100 



The old schist floor of the district is penetrated at 

 numerous points by intrusives belonging to several groups. 

 A massive, coarse-grained, grayish granite resembling the 

 Coast Range granites, cuts the sedimentary schists in 

 Yukon river below Indian river. Serpentine, derived in 

 part, at least, from peridotites, occurs at several points 

 on the crest of the ridge separating Hunker creek from 

 the Klondike, and numerous small, usually oblong areas 

 of comparatively recent rhyolites and andesites are 

 scattered irregularly throughout the district. Massive 

 diabases occur on Indian river below New Zealand creek, 

 and in dykes in the Yukon valley opposite Indian river, 

 and on Eldorado creek. Unaltered sedimentary rocks 

 consisting of clays, shales, sands, sandstones, tuffs and 

 conglomerates nearly destitute of determinable fossils, but 

 probably of Tertiary age, overlie the schists in the lower 

 part of the valley of Last Chance creek, and in separate 

 depressions at several points around the outskirts of the 

 district. These recent sedimentary rocks are associated 

 in every area with dykes, stocks, and sheets of andesite, 

 and in places, with dykes and small areas of diabase. 



As Klondike district has not been overridden by ice, 

 the surface rocks, as is usual in unglaciated regions, are 

 deeply weathered. A thick covering of decomposed schist, 

 usually intermingled with the slide rock, mantles the 

 sidehills nearly everywhere. On the ridges the covering 

 is less, and the schists, often worn into fantastic shapes, 

 in places project above the general surface, or are exposed 

 along the sides of the steeper hills. 



The surface materials are also permanently frozen. 

 The thickness of the frozen stratum varies considerably, 

 and is less on the ridges than in the valleys, and less also 

 on southern than on northern exposures. A shaft on the 

 ridge south of Eldorado creek reached unfrozen ground at 

 60 feet (18 -2 m.), while one in the valley of Eldorado creek 

 was stopped by running water at a depth of over 200 

 feet (61 m.) Another shaft, sunk through gravel on the 

 plateau between Bonanza and Klondike river, passed 

 through the frost line at a depth of 175 feet (53-3 m.). 

 The summer heat has little effect on the frozen layer, 

 except in the few places where the surface is unprotected 

 by moss. Exposed gravel beds in favourable positions 

 thaw out to a depth of 4 to 10 feet (1-2 to 3*0 m.), but 

 where moss is present, frost is always encountered close 

 to the surface. 



