41S 



VOLCANIC ACTION ON 



L A K E 



SUPERIOR. 



induration of the beds to complete obliteration of stratification and sedimentary 

 origin, so that the beds of deposition become confounded with the igneous masses 

 that have invaded them, and produced such extraordinary changes. 



BASALTIC COLUMNS, RESTING ON 

 NORTH RIinEI! OF LAKE 



SEDIMENTARY ROCKS, 

 SUPERIOR. 



