Hanging Valleys of Georgetown, Col. — Crosby. 43 
Leavenworth mountain and occupied by Georgetown, nearly 
the entire field of the study being - shown in Figure 1. Below 
the high moraines enclosing Green and Clear lakes, the valley 
of Leavenworth creek is wide and its gradient low, the stream 
meandering somewhat across its approximately base-levelled 
floor. As it approaches Georgetown, however, the creek begins 
to trench the floor of this mature mountain valley and, falling 
about 700 feet in the last mile, it escapes abruptly into the still 
broader Georgetown valley, through the deep V-shaped gorge 
shown in Figure 2, and less distinctly in Figure 1. The general 
relations of the two valleys are well expressed in Figure I, 
which affords an excellent transverse profile of the upper val- 
ley and shows it ending abruptly downward in a steep and al- 
most precipitous slope, and thus clearly holding the relation of 
a hanging valley to the lower valley. 
The main problem, of course, lies in the significance of 
this break between the two valleys ; and three general explan- 
ations demand consideration — fluvial erosion, glacial erosion, 
and displacement. 
Obviously the floor of the valley of Leavenworth creek was 
once continuous with the floor of Clear Creek valley. The first 
explanation of the existing discordance, or lack of continuity, 
would mean that Clear creek has, in later times, lowered its 
bed more rapidly than Leavenworth creek, by virtue, we may 
suppose, of the advantage which, during the elevation of the 
range, a main stream would enjoy in experiencing acceleration 
more promptly than its lateral or right-angled tributaries. This 
is an important principle, and fully competent, no doubt, to 
explain many hanging valleys ; appearing, for example, to ac- 
count perfectly for the hanging tributaries of the upper San 
Joaquin river in California. But the conditions at Georgetown 
are clearly unfavorable to its application, since the escarpment 
in which both the valley and gorge of Leavenworth creek ter- 
minate is in the lee of Leavenworth mountain with reference to 
the direct and normal course of Clear creek, and cannot pos- 
sibly be regarded as due to the erosive action of the latter. The 
hypothesis of more vigorous glacial erosion in the main valley, 
appealed to by Davis and others in explanation of some of the 
hanging valleys of the Alps, and more recently of other dis- 
tricts, is beset by still greater difficulties here; for I have failed 
