THEORY OF THE EARTH. 



45 



surface of our earth. These are rains and thaws, 

 which waste down the steep mountains, and occa- 

 sion their fragments to collect at their bottoms; 

 streams of water, which sweep away these frag- 

 ments, and afterwards deposit them in places 

 where their current is abated; the sea which un- 

 dermines the foundations of elevated coasts, form- 

 ing steep cliffs in their places, and which throws 

 up hillocks of sand upon flat coasts; and, finally, 

 volcanoes, which pierce through the most solid 

 strata from below, and either elevate or scatter 

 abroad the vast quantity of matter which they 

 eject. 



9. Of SUps, or Falling Down of the Materials of 

 Mountains. 



In every place where broken strata present their 

 edges to the day in abrupt crags, fragments of 

 their materials fall down every spring, and after 

 every storm; these become rounded by rolling up- 

 on each other, and their collected heaps assume a 

 determinate inclination or external form, regulated 

 by the laws of cohesion, forming at the bottom of 

 the crag, whence they have fallen, taluses of great- 

 er or lesser elevation, in proportion to the quanti- 

 ty of the fragments. These taluses constitute the 

 sides of the valleys in all elevated mountainous 

 regions, and are covered over by abundant vege- 

 tation, whenever these fallings-down of materials 

 from higher mountains become less frequent; but 



