1 84 H. C. COOKE 



inch in diameter. Beds of basic sediments overlie conformably 

 the porphyritic basalts and in one place are interbedded with them. 

 The beds approximate one inch in thickness, and the thickness 

 remains uniform over the outcrops, which in some cases were 

 exposed two hundred feet or more along the strike. The sediments 

 are of tuffaceous composition and vary from grayish or reddish 

 cherty rock, which may be in part a deposit from silica-bearing solu- 

 tions accompanying the lava flows, to black hornblendic material, 

 probably recrystalhzed volcanic dust. In places they are filled 

 with lenses of gabbroid material averaging about four inches in 

 length by one-quarter inch in width. 



North of the mouth of the east bay into which the Eagle River 

 empties, outcrops of andesite occur, with a northeast strike and a 

 dip to the northwest. The strike swings gradually to the north, 

 then to the east at the mouth of the Opawika River, where they are 

 overlain by rhyohte. It is doubtful what relation the andesites 

 bear to the basalts and sediments. The mapping as it stands leads 

 to the inference that faulting of some magnitude has taken place 

 along the east bay into which Eagle River empties, but it is impos- 

 sible to prove this, as the rocks here are all heavily drift covered. 

 The map, however, is a rather inferior grade of track survey, and 

 the impression gained in the field by assuming a projection along 

 the strike was that the andesites overlie the basalts and part of the 

 sediments and underlie the remainder of the sediments. 



It may be observed that the basaltic flows in this area have no 

 ellipsoidal textures, while the andesites are ellipsoidal. The sig- 

 nificance of the fact will be discussed in a subsequent section. The 

 succession in the Father's Lake area is 



Rhyolite Tuffaceous sediments 



Andesite Porphyritic basalts 



Basalts 



Windy Lake-Nemenjish area. — The structure of the Windy 

 Lake-Nemenjish (Fig. 6) area is monoclinal, so far as known, with 

 a general east-west strike and a southward dip. This structure has 

 been attained by strike faulting, with consequent repetition of out- 

 crops. One large fault, whose south side was upthrown, was 

 observed on Windy Lake, and possibly others occur to the south 



