364 REPORT UNITED STATES GEOLOGICAL SURVEY. 



more belonging to the Willow Creek drainage, the remainder passing 

 over the gentler slopes descending into the mountain basin of Fall 

 Creek. In tlie gentle ascent which rises into the first ridge north of 

 Mosquito Creek, a heavy series of (1) reddish-buff or gray sandstone 

 associated with chocolate-red shales, rarely blue shales as in the foot of 

 the bluff on the south side of the stream, appears, dipping at an angle of 

 about 45°, southerly. These deposits are here largely developed, the 

 extent of the outcrops being probably not far from three-quarters of a 

 mile across. From this first sandstone crest the way descends, passing 

 along the broken saddle-crest to a corresponding and little higher ridge, 

 perhaps a mile distant. In the sag (2) obscure sandstone exposures first 

 appear, and beyond (3) another sandstone ledge outcrops in a vertical 

 position, inclosed in deposits of red shales. The second ridge is capped 

 by (4) a similar ledge of sandstone, dipping northward, followed in that 

 direction by red shales and sandstones interbedded, which appear in the 

 saddle connecting this with the water-shed ridge on which Station XIX 

 was made. In the southerly slope of the latter ridge alternations of (5) 

 gray, thin-bedded, spar-seamed sandstone and red shales are met with, 

 but in the crest these are replaced by (C) a thick bed of dark gray and light 

 drab, fragmentary limestone, dipping X. 45° E. at an angle of G0°. The 

 only fossil observed in this bed was a small indistinct Gasteropod appar- 

 ently identical with a form prevalent in the Laramie of this region. In the 

 northeast face of Station XIX ridge, a (7) heavy deposit of red shales fol- 

 lows, and is in turn overlaid by (8) a heavy bed of gray limestone, crowded 

 with a form of small Gasteropod in a state of silicification, but so badly pre- 

 served as not to be determinable with certainty. This ledge is so compli- 

 cated by cleavage and joint planes as greatly to obscure the true bedding, 

 which, however, was found to incline about northeast at an angle of 50°. 

 This is immediately succeeded by (9) red shales, including gray brown- 

 stained sandstone, more or less exposed in the foot of the steeper decliv- 

 ity, from which the descent to Fall Creek is over a broad grassy terrace 

 slope curiously eroded by the shallow lateral draws of the deeper drain- 

 age channels, which divide this sloping bench into so many regular 

 compartments. Owing probably to the nature of the deposits is due 

 both the long and comparatively gentle slope descending to Fall Creek 

 and the hidden or limited exi>osures met with along this part of the line 

 of the section. But such as they are, and to give the facts as full 

 record as possible, they are noted down in detail, their relative position 

 being approximately indicated in one of the accompanying diagrams, 

 where it will be seen that the strata referred to below occur over a space 

 above two miles across, in a direction at right angles to their strike. (10) 

 Gray, brown-stained, coarse-grained, laminated sandstone, dip 65°, X. 

 60° B. This bed is broken up by cleavage and joint structure, the 

 planes of which incline to the southwest at angles of 20° to 35°, and, but 

 for the laniinss which portions of the rock still retain, might be mistaken 

 for the bedding. A space several hundred yards across follows, in which 

 only a single rock exposure occurs, near the middle, showing (11) a similar 

 even-bedded rusty-gray sandstone. Then follows a dike-bke exposure 

 of (12) light gray, very hard sandstone, much broken up, and tilted on 

 end, though at certain points along the line of its exposure it is slightly 

 inclined from the vertical southward; again, an obscurely laminated 

 layer of the same bed dips at an angle of 60°, X. 40° E. (13) Eed shales 

 with calcite, also small abraded or nodular limestone pebbles in surface. 

 (14) Much jointed and fractured hard, gray, spar-seamed sandstone, 

 with slickenside surfaces. The rock shows false-bedded layers, but the 

 prevalent lamination in the dark-brown stained portions indicates an 



