30 C. D. Walcott — Position of the Olenellus Fauna. 



loides, n. gen. The entire fauna from America now includes 

 57 genera, 134 species and 10 varieties. 



Relations of the Lower Cambrian to the Middle Cambrian 

 Fauna. — In the Atlantic Province the two faunas are respec- 

 tively called Olenellus and Paradoxides, from the most typical 

 genera of trilobites occurring in them. In the Cambrian sec- 

 tions of the Rocky Mountain or Pacific Province and the 

 Appalachian Province there is a Middle Cambrian fauna, more 

 or less distinctly defined, but it is not the typical Paradoxides 

 fauna of the Atlantic Province. On this account the Middle 

 Cambrian fauna of the Atlantic Province will be spoken of as 

 such, or as the Paradoxides fauna ; and the term Middle Cam- 

 brian will be used when other portions, or the entire fauna of 

 the Middle Cambrian are referred to. 



Physical or Stratigraphic Relations. — The Cambrian sec- 

 tion, on Manuel's Brook, shows a continuous deposition of sedi- 

 ments, from the basal conglomerate through Lower Cambrian 

 (Olenellus zone) time to and through Middle Cambrian (Para- 

 doxides zone) time ; a thickness of about 250 feet of shale 

 having been deposited between the typical Olenellus zone and 

 the Paradoxides zone. The same conditions of continuous and 

 conformable sedimentation appear to have prevailed on the 

 eastern side of the Atlantic Province in Sweden and Norway. 



The great conformable sections of Cambrian strata in the 

 Rocky Mountain Province do not show any break in the sedi- 

 mentation between the Lower, Middle, and Upper Cambrian 

 strata, except near the eastern shore line, as in the Wasatch 

 section of Utah, where strata of Upper Cambrian age were 

 not deposited. 



In Russia, Britain, Spain, Sardinia, and on the western side 

 of the Atlantic, in New Brunswick and Massachusetts, the 

 stratigraphic relations of the faunas are not exhibited ; and in 

 the St. Lawrence and Appalachian regions of America the data 

 are wanting by which to place the faunas stratigraphically in 

 any one, unbroken section. 



As far as known the physical relations of the faunas do not 

 furnish sufficient reason to account for the change from the 

 Olenellus to the Middle Cambrian fauna ; and there is no 

 recognized unconformity indicative of a physical break and a 

 consequent time interruption in the deposition of the sediments 

 forming the strata between the two faunas. 



Zoological Relations. — Under this head will be mentioned 

 (1) the species that range from the Lower Cambrian into the 

 Middle Cambrian, in each typical province of the Olenellus 

 fauna; (2) the relation of the genera and species, irrespective 

 of geographic distribution and vertical range ; (3) the com- 

 parison of the faunas as a whole. 



