320 SEE— THE CAUSE OF EARTHQUAKES. [October 19, 



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 its 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 contracted 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." 



It is unnecessary to dwell on the violence of the hypothesis that 

 the nucleus has shrunk away from the crust, as here outlined. So 

 far as one can see, no such result is possible, nor is the shrinkage 

 ever appreciable. 



But we may here remark that a radial shrinkage of one mile 

 will give a shrinkage in the semi-circumference amounting to 3.14 

 miles. Whether correctly or not, it has been estimated by geologists 

 that the amount of folding in the Alps exceeds one-third of the 

 whole space now occupied by these mountains, the shortening of the 

 original crust being placed by Heim at 74 miles. Analogous results 

 have been reached by Claypole and others regarding the mountain 

 ranges of America. 



It should be observed that to afiford a slack for folds amounting 

 to 74 miles, a radial shrinkage of about 12 miles is required, even 

 when all of the tangential movement is carried round to one point. 

 To carry all the tangential movement round to one point would 

 imply one of two things : ( i ) That the crust is loose from the 

 globe it surrounds, and thus can be carried around to one point 

 from a whole semi-circumference, which seems altogether improb- 

 able; (2) that if the crust is thus shrunk up without being carried 

 around loose from the globe, the matter underlying it must be 

 condensed to about three-halves its former density. The cone of 

 matter underlying the Alps, and extending to the center of the 

 earth would thus have a density 50 per cent, greater than that 



