M. 31. Kindle — Silurian Fauna in Western America. 125 



Art. XYI. — Occurrence of the Silurian Fauna in West- 

 ern America / by Edward M. Kindle. 



Introduction. — Several references to Silurian strata in the 

 Rocky Mountain region occur in the earlier papers relating to 

 "Western geology. Dana's Manual, fourth edition, while dis- 

 crediting the authenticity of some of these,* records the 

 occurrence of Niagara strata in the Black Hills region on the 

 authority of the late Prof. C. E. Beecher.f Afterwards Pro- 

 fessor BeecherJ became convinced that the supposed Silurian 

 of the Black Hills was of, Ordovician age. In recent years 

 most geologists who have had occasion to discuss the distribu- 

 tion of the Silurian fauna have expressed doubt or disbelief in 

 the occurrence of Silurian strata in the western part of the 

 continent. The general attitude toward the early determina- 

 tion of the Silurian in the West is indicated in Chamberlin 

 and Salisbury's statement that " like the older formations of 

 the Silurian, the Niagara has not been identified with certainty 

 in the western part of the continent."'! Weller has stated 

 " that the greater part of this region (west of the Mississippi) 

 was above sea level during Silurian time."! The rather com- 

 mon disbelief in the authenticity of the recorded occurrences 

 of the Silurian in the West has arisen largely through the 

 fact that the occurrence of Halysites catemdatus constitutes 

 the chief or only evidence for the presence of the Silurian 

 fauna in many cases in the AVest. This fossil, which formerly 

 was supposed to be diagnostic of the Silurian, is now known 

 to be common to both the Silurian and Ordovician faunas ; 

 consequently, as pointed out by Beecher, " the discovery of 

 Halysites in the Wasatch range by Hayden ; in the Wind 

 Biver mountains by Comstock ; in Nevada by Hague ; and in 

 the Teton range by Brady, does not necessarily imply the pres- 

 ence of Niagara strata at these localities."^ 



In view of the prevailing skepticism regarding the presence 

 of Silurian strata in the western part of the continent, it seems 

 desirable to present briefly the evidence of its occurrence 

 there, which has come under the writer's observation during 

 the last three field seasons. Silurian faunas have been recog- 

 nized in the West independently of the long-ranging Halysites, 

 by the writer. Decisive evidence of the occurrence of Silu- 

 rian faunas has been obtained in three widely separated regions. 



* Page 541. f Ibid., p. 543. 



% Am. Geol., vol. xviii, p. 33, 1896. 



§ Chamberlin, T. C, and Salisbury, R. D., Geology, vol. ii, Chicago, p. 

 384, 1905. 



I Jour. Geol., vol. vi, p. 696, 1898. 

 TfAm. Geol., vol. xviii, p. 32, 1896. 



Am. Jour. Sci. — Fourth Series, Vol. XXV, No. 146. — February, 1908. 

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