382 EEPOET UNITED STATES GEOLOGICAL SURVEY. 



In regard to tlie age of the various deposits shown in the foregoing 

 section, the probable post- Jnrassic age of the variegated red shales and 

 sandstones and calcareous deposits vv^hich appear in the belt of country- 

 lying to the southwest of the initial point proper of the detail 

 section has already been remarked. Outlying the hard quartzitic 

 ledge No. 3 on the northeast, a heavy series of drab limestone 

 deposits, with interbedded variegated red, chocolate, and blue shales 

 and reddish sandstones is met with, the fossil contents of which furnish 

 conclusive evidence of their Jurassic age. It is difficult to estimate the 

 thickness of this series, but it is probably not less than 2,000 feet, and 

 this is believed to be considerably under the truth. The connection of 

 this series with the limestones within the quartzite terminus of the spur, 

 bed No: 45, was not traced, the slope being covered ^nth volcanic mate- 

 rials and debris; but on lithologic grounds the latter deposits were 

 compared with the Carboniferous. By reference to the report of Pro- 

 fessor Bradley (Eeport U. S. Geol. Survey, 1872, p. 270), it is probable 

 that this is the locality and these the identical exposrn^es" he mentions, 

 after crossing to the southwest bank of the Snake below the mouth of 

 Fall Creek, in which he saw " a few Carboniferous fossils." The latter 

 series may extend irp to, and include, the limestone bed 43, betwixt 

 which and the Jurassic limestone, 35 and 37 (?), intervenes a rather wide 

 belt, apparently filled with reddish -tinted brittle sandstones and softer 

 materials, which occupy the i)osition of the "red beds" of the Triassic 

 series. The firmer ledges of this series are seen to good advantage in the 

 opposite steep slopes on the south side of the caiion, where they are steei)ly 

 inclined southwestwardly, as represented in the accompanying diagram 

 of the section at this locality. The strike of these deposits, throughout 

 the line occupied by the present section, is pretty uniformly southeast- 

 ward and northwestward, the exceptions to this mean direction being 

 few and merely local. Professor Bradley saw, probably a little below 

 the point visited the present season, in connection with and succeeding 

 the quartzite above, " coarse and fine white sandstones, and a very^ fine- 

 grained white dolomitic limestone, all of uncertain age, though older 

 than the overlying limestones," which latter have been identified with 

 horizon No. 45 of the present section, in which he reported the finding 

 of Carboniferous fossils. Hence it might be reasonable to infer the 

 Silurian age of these basal deposits, whose tilted edges skirt the north- 

 eastern foot of the range, but for the fact tha,t dolomitic hmestones also 

 occur in the Carboniferous. 



Above the little trachyte butte the volcanics have been swept clear of 

 the foot of the range, the Snake bottoms extending to the quartzite ledge 

 which here forms the abrupt base of the mountain for a couple of miles, 

 when the volcanics again occur in a high bench, reclining on the flanli; of 

 the range. In the angles of the debouchure of Fall Creek, perhaps a coui)le 

 of miles above its mouth, the flank of the range is composed of heavy 

 deposits of bluish-gray limestones, j)robably of Carboniferous age, ap- 

 I)earing in low foot-hills from beneath the volcanics, 500 or more feet 

 above the river. As far up the vfinding and exceedingly rugged defile 

 of Fall Creek as we can see, the sedimentaries dip up-stream, or south- 

 westward. The quartzite which forms the base of the range at Butte 

 Creek, three miles northwest, has been denuded at the latter locahty, 

 giving i)lace to the Carboniferous, which holds this position for several 

 miles to the southeastward, when it also passes into the valleys space, 

 and it is in turn replaced by the highly tilted red sandstones, as will be 

 noticed more at length beyond. It Avould seem probable that the Car- 

 boniferous deposits formed a great arch, the oi)posite flank of which is 



