THE PLEISTOCENE OR GLACIAL PERIOD. 411 



which should have been covered by water according to this hy- 

 pothesis, have no loess. Thus the loess occupies the bluffs on the 

 east side of the Mississippi river, down to the highlands of the south- 

 western part of Mississippi, where it mantles surfaces which he 300 

 or 400 feet above the present river, and overlook the lowlands of Louisi- 

 ana, where there is no loess. Between the bluffs and the lowlands, 

 there is no restraining barrier, and no shore-line, or other topographic 

 features that should have been left by an estuary, had the depositing 

 waters assumed that form. Furthermore, if the waters of rivers or 

 their lake-like expansions were high enough to cover the areas over- 

 spread by loess, it is not clear that there could have been an appro- 

 priate habitat for the abundant land fauna of the time. 



Under the eolian hypothesis, or at least one phase of it, the river 

 flats are supposed to have supplied the material of the loess, which 

 was whipped up by the winds and re-deposited on the adjacent up- 

 lands, perhaps being held, after deposition, by vegetation. The rivers 

 are thus made essential factors in the distribution, though not the 

 direct agents of deposition. The preponderance of loess on the east 

 sides of some main rivers is attributed to the prevailing westerly winds. 

 This hypothesis seems on the whole to best fit the phenomena of at 

 least a large part of the loess of the Mississippi basin. The constituents 

 of the loess, which appear to have come from the glacial grinding, were 

 derived either directly from the deposits made by glacial waters, or 

 from the secondary erosion of the glacial formations. It is probable, 

 too, that the derivation of loess silt from glacial drift directly, before 

 it became clothed with vegetation, and without the intervention of 

 rivers, should be recognized. 1 



1 References. — Loess is described in the geological reports of the following 

 States: Iowa, Vols. Ill, IV, V, VII, VIII, IX, X, XI, XII, XIII, and XIV (Calvin, 

 Bain, Shimek, and others); Illinois, Vols. V and VI (Shaw and Worthen); Missouri, 

 Reports of 1855-71, 1872, and 1873-4, and Vols. IX and XII (Pumpelly, Broadhead, 

 Marbut, Todd, Winslow); Arkansas, Report on Crowley's Ridge; Kentucky, Report 

 on Jackson Purchase Region (Loughridge) ; Tennessee, Geology of Tennessee, and 

 Resources of Tennessee (Safford); Louisiana, Reports of 1899 and 1902 (Harris 

 and Veatch); Mississippi, Reports of 1854 and 1860 (Hilgard); Minnesota, Vol. 

 1, and Report for 1880, (Winchell, Upham); South Dakota, Bull. I (Todd), and 

 Nebraska, Vol. I (Barbour). Other references are, Pumpelly, Am. Jour. Sci., Vol. 

 XVII, 1879; McGee and Call, idem., Vol. XXIV, 1882; McGee, Eleventh Ann. Rept. 

 U. S. Geol. Surv.; Chamberlin and Salisbury, Sixth Ann. Rept, U. S. Geol. Sun-.; 

 Russell, Geol. Mag., Vol. VI, 1889; Todd, Am. Assoc. Adv. Sci., Vol. XXVII, 1987, 



