204 GEOLOGICAL SUEVEY OF THE TEKEITOEIES. 



about 20° iSr. 51° E., and containing a few fossils. These beds are 

 overlaid by the quartzites before mentioned, which here form a lofty 

 mountain-crest running northward for many miles. As they show here 

 great thickness and only moderate disturbance, I consider this a very 

 favorable locality at which to examine them for fossil remains ; but 

 none were found, and the precise age of the formation is uncertain. At 

 the angle of the canon, a large kuob of the limestones, perhaps 500 feet 

 in height, gives a fine view of the whole canon. From this point, the 

 basalt appears as a high flat-topped ridge, occupying the center of the 

 valley, on the west side of which the narrow valley of Goose Creek has 

 been hollowed out of the edges of the lower quartzites. A small stream 

 also comes in from the right, and has changed its channel once or twice, 

 so that a considerable knob of limestone and some small ones of basalt 

 stand out in the valley ; but the streams finally cross to the left side of 

 the valley, leaving the basalt entirely on the right. The road crosses 

 this for some distance, passing among walls and piles of the columnar 

 rock, and then descends to the lower level near Black Eock Station, 

 where the basalt abruptly terminates. 



At the angle of the canon, we had turned sharply to the west, so that, 

 instead of following the strike of the strata, as heretofore, we were now 

 traveling directly across the edges of the outcrops. Soon after we turn, 

 we meet the outcrop of the lower quartzites, upturned at various high 

 angles and strongly metamorphosed. The continuation of this cross- 

 section is confused : one anticlinal is plain and others probably exist; 

 but quartzites, limestones, calcareous schists, all highly metamorphosed, 

 are exposed with various dips ; and time and mosquitoes forbade the 

 working out of the details. These, however, though of local interest, 

 have no general importance, since they are not in the direct line of our 

 northern connection. 



Though we encountered mosquitoes and gnats in very troublesome 

 quantities at several other j)oints on our trip, yet they nowhere equalled 

 the mass which met us between Black Eock Station and the lower angle 

 of the caiion. Hundreds of thousands, at least, i)erished at our hands, 

 as we hastened through ; and such passages are of daily occurrence at 

 this season, but with no perceptible decrease in their numbers. My im- 

 pression is that this, being a somewhat sheltered point, is a sort of gen- 

 eral rendezvous for those of them who are tired of facing the strong 

 winds which so frequently sweep over the unobstructed levels of the 

 broad Snake Eiver plain, into which the caiion now opens, ui)on turning 

 northward again, after making five or six miles of westing. 



Here, again, we encounter basalt; but it seems to belong to a lower 

 layer than that we left at Black Eock. All over the great plain, indeed, 

 we find two or more layers of basalt, separated by greater or less thick- 

 nesses of sand and gravel, partly loose, partly consolidated by ferrugi- 

 nous, silicious, or calcareous cement. If two layers should be found 

 superimposed, at any point in the upper part of the caiion, I should 

 believe that they had resulted from two distinct eruptions from the 

 volcanic source before mentioned. As it is, it is not impossible that 

 these layers in the outer plain have been ejected from some central 

 source, have overflowed the i3lain, and so have run up into the mouths 

 of the valleys opening upon it. It seems hardly possible that, after 

 flowing seventy or eighty miles, the lava should still have retained 

 sufficient fluidity to spread out in a solid layer over the plain. What- 

 ever the source, the material had evidently become quite viscid ; for, at 

 some points, where it ran over small inequalities of the surface beneath, 

 it now stands in low mounds, which would not have been the case if 



