Davis.] 
362 
[January 18, 
lakes in Canada, New England and the Adirondacks are of this 
origin, but nowhere are drift-barriers of more significance than 
in the region of our Great Lakes. With the exception already 
noted (A. 2) there is nothing to show that they are basins of 
subsidence or disturbance, for the rocks around their shores lie 
essentially horizontal ; the evidence ordinarily quoted to prove 
their glacial origin 1 proves only their glacial occupation. Much 
more important than these surmises, are the observations concern- 
ing the preglacial channels by which the lake troughs were once 
drained. To understand the possibility of such channels, it must 
be borne in mind that Northeastern America has been above 
the sea for long geological periods, at a greater elevation than 
the present, especially to the north, and so subject to subaerial 
erosion by which valleys are made ; after their formation came 
the glacial period, when many of the narrower valleys were filled 
with detritus which has not yet been washed out. The features 
of this “ extinct geography ” thus far made probable are as fol- 
lows 2 : Huron, Erie and Ontario form a system of eastern drain- 
age; Huron draining into Erie by a buried channel passing 
near London and Vienna, Erie emptying into the westernmost 
1 Newberry, Geol. Ohio, I, 45 ; ii, 72. G. J. Hinde, Canad. Journ., xv, 1877, 396. 
2 G. K. Warren, An essay concerning the important physical features exhibited in 
the valley of the Minnesota River and upon their signification, Washington, 1875. 
See also U. S. Chief of Engineers’ Report, 1868, 307 — , and Amer. Journ. Sci., xvi, 
1878, 417. 
Newberry, On the Surface Geology of the Basin of the Great Lakes, and the Valley 
of the Mississippi. Boston Soc. Nat. Hist., Proc., ix, 1862-63, 42 ; N. Y. Lyceum 
Nat. Hist., Ann., ix, 1870, 1; Amer Nat., iv, 1870-71, 193. Geol Ohio, I, 1873, 42—; 
ii, 1874, 12 — (including in the last, observations by Orton and Gilbert). Newberry 
believes also in great glacial erosion. 
E. Andrews, The North American Lakes considered as chronometers of Postglacial 
Time, Chicago Acad. Sci., Trans., ii, 1870. 
N. H. Winchell, Glacial Features of Green Bay and former outlet of Lake Superior. 
Amer. Journ. Sci., ii, 1871, 15. 
E. W. Ciavpole, On the Preglacial Geography of the Region of the Great Lakes. 
Canad. Nat., vm, 1878, 187 ; also Amer. Assoc., Proc., xxx, 1881. 
J. F. Carl), Preglacial and postglacial drainage of Erie Co., Pa., 2d Geol. Surv. 
Pa., in, 1880,331. 
J. W. Spencer, Discovery of the Preglacial Outlet of the Basin of Lake Erie into 
that of Lake Ontario; with Notes on the Origin of our Lower Great Lakes. Amer. Phil 
Soc., Proc., xix, 1881, 300; a sketch map of the old channels is given ; also Amer. 
Assoc., Proc., xxx, 1881. 
