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.