8T.J0HX.] BLACKFOOT RANGE GRAVEL CREEK. i)43 



ing the neighboring' mountain slope, as though the beds had been sud- 

 denly upturned or overturned, the weathered cleavage structure being 

 so marked as to give force to the deception ; but a careful examination 

 reveals the true planes of bedding, which, though obscure, agree with 

 the general southwesterly inclination of the strata in the adjacent mount- 

 ain declivity. The fossils noted in these beds consist of crinoidal re- 

 mains, two or more species of Zaplirentis, a Lithostrotion, resembling L. 

 proUferum, though distinct from that form; Spirifer, and Euomphalus. 

 The limestone is inteiiaminated with dark cherty bands, and more or 

 less intersected by seams of calc-spar ; at one point on the southwest 

 shoulder of the main ridge it shows an intercalated pale-reddish sand- 

 stone bed, the presence of which is regarded as indicating the approach 

 to the upper member of the series, as it seems to be developed in this 

 region. 



After emerging from its canon, the course of Gravel Creek crosses 

 a belt of rolling, grassy foot-hills, which form rather steep bluffs along 

 the stream 200 to 300 feet in height, and which are made up of a curious 

 aggregation of coarse materials arranged in more or less distinct layers 

 and inclining at a moderate angle, 15° to 20°, in the direction of the 

 mountain barrier, rising to the southwest and terminating in low, rounded 

 domes or ridges. These deposits are made up of an aggregation of more 

 or less abraded fragments of reddish sandstone, drab, and dark-blue 

 Carboniferous limestone, pebbles of white calc-spar and chert, held in a 

 matrix of very fine pinkish paste. Where it shows in heavy, weathered 

 masses, it presents the appearance of abreccia-conglomerate, the materials 

 being arranged in courses. Sometimes the coarse materials are replaced 

 by the pinkish paste, which often weathers away leaving miniature cav- 

 erns. These deposits appear to have some connection with the volcanics 

 of the vicinity, and from the nature of the cementing material or matrix 

 it seems very probable that then relations are more intimate with the 

 trachytes than with the later basaltic flows, a sort of volcanic conglom- 

 erate laid down in water. 



Immediately southeast of Gravel Creek a shallow trough skirts the 

 foot of the range, gradually deepening its bed for a distance of two 

 or three nnles, when it enters a defile between limestone ridges, in which 

 the strata incline away from the mountains southwesterly. The glade- 

 like upper portion of the little valley occupies a trough whose outer 

 rim is formed by the gently southwesterly upraised breccia-conglom- 

 erate, and whose surface of fine soil still retains traces of numerous 

 but long-abandoned buffalo-wallows, and an occasional bleached, half- 

 inhmned skull. After continuing its course in a monoclinal trough 

 between the Carboniferous limestone ridges a distance of a mile or so, 

 it receives an affluent from the mountains and suddenly bends south- 

 westerly, and thence for nearly a mile it pursues its course, choked with 

 beaver-dams, directly across the barrier ridge, and emerges into the 

 valley. Soon after entering this lower gorge the limestones are observed 

 to dip northeastwardly at an angle of 30° "to 40°, the strata holding the 

 same inclination to the debouchure, where the lower deposits are con- 

 giomeritic, which latter shows a low outlier on the west side of the 

 stream a little lower down. Still below, the breccia-conglomerate again 

 appears in the steep bluff acclivities, the latter deposit also dipping- 

 northeasterly. These latter deposits are here also accompanied by the 

 peculiar rounded, bluffy, superficial features before mentioned as char- 

 acteristic of these beds, ai*d it is further notable, in explanation of the 

 relative age of these supposed, in part at least, volcanic deposits, that 

 as soon as we gain the higher slopes just to the southeast the surface is 



