THE CLINTON GROUP OF OHIO.— PARI IV. 



HY A. F. FOERSTE. 



CHEMICAL GEOLOGY 



The Silurian rocks of Ohio Oj)en with the Cincinnati (iroiii). 

 This group is composed of a series of limestones inierhedded with 

 shales or clay. Neither the limestones nor the shales are magnesian 

 in character, the carbonate of magnesia rarely exceeding six j)er cent. 

 The amount of silica, however, varies greatly. The lower beds of 

 limestone contain from ten to twenty-five per cent, of silicious matter; 

 there is a corresponding diminution of the amount of the carbonate 

 of lime. The upper part of the series, however, contains very little 

 silicious matter, usually less than two |)er cent.; the carbonate of lime, 

 however, becomes a much more important constituent, averaging 

 ninety per cent. The interbedded shales differ from the limestones 

 chiefly in the amount of silica contained, there being a corres|)onding 

 diminution of the carbonate of lime. Thus the amount of silicious 

 matter in the shales varies between fifty five and eighty per cent.; the 

 amount of the carbonate of liuie. between four and twenty l)er cent. 

 The shales also contain more alumina than the limestones, but me 

 striking difference is evidently the amount of silicious matter contained. 

 In one of the lower series of shales belonging to the Cincinnati Group, 

 but found in Covington, Kentucky, the amount of silicious matter is 

 somewhat less, forty-three per cent., and the amount of the carbonate 

 of lime is much greater, forty-seven j)er ( ent. Otherwise the chemi- 



