Geology . Fig. 516.—The beginnings of the Great Lakes. The ice still occupied the largerparts of the present lake basins. (After Taylor and Leverett, U. S. Geol. Surv.) the Saginaw ice-lobe, lower than the Fort Wayne outlet. This pass wasthe Imlay outlet. The escaping waters then skirted the edge of theSaginaw ice-lobe to the valley of the Grand river, following whichthey crossed the lower peninsula of Michigan, and joined Lake Chicago(Fig. 517), the left horn of which had, by this time, reached thus farnorth. This constituted the second stage of Lake Maumee. THE PLEISTOCENE OR GLACIAL PERIOD
Geology . Fig. 516.—The beginnings of the Great Lakes. The ice still occupied the largerparts of the present lake basins. (After Taylor and Leverett, U. S. Geol. Surv.) the Saginaw ice-lobe, lower than the Fort Wayne outlet. This pass wasthe Imlay outlet. The escaping waters then skirted the edge of theSaginaw ice-lobe to the valley of the Grand river, following whichthey crossed the lower peninsula of Michigan, and joined Lake Chicago(Fig. 517), the left horn of which had, by this time, reached thus farnorth. This constituted the second stage of Lake Maumee. THE PLEISTOCENE OR GLACIAL PERIOD 397 Somewhat later, the Saginaw ice-lobe retired so that a crescenticlake (Lake Saginaw) gathered about its extremity, and dischargedthrough the Grand River outlet into Lake Chicago, and thence bythe Illinois route to the Mississippi. For a time, Lake Maumee con-tinued to discharge by the Imlay outlet into Lake Saginaw, and thenceto the Mississippi; but in the course of the retreat, a lower outlet across. Fig. 517.—A later stage in the development of Lakes Chicago and Maumee. The icehas retreated farther, and the outlet of Lake Maumee has been shifted. (Leverettand Taylor, U. S. Geol. Surv.) the thumb of eastern Michigan was discovered, and the Imlayoutlet was abandoned. Later, the whole Erie basin, and a portion of that of Ontario, becamefree from ice, and a lake twice the area of the present Lake Erie developed(Lake Arkona), and was marked by its own set of beaches. Accordingto the recent determinations of Taylor, an advance of the ice followed,closing the lower outlet across the Thumb of Michigan, and forcingthe water to occupy a higher one at L^bly. This stage was attendedby the formation of a beach (the Belmore) at a higher level than theArkona beaches, which were submerged but not wholly obliterated. 398 GEOLOGY.
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