STRATIGRAPHY OF FOSSILIFEROUS MEMBERS 11 



form datum planes of extreme importance for determining the strati- 

 graphic relations of the overlying and underlying formations. 



Economically the Pottsville formation is of considerable value, 

 and it has added much to the natural resources and wealth of the State. 

 Most of the iron ores which have been worked for the purpose of smelt- 

 ing in the old charcoal furnaces, particularly in Scioto, Lawrence, 

 Jackson, and Vinton counties, were from this formation. The Lower 

 and Upper Mercer ores especially are of sufficient thickness and are 

 high enough in iron content to be of some importance commercially. 

 However, they in no way rival the ores of the Lake Superior region, 

 and at the present time are used only to a very limited extent if at all. 

 The coals are utilized mostly for local purposes, but a few beds, such 

 as the Sharon coal and particularly the Quakertown or No. 2 coal, 

 have been mined for commercial use for the past forty years and have 

 been important factors in the development of industry in southern 

 Ohio. In Jackson County, the Quakertown coal is of good quality 

 and thickness, and is responsible for the rapid growth of Jackson, 

 Wellston, and other towns in the mining district. Pottsville clays are 

 also of importance economically, and the Sciotoville clay has been 

 used for many years in Scioto and Jackson counties for the manufac- 

 ture of refractory wares, for which purpose it sets a standard of ex- 

 cellence in Ohio. 1 



A study of the Pottsville fossils shows that with the exception of 

 the coal formations, the members are marine in origin for the most 

 part. The marine conditions which produced these members alter- 

 nated with the swamp conditions under which the coal was deposited. 

 During six periods marine conditions favored the deposition of lime- 

 stone, and the first six members of the series of limestones of the Penn- 

 sylvanian system were laid down, namely the Lowellville (Poverty 

 Run), Boggs, Lower Mercer, Upper Mercer, Me Arthur, and Black 

 Flint members. The marine sediments were deposited in shallow 

 waters, and as they grew in thickness the water level was approached 

 until swamp conditions, necessary for the formation of coal, were 

 brought about. A slow depression, however, successively brought the 

 swamp conditions to an end and shallow marine waters again occupied 

 the region, and another series of marine sediments was deposited. 

 The slow periodic sinking of the region and the subsequent building 

 up of the sea bottom to the water level were necessary for the alter- 

 nation of marine sediments and coals. 2 



In the following discussion the faunal horizons of the Pottsville 

 formation are treated successively, so as to show the stratigraphic 

 relations, character, and extent of each of these strata. 



'Stout, W., Geol. Surv. Ohio, Fourth Ser., Bull. 20, pp. 514, 73, 1916. 

 2 Stout, W., Manuscript on Clays of Ohio. 



