STRATIGRAPHICAL: ORDER. oral? 
already presented, from the Pennsylvania border to the point which we 
have now reached, then this unity and persistence may be counted 
established for the whole margin of the coal field in the State. 
The stratigraphical order of the Hanging Rock District was in the 
main clearly shown in my report upon that field in volume III, Geology 
of Ohio. The general section there published has proved a true one 
for almost every portion of the series, and has become an accepted 
guide in the practical development of the region. An error of some 
magnitude, and very confusing to the true order is, however, to be 
found in the position assigned to the Maxville limestone. This lime- 
stone is undoubtedly of Sub-carboniferous age, and is geologically below 
both the Wellston and the Jackson coals, whereas, the section reverses 
this true order. The view so strenuously maintained by Andrews in 
regard to this point was the true one. The number of coal seams, how- 
ever, and the intervals between them were correctly given, with the 
exception already noted in regard to coal No. 6a@ and coal No. 66. 
These two seams should be merged in one. There is also an extra coal 
seam shown about the Lower Mercer limestone that probably nowhere 
reaches any profitable development. When these errors are corrected, 
the section will serve as well as any that could be constructed now, to 
indicate the general order of the field. 
One important error in the application of the section will presently 
be noticed in treating of the Waterloo coal field of Walnut township, 
Gallia county. 
A brief resume of the essential facts will be here given, and the 
elements, as far as they can be certainly identified, will be named in 
accordance with the section, that we have brought along from Pennsyl- 
vania to the borders of the Hanging Rock field. 
The Ferriferous limestone is the key to the series, the common 
bond for the several portions of the field. 
Above it are everywhere found the two Kittanning coals, as steady 
and regular as they are in any like area of their wide extent. 
The limestone is generally covered with 5 to 15 feet of white clay, 
the well-known Kittanning clay of Pennsylvania and Eastern Ohio. 
Throughout the Hanging Rock District, this is a valuable, though for 
the most part an undeveloped horizon. It is generally a plastic or 
potters’ clay, and issometimes very pure and rich. There is sometimes 
