MIEAGES ON THE DESERTS. 



83 



unbroken sky-line before him, and not an object in sight to cast a shadow 

 on the ocean-Hke ex«panse. Mirages may be seen every day on these heated 

 deserts. Similar optical illusions give strange fanciful forms to the mount- 

 ains, and sometimes transfigure them beyond all recognition. At such 

 times a pack-train crossing the desert a few miles distant frequently appears 

 like some strange caravan of grotesque beasts fording a shallow lake, the 

 shores of which advance as one rides away. The monotony of midday on the 

 desert is thus broken by delusive forms that are ever changing, and suggest 

 a thousand fancies which divert the attention from the fatigues of the jour- 

 ney. The cool evenings and mornings in these arid regions, when the pur- 

 ple shadows of distant mountains are thrown across the plain, have a charm 

 that is unknown beneath more humid skies. The profound stillness of the 

 night in these solitudes is always impressive. 



When the heat of summer drives every drop of moisture from these 

 deserts a white saline efflorescence appears, which is formed by the crys- 

 tallization of various salts brought to the surface in solution by the action 

 of capillary attraction, and left as the water that dissolved them is evap- 

 orated. Incrustations of this nature sometimes cover areas many miles in 

 extent, especially along the borders of the playas, and render the surface 

 as dazzling as if covered by snow. 



An analysis of atypical specimen of playa mud from the southern part 

 of the Carson Desert is reported by Dr. F. W. Taylor, as follows: 



Portion soluble in water 15.16 per cent. 



