670 THE GEOLOGY OF MINNESOTA. 



[Schist. 



but it is remarkably free from the dark minerals. The schist side of the slide is 

 marked by the presence of much m-tinolit-e, with secondary feldspar and quartz. 

 There are also scattered grains of a highly polarizing monoclinic mineral, with 

 frequent parallel extinction, colorless in common light, in prevailingly sub-quadratic 

 sections, which is more fully described under No. 1123, and is probably epidote. One 

 section. 



Age. Archean granite. N. H. w. 



No. m3. SCHIST. (Ei>i<l<>ti.) 



The same schist, more indurated, from a point lower down tbe cliff. 

 Kef. Annual Report, xv, pages 331, 399; Bulletin vi, page 8. 



Meg. Actinolitic. 



Mic. Andesine-oligoclase shows a section perpendicular to n f in the broader 

 bands, and has an extinction of 72, and an angle between the macles of albite and 

 of percline(?) in the same section of 72 30 '. This may be, however, due to a micro- 

 perthitic growth, parallel to 001. The rock has some secondary quartz which 

 embraces the other minerals and occasionally surrounds cordierite. There is a light 

 green actinolite in considerable amount. 



Epidote is rather abundant, shown by its high refraction and double refraction, 

 and the position of the optic plane perpendicular to the easy cleavage in sections in 

 the zone of symmetry. Many of the cross sections also have a parti-colored polar- 

 ization, but a light yellow color in natural light. The mineral has a higher double 

 refraction than actinolite, and also higher single refraction. It occurs in small 

 scattered globular and angular grains which are fresh, evidently of secondary origin. 

 This mineral serves a leading role in giving green color to the rock. It frequently 

 shows its own crystal boundaries about a half or more of the individual grains, and it 

 has numerous globular inclusions which give it a strong resemblance to the diopside 

 in the metamorphic schists and gneiss of the long point in the northeastern part of 

 (rabemichigama lake. One section. 



Age. Archean (Keewatin). 



Remark. If, as supposed when the specimens were gathered, this is a part of the 

 prevalent green schists of the region, this greater crystallization is to be attributed to 

 the action of the great granitic mass which is intrusive in the immediate vicinity. 



N. II. W. 



No. 1124. ACTINOLITE SCHIST. 



Same place as the last. 



Ref. Annual Report, xv, pages 331, 390 ; Bulletin vi, page 8. 



Meg. Somewhat more schistose than No. 1123. 



Mir. This is similar to No. 1123, but contains more <irti,,<>lit<\ with apparently 

 one or two grains of sphene, and considerable l>iotit<: One section. 



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



