26 FIBST BOOK OF FOEESTKY 



The sandy ridges following the Brazos, Wichita, and other 

 rivers are either bare or scantily dotted with thickets or 

 clumps of the shrublike shin oak, while scattering, bush- 

 like trees of red cedar dot the bluffs of the rivers. 



Reaching the high and dry plateau of the Staked 

 Plains we find that tree growth ceases; the mesquite no 

 longer decorates the prairie, and the sand hills of these 

 plains are desolate wastes. 



We have made a long journey from a humid country 

 to an arid one, passing through many intermediate stages. 

 Neither soil, altitude, nor the temperature factor of the 

 climate has changed materially, and yet we have passed 

 from a dense and stately forest of pine through oak and 

 mesquite openings into bare prairie and sand waste. 



The great difference in the amount of moisture alone 

 is responsible for these remarkable changes. Had we 

 started from Duluth, Minn., and gone west or southwest, 

 our experience would have been similar. First, long 

 stretches of pineries, in which white and Norway pine 

 often predominate ; then, rather suddenly, oak, or else 

 poplar and oak openings ; and, within a few' hours' ride 

 by train, jthe open treeless prairies. 



This transition from the humid forests to the drier 

 prairie regions is very similar from Texas clear to our 

 northern boundary, and everywhere it is caused by the 

 lack of rain and snow, which appears to be the principal, 

 if not the only, cause of the fading out of the forest. 



