32 



THE DESEKT 



Fantastic 

 forms. 



Wash-outs. 



Sand-lines 

 in caves. 



body.* Again shafts of hard granite may make 

 tall spires and turrets upon a mountain peak, a 

 vein of quartz may bulge out in a white or yel- 

 low or rose-colored band ; and a ridge of black 

 lava, reaching down the side of a foot-hill, may 

 creep and heave like the backbone of an enor- 

 mous dragon. 



Perhaps the greatest erosion is in the passes 

 through which the winds rush into the desert. 

 Here they not only eat into the ledges and cut 

 away the rock faces, but they make great wash- 

 outs in the desert itself. These trenches look 

 in every respect as though caused by water. In 

 fact the effects of wind and water are often so 

 inextricably mixed that not even an expert geol- 

 ogist would be able to say where the one leaves 

 ofE and the other begins. The shallow caves of 

 the mountains — too high up for any wave action 

 from sea or lake, and too deep to be reached 

 by rains — have all the rounded appearance of 

 water-worn receptacles. One can almost see 

 the water-lines upon the walls. But the sand- 

 heaped floor suggests that the agent of erosion 

 was the wind. 



Yes ; there is some water on the deserts, some 



* Professor Blake of the University of Arizona ha8 

 called my attention to this. 



