THE PEDREGAL. 



285 



packs of the spring probably have more to do with the dis- 

 appearance of such escaped horses than does lack of food. 



From a utilitarian standpoint the most Interesting of 

 the Gervals plants are the cereals. These grains have been 

 Introduced, as Is usual In a new country, along the freight 

 trails, and plants of wheat, oats, barley and other northern 

 cereals are quite often seen In the summer. These make an 

 apparently normal growth, and it seems entirely possible that 

 In the future wheat fields may take the place of much of 

 the wilderness now visited only by the lonely trapper or pros- 

 pector. 



THE PEDREGAL 



A region comprising several square miles of broken 

 lava slopes encountered a few miles south of the City of 

 Mexico is known as the Pedregal, (meaning colloquial- 

 ly a rocky river-bed). The surface Is very irregular, the 

 streamways labyrinthine In their branching, while every- 



Figure 56. Dr. C. G. Pring-le examining a new prickly peur. 



