PKEFACE. 



In the following pages the author has attempted to catalogue 

 all the species of fossils known to him from the Lower Silurian 

 exposures in Ohio, Indiana and Kentucky. That many species 

 occur in these strata Avhich we have failed to chronicle is cer- 

 tain, but no labor has been spared to make the catalogue as 

 complete as possible. The number of species by far exceeds 

 that of any previous catalogue of the species of this section of 

 Lower Silurian rocks. And the end is not yet, since the two 

 score or more of energetic collectors about Cincinnati are con- 

 tinually increasing the list by frequent discoveries of new fos- 

 sils. Of the species contained in this list, at least five hundred 

 and fifty are represented in my cabinet, beside twenty-seven un- 

 determined forms. Many of the new species recorded in the 

 list, have as yet not been published. The names proposed for 

 them in my manuscript (which will be published as soon as 

 it is possible) have been given. A few species which were over- 

 looked, and consequently will not be found in their proper 

 places, have been placed at the end of the list. 



The term Cincinnati Group, as used by me, will, I have no 

 doubt, be found objectionable by many. Recent investigations, 

 however, have induced me to retain the name in the sense pro- 

 posed by Dr. J. S. Newberry, and have demonstrated that the 

 question of the retention of that term, or the substitution of the 

 names Trenton Limestone, Utica Slates aud Hudson River 

 Group, is, to say the least, an open one. In the Cincinnati ex- 

 posures it is an utter impossibility to mark a line of division 

 between the Utica Slates and the Hudson River Group. There 

 are a number of localities where a continuous section of the 

 strata from low water mark in the Ohio river, to three hundred 

 feet above that level, can be examined. These sections present 

 no stratum that may be used or marked as a divisional one. The 

 lithological characters of the lower members of this section fade 

 gradually into those of the upper beds. On palaeontological 

 grounds we find still less reasons for a separation of the Cin- 

 cinnati Group of rocks into minor groups. Here we have an ex- 

 tensive fauna belonging exclusively to the Cincinnati Group, 

 since of the s ix hundr ed and si xty for ms mentioned in this cata- 

 logue, nearl yTour hu~hdret!~~ha ve not~been recorded from any 

 other formation"! ine remaining two hundred and seventy-five 

 species occur in the Lower Silurian deposits of New York and 

 Canada, and there range in time from the Chazy to the Clinton. 



In the upper six hundred feet of the Cincinnati Group, we 

 find represented as characteristic fossils, at least fifty undoubt- 

 ed Trenton species, none of which are found below two hum 



