No. i.) GRAY AM) BOOKER ON THE KOOKY MOUNTAIN FLORA. 25 



sippi are mainly restricted to places having little or do more rainfall 

 than that mentioned above; also that where annual tires have been pre 

 rented, original prairie surfaces are changing into forests,* and that, 



generally, trees properlj planted or raised from seed, with sonic nnrs 

 ing at the start, are found to thrive along this whole border. 



In view of this, and oi' the well-known habit of the Indians to burn 

 over the dry vegetation of the plains and prairies in autumn, we had 

 thought it most probable " that the line of demarkation between otu 

 woods and our plains is not where it was drawn by nature'"; that "be- 

 tween the ground which receives rain enough tor forest and that which 



receives too little, there must be a debatable border, where compara- 

 tively Blight causes will turn the balance either way, ,? and where "dif- 

 ference in soil and exposure will tell decisively." And along this bor- 

 der, annual burnings, for the purpose of increasing and improving buf- 

 falo feed, practiced for hundreds of years by our nomade predecessors, 

 may have had a very marked effect in carrying this woodless district 

 farther eastward than it otherwise might have reached.! 



Along with this, a more hypothetical cause may be assigned, which, 

 if valid, will help in other explanations. That natural rain-gauge, the 

 Great Salt Lake in Utah, informs us that the rainfall is now increasing 

 over the western border of the region under consideration. We know 

 what the maximum height of the water was very long ago; but we know 

 not the minimum. It is not improbable that this era of increasing moist- 

 ure is of no recent commencement, but has supervened on an earlier one 

 of greater dryness than the present, and that this affected the great 

 plains east, as well as the great basin west, of the interposed Rocky 

 Mountains. In that case districts may now bear forest, under man's 

 care, which would have been incapable of it before this cycle commenced 

 or had attained the present condition. 



The western portion of these plains is not only drier, but in some 



parts alkaline, or with other characters of soil uncongenial to forage 



grasses, especially at the north, where there are only two inches of rain 



in tin- three summer and no more in the three winter months. A good 



deal of the southern part gets about four inches of summer rain, but only 



half as much in winter. In some parts, accordingly, the characteristic 



station of the ultramontane plateau intrudes. The Pulpy Thorn, 



ibatugj and its Chenopodeous associates are Largely developed <>n the 



Upper Missouri waters, accompanied by a peculiar Sage-Brush, Arte- 



cana, while the .1. trideniata i^ rather rarely established on this 



side of th<- mountains. 



We have termed this district the region of Buffalo < trass. The gi asses 

 form such an inconspicuous and unimportant a feature in the interior 

 arid region that it has n<>t been worth while to mention them, and even 

 on th<- mountains, except in the alpine region, thej an- <»t -mill account 



\. White, in Am. i Oct., 1878. 



l»liy and Arrlia-olog\ . in Aukt. .Jour. Bci., 1878 S 



