382 Tlic American Geologist. June, 1900 
dealing primarily with the marginal moraines, and also quite fully with 
all the associated drift formations, of the northern United States. 
Professor Chamberlin, in his letter transmitting this report to the di- 
rector, writes: "Early in the preliminary work special attention was 
drawn to the Illinois glacial lobe, because its morainic ridges and its 
till sheets were very widely deployed and because its relations were 
such as to make it, in some sense, a key to the whole glacial series east 
of the Mississippi, and hence it has been given precedence." 
Five or more lobes of the North American ice-sheet and of its 
drift-bearing area are broadly outlined between the gulf of Maine and 
the Upper Missouri river. In their order from east to west they may 
be named the New England and New York lobe, the Eastern and 
Western Ohio lobes, the Illinois lobe, and the Missouri and Kansas 
lobe. The one that reached farthest south is here elaborately de- 
scribed by Mr. Leverett, in respect to the area and contour of the 
land that it covered, its marginal moraines, intermorainic and la- 
custrine deposits, changes of drainage due to glaciation. succession of 
drift formations revealed by sections of wells, and stages of maximum 
advance and wavering and irregularly fluctuating retreat of the ice- 
sheet. 
Fifteen stages of the Ice age and its drift are recognized by Leverett 
in this region: i. The stage of the oldest known drift sheet, the 
Albertan of Dr. George M. Dawson: 2. The interglacial Aftonian stage 
of Chamberlin; 3, The Kansan drift sheet, formed when the ice-sheet 
attained its greatest area west of the Mississippi river; 4, The second 
interval of retreat of the ice, named by Leverett the Yarmouth stage; 
5, The Illinoian drift sheet; 6, The third interval of glacial retreat, 
Leverett's Sangamon stage; 7, The low an drift sheet and the main 
loess deposit; 8. The fourth glacial retreat, Leverett's Peorian stage, 
perhaps including the Toronto and Scarboro' interglacial beds; 9, 
The Early Wisconsin moraines and drift sheets, including four definite 
substages; 10, The fifth interval of recession; 11, The Late Wisconsin 
moraines and other formations, referable to three substages; 12, The 
first stage of the glacial lake Chicago;- 13, Withdrawal of this lake 
below its previous outlet to the Illinois river; 14, Temporary return 
of the lake level to the Chicago outlet; and 15, The present stage of 
lake Michigan. 
The time relationship of the Illinoian drift sheet with the earlier 
Kansan and the later lowan is not certainly determined; but the au- 
thor concludes, from all his observations, that a very long time in- 
terval, the Yarmouth, separated the Kansan and Illinoian stages of 
glaciation, whereas a probably shorter interval, the Sangamon, divided 
the latter from the lowan stage. 
It is impossible, within the limits of this review, to note adequately 
the vast amount, the fullness in details, and the logical arrangement 
and discussion, of the author's observations presented in this volume. 
We look forward with earnest hopes for the continuation of this 
series of reports, until all our drift area shall be thus accurately made 
