358 Prairie Flora 



From the south the Minnesota river receives such important 

 affluents as the Redwood river, the Yellow Medicine river, the Lac qui 

 Parle river, the Yellow Bank river, and the Whetstone river. All of 

 these streams head in the Choteau des Prairies and in the case of sud- 

 den rains send down from their headwaters enormous floods. From 

 the north the Minnesota receives Hawk creek which heads in the hills 

 north of Willmar, and the Chippewa and Pomme de Terre rivers which 

 both head in the Leaf hills. 



The soil o fthis region is mostly a deep black loam — formed from 

 the materials brought from the north by the glaciers, containing for 

 the most part decomposed limestone, and is very rich and fertile. 

 There are some sandy areas, apparently formed from the till by the 

 water that flowed away from the melting ice. There are areas — more 

 or less large — of loess, or wind-formed soil. 



With the exception of narrow strips along the streams or on the 

 north slopes of protected bluffs, or in ravines, such as the coulees 

 cut by streams in the slopes of the Coteau, the region under considera- 

 tion is all prairie. 



Much of this region was at one time timbered, and it is not un- 

 common to find well preserved trees deeply buried in the drift. Such 

 a tree was found in digging a well at Montevideo, in the bluff near 

 the south end of Fifth street, some 20 feet below the surface. The 

 tree was probably a pine, carried there by the last extension of the 

 glaciers. It seems likely that the reason for the treeless condition of 

 much of this region is due to diminished rainfall. At Montevideo the 

 average annual rainfall is 21.33 inches. This rainfall is sufficient to 

 produce a thrifty growth of trees in the deep rich alluvial soil of the 

 river valleys, but seems to be insufficient to induce a successful stand 

 of trees on a closely compacted soil of heavy till without cultivation. 

 It has been thought too that the rainfall is too unequally distributed 

 through the year, — sufficient perhaps in the summer, but deficient in 

 the inter. Others have suggested that the hot southwest winds from 

 the plains scorch and wither the trees and make the forest impossi- 

 ble. Many think, and with much show of reason that the treeless 

 condition of the prairies is due to prairie fires set by man. Prof. 

 Shaler has advanced the idea that the American Indians before the 

 advent of the whintes had advanced to such a degree of culture that 

 they had begun to regard the great herds of bison then living on the 

 prairies somewhat in the light of domestic animals, and that they 

 purposely set fire to the prairie and forest openings to make better 

 pasturage for them. 



Among the trees native to this region and forming the great body 

 of the native forests are the following: 



American elm (Ulmus americana). 



Green ash (Fraxinus lanceolata or pennsylvanica) . 



Bur oak (Quercus macrocarpa). 



Box elder (Acer Negundo). 



Cottonwood (Populus deltoides). 



Basswood (Tilia americana). 



Slippery elm (Ulmus fulva). 



Silver maple (Acer sacharinum). 



Cork elm (Ulmus racemosa). 



