1010 THE GEOLOGY OF MINNESOTA. 



PLATE II. 



Page. 



FIGURE * L Mesolite and mesotype ( ?) interpenetration. Kock No. 625 A, about V . 456 

 FIG. 2 Apotrachyte, showing the patchy appearance of secondary quartz. Rock 



No. 653, about 4 T 473 



FIG. 3 Granulitic gabbro. Rock No. 677, about 8 r 6 486 



p IG . 4 Volcanic tuff. Rock No. 680, about V 488 



FIG. 5 Muscovadyte, ferruginous, showing magnetite, olivine, cummingtonite and 



quartz. Rock No. 976, about V 618 



FIG. 6 Muscovadyte, showing minute olivine globules enclosed in the larger grains 



of olivine. Rock No. 976, about Jf* 618 



FIG. 7 Gneiss. Fine fragmental weathered surface. Rock No. 991, about f.... 623 

 FIG. 8 Biotite schist, showing zonal oligoclase-andesine with micro- perthitic albite. 

 Also quartz, embracing numerous cordierite grains. Rock No. 1039, 



about V 638 



FIG. 9 Quartzyte, showing wholly devitrified glass, non-de vitrified glass and 



marginal enlargements of rounded quartzes. Rock No. 1322, about 2 T 6 . . . . 692 

 FIG. 10 Quartzyte, or taconyte, showing rosettes of radiating actinolite (?) fibres, 

 resulting from the devitrification of grains of volcanic glass. Rock No. 



1327, about 2 T 5 : 693 



FIG. 11 Peridotyte, showing fayalite, augite, magnetite. Rock No. 1336, about \ 6 696 

 FIG. 12 Greenwacke, a volcanic tuff, appearing conglomeratic. Shows the weath- 

 ered surface. Rock No. 1374, about f - . 709 



