544 W. L. UGLOW AND W. A. JOHNSTON.

region but accomplished little erosion; valley glaciers were not
sufficiently extensive or long-lived to be effective agents of
erosion; while the valley bottoms were protected from erosion be-
cause of the narrowness of the valleys and the presence of outwash
deposits overlying the Tertiary gravels. A part of the Tertiary
gravels, therefore, was preserved. Some of the placers are post-
glacial in age and are the result of the concentration by streams of
the gold in the gravels, which were caught up, by means of ice-
erosion, in the glacial drift. The Tertiary belt of weathered rocks
was largely removed by ice-erosion. In places, however, deeply
weathered rocks occur beneath unweathered glacial drift showing
that the products of Tertiary weathering were not entirely re-
moved by the ice. Since the depth of post-glacial weathering is
slight, it is probable that the upper oxidized and highly fractured
parts of the veins containing free gold are, in large part, remnants
of the Tertiary belt of weathered rocks.

TOPOGRAPHY AND GENERAL GEOLOGY.

The district in which the placers occur is part of an uplifted and
highly dissected plain-like surface, which now has elevations vary-
ing from 5,500 to 6,300 feet above sea level. The streams flow,
for the most part, in comparatively narrow and deep V-shaped
valleys incised into the upland. In places, near the headwaters of
the streams, the valleys have the U-shaped cross-section character-
istic of glacially-eroded valleys. They broaden out in their lower
parts, where they are deeply drift-filled and have alluvial flats.
The main producing creeks head in Bald mountain plateau near
the central and highest part of the area, flow north, northeast and
northwest, and, at a few miles from their sources, occupy valleys,
the bottoms of which are about 2,000 feet below the plateau level
The depth of the present valleys and the geological structure show
that several thousand feet of rock have been eroded from the
region.

Two series of metamorphosed sedimentary rocks occur in
the area. The lower or Cariboo series, which consists of quartz-
ite, sericite schist, slate and limestone, underlies unconformably