THE IROQUOIS BEACH. 129 



uplift, aud a descent of the beach to the eastward, were first indicated by the reduced 

 barometric measurements (see table p. 124) ; which, although the result of several 

 observations were not accepted as evidence, for the amount was small, yet wath it 

 should have been included the loss of the former rate of rise. But the indication of the 

 Iroquois Beach beginning to descend to the east is strengthened by Mr. Gilbert's measure- 

 ments about Oneida Lake. This observation is of great importance, for henceforth we 

 may hope to be able to compare the beach with the marine terraces of Lake Champlain, 

 or those of the St. Lawrence, as at Montreal, where the Saxicava sand occurs at 520 feet 

 above the sea, and other unfossiliferous deposits at still greater elevations. 



If the axes of maximum elevation for the various triangles about Lake Ontario and 

 Georgian Bay be produced, they meet in or near lat. 51° N. and long. '74|° W., a few miles 

 west of Lake Mistassini, and east of the southern end of James' Bay. 



Although mainly radiating from the focus, the axes of maximum elevation for the 

 different triangles is not uniform, and are locally modified, as along the north-western side 

 of Lake Ontario, where there is found a secondary axis of uplift to the east. Combining 

 the more western axes with those at the eastern end of the lake, another focus of uplift 

 appears near the " height of land " between Lake Ontario and Hudson Bay, in about lat. 

 48° X. and long. *16° W. From the double foci, it may be inferred that the uplift reached 

 its maximum along a line joining the foci, or that the axis of the maximum regional uplift 

 was meridianal and located along the eastern end of Lake Ontario, increasing in amount 

 until near the " height of land," and thence with a diminishing ratio, or even depression, 

 towards the north. Still it is hardly probable that the increasing ratio is constant, as 

 there are local transverse folds on both sides of the western portion of the Ontario basin. 

 At any rate, it is in the region south-east of James Bay that the maximum differential 

 elevation of the earth's crust, which involved the Iroquois Beach, is to be looked for. 



(9.) The absence of Elevation of the Lake during the Iroquois Epoch. — The 

 recent warpings of the earth's crust in the region of the lakes have been those of elevation 

 to the north and east, not subsidence in the opposite direction. The general subsidence was 

 at an earlier period than that of the beaches, and did not produce the warpings involved 

 in the beach epoch. The elevated condition of the lake, during the epoch of the Iroquois 

 Beach is opposed by the fact that the lake would have required an unknown barrier forty 

 miles or more across, and six or eight hundred feet higher than that of the present time ; 

 also, in subsiding *700 feet — the best known and measured amount of differential chann-e 

 between the extreme eastern end of Ontario and the southern end of Lake Michigan — the 

 drainage of the adjacent rivers would have been so greatly changed as to become apparent. 

 Moreover, such subsidence is not indicated by the elevated marine terraces of the St. 

 Lawrence. The elevation of the lake during the Irocjuois epoch is known to have been 

 at sea level. Its lowest portion, at the western end of the lake, is now 363 feet above the 

 ocean, and at Cape Rutland about *700 feet, but it is necessary to go outside the basin to 

 learn the additional elevation which has affected the whole basin. The differential uplift, 

 however, between the south-eastern side of Michigan and the western end of Ontario, 

 amounts to 360 feet ; ' as measured upon beaches somewhat older than the Iroquois, but 



' At Crittenden, N.Y., ]Mr. Gilbert found an Erie beacli at 860 feet above tlie sea. At Cleveland, Ohio, this is 

 673 feet. Again, another beach at Cleveland is 743 feet, and is traceable to the eastern side of Lake jMichigan, 

 where I found it at 627 feet above tide. Thence to the south-western part of the lake there is further indication of 

 a depression of 60 feet more. 



Sec. IV, 1889. 17. 



