36 PKOGEESS : ITS LAW AND CAUSE. 



higher, as we find them to be, but they must be longer, aft 

 we also find tliem to be. Thus, leaving out of view other 

 modifying forces, we see what immense heterogeneity of 

 surface has arisen from the one cause, loss of heat — a heto- 

 rogeneity which the telescope shows us to be paralleled on 

 the face of the moon, where aqueous and atmospheric 

 agencies have been absent. 



But we have yet to notice another kind of heterogeneity 

 of surface similarly and simultaneously caused. While the 

 Earth's crust was still thin, the ridges produced by its con- 

 traction must not only have been small, but the spaces be- 

 tween these ridges must have rested with great evenness 

 upon the subjacent liquid spheroid ; and the water in those 

 arctic and antarctic regions in which it first condensed, must 

 have been evenly distributed. But as fast as the crust grew 

 thicker and gained corresponding strength, the lines of 

 fracture from time to time caused in it, must have occurred 

 at greater distances apart ; the intermediate surfaces must 

 have followed the contracting nucleus with less uniformity ; 

 and there must have resulted larger areas of land and wa- 

 ter. If any one, after wrapping up an orange in wet tissue 

 paper, and observing not only how small are the wrinkles, 

 but how evenly the intervening spaces lie upon the surface 

 of the orange, will then wrap it up in thick cartridge-paper, 

 and note both the greater height of the ridges and the 

 much larger spaces throughout which the paper does not 

 touch the orange, he will realize the fact, that as the Earth's 

 solid envelope grew thicker, the areas of elevation and de- 

 pression must have become greater. In place of islands 

 more or less homogeneously scattered over an all-embra- 

 cing sea, there must have gradually arisen heterogeneous 

 arrangements of continent and ocean, such as we now know. 



Once more, this double change in the extent and in the 

 elevation of the lands, involved yet another species of he- 

 terogeneity, that of coast-line. A tolerably even surface 



