118 WALKS AND TALKS. 



than the polar ; and consequently there has been more lateral 

 pressure around the equatorial region. That pressure too was 

 exerted east and west, and that was just the direction which 

 would give to the wrinkles a north and south trend, and a con- 

 siderable elongation. Besides this, there was a powerful tidal 

 attraction exerted by the moon (see also Talk XXXVIII). 

 That body was then much nearer the earth than now, and 

 exerted important influences on the earth. In our times, it 

 raises the ocean and the whole hemisphere in a tidal swell ; 

 then, though no ocean existed, the tidal swell was raised with 

 the forming film over its surface. But the rise of the swell 

 was not instantaneous ; it reached its height after the moon 

 had passed the meridian to the west, and the moon acting on 

 it from that position, pulled the apex slightly westward, and 

 thus established changed conditions in the crust which neces- 

 sarily had a north and south trend, and contributed something 

 to give the wrinkles which were then forming, the north and 

 south axes which we see in mountain ranges. 



Another peculiarity of mountains is the greater thickness 

 of the formations and the greater proportion of fragmental 

 strata. This has led some to conceive that the materials of 

 mountains were accumulated in the bottom of the sea, in sit- 

 uations to which ocean currents brought unusual quantities of 

 coarse deposits from neighboring continental shores. It is sup- 

 posed that these sediments depressed the bottom and thus pre- 

 served such depths as would continue to invite the currents to 

 a continuance of their work, until the mountain mass was 

 completed. The sinking of the great synclinal must have 

 subjected the materials to the metamorphic influence of inter- 

 nal heat, even without any crushing together. Probably, in 

 this state of things, metamorphism resulted from both causes. 

 Then in due tine, the synclinal was upraised, with additional 

 crushing, and the mountain was completed. 



These are but glimpses of the theory of mountain-making ; 

 but I hope they will stimulate you to further study. Let me 

 recommend the re-reading of this Talk, after Talk XXXVIII. 



