300 C. SCHUCHERT — LOWER HELDERBERG-ORISKANY FORMATIONS 



locality would ever think of running the line separating the Silurian and Devonian 

 ages, between the two. They seem so intimately blended that the exact line be- 

 tween them is an arbitrary one altogether." 



If the fauna from ik Trilobite ridge " or Barrett's zone " 5c " or Beecher's 

 " Dalmanites dentatus layers" is studied, it will be conceded that it is 

 unmistakably that of the Becraft, and cannot be included in the Lower 

 Oriskany, as is done by Beecher. The fauna as given by Barrett,* with 

 a few additions by the present writer, is the following: 



Orbiculoidea discus Hall, 0. conradi (Hall), Orlhis (Dalmanella) perelegans Hall, 

 O. (D.) planiconvexa Hall, 0. {Rhipidomella) oblata Hall, 0. (R.) subcarinata Hall, 

 0. [Schizophoria) muUistriata Hall, Leptnena rhomboidalis Wilckens, Stropheodonta 

 becki Hall, S. perplana Conrad, Stroplionella cavumboiisi Hall, & leavenworthana Hall, 

 Chonostrophia n. sp., Spirifer murchisoni Castelnau, S. concinnus Hall, S. cyclopterus 

 Hall, Oyrtina rostrata Hall, Rensselvcria sequiradiata (Conrad), Actinopteria textilis 

 Hall, Platyceras retrorsum Hall, P. gebhardi Hall, Loxonema fitchi Hall ?, Holopea 

 antirjua (Vanuxem) ?, Hyolithes centennialis Barrett, Dalmanites dentata Barrett, 

 D. pleuroptyx (Green), D. nasulus Conrad, D. micrurus (Green), and Homalonotus 

 vanuxemi Hall. 



Of this fauna with 29 species, all are Helderbergian forms with the ex- 

 ception of the following, which are Oriskany species : Stropheodonta per- 

 plana, Spinfer murchisoni, and Oyrtina rostrata. This evidence is very 

 conclusive that the three zones of Barrett's Upper Pentamerus limestone 

 are properly correlated. 



The Becraft fauna was extensively collected by Clarke, Beecher, and 

 the writer, but more particularly by the former, for the New York State 

 collection. Doctor Clarke has published "A preliminary list of the spe- 

 cies constituting the Oriskany fauna of Becraft 's mountain, New York,"f 

 which is given below, with a few alterations. Regarding this fauna, 

 Doctor Clarke concludes that — 



" This remarkable association of species furnishes the missing link in the evo- 

 lution of the Lower Helderberg into the typical Lower Devonian fauna. While 

 the presence of so many positive Oriskany types determines the faunal quantiv- 

 alence, the perdurance of species and modifications of specific expressions charac- 

 teristic of the shaly limestone fauna, and the inception of Lower Devonian specific 

 forms, render this combination altogether unusual and of prime significance in the 

 correlation of our earlier Devonian. The southwestern extension of the Oriskany 

 {Hipparionyx) fauna, as in Maryland, is complicated with the Lower Helderberg, 

 but to a less degree than here ; while in the representative of the same fauna in the 

 province of Ontario there is a great predominance of Upper Helderberg species. 

 With the 46 species which have been identified in the Hipparionyx fauna of New 

 York, the 10fi or more species of the Becraft fauna are in striking contrast, and no 



* Ann. Lye. Nat. Hist, N. Y., vol. xi, 1876, p. 2!M>, and Amer. Jour Sci., vol. xiii, 1877, p, 386. 

 t Amer. Jour. Sci., vol. xliv, 1892, pp. 411-414. 



