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Toleston Shoreline
The Toleston Shoreline is the third ancient shoreline of the precursor to Lake Michigan, Lake Chicago. It takes its name from the village of Toleston, now a portion of Gary, Indiana. The shoreline formed when Lake Chicago was high enough to drain through the Chicago outlet into the Des Plaines River. The beach is above the level of Lake Michigan. The Indiana segment and the Illinois segment, north to Evanston are still visible. North of Evanston and Michigan City, Indiana, the beach has been eroded by later ice movement or shoreline wave action.
The Toleston beach appeared to be present at Holland, Michigan, at the eastern end of Black Lake, being built out between the lake and the marsh, which extends east from Holland a short distance. It is there built up to a height of above Lake Michigan, as shown by Goldthwait's levels. From Holland it seems likely to have continued northward to the Grand River, but as that region is extensively covered with sand blown from the modern shore the beach is largely concealed. In Springport, Goldthwait's levels show the beach to be about above Lake Michigan. From the Grand River it appears to run northwestward, passing just east of Little Black Lake on the line of Muskegon and Ottawa counties and coming to the shore of Lake Michigan directly west of the north end of the lake. There is probably no point between Holland and the Grand River where its distance from the present shore exceeds , and throughout much of the distance it probably does not exceed .〔
==Correlations to other glacial landscapes==
The Toleston beach may have been only partly formed by Lake Chicago. It has a level that was closely approximated if not reached by Lake Algonquin. The occurrence of a lake at this level in Algonquin time makes this beach a part of the Algonquin beach of the upper Great Lakes region.〔 The Algonquin beach carries in a few places molluscan shells, and this beach of Lake Chicago is in places richly supplied with these shells. In this respect it contrasts with the Calumet and Glenwood beaches, from which molluscan remains have as yet been reported at but one locality, near Bowmanville, north of Chicago. Although Lake Algonquin did have two outlets (past Chicago and Port Huron), sufficient reason for its later complete discharge by Port Huron is found in the fact that the latter outlet was through easily eroded drift deposits and the Chicago outlet was over a rock sill.〔
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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