 studying the other classical area, the Appalachians, adopted a theory 

 of their formation which required the force producing them to come 

 mainly from one side — that of the ocean. In 1884, the year in which 

 his close friend^ Marcel Bertrand, made public his conception of the 



^ Manuscript received by the Secretary of tlie Society March 24, 1923. 

 This paper is one of a series composing a "Symposium on the structure and history- 

 of mountains and the causes of their development." 



(243) 



