218 W. J. McOee — Ovibos cavifrons from loiva. 



and several pulmoniferous mollusca, which are here of normal 

 size and character, while at Des Moines, a hundred miles to the 

 eastward, they are depauperate,* presumptively by reason of 

 the frigid climate of that period. Under about the same 

 latitude on the Mississippi the loess fauna includes the elephantf 

 and the woodland teindeer (Rangifer caribou), or some closely 

 allied species for which the alternative name Cervus muscalinen- 

 sis has been suggested by Leidy,;}: together with several ter- 

 restrial and fresh water mollusca only slightly, if at all, de- 

 pauperate ; but within fifty miles to the northward, in Clinton 

 County, Iowa, the loess shells are notably depauperate, and fifty 

 miles further, in Dubuque County, they are exceedingly rare 

 and reduced to a half or third, or even a fourth, of their normal 

 linear dimensions. 



This testimony of the fauna as to the temperature of the 

 loess period is corroborated by that of the deposits themselves. 

 At Des Moines the loess graduates downward into, and is more- 

 over overlaid by, glacial drift ; midway between Des Moines 

 and the Mississippi River the loess merges into the underlying 

 drift so imperceptibly that no line of demarkation can be drawn 

 between them, and it is evident that the two represent merely 

 different phases of the same deposit ; much of the loess of 

 eastern Iowa unquestionably consists of the mud of glacial 

 streams, laid down in ice-bound lakes ;§ and the Missouri River 

 loess has been shown by N. H. Winchell to graduate into 

 morainal drift in southwestern Minnesota,! just as is the case in 

 southeastern Iowa. 



It is noteworthy that while the Council Bluffs specimen 

 comes from well within the glaciated area and the Big Bone 

 Lick specimen from near its margin, the Missouri and Indian 

 Territory specimens are from localities some three degrees 

 beyond the limits of that area ; and, although the data are too 

 meagre to justify final conclusion, it may be inferred that the 

 glacial refrigeration forced the Arctic fauna about that far 

 beyond the ice margin, and that it was felt even farther south- 

 ward. This inference is in harmony with the results of recent 

 work in eastern United States. During the earlier epoch of 

 Quaternary cold, the middle Atlantic slope was submerged to a 

 depth of over three hundred feet, and its rivers — the Delaware, 

 the Susquehanna, the Patapsco, the Potomac, the Rappahan- 

 nock, the James, the Appomattox, and the Roanoke — built 

 deltas at their embouchures into the expanded Atlantic along 

 the inland margin of the Coastal Plain of to-day. A conspicu- 



*This Journal, III, vol. xxiv, 1882, 215-219. 



f Proc. Davenport Acad. Nat. Sci., vol. i, 1876, 196-9. 



% Proc. Acad. Nat. Sci. Phil., vol. xxxi, 32-3. 



§ Trans. Iowa State Hort. Soc. for 1S83, vol. xviii, 328-39. 



|| Sixth Ann. Ttep. Geol. and Nat. Hist. Surv. Minn., 1877, 104-6. 



