550 GEOLOGY. 



seems highly probable from the nature of the case that the edgewise 

 compression which resulted from sustaining the full stress before the 

 beds bent, was much greater than the crosswise compression on the 

 limbs of the folds, which came into action only after the stress had been 

 largel}^ satisfied by folding. 



Whatever the correction, and whatever the probable errors of the 

 above estimates, the amount of shortening involved in folding is large. 



Fig. 449a — Illustrations of Willis' experiments in the artificial representation of moun- 

 tain folding. The sections were formed of layers of wax of different colors, and 

 were mechanically compressed from the right. The upper section shows the original 

 state, and the offsets of the succeeding sections at the right indicate the amount of 

 shortening. (Thirteenth Ann. Rep. U. S. Geol. Surv.) 



The estimates given are merely those for certain periods of folding, and 

 represent only that portion of the compression of the circumference 

 which was concentrated in a given mountain range. The whole shorten- 

 ing of a circumference is to be found by adding together all the trans- 

 verse foldings on a given great circle, following it about the globe at 



