Page:Popular Science Monthly Volume 49.djvu/175

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161
HOW THE GREAT LAKES WERE BUILT.

From the northern portion of the Michigan basin the channel of the ancient Laurentian River is more or less buried beneath

PSM V49 D175 Map of ancient st lawrence river and tributaries.jpg

Fig. 5.—Map showing Course of the Ancient St. Lawrence and its Tributaries.

drift and also submerged in extending by way of Mackinac Straits to the Huron basin, across which its course is plainly marked at the foot of an escarpment from three hundred and fifty