(5 THE PLAINS. 



How a mountain composed of such materials should have 

 retained for ages its perfect shape is one of Nature's 

 secrets. 



The crater is very perfect, and the specimens of lava 

 and tufa are the finest to be found in any of the vol- 

 canoes. In this crater is growing a large cedar-tree, 

 which, judging from its external appearance, must be 

 more than a hundred years old. 



From evidence which will appear farther on, there 

 is no doubt that the plains were for myriads of ages 

 the sport of nature, and were successively upheaved 

 and submerged partially or wholly ; how often can 

 probably never be known to human intelligence. I 

 think, however, that every portion of land in this basin, 

 not of the first grand mountain upheaval, can be referred 

 to one of three subsequent horizontal upheavals which fix 

 the distinctive character of the country, and each leaves its 

 peculiar marks. 



The first of these, occurring probably about the 

 period of fire, brought up the immense plateau called the 

 * Eaton Mountains,' the ' Mesa de Maio,' the ' Mesa 

 Grande,' on which is Fort Union, and many other more 

 or less isolated plateaus, now having an elevation of from 

 6,000 to 8,000 feet, 



The peculiarity of this first horizontal elevation, is, 

 that its upper surface is still a plain marked with ridges 

 of burnt and half-molten rocks, and covered everywhere 

 with lava and volcanic tufa, so hard as to defy the action 

 of the elements. 



The land elevated by this upheaval rose perpendicu- 

 larly from the sea, the upper surface remaining nearly 

 horizontal, but inclining slightly to the eastward. The 

 precipitous sides, formed of the hard igneous rock, show 

 scarcely any evidence of wear even by the ages of 

 exposure to the elements ; and, although the ocean still 

 washed its foot, this plain gave off no detritus. It rises 

 from the plain below, almost as sheer and unmarked by 



