OF DENISON UNIVERSITY. 
7 
the same layers being much less. The amount of iron becomes great- 
er as well as far more regular in the upper courses of the Clinton 
Group at Todd’s Fork, here becoming oolitic in places. Farther south 
from this point it increases until it reaches some importance in tho 
southern counties. 
The specimen from Huffman’s quarry marked “ dark green ” is 
a fragment showing localized features of the ordinary limestone of that 
locality, of small extent, usually existing only as little, often far dis- 
tant, patches. In the discussion of the chemical character of the rocks 
here examined the analyses made by Dr. T. G. VVormley, and pub- 
lished in the various volumes of the Ohio Geological Survey have been 
constantly before my eyes. 
STRATIGRAPHICAL GEOLOGY. 
Stratigraphically the Clinton Group of Ohio presents no marked 
subdivision except that of the Beavertown marl, which occurs at Huff- 
man’s quarry, and also at Todd’s Fork, but not as a marked subdvis- 
ion. The top of the Clinton at Centreville and the Soldiers’ Home 
quarries, is composed of a few inches of clayey sediments, which pre- 
sent a much larger number of specimens of certain species than are 
found in the rocks below. These are : Orthis hybrida, O. elegantula, 
G.fausta, O. Dayionensis, Tf'iplesia Ortoni] Calymene Fbgdesi (the \a.r- 
ger forms), Rhinopora frondosa, and Homotrypa confliiens. But this 
seems to be a mere local variation. 
A comparison of the Ohio Silurian with the corresponding strata 
of Indiana is at the present date difficult, owing to the fact that no 
connected plan of work seems to have been followed in that state, so 
that observations made are apt to have only very local value, and dif- 
ferent writers apparently apply different values to the same stratigraph- 
ical names. Careful paleontological observations with the exception 
of the Waldron beds, are also lacking. Lithological features alone, 
unfortunately, are so often deceptive that not much reliance can be 
placed upon them. However the following conclusions seem fairly 
well drawn. ' 
The Lower Silurian series of Indiana have been well determined. 
In places, especially in Decatur and the more southern counties, the 
base of the Upper Silurian is formed by a sandy rock, varying from 
