116 



THE DESERT 



to yiew it is usually a reddish-black. At a dis- 

 tance, however, and as a mass, its beds have the 

 exact value of a cloud-shadow. Any eye would 

 be deceived by it. The great inundations of 

 lava that have overrun the plains and oozed 

 down the foot-hills and around the lomas (par- 

 ticularly on the Mojave) look the shadow to the 

 very life. The beds are usually hedged about 

 on all sides by banks of fine sand that seem to 

 stand for sunlight surrounding the shadow, and 

 thus the deception is materially augmented. 

 Many times I have looked up at the sky to be 

 sure there was no cloud there, so palpable is this 

 lava shadow-illusion. 



But perhaps the most beautiful deception 

 known to the desert is the one oftenest seen 

 mirage. Everyone is more or less familiar 

 with it, for it appears in some form wherever 

 the air is heated, thickened, or has strata of 

 different densities. It shows on the water, on 

 the grass plains, over ploughed fields or gravel 

 roads, on roadbeds of railways ; but the bare 

 desert with its strong heat-radiation is pri- 

 marily its home. The cause of its appearance 

 or at least one of its appearances is familiar 

 knowledge, but it may be well to state it in 

 dictionary terms : " An optical illusion due to 



