14 POTTSVILLE FAUNA OF OHIO 



HARRISON ORE 

 Stratigraphy and Extent 



The oldest fossiliferous member of the Pottsville formation, the 

 Harrison ore, occurs at the base of the Pennsylvanian system and 

 marks the line of contact between that and the underlying Mississippian 

 system. Although the ore is extremely patchy in its occurrence, it is 

 of comparatively wide extent and has been traced from Scioto County 

 on the south, where it is best developed in Hamilton Township, north- 

 ward through eastern Pike, Jackson, western Vinton, and Muskingum 

 counties. It is also present in the Killbuck and Walhonding valleys 

 of Coshocton County. In thickness it varies from 6 inches in Scioto 

 County to a maximum of 4 feet in Jackson County; 1 to the northward 

 in central Ohio it thins again, attaining a thickness of 10 inches in 

 Muskingum County. 2 



The Harrison ore is of special interest on account of its position 

 with reference to the Mississippian-Pennsylvanian unconformity, for it 

 consists of the first materials deposited after the long period of erosion 

 at the end of Mississippian time. The ore lies directly upon the eroded 

 Mississippian surface sometimes upon the Maxville limestone, or 

 where that formation has been entirely removed, upon the Logan 

 shales. In places it is so intimately associated with the Maxville 

 limestone that it was formerly considered the upper part of that forma- 

 tion; 3 but Morse in his detailed work on the Maxville of Muskingum 

 and Perry counties proves the horizon to 'be of Pennsylvanian age. 4 

 In southern Ohio at most localities, the ore appears as a distinct horizon 

 above the Mississippian-Pennsylvanian unconformity. 



In lithologic character the Harrison ore varies greatly from place 

 to place. It is generally coarse in texture, and is composed of a con- 

 glomeratic mass of quartz pebbles, cherty material, and fragments of 

 sandstone which, have been cemented together by iron oxides. The 

 cherty material seems to have been derived from the Maxville limestone 

 which had been weathered into small fragments during the long period 

 of erosion after the withdrawal of the Mississippian sea. These 

 products of decomposition were later reworked by the incoming Penn- 

 sylvanian sea and were cemented by iron compounds. Many of the 

 rounded quartz pebbles resemble those of the Sharon conglomerate 

 which lies only a few feet above the ore or sometimes rests directly 

 upon it. The member is generally poor in fossils, and where these 

 occur, they appear mostly as internal casts and present an extremely 

 dwarfed aspect. 



'Stout, W., Geol. Surv. Ohio, Fourth Ser., Bull. 20, pp. 28, 481, 1916 

 2 Stout, W., Geol. Surv. Ohio, Fourth Ser., Bull. 21, p. 48, 1918. 

 'Orton, Edward, Geol. Surv. Ohio, Vol. V, pp. 373-379, 1884. 

 4 Morse, W. C., Geol. Surv. Ohio, Fourth Ser., Bull. 13, pp. 35-55 and elsewhere 

 1910. 



