720 GEOLOGY OP OHIO. 



The following notes on the geological extent and character of the dif- 

 ferent groups of rocks which have been enumerated will suffice with 

 what has gone before to give a clear idea of the general geological struc- 

 ture of the county. 



THE UPPER COAL GEOTJP. 



The Coal Measures of Ohio show more or less distinctly four divisions, 

 corresponding to those which have been described by Prof. Rogers in his 

 Report on the Geology of Pennsylvania, and named by him : 



let. The Upper Barren Measures. 



2d. The Upper Coal Group. 



3d. The Lower Barren Measures. 



4th. The Lower Coal Group. 



The Upper Barren Measures are hardly shown anywhere in Ohio 

 except in Monroe county, where the deepest portion of the coal basin 

 occurs. Here the highest hills are formed chiefly of a mass of shale con- 

 taining no important coal seams, and which overlie the workable coals 

 of this and the adjoining counties, and form the summit of the geolog- 

 ical series in Ohio. Below the Upper Barren Measures is found a group of 

 six or seven coal beds, distributed through about three hundred and fifty 

 feet of ghales, sandstones, limestones, etc., constituting the Upper Coal 

 Group. Of these the lowest is the Pittsburgh seam, or Coal No. 8, of the 

 Ohio series. Immediately above this there are sometimes two or three 

 •small coals, which have been numbered 8a, 86, and 8c. Following these 

 are Coals Nos. 9, 10, 11, 12, and 13, which, with the exception of Coal 

 No. 10 (a persistent and important seam south of the National Road), are 

 generally thin, or of inferior quality, and have only local importance. 



In the southern part of Jefierson county, back from the river, in the 

 townships of Mt. Pleasant and Smithfield, the surface rises in some 

 places nearly three hundred feet above the horizon of Coal No. 8, and the 

 highlands contain Coals 8a, 86, 8c, and 10, 11, and 12. Coal No. 9 is gen- 

 erally absent, and Coal No. 12 present only in the hill tops. 



This series of coals above No. 8 is here of little economic importance. 

 They rarely exceed a foot to eighteen inches in thickness; and where 

 reaching, as Coals Nos. 10 and 11 sometimes do, workable dimensions 

 (two to three feet), they are of inferior quality. Hence it will be seen 

 that the Upper Coal Group, with the exception of Coal No. 8, can con- 

 tribute little to the mineral wealth of the county. 



An interesting fact has been brought out by Prof. Stevenson in his 

 study of the geology of Belmont, Harrison, and the southern townships 

 of Jefferson, viz., that all the Upper Coal Gfoup, with their associated 



