200 C. 1). VVALCOTT — PKE-CAMBRIAN FOSSILIFEROUS FORMATIONS 



Page 



Unconformity between Avalon terrane and Cambrian 220 



Location and cliaracter of contacts. ... 220 



Extent of nnconformity 221 



Algonkian rocks of tbe Lake Superior region 221 



Table of pre-Cambrian rocks 221 



Keweenaw series. . , 22 1 



Lower Huronian . . 223 



Upper Huronian 223 



Age of Cambrian beds resting on Lake Superior series 224 



Unconformity between Lake Superior series and Cambrian 224 



Unconformities within Lake Superior series 224 



Pre-Cambrian sedimentaiy rocks in Utah, Nevada, California, and British 



Columbia 226 



Occurrence of fossils 226 



Strata of determined pre-Cambrian age 226 



Review of evidence concerning fossiliferous character of certain pre- 

 Cambrian strata 227 



Fossils from the Algonkian 227 



Presence of graphite 227 



Pahieotrochis , 228 



Lake Superior series 229 



Newfoundland Avalon terrane 230 



Fossils 230 



Observations 231 



New Brunswick Etcheminian terrane , 231 



Arizona Grand Canyon series 232 



Fossils 232 



Formation and locality yielding Chaarid circulari.t. 234 



Some obscure forms . 235 



Montana Belt terrane 235 



Fossils 235 



Formation and localities yielding Helminlhoididinites 236 



Formation and locality yielding PlanaUtes corrngatus ■ . . 237 



Formation and locality yielding PlanaUtes superhus 237 



Crustacea 237 



Formation and localities yielding Bellina danai 239 



Explanation of plates 239 



Introduction 



The base of the Paleozoic and of the Cambrian has been placed at the 

 lowest known limit of the Olenellus fauna, all clastic rocks beneath 

 beins; referred to the Algonkian,* a name given to the period embracing 

 the time of the deposition of those clastic rocks wliich are older than 

 the Cambrian.f The base of the Algonkian is the lowest of the recog- 



*Bull. U. S. Geol. Survey, no. 81, 1891, p. 3r.2. 



t Tenth .^nn. Report U. S. (Teol. Survey, 1890, p. GO. 



