88 THE CE5rSTAL FALLS IRON-BEARING DISTRICT. 



the difficulty of determining the igneous character of the rock. In the rocks- 

 to be described the phenocrysts may still be observed, though more or less 

 deformed, and the fluxion banding has been in one case exceptionally well 

 preserved, so that no doubt is felt as to their igneous character. Dynam- 

 ically metamorphosed rhyolite-porphyry flows have been found in two areas 

 in the Hemlock formation. In the following each area will be described 

 separately, the one in which the original character of the porphyry is least 

 in doubt being considered first. 



The Deer River schistose porphyries are found in the SE. \ sec. 36, T. 

 44 N., R 32 W., beginning at 400 N., 250 W., and continuing to 600 N., 

 350 W., of the southeast corner near the bridge on the Floodwood road. 

 They occur in several outcrops which are practically continuous, being- 

 separated by very short distances, and are so much alike both macroscopic- 

 ally and microscopically that there is sufficient reason for the conclusion 

 that they belong together. Their field relations to other rocks have not 

 been observed. No data have been found which offer any clue as to the 

 time of eruption of these rocks other than the fact that they are surrounded 

 by the basic volcanics of the Hemlock formation and have undergone the 

 same dynamic action. 



The porphyries are dense, bluish-black rocks, with porphyritic crystals 

 of red feldspar. A fluidal structure is not present in them. The schistose 

 structure is apparent to the eye, especially upon the weathered surface, and 

 the cleavage of the rock also indicates it. The cleavage face of the rock 

 has a silky luster, due to the sericite and biotite flakes parallel to it. The 

 rock breaks readily in various directions at angles to the cleavag'e, so that 

 it is impossible to obtain well-shaped hand specimens. The schistosity in 

 these porphyi'ies is clearly brought out by weathering, the weathered rocks 

 showing perfect schistosity, while fresh specimens from the same exposure, 

 although splitting easiest in one direction, appear perfectly massive in hand 

 specimens when broken across the schistosity. That the dynamic action 

 was greatest along certain zones of the rock, other portions being more 

 or less exempt, is shown by the fact that of several specimens collected 

 with the view of obtaining difi'erent stages of alteration from different 

 portions of the same exposure some are markedly schistose, while the least 

 altered approach a fairly massive character. 



I shall give a brief description of this least altered phase, and then 



J 



