XVIII INTRODUCTION. 



including both the Trenton and the so-called Hudson river 

 groups, and hence could not be used when we wish to speak of 

 the group under consideration as a distinct formation from the 

 Trenton. 



In order to have a convenient name for this formation, that 

 would be applicable wherever and under whatever lithological 

 characters it might be found, and at the same time mean this 

 particular group — neither more nor less — we proposed, in a 

 paper published in the Proceedings of the Philadelphia Acade- 

 my of Sciences, August, 1865, p. 155, to call it the Cincinnati 

 group, now retained in the accompanying section, and used in 

 the first volume of this Report. We do not think it would be 

 possible to select a more appropriate name than this, Cincinnati 

 being widely known as one of the great commercial cities of the 

 west, while th,e formation named is perhaps more extensively 

 developed and exposed there than at any other place, and is at 

 the same time so highly fossiliferOus at that locality, that its 

 characteristic fossils have been widely distributed, by local and 

 traveling geologists, almost throughout the civilized world. 

 Hence when we speak of the "Cincinnati group," geologists 

 will everywhere know exactly to what horizon we refer, with- 

 out a word of explanation. 



After reading the quotations we have made from the Wiscon- 

 sin Report, it will be readily understood that one of the writers, 

 on exhibiting a section of the Illinois rocks before the American 

 Association for the Advancement of Science, at the late Buffalo 

 meeting, was not a little surprised that Professor Hall should 

 object to the term Cincinnati group, and insist upon retaining 

 for this formation the name Hudson river group, on the ground 

 that it is represented on the Hudson river by the isolated masses or 

 outliers already alluded to. That geologists will, however, sanc- 

 tion such a transfer of the name of a great geological formation 

 from the group to which it was originally applied, and for which 

 alone it is acknowledged to have been intended, to another 



