On the Silurian System. 



89 



distinguished by different groups of organic remains. They pro- 

 bably occupy more surface throughout the Union than any other 

 fossihferous rocks. 



Ludlow Rocks. 



These have not yet been subdivided, and they can only in a 

 general way be compared with Murchison's group. The organic 

 remains are in great numbers and variety, and are very unlike 

 those of the lower Silurian rocks. 



The following table is given in order to correct some errors in 

 that published in the New York reports, and to show the relative 

 position of certain fossils which may be regarded as characteristic 

 species. Though the table is necessarily incomplete, great care 

 has been taken to render it correct as far as it goes, and I trust it 

 will be found to convey a novel view of the wonderful variety of 

 strata, each w^th its peculiar organic remains, which compose the 

 Silurian system. 



OLD RED SYSTEM. 



Formations. Characteristic Fossils. 



Old red sandstone, 7 rr , . , , •,■ • 



(Blossburg, Pa.) 5 Holoptychus nobilissiraus. 



SILURIAN SYSTEM. 



Formations. 



Characteristic Fossils. 



f Dipleura Dekayi, Cryphaeus Greenii, Pterinea fas- 



22. Sandstone and shales ) ciculata, Cyrtoceras maximum, C. giganteum, Or- 



of Cazenovia, «&c. | this orbiculatus, Orthoceras pj'riforme, and many 



(_ unnamed bivalves. 



21. Shales of Moscow C Atrypa aspera, A. concentrica, Delthyris granulosa, 



and Lake Erie, ( Cryphaeus calliteles. 



20. Onondaga limestone, 



19. Oriskany sandstone, 



18. Sandstone of Clarks- 

 viIle,Helderberg, 



17. Limestone of Clarks- 

 ville, 



16. Sandstone, 



15. Blue limestone, 



14. Shaly limestone, 

 Catskill creek, 



13. 2d Pentamerus lime- 

 stone, 



12. Water limestone, 

 Vol. xxxviii, No. 1. — ' 



C Atrypa nasuta, Delthyris, twospecres, (new,) Asaph- 



\ us seleneurus. 



C Atrypa elongata, Delthyris arenosa; other large bi- 



\ valves. 



C A large Orthoceras, Pterinea, (bilobite,) Calymene 



I platys. 



) Pileopsis tubife'r. 



Fucoides cauda-galli. 

 Delthyris, (new.) 

 r Trilobites, (two new genera,) Delthyris macropleu- 



< ra, Pileopsis? (ventricore,)j Atrypa, (two spe- 

 ( cies,) Strophomena costellata. 



\ Pentamerus (Atiypa) galeatus, Atrypa lacunosa. 



r Tentaculites annulatus, Delthris, (new,) Orthis, 



< (new,) various univalves unnamed, Cytherina, a 

 ^ large species. 



Oct.-Dec. 1839. 12 



\W 



