PLACER GOLD OF THE BARKERVILLE AREA. 545

the Slide Mountain series * of Mississippian age, which is made up
of conglomerate, crinoidal limestone and thinly-bedded chert and
argillite. There are two sets of minor intrusives: felsite and
quartz porphyry dikes and sills are found cutting the Cariboo
series while diabase and diorite dikes and sills cut both formations,
but are mainly evident as concordant injections in lit-par-lit rela-
tions with the chert and argillite beds. All of these formations
are folded into an anticlinorium whose axial direction is north-
west. Two series of auriferous quartz veins, described elsewhere.
occur in the Cariboo series.

The placer deposits are partly post-glacial and partly pre-glacial.
A part also may be Pleistocene and due to concentration by glacial
streams. The pre-glacial deposits are by far the most important.
While no fossil evidence regarding their age is available, it is
evident that they are pre-glacial and Tertiary from the fact that
they lie on bedrock beneath the glacial drift and because only by
the wearing away of a considerable thickness of the bedrock and
concentration of the gold by streams could the rich placers have
been formed. As comparatively little stream erosion of the bed-
rock has taken place in Quaternary time, the rich goldbearing
gravels lying on bedrock must be Tertiary inage. The gold con-
tent of the post-glacial and glacial gravels was derived partly by
stream erosion of the glacial drift—which contains small amounts
of gold included in it—and partly from erosion of the pre-glacial
gravels and bedrock, into which the present streams have cut ina
few places. The area is largely drift-covered—especially the val-
ley bottoms, which in places are filled to a depth of 300 feet—and
erosion, since the disappearance of the glaciers, has been limited.
The post-glacial gravels are, therefore, of little importance except
locally.

Glaciation of the area, in Pleistocene time, was effected by a
large confluent ice-sheet or ice-sheets and to some extent also by
valley glaciers. The presence of erratics on some of the highest

“Previously called “ Bear River Series,’’ but here changed to “ Slide Mountain
Series’ to avoid confusion with McConnell’s “ Bear River Series” of Portland
Canal district, B. C.