118 



NORTH AMERICA 



climate, tree-growth requires a well-watered soil ; but 

 such conditions are seldom fulfilled, the soil being 

 mostly porous and the inland rivers remaining dry 

 during the greater part of the year, or running in 



FIG. 34. Taxodium trees Sacromonte. 

 Amecameca (Mexico). 



very deep canons, whose lowest parts are frequently 

 transformed into lagoons or swamps with no outlet. 

 The hill ranges, once wooded to a large extent, are now 

 mostly bare. Over the plains stretch vast steppes of 

 scattered wiry bunch-grasses, which are hardly relieved 



