The Age of the Great Lakes. — Winchell. 337 
"All our great lakes are probably very ancient, and their 
formation may have begun during the Coal Measure epoch," 
p. 72. 
''There can be no doubt that the basin of each of the great 
lakes has been produced by a local glacier," p. 74. 
"Lake Superit)r lies in a synclinal trough, and its mode of 
formation, therefore, hardly admits of question," p. 72. 
1878. E. W. Claypole: "On the Pre-Glacial Geography of 
the Great Lakes," Canad. Naturalist, New Series, vol. viii, p. 
187; Claypole believes that the great lakes, with the possible 
exception of Superior, 0(3cupied tlie valley of a pre-glacial river, 
and (p. 205), "The great American lakes, therefore, are noth- 
ing but merely drift-dammed pools," and not essentially erod- 
ed by the ice. This view gives to the lakes the same age as 
the theory of origin by glacial erosion of the basins. 
1879. J. D. Dana : Manual of Geology, 3d ed., pp. 394 and 
825. The depressions in which the great lakes lie must be 
geosynclinal. or "Intermont," in origin; thus, the lakes would 
probably have a great age. 
1881. J.W.Spencer: "Discovery of the Pre-Glacial Out- 
let of the Basin of Lake Erie." read before the Amer. Phil. 
Soc, March 18, 1881. Spencer amplifies the theory that a 
great river occupied the valley of all the great lakes in pre- 
glacial time; he presents a map of the river system in lakes 
Erie and Ontario, and asserts that all the lakes "owe their 
existence to sub-aerial and tluviatile agencies." See reprint 
of above article in Reports of Geol. Surv., Pa., vol. Q4, p. 361. 
J. W. Spencer: "A Short Study of the Features of the Low- 
er Great Lakes during the Great River Age." Proc. Anier. 
Assoc. Adv. Sci., vol. xxx. p. 131 ; another presentation of the 
above view. Lake Superior in not on the whole excepted, st-e 
p. 139. 
1882. W.M.Davis: "On the Classification of Lake Ba- 
sins," Proc. Boston Soc. Nat. Hist., vol, xxi, p. 315; Davis 
believes in the theory of a pre-glacial river, but thinks lake 
Superior, at least in part, existed in pre-glacial times. 
1886. A. Winchell: "Walks and Talks in the Geological 
Field," p. 278- "The Niagara river has been at work on avast 
gorge ever since the Devonian Age. Probabl}'^ none of the 
great Mkes except Superior, then existed." Winchell thinks 
