HOCKING VALLEY COAL FIELD. 921 
The elements that are counted valuable in the series are named in 
the preceding table. There are some horizons at which fire-clay and 
sandstone may perhaps be worked to advantage that are not named in 
this column, but the coals, limestones and ores that haye been proved to 
be of economic value all find place. A few years ago, the view was 
held by some geologists and also by practical investigators in the field 
that valuable beds of iron ore occur in the Barren Measures of this 
region, and especially in that part of them included between the Upper 
Freeport coal and the Ames limestone, and quite a system of ores, 
aggregating many feet in thickness, was introduced into the upper por- 
tion of the Hocking Valley column, but inasmuch as the stimulus to 
ore production occasioned by the establishment of the new blast furnaces 
of the valley has failed to develop any permanent supply at a single 
one of these horizons, it is safe to conclude that these so-called ores 
have no economic value. Their instability as geological elements and 
their poverty in iron forbid them to be counted as elements of mineral 
wealth. There are nuggets of hematite scattered through the red 
clays that are rich in iron, but they have nowhere yet been found in the 
field or in the State in accumulations that would repay mining. 
Structure of the Seam. 
In structure, the Hocking Valley coal always has the three benches 
of the normal Middle Kittanning seam, with some addition of its own. 
In other words, the Great Vein consists of the normal, three-bench 
seam of Middle Kittanning age, covered and reinforced by a Hocking 
Valley supplementary seam, the latter consisting of one or two or more 
benches. The supplementary seam is separated from the original seam 
by a thin shale parting, which is often disregarded in mining, but which 
is for the most part distinctly recognizable when looked for. The 
supplementary seam belongs to a later period of the Middle Kittanning 
age. In other words, there were conditions in the Hocking Valley 
portion of the Middle Kittanning coal-marsh under which the growth 
of the coal went on in the interior after it had been arrested on the 
margin. A slight warping of this portion of the marsh, by which a few 
scores of square miles were converted into a low island, would seem to 
supply the necessary conditions. 
There is no foundation whatever for:the theory whichj accounts for 
the thickness of the “Great Vein” by the coalescence with the normal 
