PHYSICAL AND FAUNAL EVOLUTION 73 



The Clinton of the best known section, that of western New York, 

 begins with the true or Upper Medina, which, along the Niagara 

 River, admits of a number of subdivisions, which are, however, of 

 only local signilicance.^ The total thickness is nearly 125 feet, 

 with 25 feet of w^hite quartzose sandstone (Whirlpool sandstone) 

 at the base, and about 8 feet of a similar sandstone at the top. The 

 middle series consists of red sandstones and green and gray sandstones 

 and shales. The red sandstones generally show aeolian cross- 

 bedding and appear to have accumulated above water. The green 

 sandstones and shales are fossiliferous. The white Whirlpool 

 sandstone exhibits beach features,^ and probably marks the advance 

 of the sea, though it is likely that the sand was originally dune sand, 

 as suggested by A. W. G. Wilson. 



The fossils are generally most abundant in the shales and thin- 

 bedded sandstones. The heavy-bedded sands are either free from 

 fossils or have only scattered shells of Lingulae. At Lockport and 

 elsewhere some layers are crowded wdth gastropod shells. The 

 characteristic fossil, Arthrophycus harlani is everywhere in New York 

 restricted to the upper beds just below the upper white sandstone. 



The fossils so far obtained from the Medina are: Arthrophycus 

 harlani Conr. ; A. sp.; Daedalus several species; ScoUthes vertkaUs 

 Hall; Dictyolithes beckii (Conr.); '^Fucoides'' auriformis and "F." 

 heterophyllus; Holopea fragilis Hall; Lingula cuneia Conr.; Whitfield- 

 ella oblata; Camarotoechiasp.; Uncinulus sir icklandi (Sowerhy); Plec- 

 torthis medinaensis sp. no v.; Rhipidomella sp.; Pentamerus sp.; 

 Modiolopsis orthonota; M. primigenius; Pterinea cf. emacerata; 

 Pleurolomaria pervetusta Conr.; P. littorea Hall; Holopea (?) 

 conridea; Bucanopsis trilobaius (Conr.) ; Oncoceras gihhosum; 

 Orthoceras sp.; O. muUiseptum Hall; Ascidaspis sp. ; Dalmanites 

 sp.; Isochilina cylindrica Hall. 



This is a Lower Siluric fauna, and favors more especially the 

 Clinton and Rochester faunas. It is so far known only from western 

 New York, with the exception of Arthrophycus harlani, which is 

 widely distributed. In western New York this species occurs at the 

 top of a heavy-bedded un fossiliferous sandstone with an aeolian type 



I See Bull. 45, New York State Museum, pp. 88-95. 

 = H. L. Fairchild, Amer. Geol., Vol. XXVIII, 1909. 



