IGNEOUS EOCKS OF STURGEON EIVER TONGUE. 485 



schist by a process which resulted in the absorption of all of them except 

 rutile. The process may have been connected with contact action, but no 

 evidence in favor of this supposition has been obtained. 



There are a few other types of greenstone occasionally met with 

 among the dike and other intrusive forms of the district, but they do not 

 differ in any marked degree from those described, except that some are 

 quite schistose. One or two of these contain oval aggregates of epidote, 

 plagioclase, and quartz, that may represent inclusions of foreign rocks. 

 They are now, however, so much altered that it is difficult to determine 

 their character with any degree of certainty. 



The rock of one or two other exposures in the area underlain mainly 

 by the conglomerates deserves mention before the banded greenstones are 

 discussed. The rock referred to is a heavy, lustrous, black schist that 

 resembles in many respects a hornblende-schist. On fresh fractures across 

 the schistosity parallel lines, darker than the main mass of the rock, may 

 be easily detected. These are the edges of cleavage planes, whose surfaces 

 are coated with brassy yellow mica plates. In thin section these rocks 

 differ very little from the schistose greenstones referred to above. They 

 consist of a heterogeneous schistose mass of green hornblende, cloudy 

 plagioclase, quartz, epidote, chlorite, and magnetite. Biotite flakes are met 

 with occasionally, but they are by no means common, except on the cleav- 

 age surfaces. Rocks of this class have not only been made schistose by 

 squeezing, but they have also suffered shearing along what are now the 

 cleavage planes. They are almost identical in microscopic and macroscopic 

 features with the hornblende-schists in the Basement Complex. 



THE BANDED GREENSTONES. 



Distincth' banded rocks, composed partly of basic material with the 

 composition of greenstone, form a well-defined hillock in sec. 17, T. 42 N., 

 R. 28 W., about 250 paces north of the west quarter post of this section, 

 and a group of outcrops on the east bank of the Sturgeon River, imme- 

 diately west of this point. 



The rocks in question are banded in mediumly coarse-grained dark 

 bands, containing large quantities of green hornblende, and in fine-grained 

 lighter ones, that resemble in the hand specimen bluish-black quartzites or 

 cherts. In some bands there are large lenticules of white quartz, that show 



