HOW THE GREA1 LAKES WERE BUILT. 



161 



From the northern portion of the Michigan basin the channel 

 of the ancient Laurentian River is more or less buried beneath 





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 



VOL. XLIX. 14 



