THE IRON ORES. 417 
of the furnace district that we find the largest number of separate ore 
seams counted, many of which have been but little worked, and which 
would never have been worked at all, except for the urgent local 
demand. 
As a result of all this sharpened inspection, the furnace managers 
have been led to recognize several locally important seams of ore in 
addition to the well-known and persistent horizons that have been 
followed thus far around the margin of the coal field. 
Of the persistent horizons, as has been often repeated in the pre- 
ceding pages, by far the most valuable element is the Ferriferous lime- 
stone. It has been found comipg clearly into the sections of southern 
Perry and Hocking counties, and from this region it extends to the 
southward with almost unbroken continuity. Its ore rates as high in 
value as in persistency. 7 
The Mercer horizon is also exceedingly serviceable. The lower 
limestone of this group can be followed without real interruption from 
the Pennsylvania line to the central part of Jackson county. From 
that point to the Ohio Valley it is not steady, but it is found often 
enough to establish the sections. ‘The ore that goes with it maintains 
its place, even when the limestone temporarily disappears. 
The coal seams are also valuable guides in following the series frou 
point to point, and when limestone, ore and coal are all brought into 
requisition, a very clear and symmetrical order comes to light. 
The ores of the Hanging Rock district can be divided on strati- 
graphical grounds into three quite natural groups. It will be more 
convenient to treat of them in these divisions, though the classification 
already proposed will not be lost sight of. The divisions are as follows: 
1. The lowest division extends from the Sub-carboniferous lime- 
stone to the Mercer group, including both. The most characteristic 
and valuable elements of this division are block ores. In fact, all of 
the block ores of the entire series are embraced within these limits. 
Three persistent and six more or less important ores must be referred 
to this group. This division embraces 225 to 250 feet of strata. 
2. The second division covers the famous ore of the Ferriferous 
limestone horizon, which is the central feature of the whole district, 
and it may also be made to include the two weaker ores that lie next 
below the limestone, and which are often known as limestone kidneys. 
27 G. 
