SURFACE GEOLOGY. 55 
evidence that Lake Michigan once extended southward over that sum- 
mit. If it should prove, as supposed by Dr. Andrews, that the highest 
lake ridge at Chicago is continuous with a much higher one on the east 
side of the Lake, this will indicate a great subsidence of the western 
shore of Lake Michigan at a comparatively recent date. But the con- 
tinuity of these ridges has not yet been demonstrated, and, therefore, 
this subsidence cannot be said to be proven. Until this theory shall be 
sustained by further evidence, it will probably be safer to suppose that 
the highest ridges on the two sides of the Lake are not identical, and 
that when the highest ridge in Michigan was formed the Lake over- 
topped the barriers that now surround it, and extended far to the south 
and west of its present limits, covering all northern Illinois and south- 
ern Wisconsin. Wemay even suppose that it covered the country about 
the confluence of the Mississippi and Missouri around St. Louis, and 
formed the body of water in which the Loess was deposited. In this 
view, the absence of higher ridges around the south end of Lake Michi- 
gan would be due simply to the fact that no shore lines were there upon 
which they could be formed. 
In Ohio the lake ridges can be traced almost continuously from the 
line of Michigan to that of Pennsylvania. Im this series three dis- 
tinctly marked ridges are to be seen in a great number of localities, and 
several intermediate ones may often be discerned. The local phenomena 
presented by these ridges have been described somewhat in detail in 
the reports of Messrs. G. K. Gilbert, J. H. Klippart, and N. H. Winchell, 
and also in the reports on the different counties through which they 
pass—Fulton, Henry, Putnam, Hancock, Seneca, Huron, Lorain, Cuya- 
hoga, Lake, and Ashtabula. . 
In the western counties, where the slope of the watershed is gentle, 
the lake ridges are widely separated, strongly marked, and continuous; 
while toward the east, where the land rises rapidly back from the Lake, 
they are crowded closely together, are often broken, and on abrupt de- 
clivities composed of hard material, are replaced by terraces. In the 
Maumee valley the ridges are frequently raised above the adjoining 
country, like railroad embankments; and being well drained and dry, 
they are generally chosen as routes for the country roads and as sites for 
residences. By Mr. Gilbert there are thought to be four lake ridges in 
the Maumee valley, of which the altitude, where they are crossed by the 
air-line branch of the Lake Shore and Michigan Southern Railway are 
220, 195, 165, and 90 to 65 feet above Lake Erie. Of these, the highest 
~ passes from Adrian, Michigan, through Fayette, Bryan, Unity, Hicksville, 
