l^Ki CAKHONIKKROl'S t'OKMATIONS AND KAl'NAS n\>' COI.OUADO. 



iiroiis ol' wcakiK'ss, wliicli wcni (•oatiiuuilly Ix'iiig puslictl up :uul eroded, a constant 

 .source of material woidd he afforded hy comparatively limited tracts. There cer- 

 tainly sooms to he evidence to favor such a hypothesis with regard to the Archcan 

 area representi'd })v the Rocky Mountains of Colorado, and pos.sibly similar 

 conditions existetl with regard to the other notable Archean areas. Somewhat as a 

 corollary to this would be the supposition that these areas were not permanently 

 al)o\e water, and though repeatedly elevated were sometimes depressed. In the 

 Rock}' iMountains these movements seem to have involved such large surfaces that 

 their effect upon the strata is often not apparent, except as indicated by overlap or 

 by the comparison of sections widely separated from one another. The great 

 amount of disturbance which the strata in Colorado have undergone would also aid 

 in concealing local evidence of unconformity. 



