SLOUGH CREEK. 209 



present sharply contrasting geological conditions. On the north Archean 

 gneisses prevail, and the sedimentary rocks which are present farther up 

 the valley are here entirely absent. The gneisses form bold but smooth 

 and glaciated exposures, extending down to the valley floor and showing 

 in abrupt hillocks and knolls, rising like islands above the meadows. The 

 Archean rocks present evidence of glaciation whose movement was from 

 the northeast, and the present topography is eminently glaciated. On the 

 opposite side of the valley the sedimentary rocks outcrop along the foot 

 slopes of Bison Peak and extend continuously along the valley wall to the 

 Park boundary. The thinly bedded shales and limestones of the Flathead 

 series form gentle slopes, whose covering of soil and vegetation generally 

 obscures the rocks. The Flathead quartzite is not seen here, the bed being 

 completely concealed beneath the alluvial bottom land. 



The lower slopes of Bison Peak below Plateau Creek show ledges of 

 a mottled, heavy-bedded, massive limestone exposed in cliffs 75 to 100 

 feet high, the summits of the beds forming flat-topped benches sloping 

 gently to the south. North of Plateau Creek the limestones extend down 

 to the valley bottom, and are well exposed on the slopes to the east, bench 

 upon bench of limestone showing on the slopes, with continuous bluffs 

 which are extremely difficult to cross in ascending the mountain. The beds 

 have a strike of N. 60° E. and dip 5° S., the highest ledges exposed being 

 found at an elevation of 6,400 feet, where the breccias rest upon them. 

 These limestones were traced along the mountain flanks as far north as 

 Elk Tongue Creek. This stream has cut along the contact between the 

 breccias and the limestones, and the exposure gives additional evidence 

 of the rugged nature of the country at the time the volcanic breccias were 

 laid down. The lower rocks exposed are thinly bedded limestones carrying 

 Middle Cambrian fossils, and the rocks are covered by groves of aspen and 

 grassy slopes whose character is readily recognized as differing from that 

 of the breccia slopes above them. 



The most conspicuous exposures of the sedimentary rocks are those on 

 the northern side of this valley, near its upper end, where the limestones 

 form cliffs which extend along the valley slopes for many miles to the 

 northward. The lowest exposures are thinly bedded limestones, light gray 

 in color, with yellowish mottlings, and lithologically similar to the Flat- 

 head limestones seen elsewhere. These strata make steep slopes which are 



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