22 PLEISTOCENE OF INDIANA AND MICHIGAN. 



uplift had brought the outlet up past the level of the St. Clair outlet and had caused a return 

 to the discharge through the St. Clair Valley. There appears to have been a long two-outlet 

 stage during which the beach known as the Nipissing was formed. The earlier beach, formed 

 during the operation of the Ottawa outlet alone, became submerged and effaced by the rising 

 waters everywhere in this lake area south of an isobase running through the head of the outlet. 



Chapter XXIII. Post-Nipissing Great Lakes and summary of glacial and non- 

 glacial lakes. — Beaches between the Nipissing and modern beaches, correlative post-Nipis- 

 sing lakes in the Erie and Ontario basins, and the Champlain Sea are discussed. The problem 

 of recent and progressing earth movement is considered briefly. 



Chapter XXIV. Postglacial development of connecting rivers of the Great 

 Lakes. — The history of St. Clair and Detroit rivers is given in some detail and that of the other 

 rivers is briefly outlined. 



Chapter XXV. Deformation of the shore lines. — The probable influence of ice 

 attraction and the resilience following depression by ice weighting are discussed. Tectonic 

 earth movements and negative eustatic and oceanic oscillatory movements are briefly con- 

 sidered. 



Chapter XXVI. Economic resources. — Marl, peat, clay, and other materials of com- 

 mercial value, underground water supplies, and the agricultural values of the soils of the 

 region are briefly treated. References are made to detailed descriptions published elsewhere. 



