﻿G. D. Walcott — Cambrian System of North America. 153 



Newfoundland. This subject will be treated in detail after the 

 completion of the study of the Upper Cambrian faunas now in 

 progress. 



As previously mentioned, I have heretofore included the 

 Grand Canon and Llano series as, in part, of Cambrian age, and 

 correlated them with the Keweenaw series (Bull. VI, Phil. Soc. 

 Washington, p. 102, 1882). In adopting the view that all of 

 these may be placed under a system of pre-Cambrian age, I 

 think there is good reason for it in the presence of the great 

 unconformity, by erosion, between the strata of the Keweenaw 

 system* and the known Cambrian formations. An examina- 

 tion of the sections shows that in each of them there is a great 

 series of disturbed and eroded strata overlaid by the horizontal 

 beds of the Upper Cambrian ; and in the Keweenaw, and the 

 Grand Canon sections, this great series of strata is in turn 

 separated from the formation below by an unconformity that, 

 in the Grand Canon, is very great, and in the Lake Superior 

 area, sufficient to indicate an orographic movement previous 

 to the deposition of the Keweenaw strata. All three of the 

 sections (figs. 4, 5, 6) agree in the evidence of an extended 

 orographic movement and a great period of erosion at the close 

 of deposition of the Keweenaw series ; and I am now of the 

 opinion that the Keweenaw system should be considered as 

 pre-Cambrian. The correspondence in the position of the pre- 

 Grand Canon strata, separated from the Grand Canon series by 

 a great unconformity, to the Huronian as described by Irving, 

 is so striking that more than calling attention to it is unneces- 

 sary. 



The presence of organic remains does not necessarily imply 

 that the strata are of Cambrian age except they show a marked 

 Cambrian facies ; and unless this is the case I should not con- 

 tend for a moment against well -proved stratigraphic evidence 

 of greater age and marked structural breaks in the stratigraphic 

 succession. It may be asking too much for the period of ero- 

 sion, between the Keweenaw system and the Upper Cambrian, 

 to say that 12,000 feet of mechanical sediments and 4,000 feet 

 of limestone accumulated in the Utah-Nevada basin while this 

 erosion was taking place ; but, if we look higher up in the 

 Grand Canon section, and that of Central Nevada, we find that 

 200 feet of Silurian and Devonian strata in the former is repre- 



* The Keweenaw system is here used to include the Keweenaw series of the 

 Lake Superior region, the Llano series of Texas and the Chuar and Grand Canon 

 series of the Grand Canon of the Colorado, Arizona, and is considered as of equal 

 value with the Cambrian, Lower Silurian (Ordovician), Upper Silurian and other 

 systems of the Paleozoic Group, and as belonging to the Paleozoic rather than to 

 the Archean. It may be that the Keweenaw and Grand Cation series belong to 

 distinct systems of strata, but until this is proven I prefer to provisionally refer 

 them to a pre-Cambrian post-Huronian system. I think the Grand Canon and 

 Llano strata belong to one system. 



