1 74 Tlie American Geologist. March, i^** 
would include temperate species of forest trees, of land animals, 
and of mollusca where the ice pushed into lakes or the sea. 
Changes in the altitude and slopes of the land, shown by suc- 
cessive moraines and the accompanying gravel, sand, and silt 
deposits, which Prof. Salisbur}' would regard as evidence of suc- 
cessive glacial epochs, ma\' have taken place within a few hun- 
dred years, as the area of the glacial lake Agassiz was differ- 
entially uplifted, to a maximum of 40(1 feet or more, during the 
departure of the ice-sheet from that area, which yet appears to 
have occupied only about 1,000 years. 
CrolFs astronomic theory of the cause of the Ice age has led 
glacialists both in Europe and America to search for evidences 
of successive glacial and interglaeial epochs: but the recency of 
the final departure of the ice-sheets, besides other arguments, 
shows that this theory is untenable, although it has been exceed- 
ingly useful in leading to careful and widely extended observa- 
tions. It now therefore seems more probable that the Ice age 
was a period of continuous glaciation, with moderate fluctuations 
of the boundaries of the ice-sheets during both their general 
growth and decline. 
Dr. RoBEaT Bell spoke of layers of peat and lignite between 
deposits of till on the Nissinaibi and Kenogami rivers, trilnitary 
to James bay, while loose fragments of lignite probaljh' derived 
from similar laj'ers, are found on the Albany and Churchill rivers. 
It ma}' be doubted, however, whether the successive ice incursions 
should be regarded as distinct epochs, since the several bound- 
aries of the ice-sheets, shown b}' the limits of the diverse drift 
sheets and courses of the terminal moraines, are nearly parallel 
with each other. 
Prof. B. K. Emerson noted the general absence of indications 
of interglaeial conditions in New England, excepting very slight 
oscillations of the ice-border during its retreat, such as at one 
locality in the Connecticut valley gave three successive deposits 
of till with intercalated clays containing fossil leaves of subarctic 
plants. 
Professor Salisbury, in closing the discussion, objected to 
arguments on this subject based on studies of the regions covered 
and much eroded by the latest glaciation, as New England and 
the greater part of Canada. The proper areas for the discrimina- 
tion of these epochs lie along the borders of the drift sheet. Im- 
