URFACE GEOLOGY. 53 



often vertical cliffs, until finally the present water level was attained, 

 and shore cliffs and beaches were formed as we now find them. 



The formation of the lake ridges and terraces was the last in the 

 sequence of events which make the history of our surface geology. These 

 bring us down to the present time, which, to our limited view, seems a 

 period of rest, but every day sees something taken from the barrier of 

 Niagara, and at no distant day, geologically speaking, Lake Erie will 

 have shared the fate of all lakes, and have been drained to its bot- 

 tom. The present shore line, with its terraces and ridges, will then 

 simply add another to the list of those that have preceded it, and which 

 we can so distinctly trace upon the surface. The lake ridges, as they are 

 commonly called, have been more or less minutely described by many 

 writers on the geology and topography of the lake basin. They are found 

 encircling all the great lakes, but more careful observation is required 

 before the relations between the different series which have been ob- 

 served can be considered established. The ridges which surround Lake 

 Ontario were first described by Lieutenant Roy and Sir Charles Lyell. 

 They found on the Canada side eleven of these ridges, rising one above 

 another, the highest being 762 feet above the surface of the Lake. On 

 the south shore a similar series has been described by the New York 

 geologists. Prof. Hall mentions five of these, while other observers have 

 reported as many as fourteen, of which the highest has an elevation 

 about the same as that of the highest on the Canada shore. On Lake 

 Superior old lake beaches have been noticed in several localities, and 

 some of them have been described in the reports of Messrs. Foster and 

 Whitney. No extended survey has been made of them, however, from 

 which the history of the decline of the water level can be fully made 

 out. Some of them approach closely to the present water line, and give 

 evidence of comparatively recent changes in that region. ' This is also 

 shown by the interesting facts reported by Prof. Pumpelly, and brought 

 to light in the excavation of the Portage Canal. Here copper imple- 

 ments and the copper shoe of a setting-pole were found in the bed of a 

 channel, which, though now dry land, was evidently once filled with 

 water, and was navigated by the ancient inhabitants of this region. 



On the Canadian side of Lake Superior, at Petit Ecris, seven terraces of 

 sand and gravel rise, one above another, to the height of 931 feet above 

 the sea level. Their elevations above the Lake are respectively 30, 40, 

 90, 224, 259, 267, and 331 feet. Terraces in the solid rock, marking old 

 water lines, have been also noticed in the north shore of Lake Superior 

 by the Canadian geologists. The ridges of Lake Huron have never been 



