GEOLOGICAL SCALE AND STRUCTURE. 7 



that it is not as well characterized by definite forms of life as most of the 

 strata that receive independent names in the geological scale. It is every- 

 where, but sparingly fossiliferous ; but while only a few of the forms that 

 t contains are found exclusively in this series of deposits, there are still 

 enough, when taken in connection with the lithological characteristics of 

 the shale, to establish and maintain its identity. 



The first of the deep wells that was drilled in Fiudlay revealed, at a 

 depth of eight hundred feet, a stratum of black shale, the fragments of 

 which, brought up by the driller or by explosion of nitro-glycerine in the 

 oil rock, contained what may be styled the most characteristic fossils of 

 the Utica shale of New York, and the black shale eight hundred feet be- 

 low the surface in northwestern Ohio, was thus positively identified with 

 the Utica shale of central New York. This bed of shale, as proved by 

 the driller, in Ohio has the normal thickness of the formation in New 

 York, viz. : 300 feet, and, taken in connection with the other elements in- 

 volved, it extended and continued the New York series into the under- 

 ground geology of northern Ohio in the most unexpected and at the same 

 time in the most satisfactory way. 



The Utica shale thus discovered and defined is a constant element in 

 the northwestern portion of the state. Its upper boundary is not always 

 perfectly distinct, as the Hudson river shale that overlies it sometimes 

 ' graduates into it in color and appearance. But as a rule the driller, with- 

 out any geological prepossessions whatever, would divide the well section 

 in his record so as to show about three hundred feet of black shale at t,he 

 bottom of the column, or immediately overlying the Trenton limestone. 

 This stratum holds its own as far as the southern central counties. In 

 the wells of Springfield, Urbana and Piqua a dark-colored stratum is 

 found in undiminished thickness, but apparently somewhat more calca- 

 reous in composition than in the locality where it was discovered. From 

 these points southward, according to the somewhat scanty facts that 

 have been secured, the formation thins rapidly until it is apparently re- 

 placed by dark-colored limestone bands, known as "pepper and salt rock" 

 by the driller. No great falling off in black shale appears in the ■ 

 Dayton wells ; but at Middletown a sharp boundary between gray shale 

 three hundred and ten feet thick (Hudson river), and black shale one 

 hundred feet thick (Utica), the latter directly overlying the Trenton 

 limestone, was reported by a driller whose observations seemed entitled 

 to confidence. The black shale was reported still further reduced in the 

 wells at Hamilton and from that point southward it was not distinctly 

 recognizable. From these and similar facts it appears that the Utica 

 shale is much reduced and altered as it approaches the Ohio Valley, and 

 is finally lost by overlap of the Hudson river shale in this portion of the 

 state and to the southward. 



The identification of the Utica shale as a distinct stratum iri the 

 lower beds of the series exposed at and near Cincinnati, which has been 



