ARCHEAN GRANITES. 257 



Relations of the different varieties of the acid intrusives of Vermilion Lake 

 to one another. — On the bare ridge south of Mud Creek Bay the granite- 

 porphyry is found cutting the feklspathic porphyry at several places. One 

 such dike may be found about north 700 paces, west 1,400 paces, from the 

 southeast corner of sec. 7, T. 62 N., R. 14 W. Again, on the high hill in 

 the Burnt Forties overlooking the lake the granite-porphyry is found in 

 contact with, and apparently cutting, the fine-grained porphyritic granite, 

 and includes fragments of greenstone and jasper. It is interesting to 

 note that immediately around these jasper inclusions the acid intrusive has 

 become green as the result of the infiltration of iron and the production of 

 secondary chlorite instead of sericite. From this green background the 

 phenocrysts of quartz stand out very prominently. A similar alteration 

 occurs in the acid sills that were intruded through the iron formation on 

 Soudan Hill. 



East of Stuntz Island there is a conical island which is made up chiefly 

 of the fine-grained feklspathic porphyry, and on which there is a dike of 

 porphyritic granite, about 25 paces in width, running from northwest to 

 southeast. At certain places in this dike, especially on the southeast slope 

 of the island, the granite grades into a rock corresponding very closely to 

 the coarse-grained granite-porphyry. On the other hand, at other locali- 

 ties, the same porphyritic granite was observed to pass into a form of rock 

 very similar to some of the phases of the feldspathic porphyry. It would 

 appear from this that these different kinds of rock were all derived from 

 the same source, and that they merely represent different phases of 

 development of essentially the same magma. Upon this conical island 

 there were noted also several small dikes of green schistose basic rock, one 

 of them running nearly east and west and having a width of from 8 to 12 

 inches. 



On Stuntz Island itself, especially upon the northwest arm of the 

 island, a mass of this porphyritic granite was found trending about east 

 and west, cutting through the feldspathic porphyry. 



Nearly all of these porphyries contain more or less oval yellowish- 

 green fragments of rock which apparently were derived from the greenstone 

 through which they were intnided. 

 MON XLV — 03 17 



