igos.] THE PHYSICS OF THE EARTH. 249 



If wrinkling resulted from uniform cooling and consequently 

 uniform shrinkage, the effect would be analogous to that of a with- 

 ered apple, with small wrinkles all over it, instead of a surface 

 presenting in one region a continuous system of folds extending 

 from Cape Horn to Alaska, and in another, a zone a thousand miles 

 wide, from the Appalachian to the Rocky ^^lountains, with scarcely 

 any evidence of disturbance whatever. 



In these considerations Major Button has forcibly expressed 

 the difficulty of supposing that a mountain range is formed by the 

 cooling of the earth contracting equally along all its radii. Such 

 a supposed mode of formation of our ranges, folded and crumpled 

 as they are, is clearly impossible ; and Major Button shares with 

 the Rev. O. Fisher the credit of having been the first to recognize 

 the total inadequacy of the contraction theory. 



It is remarkable that after this antiquated theory had been thus 

 clearly disproved, it should have continued in use. Xo one seems 

 to have been able to frame a theory based on any cause except secu- 

 lar cooling, till the present writer developed the theory based on the 

 leakage of the oceans and the formation of mountains by the expul- 

 sion of lava under the land, which perfectly explains all the 

 phenomena. 



§ 45. J^iczcs of Gcikic. — In the article '' Geology," Encyclopedia 

 Britannica, p. 375. we find the following statement of the contrac- 

 tion theory : 



" There still remains the problem to account for the original ^vrinkling 

 of the surface of the globe, whereby the present great ridges and hollows 

 were produced. 



■' It is now generally agreed that these inequalities have been produced 

 by unequal contraction of the earth's mass, the interior contracting more 

 than the outer crust, which must therefore have accommodated itself to this 

 diminution of diameter by undergoing corrugation. But there seems to have 

 been some original distribution of materials in the globe that initiated the 

 depressions on the areas which they have retained. It has been already 

 pointed out (ante, p. 222) that the matter underlying the oceans is more 

 dense than that beneath the continents, and that, partly at least, to this cause 

 must the present position of the oceans be attributed. The early and per- 

 sistent subsidences of these areas, w-ith the consequent increase of density, 

 seems to have determined the main contours of the earth's surface. . . . 



" The effects of this lateral pressure may show themselves either in 

 broad dome-like elevations, or in narrower and loftier ridges of mountains. 



