Editorial Comment. 313 
growth and decline of the ice-sheets, in their first accumu- 
lation, great recessions and readvances, and their final melting 
away. From the beginning to the end of the glaciation are 
counted several stages or epochs of growth and wane, the 
principal times of ice advance and deposition of drift sheets 
and moraines in North America being named the Albertan, 
Kansan, Illinoian, lowan, and Wisconsin stages. 
Some glacialists have estimated the antiquity of the Kan- 
san stage of glaciation, when the ice-sheet extended farthest 
on the west side of the Mississippi, as from fifteen to fifty 
times as long ago as the end of the Ice age, that is, between 
100,000 and 400,000 years ago, while the Albertan stage and 
the beginning of the ice accumulation were still older. Others, 
however, recognizing the necessary limitations of the whole 
time of life on the earth, from the very ancient Algonkian 
period until now, considered by astronomers and physicists to 
be perhaps only about 20,000,000 years and quite surely no 
more than 100,000,000 years, and comparing the somewhat 
well known ratios of the geologic eras and periods, have con- 
cluded that the portion of time belonging to the relatively very 
short Glacial period, in all its stages, cannot exceed 100.000 
years. 
Such a measure of this period would place its Kansan stage 
some 50,000 to 25,000 years before its end ; and the lowan 
stage, to which the fossil man of Lansing, Kansas, is referred, 
would be only 12,000 to , 15,000 years ago. These estimates 
seem to me compatible with the characters of the Kansan and 
lowan drift formations. Instead of the great antiquity at- 
tributed by some to the Kansan drift on account of its plenti- 
ful pebbles of decayed rock, supposed to have rotted since the 
Ice age, I would refer these to a much later derivation from 
stream gravels that had been afifected during a long preceding 
period by subaerial decay, or to glacial erosion from pre- 
glacially weathered and decaying rock surface^;. The pebbles 
or eroded rock fragments would hold their form during the 
glacial erosion, transportation, and deposition, by being then 
frozen. Again, the patchy occurrence of the oldest till depos- 
its in some places near the extreme boundary of glaciation, 
often found on bights but absent from lower ground, I would 
not refer to subsequent erosion, implying a great lapse of 
