GEOLOGICAL SUEVEY OF THE TEREITOEIES. 39 



Sou tli Pass is a gradual elevation, like a divide, between the streams 

 to the plains. Indeed, the whole country is an elevated plain, gently 

 undulating, and the traveler passes the true divide or line of separation 

 between the valleys of the two oceans without observing it. 



On the evening of the 5th we arrived at Pacific Springs, one of the 

 sources of the Sandy, a branch of Green River, a long, low, boggy piece 

 of ground full of springs, and a notable camping place for emigrants. We 

 have spoken of the low ridges of granite and gneiss, which are distrib- 

 uted here and there along our route, from South Pass to Pacific Springs. 

 Scattered over this surface, forming the water divide or pass, and filling 

 up the irregularities, is a superficial deposit of modern date, probably 

 pliocene, which once covered the area occupied by the metamorphic 

 rocks in considerable thickness. This deposit is composed of drift un- 

 derlaid by yellowish- white arenaceous marls, with greenish clay. Wells 

 are dug near Fort Stambaugh through a great thickness of this light 

 marly clay, which is undoubtedly the result of the decomposition of the 

 feldspathic granites. Just west of the pass we have several hundred feet 

 of these modern beds, which form long parallel ridges, with rather 

 marked naked white surfaces, evidently denuded of vegetation, by the 

 perpetual winds that sweep down from the northwest. Extending 

 nearly east and west, or northwest and southeast, and inclining gently 

 to the south and southwest, is a broken ridge seven hundred feet above 

 the springs, capped with a bed of coarse, rusty sandstone, evidently of 

 modern age. This ridge is covered over with huge granite boulders of 

 various textures, which seem to have come from the northeast. Just 

 south of the ridge is a still higher one, with strata horizontal, and so 

 denuded that the surface resembles " bad lands," with red, indurated 

 arenaceous clays at the base, rising up into light yellow marly clays, 

 weathering into the usual fantastic forms. The highest point to the 

 southward is Table Eock, or Steamboat Buttes, as they have been 

 named by the emigrants, rising high above the surrounding plains, a 

 monument to perpetuate a portion of the former thickness of the middle 

 tertiary formations in this region. The strata are nearly horizontal, 

 and must have reached a thickness of one thousand feet or more, extend- 

 ing over the country far to the south and southwest toward the 

 railroad. I regard the western side of the Wind River anticlinal as 

 the eastern shore of the second series or lower miocene tertiaries, which 

 reach all over the basin drained by the Green River and its tributaries, 

 southward to the junction of Henry's Fork. The northeast side of the 

 shore line is very steep and abrupt, inclining slightly, 3° to 5°, covered 

 with immense granite boulders, but little worn, wliich evidently came 

 from the Wind River range. The white and yellow marls and clays rest 

 on the metamorphic rocks, are of pliocene age, and they extend far to the 

 northwest, parallel with the range. The same formations occur near the 

 Three Crossings in the Sweetwater Valley, and are rich in remains of 

 extinct mammals, similar to or identical with those of the Loup Fork 

 group. The reddish or India ocher clays, with leaden gray bands, form 

 the base of the lower miocene group. Above them is an extensive se- 

 ries of yellowish marls and rusty-drab limestone, filled with a species of 

 Bythinella, Viviparus, and other fresh-water shells, with silicified wood. 

 One of the peculiar features of the lower clays, near this shore line, 

 which does not occur farther inland, is the numerous seams of small 

 rounded pebbles, held together loosely with fine sand. As we descend 

 the valley below Pacific Springs it soon expands into a broad meadow, 

 which yields a vast quantity of hay. Winding through the meadow is 

 a fine stream of water, which increases in size continually from springs 



