890 THE GEOLOGY OP MINNESOTA. 



[Graywacke. 



Yet it is evident that they are not now in a process of decay, but have been recon- 

 structed and hardened by metamorphism. The matrix in which these old feldspars 

 lie seems to consist of newly crystalline materials, viz., a new feldspar and quartz, 

 with scattered scales of muscovite, a little hematite, chlorite. The little fresh 

 quartzes interlock as in a granitic rock, being ihterlobed in and around each other. 



In a second slide the whole grain is coarser. A well-preserved feldspar, showing 

 n. e perpendicular, has extinction on cleavage at 12, but a refractive index greater 

 than the quartz adjacent, indicating a species lying between andesine and labradoi-itr. 

 All the quartz is so completely remodeled in both slides that there is nothing remain- 

 ing to show its original clastic nature. Indeed, the only remaining clastic feature, 

 so far as can be determined by the slides, is the decayed and then regenerated 

 condition of the feldspars. Two sections. 



Age. Keewatin. 



Remark. In the field appearance this rock, which alternates with some that are 

 coarser, is in places distinctly micaceous, being near a granitic area. N. H. w. 



No. 384G. GRAYWACKE. 



Same locality as No. 383G. 



Bef. Annual Report, xx, pages 4(i, '.Hi. 



Meg. Similar to the last, but coarser. 



Mir. This rock is not distinctly schistose. It contains a conspicuous amount 

 of calcite, chlorite and muscovite. The feldspars, some of which are large, while 

 showing the same kind of alteration, are occasionally bordered by fresh interlocking 

 growths, and this new growth penetrates and permeates, apparently, the whole 

 feldspar grain and is not observable or is less distinguishable in the body of the 

 grain because of the many muscovite scales and other inclusions which have been 

 developed. The acid feldspars seem to be but little more prone to this alteration 

 than the basic. One section. 



Age. Keewatin. N. H. w. 



No. 385G. GRAYWACKE. (SnJbiTij*lili>i<'.) 



North shore of the Kawiehiwi river, N. E. % N. E. J^ sec. 28, T. 63-10, near the same place as the last. 

 Bef. Annual Report, xx, pages 46, 99. 



Meg. Gray, firm, when fractured, glistening with scattered cleavage surfaces. 



Mic. This rock is quite similar in all respects to the last two. It is noticeable, 

 however, that it contains much epidote. It is also observable that some of the larger 

 fr/ilspars, which were plainly triclinic at first and must have extinguished alternat- 

 ingly in the albite twinning bands, in the regular manner of such twinning, now do 

 not extinguish alternatingly. They are instead, simply banded, coincident with the 

 albite macles, with lighter and darker lines and bands, but these bands extinguish 



