756 THE GEOLOGY OF MINNESOTA. 



[Greenstone. Gneiss. Dioryte. 



Age. Archean (Keewatin). 



Remark. The name gneiss is applicable only in the sense that it is a recrys- 

 tallized f ragmen tal, and contains all the elements usual in that rock, but it would 

 be correctly denominated a feldspathic quartzyte, the darker elements being merely 

 accessory. The rock is on the south side of the Giant's range of granite, and is not 

 far distant from a deposit of jaspilitic hematite. It was no doubt once covered by 

 the Animikie, as well as by the gabbro, and it may owe its recrystallization either 

 to the gabbro or to granite. N. H. w. 



[NOTE. Nos. 1643 to 1669, inclusive, were collected outside of Minnesota. We 

 have sections of only two (Nos. 1644 and 1649) of these specimens described below. 

 Notes concerning Nos. 1643 to 1669 can be found in the Twenty-first Annual Report, 

 pages 153 and 154; also, on pages 86 to 112.] 



No. 1644. GREENSTONE. 



From the north side of the Republic hill, Republic, Michigan. 

 Ref. Annual Report, xxi, page 153. 



Meg. Approaching hornblende schist. 



Mic. Feldspar, hornblende, quartz, leucoxene, evidently sheared basic eruptive, 

 originally of coarse grain. One (thick) section. 



Age. (?) N. H. w. 



No. 1649. GNEISS. 



At the dain in the Racket river, at Potsdam, New York. 

 Ref. Annual Report, xxi, page 154. 



Meg. Very quartzose, medium grained, sometimes reddish and sometimes gray. 



Mic. Fresh, glassy microcline, quartz these are plainly of the latest generation. 

 There are older (at least centrally altered) grains of a triclinic feldspar, having 

 extinctions near oliaoclase, a little hornblende, magnetite, sphene, biotite, leucoxene. Calcite 

 appears as a product of decomposition, lodged in the cores of the altered feldspars. 

 The small, isolated sphenes are in the fresh quartz and microcline. Two sections. 



Age. (?) N. H. w. 



No. 1670. DIORYTE (?) (withqiiartz). 



Segregation from the slates at Little Falls, Morrison county. 



Ref. Annual Report, xxi, page 154; Strong and Kloos, Annual Report, xi, pages 74-7G. 



Meg. One of the smaller segregations. 



Mic. Hornblende and garnet, both presenting idiomorphic contours, thus 

 appearing to be of earlier date, lie in a groundmass of fine interlocking quartz, the 

 grains of which they enclose poikilitically, and hence are of later date than the 

 quartz. The groundmass also embraces a few grains of sphene and irregular dust- 

 like spangles of dark leucoxene( ?) approaching magnetite in opacity. One section. 



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



