364 The American Geologist. " '"'• ! - '"" :; 
sharply defined differences between different portions of the 
loess. Such differences have been observed by Todd and other 
earlier observers. Tilton reported two loesses in Warren coun- 
;iik1 in Madison county. Iowa.f The present writer report- 
ed differentiation in the loess at Council Bluffs.? Calvin dis- 
covered two distinct beds of loess in Page county, lowa.S Dur- 
ing the past summer professor Calvin found two superimposed 
loesses in sec. 20, Bluffton township, Winneshiek county, Iowa, 
the lower, evidently pre-Iowan, being bluish-gray, with very 
large iron-tubules and numerous lime-nodules, while the upper 
is vellow and homogeneous. The writer subsequently exam- 
ined a similar exposure in sec. 3, Decorah township, and sev- 
eral were observed in other parts of the county. In these ex- 
posures the line separating the two loesses is distinct, and they 
evidently differ very much in age. Even more striking is the 
case of two loesses, both fossiliferous, discussed by Udden in 
Rock Island county. Illinois, and reported by Leverett, || for 
these are separated by more than 90 feet of drift and black soil. 
Loess is found upon the Wisconsin, the Iowan, the Illinoisan 
and the Kansan drift-sheets, and some of it is evidently pre- 
Iowan. Certainly all of it is not Iowan. 
Southward, in the regions not reached by the later drift- 
sheets, including therefore the vicinity of Lansing, there were 
no such abrupt interruptions in the deposition of loess, and this 
continued to the present time, possibly in varying degree, 
through all the climatic changes which so materially modified 
the northern surfaces, but southward probably affected only the 
character of the vegetation. Thus a deposit of southerly loess 
might be the equivalent in age of several of the northern drift- 
periods, without showing lines of demarkation between the sev- 
eral periods, which in the south were more or less merged into 
one. With our present knowledge it is certainly impossible to 
correlate southern loess, or any part of it, with any particular 
drift-sheet. 
The seventh proposition, that loess and drift intergrade, is 
emphasized by Winchellfl for the purpose of showing that the 
*Ia. Gcol. Sur., vol. v, pp. 318-19. 
fProo. la. lead. .Set., vol. iv, p. 49. 
tProc. la. Acad. 8ci., vol. vi, pp. 107-8; Jour, of Gcol., vol. vii, pp. 
132-3, 1899. 
; la. Geol. 8ur., vol. xi, pp. 444-5, 1901. 
r. S. Geol. Sur.. vol. xxxviii, p. 11.".; 1.S99. 
•Hull Urol. Soc. of Am., vol. 14. pp. 141-2; Am. Geol., vol. xxxl, pp. 
279-282 
