270 GEOLOGICAL SURVEY OF THE TERRITORIES. 



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

 laminated porphyritic trachytes appear on the northeastern sjde, 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; bat the valley soon opens out 

 again, with broad bottoms on the east for several miles, to oi3posite the 

 mouth of Fall Creek, whei;e 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 

 specific 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 fiber which elsewhere commonly 

 forms so hard a covering to the rose-hips. AW through the caiion, as 

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

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

 growth as soon as the short summer opens. 



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, with 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 white, partly dark greenish and rusty bi-own, and con- 

 siderably cemented with iron. These sands include great numbers 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 upheaval. At another point, the basalt is curved above 

 beds of sand and gravel having a curved surface, v.diich plainly formed 

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

 of limestones and sandstones of the mountains on either side. 



At the base of the mountain on the south vTest 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 of Swan Valley. The base of these western mountains is com- 

 l)osed 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 down fragments of red sandstone, which indicate 

 that the higher beds here occupy their regular position. 



The lower caiion is walled with basalt for from 200 to 400 feet, in 

 many places perpendicularly, though elsewhere the slojies are more mod- 



