116 POTTSVILLE FAUNA OF OHIO 



McARTHUR MEMBER 

 Stratigraphy and Extent 



The next fossiliferous horizon above the Upper Mercer limestone 

 and flint with its accompanying ore is the McArthur member which in 

 ascending order forms the fifth marine limestone of the Pennsylvanian 

 system in Ohio. The horizon includes the impure fossiliferous lime- 

 stones, the calcareous shales, and the shaly sandstones which occur 

 directly above the Tionesta or No. 3b coal. The name McArthur lime- 

 stone was given to the stratum by Stout in 1919 from typical exposures 

 in the vicinity of the town of that name in the central part of Vinton 

 County, where the member consists of massive, bluish gray, extremely 

 fossiliferous limestone. 1 It is best developed in Vinton and Jackson 

 counties, but pinches out and disappears south of Monroe Furnace, in 

 the southern part of the latter county. In Lawrence and Scioto coun- 

 ties a dark, tough, sparingly fossiliferous shale wedges in from the south 

 across the Ohio River and occupies the position of the McArthur mem- 

 ber above the Tionesta coal. North of Vinton County the member is 

 well developed in Hocking and Perry counties, and has been found in 

 a few places in Muskingum and Coshocton; however, in the latter 

 counties a massive sandstone, the Homewood or Tionesta, and clays 

 occupy the position of the McArthur member and sometimes fill the 

 entire interval between the Tionesta and Brookville coals. In places 

 even the two coals as well as many feet of rock above and below them 

 are replaced by the Homewood sandstone which sometimes reaches a 

 thickness of 70 feet and bridges the dividing line between the Potts- 

 ville and Allegheny formations. 



The McArthur member is found just above the Tionesta coal 

 which forms a fairly persistent and well-marked horizon in southern 

 and south-central Ohio, and measures 1 to 6 feet in thickness. The 

 coal occurs midway between the Upper Mercer ore and the Brookville 

 coal, the basal member of the Allegheny formation. The interval be- 

 tween the Upper Mercer ore and the Tionesta coal in Lawrence County 

 measures about 32 feet; northward in Jackson and Vinton counties the 

 same interval averages 25 feet, while 22 feet intervenes between the 

 Tionesta coal and the Black Flint horizon which occurs just below the 

 Brookville coal. 2 These intervals are about the same in Hocking and 

 Perry counties, but they thin gradually as they are followed into Mus- 

 kingum County where the distance between the Tionesta and Brook- 

 ville coals measures 8 to 20 feet, while that between the Tionesta and 

 Brookville is about 8 feet. 3 



, W., Geol. Surv. Ohio, Manuscript on Clays of Ohio. 

 2 Stout, W., Geol Surv. Ohio, Fourth Ser., Bull. 20, pp. 171-179, 305-309, 584- 

 588, 1916. 



3 Stout, W., Geol. Surv. Ohio, Fourth Ser., Bull. 21, pp. 115-118, 1918. 



