236 Onto 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 years has already caused the accumulation of many 
acres of sand. 
CONCLUSION. 
LooKING BACKWARD. 
The broad and shallow rock valley occupied by Sandusky 
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 clay 
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 
