GLACIAL LAKES TAYLOR. 



323 



strength, until in the area of horizontaHty it seems httle if any stronger 

 than the Algonquin beach. 



In the western end of Lake Superior the Nipissing beach appeai-s 

 to pass a Uttle under the present lake level, a relation which probably 

 accounts for the drowned condition of the shores and stream mouths 

 of that region. 



Supposing a short period of southward discharge passed Port Huron 

 at the time of early Lake Algonquin, then the Port Huron outlet and 

 the St. Clair and Detroit Rivers have twice been abandoned and left 





Fig. 9. — Isobases of Nipissing Great Lakes. 

 By Frank B. Taylor and Frank Leverett, 1911. 



dry, and at both times Niagara River was robbed of the overflow of the 

 upper three lakes. 



The Nipissing Great Lakes came to an end when the northern 

 uplift raised North Bay, so that that outlet was left dry and the whole 

 discharge returned to Port Huron. With this change the modern 

 Great Lakes have their beguiniii":. 



THE POST-NIPISSING GREAT LAKES. 



Since the overflow came back to Port Huron the northern upUft- 

 ing has continued, but apparently at a relatively slow rate, for there 

 is a numerous series of fainter beaches on the slope below the Nipissing 

 beach. One especially is sUghtly stronger than the rest and seems 



