158 REPORT UNITED STATES GEOLOGICAL SURVEY. 



which breaks the force of the wind, there we find the greatest accumu- 

 lations of sand. It is carried thither, but the wind is forced to take an 

 upward course, and much of the sand must fall. Near the Sweetwater 

 and Whiskey Gaps, and at Sandy (.'reek Pass, the line sand is blown up 

 upon the hillsides for a distance of 500 to GOO feet. It is always found 

 most abundantly on those hills which present a face to the southwest. 

 The southern slopes are covered with a thin layer, but upon them we 

 rarely find an accumulation of dimes. On account of the persistency 

 of the wind the upper portions of this sand are very loosely deposited, 

 and are constantly shifting. An animal in passing over it will sink in to 

 the knees. jSTo vegetation can take hold on the dunes. At a few places 

 depressions were found in which the sand had somewhat hardened, and 

 sagebrush took advantage of these occurrences. 



From a distance the dunes resemble the waves of a " chopped " sea. 

 Sloping gently toward the west, each wave shows a steep incline on the 

 opposite side. " Ripple-marks," not distinguishable in their form from 

 those produced by water, cover the western slope. In very windy weather 

 a long-continued yellow cloud of dust may be seen along this " sand- 

 belt." It rises high into the air and deposits its sand in a line parallel 

 with the direction of the wind. With but little motion of the atmos- 

 phere the movement of the dunes could be favorably studied. Boiling- 

 upward along the western slope of an individual dune, the particles of 

 sand steadily advance in parallel, successive rows. Reaching the cap 

 of the wave, each row^ rolls down the eastern incline, there again to be 

 picked up and marched farther eastward. 



An interesting occurrence to us was the fact that many of the lakes 

 which were located in the immediate vicinity of this series of dunes con- 

 tained water, while those removed some distance from it were dry. I 

 explain this by assuming that the precipitated moisture, the quantity of 

 which is small at best, can more readily soak into the sand and be re- 

 tained for a long time, preserved from evaporation. In this way small 

 springs or underground water-courses can be formed, which will furnish 

 the lakes near by with a greater absolute quantity of water than those 

 receive which are dependent upon surface-drainage and direct precipita- 

 tion. Whether such springs remain even only partially active during 

 the entire summer is very doubtful. The quantity of water which is 

 carried into the lakes during the wet season is so much in excess, how- 

 ever, over that which others receive having the same drainage area that 

 it is not reduced to the same extent by evaporation. Another factor 

 here enters into consideration, the capacity for saturation. While the 

 moisture which appears during the summer in the form of slight precipita- 

 tions, such as dew and brief showers, is mostly lost very rapidly by 

 evaporation, the peculiar physical conditions of the sand permit it to pen- 

 etrate to some depth. In this manner the supply of the lake is not- 

 drawn upon by exhausted surrounding beds of the same level, and will 

 be diminished more slowly in consequence. 



As a necessary consequence of the vicinity of these lakes to the sand 

 area, we find considerable masses of quicksand along some of their shores : 

 Xear Sandy Creek Pass a considerable number of lakes, of varying sizes, 

 occur directly in the sand dunes. On account of the saturated condition 

 in which the sands have here remained for a long period of time, they 

 could not be transported by the wind wherever the grains were thus 

 bound together by moisture. In consequence some soil was formed there. 

 Grassy vegetation soon took advantage of this, and we now find some 

 very fine meadows bordering the lakes. Rising only a short distance 

 above their level, however, we are in loose sand once more. 



