THE AHCH^AN EOCKS. 



main or west channel of the river, between island No. 4 and the main-land, shows large 

 exposures both in the bed and on the walls of the gorge, which are 15 to 20 feet in height. 

 A section in this channel on the line A B, bearing N. 10 W., and beginning a short dis- 

 tance (100 feet) above the bridge, showed the following succession, the measurements 



being horizontal distances : 



Feet. 



FIG. 17. 1. Moderately coarse syenite (912, 941): brown- 

 ish-pink to gray, mottled with black, weath- 

 ering with a dark-brown, uniform-tinted 

 surface. Of the three ingredients, all of 

 which are very plainly perceived by the 

 naked eye, the felspar is much the coarsest, 

 its facets reaching % inch in diameter; in 

 color the felspar is brownish-pink to gray, 

 and it is without striations. The several 

 ingredients are quite uniformly intermin- 

 gled. In most of this measurement the 

 bedding is quite distinct, except in one or 

 two places where it is obscured by cross- 

 joints. On island No. 3 prominent joints 

 trend N. 78 E. and dip S. E. 75. On the 

 west side of the stream, just below the 

 \ragon bridge, the bedding planes show 

 finely in a rock somewhat more pink than 

 usual, the dip being 38 N. W. and the 

 strike N. 80 E. The same rock as that of 

 this measurement shows also at the north 

 end of island No. 4, and on the small rocky 

 islet, No. 6 490 



2. Finer-grained syenite (907): similar to the 



rock of No. 1, but of grayer color from the 

 gray color of the felspar; less weathered 

 and of a finer grain. In the middle of the 

 stream, the surface of the layers of this 

 rock dip very plainly 30 N. "W. Vertical 

 joints occur here nearly along the strike. . . 116 



3. Still finer-grained syenite (908) : dark gray 



to black in color; much more hornblendic 

 and less quartzose than the preceding kinds. 

 The junction of this rock with No. 2 is quite sharp, and shows well on the 

 east side of the gorge, where the bedding is also quite plainly to be seen, 

 with a strike of N. 75 E., and a dip of 38 N. W. Prominent cross- 

 joints occur at this place, trending with the strike direction, and standing 

 vertically 202 



4. No exposures 62 



5. Coarse syenite (911): allied to the rock of No. 1 (912, 907), but containing 



much more pink orthoclase; penetrated by many patches and veins of a fine- 

 grained, but distinctly crystalline, dark-gray to black, hornblendic rock. A 

 large one of these veins is represented by Fig. 17 165 



6. No exposure 70 



7. Very coarse syenite (910j: bluish-gray, showing large unstriated grayish fel- 



spar surfaces, and coarse brilliant black hornblende, in pieces up to % inch 



BLACK VEIN IN S YE NITS, 

 WAUSAU. 



