152 THE JOURNAL OF GEOLOGY. 



In the discussion of Professor Hall's paper at the Rochester 

 meeting, the question came definitely before us as to the relative 

 value of fossils and structure as means of determining or tracing 

 equivalency of age of formations. In that discussion I main- 

 tained that fossils are always the only certain means of carrying 

 from one geological basin to another the evidence of time- 

 relations of the deposits, that structure was indicative of equiva- 

 lency only when actual continuity of a formation can be traced. 

 Both of Mr. Stevenson's '^ papers recognize the physical features 

 of the formation to be of great importance in determining its 

 position in the time-scale, and in his use of terms he appears to 

 be classifying formations and yet using the language of the time- 

 scale. In his presidential address he maintained, as quoted by 

 himself, that the series of beds included within the Catskill and 

 Chemung Periods should be grouped into one period, the 

 Chemung, with three epochs, the Portage, the Chemung and the 

 Catskill (page 320), and in his paper in 1893, ^^ insists that the 

 Chemung, and not the Catskill, is the epoch whose name should 

 be applied to designate the whole group, while Catskill must be 

 retained in its original signification only. 



Mr. Darton, on the other hand, is discussing the formation- 

 scale alone. The principal purpose of his investigation is said 

 to be to determine the relations and distribution of the Oneonta 

 and Chemung formations (p. 203). In the passage on the status 

 of the name "Catskill" the author proposes to discontinue the 

 use of Catskill as a coordinate formation term, and use the term 

 " Catskill group," to include the Portage and Chemung 

 formations (p. 209). He maintains, correctly, I think, that the 

 term Catskill has been applied in the past to beds of a certain 

 lithologic character — the hard sandstones and red shales — and it 

 has had no definite stratigraphic significance. The rocks of the 

 Catskill Mountains and westward have no distinctive fauna of 

 stratigraphic significance, and they cannot be correlated on 

 paleontologic grounds (p. 208). 



' The Chemung and Catskill (Upper Devonian on the Eastern Side of the Appal- 

 achian basin). A. A. A. S., Vol. 42. 



On the use of the name Catskill. Am. Jour. Sci., Vol. XLVI., p. 330. 



