444 EEPORT UNITED STATES GEOLOGICAL SUEVEY. 



peaks of tlie range, found evidence tliat persuaded them of the glacial 

 origin of the low parallel debris-ridges which there skirt the foot of the 

 mountains. To the south the evidence is far less convincing, indeed the 

 terraces not exhibitiug in their conformation other features than those 

 which are readily explained by flluviatile action in working over and 

 rearranging the loose materials accumulated along the base of the 

 mountains. Local glaciers may have and doubtless did occupy the 

 gorges that so deeply score the Teton and opposite mountain ranges ; 

 but one, in the course of a hasty visit, seeks in vain for those indubitable 

 signs which are the conspicuous infallible records of former glacial action 

 in other regions. This absence of scoring and grooving, the concomi- 

 tants of giaciation, may not seem so strange on maturer reflection, 

 esi)ecially when we take into consideration the potency of simple-acting 

 atmospheric influences, which involve.in their effects far more significant 

 results than the feebly engraved records of the reign of the glaciers. 



These high terraces terminate along Fighting Bear Creek in steep 

 dechvities 40 to 60 feet in height, reappearing at intervals lower down 

 the valley, but less and less conspicuous, while to the north the reverse 

 is true, the terraces increasing in magnitude, especially in the debouch- 

 ures of the principal gorges where they have formed barriers 500 feet 

 above the present level of the Snake, behind which nestle pretty lake- 

 lets, which Professor Bradley refers with good reasons to morainal 

 origin. So far as the present observations extend the local character of 

 these accumulations is manifestly apparent in the nature of their com- 

 ponents; the west-side terraces being almost exclusively made up of 

 granitic, gneiss, schists, and quartzite bowlders, with, as has before been 

 mentioned, reddish buff laminated sandstone and limestone debris preva- 

 lent in the later-formed benches, as along East Pass Creek in its passage 

 across the higher benches. Above the confluence of East Teton Creek 

 a high terrace sets in, which forms an extensive grassy plain 200 feet 

 and more in height above the river, gently rising to the west, where it 

 is bordered by the before-mentioned wooded morainal ridges, which lat- 

 ter, in places, project far out into the basin south of Jackson's Lake. 

 Professor Bradley has given a profile of this x)ortion of the valley, irom 

 levellings made by Mr. Hering, from which we gather a more correct 

 knowledge of its contour than is apparent when viewed at a distance 

 from the east side of the valley. This profile is incorporated in an 

 accompanying i3late of diagrams, which sufficiently explains those fea- 

 tures of surface reliefs dependent on the character of the sux)erficial 

 materials which fill the basin south of Jackson's Lake. 



On the east side of the basin there exists a greater diversity in super- 

 ficial contour, in part due to the presence of island -like remnants of sed- 

 imentary formations and eruptive effusions, but mainly to the modifying 

 changes wrought in the superficial deposits by considerable tributaries 

 which flow out into the basin from the eastern highlands. The more 

 imijortant of these are the Gros Ventre, Elkhorn, and Buffalo Fork ; but 

 there are other smaller water-courses which have effected marked local 

 changes in the materials in the way of their channels, and which have 

 thrown the ancient terrace into much confusion, eroding shallow basins 

 and building up low terraces of their own out of the materials which they 

 have swept down from the neighboring hills. This is true of the Little 

 Gros Ventre, and several small streams that drain the western flank of 

 Mount Leidy highlands between the Gros Ventre and Elkhorn. Out of 

 the old terrace the former stream has formed an abrupt barrier along its 

 right bank, 100 to 150 feet high, its face thickly strewn with bowlders and 

 pebbles. This barrier slopes off on the northwest in a long glacis to 



