356 A. P. Coleman — Wave Work as a Measure of Time: 



waves measures from 2^ miles to about 3 miles. In my earlier 

 account it was given as 2J miles or 13,000 feet in round num- 

 bers, which corresponds with the average distance from shore 

 of the 15-fathom line of the new chart. 



Dr. Spencer casts this measurement aside and replaces it in 

 his own paper by a line drawn at a distance of 4,000 or 4,400 

 feet, his only assigned reason for this being that " its slope 

 should correspond to that of the country between the Iroquois 

 beach and the low shore just west of Victoria Park." As this 

 slope is on the rapid lakeward descent of an Iroquois gravel 

 bar and not on a carved terrace cut in the clay, such as that 

 south of Davenport ridge a few miles to the west, it is evident 

 that he has not distinguished between the two quite different 

 forms produced by wave-action. As shown before, the carved 

 terrace slopes only 170 feet in 2J or 3 miles, while the built 

 terrace descends much more steeply. As we are dealing with 

 a terrace carved from interglacial clay and sand and the suc- 

 cessive bowlder clays above, it is clear that the slope should 

 correspond, and the more rapid descent 2^ miles from shore 

 must be considered the lakeward end of the promontory. 



Thirteen thousand feet divided by 1'62 feet, the rate of 

 annual recession shown in 50 years, gives 8,000 years as the 

 length of time required to cut back the old Scarboro' promon- 

 tory. 



When the time required to cut back Scarboro' Heights to 

 its present position had been worked out, it seemed advisable 

 to take up the other end of the problem, i. e., the length of 

 time needed to build Toronto Island out of the sand trans- 

 ported from Scarboro'. For this purpose an estimate was 

 made of the amount of sand deposited northeast of a pier at 

 the eastern channel into Toronto bay during the thirteen years 

 since it had been constructed. The annual increment of sand 

 against the pier was estimated at about 42,000 cubic yards, 

 and the bulk of the island w^as roughly put at 337,000,000 

 cubic yards, which works out to a little over 8,000 years. 

 Owing to the short number of years during which sand had 

 accumulated east of the pier and to other uncertainties no 

 great stress w^as laid on this computation, though it seemed to 

 con-oborate the conclusion drawn from the Scarboro' recession. 

 For some reason not very clear to me. Dr. Spencer has reversed 

 things and assumed that vaj time estimate depended on the 

 growth of the island rather than the recession of the cliffs and 

 states that " the enormous mass of sand deposited here is of 

 more than local interest, having given rise to fatal chronologi- 

 cal speculations." He proceeds to demolish my line of argu- 

 ment by stating that only the upper 30 feet of the island 

 belong to the Ontario beach, the materials beneath being delta 

 deposits from the river Don. 



