STRATIGRAPHICAL ORDER. 15 
and therefore the most available guide in establishing the order of this 
varied series of deposits. 
(6) At an interval varying from twenty to forty feet above the lime- 
stone already described, another limestone, bearing another ore and cover- 
ing another coal seam, is often found. It was first named by Rogers in the 
reports of the (first) Pennsylvania Survey, where it was designated the 
Mahoning Limestone (vol. II, part I, p. 567). This name has been 
dropped by the geologists of the Second Pennsylvania Survey for good 
reason, and the stratum is now known as the Upper Mercer Limestone. 
(White’s Report on Lawrence County, Q 2, p. 57.) It has been recog- 
nized by all of the geologists who have worked to any extent upon the 
Lower Coal Measures of Ohio, but the only distinctive name that has 
been given to it here is the Gore Limestone. (Geol. of Ohio, vol. III, 
pp. 898 and 903.) Newberry refers to it in Mahoning county (vol. III, 
p- €95), Reed in Coshocton county (vol. III, p. 567), and Andrews in 
Perry and Muskingum counties (vol. III, pp. 823, 824 and 825). 
It everywhere lacks the remarkable steadiness and continuity of 
the Lower Mercer Limestone, but in all other respects it is almost the 
exact counterpart of that well-marked stratum. It has, in the main, 
the same chemical composition, the same color, and other physical 
properties, and also the same fossils. In many instances the limestones 
can be distinguished only by their stratigraphical relations. But though 
generally agreeing with the lower limestone, it has some local peculiari- 
ties which serve to mark it for particular districts. In Central Ohio it 
is quite frequently a flint, constituting one of the main flint horizons of 
the series. Like the lower limestone it is occasionally, though rarely, 
found pure enough for furnace use. In such cases it assumes a lighter 
color, and this has sometimes led to its being confounded with a lime- 
stone that belongs above it in the series. 
The ore that accompanies it is less valuable than the Lower Mercer 
ore, but its coal seam is in Ohio of at least equal value with the Lower 
Mercer Coal. 
The interval between the limestones is generally occupied with fire- 
clay and shale, but sometimes a sandstone occurs. The clay beneath 
the Upper Mercer coal is occasionally a workable bed, and another 
workable bed is found associated with the Lower Mercer Limestone in 
many localities. 
From this brief description of the Mercer Limestones and of the 
