THE IRON ORES. 385 
a prominent factor in the supply of the stone-coal furnaces of the last 
decade. 
This ore does not exist in characteristic form in Columbiana county. 
The limestone, it will be remembered, is itself weak and often wanting 
in this district, but the iron which belongs to the horizon does not fail. 
The form which it takes has been modified by the absence of the lime- 
stone, and instead of segregating at one definite line, viz., the surface 
of the limestone, and thus forming a “limestone ore,” it is diffused in 
kidneys, often of large size, through a number of feet of shale. These 
scattered kidneys it would not repay the miner to follow in their native 
beds, but when accumulated and concentrated in the valley deposits 
after the fashion of other placer deposits, it has been found economically 
possible to reclaim them for furnace use. A considerable part of the 
Columbiana county ores, it will thus be seen, belongs to the Ferriferous 
limestone horizon. 
The kidneys between the Kittanning coals are gathered into a more 
definite horizon, and it may be possible to find localities in the county 
in which they can be worked with profit in their native beds, as in ad- 
joining counties. So far, however, no such accumulations have been 
reported, and their whole production is confined to the placer accumula- 
tions of the valley of the Middle Fork. 
The ore exists in all cases as weathered ore. The crust, at least, 
of all the kidneys has been converted into limonite by atmospheric 
agencies. These ores are within reach of such agencies in the valley 
deposits, which are freely permeable, and it is also quite possible that a 
part of the process of oxydation was carried on before the kidneys were 
buried here. These accumulations stand for the work of ages, thé 
separate blocks having been mined vut by the erosive agencies of the 
drainage streams through many thousands of years. Even if the work 
of accumulation should be limited to the time that has elapsed since the 
Glacial epoch, a vast period would be available for this history, but 
there does not appear to be sufficient reason for RECLINE the work to 
post-glacial time. 
It is believed that the best of these supplies has already been taken. 
A large acreage 1s exhausted, and no considerable territory remains to 
be attacked, at least under the same favorable conditions that have been 
found hitherto. The excavations are carried as low as 20 feet in 
25 G. 
