PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 833 



Mountain masses form the most conspicuous features of conti- 

 nents, and the study of their structure, scenery, geology and min- 

 erals, is the most interesting lesson in the curriculum of the geog- 

 rapher. 



We shall obtain the clearest conception of the Rocky mountains, 

 by understanding that the great interior of the United States, from 

 the Mississippi river to the Pacific ocean, was at one time in the 

 history of the North American continent, a vast level plain, simi- 

 lar in its physical features, and geological construction with the 

 southern half of New Jersey. 



This plain, west of longitude 105° of Greenwich, has been ele- 

 vated above the ocean from 5,000 feet to 10,000 feet, and main- 

 tains a great elevation westward to longitude 125°, Avhere it begins 

 rapidly to fall off in height to the level of the sea. Along this 

 elevated plain, four grand mountain ranges have been pushed 

 through, breaking and distorting the rocky crust of the plain, and 

 carrying up fragments on their steep slopes and summits until 

 their hoary heads are lost in the clouds, or are capped with eter- 

 nal snow. 



The first or eastera range, enters the United States in latitude 

 30° N, in two parallel systems. One crossing the Rio Grande 

 river, at the Grand Canon, the other at El Passo, and pursuing a 

 northward course, sends off spurs in various directions. It winds 

 in and about the parks, then trends off north-westwards into the 

 British possessions, and pursues its course to the Arctic ocean. This 

 elevation forms the line of demarcation between the waters flow- 

 ing east and west. 



The second grand range lies west of the main or first range, and 

 consists of numerous short spurs and mountain masses, of which 

 Mintah, Bear, Wasatch, and Humbolat, form the most prominent. 



The third and fourth are double ranges, trending off from the 

 sources of the Rio Grande to Point Conception, and from thence 

 are continued northAvards in the Coast-range, Sierra Nevada and 

 Cascade mountains throujrh Orejron and Columbia, into the Hud- 

 son Bay Company's possessions, where they are finally merged 

 into the Rocky mountain range. Fortunately for men dwelling 

 upon either side of these mountains, they are not continuous, but 

 gaps are left, which show remnants of the original plain, and offer 

 low summits for the passage of emigrant trains, and the future 

 locomotive, 



[Am. Inst.J AAA 



