FROM THE OHIO TO THE MISSISSIPPI RIVER. 



GENERAL SKETCH. 



By ('•. K. Gilbert. 



This is for the most part an area of Paleozoic strata lying nearly hori- 

 zontal. The Coal .Measures constitute the underlying rocks from Bell- 

 aire on the Ohio River to Newark, Ohio. The lower members of the 

 Carboniferous constitute the underlying beds from Newark to a point 

 just west of Chicago .Junction, Ohio. From this point to Tiffin, Ohio, 

 the Devonian rocks underlie. From Tiffin to a point west of New- 

 Baltimore the region is underlain by Upper Silurian rocks. From New- 

 Baltimore, Ohio, to a point west of Union Mills, Ind., the Devo- 

 nian rocks again constitute the substructure; and from the last-named 

 point to Watertown, Wis., the Upper Silurian fcerrane underlies the 

 drift. From Watertown, Wis., for a lew miles the Lower Silurian 

 rocks come to the surface, except where concealed by drift, and thence 

 to La Crosse the Cambrian rocks appear. The disturbance of these 

 strata throughout the region of the route is so slight that it nowhere 

 expresses itself in well-marked surface features. 



The greater part of the route is through a region overspread with 

 glacial drift, the southern part of the great North American glaciated 

 area. From Dear Newark, Ohio, to Kilbourn City. Wis., the older for- 

 mations are generally concealed by the drift deposits. The surface 

 features by which this region is characterized and by which it is dis- 

 tinguished from the territory south of the limit of glaciation include 

 an imperfect drainage system abundant in lakes, lakelets, ponds and 

 marsh meadows, and the replacement of the topographic forms de- 

 veloped by subauial erosion by the less regular but equally character- 

 istic forms of glacial deposit. 



The layer of drift ranges from a few feet to several hundred feet in 

 thickness, and its most important element is till or boulder-clay. It is 

 exhibited in a general sheet of ground moraine, traversed by relatively 

 thick bands of the nature ot terminal moraines. .The moraines are 

 usually several miles broad and their ensemble is not commanded by 

 the tourist, who is able only to observe changes in the topographic 

 character of the country as he enters and leaves their belts. The sur- 

 faces ol terminal and ground moraines are alike undulatory, but the 

 slopes of the terminal moraines are relatively steep. Hillocks, often 

 somewhat elongated, alternate rapidly with hollows for the most part 



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