180 The Hydraulic Beds, etc, at the Falls of the Ohio, 



equivalent of the Hamiltou group of ISfew 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, sedi- 

 ments, which characterize the formation for three hun- 

 dred miles of its outcrop within the state of N"ew 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 the volumes of the New York Palaeontology, and other 

 reports and papers upon geology and palaeontology, the 

 fossils contained in these Hamilton beds have been re- 

 ferred to the Upper Helderberg group. 



^ A single exception has 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 local- 

 ity," of Megistocrinus rvgosus, use tlie following language : " It is found 

 in the Devonian rocks of the age of the Hamilton group, associated with 

 Orthis siiborhicularis, Atrypa reticularis, A. aspera, Euomphalus cyclosto- 

 mus? etc. This is about the same horizon in which Hall found his 

 Megistocrinus latus." 



This is the only reference of any of these fossils to the Hamilton group 

 which I have been able to find among the writings of Lyon and Casseday, 

 or of Major Lyon. 



