THE L 0 UIS V1LLE LIMESTONES. 147 
inferred, from the fact that certain species of known Hamilton fossils are 
published in the Ohio Geological Reports as from the Corniferous group. 
In the State of Wisconsin, the magnesian limestones of the Humboldt river, 
near Milwaukee, are charged with characteristic Hamilton fossils, and doubtless 
represent the hydraulic limestone and superincumbent beds at the Falls of the 
Ohio. I shall, at some future time, give a list of species which I have recog¬ 
nized in that locality during a former geological survey of the State. In the 
States of Illinois and Iowa, the Hamilton group is everywhere partially or 
entirely represented by a limestone, and the term “Hamilton limestone” 
has been used in the geological reports of the former State. In those portions 
of the country where the Upper Ilelderberg limestone is not known as a 
member of the series, there seems less difficulty in recognizing the age and 
character of the Hamilton limestones. It is in those localities where the Upper 
Ilelderberg limestone is well developed, and where the superincumbent beds 
are conformable, that they are likely to be regarded as a component part of the 
formation, and their fossils grouped together in accordance with this view. 
The number of species of the hydraulic and encrinital limestones which are 
common to these beds and the Hamilton group of New York, as shown in the 
list above presented, certainly offers very strong evidence in support of the view 
which I am compelled to take, that they are the equivalent of the Hamilton 
group of New York; and not only the equivalent, but the actual extension of 
the group in a southwestern direction, in the form of calcareous beds, beyond 
the limits of the littoral and off-shore sediments, which characterize the 
formation for three hundred miles of its outcrop within the State of New York. 
The erroneous determination of the age of these beds having permeated all 
the literature of the science for years past,* it will be necessary to make the 
correction wherever in this and the preceding volumes of the New York 
Palaeontology, and other reports and papers upon geology and palaeontology, 
the fossils contained in these Hamilton beds have been referred to the Upper 
Helderberg group. 
* A single exception lias come under my observation. Messrs. Lyon and Casseday, in a paper describing 
new species of Crinoidea ( American Journal of Science, vol. 28, p. 244), under “ Geological position and 
locality ,” of Megistocnnus rugosus, use the following language : “It is found in the Devonian rocks of the 
