NO. 2 PRE-CAMBRIAN ALGONKIAN ALGAL FLORA 8l 



ment of limestone 4,800 feet (1,463 m.) in thickness in addition 

 to nearly 20,000 feet (6,093 ^•) of siliceous and arenaceous beds/ 

 To the north, the Siyeh limestone has a thickness of 4,000 feet 

 (1,220 m.).' 



In western Alberta and eastern British Columbia to about 54° 

 north latitude the Algonkian sediments are much like those of 

 Montana. In the Montana region of greatest accumulation of 

 Algonkian sediments the Cordilleran trough appears to have been 

 filled to such an extent before Cambrian time, possibly by a river 

 delta, that the Cordilleran Cambrian sea, advancing to deposit its 

 sediments, encountered a central barrier ' extending out from the 

 eastern side of the trough. 



From the Cordilleran trough depressions probably stretched east- 

 ward to central Texas, central Colorado, South Dakota, and it may 

 be to the Lake Superior basin.'' 



Briefly summarized, the Algonkian period in North America with 

 its great epicontinental formations was a time of continental eleva- 

 tion and largely terrigenous sedimentation in non-marine bodies of 

 water, and of deposition by aerial and stream processes in favorable 

 areas. Marine sediments accumulated in the waters along the outer 

 ocean shores of the continent and great quantities of eruptive 

 matter were extruded into the central Lake Superior region (Ke- 

 weenawan). The agencies of diastrophism continued to exert their 

 influence for a long period, though with decreasing energy, until 

 they became practically quiescent during the latter part of Al- 

 gonkian time. 



The North American continent was larger at the close of Algon- 

 kian time than at any subsequent period other than possibly at the 

 end of the Paleozoic and the end of the Cretaceous, when the land 

 was equally extensive. Indeed, it is highly probable that its area 

 was greater then than even now, for no marine deposits of Algon- 

 kian age containing pre-Cambrian life, as they were laid down in 



^ Bull. Geol. Soc. America, Vol. 17, 1906, p. 7. 



^ Daly has placed the Siyeh limestone of the Algonkian in the Cambrian, 

 but, in the absence of direct areal stratigraphic relations and all Cambrian 

 fossils in the Siyeh limestone, I do not see my way clear to accept his con- 

 clusions based on lithologic similarity of the Siyeh and the Middle Cambrian 

 limestones of the Bow Valley and Kicking Horse Canyon. 



Rept. Chief Astronomer for year 1910, Ottawa, 1913, Geol. North ^American 

 Cordillera, Pt. I, R. A. Daly, pp. 174-178 and accompanying table. 



^ Smithsonian Misc. Coll., Vol. 53, No. 5, 1908, p. 169. 



■* See map of Van Hise and Leith (Bull. No. 360, U. S. Geol. Survey, 1909, 

 p. I). 



