54. GEOLOGY OF OHIO. 
carefully examined, but they are mentioned as occurring in various 
places, and at different levels, by Dr. Bigsby and Sir William Logan. 
On Owen’s Sound three are mentioned, which lie at 120, 150, and 200 feet 
above the present level of Lake Huron. At Piette’s Harbor two ancient 
beaches are found, one at 149, and another at 175 feet above the Lake; 
besides others at lower levels. In many of the lower beaches of Lake 
Huron fresh-water shells of species now inhabiting the Lake are found 
in great numbers, also human and other bones, twigs, trunks, and the 
bark of trees; in fact, all the things that wash up on the beach and are 
buried there in the sand. On the west side of Lake Huron lake ridges 
are mentioned by Prof. Winchell as occurring in many places, and old 
water lines are plainly traceable, both by ridges and rock terraces, at 
Mackinaw. Near Detroit parallel ridges are described as occurring on 
opposite sides of the Detroit river, 130 feet above the stream. 
The old beaches of Lake Michigan have been studied and described 
with much care by Dr. E. Andrews, of Chicago. On the west side of 
the Lake the land is usually low, and the highest ridge below Milwaukee - 
is 54 feet above the surface of the Lake. This sweeps around the south 
end of Lake Michigan, and is supposed to be continuous with a ridge 
which has an elevation of 140 feet on the east side of the Lake. At the 
head of Lake Michigan there are three parallel ridges, with several 
broken ones, and many sand dunes formed by the wind. Of these ridges, 
the highest is that before mentioned, 54 feet above the Lake. Thesecond 
is 15 to 18 feet lower, and the third is just above the water line. The 
interesting fact is mentioned by Dr. Andrews, that of the three ridges 
on the south shore of Lake Michigan, the highest was formed first, the 
lowest next, and the middle one last; showing that a depression of the 
water level took place somewhat suddenly from the upper to the lower 
ridge, and that subsequently the water rose again to form the middle 
ridge. This is indicated by a bed of peat, which, in places, reaches from 
the upper to the lower ridge beneath the middle one. Dr. Andrews’s the- 
ory is that this peat bed was formed in a marsh behind the lower ridge, 
and was subsequently covered with sand washed from the lower ridge to 
form the middle one. The upper ridge, about the south end of Lake 
Michigan, is said by Dr. Andrews not to be continuous back of Chicago, 
but to form two converging lines, which pass westward on either side of 
an old river bed through which the water of Lake Michigan once flowed 
into the Mississippi, precisely as the water of Lake Erie once drained 
into the Wabash. fresh-water shells are also said to be found in the 
surface deposits on the Kankakee summit, and these are regarded as 
