42 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 64 



Valley Canadian and Ozarkian will be found on the Asiatic conti- 

 nent, but at present we must be content to close the Cambrian with 

 the upper horizon of the Kiu-lung group, and wait for further data 

 on the faunas of the Tsi-nan formation and their relation to the 

 Cambrian and Lower Ordovician faunas of North America and 

 Europe. 



The presence of the genera Syntrophia, Huenella, Cyrtoceras, 

 and Tsinania in the Ch'au-mi-tien limestone proves that the Upper 

 Cambrian fauna was beginning to assume a post-Cambrian aspect 

 toward the close of the deposition of the Ch'au-mi-tien limestone. 

 It is quite possible that the fauna of the lower portion of the Tsi- 

 nan formation, when found, will have an Upper Cambrian aspect, 

 but it is more probable that it will have the general facies of that 

 of the lower Pogonip of the Nevada Cordilleran sections.^ 



At present the trilobite fauna of the Upper Cambrian in .the 

 Pacific and Cordilleran provinces is readily recognizable at nearly all 

 localities by the presence of such genera of trilobites as Ptychaspis, 

 Tsinania and various genera of the Ptychoparidse. Dikelocephalus 

 is restricted in geographic distribution to a few localities in North 

 America. I would place the formations containing a typical Cam- 

 brian trilobitic fauna in the Cambrian, and where a formation has a 

 fauna characterized by a new group of forms that evidently belong 

 to a later fauna it should be assigned to a post-Cambrian system 

 even though it may have a few Cambrian genera of trilobites in- 

 cluded in it. 



In North America we find that the fauna of the Upper Cambrian 

 in the Cordilleran region is quite distinctly marked by the presence 

 of typical Cambrian genera and the absence of typical post-Cam- 

 brian genera. In the central area between the Rocky Mountains 

 and the Appalachians the Upper Cambrian fauna as characterized 

 by the trilobitic genera Agnostus, Ptychaspis, Dikelocephalus, Pty- 

 choparia, and Tsinania is singularly free from commingling of typi< 

 cal post-Cambrian genera except in the case of the Eminence " 

 fauna, where a few trilobitic genera have persisted into Ozarkian 

 time." 



' Walcott, C. D. Bull. U. S. Geol. Survey, No. 10, 1884, On the Cambrian 

 faunas of North America; Preliminary studies, p. 3. 



^ By error the Gasconade fauna was inserted in this place. The Gasconade 

 is a later fauna. Neither the Eminence nor the Gasconade fauna includes the 

 genus Dikelocephalus. 



^Ulrich, E. O. Bull. Geol. Soc. America, Vol. 22, 191 1, Revision of the 

 Paleozoic systems, p. 631. 



