THE HYDRAULIC BEDS AND ASSOCIATED LIME- 

 STONES AT THE FALLS OF THE OHIO. 



By James Hall. 



[Read before the Institute December 4, 1877.] 

 At the Falls of the Ohio and adjacent localities, the 

 lowest beds of the limestone formation are marked by the 

 presence of Halysites catenulatus, and for a long time have 

 been locally known as the " Catenipora beds." This Si- 

 lurian limestone is succeeded by the great coral-bearing 

 Devonian limestone, which is everywhere, in that part of 

 the country, a well defined geological horizon ; and though 

 the higher beds of the formation are distinguished by the 

 presence of other fossils than corals, there is no marked 

 physical change from the base to the upper stratum which 

 is characterized by Spirifera acuminata. The whole is more 

 generally recognized by its numerous corals, and the • 

 genera Favosites, Michelinia, Zaphrentis, Heliophyllum 

 and Cystiphyllum are prevailing forms.^ This limestone 

 is succeeded by beds of an argillaceous magnesian lime- 

 stone, known as the " Hydraulic limestone," which gradu- 

 ally merges above into thin, slaty beds, some of which are 

 highly siliceous, and these are followed by what is known 

 as the " Encrinal limestone ;" the whole terminated above 

 by the black slate. This entire limestone formation above 

 the " Catenipora beds" has been generally, if not universally, 

 recognized as of the same age and as the western extension 

 of the Upper Helderberg group of New York (represent- 

 ing all that was originally included by Eaton under thede- 



^ It was from the presence, in this locality, of numerous species of corals, 

 identical with those of the New York formations, that, in 1841, I recognized 

 these limestones as of the same age. 

 Trans, ix.] 22 



