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the plains. This feeling- is also mixed with surprise at the 

 sudden change from plain to mountain, the cause of which 

 has been a puzzle to many a traveller. The abrupt change 

 from plain to mountain is not more sudden, however, than 

 the change in the geological composition of the two systems 

 under consideration. The mountains rising along the border 

 line present in their rough and precipitous faces the strong, 

 bold outlines produced by the metamorphic rocks, the granite, 

 gneiss and the shists; while the sedimentary rocks at their 

 bases, the limestones, shales, slates, clays and chiefly sand- 

 stones, present a very different appearance. 



This border line extends in a nearly north and south line 

 about twenty miles west of Denver, and is admired for the 

 beauty of its outlines. The rapidity of its slopes (a marked 

 feature of the chain) afford a grand opportunity for the dis- 

 play of the effects of erosion, the summit of the range being 

 in many cases scarcely ten miles from the edge of the plains. 

 Any one looking at the map of Colorado will also be struck 

 by the beautiful arrangement of these chains en echelon. 



Geologists tell us that this range was first elevated from 

 the sea, and then that all these sedimentary rocks were de- 

 posited against their base. These sedimentary rocks at their 

 point of contact with the granites are not horizontal, but have 

 been turned up on end by the force exerted by the granite 

 mass, against which they were deposited, when it lifted them 

 to their present positions. Their slope to the east from this 

 point is not more than 60 at any place. They form the 

 basis of the great plain, and were once the bed of the sea 

 which covered them, and which on receding left those thou- 

 sands of feet of sediment to be carved out and carried off by 

 the ice and water, which have left such wonderful traces of 

 their power in this western country. 



The first feature of the lowlands that strikes the eye is the 

 low series of hills of a very even line of elevation, forming a 

 sort of horizon or belt near the foot of the mountains, cut at 

 intervals by the streams which descend from the mountains. 

 The ends of these hills that overlook the streams being after- 

 ward rounded, give each section a long, gently curved line at 

 their upper surface, which has earned for them the rather un- 

 fortunate name of " hogbacks." They seem to be a very 



