94 POTTSVILLE FAUNA OF OHIO 



formerly used extensively for smelting in the old charcoal furnaces of 

 Lawrence, Scioto, and Jackson counties, and next to the Ferriferous 

 ore (Allegheny formation), it was at one time more extensively worked 

 than any other of the ores of the Pennsylvanian system. Northward 

 in Vinton and Hocking counties the limestone phase is much better 

 developed and is more persistent than to the south. 



In the central part of the Upper Mercer outcrop in Ohio the mem- 

 ber is either represented by only one bench or layer (Muskingum and 

 Tuscarawas counties) or by as many as six layers, each separated by 

 shaly partings (Perry and Coshocton counties). 1 The characteristic 

 type of deposit is flint which entirely replaces the limestone or is 

 present with it. Where the limestone phase is found, it is dark in 

 color, flinty, ferruginous, and sparingly fossiliferous. The flint is 

 extremely hard, breaks with a conchoidal fracture, and is dark gray to 

 black in color due to inclusions of carbonaceous matter; it is char- 

 acterized by small cavities lined or completely filled with quartz crys- 

 tals. Although fossils are present, they are by no means abundant 

 and are essentially the same as found in the Lower Mercer limestone. 

 However, Fusulina secalica (Say), which is so abundant in the higher 

 Pennsylvanian formations, is present here for the first time in suf- 

 ficient numbers to be conspicuous, although it is found very sparingly 

 also in the Lower Mercer member. The flinty phase is everywhere 

 characterized by large branching tubes, ranging from one-half to almost 

 an inch in diameter, which although sometimes hollow are generally 

 filled with hard impure iron ore. This filling is either wholly or partially 

 decomposed to a soft, limonitic material, the decomposition taking 

 place first around the edges of the tube and progressing inward. The 

 branching tubes have the appearance of plant stems, but a microscopic 

 study of the filling from various localities showed no evidence of organic 

 structure. It seems probable, therefore, that they originated as con- 

 cretionary formations of impure hematite, similar to those, often found 

 in the Lowellville limestone, which have later undergone partial or 

 complete decomposition. 



In northeastern Ohio the horizon is characterized by hard, dark 

 blue, somewhat siliceous limestone which is fairly persistent and mod- 

 erately fossiliferous. Lamb states that in Mahoning County it is 

 present equally as often as the Lower Mercer limestone 2 which it re- 

 sembles closely in lithologic character, composition, and fossil content. 



The thickness of the Upper Mercer deposit varies from a few inches 

 in southern Ohio to about 3| feet hi the northeastern part of the State. 

 In the south where the horizon is represented mostly by an iron ore, 5 

 inches to 1 foot 6 inches, with a maximum of 2 feet, is present. 



'Stout, W., Geol. Surv. Ohio, Fourth Ser., Bull. 21, pp. 102-103, 1918. 

 2 Lamb, G. F., Pennsylvanian Limestones of Northeastern Ohio below the Lower 

 Kittanning Coal, Ohio Naturalist, Vol. 10, p. 130, March, 1910. 



