times whipped into foam- 
ing turbulence as they 
dash over stretches of 
steep stony bed, and again 
placidly winding a sinu- 
ous course through level 
reaches of grassy mea- 
dow. 
Many of them come 
from the tips of melting 
glaciers. The latter in 
their forward movement 
pulverize to a "flour" por- 
tions of the rock surfaces 
over which they flow. As 
a result the streams issue 
surcharged with fine sedi- 
ment, which gives to them 
a strong whitish or milky 
appearance. 
In the smallest streams 
this milkiness is most ap- 
parent late in the day, 
while during the early 
morning and forenoon the 
water runs perfectly clear, 
a phenomenon due no 
doubt to the influence of 
the heat of the day on 
the volume of the flow and 
therefore on the stream's 
ability to carr}^ the sedi- 
ment given to it. 
The Sisters peaks oc- 
cupy the apices of a flatly 
triangular area, the short- 
est distance between an- 
gles being about 5 miles, 
from North to South Sis- 
ter. Middle Sister stands 
intermediate and but 
slightly out of line to the 
west. 
These three points mark 
the roughly curved boun- 
daries of a former vast 
amphitheater, i n which 
the snows of ages past 
accumulated to form a 
large glacier that flowed 
eastward down the moun- 
tain slopes. The extension 
of this ancient ice-stream 
to a distance of at least 10 
miles from its source is 
today indicated by the 
presence of massive mo- 
582 
