;)88 Tne American Geologist. May, i897 
the other lakes were caused by glacial erosion and drift ac- 
cumulation in a pre-existing river valley. 
1888. G. K. Gilbert: "Changes pf Level of the Great 
Lakes." The Forum, June, 1888. See pp. 419, 420, where Gil- 
bert gives a glacial erosion origin to all the great lakes. 
J. W. Spencer: "Origin and History of the Great Lakes of 
North America," Proc. Amer. Assoc. Adv. Sci., vol. xxxi, p. 
197. 
J. W. Spencer: "The St. Lawrence Basin and the Great 
Lakes," Canad. Rec. Sci., vol. iii, p. 232. 
1889. G.F.Wright: "The Ice Age in North America," on 
page 316 and 317 Wright ascribes the excavation of the basins 
of all the lakes except the western end of lake Superior to 
the action of the great ice-sheet. 
1890. J. W. Spencer: "Origin of the Great Lakes of A- 
merica," Quart. Jour. Geol. Soc, vol. xlvi, p. 523. 
1891. J. LeConte: "Elements of Geology," 3d ed., p. 560, 
The basins of the great lakes "probably did not exist in the 
Tertiary period but in their place was a great depression drain- 
ing northeastward." 
J. W. Spencer: "Origin of the Basins of the Great Lakes of 
America." Amer. Geol., vol. vii, p. 86; Spencer here gives a 
map of the pre-glacial river system occupying the valley of 
lakes Michigan, Huron, Erie, and Ontario. 
1894. J. W. Spencer : "Deformation of the Lundy Beach 
and Birth of Lake Erie," Amer. Jour. Sci., Ser. Ill, vol. xlvii, 
p. 207. 
J. W. Spencer: "A Review of the History of the Great 
Lakes," Amer. Geol., vol. xiv, p. 289. 
1895. I. C. Russell : "Lakes of North America." P. 29 : 
"While lakes in synclinal basins might be expected to be of 
common occurrence, they are in reality so rare that so far 
as I am aware none of the tens of thousands of the lakes of 
America can be pointed to as examples." Russell probably 
forgets lake Superior. See also p. 97. 
1896. J. W. Spencer : "How the Great Lakes Were Built," 
App. Pop. Sci. Mon.,vol. xlix, p. 157; This is Spencer's lat- 
est and fullest amplification of his theory: "The lake basins 
are simply fragments of the old valleys of the St. Lawrence 
river and its tributaries." These fragments were cut off by 
