SILURIAN VERTEBRATE LIFE AT CANYON CITY. 427 



SILURIAN VERTEBRATE LIFE AT CANYON CITY. 

 [By C. D. Wai.cott.] 



Canyon City is situated near the southwestern shore of a great bay 

 of early Silurian (Ordovician) time, an arm of which reached inland as 

 far as Parkdale. Along the western shore of this bay sediments were 

 deposited that now form the sandstones and limestones of the mono- 

 clinal valley above mentioned. 



The lower division of the Silurian consists of sandstones (SG feet). 

 J n these, 11 genera and 11) species of invertebrate fossils have been 

 found and an immense number of fragmentary remains of ganoid 

 fishes. The invertebrate fauna is of the t \] >eof the basal Trenton of the 

 New York section. The icthyic fauna includes fragments of a Placo- 

 derm closely allied to Astcrolcpis, numerous scales of the character of 

 those of Holoptychius, and what is considered to be the calcified chordal 

 sheath of a form allied to the recent Chinuvra monstrom. This fauna 

 was the subject of a paper read before the Geological Society of 

 America at its recent session. 71 



The typical section is seen at Harding's quarry, which is about one 

 mile northwest of the State penitentiary at Canyon City. 



The invertebrate fauna, occurring three feet above the uppermost fish- 

 bearing stratum, includes 31 genera and 66 species, of which 27 

 have been identified. At an horizon 180 feet higher in the section, 33 

 genera and 57 species occur, of which 33 species have been identified. 

 These faunas are respectively of the types of those of the Lower and 

 Upper Trenton faunas of the New York section, or the Lower and 

 Upper Bala of Wales. 



The character of the fauna at the lower horizon is shown by Rcc<i> 

 faculties Oweni, Halysitcs catcnulatus (a Lower Bala and Llandeilo 

 species); Golumnaria ulreolata: Strophomena aUernata; titnj>t<>- 

 rhynchus Jilitextum; S. Sulcatum; Orthis biforata; O.JIabellum; 0. 8Ub- 

 quadrate; 0. tricenaria; Rhynehonella oapax var. inenbescens; li. 

 Aentata Hall; Ambonyckia heUaetriata, Hall: Modiolopsis plana, Hall; 

 M urchisonia tricarinata, Hallj CycUniema bilcx; BcUcrophon bilobatus, 

 Sow; Endoccras protciformc, Hall; Ormooeras tenuifihm; 0. crebriscp- 

 tum; Orthoccrasrertebralc, Hall; O.multicamcratum, Hall; Gomphoccras 

 powersi, James; Asaphus, like A. platyccphalus; Ilhcmis crassicauda; 

 I. milleri. Of these, 11 species pass up into the fauna 180 feet above. 

 Six miles north of Canyon City limestones are exposed beneath the 



