210 Ou1o State ACADEMY OG SCIENCE 
under the bay until the water broke through the roof of the mine. 
Gypsum has also been found near shore between Fletcherville 
and Plaster Beds, and in 1902 a good bed was found 11% miles. 
south of the bay on Mr. Meggit’s farm in Margaretta Township. 
In view of its occurrence both north and south of the bay and 
near the bay near the north shore it seems probable that it 
once extended over considerable of the region now occupied by 
the portion of the bay west of the bay bridge. The relatively 
rapid solution and erosion of the gypsum compared with the 
more resisting limestone may have produced this broad valley. 
Much of the earlier plaster was derived from boulders, so it is 
likely that the glacier assisted in enlarging this valley. East of 
Sandusky the depth of limestone below the surface 1s shown on 
Map VI. An inspection of this chart will show that over most of 
the region the rock is not far from level. It rises near the 
Sandusky shore and near Biemiller’s cove. It drops off rapidly 
to the north just as it does along the city front, also to the east 
of a line extending from the Jarecki Chemical Works to the Lake 
Laboratory. 
In other parts of the bay I have never struck rock except in 
a few places near shore, e. g., near the mouth of Mill Creek and 
near the south end of Johnson’s Island. 
CEDAR POINT. 
Cedar Point is the peninsula, 734 miles long, forming part 
of the eastern boundary of Sandusky Bay. It is not, as has 
been supposed, a mere sand spit, but has a foundation of clay 
resting upon the rock and extending, in the middle section, nearly 
up to low water level. It may be divided into three portions 
which we will call the bar, :the middle or dune section, and the 
terminal or ridge section. 
THE BAR. 
This is a low narrow strip of sand extending from Rye 
Beach, 2144 miles west of the Huron River, to the Carrying 
Ground, a distance of about 434 miles. The height of the crest 
above mean lake level averages about 61% feet, in the highest 
places barely exceeding ten and in the lowest descending to a 
little less than five. From the crest toward the lake a bare 
beach slopes steeply for a foot or two then gradually to the water 
whose height of course determines its breadth. At low stages of 
the water, such as prevail in fall and winter, the breadth is about 
four rods, continuing for miles with little variation. It does not 
