64 GEOLOGY OP OHIO. 



tinuity, and definiteness of form which we see in the lake ridges. Second, 

 the materials that compose the ridges are frequently quite coarse, the 

 stones which they contain sometimes heing several inches in diameter, 

 so coarse, indeed, as to be quite beyond, the transporting power of currents 

 in open water. Where the ridges widen out into knolls and plateaus, 

 not composed of wind-drifted sand, we may very well suppose such sand- 

 banks to have been formed by shore waves sweeping over flats or shallows. 

 But the ridges proper are now under consideration, and these are seen to 

 run, with almost mathematical accuracy, as contour lines around all the 

 irregularities of the topography of the slope on which they were formed. 

 Their summits are less uniform in altitude than their bases, because in 

 some places they were built up higher than elsewhere by the wind, just 

 as we see the sand of the beach now forming at Michigan City piled up 

 by the wind in hills 175 feet in height. The ridges have been un- 

 equally eroded, too, in the thousands of years during which they have 

 been exposed to the action of rain, frost, and wind, since their first forma- 

 tion. 



By Mr. N. H. "Winchell all the lake ridges are considered as moraines, 

 more or less affected by the waves of the Lake. But, as we have seen, he 

 has placed the kames, the broad ridges of bowlder clay — which may very 

 well be considered as moraines — and the old lake beaches in the same 

 category; whereas the narrow, continuous ridges, so constant in level 

 and so nearly uniform in height — such -as the lower three of his series — 

 have very little in common with his upper so-called lake ridges, and are 

 the products of a different cause. That these are not moraines, is plainly 

 shown by the positions they frequently occupy ; resting, as they do, on 

 stratified sands and gravel, which would have certainly been broken up 

 if the glacier had reached to the line of the ridges. It should be remem- 

 bered that the polished floor of the old ice-excavated lake basin is cov- 

 ered with thick sheets of unstratified and stratified Drift, and that the 

 lake ridges — when not terraces — are on the surface of these, and were 

 formed by agencies acting long subsequent to. the departure of both con- 

 tinental and local glaciers. The force which raised the ridges acted sim- 

 ply along the water lines formerly existing. It is possible that sheet- 

 ice floating on the water surface may have contributed to their forma- 

 tion; and if in former ages the winters, colder than now, had covered 

 our lakes with sheets of ice five or ten feet in thickness, their expansion 

 in freezing would have been certain to leave some marks upon the shore, 

 and we should have had our great lakes walled, as the little ones are now 

 in Iowa. But in that case rocks and stones would have most sensibly 

 felt the thrust of the ice, and would have been pushed up into the ridges. 



