h;4 TIIK AMKKIOAN MONTH LV [.Innc 



noidal liincstoiK-. Tlu" crvstals inakintj up the icinaiiulLM" of the 

 rock arc calcito. Almost all of the .sfctit)ns contain sonic fiaLj- 

 incnts of crinoiiis, and this was an aije of crinoids, in distinction 

 from tiu" lower jj^roup. 



Niagara Series. — Consistin<j of shales and a maj^nesian lime- 

 stone, with considerable fossil life, which is mainly preserved in 

 tlie form of internal casts, the characteristic forms hcinjj Pcn- 

 tanicrus, Trimerclla, Monomcrclla, ami Atrpya. This marks 

 the second •jreat limestone formation in the scale, and doubtless 

 was deposited in the Niajjara sea as a pure carl)onate of lime, 

 hut. by a slow dolomitic replacement, was chansi^eil into a fairly 

 pure dolomite, and now is useil (juite extensively as a source of 

 ma«;nesian lime. From these facts it will be seen that a micro- 

 scopical study will not be as satisfactory as heretofore, for but 

 little ori<jinal fossil matter is left. The dolomite crvstalsare very 

 apt to break out in the process of <j^rindin<j, thus leaving; open ir- 

 rej^ular spaces throuj^h the section. 



Lower Helderberg Formation.— or waterlimc <::roup of 

 Ohio, which cunsisis of a mi^nesian limestone, inclosing at a 

 number of points large beds of rock salt and gypsum. 

 This formation covers two dozen counties of the State, and the 

 limestone contains a notable percentage of bituminous matter, 

 appearing in streaks through the rock, which accounts for the 

 odor of petroleum when it is struck with the hammer. It has 

 long been regarded unfossiliferous. with the exception of a few 

 casts, the most common being the small coH'ee-grain fossil, Lep- 

 erditia alta. In iSSo some blocks of this limestone were pol- 

 ished tor the National Museum, and it was stated tiiat " one pol- 

 ished upon the surface parallel to the plate of stratification showed 

 a fossil brvozoan, and thus proved that it was fossiliferous." 

 We are forced to say that the Helderberg limestone of Ohio is 

 very sparingly fossiliferous. even in microscopic sections, but we 

 cannot say the Ilelderljcrg sea in Ohio was without life. 



Devonian, or Coniferous. — Extends as a narrow strip, S-20 

 miles in width, through the central portion of the State. The 

 limestone is quite a pure carbonate, abundantly fossiliferous. con- 

 taining braciiiopods and reef-building corals in great abundance. 

 It is here that we find the first abundant plant and fisii life pre- 

 served. 



At Columbus probably the best development is to be found. 

 The upper portion is shaly. with very few fossils, and these are 

 mainly fish remains : below tiiis stratum comes a brown and 

 white chert, which is not acted upon by acids. The fossils in 

 this chert are very finely preserved, even the delicate markings 

 coming distinctly to view. Below this comes the bone bed, a 

 comparatively thin layer made up of the teeth and remains of 

 fish, while below this lies the great mass of limestone used for 

 lime and building purposes. The microscope reveals many in- 

 teresting and puzzling fossil forms. 



