 STRATIGRAPHICAL ORDER. gia peaiaeainl (4 (2) 
of coal and slate that are here found are counted by him as the true 
Nelsonville coal. But these 7 feet of coal and slate are capped with 
5"feet of as characteristic Lower Mercer limestone as there is in Ohio. 
This coal seam has an elevation above Lake Hrie of 103 feet. The 
Ferriferous limestone with its ore, a worked horizon, is found 102 feet 
above it; the Carbondale coal, 136 feet above it; and the Cambridge 
limestone, 348 feet above it, all in the same section. There is not a 
clearer or less ambiguous section in the Lower Coal Measures of Ohio. 
The combined section at Carbondale is shown in Fig. XXII, in 
which most of the elements and measurements already given are 
incorporated. By the side of it is shown the Brewer’s cut section, 
Brown township, to which reference has just been made, and which was 
also given on a previous page. The combined section A has the fault 
of its kind, that it gives in a single column elements that are not found 
in any one vertical series, and some minor deviations will therefore be 
found from the measurements obtained in the separate sections, but no 
difficulty will be experienced in understanding the facts as thus repre- 
sented. 
The accompanying sketch map, Fig. X XIII, shows the locations of 
most of the points involved in the immediate vicinity of Carbondale. 
The differences in elevation were determined by the engineer’s level. 
The name and place of the Carbondale coal have been treated thus 
at length because a wrong determination would vitiate all of the con- 
nections of the Hocking Valley coal field with the Hanging Rock 
District. The reference of it, first made by Andrews, to the Nelson- 
ville coal proves to be the correct reference, and the question may now 
be counted among the settled ones in Ohio geology. 
The sections which we have last considered have carried us into a 
new field, viz., the Hanging Rock District of Southern Ohio. We have 
now reached the most northerly of the great furnace tracts that are 
located upon the outcrop of the Ferriferous limestone. To continue 
the examination of the series in the same detail with which we haye 
thus far advanced, is no longer necessary, for from this point to the 
Ohio River there is one dominant horizon, which is everywhere worked, 
and which every one knows, and about which dispute is out of the 
question. 
If the unity of. the Lower Coal Measures of Ohio, and the per- 
sistence of their main beds are considered established by the facts 
