OF DENISON UNIVERSITY. c 



Of the specimens here analyzed, those marked "dark red" and 

 " Hght red " represent the typical forms of Clinton as they occur at 

 Huffman's quarry. With these may be compared the following analy- 

 ses of Clinton rocks from other parts of the state. CentervilJe, Mont- 

 gomery county: CaCO^, 86.30; MgCo,, 11.34; SiO,, .85. P:aton, 

 Preble county: CaCO,, 85.21; MgCo.,, 13.56; SiO.^, .^y Brown's 

 quarry, New Carlisle, Clarke county: CaCOa, 95.60; MgCO,, 393; 

 SiO-i.-not discovered in the analysis, if present at all, then only in in- 

 appreciable quantities. Ludlow Falls, Miami county: CaCOa,, 91.30; 

 MgCOa, 6.51; SiO,, .80. 



Comparing the limestone of the Clinton Group with those of the 

 upper part of the Cincinnati Group, we find a close resemblance in 

 the small amount of silica present in each. The magnesium carbon- 

 ate, however, which in both the shales and limestones of the entire 

 Cincinnati Group was present only in inconsiderable amounts, now 

 begins to be a very variable quantity, varying from less than one per 

 cent, to almost fifteen per cent. This variation causes a compensating 

 .change in the amount of calcium carbonate present. It will also be 

 noticed that the central locality, near Dayton, has the least amount of 

 magnesium carbonate, but that the amount increases in all directions, 

 moderately so towards the northeast, Brown's ([uarry, and the north- 

 west, Ludlow Falls; but markedly so towards the south, Centreville, 

 and the west, Eaton. In other words there seems to be a slight ten- 

 dency of the Clinton Group, beginning witli Dayton as the center, to 

 become more magnesian towards the circumference of the exposed 

 parts. 



The same thing is true, but in a far more marked and satisfactory 

 sense, of the Dayton limestone. Here again the series of (juarries of 

 which Huffman's quarry is the center, contain the least amount of 

 magnesium carbonate. At a distance these exposures become more 

 and more magnesian until finally they can no longer be ioU] from thr 

 Niagara shales above. 



But there is not only an increase in the amount of d()U)miii>aliun 

 laterally, but also vertically. To be sure, in Huffman's tpiarry this 

 change is very sudden. There is a fairly sharp line between the Clin- 

 ton Group and the Beavertown marl. At Todd's Fork, near Wilming- 

 ton, Clinton county, they gradually run inty each other, ami there is 

 a commingling of fossils. The Niagara shale at Huffman's (juarry is 



