/ 
DENVER & RIO GRANDE WESTERN ROUTE. 159 
seen on the right in the cut edge of a well-developed terrace.*® The 
top of this terrace, when seen from a high point, appears to be a part 
of what was once the floor of the valley. 
Remnants of a similar 
though higher terrace may be seen in the foothills on the left at a 
much greater elevation. 
(See Pl. XLIV, p. 90. 
The traveler is now near the high mountains, and he may look up 
on the left to lofty peaks on which the snow banks of the preceding 
winter linger well into the 
summer and on which a 
fleecy mantle falls dur- 
ing the first snowstorms 
of early autumn, or even 
occasionally during a 
cold midsummer storm. 
The commanding summits 
which may be seen from 
time to time are Ouray 
Peak (altitude, 13,955 
Ficurs 40.—Formation of a rock terrace. 
feet), near Marshall Pass (altitude, 10,856 feet), and Mount Chipeta 
on the left, and a group of peaks known as Mount Shavano (altitude, 
“The mode of formation and hence 
the meaning of terraces is of great 
interest to the geologist who is at- 
tempting to unravel the history of the 
a 
sd very little by lakes, so that most 
f the terraces here were formed by 
cach water. 
treams may form terraces of two 
kinds, known as cut terraces and built 
terraces. A stream may flow against 
a bluff of solid rock and cut it away 
ed a terrace or ben uch a 
terrace is represented in figure a3 
a, has cut a vy: 
stream, alley in 
a , represented by the sank 
. After the stream has form 
flood plain it begins to meander or 
Swing from side to side acrosg the flood 
Plain. In the course of such a swing 
it may flow against the slope on the 
right and then, if the stream is ac- 
celerated by uplift, it will clean out 
its old valley and cut a trench (c) in 
its rock floor, leaving the part at 6 un- 
touched. The part at b is then a rock 
terrace on the side of the valley and 
merely a remnant of the old yalley 
formed when the stream was 
at a higher level. Such terraces are 
called cut terraces and are rather rare. 
The second kind of terrace is known 
A terrace is generally not built up di- 
y by a stream but is the result of 
the filling or partial filling of the val- 
ley and of its partial excavation by the 
taries, should be dammed by 
lava or other obstruction, it would be 
e load of this ma- 
terial, which would be dropped in the 
pond above the obstruction. In time 
