THE ARCHiEAN ROCKS. 



473 



9. Red granite {Ml): medium-grained, straotuveless, pinMsh to red, highly fels- 



patliio. By following the strike 

 ^^^- '■ directions south-westward for 



some hundreds of feet, the junc- 

 tion between this and the preoed- 

 mg dark-colored rock is found 

 on a large water-worn surface 

 near the dam at the Grand Ra- 

 pids foundry. Here the two rocks 

 are seen to interlock in a curious 

 manner, the granite occurring 

 in large masses, entirely sur- 

 rounded by the other rock. The 

 contrast between the bright red 

 color of one, and the black of 

 the other, makes their ir'-egular 

 junction-lme very marked. Fig. 



7 shows tliis junction line. Pig. 



8 is the part of Fig. 7, at A, en- 

 larged. Where the sketches, 

 were taken the granite (894) is 



Feet. 



Junction off Granite and Hornblende Rock. 

 Scale 100 feet to the inch. 



to. 



somewhat deeper red in color and of coarser gram than on the line of sec- 

 tion, its deep red color being due to the abundance of red felspar, which is 

 sometimes in facets % inch in diameter, and is blotched with large patches 

 of translucent quartz. The rock is a very handsome 'one, and would have 

 value as an ornamental building stone 35 



Hornblende rock (848) : 



Fig. 8. 





rather fine-grained, 

 highly crystalhne, dark 

 colored; strike and dip 

 obscure. Hornblende 

 and a whitish felspar ap- 

 pear to be the main in- 

 gredients. Magnetite is 

 present, and with a 

 magnifier, can be seen 

 in bright, metaUic par- 

 ticles. Quite coarse 

 fragments are held up 

 by the magnet. At 100 

 feet this rock becomes 

 very iine-grained (849), 



and i-ises into large exposures, over which the dip needle stands vertical. . . 

 Red granite (850): moderately coarse, pink to red; weathered surface bright 

 red,- much jointed; no bedding; sunilar to No. 9. The mica in this rook is 

 very subordinate, and in patehes of small flakes; the quartz is hyaline, in 

 considerable blotehes of granular appearance; the felspar is pink to red, 



bright-lustred, large-surfaced, and very abundant ■ • 57 



12. Hornhlende rock: fine grained, dark-colored, much jointed; strike and dip 

 obscure 



M'< ,<: 



Enlargement or Portion of Fig. 7. 

 Scale 4 feet to the inch. 



120 



11. 



58 



