THE CARBONIFEROUS SYSTEM. 129 
donville hills, composed of Waverly rock, seem to have presented a 
somewhat abrupt declivity toward the coal basin, against which the 
Coal Measures were horizontally deposited to the depth of several hun- 
dred feet. This is shown by the sections exposed on opposite sides of 
the valley of the Mohican. On the east, the hills which bound the val- 
ley contain seven workable seams of coal, while on the west there are 
none. 
BOUNDARIES OF THE COAL FIELD. 
The margin of the coal basin forms a tortuous line which enters the 
State in the northern part of Trumbull county, passing thence south- 
westerly to the valley of the Mahoning, where it is deflected far to the 
south-east. West of Youngstown it runs through the southern town- 
ships of Trumbull county, where it is deflected north nearly to the cen- 
ter of Geauga county, where it incloses a long tongue and two or three 
small islands. Thence returning into Portage, it passes south-easterly 
through the southern part of Summit to New Portage, where it is de- 
flected to the north-west and incloses a considerable area in south-eastern 
Medina. Thence it runs south-westerly again through the corner of 
Wayne to the south-western corner of Holmes. Thence it passes nearly 
southward along the western margin of Holmes and Coshocton ; thence 
south-westerly through the eastern part of Licking nearly to Newark. 
Its course is thence for fifty miles nearly south to the center of Hocking, 
where it turns slightly westward and passes through Vinton, Jackson, 
the eastern portion of Pike and Scioto to the Ohio, which it crosses a 
little above Portsmouth. The counties of which the surface is wholly or 
mostly underlain with coal are Mahoning, Columbiana, Portage, Stark, 
Holmes, Carroll, Tuscarawas, Jefferson, Harrison, Belmont, Guernsey, 
Coshocton, Muskingum, Perry, Noble, Morgan, Washington, Monroe, 
Meigs, Athens, Jackson, Gallia, and Lawrence. Valuable deposits of 
coal are also obtained in some of the townships of Trumbull, Summit, 
Medina, Wayne, Licking, Hocking, Pike, and Scioto. Patches of Coal 
Measure rocks also occur in Geauga, Richland, and Knox, but it is doubt- 
ful if they contain any valuable seams of coal. 
CLASSIFICATION OF THE COAL STRATA. 
The brothers Rogers (Profs. W. B. and H. D.) and J. P. Lesley, who 
have studied most carefully that portion of the Alleghany coal field 
which lies in Pennsylvania and West Virginia, have divided the Coal 
Measures into four groups, viz., the Lower Coal Measures, the Lower 
Barren Measures, the Upper Coal Measures, and the Upper Barren 
Measures. Of the upper division—a series of sandstones and shales 
9 
