THE L 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 Helderberg 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 

 Helderberg 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 

 gronp 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 etiogle exception has come under my observation. Messrs. Lyon and Cafseday, in a paper describing 



new RMetal "f ('isini)idea (American Journal of Science, vol. 28, p. 244), under "Geological position and 



I," of Mi [/intocrinas rugosus, use the following language: "It is found in the Devonian rocks of the 



