THE HAMILTON IN OHIO 593 
characteristic of this fauna, Dr. Clarke tells us,t invaded New York 
from the west, part coming up through the Indiana basin and another 
part through the Traverse strait from the Dakota sea, but the great 
majority of the species were probably developed from the Onondaga 
fauna of the northwestern Mississippian sea. Professor Schuchert 
thinks that the Connecticut channel still continued to admit a few 
European species during the Hamilton time,? but Dr. Grabau says 
that its efficiency ‘“‘was greatly diminished.”3 We thus see the 
heterogeneous character of the Hamilton fauna, which is most marked 
in regions, such as Ontario and western New York, where all of these 
elements blended, and thus an excuse, in more isolated regions, for 
great variation even in true faunas of this age. 
Following the base of the Delaware northward, it soon loses its 
shaly character, and yet even at Stratford, 20 miles north of Columbus, 
blocks of the massive blue layers from this horizon split into thin, 
somewhat shaly fragments after extensive weathering, and still con- 
tain the same fauna characteristic of these beds in Franklin County. 
Above the 6-foot shaly zone occur 30 feet of blue limestones, varying 
from thin-bedded to massive, and sometimes, as at Delaware and 
Owen, having bands of soft, blue shale from a few inches to a foot in 
thickness, at different horizons. In Franklin County the formation 
contains much black chert, which usually occurs as layers alternating 
with limestone, or sometimes taking the nature of zones; but north- 
ward the amount of this material decreases, until at Sandusky little or 
none occurs. In studying this formation and its fauna, it appears to 
me that this physical feature has been an influential factor in classify- 
ing this deposit among the ‘“‘Corniferous” rocks. There is little in 
the lithological appearance of this formation, it is true, which suggests 
the soft, blue shales of the Eighteen Mile Creek outcrops, except per- 
haps its persistent blue color; but, on the other hand, the Hamilton 
deposits of Indiana and Michigan are mainly limestones. It appears, 
then, that the distinction must rest on the faunal evidence which may 
be extracted from the various outcrops. 
The important outcrops of this formation follow the eastern and 
t New York State Museum Bulletin No. 52, p. 669. 
2 Schuchert, American Geologist, Vol. XXXII, p. 162. 
3 Grabau, New York Museum Bulletin No. 92, p. 233: 
