4.0 GEOLOGICAL SUEVEY OF THE TEEEITOEIES. 



until it unites with the Sandy. On the Little and Big Sandy the forma- 

 tions are like those near Bryan and on Green Biver, and on the denuded 

 hills the remains of turtles were found. At our camp on the Big Sandy, 

 September 7th, we caught the best view of the Wind Biver mountains we 

 have yet seen. As the morning sun shone on them and scattered the 

 mist and smoke from their summits, they seemed not far distant, and 

 loomed up along the horizon with a sharp, clear outline, that rendered 

 the view most grand and imposing. Fremont's and Snow Peaks were 

 clearly defined, and the series of sharp peaks that project from the 

 main ridge seemed to diminish in height far toward the sources of Green 

 Biver. In no country in the world, it seems to me, can such a compre- 

 hensive view be presented to the eye at a glance as at this point, where 

 it can take in one of the loftiest of the ranges which form the main 

 chain of the Bocky Mountaius, stretching along the horizon for at 

 least one hundred and fifty miles. I could not ascertain that any of the 

 older sedimentary rocks are exposed along the western side of this 

 range, from the South Pass to the sources of Green Biver. Bidges of 

 the lower miocene tertiary strata along the western limit of the nieta- 

 morphic rocks form an unmistakable shore line of the ancient lake. 

 Between this shore line and the foot-hills of the mountains is a belt of 

 metamorphic slates and gneiss, covered here and there with pliocene 

 marls. The erosion all along the western side of the mountains has 

 been tremendous, sweeping down in a northeast direction to the Sweet- 

 water Valley. In a preceding chapter I described the Sweetwater Val- 

 ley as one of erosion, on a most remarkably grand scale, and that the 

 Sweetwater and Seminole Hills formed the south side of the anticlinal, 

 and that the north side is seen at the present time only in fragments 

 here and there, most of it having been swept away or concealed by the 

 Wind Biver deposits. I am also inclined to believe that the Sweet- 

 water Valley is only an extension to the east or south of east, of the 

 axis of the Wind Biver range. 



Prom the Big Sandy to our camp on Black's Pork, near Granger Sta- 

 tion, we passed over the Green Biver beds, capped here and there with 

 ridges of the leaden-gray, indurated arenaceous clays of the Bridger 

 group. In the Green Biver beds are quite abundant remains of reptiles, 

 as Orocodilus EUiotti,and the fragments of fishes, Unios, 31elanias, Palu- 

 dinas, Planorbis, &c, and found in the lower miocenee, and Unios, Lymneas, 

 and remains of turtles and mammals in the Bridger group. On either side 

 of our road we can see in the far distance a high ridge or table-top butte, 

 like the Pilot Buttes which the erosive forces have passed by as remnants 

 of the old surface. Among the rugged hills along the Big Sandy, and 

 in many other localities, are long cylindrical concretions, which look much 

 like silicified wood. They form the central portions of high, rusty-drab 

 concretionary sandstones, and on exposure the sandstone exfoliates from 

 che brown silicified interior, and the latter breaks in pieces, oftentimes in 

 sections, which show the most perfect concentric rings, like the layers of 

 growth in wood, with cavities filled with chalcedony. Most beautiful spe- 

 cimens can be obtained of what appears to be a thin, woody, exterior 

 shell, covered with bark, and lined inside with beautiful crystals of quartz 

 or chalcedony. Similar concretions occur in the Wasatch group near 

 Piedmont, on the railroad. It is not surprising that Stausbury (see 

 Beport, p. 72) should have mistaken these singular concretions for silici- 

 fied trunks of trees, which they very closely resemble. All over the 

 surface, and especially on the tops of the hills, are distributed immense 

 quantities of partially-worn flint rocks, which come from the debris of 

 these concretions. It is from these rocks that the masses of chalcedony, 



