GROWTH OF GEOLOGY. 239 



areas, on an average three miles above the ocean 

 floor and to be folded into mountain chains, is one 

 of the most difficult of geological problems, but there 

 are several factors on which the evolutionary geolo- 

 gist relies. Perhaps the most important is the 

 contraction of the centrosphere. But, before noting 

 a few opinions of experts on this subject, it may be 

 useful to recall that, stupendous as mountain-chains 

 are, their height is minute when compared with the 

 radius of the earth. Indeed, it has been pointed 

 out that on an artificial globe a foot in di- 

 ameter, they should not stand out more than the 

 slight elevations which might result where the edges 

 of the covering paper-slips overlap. 



"As the solid centrosphere slowly contracted from 

 loss of heat, the primitive lithosphere, in accommodat- 

 ing itself through changes in the tektosphere to 

 the shrinking nucleus, would be buckled, warped, and 

 thrown into ridges. . . . The compression of moun- 

 tain chains has most probably been brought about in 

 this manner, but the same cannot be said of the eleva- 

 tion of plateaus, of mountain platforms, and of con- 

 tinents." * 



" It was at first imagined that during the flow of 

 time the interior of the earth lost so much heat, and 

 suffered so much contraction in consequence, that the 

 exterior in adapting itself to the shrunken body, 

 was compelled to fit it like a wrinkled garment. This 

 theory, indeed, enjoyed a happy existence till it fell 

 into the hands of mathematicians, when it fared very 

 badly, and now lies in a pitiable condition, neglected 

 of its friends." f The mathematicians maintained 



* Sir John Murray, Rep. Brit. Ass., 1899, p. 797. 

 tSollas, Rep. Brit. Ass., 1900. See Mature, Sept. 13, 1900, 

 p. 487. 



