DENVER & RIO GRANDE WESTERN ROUTE. 



209 



Mesaverde formation 



to the absence of streams and to the presence of a greater number of 

 beds of sandstone in the west than in the east, as well as to the more 

 massive character of these beds and to the greater dips which pre- 

 vail in this part of the plateau, for all these characteristics would 

 give a very different result in the forms produced by erosion. The 

 Book Cliffs west of Green Eiver are characterized by many bands 

 of sandstone, which may be followed by the eye for long distances 

 and which produce slight benches on the slope. A profile of a part 

 of the front of the Beckwith Plateau is shown in figure 55. 



A geologist accustomed to interpret the meaning of land forms 

 sees almost everywhere in these shale areas fragments of older sur- 

 faces of the land, preserved in terraces and benches. Some of these 

 remnants of an older surface were pointed out west of Grand Junc- 

 tion and again near Thompson. West of Green River they grow 

 more and more prominent as the traveler approaches the head of the 

 stream. They stand at 

 different heights above 

 the present general sur- 

 face, but commonly 

 some particular ter- 

 race — one that ranges 

 in height from 50 to 

 200 feet above the pres- 

 ent surface — is more 

 prominent than the 

 rest. The old surface 

 in this region was 

 probably more nearly 

 smooth and regular than the surface of to-day, and its slope 

 was doubtless not so great as that of the present surface. After 

 this old surface had been well developed, the lower country, though 

 it showed considerable differences in elevation between the higher 

 and the lower parts of its slopes, must have formed one general 

 plain. Then came a change, either an uplift of the land or an in- 

 crease in the rainfall. At any rate, the streams were able to cut; 

 deep trenches in this old surface, and their work has been continued 

 so long that it has left, here and there, only remnants of tlie once 

 continuous surface, and these remnants are the terraces and benches 

 that we see to-day. Terraces are very prominent in places west of 

 Woodside, and the traveler may be interested in studying them, not 

 as terraces but as remnants of that old surface. Indeed, he may be 

 able in imagination to reconstruct from them the old surface as it 

 existed before the streams had cut into it and carved the valleys of 

 to-day. 



Mancos shale 



Figure 55. — Profile of front of Beckwith Plateau. 



