THE HAMILTON IN OHIO 595 
Chonetes scitulus Hall, Spirijer pennatus (Atwater), Leiorhynchus 
laura (Billings), Pleurotomaria sulcomarginata (Conrad), Tentaculites 
bellulus Hall, Phacops rana (Green). 
No argument is sufficiently strong to place such a collection of 
species on the Onondaga list. It is, in fact, a true Hamilton fauna. 
How much of southeastern Ohio may contain Marcellus deposits, 
or to what extent, we do not know, but it is certain that the eastern 
shore of the Cincinnati island felt the effects of the changed condi- 
tions which this invasion brought about, while Franklin and Dela- 
ware Counties have recorded a trace of the black muds which these 
swampy seas have left. The impoverished and diminutive fauna 
which we find in the base of the Delaware proves that the luxuriant 
life which flourished during the Columbus stage was all but blotted 
out, and when more favorable conditions were restored, approaching, 
although never reaching, those which had previously existed, it was 
not the same fauna that took possession, but one composed of the few 
surviving Columbus species and a new lot probably wandering south 
from the hoards which were invading New York at this time. On the 
northwest coast of the island, however, conditions were different. 
It is probable that the Marcellus invasion never reached this point, 
but that the change from the Columbus to the Delaware fauna was 
gradual. Unfortunately the outcrops visited did not show the con- 
tact of these two formations, but the upper part of the Columbus in 
the sections of that part of the state shows evidence of a marked 
change in the fauna, which, by the time the shale-forming conditions 
of the Ten Mile Creek section had set in, had reached a complete 
conversion into that of the Traverse-Hamilton. ‘To a certain extent 
the same is true at Sandusky, where these changes in progress in the 
upper part of the Columbus misled even Dr. Newberry and caused 
him to call it Delaware. The difference between the Delaware out- 
crops in the northwestern and central parts of the state may be 
accounted for in part by supposing, what seems to have been the 
case, that a spur or peninsula from the Cincinnati island extended as 
far northward, perhaps, as the present Canadian shore of Lake Erie, 
thus forming a more or less effective barrier against the fauna which 
was crowding eastward, and that in this somewhat protected central 
part of the state the Hamilton invasion was less intense, and thus 
