4 ; GEOLOGY OF OHIO. 
the first volume of the Geology of Ohio, great additions have been made 
to our knowledge of the forms of life contained in these rocks, through 
the contributions of Messrs. Meek, Hall, Whitfield, and Nicholson. These 
are contained in Vols. I and II of the Paleontology of Ohio, in which the 
descriptions of species occupy 382 pages, and are illustrated by twenty 
plates. For the means of making this important contribution to pale- 
ontological science, the Survey is greatly indebted to Messrs. C. B. Dyer, 
U. P. James, S. A. Miller, D. H. Shaffer, and Drs. Miller, Hill, and Byrnes, 
all of whom generously placed their splendid collections of fossils in the 
hands of the paleontologists mentioned, for description. More new ma- 
terial. is constantly being obtained from this vast storehouse of ancient 
life, and it is hoped that some of the species discovered since the publi- 
cation of the second volume on Paleontology, will be described in the 
third and last volume, which is now in preparation. _ 
Perhaps the most interesting fossils recently discovered in the Cincin- 
nati group, are numbers of minute dental organs, collected about Cin- 
cinnati, by Professor Wetherby and Mr. EH. O. Ulrich. Their zodlogical 
relations have not yet been accurately determined: they have much 
resemblance to the jaws and teeth of fishes, but are perhaps still more 
like, in form and microscopic structure, the teeth of annelids. Although 
at first supposed to be fish-teeth, it is much more probable that they 
formed the dentition of mollusks or articulates; at least, much stronger 
proof that they afford will be required, before the existence of verte- 
brates in the Lower Silurian Sea can be conceded. 
aie UPPER SILURIAN SYSTEM. 
THE MEDINA GROUP. 
Nothing new has been learned since the publication of our first vol- 
ume, in regard to the existence, in Ohio, of representatives of the Medina 
sandstone. Deep borings in the northern and central parts of the State 
indicate the presence there of a stratum of red, mechanical sediment be- 
tween the limestones of the Cincinnati group and those of the Upper 
Silurian, and there is little doubt that this represents the Medina sand- 
stone of New York. In south-western Ohio, a sheet of calcareous, colored 
clays occupies the same position. Professor I’. H. Bradley reports that 
in Indiana the fossils of the Cincinnati Group extend up through this 
band to the base of the Clinton. We have, however, found this not to 
be the case in Ohio, nor has any evidence been gathered here which is 
inconsistent with the supposition that these clays form the extreme 
edge of the Medina. This is rendered the more probable by the great 
