38 C. R. VAN HISE 



be agreed that complex deformation is the rule instead of the 

 exception, as I have maintained in another place, 1 it is evident 

 that longitudinal shortening is an important factor in deforma- 

 tion. As a consequence of cross folds, of reverse faults, and of 

 other cross structures, it may be that the shortening of the crust of 

 the earth in a longitudinal direction during the mountain-making 

 processes is as great or greater than the transverse shortening. 



This becomes evident as soon as the ratios between the 

 length and breadth of the mountain chains are considered. The 

 Appalachian system, in its broadest sense, extends from Alabama 

 to the St. Lawrence River, a distance of about 1300 miles. Its 

 breadth is about 75 to 100 miles. The ratio between the length 

 and breadth is about 15: 1 . The Cordilleran system of North 

 America in its broadest sense extends from western Alaska to 

 southern Mexico, a distance of about 4800 miles. The breadth 

 varies from 100 miles at the ends of the system to 1000 miles at 

 the middle. But where this greater breadth occurs there are 

 considerable distances between the different chains so that 

 the folded area is probably not more than from one-half to one- 

 fourth of the total amount. The average width of the folded 

 part is probably somewhere between 300 and 500 miles. Thus 

 the ratio between the length and breadth in this case would be 

 between 16:1 and 10:1. The Andean system extends the 

 entire length of South America, 4500 miles. This system is a 

 comparative^ narrow one, its average width being about 200 

 miles. The ratio of length to breadth in this case is therefore 

 about 22:1. 



It thus appears in the cases of these great mountain systems, 

 if the longitudinal shortening involves from one-tenth to one- 

 twentieth as much shortening as the transverse deformation per 

 mile of linear distance, that the shortening of the crust of the earth 

 as a result of the existence of the mountain systems is as great 

 longitudinally as transversely. 



In the case of some mountain systems which have con- 

 siderable breadth as compared with their length, as for instance 



1 Loc. cit., p. 626. 



