WHITE.] AGE OF THE POTTS VILLE FORMATION. 911 



Fayolta ^p. 



Althouoh the collections in the National ]\Iuseum already contain 

 specimens from the Allegheny series (XIII) at Mazon Creek, Illinois, 

 referable to this genus, it is represented, so far as I know, in the col- 

 lections from the Pottsville series l)y only two obscure specimens. 



From an examination of the material from Mazon Creek, and of the 

 types from the Chemung of northwestern Pennsylvania, described by 

 Dr. Newberry as Sjjirasi'f's,^ I am convinced that the latter genus is essen- 

 tialh' identical with the FayoJia ~ of the Old World. 



AGE OF THE POTTSVIELE FOE3IATION. 



In the absence of the full descriptive paleontologic evidence, I 

 should prefer to refrain from a definite statement of conclusions as to 

 the age or the equivalents of the Pottsville formation. Since, how- 

 ever, the questions of age and correlation directly affect the classi- 

 fication and nomenclature of the formations now being mapped in the 

 Appalachian province, it is proper to offer a few brief generalizations 

 which ma}' be considered as preliminary and, so far as they relate to 

 European coal fields, as tentative or suggestive. 



The persistency of the formation, or some portion of it, in some 

 phase or other throughout the American Carboniferous basins, its 

 generally well-marked lithologic characters, the different conditions 

 governing its deposition, its thickness, which may exceed 2.. 500 feet 

 in the Virginia-Tennessee region, and its mostly ver}' distinct vege- 

 table contents, as compared with the basal portion of the Lower Coal 

 Measures, or the Allegheny series, in Pennsylvania and Ohio, appear 

 to me to merit for these terranes distinct recognition as a forma- 

 tion or series, coordinate not only with the Allegheny series, Cone- 

 maugh series, etc., but with Lower, Middle, and Upper Coal Measures, 

 as those terms are used in this country. It is to be regretted that while 

 vmder the name "Pottsville series" the formation is ranked by most 

 geologists with Allegheny series,^ etc., man;\' authors treat it as a part 

 of the Lower Coal Measures, although it was originall}" distinguished 

 by Rogers as coordinate with the latter. Its occasional inclusion bv 

 geologists in the more comprehensive, but equivocal, "Coal Measures" 

 is perhaps not wholly satisfactory, even when that term is used in the 

 broader sense of "Upper Carboniferous." As has already been 

 remarked, no conclusive proof that the oldest beds of the Pottsville 

 ma\' be contemporaneous with the last beds of the red shale, or other 

 marine Lower Carboniferous sediments, has yet come to light. Never- 

 theless, if the explanation of the conditions of the deposition of the 



iXewborry, Annals New York Acad. Soi., Vol. Ill, 18*5, p. 217. 



2ReniUilt iuifl Zeiller, Comptt-s Kendus Acad. Sci., Vol. XCVIII, p. 1393; Fl. Foss. ba.ssiu hoiiill. 

 Commentry, 1888, Pt. I, p. 15; Pt. II. l>-90, p. 3(i9. 

 3 Bull. U. S. Geol. Survey No. tib, p. 1-9. 



