208 NEW YORK STATE MUSEUM 



area on the other. 1 Our present evidence seems to indicate with a measure 

 of conclusiveness that the encroachment of the enlarging Oneonta lake was 

 continued beyond the close of the Chemung and Devonic time into the 

 period of Lower Carbonic deposits. The recent study of the Upper 

 Devonic and higher strata of southwestern New York (Olean and 

 Salamanca quadrangles) indicates that a marked change in the fauna, one 

 which involves the disappearance of the majority of Chemung species and 

 the sudden introduction of forms of Carbonic type, manifests itself at a 

 horizon directly beneath the red sand beds with Holoptychius, Bothriolepis, 

 etc., which have long and correctly been looked on as a westward extension 

 of Catskill sediments. If thus the later strata of the great Catskill forma- 

 tion both in eastern and southern New York and in central western 

 Pennsylvania represent in some measure time later than Devonic, we shall 

 find this ancient Old Red lake again in full correspondence with those of 

 Scotland, which have been shown to be areas of localized lacustrine deposit 

 during a period of rapid erosion extending from before the close of the 

 Siluric till after the close of the Devonic. The varying extent of these 

 fresh and brackish water boundaries is well expressed in the existing sedi- 

 ments, and we may hence with convenience designate those successive 

 stages in time and growth as follows : 



(i) The Oneonta stage, a relatively small area of deposit almost land- 

 locked, probably restricted to Portage time ; (2) the Catskill stage, the 

 enlarged area of deposit extending from the Catskill mountains southward 

 into Pennsylvania 2 and continuing through Chemung time; and probably 



1 Lest this should be interpreted as positive evidence of open connection between the 

 fresh and salt waters, it is to be borne in mind that in the case of the Scotch Old Red 

 lakes the same conditions prevail, with evidences of interlamination of marine and fresh- 

 water sediments at the feather edges of both and occasional irruptions from the heart of 

 the sea over the lacustrine deposits. 



2 The character of Catskill beds in Pennsylvania, Maryland, West Virginia and Virginia 

 has been the subject of careful study by Stevenson, Claypole, Prosser, White, Campbell 

 and others, but we still lack the requisite information concerning their relation to the 

 estuarine conditions farther north, and to the marine deposits of the heart of the gulf. 



