116 REEOET UNITED STATES GEOLOGICAL SURVEY. 



ains. A secondary class of drift, removed by fluviatile action, is found 

 in the accumulations of sand in the immediate vicinity of the river and 

 in its bed. When found in the latter position it appears frequently as 

 quicksand, rendering* the foining of the stream a rather risky under- 

 taking at some places. 



SOIL. 



Owing to the character of the strata near the river, the majority of 

 drift material in its valley, as well as in those of its tributaries, is found 

 in the form of soil. All along the Sweetwater we find widening portions 

 of the valley which are covered with good soil. A similar state of affairs 

 may be observed in all the broad valleys of the Lower Sweetwater drain- 

 age. Along the southward slope of the plateau soil covers the strata 

 and sustains a thriving crop of sage-brush. Professor Comstock has 

 furnished some interesting data in his report* upon the " conservative 

 action" of sagebrush in loose soil. For more detailed information upon 

 the character and probable productiveness of the sod within the Sweet- 

 water region I would refer to the report of Prof. Cyrus Thomas, con- 

 tained in the report of the United States Geological Survey of Dr. Hay- 

 den, 1S70. He has made the agricultural resources of the West a special 

 study for a number of years and is qualified to discuss questions of this 

 nature that may at some day prove to be of considerable importance. 



SAND DUNES. 



On several places along the Sweetwater we observe accumulations of 

 loose sand that owed their present position to the transporting action of 

 wind. They are particularly noticeable in the vicinity of Whiskey Gap. 

 Through the disintegration of the arenaceous marls and loosely-cemented 

 sandstones of the region, large quantities of free sand are scattered over 

 the bluffs and ridges. Westerly winds, which prevail in this section of 

 country, drive the sand before them, until it reaches some x>eraianent 

 obstacle, and is arrested thereby in its progress. Thus we find deep 

 banks of sand several hundred feet long piled iip against small granitic 

 outcrops, which have proved to be obstacles in their eastward course. 

 In size they cannot be compared with the sand dunes farther south, but 

 they are due to the same causes, and show the same detail features which 

 there are exhibited on a much grander scale. Sandy Creek Pass leads 

 over a series of sand dimes, which form the eastern termination of the 

 extensive succession of such deposits in the southern area. As this will 

 be considered fully in Chapter IV, this allusion may suffice. Wherever 

 large masses of arenaceous rocks disintegrate, we find local accumula- 

 tions of sand partaking somewhat of the character of dunes. 



EESUME OP THE SWEETWATEE BEGIOK. 



Within the area to which the third chapter is devoted we observe a 

 number of features of great interest. One of the most prominent is that 

 of the prozoic range. Beginning near the southern end of the Wind 

 Eiver Eange, this chain of hills extends for more than eighty mfles, sus- 

 taining, substantially, but two breaks. While the older or metalliferous 

 . schists disappear from view, we find the younger metamorphic rocks oc- 

 cupying a prominent position. A very large proportion of these latter 

 undoubtedly retain their normal position, but a part of them has been sub- 

 jected to the influence of dynamic forces, and has totally changed its rela- 

 tions to older groups. Taking the prozoic range as a base, we find that it is 



* Report Reconnaissance of Northwestern Wyoming, Captain Jones, 1873. "Wash- 

 ington, 1874, p. 171. 



