DENVER & RIO GRANDE 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 Pl. IV, A). This red sand- 
stone is tilted up against the gneiss (pronounced nice) 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 coy- 
MIDDLE PARK : 
ae GREAT PLAINS 
SSS 
Bey Kota me Ce ad ats 
Horizontal scaie 
10 20 Miles 
Figure 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 
PAR re grec ee ER 
2 
ne ee the crystalline rocks of 
mountains are referred to in this 
guide they are called granite, though 
they really 
they may be different forms of the 
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 
