igoS.J 



THE PHYSICS OF THE EARTH. 237 



range is under water, and not at all in the secular cooling of the 

 globe. 



V. Comparison of the Old and New Theory of Mountain 

 Formation Continued. 



(B) Views of Eminent Geologists on Mountain Formation 



IN General. 



§ '^J. Elie de Beaumont's Theory of the Secular Cooling and 

 Collapse of the Globe. — This venerable theory is thus condensed 

 by Lyell : 



" The origin of these chains depends not on partial volcanic action or a 

 reiteration of ordinary earthquakes, but on the secular refrigeration of the 

 entire planet. For the whole globe, with the exception of a thin envelope, 

 much thinner in proportion than the shell to an egg, is a fused mass, kept 

 fluid by heat, but constantly cooling and contracting in dimensions. The 

 external crust does not gradually collapse and accommodate itself century 

 after century to the shrunken nucleus, subsiding as often as there is a 

 slight failure of support, but it is sustained throughout whole geological 

 periods, so as to become partially separated from the nucleus until at last 

 it gives way suddenly, cracking and falling in along determinate lines of 

 fracture. During such a crisis the rocks are subjected to great lateral pres- 

 sure, the unyielding ones are crushed, and the pliant strata bent, and are 

 forced to pack themselves more closely into a smaller space, having no 

 longer the same room to spread themselves out horizontally. At the same 

 time, a large portion of the mass is squeezed upwards, because it is in the 

 upward direction only that the excess in size of the envelope, as compared 

 to the nucleus can find relief. This excess produces one or more of those 

 folds or wrinkles in the earth's crust which we call mountain-chains." 



De Beaumont's theory is given more from its antiquity than 

 from its present day importance, and yet in some form it still holds 

 its place in all our treaties on geology. Indeed the latest works 

 include discussions of the strength of domes, as if the nucleus of 

 the globe were shrinking away from the crust, and the latter thus 

 subjected to crushing from its own weight. 



§ 38. Views of Lyell. — This great geologist always rejected Elie 

 de Beaumont's theories of mountain formation, and gave the most 

 cogent reasons for his course. He adopted the theory that the 

 land is occasionally depressed and elevated, by internal forces, but 

 did not definitely decide what forces produced these progressive 



PROC. AMER. PHIL. SOC. XLVU. 189 P, PRINTED SEPTEMBER 23, I908. 



