. Annual report. New York State Museum; Science; Science. THE GEOLOGICAL HISTORY OF NEW YORK STATE 97 lake basins were appreciably deepened. Even so, however, we have not yet accounted for the present closed basins. In the writer's opinion the two most important phenomena which have contributed to the formation of the closed basins of the Great Lakes are the great drift accumulations along the south side and the tilting of the land downward on the north side of this region. The deep drift deposits must certainly have been very effective in damming up the south or southwesterly-flowing preglaci
. Annual report. New York State Museum; Science; Science. THE GEOLOGICAL HISTORY OF NEW YORK STATE 97 lake basins were appreciably deepened. Even so, however, we have not yet accounted for the present closed basins. In the writer's opinion the two most important phenomena which have contributed to the formation of the closed basins of the Great Lakes are the great drift accumulations along the south side and the tilting of the land downward on the north side of this region. The deep drift deposits must certainly have been very effective in damming up the south or southwesterly-flowing preglacial streams of the region. For example, the deep channel of the so-called Dundas. <^-^«i^-- x. Fig. 30 The first stage in the formation of the Great Lakes, when most of the region was still buried under the ice. After Taylor & Leverett river (see figure 27) has been drift-filled as proved by many well borings, and a distinct moraine extends around the southern half of Lake Michigan. The great clumping ground of ice-transported materials from the north was in general along the southern side of the Great Lakes and southward. Late in the Ice age the land on the northern side of the Great Lakes region was lower than it is today as proved by the tilted character of certain well-known beaches of extinct glacial lakes (see below). Such a differential tilting or warping of the land must have helped to form the closed basins by tending to stop the southward or southwestward drainage. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original New York State Museum. Albany : University of the State of New York
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