sT.joiLv.] JACKSON'S BASIN — QUATERNARY, 445 



the Gros Ventre, where it terminates in low benches less than 20 feet 

 above the stream, a couple of miles above its mouth. To the south it 

 soon merges into the eastern face of the group of low hills belonging to 

 the Lower Gros Ventre Buttes, and where the barrier of the chafing 

 brook is formed of early Palceozoic rocks. On the Gros Ventre below its 

 debouchure, a series of more regidar terraces is met with, with remnants 

 of tlie ancient terrace appearing on the south, where it is 100 feet or more 

 above the stream, and partlj'' encircles the low Tertiary hills, on which 

 erratics are occasionally met with at a much higher elevation. 



To the north of the Gros Ventre the ancient terrace, at lii'st much cut 

 up by minor water-courses, gradually assumes its pristine condition, form- 

 ing a broad, grassy, outlying glacis, bordering the wooded Tertiary foot- 

 hills of the Mount Liedy highlands, and terminating in a line of bluffs 

 hemming the east side of the Snake Bottoms, and which as suddenly 

 breaks down in steep decli^dties south of the debouchure of the Elkhorn. 

 Its surface .in the immediate vicinity of the foot-hills is moditied by a 

 series of low benches which run out diagonally into the basin, erosion 

 having swept away the finer materials, leaving long trains of rubble- 

 stones. Farther south, however, the light brown surface soil is generally 

 prevalent, here and there patches of light marly soil and limestone frag- 

 ments appearing in the midst, indicating subjacent late Tertiary deposits. 

 The coarse materials of this portion of the terrace show a variety of 

 rocks, chiefly quartzite, with rarely bowlders of volcanic rock. 



Between the broad basin-like debouchures of the Elkhorn and Buffalo 

 Fork, which are paved with water- worn bowlders, and interspersed with 

 meadow-flats and willow-fringed beaver-ponds, projects a tongue of low 

 Tertiary upland, which is enveloped in a heavy mantle of drift-like de- 

 posits. There is also here found a deposit which seems to be of Qua- 

 ternary age, composed of yellow earth and pebbles arranged in layers, 

 sometimes forming a homogeneous mass, the surface strewn with bowld- 

 ers. In places, as in the bluff's on Elkhorn Canon, and elsewhere in this 

 upland, a dark brown soil deposit is observed, probably the slow accu- 

 mulation during the time the waters of the Snake occupied a much 

 higher level than at present. 



The incipientterraces which are to-day in process of formation over the 

 wide-spreading beds of some of these little streams offer most interest- 

 ing subjects to detain the observer. AVe here see going on, in miniature, 

 the same fluvial actions to which are ascribed the various phenomena 

 observed in connection with the terrace formations of more ancient date. 

 But these later manifestations show the impotency of the currents of the 

 present streams, even in times of freshet, to wield the heavy materials 

 in their path ; hence their channels show a tendency to spread laterally 

 instead of confining and deepening theu" beds in the loose materials over 

 which they flow. 



Above the Gros Ventre we encountered the remains of a ditch, which, 

 it is said, was constructed some six or seven >'ears ago for the purpose of 

 couve;siug Avater to some placer mines opened in the gravels in the lower 

 bottom level. What success attended this enterprise we are unable to 

 learn. "Prospect pits" were found at several places in the valley, 

 which is periodically resorted to by small parties and solitary individuals 

 in quest of gold and adventure. Possessing a fertile soil and an abun- 

 dance of water, nought but its northern latitude (near the 44th i)arallel), 

 its altitude (0,500 feet), and the consequent shortness of the season, pre- 

 vent this becoming a prosperous agricultural district. During the time 

 of our visit (latter part of August) heavy frost was of daily occurrence, 

 ice forming an eighth of an inch thick overnight in the camp utensils j 



