THE ARCHAEAN ROCKS. 



9. Red granite (847): medium-grained, structureless, pinkish to red, highly fels- 



pathic. By following the strike 



Feet. 



FIG. 7. 



JUNCTION OF GRANITE AND HORNBLENDE ROCK. 

 Scale 100 feet to the ineh. 



directions south-westward for 

 some hundreds of feet, the junc- 

 tion between this and the preced- 

 ing 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 irregular 

 junction-line very marked. Fig. 



7 shows this junction line. Fig. 



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

 larged. Where the sketches 

 were taken the granite (894) is 



10. 



somewhat deeper red in color and of coarser grain 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 crystalline, 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, metallic par- 

 ticles. Quite coarse 

 fragments are held up 

 by the magnet. At 100 

 feet this rock becomes 

 very fine-grained (849), 

 and rises into large exposures, over which the dip needle stands vertical. . . 



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



red; much jointed; no bedding; similar to No. 9. The mica in this rock is 

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

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

 bright-lustred, large-surfaced, and very abundant 



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



obscure 



ENLARGEMENT OP PORTION OF FIG. 7. 

 Scale 4 feet to the inch. 



120 



57 



58 



