DEN^^R & EIO GRAiSTDE WESTERN ROUTE, 9 



nels, and the traveler has ample opportunity to study its character-, 

 istics as the train turns and twists around the ravines or dives head- 

 long through the rocky tunnels. (See PI. IV, A). This red sand- 

 stone is tilted up against the gneiss (pronounced 7uce) or granite- 

 like rock that forms the bulk of the Front Range. 



When these beds of sandstone were formed they consisted of hori- 

 zontal layers of sand, which were laid down along the shore of a 

 body of water, just as sand accumulates to-day along the shore of 

 the ocean or of a large lake. The rocks upon which the sand rested 

 were granite and gneiss, from which some of it was derived, and the 

 sand lapped onto the shore irregularly, some beds extending much 

 farther inland than others, the distance inland reached by them at 

 one place or another depending on the form of the surface and the 

 height of the water. Finally, after the entire region had been cov- 



Oakota 

 Grand Lake .'.■, ^ _ , '-flo/j^ 



MJODLE PARK 



GREAT PLAINS 



Horizontal scale 



FiGUEB 3. — Arch of the Front Range restored. After Lee. 



ered by layers that eventually became sandstone, shale, and limestone, 

 the region on the west was lifted up hundreds or perhaps thousands 

 of feet, and the red sand, which had hardened into sandstone, was 

 bent upward in a great arch that may have extended entirely over 

 the present Front Range. The streams probably cut away the upper 

 part of this arch almost as fast as the land was raised, so that the 

 mountains may never have been much higher than they are to-day. 

 The work of the streams has been continued until all of the upper 

 part of the sandstone arch has been removed, as shown in figure 3, 

 and only the sharp upturn on the flanks, which can be seen so well 

 from the " Moffat road," has been preserved. 



The train climbs steadily, affording here and there beautiful views 

 far out over the plains to the east, and finally, when nearly above 

 Eldorado Springs, it turns suddenly to the left and enters a tunnel 

 that leads through the heart of the mountains. Beyond this tunnel 

 the roadbed is in granite,^ and the banding of this rock gives little 



'Wherever the crj'stalllne rocks of 

 the mountains are referred to in this 

 guide they are called granite, though 

 they really consist of granite, gneiss, 

 and schist. In some places the rock 

 may be entirely granite, and in others 

 it may be gneiss or schist; but at 

 many places these three kinds of rock 

 are intimately mixed, showing that 



they may be different forms of the 

 same rock. 



G. P. Merrill describes gneiss (A 

 treatise on rocks, rock weathering, 

 and soils, pp. 142-145, New York, 1906) 

 as follows : 



" The composition of the gneisses 

 is essentially the same as that of 

 the granites, from which they differ 



