236 Ohio State Academy of Science 



surface to furnish more material. Most of the sand in the recent 

 ridges and present beach has either been transported many miles 

 from the southeast or carried by currents at the mouth of the 

 bay. 



The extension of Cedar Point lakeward and the formation 

 of so many ridges in the last half century is probably due to the 

 washing away of Peninsula Point on the other side of the entrance 

 to the bay, the material being derived largely from that source. 



Surveys show the width of Cedar Point from Rosebush 

 Point to the lake to have been about 2350 feet in 1896, about the 

 same in 1872, and about 2340 feet in 1826. If these measure- 

 ments are correct the bay has worn away about as fast as the 

 lake has built up. The jetty begun in 1896 and not completed 

 for several A^ears has already caused the accumulation of many 

 acres of sand. 



CONCLUSION. 



Looking Backward. 



The broad and shallow rock valley occupied by Sanduskv 

 Bay was formed partly by preglacial, partly by glacial erosion. 

 Upon the retreat of the glacier the greater part of this valley was 

 filled with glacial clay nearly or quite to the present water level. 



When the melting of the ice made an outlet to the east for 

 the glacial lake, Lake Erie was established. At first it occupied 

 only the eastern part of the basin it now occupies. The San- 

 dusky River then flowed much farther than now, cutting a valley 

 in the clay. Its tributaries also made valleys. The depression 

 of the west end of the Erie basin relative to the point of outlet 

 caused the lake to extend westward. In time slack water 

 extended up the valley of Sandusky River as far as the present 

 entrance to Sandusky Bay. The depression of the land con- 

 tinuing, marshes were formed along the river and its tributaries 

 and after a time the water southeast of Johnson's Island had 

 become so deep and wide that the waves cut away the clav 

 between the valleys. The bay thus started was enlarged both 

 by the rising of the water and by wave action, the latter pro- 

 ceeding more rapidly as the enlargement went on. 



The rising of the water has continued with a nearly or quite 

 uniform rate — about two and one-seventh feet a century — for at 

 least four centuries. If the rate was about the same during the 

 preceding centuries we may conclude that at the beginning of the 

 Christian Era slack water extended up the Sandusky River valley 

 as far as Johnson's Island. Fifteen hundred years ago it 

 extended up the valley of Mill Creek about a mile and a half from 



