162 Association of American Geologists and Naturalists. 
In reply to Prof. Rogers, Mr. Hall said he did not consider the 
black bituminous shale of the west as the equivalent, but as the 
only representative of the Marcellus shales and the Hamilton 
group. 
The President replied, that there was no equivalent of the 
Hamilton group at the west; the Marcellus shales were far 
more persistent, and were found where the other was entirely 
wanting. And such, too, was the case with regard to some 
other of the New York formations. There was another fact 
worthy of observation, that those species which we are apt to 
deem characteristic, are found to make strange aberrations, 
and may occupy dwellings, to which we perhaps think they 
have no title. Thus he had found in the blue limestone of 
Cincinnati the Dictuolites Beckii and F'ucoides biloba, fossils 
which were typical of the Hudson River shales, associated with 
those of the Trenton and Clinton groups. Now he would ask, 
were these species created at an earlier period in the western 
ocean, and did they remain there during the convulsions which 
had elevated the New York rocks? Or did the earlier species of 
the Hudson River group continue on in the west, and thus be- 
come associated with the beings of another era? One or other 
of these suppositions must be correct, if the species have been 
correctly identified. 
Mr. Hall in reply to what had fallen from the President in 
relation to the fossils which he supposed he had found out of 
place, remarked that there were indeed fossils in the Hudson 
River group resembling the Strophomena rugosa, but there was 
great doubt whether they were that fossil. He referred to the 
figure, in the Silurian Researches, of the Leptena tenwistriata, 
which was corrugated in a manner similar to the Strophomena 
corrugata. Similar differences exist in respect to other fossils. 
Mr. Murchison has given a figure of Orthis canalis, which he 
considers distinct from the O. elegantula of Dalman. Von Buch, 
in speaking of this shell, remarks that it is found at the Iron 
Bridge at ———, in England, and that it differs from those from 
Sweden only in being smaller. Similar observations might be 
made in regard to other fossils, and they could only be declared 
distinct or identical by comparison in hand. 
In relation to the F'ucozdes biloba, he had seen a similar fossil, 
as well as several other species of Fucoids in the Hudson River 
