208 Ohio State Academy of Science 



Besides the valle}^ 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 valle}^ 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 b}^ Sandusky Ba}^ resulted from 

 preglacial erosion I have no means of judging. 



