700 THE GEOLOGY OP MINNESOTA. 



[Slate. Grit. 



Mic. This slate is made up of a fine clastic dust of hornblende, biotite, feldspar 

 and quartz, colored, also, in part, apparently, by leucoxene, the quartz being rather 

 rare. One section. 



Age. Probably Upper Keewatin. N. H. w. 



No. 1352. SLATE. 



Same place as the last ; same rock. 

 Ref. Annual Report, xvi, pages 90, 122. 



Meg. Coarser slate. 



Mic. It is apparent that the quartzes and the feldspars have been enlarged by 

 later growth, as they extend in small hooked projections into the surrounding matrix 

 with the same orientation, embracing the biotite leaves and the actinolite spicules. 

 It is noticeable that numerous microgranulitic inclusions have a tendency to a 

 globular outline, some of which are also of devitrified glass. Some glassy feldspars 

 are entirely developed new and some old ones are clouded. Sometimes the biotite 

 is clustered about a magnetite grain. The biotite is frequently pierced -by spicules of 

 actinolite. One section. 



Age. Probably Upper Keewatin. N. H. w. 



No. 1353. GRIT. (Gray.) 



Same place as the last ; same rock mass. 

 Ref. Annual Report, xvi, pages 90, 122. 



Meg. Coarser slate, a gray grit, with quartz grains. 



Mic. This is a more freshly and coarsely fragmental rock than the last. There 

 were sizable grains of feldspar^ quartz and of hor//li/<'iide, with a great amount of 

 liner debris concerned in the original composition. There is no apparent recompo- 

 sition, but a degradation visible in the present condition of these grains. There 

 was also apparently a porphyritic or trachitic zirkelyte which furnished pebbles as a 

 debris for the constitution of this rock. Such fine pieces are now nearly isotropic, 

 but sometimes embrace the forms of small crystals which are shown by the predom- 

 inance of doubly polarizing fine minerals over spaces having geometric forms. These 

 supposed zirkelyte pebbles have prevailingly rounded outlines and are sprinkled with 

 fine dust which appears to be of the same nature as the coloring matter of the rock 

 in general. One section. 



Age. Probably Upper Keewatin. N. H. w. 



No. 1354. SLATE. 



A little south of the centre of sec. 29, T. 65-5. 

 Ref. Annual Report, xvi, pages 90, 122. 



Meg. Samples of the same rock, one coarser than the other. 



