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paths, as much as 100 feet wide and 4 mile long, lie in incongruous positions
on the slopes and valley floors, and attest to the presence of englacial and
perhaps superglacial streams.

Laminated silts and clays are widespread; many of them were probably
deposited in small, ephemeral, ice-dammed lakes. Most of the silt is inter-
layered with some gravel. The thickest observed section of apparently
lacustrine material consists of about 45 feet of laminated silt, clay, and
fine sand, deposited in a basin that covers the junction of the present
Tomias Lake, Ravenal Creek, and Swannell River Valleys.

The various minor topographic forms characteristic of glacio-fluvial
deposits made in contact with the glaciers themselves, such as eskers,
kames, crevasse fillings, etc., may be observed in many places; Tutizika
River Valley is outstanding in this respect. Weathering of the thicker drift
deposits has developed characteristic hoodoos and furrowed slopes (Plate
V A).

FROST ACTION

FELSENMEER AND TALUS

The most active single weathering agent at present effective in the
map-area is undoubtedly frost action. More than one-quarter of the
map-area is above timber-line and lacking in tundra vegetation, and is thus
exposed to direct mechanical disintegration; and on most of such areas the
slopes are sufficiently steep that disintegrated rock material is relatively
rapidly removed by gravity. Disintegration of the rock by frost action
appears to be the major process in the erosion of peaks and ridges, and
is thought to be the main factor in the development of a general accordance
of summit levels (Daly, 1912, p. 631).

The efficacy of frost action above timber-line is shown by the highly
shattered condition of most of the exposed bedrock, and by the immense
amount of angular rock waste, which occurs mainly as felsenmeer and
talus. Except in those cirques still occupied by active glaciers, the removal
of frost-riven fragments is accomplished by four main processes: (1) wind
action is remarkably effective in some places, and has commonly removed
all loose surface material less than an inch in diameter. The large snow
cornices that line the lee crests of ridges in late spring contain occasional
stones weighing up to a pound or more, which must have been blown
over the crest of the ridge onto the cornice by strong winter winds. There
is evidence that large marker cairns on high ridges, probably loosened and
heaved into unstable positions by frost action, have been literally blown
down within 3 years after their construction. (2) The more gentle ridge
crests and rounded shoulders are covered with a uniform mantle of frost-
riven fragments, or felsenmeer, which creeps slowly, more or less en masse,
directly down the slopes (Plates IT B, V B). The rate of creep is not
known, but in many places it is so slow that lichens cover the blocks, and
rock contacts can be followed across the felsenmeer in places, displaced
downslope but, apparently, relatively little distorted. (3) Where slopes
are steeper, or are interrupted by cliffs, the rock fragments descend rapidly
and chaotically as rock-fall, rock-slide, or avalanche, to collect on less
precipitous lower slopes as talus, nivation ridges, avalanche debris, etc.

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