272 A TENTURY OK GP:OLOGY. 



of the hitter, because these are most conspicuous. The new evolution- 

 ists add also the former and show its more fundamental character, and 

 thus introduce law and order into the previous chaos. The former is 

 the one movement which runs ever in the same direction through all 

 geologic time. The latter are the most common and conspicuous now 

 and in all previous geologic time. The former underlies and condi- 

 tions and unities the history; the latter has practically determined 

 all the details of the drama enacted here on the surface of the earth. 

 Of the causes of the former we know something, though yet imper- 

 fectly. Of the causes of the latter we yet know absolutely nothing. 

 We have not even begun to speculate profitably on the sul)jiM't, and 

 hence the apparent lawlessness of the phenomena. A fruitful theory 

 of these must be left to the coming century. 



3£ou)ita!n range^^. — If oceanic basins and continental domes constitute 

 the greatest features of the earth's face, and are determined l)y the 

 most fundamental movements of the crust, surely next in importance 

 come great mountain ranges. These are the glory of our earth, the 

 culminating points of scenic beauty and grandeur. But they are so 

 only because they are also the culminating points, the theaters of 

 greatest activity, of all geological forces, both igneous and aqueous — 

 igneous in their formation and aqueous both in the preparatory sedi- 

 mentation and in the tinal erosive sculpturing into forms of beauty. 

 A theory of mountain I'anges, therefore, lies at the bases of all theo- 

 retical geology. To the pre-geologic mind mountains are the type 

 of permanence and stability. We still speak metaphorically of the 

 everlasting hills. But the first lesson taught l)y geology is that noth- 

 ing is permanent; ever3'thing is subject to continuous change by a 

 process of evolution. Mountains are no exception. We know them 

 in embr^-o in the womb of the ocean. We know the date of their liirth; 

 we trace their growth, their maturity, their deca3^ their death; we 

 even find in the folded structure of the rock, as it were, the fossil bones 

 of extinct mountains. In a word, we are able now to trace the whole 

 life history of mountains. 



Mountains, therefore, have always been a subject of deepest interest 

 both to the popular and the scientific mind — an interest intensified by 

 the splendors of mountain scenery' and the perils of mountain explora- 

 tion. The study of mountains is therefore coeval with the study of 

 geolog}". As early as the beginning of the present century Constant 

 Prevost observed that most characteristic structure of mountains — 

 viz, their folded strata — and inferred their formation })y lateral pres- 

 sure. All subsequent writers have assumed lateral pressure as some- 

 how concerned in the formation of mountains. But that the whole 

 height of moimtains is due wholly to this cause was not generally 

 admitted or even imagined until recently. It was universally sup- 

 posed that mountains were lifted by volcanic forces from beneath, that 



