t> GEOLOGT OF OHIO. 



The waves of the Upper Silurian Sea washed against the base of the 

 Cincinnati arch, as upon the sloping shores of the Canadian and New 

 York highlands, in all localities producing their legitimate and charac- 

 teristic effects, viz.: grinding up and spreading as mechanical sediments 

 the rocks which formed the barriers against which they dashed. The 

 colored calcareous clays, to which allusion has been made, are the prob- 

 able representatives of the Medina, deposited here at a period anterior 

 to the deposition of the Clinton limestone when the water was shallow, 

 and rendered turbid by a fine mechanical sediment washed down from 

 the land on the north and east. Passing eastward from Ohio, the mate- 

 rial of the Medinabecomesprogressivelycoarser, until in the Shawangunk 

 Mountains it is represented by the Oneida conglomerate — the gravel 

 formed by the dashing of the waves of the Upper Silurian Sea against 

 bold shores composed largely of silicious rocks. 



As the submergence progressed the water-line rose on the fianks of the 

 Cincinnati arch, and in the Clinton conglomerate, composed of rolled 

 fragments and fosSils of the Cincinnati Group, we have the record of the 

 mechanical action of the Clinton Sea. The materials composing the 

 Cincinnati arch were all calcareous, although hardened into solid lime- 

 stone, so that no quartzose gravel and sand, or shale, constituted the wash 

 from the land, and hence no beds of quartz-conglomerate, sandstone, or 

 shale are found here. In New York the Clinton Group is mostly shale, 

 an off-shore deposit laid down in the deepening sea over the coarser 

 material of the Medina, the product, as has been stated, of shore action. 



The oolitic iron ore so characteristic of the Clinton, and found through- 

 out the line of outcrop of this formation, from Dodge county, Wisconsin, 

 east to Clinton, New York, and thence south to Eome, Georgia, is repre- 

 sented in Ohio sometimes by a band of iron ore from two to three feet in 

 thickness, and sometimes by merely a red ferruginous stain imparted to 

 the limestone. No satisfactory explanation of the formation of this iron ore 

 has ever been published Professor Dana, in the last edition of his Manual, 

 p. 231, speakingof theClintonGroup,says: "The beds of argillaceous iron 

 ore which spread so widely through New York and some of the other States, 

 west and south, could not have been formed in an open sea, for clayey iron 

 ore deposits do not accumulate under such circumstances; they are proofs 

 of extensive marshes, and therefore of land near the sea level." This para- 

 graph could only have been written with an imperfect knowledge of the 

 remarkable deposit to which it refers. The Clinton ore is not, in any sense, a 

 clay iron-stone, and has nothing in common with the clay iron-stones o 

 the Coal Measures, except that it contains iron, and of this it holds nearly 

 twice as much. It is a red hematite or anhydrous sesquioxyd of iron 



