610 GEOLOGY OF OHIO. 
tu ninety-five per cent. It is the nearest approach toa pure carbonato 
of lime that is burned, in the large way, in the State. The lime of New 
Carlisle, Clarke county, has a somewhat higher percentage, but it dces 
not enter the peneral market. Tor all purposes, where a strong and hot 
lime is desired, this particular layer would meet every requirement. It 
is called the “ smooth rock,” as has been already stated. This name is we:! 
applied to it, on account of the planed surface that the upper face of the 
rock presents. It could very easily be mistaken for a glacial-planed sui- 
face; indeed, it would seem to have been acted on by some force 
precisely of this character. Fossils that belong in its’ substance have 
been cut down just as they have been worn in the surface beds, by agen- 
cies of the recent Drift period. No explanation of this unusual phenom- 
enon is offered. Modern researches indicate that ice periods must have 
prevailed at wide intervals throughout geological time; but no instance 
is known to be recorded in which the planing and polishing of ancient 
glaciers, or icebergs, are preserved in rocks of such high antiquity as 
this Devonian limestone. 
The smooth rock is overlain by four feet of what is called by the 
quarrymen, the “‘blue rock”. It lies in very thin courses, and is valueless 
for building stone, and of little worth for lime. 
The course that covers it is the most interesting stratum, not only of 
the section now under consideration, but of the whole Corniferous forma- 
tion of Ohio as well. It is one of the most remarkable layers, indeed, in 
the entire series of American Paleozoic deposits. Reference has already 
been made to it under the name of the bone bed. The name describes 
the stratum. It is six inches in thickness, and is literally made up 
hrough considerable portions of its extent, of the teeth, and plates, and 
bones of fishes. These remainsare in excellent preservation. The teeth 
retain the polish and structure of life, but in color they have been uni- 
formly changed to light brown; the plates and bones are usually black 
or brownish black. The surfaces of the plates frequently retain the 
dermal tubercles, or other ornamentation, with perfect distinctness. The 
teeth belong mainly to one genus, viz.: Onychodus, and it is not certain 
that the forms, shown so abundantly at this horizon, differs specifically 
from those described from other beds. The crest of teeth in the end of 
the jaw, which is characteristic of this genus, is sometimes, though 
rarely, found here, the teeth occurring usually detached, but a large num- 
ber of them being entire. Other fossils are found to a limited extent in 
the bone bed, the most abundant and conspicuous being an Athyris, which 
closely resembles A. vittata, Hall, from the same general horizon at Louis- 
ville, Kentucky. | 
