316 THE GEOLOGY OF MINNESOTA. 



[Granite. 



seems that a fissure of some depth must have existed here, and that from it have 

 come solutions bearing silica, and also gases. See rocks Nos. 835-841 (W.), Nos. 

 676-680 (G) and No. 2046. u. s. G. 



No. 319. GRANITE. (Decayed.) 



Saganaga lake; southwest corner of an island just north of that on which No. 320 was found; S. W. % N. 

 W. % sec. 14, T. 66-5 W. 



Ref. Annual Report, ix, page 84. See, also, under No. 318. 



Meg. Apparently a highly siliceous rock, containing some feldspar and pyrite, 

 and in spots stained brownish yellow. 



Mic. The section is composed of quartz and much decayed feldspar. There are 

 also numerous small rhombs of what appears to be siderite, and some pyrite crystals. 

 The siderite is seen in connection with a brownish yellow material (limonite), and 

 this same substance is common throughout the section. It seems most probable 

 that all of the limonite is an alteration from the siderite. 



One section. 



Age. Archean. 



Remarks. This rock is regarded as part of the decayed granite mentioned under 

 No. 318. u. s. G. 



No. 320. GRANITE. (Decayed.) 



Saganaga lake; N. W. % sec. 10, T. 66-5 W. 

 Ref. Annual Report, ix, pages 84, 85. 



Meg. A coarse-grained rock composed of large, sometimes roughly rounded, 

 areas of quartz, and feldspar which is much decayed and is pinkish, gray or yellowish 

 in color. There are also small areas of a rather soft greenish-yellow material. 



Mic. The section is composed largely of quartz and very much decayed feldspar. 

 There are areas which are now opaque and greenish or gray in color, which seem to 

 represent old chlorite areas; these are probably the greenish-yellow material seen in 

 the hand sample. A few small grains of a green mineral are seen; the nature of 

 this cannot be determined owing to the thickness of the section. Two rusty, reddish 

 brown spots are also seen, possibly an alteration product from some ferruginous 

 mineral. 



One section. 



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



No. 321. GRANITE. 



Lake Saganaga. Probably near the northwest corner of sec. 16, T. 66-5 W. 

 Ref. Annual Report, ix, page 85. 



Meg. Greenish-gray, with quartz and a pinkish feldspar, and a chloritic mineral. 

 Mic. Essentially composed of quartz and a saussuritized feldspar which cannot 

 be determined on account of the loss of cleavage and twinning lines. 



