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Despite the activity on its surface, most of the talus is probably quite
stable, except for a small amount of compaction, unless its base is under-
cut by stream action or glacial erosion. The lower adit on the Granite
Basin mineral claims, for example (See page 217), has been driven 104
feet through talus blanketing the wall of the cirque. The outer slope of
the talus lies at the angle of repose of large fragments, which here as
elsewhere (Behre, 1933) attain a uniform maximum angle of about 36
degrees. Rock-fall on this talus was sufficiently abundant that exploration
of the mineral deposits was hazardous in places, and open-cuts at the
edge of the talus and trails on the talus itself were soon obliterated. The
adit had been abandoned for 12 years when visited by the writer, but
showed no sign of displacement or distortion by movement of the talus,
and its relatively light timbers had not been destroyed. In a few places,
especially at the foot of couloirs carrying considerable water, wedging and
heaving by interstitial ice may be a factor, along with the accumulation of
avalanche debris at the foot of the slope, in producing an irregular, concave
profile of the talus. (4) In places, frost-riven fragments have formed
‘streams’ that are flowing, in a manner that resembles the behaviour of a
viscous mass; these ‘streams’ are the puzzling rock glaciers, some of whose
features, and the problems they present, are discussed below.

Of the total amount of disintegrated rock removed from the higher
mountains, the proportion removed by wind is not known, but may be
considerable, especially with rocks such as gneissic quartzites and schists,
which tend to disintegrate to small flaky fragments. The remainder of the
material mainly becomes felsenmeer, and creeps slowly down the slopes.
About half of the sheets of felsenmeer terminate at cliffs or on over-
steepened valley slopes, where the fragments break free and plunge head-
long to the lower slopes, there to become talus. A smaller proportion of
material travels directly, via rock-fall or avalanche, from the outcrop to
talus. The amount of material transported by rock glaciers, over the
map-area as a whole, is small; it is probably of about the same order of
magnitude as that carried by the normal ice glaciers under present climatic
conditions.

Rock GLACIERS

Rock glaciers have been observed in all the higher mountain units in
Aiken Lake map-area, but are best developed in the region of rugged,
alpine topography in the west and southwest parts. They occur at eleva-
tions down to 4,900 feet above sea-level. The largest observed rock glacier
measured 2,700 feet from its snout to the distinct junction with the talus
slope at its head. Most of these bodies head on steep slopes at the angle
of repose of talus (36 degrees maximum), but the main body of the rock
glacier may flow on much flatter slopes, and tongues have pushed down
valleys with an average gradient of as little as 12 degrees. Some rock
glaciers, still active, have become detached from the steep slope at their
head. All are discrete bodies, with unstable, oversteepened sides and snout,
and an upper surface raised a few tens to as much as 200 feet above the
surrounding talus. The upper surface commonly has a billowy, rolled
appearance (Plate VIA). At least four of the rock glaciers examined are

advancing, and are overriding ground that has not received talus or moraine
in the recent past.