496 NEW YORK STATE MUSEUM 



tern of rocks, and belonging to one geologic age, tliuis oreaiting 

 -confusion in whatever aspect they were regarded". The occur- 

 rence of lithologically homogeneous, but faunistically hetero- 

 geneous terranes^ forming apparently a stratigraphic unit, has 

 been the cause of endless discussion and confusion, as the Tbt 

 €onic, Quebec and this, the Hudson river group controversy fully 

 demonstrate. It appears, now, that, while Hall freed the Hudson 

 river group, by insisting on its upper Champlainic (Siluric) age, 

 from being farther involved in the Taconic controversy, he, to a 

 certain extent, committed a similar error by uniting the Lorraine 

 and Normans kill faunas in one group, for this correlation is, as 

 will be shown still farther on, the principal cause of the con- 

 troversy in regard to the age of the Hudson river group. 



R. P. Whitfield 



The composite character of the Hudson river beds was first posi- 

 tively asserted by R. P. Whitfield in a letter written in 1875 to Dr 

 €. A. White (16). Prof. Whitfield's most important statements 

 In regard to our investigation are: 



From the evidence furnished by these fossils (graptolites), I 

 liave reached the conclusion that the graptolite-bearing layers 

 there are of the age of the Utica slate^ the following being a sum- 

 mary of the factfii I have observed. 



I have found the following species common to both the grapto- 

 lite layers at Normans kill and those of the Utica slate formation 

 at the mouth of Oxtungo creek near Fort Plain N. Y. : G r a p t o - 

 lithus (Monograptus) serratulus. Hall, G. (D i p - 

 lograptue) pristis, Hall (not Hisinger), G. ( C 1 i m a - 

 c o g r a p t u s ) b i c o r n i s , Hall and G. (Dicranograp- 

 tus) ramosus. Hall. 



Just south of Troy, in the shaly partings between layers of 

 metamorphic limestone, I have found a species of graptolite in 

 great abundance indistinguishable from G. amplexicaulis 

 Hall from the Trenton limestone of Herkimer county, N. Y. 

 The same species was also found abundantly in the yard of the 

 arsenal at Watervliet by Capt. C. E. Button, U. S. A. 



From the foregoing facts I infer that the slates below Troy and 

 in the arsenal yard, together with the associated metamorphic 

 limestones, are the equivalents of the Trenton limestone. 



