18 GEOLOGY OF OHIO. 



dred feet of limestone. At any rate, a sandstone found at this depth 

 has very much the same character as that from the Sylvania quarries. 



That there is another sandstone of character similar to that of the 

 Sylvania sand, and which is included in the Corniferous limestone, is 

 beyond question. This formation will be described in the next succeed- 

 ing section. The Sylvania sand can henceforth be counted an Upper 

 Silurian sandstone and a part of the Lower Helderberg series. 



Whether the sandstone beds of Champaign and Logan counties are 

 all to be referred to one horizon remains to be determined by further 

 study. At present such a reference seems very doubtful. 



8. The Upper Helderberg Limestone. 



All of the limestone of Devonian age of Ohio has been referred by 

 Newberry to the Corniferous limestone, and this term is in general use 

 at the present time. It may be questioned whether it is wise to break 

 in upon this use, but inasmuch as several geologists hold that the 

 Devonian limestone of Ohio co.vers more than the simple epoch known 

 as the Corniferous in New York, a more comprehensive term, viz., the 

 Upper Helderberg limestone, is on the whole counted decidedly preferable. 

 A two-fold division of this series in Ohio is possible and proper, the divi- 

 sions, being based on both lithology and fossils. The divisions can be 

 known as the Lower and Upper Corniferous, if the old term is still 

 maintained in use; or, on geographical grounds, as the Columbus and 

 Delaware limestones. For the upper division the designation Sandusky 

 limestone might well be used. In central Ohio, at a few points, there is 

 a marked contrast between • the lower and the upper beds, the latter being 

 thin and shaly, non-fossiliferous in the main, and interrupted with fre- 

 quent courses of black flint. This phase is seen at the state quarries 

 near Columbus. Generally, however, both divisions are calcareous and 

 fossiliferous, and the differences consist in changes of color and com- 

 position, in the thickness of the several beds and in the distribution, and 

 also in the kinds of fossils present. The maximum thickness of the 

 Upper Helderberg series in Ohio, so far as present records, show, is 

 between seventy-five and one hundred feet. 



Included in the lower beds of the limestone there are at many 

 points, deposits of sharp sand of the same general character as the 

 deposits that have been already described under the names of Hillsboro 

 sandstone and Sylvania sandstone. These beds may be known under 

 the name of the West Jefferson sandstone, one of the localities at which 

 the sand is found being near this village. This Upper Helderberg sand- 

 stone is not Oriskany in age. It has nowhere been found to underlie 

 the Corniferous limestone, but it is always interstratified with the latter, 

 at least where its place in the series can be fully determined. It attains 

 a thickness of but few feet at most, and is' nowhere worked for economic 

 uses except upon a very small scale. 



