SUN AND WIND IN LANDS OF INFREQUENT RAINS 201 



Dry weathering the red and brown desert varnish. In 

 desert lands the fierce rays of the sun suck up all the available 

 moisture, and the water table may be hundreds of feet below the 

 surface. Roots of trees a hundred feet or more in length have 

 been found to testify to the 

 fierce struggle of the desert 

 plant with the arid conditions. 

 In humid regions the meteoric 

 water dissolves the more 

 soluble sodium salts near the 

 surface of the rock and carries 

 them out to the ocean, where 

 they add to the saltness of the 

 sea. In the desert the rare 

 precipitations prevent an out- 

 flow, but the sun's strong rays suck out with the moisture the 

 salts from within the rock, and evaporating upon the surface, the 

 salts are left as a coat of " alkali/' which is in part carried away on 

 the wind and in part washed off in one of the rare cloudbursts. 

 In either case these constituents find their way to the lowest de- 

 pressions of the basin, 



FIG. 207. Borax deposits upon the floor 

 of Death valley, California (after a pho- 

 tograph by Fairbanks). 



where they contribute 

 to the saline deposits 

 of the desert lakes (Fig. 

 207). 



Certain of the saline 

 constituents of the 

 rocks, as they are thus 

 drawn out by the sun's 

 rays, fuse with the rock 

 at the surface to form a 

 dense brown substance 

 with smooth surface 

 coat, known as desert 

 varnish. Within the interior a portion of the salts crystallize 

 within the capillary fissures, and like water freezing within a pipe, 

 they rend the walls apart. As a direct consequence of this 

 disintegrating process the interior of rock masses may crumble 

 into sand; and if the hard shell of varnish be broken at any 



FIG. 208. Hollowed forms of weathered granite in 

 a desert of central Asia (after Walther). 



