ESTIMATES AND CAUSES OF CRUSTAL SHORTENING II 



the Alps to be seventy-four miles. Le Conte 1 estimates the 

 transverse shortening of the Coast Ranges of California to be 

 from nine to twelve miles. Claypole 2 estimates the transverse 

 shortening of the Appalachians in Pennsylvania to be forty-six 

 miles. McConnell 3 thinks the folding of the Laramie range of 

 British America required a transverse shortening of twenty-five 

 miles. 



In the above estimates of shortening by Heim, Claypole, 

 Le Conte, and McConnell, I have inserted the word transverse, 

 to call attention to the fact that shortening in only one direction 

 has been considered by these authors. It is clear that to obtain 

 an adequate idea of the effect of crustal corrugations, it is neces- 

 sary to know in square miles the surficial lessening of the crust 

 of the earth as a result of deformation. However, it appears 

 that if in other mountain ranges the shortening is proportional 

 to the estimates above given, the total amount of surficial 

 decrease must be enormous. This would be true even if the 

 deformation of ancient mountain ranges, the stumps of which 

 are buried under later rocks, were ignored. Moreover, it is 

 possible that the amount of folding and consequent shortening 

 of the Paleozoic and older rocks, buried under the Mesozoic and 

 Cenozoic strata, may be as great or even greater than the amount 

 of shortening involved in the deformation observable at the 

 surface. 



The theory of mountain-making as a result of secular cooling 

 has been repeatedly attacked along the lines of the vast con- 

 traction demanded by the supposed facts of the field, and the 

 small contraction resulting from secular cooling, the only cause 

 ordinarily assigned for contraction. Dutton 4 calculates that the 



1 On the structure and origin of mountains, with special reference to recent 

 objections to the contractional theory, by Joseph Le Conte : Am. Journ. Sci., Vol. 

 XVI, 1878, p. 98. 



2 Pennsylvania before and after the elevation of the Appalachian mountains, by 

 E. W. Claypole : Brit. Assoc. Rept., Montreal meeting, 1884, p. 718. 



3 Geological features of a portion of the Rocky mountains, by R. G. McConnell : 

 Geol. Surv. of Can., Ann. Kept, Vol. II, Pt. D, 1886, p. 31. 



4 Loc. cit., p. 120. 



