OF DENISON UNIVERSITY. 
5 
Of the specimens here analyzed, those marked “dark red” and 
“ light 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. Centerville, Mont- 
gomery county: CaCOs, 86.30: MgCos, 11.34; SiOa, .85. Eaton, 
Preble county: CaCOs, 85.21; MgCos, 13.56; SiO^, .35. Brown’s 
quarry. New Carlisle, Clarke county: CaCOs, 95.60; MgCOg, 3.93; 
SiOg, not discovered in the analysis, if present at all, then only in in- 
appreciable quantities. Ludlow Falls, Miami county: CaCOg,, 91.30; 
MgCOa, 6.51; Si02, .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 quarry, 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 with 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 quarries 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 told from the 
Niagara shales above. 
But there is not only an increase in the amount of dolomitisation 
laterally, but also vertically. To be sure, in Huffman’s quarry 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 into each other, and there is 
a commingling of fossils. The Niagara shale at Huffman’s quarry is 
