270 GEOLOGICAL SURVEY OP" THE TERRITORIES. 



As the valley turns westward, it becomes somewhat narrower ; and 

 laminated porphyritic trachytes appear on the northeastern side, at first 

 capping the spurs like isolated forts, and then forming, as it were, a row 

 of casemates just below the crests of the hills. At two points this rock 

 descends nearly to the water's edge; but the valley soon opens out 

 again, with broad bottoms on the cast for several miles, to opposite the 

 mouth of Fall Creek, where basalt appears upon the eastern side as it 

 had done on the western some miles higher up. The upper part of this 

 valley-flat is covered with sage-brush, but the lower half is full of the 

 richest of pasturage, except only such portions as are occupied by 

 beaver-dams and bayous. Along these water-courses, large thickets of 

 black-haws were most thickly covered with ripe fruit, but the crop of 

 service-berries was almost an entire failure in all this region. At sev- 

 eral points we noticed the abundant rose-bushes covered with hips, 

 which were so soft when ripe as to have the translucent appearance of 

 berries and to be very pleasant eating. This did not appear to be a 

 si)eciiic character, but was probably consequent upon the shortness of 

 the season, which, after the fruit is well developed, prevents the secre- 

 tion of the large amount of woody liber which elsewhere commonly 

 forms so hard a covering to the rose-hips, ^li through the caHon, as 

 well as along this lower valley, we noticed innumerable young plants of 

 the lupines, which abound in this region, prepared to make vigorous 

 growth as soon as the short summer o[»ens. 



Fall Creek heads some miles to the southward, in John Gray's Lake, 

 near the Caribou mines, and here leaps into the river over a terrace of 

 basalt perhaps 30 feet high, forming a very pretty fall, which has given 

 the local name to the stream. A short distance below, we forded with 

 difficulty, the water coming over our saddles. From this point the 

 basalt lines both sides of the river, wnth very slight exceptions, to the 

 Great Snake Eiver Basin, and, according to report, to the Columbia. 

 About four miles below Fall River, these basalt-walls close in the river's 

 edge and form the lower canon. At .this point, two distinct beds of 

 basalt appear, separated and underlaid by beds of river-sand, partly 

 loose and nearly wliite, partly dark greenish and rusty brown, and con- 

 siderably cemented with iron. These sands include great nund)ers of 

 pebbles of basalt partly rounded. At one point, the lower bed of basalt 

 slopes eastward at an angle of about 15°, indicating a probable source 

 of flow situated in the mountains to the southwestward, though possibly 

 due rather to ui)heaval. At another point, the basalt is curved above 

 beds of sand and gravel having a curved surlace, which {)laiuly formed 

 a bar in the old river-bed. These deposits spread ui) against the edges 

 of limestones and sandstones of the mountains on either side. 



At the base of the mountain on the southwest side of the valley, just 

 above the head of this lower caiion, calcareous deposits, from now extinct 

 springs, form a heavy .mass, reaching about 100 feet up the mountain 

 side. A small butte, nearly separated from the mountain behind, 

 divides from the main valley the basin of a small stream which goes by 

 the name ot Swan Valley. The base of these western mountains is com- 

 posed of gray quartzites. followed by coarse and fine white sandstones, 

 and a very fine grained white dolomitic limestone, all of uncertain age, 

 though older than the overlying limestones, which contain a few Car- 

 boniferous fossils. The dips are sharp to the southwest, and the wash 

 of the stream brings downi iragments of red sandstone, which indicate 

 that the higher beds here occu[)y their reguhir position. 



The lower canon is w^alled with basalt for from 200 to 400 feet, in 

 many places perpendicnlarly, though elsewhere the slopes are more mod- 



