PliAYA-LAKES AND PI.AYA8. 



The name "playa-lake" has been applied to inclosed water bodies of dry 

 climates which have little depth and frequently evaporate to dryness, leaving 

 mud-plains, or playas. In the typical examples found throughout the Great 

 Basin, their waters are somewhat alkaline and saline, and almost always 

 turbid with fine silt, and, probably, chemical precipitates. This material is 

 retained in suspension not only because the shallow lakes are frequently 

 agitated to the bottom by the wind, but, also, for the reason that in waters 

 containing alkaline salts tlie precipitation of suspended matter is greatly 

 retarded. Lakes of this class exhibit great variety, and are the most irregu- 

 lar of water bodies. In many instances they hold their integrity for a num- 

 ber of 3'ears, and only evaporate to dryness during exceptionally arid seasons. 

 Again, desiccation is apparently the normal condition, and the basins are 

 only flooded during times of unusual liumidit}^ Many lakes of this class 

 exist only during the humid season, and are dry throughout the summer. 

 In the spring and fall, as already mentioned in describing the general fea- 

 tures of the Great Basin, they appear with every storm tliat gathers and 

 vanish when the lieavens are again bright. Their outlines consequently 

 fluctuate with the humidity of the season, and, owing to the extreme shal- 

 lowness of their basins, a variation of an inch or two in depth may make 

 a diff"erence of many square miles in area. 



Examples of tlie more permanent playa-lakes of tlie Lahontan basin 

 are furnished by Honey Lake and tlie lakes of the Carson Desert. Another, 

 of less permanence, on tlie Black Rock Desert, has been noticed on page 10. 

 The positions of others, some of which are many miles in extent during the 

 winter, but disappear completely when the breath of summer touches tliem, 

 are indicated on the accompanying pocket-map. Examples might be 

 multiplied, and the curious effects that these epliemeral lakes exert on tlie 

 scenery of arid lands might be dwelt upon, but tliis would perhaps carry 

 us beyond their geological interest. 



The lakes described above are commonl}^ uninhabited by fish, but 

 frequently afi'ord a congenial abode formollusks, especially for the Limnseidte 

 and allied forms. 



MON. XI— 6 81 



