354 THE GEOLOGY OP MINNESOTA. 



[Schist. Gneiss 



Mic. The sections are too thick for careful study. They however show that 

 the rock is a granite composed of feldspar, quartz, biotite and chlorite. The feldspar 

 is frequently much clouded. It seems to be orthoclase, microcline and a plagioclase 

 near anorthoclase. The biotite and chlorite are quite dark and filled with inclusions 

 and are frequently opaque. 



Two sections. 



Age. Archean (igneous). u. s. G. 



No. 405. BIOTITE SCHIST. 



"A few rods further a ridge of this rock appears. This is a firm mica schist, with reticulations and inter- 

 laminations of gray quartzyte and quartz, and also cross layers and interlaminations of syenyte. In the main 

 the syenyte is coincident with the schistose structure." Near the same locality as No. 404. 



Ref. Annual Report, ix, pages 99, 100. 



Meg. A fine-grained, dark-gray schistose rock composed of biotite, quartz and 

 feldspar. 



Mic. The section is composed of flakes of dirty brown biotite, chlorite, feldspar 

 and quartz. The arrangement of the biotite and chlorite scales causes the schistosity 

 of the rock. The chlorite is charged with minute black particles and appears to be 

 an alteration product from the biotite. The feldspar is very largely altered to kaolin 

 and chlorite; its species was not determined. 



One section. 



Age. Archean (Coutchiching). u. s. G. 



No. 406. BIOTITE SCHIST AND GNEISS. 



Near the same locality as No. 405. 



Ref. Annual Report, ix, page 99; Annual Report, x, page 95. 



Meg. A fine-grained, gray biotite schist, with laminations'of a light-gray granitic 

 rock which is composed of white feldspar, quartz and a little biotite. 

 No section. 

 Age. Archean (Coutchiching). u. s. o. 



No. 407. HORNBLENDE SCHIST. 



Near the same locality as No. 406. 

 Ref. Annual Report, ix, page 99. 



Meg. A fine-grained, gray, somewhat schistose rock, composed of hornblende 

 and quartz and feldspar. 



Mic. The section is composed essentially of a granular aggregate of green 

 hornblende, quartz and feldspar. A little epidote, pi/rife, magnetite and apatite are also 

 present. The feldspar is quite largely altered to kaolin and a gray opaque substance, 

 although much of this feldspar is rather fresh. Most of it shows no twinning lamellae. 

 One grain, which gave a positive bisectrix perpendicular, showed an extinction angle 



