198 REMARKS ON SANDSTONE AND 



of iron abound principally in those varieties nearest the gra- 

 nite, which are usually of a reddish colour. When these en- 

 ter into the composition of the rock in certain proportions, 

 they seem to disqualify it for withstanding the attacks of the 

 various agents, whose effect is to hasten dissolution and de- 

 cay. Highly elevated rocks of this descri|)tion may well be 

 supposed in a state of rapid and perceptible change. The 

 sharp angles and asperities of surface which they may have 

 originally presented, are soon worn away. The matter 

 wliich is constantly removed, by the agency of water, from 

 their sides and summits, is deposited at their feet ; their ele- 

 vation gradually diminishes, and even the inclination of their 

 strata becomes obscure, or is rendered wholly undiscover- 

 able. A soil is at length formed over the whole surface, 

 which gives support to a covering of vegetables. This is 

 probably the process by which have been formed the nume- 

 rous conic hills and mounds, that are now seen interspersed 

 among the highly inclined naked rocks of which I have been 

 speaking. These liills, often clothed with considerable 

 verdure to their very summits, add greatly to the beauty of 

 the surrounding scenery. The contrast of colours which is 

 here seen, often produces the most brilliant and grateful ef- 

 fects. The deep green of the small procumbent cedars and 

 junipers, with the less intense colours of various kinds of 

 deciduous foliage, acquire new beauty by being placed as a 

 margin to the glowing red and yellow which is seen on the 

 surface of many of the rocks. In the narrow but verdant 

 valleys, small pyramids and columns of the purest wiiite arc 

 met with, standing solitary and detached from any surround- 

 ing rocks. 



The district of country of which we have now been speak- 

 ing may, without impropriety, be denominated the valley of 

 the Platte, as the waters which flow from it are dischaiged 

 into that river. 



Near the summit of the small ridge which, running east 

 from the Rocky Mountains, divides the waters of the Platte 



