4 BIG SPRING PRAIRIE. 



The climatic factors of irregular and scanty rain- 

 fall and the general low humidity of the atmosphere are 

 potent causes of the western type of prairie. These 

 factors in combination with the occurrence of frequent 

 prairie fires are sufficient to account for the absence of 

 trees upon this type of prairie. 



The origin, development, and future of the eastern 

 type of prairie must be considered apart from the west- 

 ern type, as each possesses its own peculiar factors and 

 specific characteristics. Prairies may be studied by a 

 comparative survey of the likenesses and differences of 

 the various types of prairie areas, and the causes which 

 led to them. Again we may study each type compara- 

 tively with the topographic features and vegetative 

 characteristics immediately surrounding it. This latter 

 survey should be conducted along the border line of 

 prairie and forest, where the struggle can be said to be 

 fairly on, and where the effects and results of this rather 

 uneven struggle can be most advantageously observed. 

 A life-time is frequently long enough to observe the 

 forest encroachment upon the eastern prairie, ages 

 might be required to note the same degree of encroach- 

 ment upon the western type of prairie. 



Many theories have been advanced to account for 

 the absence of trees on prairies; as the prairie fire theor) ;, 

 the fine soil theory; the ulmic acid theory; etc. 

 Lesquereux states that prairies are formed from old 

 lakes, or bays extending from them with the marsh as 

 the intermediate formation, and he furthermore asserts 

 in regards to these: "Trees never invade them, never 

 grow upon them, even when drained." This latter 

 statement may need some modification, as observation 

 does not bear out the assertion "even when drained." 



In the West, the prairie is the natural formation^ 

 the presence of the forest is especially to be explained. 



In the Bast, the forest formation is the natural one^ 

 the presence of the prairie is to be explained. The 



