448 Spencer — Deformation of Iroquois Beach' and 



the sea level (363 feet), as the amount of movement that must 

 be added to the Iroquois plain in order to represent the terres- 

 trial uplift of the Ontario basin since the Iroquois shore was 

 formed. Therefore, it is apparent that the great Iroquois 

 Beach was constructed approximately at sea level. The total 

 amount of uplift since the episode will then be the height of 

 the beach, at any place, measured above the sea level, which, 

 at Fine, is 972 feet. 



Were the Erie beaches recognizable in the Adirondack 

 wilderness near Fine, they would be found at altitudes of 1600 

 feet and more above the sea. But this is a calculation outside 

 of our subject, which is based upon measurements. 



The terrestrial movements recorded in the beaches have not 

 been those of subsidence towards the west, but of uplift to- 

 wards the east, in the same direction as those changes which 

 have left unquestioned marine remains deposited at high alti- 

 tudes in the St. Lawrence valley. 



One focus of the warping about the western end of Lake 

 Ontario and about Georgian Bay appears to have been in the 

 region of lat. 48° N., long. 76° W. Another focus of uplift is 

 somewhere beyond the last point of rise measured in the 

 Adirondacks. Thus the axis between these foci appears to 

 coincide, more or less, with the old Archaean axis of the conti- 

 nent, as suggested by Professor Dana. 



The uplift of the Iroquois Beach has been since the episode 

 of the uppermost deposits of drift or till, for higher and older 

 beaches than the Iroquois rest upon the newest stony clays of 

 Ontario, Michigan and other slates. The Iroquois Beach rests 

 upon the mud floors of the earlier sheets of water which cov- 

 ered the till deposits. The rate of northeastward regional 

 uplift has been gradually diminishing, for we find other 

 beaches, lower than the Iroquois, whose rate of rise is much 

 reduced below that of the great beach. But the Iroquois plain 

 was the great event in the history of the Ontario basin. 



In the rising of the land, after the Iroquois episode, there 

 were pauses, but not of such duration as to permit of the 

 formation of great shore-lines like that just described. After 

 the waters had fallen about two hundred feet below the 

 Iroquois plain, there was a conspicuous rest. This is recorded 

 in a terrace near Watertown at 535 feet above the sea. At 

 Oswego, we find a beach descending to near water level, at 

 about 185 feet below the great Iroquois beach. Farther west- 

 ward, it passes below the lake. The dip of the Iroquois Beach, 

 between the region of Oswego and the western end of the lake, 

 is about 78 feet ; and accordingly we should find the remains 

 of this younger shore-line (for a large proportion of the re- 

 gional uplift has been effected since its formation) submerged 



