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



The most striking physiographic feature in the vicinity of 

 Toronto is Scarboro' Heights to the northeast of the city, 

 extending as bold clifis of stratified clay and sand capped with 

 bowlder clay, for a distance of nine-and-a-half miles in a nearly 

 straight line, and rising for a short distance near the center to 

 350 feet above Lake Ontario. These cliffs have been studied 

 by the present writer every year since 1890, and the undercut- 

 ting by waves and the land slips occurring in the spring give 

 clear evidence of recession. During the time of observation 

 the shore has receded in a nearly straight line, and the most 

 satisfactory mode of determining the rate of recession would 

 be to compare the results of careful mapping of the shore, 

 repeated after a lapse of years. Unfortunately no such map 

 has been made, the only accurate measurements available hav- 

 ing been carried to the top of the cliff and not to the shore. 

 However, it has been found in more than 20 years of observa- 

 tion that the slope of the cliffs has remained very uniform, so 

 that results obtained from the edge of the heights must corre- 

 spond closely on the whole with the recession of the shore 

 beneath. 



It has been noted also that, with the clearing of the forest 

 ravines due to rain, erosions have become more frequent and 

 are cut backwards more rapidly than formerly. In some cases 

 such rain gullies have advanced more than fifty feet inland in 

 a single season, and it is evident that only the actual edge of 

 the cliffs, corresponding to the nearly straight shore beneath, 

 can be taken into account in determining the rate of recession. 



The first survey of Scarboro' was made in 1792, as shown 

 by plans at the Crown Lands Department of Ontario, but no 

 accurate work was done until 1862 and '63 when Mr. F. F. 

 Passmore carefully re-surveyed the township, planting corner 

 stones to fix the road allowances and the boundaries of proper- 

 ties. In 1912 I was asked by the City Commissioner of 

 Toronto, Mr. H. C. Harris, to report on the rate of recession 

 of the cliffs, since the location of a reservoir on the heights 

 was under consideration. On my recommendation Messrs. 

 Speight and Van Xostrand repeated Passmore's measurements 

 toward the end of 1912, fifty years after the original survey. 

 Beginning at the southwest, the recession at the seventeen 

 points where corner posts were available is as follows : 8, 98, 93, 

 120, 85, 55, 198, 31, 76, 50, 167, 199, 127, 128, 62, 39, and 89 

 feet. An examination of the edge to which the measurement 

 was made at these different points showed that the three larg- 

 est recessions, 198, 167 and 199, occurred where ravines were 

 being actively cut, and so should not be included in the com- 

 putation. Tiie first one, of 8 feet, was on low ground at the end 

 of the cliff where little wave work was going on and was left 



