48 POTTSVILLE FAUNA OF OHIO 



inches, although the member may vary from 1 to 20 feet in different 

 places; the same thickness is found in Licking County where the stratum 

 is excellently developed along Flint Ridge, Hopewell Township. 1 In 

 southern Coshocton County in Opossum Hollow 4 feet is present 

 which is the same thickness found at Bolivar in the northern part of 

 Tuscarawas County near the type locality for the "Zoar limestone." 

 The stratum consists of very hard, blue to black limestone which may 

 or may not be interbedded with or replaced by impure shaly limestone 

 and black calcareous shale. At some localities the hard, blue lime- 

 stone consists of only one layer about a foot in thickness, while at 

 others two or more layers are present, separated by calcareous shale or 

 impure shaly limestone. The hard, blue limestone varies in composi- 

 tion from place to place, often becoming ferruginous and siliceous in 

 character; chert nodules are not an uncommon constituent. In a few 

 localities, especially in Newton Township, Muskingum County, the 

 member is entirely replaced by sandstone. The geologic sections from 

 the counties in the central part of the Lower Mercer outcrop in Ohio, 

 given later in the discussion, will show the relation of the hard, blue 

 limestone to the impure, shaly limestone and the dark calcareous shales, 

 as well as local variations in thickness. 



As in southern Ohio the stratum is extremely fossiliferous, especially 

 the dark shales and impure shaly limestones, which contain a profusion 

 of species as well as of individuals. The fauna consists largely of 

 brachiopoots and pelecypods. The black calcareous shales overlying 

 the limestone furnish easy and profitable collecting, as is also the case 

 along weathered outcrops of the impure shaly limestone which splits 

 up easily into thin layers upon exposure, revealing a wealth of fossils 

 between the layers. The hard, blue limestone, although fairly fossil- 

 iferous, does not afford such good collecting on account of its extreme 

 hardness; its fauna is largely one of brachiopods and large crinoid 

 stems which often attain a diameter of almost an inch. 



Outcrop in Northeastern Ohio. In northeastern Ohio, including 

 Stark, Summit, Portage, and Mahoning counties, the Lower Mercer 

 member is present also with great persistence. Where characteris- 

 tically developed it consists of two layers or benches of hard, tough, 

 blue to black limestone generally without shaly partings between them. 

 However, a layer of black shale is usally present beneath the limestone. 

 In thickness the member varies from 1 to 3 feet in Stark County, 

 but it becomes more massive in Mahoning County where it shows an 

 average depth of 3 feet. The upper layer is as a rule much thicker than 

 the lower and often becomes flinty toward the top; it is likewise spar- 

 ingly fossiliferous. The thin lower layer possesses an abundance of 

 animal remains, while the black shales below the limestone are also 

 extremely ric-h in fossils. The faunal content is similar to that in the 



, W., GeoL Surv. Ohio, Fourth Ser., Bull. 21, pp. 82-90, 1918. 



