164 Ciiiriiinafi Socie/y of Natural Hi'-.lory. 



Ohio, and a smaller area in the northern part of the State. 

 This marks the second great limestone formation in the scale, 

 and donbtless was deposited in the Niagara Sea as a pure car- 

 bonate of lime, but, by a slow dolomitic replacement, was 

 changed into a fairl}- pure dolomite, and now is used quite 

 extensively as a source of magnesian lime. From these facts 

 it will be seen that a microscopical study will not be as satis- 

 factory as heretofore, for but little original fossil matter is left. 

 The dolomite crystals are very apt to break out in the process 

 of grinding, thus leaving open, irregular spaces through the 

 section. Fossil structure is seen in very small amount, con- 

 sisting of a few fragments of crinoids, which seem to have 

 withstood the change, and a few small fragments of coral of 

 the form Clathropora. The shells are completely obliterated, 

 and a careful observation has failed to reveal the slightest 

 trace of such structure. 



The casts indicate an abundance of life, so we would infer 

 that the Ohio deposit has had bad luck, probably shut off from 

 the ocean to form an evaporating basin, which greatly aided 

 the change from a limestone, like those before it, into the 

 compact, almost structureless, rock we now find. Doubtless 

 there was here a great diversit}- of life, of which even the 

 record has perished. 



All the formations studied thus far have proven fossiliferous 

 to a high degree, life seemed to be abundant, but now we 

 come to a break, to a series which seems to be unfossiliferous, 

 the 



LOWER HELDERBERG FORMATION, 



Or waterlime group of Ohio, which consists of a magnesian 

 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 excep- 

 tion of a few casts, the most common being the small coffee 

 grain fossil, Leperditia alta. The explanation which has been 

 given is based on the existence of the beds of salt and gypsum, 

 r.iany regarding this portion of the geological series as the 



