918 THE GEOLOGY OP MINNESOTA. 



[Chlorite schist . Amphibolyte . 



Mic. Similar to No. 15H but less altered, the pyroxene being still somewhat 



preserved. Large sphenes, with crystal outlines, 

 are frequent. These crystals, as well as all the 

 smaller grains which do not show definite crystal 

 form, are secondary to the hornblende. Not 

 only is the sphene indented by hornblende about 

 its margin, but it surrounds completely several 

 globular grains of hornblende, as shown in the 



FIG. 51. SECONDARY SPHENE IN NO. 19H. 



accompanying figure. It also encloses two 



other grains that are apparently calcite and feldspar. One section. 



Age. Archean (Keewatin). N. H. w. 



No. 22H. CHLORITE SCHIST. (Greenstone.) 



From the top of Sunset peak, north of the east end of Long lake, sec. 22, T. 63-12. 

 Ref. Annual Report, xv, pages 404, 416. 



Me;/. Greenish, schistose. 



Mic. In the midst of the chlorite, which is in fine, radiating or fan-shaped forms, 

 are a few spicules of hornblende, and a finer, granular feldspar fills some of the inter- 

 spaces. The most of the rock consists of chlorite. A few minute sphenes, some pi/rite 

 and leucoxene are also visible. Two sections. 



Age. Archean (Keewatin). 



Remark. Another section bearing the same number is from what was probably 

 originally an igneous rock, but which now has no feldspar, there having been substi- 

 tuted for it a very fine granular mass of secondary products which, owing to the 

 thickness of the section, cannot be minutely studied, but in which calcite seems to 

 enter largely, probably consisting of feldspar and quartz. In this fine substance lie 

 numerous hornblendes, much chloritized, whose size is in strong contrast with the 

 very fine matrix in which they lie. N. H. w. 



No. 26H. AMPHIBOLYTE. 



Sec. 15, T. 63-12, ridge north of Long lake. 

 Ref. Annual Report, xv, pages 404, 416. 



Meg. The crystals of hornblende stand out on the weathered surface, giving a 

 darker and rougher appearance. 



Mic. The 1'ock consists almost entirely of hornblende, but also contains Muscovite, 

 which is also intimately associated with chlorite, with a little epidote. Between the 

 hornblendes, which in one section lie uniformly in one direction, is a fine granular 

 matrix of muscovite and feldspar, the contrast with the nearly idiomorphic horn- 

 blendes being quite remarkable. Two (thick) sections. 



Age. Archean. N. H. w. 



