292 Annals of the Carnegie Museum. 



pended, and during the impact of the water upon the bottom, as the 

 wave topples over, the sand or gravel may be knocked and churned 

 about to a considerable extent. From the breaker the water rushes 

 quickly landward and then more slowly recedes, carrying the sand and 

 gravel forward and backward, but, owing to the establishment of a 

 certain equilibrium between the greater shoreward thrust and the com- 

 bined weaker outward flow and the action of gravitation there results 

 a more or less constant slope of the beach. 



The ordinary littoral current unaided would not be strong enough 

 to transport any considerable amount of coarser material, but in the 

 line of the breakers there is a suspension of more or less of the coarser 

 sand and gravel at the impact of each breaking wave, and the littoral 

 current may thus cause a lateral displacement of the debris during its 

 suspension in the water. In this manner there may occur a gradual 

 drifting of shore debris along the line of the breakers, the material 

 being replaced from the upper parts of the beach as fast as it is carried 

 away. 



From the mouth of the Vermilion River, Ohio, eastward to Dun- 

 kirk, New York, a total distance of about one hundred and. sixty 

 miles, the immediate shore of Lake Erie consists of the soft blue De- 

 vonian shale, named by Dr. Newberry the Erie Shale, ^ covered with 

 a varying thickness of drift-clay, thus constituting an easily eroded 

 shore-line favorable to the formation of a typical beach. In the 

 vicinity of Cleveland, Ohio, "The mean recession of a line of promi- 

 nent sea-cliffs in boulder clay, for a period of forty years, has been 

 about six feet per annum." * 



There is thus a large amount of beach debris annually taken into the 

 waters of Lake Erie from this region and almost the entire shore of 

 Lake Erie from Sandusky Bay eastward presents a typical beach of 

 sand or gravel, strewn here and there with boulders from the drift-clay 

 above. Such a beach under the action of suitable currents will develop 

 the various beach structures, as barriers, terraces, bars, spits, hooks, 

 loops, etc. 



The littoral current, following the line of agitation of the surf-line, 

 may deviate from this course in three ways. It may (a) cut across 

 bays, etc., and join the surf-line again at the other side, forming a 

 "spit," "hook," "bar," or "loop." It may (/^) leave asa surface- 



8 Newberry, J. S. "Geological Survey of Ohio. Report I." Pp. 163-167, 1873. 



9 Russell, T. C. /. c, p. 61. 



