PHYSICAL GEOGEAPHY. lix 



owever, are sometimes washed down to very inconsiderable 



mensions, so as to form a number of separate little basins. 



'lie well-preserved water-marks whicli are everywhere visible 



Indicate extreme drjTiess, upon wbicli dryness most of tlie 



eculiar characteristics of the country depends. Artemisian 



crub (sedge-brush) and grease- wood* alone spring from the 



r 



y, parched earth, except where some stream of unusual 

 ersistence supports a row of cotton-wood trees f and a few 

 ^cres of grass along its edges. From the decomposition of 

 ..oleanic rocks, the soil in its ingredients is very rich, and, 

 ^here irrigation can be supplied, yields most abundant crops. 

 here are broad, level districts, however, called by the settlers 

 ' alkali flats," which are covered with salts, usually nitrate 

 f soda, and are thereby rendered perfectly barren. These 

 '"hite, glistening sheets, in the dry, unsteady atmosphere of 

 the desert, form the most tantalising mirages to which a 

 thirsty traveller could be exposed. At certain seasons they 

 are covered for a short time with a thin coating of water — 

 the local drainage of the surrounding district— which is soon 

 dissipated by the scorching sun. ♦ 



The plateaux of the basin-region were undoubtedly the last 

 portions of the Western Continent raised from the sea — the last 

 from which the Gulf of California retired. Even now sub- 

 terranean fires are active, and the process of gradual upheaval 

 may still be going on. Earthquakes are frequent; mud 

 volcanoes are still to be found in places ; huge cracks in the 

 earth's surface have occui-red within the memory of li^'ing 

 men ; craters, recently active, dot the whole district ; and hot 

 springs are so numerous that I have counted fifty- two jets of 

 Bteam issuin<? from the ground like pillars of smoke in one 



valley alone. 



* Obione amescene. - t Populua anymti/oUa, 



