THE NORTHERN PACIFIC ROUTE. 
187 
past, flowed in this valley instead of in its present course below Eagle 
Gorge.! 
1The old and new valleys of Green 
River afford an excellent example of 
changes that may take place in the drain- 
age system of a country as a consequence 
of the invasion of a glacier. The river 
valleys on the west slope of the Cascade 
Mountains are in general well developed, 
showing that the streams have occupied 
them foralongtime. The original course 
of Green River below Eagle Gorge was 
doubtless north by way of Page Mill and 
Barneston, for the present canyon below 
Eagle Gorge is so narrow that it must have 
been formed comparatively recently. The 
relative size of the two valleys is shown in 
figure 38, which representsa cross section 
about 3 miles below Eagle Gorge. 
To divert a stream intrenched in a 
valley from 2,000 to 3,000 feet deep must 
have required a formidable barrier. Such 
a barrier could have been produced only 
+ ry Soot 
The exact manner in which the ice 
blocked this outlet of Green River is a 
matter of speculation, but probably the 
glacier came down the Sound after the 
local glaciers in Green and Snoqualmie 
valleys had melted back from the moun- 
tain front and crowded up the valley of 
Green River until it completely blocked 
that valley with a great dam of ice, hun- 
eds and possibly thousands of feet in 
thickness. This barrier seems to have 
been sufficient to raise the water of Green 
River until it flowed over a low divide 
River valley and a small stream flowing to 
the west past Palmer Junction. Beyond 
this divide the river found an unob- 
donsntond Wnt eth te ke +4 
to deepen and which it finally cut below 
the level of the former outlet by Barnes- 
By the time the ice had disappeared 
ton. 
Abandoned valley 
S of Greer Fiver 
YY y 
Ficurr 28 —Sacti 
URE 55, g 
Eppa Feige C 
f the valley of Green River below Eagle Gorge, Wash., com- 
ca aes Sega. ae" 
vhen it y 
1, +} ety : 
pareGa Witil LUO Valley i 
in one of four ways—(1) by a landslide 
which filled the valley below the point 
of diversion; (2) by a lava flow occupying 
ment of the land below the fault; or (4) 
by the blocking of the valley by ice. If 
were due to any one of the 
remain in the old valley some traces of 
the barrier, but, as no such features have 
been observed, it must be concluded that 
ice was the agent that caused the change. 
Ice would leave no permanent barrier, 
and so no surface indications would be 
expected, except the ordinary deposits 
are made by a glacier. Evidence 
—s 4s 7 j 
ee I eRe 
ice at a recent geologic date. 
Green River had become so deeply in- 
trenched in its new course that it per- 
sisted, and it remains to this day in the 
new valley it was thus compelled to 
occupy. ; 
Although this change occurred during 
the Great Ice Age, geologically it was 
valley in the vicinity of Eagle Gorge into 
the dim shadows of the narrow canyon 
below, in which there is barely room for 
the track between the river and the 
bluffs, and even to make this passage 
/ deep rock cuts and many crossings of 
| the stream are necessary. 
