PIGEON POINT PLATE, 1899. N. H. WINCHELL. 



throughout this area the denudation has been so profound that, so far as known, they 

 are entirely distinct at the present surface, and the later date of the dikes seems to 

 be plain. This great gabbro invasion gave origin to the red rocks of the region and 

 their variations, by contact fusion of the sedimentaries. 



4. Erosion interval, commencement of the Keweenawan clastic rocks (or 

 Potsdam), conglomerate, quartzyte and sandstone of Potsdam age. 



5. Eruptions more or less cotemporary with the fragmentals of No. 4, and very 

 copious after the completion of the quartzyte, forming surface flows. Grand Portage 

 island (Manitou). 



6. Dikes later than No. 5. So far as known the eruptives of No. 5 and No. 6 

 were only basic, mainly diabase, with amygdaloidal diabase. The dikes of No. 6 cut 

 the surface flows of No. 5 on Grand Portage island. N. H. w. 



