﻿C. D. Walcott — Cambrian System of North America. 155 



of the Rocky Mountains of Colorado show only the thin 

 Upper Cambrian formations resting on the Archean ; and the 

 same is true in the Black Hills and in Central Wyoming. The 



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111 



Pig. 8. — Hypothetical map showing- the supposed Keweenaw land or continent 

 as it existed just before the deposition of the Upper Cambrian (Potsdam) sedi- 

 ments. The latter probably extended over most of the area marked X, X, X, 

 although now concealed by the later sedimentary deposits. The age of the 

 eastern and western belts, marked L?, is still in doubt, but the presence of the 

 eastern belt is strongly indicated by the geographical distribution of the Cambrian 

 faunas. L, Laurentian and other Archean formations ; K, Keweenaw ; T, Llano 

 formation ; C, Grand Canon formation ; X, X, X, area supposed to have been 

 land surface but now concealed by later deposits. 



existence of these Archean areas with the Upper Cambrian 

 deposits proves the early date of their elevation, and that they 



