Page:Popular Science Monthly Volume 61.djvu/239

Rh numerous adits penetrate the white gravel, and are marked by long heaps of tailings which descend from them towards the creek.

What little is known of the geology of the Klondike district can be stated in a few words. The auriferous area is occupied by Palæozoic schists, which may be roughly distinguished as grey or green chlorite-schist and mica-schist, and a light colored or white sericite-schist. These are bounded on the north—upon the right bank of the Klondike River—by a mass of diabase and serpentine, winch constitutes the Moosehide Mountain; and on the south—on the left bank of the Indian River—by a series of quartzitic slates, schists and crystalline limestones.

The auriferous creeks are entirely situated in the micaceous schists, which constitute the bed-rock everywhere. Mr. McConnel, the government geologist, regards these schists as having originated from quartz-porphyry and other eruptive rocks, but they have been much crushed and altered and entirely recrystallized from their original condition. They are intersected by numerous bands and bosses of more recent eruptive rocks—quartz-porphyry, rhyolite, augite-andesite, diorite, basalt, etc.—and also by numerous quartz veins. In the northern and northwestern portions of the area occupied by these Klondike schists, are both broad and narrow bands of a black graphitic schist, which can sometimes be traced across the valleys.

The veins and stringers of quartz which are so frequent throughout the district have for the most part a very barren appearance, but they are sometimes mineralized to a small extent and contain a little iron pyrites, argentiferous galena, and—very rarely—gold.

Up to the present, however, the gold has been exclusively won from the gravels in the valleys, and not from the quartz veins.

The gravels are mainly of two sorts:—(1) those which constitute the floors of the present valleys and have been laid down by the present streams; (2) those which cover terraces upon the sides of the valleys and represent old valley gravels which have been cut through by the present streams.

The gold mining was at first carried on entirely in the lower gravels, and it was in them that the precious metal was first discovered. These are sandy gravels consisting of pebbles of quartz and schist—in fact, they are made up of the same materials as the bed-rock, and contain nothing that might not have been derived from the breaking up of the rocks of the district. There is no reason to believe that they were derived from any other source, and some of the pebbles are so lightly rounded that they have clearly not traveled far. Among the minerals which I have seen from these gravels are haematite, rutile, pyrites, graphite, cyanite, garnet, cassiterite, epidote and tourmaline; also barytes and mispickel.