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. The second 

 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 



