154 THE JOURNAL OF GEOLOGY. 



New York and farther southwest. It should not be applied to 

 cover the three divisions of the Upper Devonian, because as a 

 time indicator it is inappropriate, as just stated ; and as a form- 

 ation name it has already a use, and should not be used in two 

 senses ; and, thirdly, even if used in the more comprehensive 

 sense, it is inapplicable because the Portage and Chemung are 

 not represented, at least only imperfectly, in the geological area 

 named Catskill. 



The Catskill is a distinct and well defined geological form- 

 ation, but it is not a period or an epoch, nor does it represent 

 any particular period of geological time. The classification of 

 the Upper Devonian deposits is a very difficult matter when it is 

 attempted to make a continuous series of the formations of New 

 York alone. As I have previously shown, the succession of 

 faunas in the sections of New York rocks at distances of not 

 over fifty miles apart make plain this fact. At the Cayuga lake 

 meridian, the section is Hamilton, terminating with TuUy lime- 

 stone and Genesee shale, then the Ithaca group, which has first 

 a Portage fauna, then the Ithaca fauna, third, the Portage fauna 

 again, and finally Chemung capped by Catskill and Carboniferous. 

 A little further east of the Chenango valley, it is Hamilton; then 

 a fauna intermediate between Hamilton and Ithaca (but no TuUy 

 or Genesee) ; then the Oneonta, a brackish and fresh water fauna; 

 then the late Ithaca fauna, still with Hamilton types in it; no Port- 

 age fauna, but Chemung fauna following the upper Ithaca fauna. ^ 



In this faunal succession there is a clear indication of the age 

 of the Oneonta sandstones. It is clearly in the midst of the 

 rocks characterized by the Ithaca fauna. As I have shown in the 

 paper referred to,^ the marine Brachiopod faunas occupying the 

 place between the Hamilton and the Chemung faunas in Central 

 New York, of which the Ithaca is the best known, are modified 

 successors of the Hamilton, or Mesodevonian fauna, and the 

 Oneonta group, with its fresh and brackish water fauna is in the 



^Williams: The Classification of the Upper Devonian. Proc. Am. Assoc. Adv. 

 Sci., Vol. XXXIV., p. 225, 1886. 



2 Proc. A. A. A. S., XXXIV., 1885, pp. 222-3. 



