654 THE GEOLOGY OF MINNESOTA. 



[Greenstone. Conglomerate. 



Mir. This slide has a varied composition. One part is made up of loosely set 

 imperfect green spheruliths though without marked radial structure, lying in a 

 matrix which is sub-translucent, or nearly isotropic. Amongst these spheruliths are 

 a few scattering idiomorphic crystals of feldspar, each crystal about as large in cross 

 section as 8 to 12 of the spheruliths. Another portion consists of actinolite and 

 chlorite, with more or less of feldspar, being in general much more transparent than 

 the last, though containing also some of the same spherulitic forms and some 

 magnetite. A third portion, not well separated from either of these, is fine grained, 

 but consists of about the same elements. 



The porphyritic aspect, the fine and almost isotropic nature of the substance 

 embracing the little spheruliths, the varied nature of the structure connected with 

 the essential unity of the composition, conspire to indicate that this rock was 

 originally a basic basalt, somewhat porphyritic, a diabase porphyryte. One (thick) 

 section. 



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



No. 1078. GREENSTONE. 



Near the same place as Nos. 1076 and 1077 ; hills in sec. 3.~>, T. 65-6 ; south of Ogishke Muncie lake. 

 Ref. Annual Report, xv, pages '568, 372, 373, 397. 



Meg. Coarse jointed, massive, porphyritic. 



Mic. The much decayed feldspars are crowded with zoisite, ca/cife and other 

 impurities. The pyroxene element is changed to hornblende, about which are gathered 

 hematite and more or less leucoxene, the latter also being in other parts of the slide. 

 Two crystals of apatite of the first generation also are conspicuous. One section. 



Age. Archean (Keewatin). 



Remark. This rock was probably originally a massive diabase with ophitic 

 structure. N. n. w. 



No. 1079. CONGLOMERATE. (Matrix of the pebbles. ) 







Southern portion of sec. 23, T. 65-6 ; one-third of a mile north of the shore of Ogishke Muncie lake. 

 Ref. Annual Report, xv, pages 374, 397. 



Meg. Matrix of the Ogishke conglomerate. 



Mic. The rock consists, besides the finest matrix, of the following pebbles: quartz; 

 diabase, both fine and coarser, particularly the former; hornblende crystals; feldspar 

 crystals, which have the striking multiple twinning of those in rock No. 1061, at Keke- 

 quabic lake and in the porphyrel of Zeta lake; fine-grained rock like the matrix of 

 the crystals of the Kekequabic Lake -rocks, numerous; quartzyte, in which several 

 orientations are in one pebble. One section. 



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



