546 W. L. UGLOW AND Ww. A. JOHNSTON.

summits and the existence of glacial strice at high levels show that
an ice-sheet covered the whole area and that the general direction
of ice-movement was towards the southwest. That this move-
ment, however, was slight is shown by the fact that the greater
part of the drift in the several valleys is local in origin. At the
close of the Ice Age, small glaciers occupied several of the valleys
and accomplished some erosion of the bedrock. This erosion
probably accounts for the absence of placer gold in the upper parts
of some of the valleys. Glacial drift, consisting of boulder clay,
and stratified silt, sand, and gravel is abundant in the area, €x-
cept at the higher levels, and shows that in places at least there
was considerable ice-erosion of the bedrock. The presence of pre-
glacial gravels in the valley bottoms, however, shows that the
pre-glacial topography was not greatly modified by ice-erosion.
Outwash gravels formed in advance of the ice and the narrowness
of the valleys protected the valley bottom in many places from
erosion.

DERIVATION OF PLACER GOLD FROM AURIFEROUS QUARTZ VEINS.

The placer gold occurs along with other heavy residuals such as
pyrite, galena, scheelite and barite most abundantly in poorly as-
sorted angular and partly rounded gravel mixed with yellow or

Fic. 72. Crystals of placer gold, from Stouts gulch and Lowhee Creek,
Barkerville, B. C.; natural size. Loaned by John Hopp.

blue clay derived from disintegration of the gravel, and in broken
and partly disintegrated bedrock (in part ancient talus or “ slide-
rock’) and in cracks and crevices in the bedrock in the bottoms