508 EEPOKT UNITED STATES GEOLOGICAL SUEVEY. 



summits of tlie loftiest peaks were above the surface. It is barely possi- 

 ble that we might make an exception in the case of the Grand Tetons. 

 We may suppose that the materials were supplied from the numberless 

 volcanic fissures in unlimited quantities in a comparatively brief space 

 of time; but the period which would be required for the waters to 

 arrange this matter in the remarkably uniform and compact series of 

 strata Avhich we find at the present time must have been great. The 

 residts have been carried on upon such a stupendous scale that the mind 

 finds with difiicidty the courage to grapple with them or attempt to 

 explain them. And then, subsequent to the deposition of these enormous 

 beds of conglomerates, has been the Avearing out of cafions and valleys 

 2,000 to 4,000 feet in depth, the sculpturing of some of the most marvel- 

 lously grand and unique scenery on the continent." 



The relative age of this vast accumulation, a measure of which miay 

 be sought in the character of its components, leads us to infer its cOmr 

 paratively recent date. The coarse materials which enter so largely into 

 the composition of the stratified mass, especially noticeable in the con- 

 glomeritic portions, consist of fragments of all the older valcanic products, 

 as trachytes and laminated porphyritic trachytes, while the more modern 

 flows and eruptions have contributed fragments and bowlders of basalt 

 and scoriaceous lava. The base of the deposit, its contact with older 

 volcanic deposits and sedimentary formations, is so concealed by the im^ 

 mense talus accumulations wliicii bury the foot of the mountain-walls, 

 into which the deposit has been eroded, that we as yet possess few and 

 perhaps no satisfactory facts exposing the character of the earliest stages 

 of this remarkable deposit. In the approaches to Togwotee Pass huge 

 outliers of exceedingly sombre, jagged breccia, apparently in situ, and 

 in places disturbed or tilted from the original horizontal i)osition, are 

 met with at a level 1,500 to 2,000 feet or more below the neighboring 

 mountain-summits, and which may indeed belong to the foundation of 

 the deposit. The latter masses bear every appearance of intense vol- 

 canic action, as though their materials, rock fragments, sands, and mud, 

 have passed through a fiery ordeal and been so rapidly ejected as not to 

 allow their rearrangement by aqueous currents, but which latter pea?- 

 formed so prominent a part in the redistribution of the later accessions 

 to the great deposit. 



