A. Fendler on Prairies. 157 
low regions of South America, prevailed all over the continent 
up to high latitudes. Here, then, all the conditions for the exist- 
ence of a vast continuous forest all over the land are given, and 
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forest. into prairie by the agency of fire can be accomplished 
much faster, 
On the other, hand in regions perpetually moist and wet the 
rests are safe enough against all encroachments from prairies, 
e fire can do no mischief here. But also in comparatively 
dry climates the forest will be safe against the intrusion of prai- 
nes, if the trees stand on a deep fertile soil, where their roots 
May go down deep and support the tree from falling, and where 
the trees have a tendency to sprout from their roots; for it 
Would take many repeated firings of the undergrowth to lay that 
8round open to the baking influence of the sun. 
; in, at Santa Fe, New Mexico, the atmosphere is so exceed- 
Ingly dry that, with the exception of the sides of a deep, narrow 
mountain-valley, through which a creek flows, I have never seen 
— The dry, gravelly soil is for the greater part covered with 
Wests of Coniferze, not only on the higher mountains, but al 
_ 0n the low hills. The sterile soil is so dry during summer and 
