602 HISTORICAL GEOLOGY. 



observes that the facts from the Devonian of Manitoba and Mackenzie rivers described by 

 Whiteaves confirm this view. 



5. MoUusks. — (a) Lamellibranchs. — Fig. 912, Orthonota undulata Con. ; 913, JPterinea 

 flahella Con.; 914, Grammysia hisulcata Con. {Hamiltonensis of Verneuil), also Euro- 

 pean, in tlie Eifel ; 915, 3Iicrodon hellistriatus Con. Of the genera of Lamellibranchs 

 represented, Grammysia has 15 species (all in the Hamilton), Modiomorpha 9 (all Ham., 

 1 also Marc), AviciUopecten 15, one, A. princeps, occurring in New York, Ontario, Ken- 

 tucky, and Indiana. Nucula 9 (all Ham.), Leda 4 (all Ham.), Paracyclas (Liicina) 4, 

 Schizodus 3, Solemya 1, Orthonota 4 (all Ham.), Lunulicardium 5 (all Marc, and 2 con- 

 tinuing into the Hamilton). 



(&) Gastropods. — Of the 10 species of Platyceras, P. conicum, P. erectum, P. cari- 

 natum, P. thetis, P. symmetricum and P. rectum come up from the Corniferous. There 

 are a dozen species of JBellerophon, several of them like B. patulus, large and beauti- 

 ful, much exceeding, in both respects, any of the Silurian species. 



(c) Pteropods and Cephalopods. — For figures and descriptions of many species, see 

 Hall, vol. V. ; also publications of Meek and Worthen, Whitfield, Beecher, Billings, and 

 others. Among the species are Orthoceras crotalum H. {8pyroceras of Hyatt); Gom- 

 phoceras oviforme H. (Acleistoceras Hyatt) ; Gyroceras transversum H. {Butoceras Hyatt) ; 

 Naxitilus huccinum H. (Nephriticeras Hyatt, a type having many Hamilton species) ; 

 Goniatites {Discites) Marcellensis Van. (Centroceras Hyatt) ; Goniatites discoideus H. 

 {Parodiceras Hyatt). 



6. Crustaceans. — For figures of the Hamilton (and other Devonian) species of these 

 tribes, see Hall, N. Y. Pal., vol. vii. ; Beecher, Pep. Geol. Pa., vol. PPP, 1884 ; Packard, 

 Monograph on N. A. Phyllop., 1883; Whitfield, Am. Jour. Sc, xix., 1880; and J. M. 

 Clarke, Ain. Jour. Sc, xxiii., 1882; and ib., xxiv., 1882 (on Turrilepas). Dithyrocaris 

 Belli Woodw. {Geol. Mag., 1871) is from Gasp^. 



Some of the characteristic Marcellus fossils are : Productella truncata H., Orbiculoidea 

 minuta H., Leiorhynchus limitare H., Chonetes mucronatus H., Leiopteria Icevis H., Pleu- 

 rotomaria virgulata H., Styliolina fissurella H., Orthoceras subulatum H. 



The Iowa Hamilton has afforded species of Megistocrinus, Taxocrinus, Synbatho- 

 crinus, Pentremites ; Orthis suborbicularis H., 0. Vanuxemi H., O. lowensis, 0. ince- 

 qualis, 0. prava, Stropheodonta arcuata H., S. nacrea H., S. reversa H., S. demissa, 

 S. perplana, Productus dissimilis H., Productella pyxidata H., P. subalata H., Productus 

 Shumardianus H., Spirifer Hungerfordi, S. Whitneyi H., S. fimbriatus Con., ^S*. bimesia- 

 lis H., ;S'. asper H., *S'. Parryanus H., S.p>6nnatus Owen, ;S'. Marionensis Shumard, Cyrtina 

 umhonata H., C. triquetra H., Gypidida occidentalis H., Atrypa aspera, A. reticularis, 

 Euomphalus cyclostomus H. 



4. Chemung Period, or Later Devonian, 

 rocks— kinds and distribution. 



The Chemung Period includes (1) the Portage epoch, represented by 

 the Genesee shale below, and the true Portage group above ; and (2) the 

 Chemung epoch. The Catskill group, which has usually been made to repre- 

 sent a third epoch, is mainly, as stated on page 576, the sea-border part of 

 the Upper Devonian. 



The Genesee shale, at the base of the Portage, is black and bituminous, 

 like the Marcellus shale, and rather sparingly fossiliferous. It is 100 to 

 150 feet thick in central New York, along Cayuga Lake, where it overlies 



