312 EXPLORATIONS ACROSS THE GREAT BASIN OF UTAH. 



and of evidently lacustrine origin. They impart no peculiar character to the valleys, 

 most of which have derived their configuration from lakes and inland seas, which must 

 have covered a large portion of this country within the present era, after the last great 

 geological changes had taken place, and the continent had attained its present outlines. 

 The valleys are generally formed by corresponding slopes, steeper near the mountains, 

 and so gradually converging toward a center, that it would frequently require instru- 

 mental observations to decide whether the ground is horizontal or inclined. In some 

 places we find wide flats many miles in extent. Part of these valleys are not immedi- 

 ately connected with water-courses, but form separate basins, and, when of consider- 

 able length, they are subdivided by a rising ground into a number of smaller ones. 

 Others have a regular descent in their longitudinal direction, and a drainage on the 

 surface, sending large volumes of water to lower points, especially during the season 

 of melting snow, while later in the season most of the creeks dry up entirely. 



Besides their general shape we have other numerous evidences that large bodies 

 of water occupied the valley at a former period. At some points, as stated above, we 

 find horizontal strata. No fossils have been noticed in them, but their petrographical 

 character clearly indicates a recent origin. Such strata, for instance, were found in 

 Kobali Valley, where it is interesting to observe how the drainage toward Pah-hun- 

 nu-pe Valley was finally effected by the erosion of Swallow Canon. In many of the 

 valleys regular "benches" of shingle and detritus have been formed along the sur- 

 rounding heights, and around the Island Mountains, indicating a former beach, 

 sometimes of considerable width. They frequently appear as distinct water-marks 

 of equal height all around. A striking evidence of this kind is found in the Salt 

 Lake Valley, where such a bench-mark can be seen at a glance, extending con- 

 tinuously nearly 20 miles, and more than 200 feet above the present level of 

 the lake, while others are lower down. Captain Stansbury mentions a place at the 

 northern end of Salt Lake where he counted 13 such successive benches, the highest 

 200 feet above the valley, and he states that the water-marks extend to near the sum- 

 mit of Fremont's Island, which is from 800 to 900 feet high. Less distinct, but still easily 

 recognizable, such benches were observed in most of the valleys, though not in so 

 large number. 



Instead ot benches, we find at some points a continuous rim of calcareous tufa 

 along the mountains, also proving conclusively a higher state of water at a former 

 period. This was observed especially on a branch of the Great Salt Lake Desert near 

 the Fish Springs, and in the neighborhood of Carson Lake. Such formations may also 

 exist unnoticed in many corresponding localities. They can be readily distinguished 

 from the tufaceous deposits of springs, as noticed at other points of the route. Inter- 

 esting deposits of this kind and on a more extensive scale have been described by Mr. 

 Blake from the Colorado Desert, in Lieutenant Williamson's Report of the Pacific 

 Railroad Explorations. 



The material composing the bottom of the valleys, although differing according 

 to local circumstances, is generally such as cannot well have been formed in any other 

 way than as the slowly increasing deposit of a quiet water. Except in the immediate 

 vicinity of the mountains, wdiere coarser fragments of rocks are mixed with it, it con- 



