240 SEE— FURTHER RESEARCHES ON [April 24, 



Appalachian and other American mountain regions. To explain 

 such deposits he supposed that marine currents had formerly 

 traversed these regions and by gradually depositing sediments of 

 great weight had also sunk the crust till at length a great thickness 

 was attained. When the rocks thus formed had become solidified 

 and crystallized the borders of the continent were afterwards up- 

 raised somehow. He did not indicate how the uplift had come 

 about, nor did he think that the mountain regions had been raised 

 separately. Denudation had then commenced, and finally given the 

 mountains the forms they have today. 



Keferstein, Sir John Herschel, Dr. T. Sterry Hunt and others, 

 along with Hall, or even before him, in some cases, had de- 

 veloped the theory of aqueo-igneous fusion, which was supposed 

 to produce a plastic zone between the consolidated crust and the 

 solid nucleus. This theory supposed that the isogeotherms rise in 

 regions of heavy sedimentation. Hall held that this would 



" cause the bottom strata to establish lines of weakness or of least resis- 

 tance in the earth's crust, and thus determine the contraction which results 

 from the cooling of the globe to exhibit itself in those regions, and along 

 those lines where the ocean's bed is subsiding beneath the accumulated 

 sediments." 



Many of the views afterwards more fully developed by Leconte 

 are here faintly traced by Hall, and for that reason these early 

 views of mountain formation are worthy of attention. 



§ 42. Jlcws of Lccoiitc. — This veteran geologist gave great 

 attention to mountain formation throughout a long career, and his 

 residence on the Pacific Coast gave him exceptional facilities for 

 studying the ranges of our western states, and especially of Cali- 

 fornia, which includes the most remarkable developments in North 

 America. The views at which Leconte arrived, as set forth in his 

 " Elements of Geology," edition of 1896, are as follows : 



"Mountain Origin. 

 " Leaving aside for the present all disputed points, it is now universally 

 admitted that mountains are not usually pushed up by a vertical force from 

 beneath, as once supposed, but are formed wholly by lateral pressure. The 

 earth's crust along certain lines is crushed together by lateral or horizontal 

 pressure and rises into a mountain-range along the line of yielding, and to 

 a height proportionate to the amount of mashing. But the yielding is not 

 by rising into a hollow arch, nor into such an arch filled beneath with liquid 



