488 GEOLOGY OF OHIO. 
blue limestone ore usually being the richer, when roasted they are 
reported to yield about 40 per cent. of pig-iron. They contain less 
phosphoric acid, but usually more sulphur than the “red limestone” 
portion of the seam, and as mixture they are found to work excellently 
in the furnace, and to a certain extent are self-fluxing from the lime 
and alumina contained. In places the limestone seam of ores is largely 
composed of rounded masses or kidneys, all the varieties being found in 
such condition as the “red limestone,” “ 
gray limestone,” and blue 
limestone kidneys already mentioned. From the rising of the strata, 
as one passes to the west part of the region, it follows that the limestone 
ore rises and eventually is wanting entirely in the hills. Thus there is 
but little limestone ore obtained on the west side of the Portsmouth 
branch of the M. & C. R. R. from Hamden southward, while in the 
central and eastern part it is almost the exclusive ore. This is the only 
seam of ore in the region upon which any regular mining operations 
have been conducted, and the seam being only about 12 inches thick, it 
requires considerable skill in its extraction. The Hecla Furnace Co., 
in the central part of Lawrence county, have for some 10 or 16 years 
pursued quite extensive mining operations by drifts and shafts, and this 
method of extraction is necessarily becoming more extended. 
The Block ores are of much less importance than the ores of the 
limestone seam already mentioned, and lying beneath this stratum at 
different depths, from 50 feet and more, are accessible only in the 
valleys of the western part of the region. They are limonite ores con- 
taining from 30 to 40 per cent. of iron, but are chiefly character- 
ized as being more or less silicious. The name “block ore” arises from 
the strata being cut by vertical seams, which divide it into blocks of 
quite regular shapes. Each of these blocks is oxidized in concentric 
layers, giving the ore a banded appearance around a central nucleus, 
which is often hollow and sometimes is filled with soft ochre or clay. 
Three beds of these block ores have been recognized. The first is the 
“‘ Big Red Block” ore, from 6 to 18 inches in thickness, and about 100 
feet below the limestone seam. The second, the ‘‘Sand Block” ore, 
about 6 inches in thickness, is about 20 feet below the ‘‘ Big Red Block,” 
and is generally more silicious in character and poorer in iron than the 
others. Below this, about 40 feet, is the “ Little Red Block” ore, in a 
seam about 4 inches in thickness, and is usually somewhat richer in iron 
than the “ Big Red Block,” to which it is quite similar. In general, 
