6 GEOLOGY OF OHIO. 



which have a thickness respectively of one hundred and thirty and three 

 hundred feet, the entire set of unbroken limestones, beginning with the 

 Trenton, and including the two. formations above named, being thus 

 about six hundred feet in thickness. 



It is altogether probable that these three limestones constitute the 

 solid mass which the drill has so often penetrated in Ohio within the last 

 few years to a depth of five or six hundred feet. The formations, which 

 the geologists separates when they rise to the surface, are counted by the 

 driller as a single limestone, for which he needs no other name than that 

 with which he begins, viz.: Trenton. The several divisions, however, 

 are found to vary somewhat in grain, in color and in chemical composi- 

 tion as well as in the fossils they contain. 



Below this great limestone mass a sandstone, more or less calcareous, 

 is reported in many of our deep 'wells. This is probably on the horizon 

 of the St. Peter's sandstone of the northwest and very likely deserves to 

 be called by this name. It is forty to sixty feet thick, as generally re- 

 ported, and is charged with the rank salt and sulphur water which is 

 known in Kentucky as Blue Lick water. It must, however, be ac- 

 knowledged that water of quite similar composition is sometimes found 

 in or between the limestone beds above named as well as in the under- 

 lying stratum. 



Still deeper, impure magnesian limestones are found, at least in the 

 Ohio series, for the next one thousand feet of descent. This was well 

 .shown in the deep wells of Springfield and Dayton. These beds must 

 be referred to the Calciferous period of the general scale, so far as, at least, 

 as their uppermost portions are concerned. 



To the question so often asked, and to which a sharp and exact 

 answer is expected, "How thick is the Trenton limestone?" it is thus 

 seen that it is not only not easy, but not even possible to give such an 

 answer, on account of the ambiguity of the term as it is popularly used. 

 The interest of the question, however, is practical, and centers in those 

 portions of the limestone that yield gas and oil. Restricting the scope 

 of the question to this point of view, it can be stated that no part of 

 the Trenton limestone, more than a hundred feet below its uppermost 

 surface, has thus far proved productive of either gas or oil, in the large way. 



2. The Utica Shale. 



The immediate cover of the Trenton limestone in the locality from 

 which the latter derives its name, is a well-known stratum of black shale, 

 three hundred to seven hundred feet in thickness, and, possibly, in por- 

 tions of eastern New York, much thicker than the maximum above given. 

 This conspicuous stratum received from the New York geologists the 

 name of Utica shale, from the fact that very many outcrops of it occur in 

 the vicinity of the city of Utica. This bed of slack shale has proved to 

 be very persistent and wide-spread. It must be acknowledged, however, 



