DUNKA RIVER PLATE OP THE MESABA IRON RANGE, 1899. N. H. WINCHELL. 



and pyroxene in the valley of Birch lake belongs to the Keewatin rather than the 

 Animikie, and is a metamorphic phase of ore lodes peculiar to the Lower Keewatin, 

 due to the gabbro revolution. The peculiar lithology of these Keewatin ore bodies 

 is discussed in volume v. The ferromagnesian minerals in the ore were probably 

 derived from basic debris which was originally associated with the sedimentary 

 jaspilyte. These increase in amount and in variety, the iron and the quartz dimin- 

 ishing until the rock changes to muscovadyte, and thence into gabbro. N. H. w. 



