126 GEOLOGY OF OHIO. 
STRUCTURE OF THE COAL BASIN. 
One of the most important results of our study of the Coal Measures 
of Ohio is the discovery that instead of forming one symmetrical basin 
with a uniform dip toward the south-east, they lie in a series of subordi- 
nate troughs which are in a general way parallel with the axis of the 
great one of which they are parts. In other words, that the western 
slope of the basin exhibits a series of undulations which locally neutral- 
ize or reverse the general easterly dip. Such a series of subordinate 
basins have been shown to exist in western Pennsylvania, and those 
traced by our Corps, though less strongly marked, are similar in character 
to those described by Prof. Rogers and his assistants, and evidently be- 
long to the same system. The outlines of these basins have not been 
fully traced, but those which lie on the northern half of the State are 
described in our Report of Progress for 1870. 
Their existence may be demonstrated by a few profiles drawn across 
the coal area from west to east. For example, beginning on the western 
margin of the coal basin at Nashville, in Holmes county, and tracing a 
line directly eastward, we find that the dip is rapid to the valley of 
the Killbuck, at Millersburg; thence eastward the strata rise gently in 
a fold which lies between the valleys of the Tuscarawas and the Kill- 
buck. Passing this, the dip is again eastward to Dover, from which 
place the strata gently rise over an arch in Carroll county, thence de- 
scend rapidly to the Ohio. Owing to this arrangement, the section of 
the rocks exposed in the valley of the Tuscarawas, at New Philadelphia, 
is precisely the same as that seen in the valley of the Ohio at the mouth 
of Yellow Creek, and in the valley of the Little Beaver, on the Penn- 
sylvania line. Further south we find indications of similar undulations. 
From the west line of Coshocton county to Coshocton, the dip is over 500 
feet, and this continues till the bottom of the trough is reached near 
Jacobsport ; thence the strata rise easterly until at Bridgeport they lie 
135 feet higher than in the bottom of the trough further west. In carry- 
ing the line further east, two narrow synclinal basins are passed before 
reaching that in which the Ohio flows. In the.reports of Prof. Steven- 
son on Harrison, Guernsey, and Muskingum counties, the folds which 
traverse the Coal Measures in this region are described at some length, 
and he there refers to localities where the westerly dip amounts to as 
much as 100 feet to the mile. In following the line of the Pittsburgh, 
Cincinnati and St. Louis Railroad from Coshocton to Steubenville, traces 
of the folds referred to are distinctly seen, although they are not crossed 
at right angles. For example, taking coal No. 6, the most continuous 
and important seam in this region as a guide, we find that its altitude 
