360 A. P. COLEMAN — IROQUOIS BEACH IN ONTARIO 



case we must suppose that the isobases are curves of long radius, with 

 the area of greatest uplift at the center, so that the direction must vary 

 in different parts of the Great Lakes region. The Hamilton beach (116 

 feet above lake Ontario) was the lowest point recorded on the shore, and 

 the beaches at Trenton, in Ontario (at 386 feet), and one near Adams 

 Center, in New York (at 411 feet), or Prospect farm (at 484 feet) were 

 the highest noted. Doctor Spencer estimated the rate of differential 

 elevation at 1.6 feet per mile between Hamilton and Carlton (now Toronto 

 junction) and 5 feet per mile in the Watertown region, with intermediate 

 rates between. 



During the present survey of the Iroquois beach a number of eleva- 

 tions have been determined, partly in old localities, but largely in new 

 ones, and some changes in the probable rate and direction of the warp- 

 ing result from these determinations. In general the top of gravel bars 

 has been taken as giving most definitely the old water levels, though 

 these were no doubt often a few feet above mean water level, perhaps 

 5 feet on the average, as we find to be the case on the shore of lake 

 Ontario at present. Lake Iroquois was, of course, larger than Ontario, 

 and wave action must have been somewhat more powerful, but the old 

 bars can hardly have risen more than 10 feet at most above the level of 

 the water, and may be assumed to have a fairly uniform relation to that 

 level on all parts of the shore. The foot of shore cliffs is more uncertain, 

 owing to the slipping and creeping of clay and other loose materials 

 since Iroquois times. 



An attempt has been made to work out isobases with somewhat con- 

 flicting results, but, using my best determinations of the water levels, the 

 most probable direction of elevation is found to be north 20 degrees east, 

 and this will be assumed to be correct in the following work. 



In determining the rate of deformation of different sections of the 

 Iroquois beach three equal subdivisiors have been made — from Hamil- 

 ton to York, from York to Quays, near Port Hope, and from Quays to 

 the last point where the beach has been found. 



At Hamilton the beach stands 116 feet above Ontario, and at York 

 190 feet (as averaged from three determinations at different points on 

 the old bar), the difference of level being 74 feet in a distance of 36£ 

 miles, as measured in a direction north 20 degrees east, giving an aver- 

 age inclination of 2 feet per mile. 



Between York (190) and Quays gravel pit (311) there is a difference 

 of 121 feet in 35£ miles, averaging 3.4 feet per mile. Be}^ond Quays, or 

 rather beyond Colborne, a few miles to the northeast, the beach is found 

 to be split up, as shown in earlier parts of this paper, and the question 

 of the amount of deformation per mile becomes much more complicated. 



