314 POPULAR SCIENCE MONTHLY. 



dermining 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 1 have debited it is purely hypothetical or con- 

 jectural, but it may serve a purpose in the elucidation of the main 

 problem. 



In its more distinctively geological relations the Klondike re- 

 gion 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 out- 

 crop 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 suffi- 

 cient 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 anti- 

 clinals 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 



