LOESS AND THE IOWAN DRIFT. 353 



to show the unsatisfactory character of such reference, but 

 since its first publication, Mr. Frank Leverett reiterates and 

 emphasizes the reference of loess to the Iowan drift period.* 

 The reference of loess to any drift period must be objected to, 

 and not the least on account of the frequent presence of num- 

 erous land-snails, which indicate also the existence of a vig- 

 orous vegetation. f The several loesses represent interglacial 

 and post-glacial periods during which conditions could not 

 have been materially different from those which exist at 

 present, and nothing has yet been presented which would 

 shake their evidence. Leverett himself recognized this when 

 he stated! that the fossils "bear clear evidence of having lived 

 during its deposition." It may be true, as Leverett says in the 

 American Geologist, that "the study of fossils alone will be 

 insufficient to fully clear up the question of the mode or modes 

 of deposition of the loess," — and so far as the writer knows no 

 one has attempted this,— but neither can the question be cleared 

 up by disregarding entirely, or distorting the evidence which 

 the fossils offer, as has been done by several of those who have 

 recently taken part in the discussion of the loess question. 



It is interesting in this connection to scan the evidence 

 which Leverett offers in his published papers in support of 

 the contention that the loess is Iowan. § 



In the proceedings of the Iowa Academy (1. c.) he defines 

 loess as "that sheet of loess which connects at the north with 

 Iowan the Iowan till sheet," and refers to it a number of times 



*Am. Geol. , vol. xxxiii., pp. 56-7, Jan., 1904. 



tThe writer has repeatedly called attention to the fact that these mol- 

 luscs are herbivorous. See: Proc. la. Acad. Sci. , vol. iii, p. 85, 1896; 

 vol. v, p. 39, 1898; vol. x, p. 46, June, 1903. Bull. Lab. Nat. Hist. S. 

 U. of la., vol. v, p. 212, May, 1901. 



% Monographs U. S. Geol. Sur. , vol. xxxviii, p. 165, 1899. 



§The following are the most important: Geol. and Nat. Hist. Sur. of 

 the Chicago Acad. Sci., Bull. no. II, pp. 16-17, 18^7; Proc. la. Acad. 

 Sci., vol. v, pp. 74-5, 1898; Monographs U. S. Geol. Sur., vol. xxxviii, 

 pp. 153-187, 1899; Am. Geol., vol. xxxiii, pp. 56-7, Jan., 1904. 



