214 NATUEAL HISTORY BULLETIN 



views. Engelmann (1862) regarded imperfect drainage as the 

 cause because standing water prevented oxygen from reaching 

 the roots of plants, and Alexander Winchell (1864, 1876) con- 

 sidered the origin lacustrine and the absence of trees due to 

 sourness of the soil. Shaler (1891) objected to the lacustrine 

 origin. Geikie (1898) ascribed it to sediment and wind action. 

 It is a well-known fact that ordinary trees will not grow on 

 undrained areas, but unfortunately for the application of this as 

 a general cause of the prairie, the latter is frequently found upon 

 old, well-drained surfaces, — indeed typical prairie does not de- 

 velop upon undrained areas, the plant-formations of the latter 

 being entirely distinct. 



The Sea. 



The prairie has also been regarded as a plain left by the waters 

 of the receding ocean. This was offered chiefly in explanation 

 of the southern prairies by McGuire (1834) and Desor (1856. 

 1865). The fact that in the prairie region of the upper Missis- 

 sippi valley several glacial drift sheets, the fresh-water Aftonian 

 and several terrestrial loesses have been formed since the ocean 

 withdrew is sufficient proof of the inadequacy of this theory. 



Geological Formations. 



Geological formations were formerly held of great importance 

 in determining the character of a flora, and D. D. Owen ex- 

 pressed this opinion as early as 1852. Whitney (1858) said that 

 prairie was confined to regions underlain by soft sedimentary 

 strata, but we find prairie over the Sioux Quartzite. McGee 

 (1878) in northeastern Iowa found forests restricted to the loess, 

 and (1883) the drift plains . timberless, while Howell (1883), 

 more familiar perhaps with the western loess, declared that the 

 loess will not sustain a forest. Pammel (1895) and the writer 

 (1900) also attached importance to geological formations in rela- 

 tion to flora, and later Willard (1902), Upham (1902) and 

 Gleason (1909) connected the origin of the prairies ^\ith glacial 

 action. Quite recently (1911), and again in this paper the writer 

 was able to give specific illustrations of the fact that prairie 

 occurs irrespective of geological formations, and the latter can 



