INTRODUCTION. XVII 



which, when the sequence is complete, are separated from the 

 Hudson river rocks by a great limestone formation." 



"I have therefore," he goes on to say, "dropped the term 

 Hudson river group, in its application to the rocks of Wisconsin 

 which are of the age of the Lorraine shales of New York and 

 the Blue limestone group of Ohio." 



For the reasons thus clearly stated, he denominates this 

 group, on pages 47 to 56 of the Wisconsin Report, quoted above, 

 simply as the " Green and Blue shales and limestones" stating 

 there, also, in another note on page 47, that the term Hudson 

 river group had been improperly extended so as to include the 

 beds of this age west of the Hudson river, and could "no longer 

 with propriety be applied to these western rocks." 



Perfectly concurring in this opinion, and being equally well 

 satisfied that such a descriptive phrase as the " Green and Blue 

 shales and limestone" could not be retained, in geological nomen- 

 clature, as a name for a great formation, widely extended in the 

 United States and Canada, under various aspects of color and 

 composition, we felt greatly at a loss for a convenient name for 

 this group. As the local names Utica slate, Lorraine shales, 

 etc., had been originally applied, and long in general use, for 

 subdivisions of this formation for which it is convenient and 

 necessary to have separate names, when we wish to speak with 

 precision of these subordinate rocks, they will of course always 

 be associated, in the minds of geologists, with the beds in con- 

 nection with which they have been so long used ; consequently 

 none of them could, without creating confusion, be extended to 

 the whole group. The term "Blue limestone," long since used 

 for this group by the Ohio geologists, is open to the same 

 objection as that used in the Wisconsin Report, being equally 

 derived from such unstable characters as mere color and com- 

 position. Nor could we retain Prof. Rogers's term "Matinal," 

 nor Prof. Safford's name " Nashville group," for the reason that 

 they were each originally applied to, and since used for, a series 



3 Nov. 10, 1866. 



