Page:Popular Science Monthly Volume 55.djvu/328

314 action of the stream. Let it be remembered that the Yukon has a current ranging up to seven miles, or to eight, as some of the navigators say, and that in certain months it is swiftly ice-bound both on top and at the bottom, and heavily charged with bowlders, and one may well realize the work of which it is capable. That with which I have debited it is purely hypothetical or conjectural, but it may serve a purpose in the elucidation of the main problem.

In its more distinctively geological relations the Klondike region may be broadly defined as one composed in the main of schists and schistose rocks, defining an area of considerable disturbance. Owing to the limited number of outcrops, by far the greater part of the surface being still buried beneath vegetation of one kind or another, the variety of rocks included within the region can best be told from an examination of creek bowlders or the different dumps that mark hundreds of diggings and prospect holes along the various valleys and gulches. Some of this output in which may be found fragments of quartz and quartzitic schist, of mica, hornblende, and chloritic schists and slates, of granitic gneiss and gneissose granite, porphyry, diabase, diorite, and quartz (quartzite), is probably extra-territorial, having been washed in at a time when a more extensive foreign water had access to the region; but there is enough of outcrop to show that most, and perhaps all, of the types here indicated are really a part of the tract. The schists and schistose rocks, whose age from direct evidence in the field I was unable to determine, but which are almost certainly the equivalents in greater part of the Birch Creek series, as described by Spurr from the American side (Birch Creek and Forty Mile districts), constitute the kernel of the region. Observation is as yet too limited to permit of a positive classification of these schists according to their natural relations, and the reasons that have prompted some to consider them as being in part of pre-Paleozoic age are not quite clear to me, although they may easily be such. Of granite and true gneiss in position I saw practically nothing, and the limestones and marble were not sufficient in quantity to permit me to identify the heavy beds which are considered to be the distinguishing element of the Forty Mile series. The beds where exposed show in most parts steep dips—in places standing almost vertically—but in how far these dips are uniform or the reverse, or in any way define a line of strike with anticlinals and synclinals, must be left for future close examination to ascertain.

Great lumps of white or pinkish quartz, some of them in situ, others washed or rolled down the open slopes, occur at many points of some of the mountain elevations, indicating the presence of dikes