THE CARBONIFEKOUS 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 carried far to the 

 south-east. West of Youngstown it runs through the southern town- 

 ships of Trumbull county • it is there 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 bends 

 around 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 contained in some of the townships of Trumbull, Summit, 

 Medina, Wayne, Licking, Hocking, Pike, and Scioto. Patches of Coal 

 Measure rocks occur in Geauga, Richland, and Knox, but it is doubtful 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 

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