494 A. W. G. WILSON SHORELINE STUDIES ON ONTARIO AND ERIE 



strong enough to hold even fine sands in suspension for any length of 

 time — a fact which may be readily ascertained by experiment, or as is 

 shown by the rapidity with which the water in the shore zone clears as 

 soon as the waves cease. During the late autumn, following the autumn 

 gales, and during early spring, following the winter storms, there is a 

 belt of water along the shore in which there is a great deal of fine clay 

 in suspension. In Ontario at times this belt is as much as a mile or 

 more in width; in Erie, which is much the shallower of the two lakes, 

 it may be 2 or 3 miles wide. This suspended clay is carried for some 

 time by the longshore currents and also by the currents of the general 

 circulation; but transportation of the sands and all coarse materials on 

 and along the shores ceases as soon as the swells stop. The coarse mate- 

 rials — boulders, cobbles, and pebbles — are shifted almost whollj' by the 

 waves, the smaller gravel and the sand by both waves and currents, the 

 finer clays largely by the currents. During a period of heavy storms a 

 longshore current may acquire a velocity as much as 4 miles an hour. 



The Supply of Materials 



CHARACTER OF THE MATERIALS 



The materials in general. — The materials found on the shore and 

 adjacent to it, which have been distributed there by the shore processes, 

 are fine clays and silts, sands and gravels, cobbles, and boulders. The 

 clays and silts in large part are derived from similar materials in situ 

 and are brought to the shores by various processes ; in small part they are 

 produced at the shore by the grinding of the coarser materials upon one 

 another and on the bedrock in the process of transportation. The sands 

 are derived almost wholly from sands of glacial origin. The gravels 

 and cobbles come from beds of till in large part ; along those portions of 

 the shore where there are bedrock exposures often almost all of them are 

 derived from the bedrock in situ. ' Generally there is a slight admixture 

 of material of glacial origin. The boulders and large blocks are usually 

 of glacial origin, though here and there one may note blocks of the adja- 

 cent bedrock only shifted a short distance from its source. 



Bedrocli. — The shores of the lakes are rock-bound only in a few places. 

 The north shore of lake Ontario westward as far as Presque Isle is 

 largely Trenton limestone. Between this point and the mouth of 

 the Humber, west of Toronto, there are only three small areas in which 

 rock (Trenton limestone) is exposed at the shoreline. West of the 

 Humber, Lorraine shales are exposed for a short distance, and then 

 (here is an interval of several miles to a point just west of Lome Park 



