THE FLOODS OF THE GBEAT LAKES. 41 



VII. THE KLOODS OK THE GREAT LAKES. 



LACUSTRINE DEPOSITS AND TERRACES. 



PERSONS living along the borders of the " Great Lakes" 

 well understand what is meant by "The Ridge Road." 

 That road is a geological phenomenon. It is a record of high 

 waters in the lakes. It possesses much significance, and opens 

 an interesting vista through a chapter in the world's history. 



The Ridge Road runs parallel with the lake shore for many 

 miles at a stretch. It is almost perfectly level and serves as a 

 ready made road-bed for country roads. It consists of gravel 

 and sands, and presents oblique lamination or cross-bedding in 

 its internal structure. The materials have evidently been ar- 

 ranged by water. It has the general characters of a beach, 

 and like a beach retains a level nearly uniform, Generally 

 two or more of these ancient beaches run parallel with the 

 lake, at different altitudes. The "ridge-road" south of Lake 

 Ontario is 190 feet above the lake. The principal terrace 

 bordering Lake Erie is 220 feet above the lake on the south 

 side. On the north side, near Toronto, there are terraces from 

 30 to 500 feet above the lake. The Davenport ridge west of 

 Toronto is 250 to 300 feet. At the west of Lake Ontario, 

 near Dundas, the ridge is 318 feet high. Around Lake 

 Huron are clayey deposits up to 500 feet. North of Lake 

 Superior the upper terrace reported is 331 feet above 

 the Lake. 



There are other indications that the Great Lakes have 

 formerly stood much higher than at present. Mackinac Island 

 is a monument commemorating in stone the fact of the ancient 

 high tides of the lakes. Get into a Mackinac boat and sail 

 around the island. On all sides a wall of limestone rises per^ 

 pendicularly from the water's edge to a height of about 150 

 feet. Only on the south, for a narrow space, is the approach 

 practicable. Here is the village ; back of it, on the first rock- 

 terrace, is the modern fort. The old Fort Holmes, captured 

 by the British, is on the highest dome of the island, 350 feet 



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