Iviii IXTEODUCTIOX. 



There is great uniformity throiiglioiit the whole of the 

 country ; the surface is covered every where with short ranges 

 of volcanic mountains of recent origin. Their general trend 



be influenced mostly h^ 



;pect 



the Siei 



ISTevada and the Wahsatch Mountains ; for the tendency is to 

 run parallel to whichever of these they are nearer to, and m 

 the centre of the basin tlie general direction is north and 

 south. " In crossing the Great Basin, from Domier Pass m 

 the Sierra Nevada to the "Walisateh range at Salt Lake, we 

 passed over no fewer than twenty of these ranges, the basm 



being 700 miles across. On 



! 



ossed ; on the 32nd, a less number ; as m 

 stance across was less than 300 miles, and 



in the other under 200. 



The ranges consist chiefly of volcanic tufa, trachytic 

 breccia, trachyte, and diversely-coloured porphyry, all more or 

 less decomposed. They are mountains in miniature, beautiful 

 in outline, variegated by many-tinted rocks, and usually per- 

 fectly bare of trees, or even, shrubs. They show on then* 

 sides the effect of rains and water to an enormous extent, for 

 the volcanic rocks of which they consist are easily decom- 

 posed by the elements, and then washed away. The ranges 

 may in former times have been very long and contianons , 

 but it is evident that, ever since their formation, water bas 

 been cutting them through, washing them down, and miva 

 up the valleys with di'ift from their sides. 



The average width of the ranges would be about twelve 

 miles, the heis-ht above tbn P-Pnornl Ipvel of the basin froi^ 



1,000 to 4,000 feet. 



itly about 



miles wide, and often of great length ; but more frequently they 

 are limited above and below by transverse ranges, which, 



i 



T 





14. 



Is 







■* 



