B64 The American Geologist. May,i894 
forms, or of Like lithologic character, apart in small hoards or places of 
ptment, I still believe that men making stone implements were here 
while the modified drift was being deposited. Nor was this geologically 
long ago, for Prof. N. II. Winchell's well known studies of the recession 
of the Falls of St. Anthony from Ft. Snelliug to Minneapolis indicate 
that the time since the departure of the ice-sheet from Minnesota has 
been probably between 6,000 and 9,000 years, his average from three es- 
timates being 7,800 years.* 
Professor Holmes suggests that tornadoes and overturned trees up- 
rooting the ground to depths of several feet can account for the f requenl 
occurrence of flaked quartz fragments in the superficial part of the 
modified drift in the vicinity of Little Falls, where they had been found 
by Prof. Winched previous to Miss Babbitt's discoveries. If we con- 
sider the iofrequency of the passing of tornadoes over any one place and 
the scarcity of t he quartz chippings upon and in the surface soil, I think 
that this hypothesis seems improbable. 
There is no inherent presumption against the presence of men at this 
locality when the ice-sheel was being rapidly melted away by a temper- 
ate climate. ( )u the shores of the glacial lakes Au'assiz and Iroquois, in 
and beneath their beach ridges of gravel and sand, Tyrrell and Gilbert 
have reported reliable evidences of man's presence, and these belong to 
the same time of final melting of the ice-sheet. Likewise the somewhat 
earlier stone implements found in glacial gravels in Ohio and New Jer- 
sey, and those of the auriferous gravels under lava Hows which now are 
the cap of "table mountains - ' in California, all represent probably near- 
ly the same late portion of the Pleistocene period. 
Seeing the widely differentiated condition of the many tribes and 
larger divisions of the American race, some attaining much skill in arts 
and government, as in Mexico. Central America, and Peru, before 
the advent of Columbus and the conquering Spaniards, I cannot doubt 
that the first coming of men to this continent was previous to the geo- 
logically short and recent Ice age. Following Flower and Lydekker in 
regarding the American as a branch of the ureal Mongolian stock, we 
have in the general uplift of northern lands preceding and finally in- 
augurating the Ice age an easy route of immigration from Asia across 
a broad land area that lias been since covered by the shallow Bering sea. 
No less time, probably, than the duration of the Glacial and Postglacial 
periods could suffice for t he variations in physical types and in languages 
that have come about since the earliest migration of men to America. 
In my recent paper in the Bulletin of the Geological Society of Amer- 
ica (vol. v. p. 99, Jan., 1894), the duration of the preglacial time of 
increased elevation of northern lands is estimated as some 60,000 to 
120,000 years ; of the Glacial period, attending the culmination of the 
uplift, but terminating after the subsidence of the glaciated region, 
30,000 to 30,000 years ; and of the Postglacial or Recent period, extend- 
ing to the present time, 6,000 t<> 10,000 years. Warreh Upham. 
Man-h .11, IS'.) J,. 
'Geology of Minnesota, Final Report, vol. n. 18S8, pp. 313-341, with maps andplatos. 
