GENERAL DESCRIPTION. 7 



the elements as if upheaved but a year ago. Wherever 

 found in the volcanic regions, the distinctive features of 

 this first plain are always the same. 



Farther north, out of the region of fire, this up- 

 heaval brought up the same rocks, though unburned, and 

 preserved the same characteristic perpendicularity of 

 elevation. This has, however, been very greatly modified 

 by the subsequent action of the elements ; and while the 

 upper surfaces even yet retain their general level, their 

 sides are scored with ravines, and the debris falling from 

 the top has rounded out the bottoms into almost the 

 semblance of ordinary hills. 



The second great horizontal upheaval pushed still 

 farther above tide-water, the continent already formed, 

 and added to it an immense area, forming what is now 

 known as the ' High Plains,' with a present elevation of 

 from 4,000 to 7,000 feet. 



Like the first upheaval, it evidently rose sheer from the 

 water ; but being of softer material it is, except in some 

 marked places, washed by rains and the action of the sea 

 into an apparent continuation of the third or lowest 

 plain. In many places this second plain stands up almost 

 as sharp and straight as the first, from which, however, it 

 is readily distinguished by the more recent character of 

 the rocks. It is through this second plain that the 

 streams have cut the deep canons which are so marked a 

 feature in plains scenery ; and when, as sometimes 

 happens, a stream has had to work its way through the 

 mass of material forming both first and second plains, 

 the canon formed is often sublime in its magnificent 

 profundity. 



The third plain, comprising all the portion from 

 3,000 or 4,000 feet above tide-water to the general 

 level of the Mississippi and Missouri Valleys, appears 

 to have been very recently formed of material brought 

 from the mountains and upper plains, and to have 

 been slowly and gradually lifted, or rather silted, out 



