REVIEW OF GEOLOGICAL STRUCTURE. 3 
The name Cincinnati Group is retained for the rocks under considera- 
tion in our report, since they are not the exact equivalents of any strata 
described under other names elsewhere, and are the typical series to which 
this name was first applied by Messrs. Meek and Worthen; but it should 
be distinctly understood that the term is not, as is represented by these 
authors and others, synonymous with the “ Hudson River Group.” - 
If it were so, it would have been much better to retain the older name, as 
the argument advanced for the change, viz.: “that as the ‘Hudson River 
Group’ does not reach the Hudson River, it was, therefore, a misnomer” 
—has no foundation in fact. As it is, the law of priority, as well as the 
interests of science, require the retention of the name Hudson River 
Group, for the rocks to which it was applied, but it should not be con- 
founded with the Cincinnati Group. 
In the State of New York, the differences between the Trenton and 
Hudson Groups are chiefly local and lithological; nearly all the fossils of 
the Hu 'son being found in the Trenton. The only fossils characteristic 
of the Utica shale, are graptolites which seem to have grown in great 
profusion in certain shallow and quiet parts of the Lower Silurian Sea. 
Subsequently, with the progressive shallowing of the portions of this 
sea adjacent to the shores of the Adirondack and Canadian highlands, 
the sediments deposited became more purely mechanical and coarser, and 
the Oswego sandstone, the Lorraine and Pulaski shales were laid down. 
These changing local conditions produced different groupings of mollus- 
cous life in the subdivisions of the Trenton group; but further south 
and west, where an open sea prevailed, the physical conditions were 
much more constant, and there were few changes in the fauna through- 
out the entire period of the deposition of the Lower Silurian limestones. 
With all the facts brought out by a careful study of the Cincinnati 
Group and its fossils, we were compelled to qualify, in our first volume, 
as has been specified, the definition before given to it. Subsequent ob- 
servations have strengthened the arguments then used, and no conflict- 
ing evidence has been advanced by others. Hence, we protest against 
the course pursued by those who represent the Cincinnati Group of Ohio 
as the equivalent of the Hudson River Group of New York, and call it 
by the latter name; and that of those others who, committing the same 
error of identification, employ the name Cincinnati Group, and represent 
it to be only the upper portion of the Lower Silurian system, and as 
overlying all the Trenton series of New York. In the light of all the 
_ facts cited in our reports, we cannot but regard adherence to these errors 
as a willful perversion of the truth. ; 
Since the publication ef the description of the Cincinnati Group, in 
