INTRODUCTION. XIX 



group, simply because there happens to be a few patches of the 

 latter, of "insignificant extent," in the same region, we cannot 

 believe. Such a misnomer would impose upon the student the 

 perplexing confusion of ideas resulting from the necessity of 

 having always to bear in mind that the Hudson river rocks, so 

 greatly developed along that stream, are not the Hudson river 

 group, but something else; and that the Hudson river group, if 

 existing on the Hudson river at all,* is only represented there 

 in the form of a few insignificant masses, so small that very 

 few geologists have ever been so fortunate as to see them. 



F. B. M. and A. H. W. 



* It is worthy of note that the few fossils mentioned to prove these little patches 

 identical with the Cincinnati group — that is, Leptxna sericea, Orthis testudinaria, Asa- 

 phut and Trinucleus — are forms that also occur in the Trenton group, so that unless 

 some decidedly characteristic species of the group under consideration, not yet men- 

 tioned, also occur there, we would, from the stratigraphical relations of these forma- 

 tions, have better reason to refer even these outliers to the Trenton period, than to 

 a later formation. Even if they should, however, be found filled with the characteristic 

 fossils of this western formation, their presence there, under such circumstances, would 

 not warrant us in transferring to them the name Hudson river group, from the great 

 series of older rocks to which it was originally applied. 



