28 GEOLOGY OF OHIO. 



series, that it is in' fact valley Drift, such as was transported by the 

 Mississippi while the continent was several hundred feet higher than 

 now, and the river current swift enough to carry material from its head- 

 waters to the Gulf. The Champlain epoch came long afterward, when 

 the Gulf coast was sunk one thousand feet lower than when the valley 

 Drift of Louisiana was deposited. In that submergence the valley of 

 the Mississippi was an arm of the sea. Still water then filled the val- 

 ley of the Ohio, and the upper Drift deposits of the Ohio valley were 

 laid down over not only the bowlder clay, but the Forest Bed that covered 

 it. If this submergence was synchronous with that of the Atlantic 

 coast, in which the Champlain clays were deposited— a point not yet 

 established— then our representatives of the Champlain are the upper 

 Drift deposits of the Ohio valley, the Lacustrine clays of the lake-basin, 

 and the Loess of the Western States. Even if synchronous with the 

 marine Champlain clays, our Erie clays, where stratified, are fresh- 

 water deposits made in a different water-basin and at a higher level, as 

 some portions of our laminated Erie clay are found nearly one thousand 

 feet above the level of the sea. 



MODE OF FORMATION OF THE ERIE CLAY. 



As some misapprehension, as it has seemed to me, has prevailed in re- 

 gard to the manner in which the materials forming the Erie clay were 

 deposited, I venture to suggest a view of the mode of formation of this 

 member of the Drift series to which a careful study of the phenomena 

 it presents has led me. As we learn from all observations on the erosive 

 action of glaciers, the materials excavated and comminuted by a glacier 

 are carried forward by it, and are thrust out at its extremity. If coarse, 

 they are left there, with whatever blocks it transports on its surface, 

 as a terminal moraine. If fine, they are more or less completely washed 

 away by the water draining from it. This finer material is what renders 

 all the streams flowing from a glacier " turbid, or milky." The character 

 of the material ground up and transported by a glacier, and the propor- 

 tion of fine to coarse material deposited by it, will vary with the nature 

 of the rock over which it passes, the freedom of the drainage from it, and 

 the presence or absence of overhanging cliffs and pinnacles, from which 

 blocks may descend upon its surface. The great glacier which once cov- 

 ered so much of Ohio, like all others of ancient and modern times, un- 

 doubtedly pushed out and left behind it the coarse and fine flour which 

 it ground. As the rocks over which it passed were, for some hundreds 

 of miles northward, soft sedimentary strata, mostly shale and limestone, 



