438 POPULAR SCIENCE MONTHLY. 



form characteristic of early thought. The forces originating 

 oceanic basins still continue to deepen them and to increase the size 

 and height of continents, but other forces are at work, some antago- 

 nizing (i. e., cutting do^-n the continents and filling up the ocean 

 beds), and still others determined by causes we little understand, 

 by oscillations over wide areas, greatly modifying and often ob- 

 scuring the effects of the basin-making movements. Here, then, 

 we have two kinds of crust movements: the one fundamental and 

 original, determining the greatest features of the earth and moving 

 steadily onward in the same direction, ever increasing the features 

 which it originates; the other apparently lawless, uncertain, oscil- 

 lating over very wide areas, modifying and often obscuring the 

 effects of the former. The old unif ormitarians saw only the effects 

 of the latter, because these are most conspicuous; the new evolu- 

 tionists add also the former and show its more fundamental char- 

 acter, 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 com- 

 mon and conspicuous now and in all previous geologic time. The 

 former underlies and conditions and unifies 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 imperfectly. Of the causes of the 

 latter we yet know absolutely nothing. We have not even begun 

 to speculate profitably on the subject, and hence the apparent law- 

 lessness of the phenomena. A fruitful theory of these must be 

 left to the coming century. 



Mountain Ranges. — If oceanic basins and ■ continental domes 

 constitute the greatest features of the earth's face, and are deter- 

 mined by 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 culmi- 

 nating points, the theaters of greatest activity, of all geological 

 forces, both igneous and aqueous — igneous in their formation, and 

 aqueous both in the preparatory sedimentation and in the final ero- 

 sive sculpturing into forms of beauty. A theory of mountain 

 ranges therefore lies at the bases of all theoretical 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 by geology is that notliing is per- 

 manent; everything is subject to continuous change by a process 

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

 embryo in the womb of the ocean. We know the date of their 



