: 1895.] Minor Time Divisions of the Ice Age. 235 
MINOR TIME DIVISIONS OF THE ICE AGE. 
By Warren UPHAM. 
The following study, forming the conclusion of Part VI in 
the Twenty-third (1894) Annual Report of the Minnesota Geo- 
logical Survey, may be regarded as a continuation or supple- 
ment of my paper, on the periods of the Quaternary era, given 
in the AMERICAN NATURALIST last December. It seems to sup- 
ply a compromise between the doctrine of unity of the Glacial 
period as held by Dana, Wright, and others, and the alterna- . 
tive doctrine of its duality or greater complexity as held, 
among American glacialists, by Chamberlin, Salisbury, 
McGee, and others. Unity or continuity of our Plistocene 
glaciation, with moderate fluctuations of the ice margin, ap- 
pears to the present writer the more acceptable view and ex- 
pression, when the whole period and the whole drift-bearing 
area are considered. This time was long as measured by 
centuries or thousands of years, but was in a geologic sense 
brief as compared with all other geologic periods or epochs, 
excepting only the shorter, unfinished Recent or Present 
period. 
Seeking to subdivide the Ice age with reference to its dy- 
namic causes and secular fluctuations in climatic conditions, we 
find, first, a long epoch of general snow and ice accumulation. 
In its early part the growth of the ice-sheet was interrupted, 
at least locally and temporarily, by moderate oscillations of its 
boundary, as shown by layers of lignite between deposits of 
till observed by Dr. Robert Bell on branches of the Moose and 
Albany rivers tributary to the southwest side of James bay.’ 
Later, after the ice-sheet attained its maximum stage in the 
Mississippi basin, reaching south to northeastern Kansas, 
central Missouri and southern Illinois, this epoch included a 
long interval of extensive retreat of that part of the ice-sheet, 
followed by renewal of its growth until it again reached far 
1 Geol. Survey of Canada, Report of “Viegas for 1877-78, p. 4C; and Annual 
Report, new series, vol. ii, 1886, p. 38 G 
