518 C. SCHU CHERT PALEOGEOGRAPHY OF NORTH AMERICA 



Along the Pacific the sea became widespread in the Great Basin region 

 to the southeast of the positive element Cascadia. Here again the same- 

 phenomena existed as along the Atlantic — that is, interior seas, with 

 great depth of sediments originating along the inner sides of positive 

 elements that evidently were moving inward and away from the oceans. 



At the close of the Georgic the first marked post-Proterozoic crustal 

 movement of the Appalachian region occurred, and a complete land bar- 

 rier was thrown up, which effectually prevented the later Cambrian 

 faunas of the Pacific realm from passing into the Atlantic. Previous to 

 this movement the Olenellus biotas of the Pacific and Atlantic were very 

 much alike — that is, they were cosmopolitan — but as yet it is not known 

 where the intercommunication existed. It may have been across north- 

 ern Mexico, but more probably occurred across southern Mexico or Cen- 

 tral America. 



The longest and the least broken Cambrian sections are those of the 

 Cordilleran sea. Walcott 140 has recently given the details of these mag- 

 nificent sections. The Waucoba Springs sequence, of Inyo county, Cali- 

 fornia, has a total thickness of 5,670 + feet, of which the upper 1,300 

 feet consist of limestone. This is the oldest Paleozoic anywhere known. 

 It comprises all of Georgic time, and in the lower third is marked 

 by Arcliceocyathus, Ethmophyllum, Mickwitzia, Trematobolus, Holmia, 

 and rarely by Olenellus. Holmia rowei ranges through 3,150 feet, and H. 

 weelcsi, of higher zones, through 1,370 feet. The genus Olenellus (in- 

 cluding Holmia) extends through 4,900 feet of this section, Holmia in 

 the lower portion and Olenellus in the higher part. 



Other characteristic fossils of the Cordilleran Georgic are Olenellus 

 gilberti, Protypus, Microdiscus, Kutorgina cingulata, Swantonia, Nisusia,. 

 smooth Billingsella, Hyolithellus, and Salterella. The Pioche shale at 

 the top of the Georgic still has O. gilberti, but Middle Cambrian forms 

 here begin to appear, as Z acanthoides and Crepicephalus. 



In the region of Georgia, Vermont, and in eastern N"ew York occur- 

 many others — Olenellus thompsoni, Mesonacis vermontana, Holmia or 

 Elliptocephala asaplioides, Bathynotus liolopyga, Protypus, Microdiscus, 

 Conocoryphe, Hyolithellus, Salterella, Nisusia, Swantonia, Kutorgina 

 cingulata, and Paterina labradorica. At York, Pennsylvania, AYanner 

 found Holmia tualcottana. 



The Protolenus fauna of Matthew 141 appears to be best placed at the 

 base of the Middle Cambrian or Acadic. 142 



140 Walcott : Smithsonian Miscellaneous Collections, no. 53, 1908, pp. 167-230. 



141 G. F. Matthew : Trans. New York Academy of Sciences, vol. 14, 1895, pp. 101-153. 



142 C. D. Walcott : Proc. Washington Academy of Sciences, vol, 1, 1900, p. 302. 



