SUMMAKY 367 



climate in the region during the life of lake Iroquois, which would ac- 

 count for the slowness in melting of the ice-sheet which shut it out from 

 the Saint Lawrence valley, and so give a reason for the great permanence 

 of this ice-dammed lake. 



If the differential elevation toward the northeast, which it has been 

 shown took place during the existence of lake Iroquois, was due to the 

 unloading of the land in that quarter by the removal of ice, we must 

 suppose that a great part of the original thickness of the ice sheet had 

 alread}' vanished, not only toward the edge, but also toward the center 

 of accumulation, for the tilt is greater toward the northeast than toward 

 the southwest. This explanation of the relationships is opposed to Mr 

 Warren Upham's view that the ice toward the end of the glacial period 

 oscillated considerably, presenting a steep front toward a region having 

 a relatively warm climate. The considerations just brought forward 

 indicate, on the contrary, a great thinning of the ice-sheet as a whole, 

 accompanied, no doubt, by a stagnant condition of the edge of the ice, 

 but with a cool climate in the adjacent land, causing only a slow rate of 

 melting. 



Summary 



• 



The Iroquois beach in Ontario can be followed without important 

 interruptions from the Niagara river to Hamilton, and then northeast 

 to Colborne as a single shoreline of a very well marked kind. From 

 the evidence of old soils, the bones of mammoths, etcetera, and the 

 structure of gravel bars and other deposits at Hamilton and Toronto, it 

 is certain that the earlier levels of lake Iroquois toward the southwest 

 end were 80 feet or more below its last beach. 



From Colborne east and north the shore is split into several beaches, 

 which are more widely separated as one advances northeast, though not 

 in a very regular way. The beach appears on promontories and islands 

 as far as Trent bridge near Havelock on the north and West Hunting- 

 don on the northeast, but can not be traced farther, though high enough 

 hills with a suitable surface occur in the region. This is probably be- 

 cause an ice-sheet covered the region to the east and north. 



The direction of greatest inclination is north 20 degrees east, and an 

 isobase drawn at right angles to this from the Rome outlet cuts the 

 northern shore at Quays, near Port Hope, about at the point where the 

 beach begins to split up. On the south and east sides of lake Iroquois 

 the same relations exist, the old shore being a unit as far east as the 

 Rome outlet, but split up into several beaches to the northeast. 



The best explanation of these facts is found in the theory of differen- 

 tial elevation toward the northeast during Iroquois times. The defor- 



