DEVONIAN. 305 



It is difficult to follow any description of the Middle and Upper Devonian of 

 New York without a knowledge of the conditions which have led to different classi- 

 fications by several geologists for sections occurring in the eastern or western parts 

 of the State. The strata are chiefly shale, sandy shale, shaly sandstone, or sand- 

 stone, which in any one section may present distinctly recognizable differences but 

 which do not retain the same characters or distinctions from place to place. The 

 faunas also vary in vertical and horizontal distribution and are to some extent 

 recurrent. The divisions particularly involved in this vaguely classified series are 

 those above the Hamilton, namely, the TuUy limestone, Genesee shale. Portage 

 group, and Chemung formation. 



The TuUy limestone was weU described by HalP^^^ and has been made the 

 subject of a special paleontologic and correlative study by WOliams,"" who states : 



The Tully limestone is a zone of argillaceous limestone, ranging from a few feet to over 50 

 feet in thickness, the outcrop of which crosses the middle counties of New York State from 

 Ontario to Chenango counties but is not clearly recognized in the sections south of New York. 

 In New York the outcrop is lost to the eastward and to the westward, not so much by thinning 

 out as by a decrease, until unrecognizable, of the calcareous elements, and a failure of the pecul- 

 iar species. In the central part of its outcrop this hmestone appears at the top of the Ham- 

 ilton formation, which consists of a series several hundred feet thick of soft shales, with a few 

 more or less calcareous zones; and it is followed immediately by a black shale which gradually 

 loses itself by alternate oscillation in a gray, more or less arenaceous shale and argillaceous 

 sandstone, known in New York as the Genesee shale and the Ithaca group, and the more sandy 

 portion above as the Portage group. In the region where the TuUy limestone is well developed 

 the black shales contain a fa,una corresponding to that of the Cardiola retrostriata zone of Europe, 

 and there is in the sandy shales above a fauna rich in Goniatites where best developed. * * * 



For this study the more important species in the TuUy Hmestone of New York are the 

 brachiopods." * * * Besides these are species belonging to other orders." 



I have examined a large amount of material from genuine TuUy hmestone, and also con- 

 siderable more doubtfuUy referred to that horizon. In most places the HamUton rocks are 

 richly fossihferous immediately under the TuUy hmestone. These former, though mainly shales, 

 contain hmestone beds which in hand specimens are rarely distinguishable from the genuine 

 TuUy above; but the characteristic species of the TuUy are wanting and characteristic Hamil- 

 ton species are abundant in them. Much confusion has thus arisen, and the TuUy fauna, as 

 reported in Usts,* is very imperfect by the inclusion of many species which do not belong in 

 the Hmestone. 



There are about 50 genuine TuUy Hmestone species. Of these less than 25 are at all com- 

 mon, and the other 25 are Hamilton species which do not appear above the TuUy, or are unique 

 forms of Hamilton types. Of the more or less common TuUy forms fuUy one-haLf are also 

 clearly HamUton species or their descendants, or are unique forms. 



The change in fauna which begins with the TuUy limestone and makes the characteristic 

 upper Devonian fauna includes the appearance in New York of at least ten or a dozen species 

 which have closer affinities with species of the middle Devonian in Europe than with any pre- 

 vious species in the New York series. 



"■ For lists see the work cited.^ — B. W. 



b See list furnished by S. G. Williams (Sixth Ann. Kept. State Geologist, Albany; 1887, p. 26). A considerable 

 number of the species reported in this list I have examined in the collection made by the author of the list and find 

 them and the rock containing them indistinguishable from specimens obtained at the same locality below the Tully 

 limestone layers filled with Hamilton species but never in the Tully limestone itself. 

 48011°— 12 20 



