ILLUSIONS 



115 



that has not to do with perspective but with 

 shadow and local color. The appearance is that 

 of shadows cast down along the mountain's side 

 by the ridges or hogbacks. Any little patch of 

 shadow is welcome on the desert, particularly 

 upon the mountains which are always so strongly 

 flooded with light. But this is only a counter- 

 feit presentment. The ridges have no vegetation 

 upon them to hold in place the soil and rocks 

 and these are continually breaking away into 

 land-slips. The slips or slides expose to view 

 streaks of local color such as may be seen in 

 veins of iron and copper, in beds of lignite or 

 layers of slate. It is these streaks and patches 

 of dark color that have broken away and slipped 

 down the mountain side under the ridges that 

 give the appearance of shadows. They have 

 the true value in light, and are fair to look upon 

 even though they are deception. The weather- 

 beaten rocks of a talus under a peak may create 

 a similar illusion, but the shadow effect loses a 

 velvety quality which it has when seen under 

 the ridges. 



The illusion of a cloud-shadow resting upon 

 the foot-hills or in the valley, is frequently pro^ 

 duced by the local color of lava-beds. Lava 

 may be of almost any color, but when seen close 



Shadow 

 illuaiona. 



Color- 

 patches on 

 mountaina. 



