PALEOZOIC STRATIGRAPHY OF ROCKY MOUNTAINS 393 



early Devonian time; and where they lie on the Cambrian, the pre- 

 Bighorn emergence also must be reckoned with. Again, it is 

 probable that parts of the region never were covered by strata of the 



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age of some of the formations which appear elsewhere. The 

 extreme view, that none of the existing Middle Paleozoic formations 

 ever extended much beyond their present limits, is certainly not 

 true in the central Rocky Mountain region. The other extreme, 



