228 The American Geologist. October, 1S93 
of the ice border were often much changed in their relations 
to each other, so that, although the moraines are in general 
approximately parallel, they often are found interlocking and 
sometimes the newer extend obliquely across the older. When 
the ice-sheet re-advanced after the deposition and considerable 
erosion of the loess, the land was somewhat higher than now: 
but no great altitude is indicated for that or any other time 
in the long continued and diversified records of the Ice age. 
At its end, as long before when the loess was mostly deposited, 
the land was depressed, being lower than now at the north 
where the Champlain marine beds overlie the till. 
Mr. Warren Upham directed attention to the uniqueness 
of the climatic conditions during the glacial portion of the 
Quaternary era. Liberal estimates of the length of this era. 
from the beginning of the preglacial uplifts of drift-bearing 
countries to the present time, range from 100,000 to 200,000 
years, the lower of these figures being regarded by the speaker 
as the more probable. During a portion of this time contin- 
uously cold or cool climates with plentiful snowfall covered 
extensive regions in both the eastern and western hemispheres, 
and in the present temperate and higher latitudes about each 
pole, with deep ice-sheets, producing the glacial drift. But 
for the whole of the far longer Tertiary and Mesozoic eras, 
together probably a hundred times as long as the Quaternary, 
no record of extensive glaciation has been found in any part 
of the world. So exceptional climate in the Glacial period 
doubtless resulted from unusual causes, ami these could not be 
astronomic, for in that case frequent glacial periods would 
have occurred during the preceding long eras. Great epeiro- 
genic uplifts of the glaciated countries to form plateaus 
with cool climate all the year are thought to have given all 
the precipitation of moisture in the form of snow, by which 
the ice-sheets were amassed. Beneath the vast weight of the 
ice the land finally sank, but for a while the accumulation of 
ice went on faster than the rate of sinking, so that the great- 
est extent of the glaciation was reached about the same time 
with the maximum depression of the land, by which a warm 
climate was restored along the ice border. A chiefly rapid 
retreat of the ice ensued, interrupted at times by series of 
colder years and much snowfall, whereby the ice front was 
