THE HIGH CASCADES IN CENTRAL OREGON 
591 
dence of the recency of volcanic activity 
is to be seen in the innumerable lesser, 
though more perfect, cones scattered up 
and down the range and the hundreds of 
square miles of barren scarcely traversi- 
ble broken rock surfaces resulting from 
their outpourings. 
Near by to the northward stand Black 
and Belknap craters, a bird's-eye view of 
which reveals clearly the manner of 
eruption, successive gigantic tongues and 
lobes of ropy, viscous, seething-hot lava 
spreading, like thick molasses, from an 
overflowing subterranean reservoir of 
supply. At times the eruptions were vio- 
lent and the ejectamenta blown into the 
atmosphere in the shape of volcanic 
gravel, lapilli. and dust. Enormous quan- 
tities of such fragmental material have 
been scattered over the region. The so- 
-called cinder cones are largely built in 
this way. 
With the exception of North Sister, 
the ascent of the peaks is not difficult. 
South Sister is readily approached from 
the westward, a course taking advantage 
of the several snow slopes on the south 
■of west side having been found most 
feasible. The summit of North Sister 
<:an be reached by following up the 
notched apex of the ridge from the south. 
The entire structure of this mountain 
is in such a state of decay that all of its 
rsteeper slopes are occupied by unreliable 
slide-rock. These are being constantly 
replenished from the rapidly disintegrat- 
ing ledges above, so that a secure footing 
or even trustworthy hand-holds are not 
-among the certainties afforded him who 
■essays the climb of North Sister peak. 
For the average climber the ascent of 
Middle Sister from timber-line is a vigor- 
ous five hours' work. The early part of 
the climb is chiefly a clamber over rough 
boulder slopes, interspersed with long 
snow inclines, interest in which in climb- 
ing up is not to be compared with the 
-exhilaration of tobogganing them on the 
way down. 
At intervals one travels over fairly 
smooth areas of glass-like obsidian, dark, 
"brilliantly reflecting surfaces, often stri- 
ated or furrowed, or exhibiting the char- 
acteristic billowy roches mouttonnees 
produced by past glacial action. 
x\gain, a detour is necessary to avoid 
steep faces or abrupt masses of beauti- 
fully columned basalt, individual speci- 
mens of which show a dense black matrix 
flecked with a plentiful scattering of 
bright green olivine grains, and less fre- 
quently of phenocrysts of plagioclase 
feldspar. Emerging promontories of 
porphyritic andesite of towering propor- 
tions, displaying conspicuous structural 
peculiarities, are also objects of interest. 
These features all lend support to the 
fact that the process of eruption in the 
formation of Middle Sister was predomi- 
nantly a quiet one. From an unknown 
number of breaks in her sides vast cou- 
lees of molten lava stiffly flowed down 
her slopes and deluged the surrounding 
country. The extensive work of the 
glaciers and the ceaseless action of the 
weathering agents have so far obscured 
the original course of events here that 
only the keen, interpretative eye of the 
geologist is able to decipher the moun- 
tain's life-history. 
About a mile of the ascent of Middle 
Sister can be made over the ice and snow 
fields of the Renfrew Glacier. Its sur- 
face is not badly interrupted by crevasses, 
and rarely is it so steep as to render re- 
course necessary to more rigorous means 
than a safe, dependable alpenstock. The 
last i,ooo feet to the summit is again a 
clamber up an increasingly steep incline, 
covered for the most part with alternat- 
ing loose slide-rock and coarse boulders 
of all shapes and dimensions. Over the 
latter hands and feet about divide honors 
in facilitating ascent. 
The view from the top of Middle Sis- 
te-T is one of surpassing interest. To the 
westward the undulating forest green 
blends dimly, through the August haze, 
into ;hc darkened outline of the distant 
Oregon Coast Range. Down the Cas- 
cade Range looms South Sister, with her 
guardian ramparts, the Husband and 
Broken Top, to the right and left respect- 
ively. Beyond, Diamond Peak is within 
the range of vision, and, somewhat be- 
dimmed. Mount Thielsen, 75 miles away. 
At all angles to the westward the placid 
blue of nestling mountain lakes is a 
pleasing relief in the monotony of forest 
landscape (see page 584). 
