76 BULLETIN 61, UNITED STATES NATIONAL MUSEUM. 



Range. — The geographic location of radix is the prairies and plains 

 of central North America north of the 37th parallel. Tliis region is 

 a continuation of tlie prairie and plateau regions of Texas, and like 

 tliese regions is bounded on the west by the Rocky Mountains and 

 on the east by the forests of eastern North America. The prairie- 

 plains region lies against the foot of the Rockies, at an elevation of 

 about 5,000 feet, and from here eastward descends gradually in broad 

 flat surfaces to eastern Nebraska and Kansas. From here eastward 

 it extends as a slightly descending peninsular extension of the tree- 

 less conditions of the great plains, through Minnesota, low^a, Missouri, 

 and Illinois into the western part of Indiana, ever3"where abutting 

 against the forests of eastern United States. The topography of the 

 greater part of the prairie peninsula is glacial, and is characterized by 

 a thick mantle of waste evenly spread, or heaped into rolling moraines 

 or loess bluffs, w4th intervening depressions containing lakes, ponds, 

 or swamps, according to their deptli. Tlie characteristic vegetation 

 consists of grass formations that not only occupy the uplands, but 

 also the sloughs. The river valleys and lake shores alone support 

 arborescent associations. 



The western part of this prairie region (approximately between the 

 eastern boundary of Kansas and Nebraska and the 98th meridian) is a 

 continuation of the prairie region of central Texas, with which it con- 

 nects in a narrow belt just west of the Ozark Highlands, and it extends 

 to the northward in eastern Kansas, Nebraska, and Dakota far to the 

 north of the Canadian boundary. The plains region wliich lies between 

 the prairie and plateau regions inch ides the Staked Plains of Texas 

 and extends to the northward beyond the Canadian boundary. The 

 topography is without striking relief and the valleys of the rivers are 

 })road and sliallow. The vegetation is characterized by the peculiar 

 bunch-grass formation, although the valleys carry the prairie forma- 

 tions far beyond the prairie region proper. 



The drainage of the entire treeless area of central North America 

 north of the 37th parallel is tributary to the Mssissippi, with the ex- 

 ception of the areas that lie within the hydrographic basins of the 

 Great Lakes and the rivers draining into Hudson Bay and the Arctic 

 Ocean. In the United States the streams flow eastward across the 

 plains, the larger ones (the Arkansas, Platte, and the Missouri) hav- 

 ing their origin far up in the Cordilleras. Across the great plains 

 they flow" in broad shallow valleys, but as the altitude increases 

 toward their source the main waterways sink their channels into the 

 level surface of the plateaus, dividing tliis major physiographic 

 feature into a number of table-lands wdiose margins are deeply <lis- 

 sected into bad lands by the secondary tributaries. Topographically, 

 therefore, the aspect of the prairie-plains region is essentially that 

 of a level plain; there are no distinct physiographic barriers, and 



