CONCLUSION 225 



in mind. Whatever the cause may have been, its distributive characters 

 appear to be precisel}^ the same as those which belong to an increase of 

 oblateness of the oceanic figure. Why should we look for two separate 

 causes for two sets of phenomena which appear to require precisely the 

 same kind and distribution of force to produce them? 



The first author to suggest oscillations of the figure of the ocean as the 

 cause of displaced strand-lines appears to have been Emmanuel Sweden- 

 borg. Suess traces this idea back to him through Eobert Chambers and 

 P. Frisi (II, 7, 11, 16, and 21). But whether Suess regards increased 

 oblateness as the cause of crustal movements or not, it seems certain that 

 he would have reached this conclusion long ago if he had held stead- 

 fastly to his first conception that the mountain ranges of western N'orth 

 America were folded toward the Pacific, instead of receding from that 

 position in deference to the contrary opinions of certain American and 

 Canadian geologists; for if he had found North America folded toward 

 the Pacific Ocean, he would also have found that the evidence of general 

 crustal creep and dispersion from high toward low latitudes is complete 

 for the northern hemisphere. 



All forms of the contraction hypothesis meet with two insurmountable 

 difficulties with reference to the Tertiary period of mountain making. 

 They fail to explain in a satisfactory way the distribution of Tertiary 

 mountain ranges upon the earth's surface, and they do not explain how 

 so great a period of mountain making could have occurred in so recent 

 time. If due to contraction arising from cooling, it is necessary to sup- 

 pose a very long period of accumulation and storage of mountain-making 

 force before the beginning of the folding movement. The amount of 

 crustal movement which occurred during the Tertiary period seems to 

 be far in excess of the most that can be attributed to cooling and shrink- 

 ing since the time of the Permo-Mesozoic (Appalachian) folding, even 

 on the most liberal estimate. It is scarcely credible that any considerable 

 mountain-making force derived from cooling before the time of the 

 Permo-Mesozoic folding could have survived that event so as to be an 

 important element in the Tertiary folding. 



Eef erring to the tangential crustal movements in Asia, Willis, in a 

 recent development of the contraction hypothesis based on isostacy, says : 

 "What Suess considers an outward advance, I regard as a retarded super- 

 ficial layer, beneath which the deeper mass has been squeezed northward 

 into narrower space. "^^ Willis supposes subsidence of the earth-segment 

 under the Pacific and Indian Oceans, with northward spreading or un- 



^ Bailey Willis : Research in China, vol. 2, Systematic geology. Carnegie Institu- 

 tion of Washington, 1907, p. 126. 



