208 Onto STATE ACADEMY OF SCIENCE 
Besides the valley now partly filled by Sandusky Bay several 
other rock valleys in the vicinity lie sensibly parallel to the main 
axis of Lake Erie. 
The parallelism of these valleys to each other and to the 
grooves makes it probable that all of them were made by the 
glacier. Although the general movement of the glacier over 
Ohio was more nearly southward the motion of the lower portion 
of the ice in this vicinity during the time that most of the erosion 
was done was about seventy-five degrees west of south, the 
direction being determined by the valley now filled by Lake Erie. 
Under the bay the glacial deposits are of the same character 
as on the land. Overlying the rock is hardpan from a few inches 
to two feet or more in depth, containing pebbles and boulders in 
abundance, the greater part of them of limestone which the 
glacier transported but a short distance. The matrix in which 
the stones are imbedded contains a large percentage of calcium 
carbonate which probably accounts for its toughness compared 
with the clay above it, which the auger penetrates with much 
less difficulty. In the lower part of the clay are boulders but 
not so many as in the hardpan. Pebbles are very numerous 
within a foot or so of the rock. Limestone boulders appear to 
predominate near the rock to a greater extent than at a higher 
level—judging from some exposures on the land. Except 
within four feet of the rock the clay seems to be almost free from 
stones of any size. It must have been held in suspension by the 
water of the glacial lake and gradually settled to the bottom at 
a distance from the foot of the glacier. 
PREGLACIAL CHANGES, 
No deep preglacial valley runs through Sandusky Bay. At 
the power house on Cedar Point the rock is 46 feet below water 
level. Off the end of Cedar Point the water is 40 feet deep. 
West of the entrance to the bay in 1842 was a circular depression 
in which the water was 42 feet deep. In the vicinity of the old 
range lights south of Johnson’s Island soft mud extends to a 
depth of forty feet or more below mean lake level. I know of 
no attempts to find the rock at greater depths at the entrance to 
the bay or west of it. In the bay bridge of the L.S. & M.S. Ry. 
the piles are driven to rock which is in most places less than 30 
feet below the surface of the water. The longest space without 
piles is 1700 feet but the rock does not slope toward it in such a 
way as to indicate a rock valley there. How much of the broad 
but shallow valley occupied by Sandusky Bay resulted from 
preglacial erosion I have no means of judging. 
