INEQUALITIES OF SEDIMENTATION 341 



The shores of the Great Lakes afford examples of these massed 

 aggregations of sand and gravel flanked by extended areas of shore- 

 line along which little or no deposition of sediment occurs. The 

 south shore of Lake Erie east of Sandusky is nearly everywhere 

 composed of Devom'an shales or glacial till, the wave and current 

 action being destructive instead of constructive. At Erie, Pennsyl- 

 vania, however accretion dominates the elsewhere prevailing 

 erosion and a long, broad spit has been built into the lake inclosing 

 Erie harbor. 



On the Canadian shore of Lake Ontario at Toronto, in sharp 

 contrast with the bare rock bottom frequently found near the 

 shore of Prince Edward county, there is a sand spit building out 

 into water nearly 200 feet deep. In the Burlington bar which 

 extends from the north to the south shore of Lake Ontario five miles 

 from the western end of the lake we have in the maximum depth of 

 the enclosed lagoon, 80 feet, an approximate measure of the 

 total thickness of the bar deposit which has been built up during 

 the relatively short life of this lake. Convincing evidence that 

 bars form even far more rapidly than such a figure would suggest 

 is furnished by the observations of RusselP on a bar at Round 

 Island in Lake Huron. Two photographs by Russell taken ten 

 years apart show that the bar increased 1000 feet in length during 

 this interval. Observation of the movement of littoral drift 

 along the shore of Lake Ontario affords equally clear evidence of 

 the rapid movement of very coarse sediments and shingle. In 

 the vicinity of OakvlUe the littoral drift is westward. Two piers 

 built out into the lake at this point on opposite sides of a river 

 mouth to protect navigation act as groins. Nothing accumulates 

 on the beach behind the west pier, thus showing that there is no 

 movement of material toward the east. Alongside the east pier, 

 however, the beach is growing out into the lake and during 

 periods of rough weather the westerly moving shingle nearly 

 overwhelms the base of the pier and the building near it. 



In the Great Lakes the vigorous action of currents is by no 

 means confined to the immediate vicinity of the shoreline. A 



'Russell, "A Geological Reconnaissance along the North Shore of Lakes Huron 

 and Michigan," Geol. Surv. of Michigan (1905), p. 104, PI. 15. 



