Barrett — Growth of Knowledge of Earth Structure. 153 



Hitchcock tried to reconcile the evidence by a series of 

 unconformities and inclined deposition, but finds the solu- 

 tion unsatisfactory. 



In this same year, 1833, Elie de Beaumont, a dis- 

 tinguished French geologist, published his theory of the 

 origin of mountains. He advanced the idea that since 

 the globe was cooling it was condensing, and the crust, 

 already cool, must suffer compression in adjusting itself 

 to the shrinking molten interior. He concluded from the 

 evidence shown in Europe that the collapse of the crust 

 occurred violently and rapidly at widely spaced intervals 

 of time. This hypothesis introduced the idea of moun- 

 tain folding by horizontal compressive forces. The the- 

 oretical paper of de Beaumont, together with further 

 observations by Hitchcock and others, led the latter in 

 1841 to a final belief in the inversion of strata on a large 

 scale by horizontal compression. His conclusions are 

 expressed in an important paper published in the Journal 

 (41, 268, 1841) and given on April 8, 1841, as the First 

 Anniversary Presidential Address before the Associa- 

 tion of American Geologists. This comprehensive sum- 

 mary of American geology occupies 43 pages. Three 

 pages are given to the inverted structure of the Appa- 

 lachians from which the following paragraphs may be 

 quoted : 



''We have all read of the enormous dislocations and inver- 

 sions of the strata of the Alps ; and similar phenomena are said 

 to exist in the Andes. AVill it be believed, that we have an 

 example in the United States on a still more magnificent scale 

 than any yet described? . . . 



Let us suppose the strata between Hudson and Connecticut 

 rivers, while yet in the plastic state, (and the supposition may 

 be extended to any other section across this belt of country from 

 Canada to Alabama,) and while only slightly elevated, were 

 acted upon by a force at the two rivers, exerted in opposite 

 directions. If powerful enough, it might cause them to fold 

 up into several ridges ; and if more powerful along the western 

 than the eastern side, they might fall over so as to take an 

 inverted "dip, without producing any remarkable dislocations, 

 while subsequent denudation would give to the surface its 

 present outline. ... 



Fourthly, we should readily admit that such a plication and 

 inversion of the strata might take place on a small scale. If for 

 instance, we were to press against the extremities of a series of 

 plastic layers two feet long, they could easily be made to assume 



