382 C. D. 'Walcott — Position of the Olenellus Fauna. 



The relative position of the Middle and Lower Cambrian 

 faunas is now changed in the American scheme of classifica- 

 tion ; * the Paradoxides zone being removed to the Middle, 

 and the Olenellus zone to the Lower division. The three divi- 

 sions — Lower, Middle, and Upper — are useful in classification, 

 as they indicate both physical and faunal changes during the 

 deposition of the sediments forming the American, Swedish, 

 and English sections. In the Appalachian and Rocky Mountain 

 areas of the United States, the genus Paradoxides is unknown, 

 and most of the typical fossils of the zone are unrepresented ; 

 but in the great Cambrian section of Eastern New York it is 

 indicated by Agnostics desideratus, n. sp., Agnostus of the 

 type of A. pisiformis, Microdiscus connexus, Linnarssonia 

 Taconica and Zacanthoides Eatoni. The third and fourth 

 species may prove to be identical with Microdiscus punctatus 

 and Linnarssonia Sagittarius from the Paradoxides zone of 

 Newfoundland. In Nevada a peculiar fauna that is recognized 

 by the trilobitic genera Olenoides, Zacanthoides and Asaphicus, 

 occurs midway between the Olenellus and Dicellocephalus or 

 Upper Cambrian faunas. Brogger has noted that the genus 

 Agnostus is first characteristic of the Paradoxides zone, and by 

 it he has correlated certain horizons in Nevada witn those of 

 Sweden. This will undoubtedly hold good in many instances, 

 and be of value when taken in connection with other genera.f 



The following table exhibits the order of stratigraphic suc- 

 cession of the three subdivisions and sub-faunas of the Cam- 

 brian System as known in America to-day. 



As previously stated the three divisions of Lower, Middle and 

 Upper Cambrian are recognized in America and Europe. The 

 names of the subdivisions of these three primary divisions of 

 the period in America are the names of the typical terranes 

 that are respectively included in each of the primary divisions. 

 Thus under the term Prospect, of the Lower Cambrian, are 

 included the strata of the Olenellus zone in Nevada, Utah, and 

 the Rocky Mountain region north into British America. The 

 typical section is that crossing Prospect Mountain in the Eureka 

 district, Nevada. In this section the sedimentation and fauna 

 are essentially the same as in the Rocky Mountain area. 



letter telling of localities from Mr. J. P. Howley. The geological map of the 

 Avalon Peninsula, by Mr. Howley, was of great service. In the six weeks' 

 search for the Olenellus fauna about Conception Bay, Mrs. Walcott was my con- 

 stant companion and efficient assistant, and shared with me the pleasure given by 

 the finding of the fauna on Manuel's Brook. 



*In all my previous papers with the exception of the note in "Nature," Octo- 

 ber, 188S, the term Middle Cambrian is to be changed to Lower Cambrian and 

 Lower Cambrian to Middle Cambrian. 



f Om alderen af Olenelluszonen; Nordamerika. Aftryck ur Geol. Forenin- 

 gens; Stockholm Forhandl., No. 101, vol. viii, H. 3, 1886. 



