324 THE GEOLOGY OP MINNESOTA. 



[Hornblende schist. Dioryte. 



Mic. The section is composed essentially of green hornblende, feldspar and 

 quartz, the last two in rather small grains. The feldspar seems to be similar to that 

 of the other rocks from this locality- -i. e., neaxqndesine-oligoclase; many of the grains 

 are clear and glassy. Quartz is not as common as at first sight would be supposed, 

 but still is present. The other minerals of the rock are biotite, epidote, sphene and 

 apatite. 



One section. 



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



No. 339. HORNBLENDE SCHIST. 



" Hornblendic schist, from the shore of the same lagoon, on the north side, where the same interstratified 

 condition of the same kinds of rock appears again." Near the same locality as No. 332, etc. 

 Ref. Annual Report, ix, page 89; Annual Report, x, page 95. 



Meg. A dark rock, very rich in hornblende. Besides this mineral there is a fine- 

 grained granular aggregate of glassy grains. 



Mic. The section shows much green hornblende, sometimes very dark and 

 practically opaque. Between the hornblendes and sometimes in them are fine grains 

 oi feldspar. This is sometimes cloudy and sometimes quite clear. The section is 

 very thick and no careful determination of the feldspar could be made, but it seems 

 to be of the same nature as the feldspar of the associated rocks. Quartz may be 

 present in small amount, though none was determined. 



One section. 



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



No. 339B. DIOKYTE. (Coarse.} 



" From the shore near Nos. 337 and 338, not in place, but supposed to be from these beds." 

 Ref. Annual Report, ix, page 89. 



Meg. A very coarse-grained aggregate of green hornblende, biotite and gray to 

 pinkish feldspar. 



Mic. The section shows large plates of more or less fibrous green hornblende. 

 large and small grains of feldspar and some biotite. The feldspar is mostly cloudy. 

 One grain which gave a positive bisectrix almost exactly perpendicular shows an 

 extinction of 6. This might indicate oligoclase-andesine or o/f/wA/.sr, but in this case 

 the general characters of the mineral and its similarity to the feldspar of the 

 associated rocks make it more probable that the feldspar is of the oligoclase-andesine 

 series. Considerable sphene is present, and one peculiar feature of the section is the 

 abundance of large stout prisms of apatite. This mineral occurs in the hornblende, 

 biotite and feldspar, but more especially in the last. A little cale/'fe is present. 



One section. 



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



