330 The American Geologist. May, 1895 
norlliwurd, ai?ain an iisct'iit of about 25 feet. The average differential 
uplift of the land, since tiie time of the lake existence and the closing 
part of the Ice age, is thus about two feet per mile, being intermediate 
in amount between that of the southern half of lake Agassi/ and that of 
the east end of lake Iroquois. The maximum width of lake Passaic 
was about ten miles, and its maximum depth was about 225 feet. 
w. u. 
CORRESPONDENCE. 
Divisions of the Ice Age in the United States and Canada. After 
reading Mr. Upham's papers in the last December and March issues of 
the American Naturalist, I have been led to reflect further upon the suc- 
cession of the glacial deposits in North America, and to send in this 
letter informally some of mj' conclusions. A year ago, in correspondence 
with a brother geologist, I remarked that the criteria for a satisfactory 
classification of the glacial series depend upon the terminal edges and 
moraines. Ever}' terminal moraine denotes necessarily a readvance of 
the ice-sheet, or some temporary halt or slackening of its final retreat. 
Hence there must have been as many glacial stages as there are mo- 
raines, separated by as many gaps or ad interim deposits. Mr. Upham 
has described no less than twelve terminal moraines in his western field 
of labor; hence at least twenty-four successive phases of climate must 
be predicated. A still larger number of moraines, fifteen or moie, are 
mapped by Mr. Leverett north of tiie Ohio river. It is likely that the 
mild intervals have varied in their importance; but whatever truths are 
involved in these premises, I remarked, I was ready to accept. I find 
now that these premises lead to the establishment of a grand unity, not 
unlike that of the Federal Union, E pluribm itnum. 
Prof. James Geikie has recently reclassified the.se epochs in the third 
edition of The Great Ice Age, noting the existence of thirteen of them. 
The first number is the early and greater part of the Pliocene, and the 
last is the present or only postglacial time, while between these are si.x 
glacial and five interglacial epochs, together making the Ice age. The 
first glacial and interglacial epochs (Nos. 2, 3) belong to the late Plio- 
cene, being represented by the Weybourn crag and Chillesford clay for 
the glacial (2), and by the forest-bed of Cromer for the warmer terrane 
(B). Hence it is apparent that the Age of Ice is partly Pliocene and 
partly Pleistocene or Quaternary. In America, also, a great difficulty 
is removed by assigning epochs 2 and 3 to the latest Tertiary: for. in 
doing this, the Lafayette pi'riod is disposed of. It is so obviously re- 
lated to the Ice age that Upham and others have referred it to the Qua- 
ternarj- era; but according to the Lyellian classification it must appar- 
ently be Pliocene. The Glacial age then belongs partly to the Pliocene 
and partly to the Pleistocene. Nothing except our hesitation to change 
