218 C. S. Prosser — Devonian System 



fied that would be almost conclusive proof of its Chemung 

 age. But the writer has failed to find this species on the 

 eastern side of the Pocouo and Catskill mountains and is in- 

 clined to think that Spirifera mesastrialis Hall, an allied 

 species which is not uncommon, is the one reported for S. 

 disjuneta, especially since the Cascade section of Susquehanna 

 ■ County, Penn., has been reported to contain "well-known 

 Chemung shaly and flaggy strata full of Spirifera disjuneta."* 

 When the section was examined in company with Professor 

 H. S. Williams it was found that the common species was S. 

 mesastrialis, which had evidently been mistaken for the S. 

 disjuncta.-f 



After considerable field work in southeastern New York and 

 northeastern Pennsylvania, the conclusion is reached that the 

 marine faunas terminated either slightly in advance or soon 

 after the appearance of the Chemung stage. In central and 

 southern Pennsylvania and western Maryland, the conditions 

 seem to have been more favorable and Spirifera disjuneta 

 with other Chemung species occurs in rocks which are strati- 

 graphically equivalent to the unfossiliferous beds farther 

 toward the northeast. The geological collections of Johns 

 Hopkins University contain a few specimens of Spirifera dis- 

 juneta from near Cumberland, Maryland,;}: and Professors 

 Claypole,§ White, |j Stevenson,^[ Ashburner,** and Meekff 

 have reported the species from a number of localities in Penn- 

 sylvania and Virginia. 



These shales and sandstones of the Chemung series, which 

 contain the highest fossil shells seen by Professor White, are 

 succeeded by greenish-gray, thick-bedded sandstones — the 

 Starucca sandstone of Prof. White — which at that time he 

 considered the base of the Catskill.^ Later, Professor White 



*G 5 , p. 78. 



fSee the remarks on the Cascade section by Prof. Williams, who states: 

 " When I examined the section I found no trace of several of the species cited, 

 and only rare and imperfect specimens of Spirifera disjuneta and the last stage 

 with Rhynchonella contracta; but all the mass of the fauna was Spirifera mes- 

 astrialis and its legitimate associates, which is a lower fauna belonging to the 

 more eastern part of this general area. The difference between the two Spiri- 

 feras appears at first glance slight ; but they are clearly distinct " (Proc. Am. 

 Assoc. Adv. Sei.. vol. xxxiv. p. 231} 



% See list of Chemung fossils from Maryland by Charles R. Keyes in Johns 

 Hopkins Univ. Circulars, vol. xi, December, 1891, p. 29; which specimens 

 through the courtesy of Dr. W. B. Clark have been personally examined. 



§F J , pp. 74, 77, 289, 291. 



|| T 3 , pp. 98, 183, 194. 



«[[T'-, pp. 76, 80, 133, 212, 214, 216, 225, 226; and Amer. Geol , vol. ix. pp. 10 

 26. 



**F, pp. 221, 225. 



ff Bull. Phil. Soc . Washington, vol. li. Appendix, Art. viii, p. 34. 



%%&*. pp. 102. 103. See G 5 , 1881, pp. 59, 70, 73 and fig. 10 on p. 77 for the 

 original description of this zone. 



