34 GEOLOGY OF OHIO. 



ous. They are the upper and lower Meadville limestones of White, and 

 can be followed into Ohio from Crawford county, Pennsylvania, where 

 thej 7 were first described. 



The Logan sandstone that succeeds the Waverly conglomerate in 

 the full section is an uncertain and inconstant element, for the reason 

 that it plays fast and loose with the stratum last described. Much could 

 be said in favor of counting it the upper portion of the conglomerate. 

 In typical exposures it is a fawn-colored, fine-grained, even-beded sand- 

 stone. In this phase of the formation the most favorable conditions for 

 the marine life of the period seem to have been attained, the sandstone 

 being prolific in fossils. The characters above given are quite widely held 

 throughout the state. The Logan sandstone is often found directly 

 underlying the lowest coal seam. 



The Olive shales of Read are probably the exact equivalent of the 

 Logan sandstone in age. They seem to take its place in the central 

 counties in part. Overlying the coarse rock in Knox and Coshocton 

 counties, Read reports more than three hundred feet of sparingly fos- 

 siliferous shales, to which he gives the name here used. 



Diverse as these elements are, they are blended and interlocked in 

 the Logan group, leaving it in stratigraphy and fossils a well-defined and 

 easily followed series throughout all parts of the territory in which it is 

 due, except in possibly a small area in northern Ohio, as already noted, 

 and even here, there is no difficulty in recognizing the presence of this 

 series. The several elements are, however, of smaller volume here than 

 elsewhere. Under cover, throughout southeastern Ohio, the series is in the 

 highest degree persistent and regular, much more uniform, indeed, than 

 in its outcrops. It consists of two hundred feet or more of prevailingly 

 coarse rock, almost everwhere pebbly in spots, but interrupted with sheets 

 of shale, yellowish and reddish colors being the characteristic ones. It 

 has considerable interest in connection with gas, oil and salt water in 

 Ohio, being the reservoir of the brines of the Hocking and Muskingum 

 valleys, and furnishing in the latter large supplies of gas in the early days 

 of salt manufacture in this state. It is also the "Big Indian" sandstone 

 of the oil well drillers of western Pennsylvania, West Virginia and 

 Southeastern Ohio. 



The Sub-carboniferous series of Ohio has now, with the exception of 

 a single element next to be named, been passed in review. It is seen to 

 be a very sharply characterized series, a most persistent sandstone, though 

 not a thick one, lying near its base, bedded in shale and covered also by 

 shale, the lower shale being often red in color and the roof shale being 

 always black, and another sandstone or conglomerate stratum, two hun- 

 dred feet or more in thickness, forming the upper member of the series ; 

 these two persistent sandstone formations being separated from each 

 other by three hundred or more feet of light-colored, soft, argillaceous 

 shales. No conditions could be more favorable for tracing such a group 



