. Bulletin of the Geological Society of America. Geology. STAGES OP RECESSION OF NORTH AMERICAN ICE-SHEET 207 Age of Lake Ikoquois Beginning with the age of the upper shelf worn in the deposits at Toronto, approximately about 200 feet above the level of Lake Ontario, it is to be noted as bearing on the subject: 1. That it is younger by several thousand years than the beaches of glacial origin about the south end of Lake Michigan and than those formed on the shores of Lake Warren on the south side of Lake Erie. No one will question the statement that the final retreat of glacial ice from the Un
. Bulletin of the Geological Society of America. Geology. STAGES OP RECESSION OF NORTH AMERICAN ICE-SHEET 207 Age of Lake Ikoquois Beginning with the age of the upper shelf worn in the deposits at Toronto, approximately about 200 feet above the level of Lake Ontario, it is to be noted as bearing on the subject: 1. That it is younger by several thousand years than the beaches of glacial origin about the south end of Lake Michigan and than those formed on the shores of Lake Warren on the south side of Lake Erie. No one will question the statement that the final retreat of glacial ice from the United States and Canada proceeded from the southwest, uncovering successively the western areas of the Great Lakes, until finally the ice barriers to the east over central New York and Quebec gave away and. FtGURE 2.—Map showing Stages of Recession of the North American Ice-sheet (Upham) permitted the drainage of the Great Lakes to pursue its present outlet (see map on opposite page). But for a considerable period there was a drainage leading to the Hudson Valley at a higher level along the ice- front through the valley of the Mohawk Eiver in central New York. Whatever age, therefore, we assign to the erosion of the 200-foot shelf at Toronto, the shorelines at the south of Lake Michigan and those of Lake Warren in Ohio must be much older. 2. But we are compelled to set moderate limits to the time which has elapsed since the ice withdrew from the southern end of Lake Michigan. a. The dunes at the south end of Lake Michigan represent accumula- tions which have been going on ever since the ice withdrew from that region. They are composed of sand, which is borne along by the waves and currents on the west shore of the lake and is finally caught up by. 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 Geological S
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectgeology, bookyear1890
