REVIEW OF EPEIROGEXIG UPLIFTING. 237 



northern part of the basin, on the kxtitude of 52° north, about 400 feet, if 

 we neglect the fall of the lake level, in comparison with Lake Traverse. 

 At the same time, or possibly still later, the northern end of the area of 

 Lake Agassiz and the adjoining- portion of the Churchill basin were uplifted 

 a similar amount. Last of all, when Lake Winnipeg and the Nelson River 

 had come into existence, the shores of Hudson and James bays were raised 

 300 to 500 feet from their temporary postglacial marine submergence. 



The elevation of the eastern shore-lines of Lake Agassiz, in Minnesota, 

 exceeded that of the western shores, in North Dakota; and the ratio of this 

 eastward ascent of the old lake levels to their doubly greater northward 

 ascent implies that the tilting of this area was from south-southwest to 

 north-northeast. Again, at the north end of Duck Mountain, the west-to- 

 east portions of beaches observed by Mr. Tyrrell, Ijetween the Swan and 

 Duck rivers, show a similar eastward ascent, about half as much as the 

 northward rise along the eastern base of this highland. It thus appears 

 true of the greater tilting of that northern district also, after the formation 

 of the Campbell beach, that its maximum ascent was toward the north- 

 northeast; but, like the elevation Ijetween Lake Traverse and Gladstone, 

 this movement was doubtless of limited extent, so that the country adjoin- 

 ing Hudson Bay retained nearly or quite its maximum depression until the 

 somewhat later time wlien the sea was admitted to that basin. 



MOLiLUSCAX FAUKA OF LAKE AGASSIZ. 



Fossils have been found in the deposits of Lake Agassiz at two locali- 

 ties. They are all fresh-water shells of species now living in this district, 

 occuiTing in beach ridges where excavations have been made to obtain 

 sand for masons' vise. The Campbell beach, about 6 miles southwest of 

 Campbell, Minn., at an elevation approximately 985 feet above the sea, has 

 thus yielded shells of Unio ellipsis Lea, a common species of the Upper 

 Mississippi region. In the Gladstone beach, a half mile northeast of Glad- 

 stone, Manitoba, about 875 feet above the sea and 165 feet above Lake 

 Winnipeg, four species occur in considerable abvmdance from 2 to 4 feet 

 below the surface, namely, Unio luteolus Lamarck, SphcBrium striatinum 



