226 Frank Carney 



the waves, thus keeping the base exposed to fresh attack. At 

 some places on the lake, cliff-cutting has proceeded very rapidly 

 even during the short period that the shores have been inhabited. 

 Farmers have lost fields, and cottagers have had their property 

 destroyed. 



Beaches. Vigorous waves striking the shore are thrown some 

 distance above the level of the lake. These waves push ahead of 

 them the cobble, gravel, sand, etc., along the shore. Under the 

 impulse of heavy winds, the huge waves drive material far up on 

 the shore. This material then is pushed beyond the reach of 

 waves. In the course of time a ridge is thus constructed, called 

 a beach ridge. It consists of fine and coarser products, depending 

 sometimes on the location of nearby cliffs, which furnish the mate- 

 rial, and sometimes on the strength of the waves. Beaches 

 Usually alternate with cliffs. Recalling the preglacial irregularity 

 of topography, you understand how Lake Erie could not be bor- 

 dered by either continuous cliff or beach; in some parts one pre- 

 vails and in some parts the other, but in no case can you travel 

 many miles without finding both forms. 



Alo7ig-shore currents. Under a fairly constant wind, the waves 

 necessarily meet the shore, which is irregular, at various angles. 

 If a wave strikes the shore directly, the water, after the impulse, 

 settles back along the same line. With the continuance of oblique 

 waves, the water is given a general movement along the shore. 

 This constitutes an along-shore current, which is efficient in trans- 

 porting the products of wave work, 



Under-tow. When winds, even for an hour, drive waves against 

 the shore, the water is piled up ; and since a shoreward movement 

 is continuous on the surface, the only escape for the accumulated 

 water is along the bottom outward. This movement is called an 

 ''under-tow." The velocity of the under-tow depends directlj^ on 

 the strength of the winds causing water to accumulate along the 

 shore. The higher the water becomes, the faster it will move 

 down along the slope in response to gravity. An under-tow 

 current, like any other water current, is a transporting agent. 

 But, because of its relatively low velocity, the undertow^ carries 

 only small material. These smaller pieces of sand, etc., represent 

 the finer products of comminution by waves. As the result 

 of deposition by undertow currents, the shore slope is gradually 

 lessened. 



