IRON MANUFACTURE. 489 
these block ores may be said to average about 8 or 10 inches, and to 
yield in the furnace about 33 per cent. of iron. They are used in many 
of the furnaces of the region, but rarely in a larger proportion than { to 
? of the limestone seam. Alone, they are not found to work well from 
their poverty and silicious character; thus, in 1870, the Empire furnace 
was using 4 of these ores and } of the limestone and kidney ores, and 
there were required about 33 tons of ore and from 2 to 4 times the 
usual amount of lime for flux to make a ton of iron. The furnace has 
since been abandoned. 
Various estimates of the yield of these seams of ore in the entire 
region have been made, but they can only mislead, as from the manner 
in which the beds have been cut out by the valleys a true estimate of 
the territory actually covered by them becomes almost an impossibility. 
Prof. C. Briggs, jr., of the former Geological Survey, estimates “that 
the iron region from the Ohio river, near Franklin furnace, northward 
' by Jackson to the Hucking river, occupies an area equal to an unbroken 
stratum 50 miles long and 6 miles wide, capable of yielding 3,000,000 
tons of good iron ore to each square mile, and that the quantity of ore is 
so great that Jackson, Lawrence and Scioto counties are capable of pro- 
ducing 400,000 tons of iron annually for 2,700 years.” This is un- 
questionably an overestimate. We may, however, consider, assuming 
the very low figures of 10 inches and specific gravity 3, for the thick- 
ness of the ore, that each acre underlaid by it will yield about 2,843 tons 
(of 2,240 lbs.) of iron ore, while the furnace-men estimate about 2,800 
tons per acre. l 
Beside these stratified ores mentioned, the shales of the Coal Meas- 
ures contain frequently large accumulations of kidney ore, the argilla- 
ceous carbonate or clay ironstone. They occur in masses from very large 
size to those of quite small dimensions, usually, however, as flattened 
nodules about the size of one’s fist. This ore is exceedingly uncertain 
in its distribution, as sometimes the nodules will be so closely approxi- 
mated as to form almost a continuous stratum, while more frequently 
they are scattered without any regularity through the entire bed of 
shale. Hence, from their manner of distribution, it is an ore which 
very rarely, if ever, will pay for a regular system of extraction. Quite 
considerable quantities are, however, obtained by stripping, or simply 
by collecting them from the surface or the valleys, where they have 
been washed or weathered out from the enclosing rock. This kidney 
