TERTIARY 309 



basins, either of lacustrine or flnviatile origin. That described here 

 ai^pears, in part at least, to be of fluviatile origin. The distribution, as 

 represented on the map (figure 2, page 278), indicates that a belt of 

 the Kenai rocks runs parallel to the Yukon from Eagle to Birch creek. 

 While this zone has not been traced continuously, it is sufficiently well 

 known to justify the opinion that it was originally deposited as one con- 

 tinuous belt. The otitline of this formation, as represented on the map, 

 is in part based on the observation of Prindle and on statements made by 

 prospectors. The distribution, as will be seen, is very suggestive of an 

 old river channel, and the lithologic character rather bears out this as- 

 sumption. ]\Ioreover, the conglomerate of the Kenai on Woodchopper 

 creek and Seventymile have been found to be auriferous, which also lends 

 weight to the assumption that the deposits are of fluviatile origin. 



No beds have been identified on the Yukon which are positively known 

 to l)elong to the Pliocene or Miocene. It seems probable, however, that 

 some terrace deposits may be of late Tertiary age. Such interpretation 

 of the facts in hand has been made by both Spurr^^^ and Collier.^^^ 

 These beds were not studied by the writers, and will therefore not l)e 

 described here. 



QUATERNARY 



The deposits included in the Quaternary embrace two groups: (1) the 

 sand, gravels, and silts of the present drainage system, and (2) the 

 gravel, sands, and silts occurring as terraces along the Yukon and its 

 tributaries, which, in the absence of evidence to the contrary, can be 

 assigned to the Pleistocene. The scale of the map and the lack of detailed 

 information have made it necessary to indicate both groiips of deposits 

 simply as Quaternary. 



The recent deposits need no detailed description. Along the Yukon 

 tliey include coarse gravel, found both in the river bars and in low ter- 

 races, while in the smaller triliutary streams they constitute the flooring 

 of the valleys. Near Circle, where the flat of the Yukon begins (see map, 

 page 278), the stream deposits are chiefly fine silt, often frozen, and at 

 low and medium waters standing as a bluff 10 to 20 feet above the river 

 level. The gravels of the smaller streams are usually coarse, containing 

 very little silt. 



The deposits here grouped as Pleistocene embrace some stream terraces 

 and extend from 25 to 200 feet above the present waterlevcl. Specially 



1^ Geology of the Yukon gold district, pp. 196-200. 



133 The coal resources of the Yukon. Bulletin no. 218, pp. 16-18. 



