190 Tlie American Geologist. Marcii, i893 
most couclusively exhil)ite(l along the marginiil portions of the 
drift; but this belt has been specially examined by Prof. Wright 
from the Atlantic to the Mississippi, and in Nebraska and South 
and North Dakota, from which he thinks that the best explana- 
tion is b}- a single glacial epoch, with moderate retreats and re- 
advances of the ice. In the light of Kussell's observations of the 
3Ialaspina glacier or ice-sheet, which show that the forest beds of 
Illinois, Iowa, and adjoining states, may be readily explained hy 
oscillations of the ice-border, the doctrine of continuous glacia- 
tion seems to me more probable than that of duality. It is help- 
ful to have both views under consideration, since thereb}' more 
careful attention is given to the examination of the drift and to 
the study for a consistent and complete explanation of the Ice age 
and of the diverse ways in which the various deposits of glacial 
and modified drift were produced. 
Some of Prof. Wrights reviewers think that there is so strong 
a presumption against the presence of man in America during the 
Ice age, that all the stone implements and flakes of their manu- 
facture discovered in deposits of Glacial age l)y Abbott, Putnam, 
Shaler, Metz, Mills, Miss Babbitt. Tyrrell, McGee, Whitney, 
King, and o'hers, should be rejected, as l)elonging instead to post- 
glacial times, because of this assumed improbal)ility that men 
could have reached this continent before the end of the Glacial 
period. This prejudice seems to have no sufficient foundation. 
Before the lieginning of written or traditional histor}-, the three 
great races of mankind had become apparently as distinct from 
each other as they are to-day, and this historic period extends 
back nearly or quite to the time when the North American ice- 
sheet finally melted awa}'. To me it seems far more probalile 
that the native American peoples, now generall}' considered a 
division of the Mongolian race, had migrated to our continent 
from northeastern Asia during the early Quaternary time of gen- 
eral uplift of northern regions which preceded the Ice age. as 
shown by their fjords and subtnarine valleys. Then land prob- 
ably extended across the present areas of Bering sea and strait; 
but during the Postglacial epoch, according to Dall, Bering strait 
has been somewhat wider and deeper than now, and the neighbor- 
ing coasts have undergone recent elevation. The many divergent 
branches of the American peo])les. and their remarkal)le progress 
toward civilization in Mexico. Central America and Peru, before 
