THE AHCH^AN ROCKS. 



487 



Feet. 



Fm. 17. 



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

 exposures botli in tlie bed and on the walls of the gorge, wMch are 15 to 20 feet in height. 

 A section in tliis 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: 



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 

 wagon 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° B. The same rook 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 

 rook 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 

 rook dip very plainly 30° N. W. Vertical 

 joints occur here nearly along the strike. . . 



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

 to black in color; much more homblendic 

 and loss quartzose than the preceding kinds. 



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

 cast side of the gorge, wliere tlie beddhig is also quite plamly to be seen, 

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

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



vertically 



i. No exposures 1,' "," " T , . • " 



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

 much more pink orthoclaae; penetrated by manypatches and veins of a fine- 



116 



Black Veik in Sybnitk, 

 Wausau. 



2oa 



62 



165 



grained, but distihctly ciystaUine, dark-gray to black, homblendic rock. 



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



6, No exposure ■ ' ,' ' ij ■i. t^^' 



7 Very coarse symUe (910): bluish-gTay, showmg large unstnated grayish fel- 

 spar surfaxjes, and coarse brilliant blax^k hornblende, in pieces up to H mch 



