354 NATURAL HISTORY BULLETIN. 



without, however, submitting any evidence of its contem- 

 poraneousness with the Iowan. 



In the monograph of the Illinoisan Glacial Lobe he says 

 (p. 131): "The sheet of drift to which the name Iowan is here 

 applied, is referred to the Iowan stage of glaciation, not because 

 of direct connection with the Iowan drift of eastern Iowa, but 

 because of an apparent similarity with the Iowan drift of east- 

 ern Iowa in its connection with the great sheet of loess in the 

 Mississippi Basin." On p. 143 he argues that the presence of 

 loess-like silt "brings strong support to the view that the ice- 

 sheet, at the Iowan stage, did not fall short many miles of 

 reaching the line occupied at a later date by the Wisconsin 

 ice-invasion." In both these cases, as well as in the discussion 

 on p. 133, he seems to take it for granted that the loess is 

 Iowan, and uses it to determine the age of the drift sheet! 



His reference to the relation between the loess and the Iowan 

 drift on p. 153 is much more cautious than his later utter- 

 ances, for he says: "Deposits of silt, tentatively classified with 

 the loess and supposed to be of Iowan age, cover the entire 

 surface of the Illinoisan drift so far as it lies outside the limits 

 of the Iowan and Wisconsin drift sheets." Indeed, he seems 

 to question the identity of the drift in Illinois with the Iowan, 

 as is shown in the citation from p. 131, and on p. 141, where 

 he says that "there is some evidence suggesting a slight exten- 

 sion of ice from Iowa into northern Illinois at the Iowan 

 stage." Similar doubt is expressed in the discussions on pp. 

 141-2, 148-9, 151, 154, etc. 



The writer does not here raise the question of the identity 

 of the deposits in question with the Iowan drift, but refers to 

 the citations merely to call attention to the doubt which ex- 

 isted in Leverett's own mind at a time when the supporting 

 field observations were still fresh in mind. He also recognizes 

 the fact that a field-worker might have legitimately changed 

 his views in the period of five years which has elapsed since 

 the publication of the work cited, but so far as he is aware, 

 Mr. Leverett has published no additional observations to for- 



