PLATE III. 



[To accompany Paper BB. ] 



Figure 1. A map of Central Wisconsin showing a sandstone covered 

 area in the southern portion, the possible extension of the Menominee 

 schists to the vicinity of Black River Falls from the northeast and the 

 probable Archaean character of the underlying rocks of the northern portion 

 of the area mapped. The whole area is drift covered. In part based on 

 the general geological map of Wisconsin, 1881. 



Fig 2. Profile along the Wisconsin river from Rhinelander south- 

 wards beyond the point where the gneisses disappear beneath the Potsdam 

 sandstone. 



Fig. 3. From the altered gabbro at Rhinelander to show the altera- 

 tion of augite into hornblende and the contiguity of biotite which doubtless 

 sprang from the hornblende, a, augite ; b, hornblende ; c, biotite ; f/, sur- 

 rounding plagioclase individuals. See page 255. 



Fig. 4. Microcline matrix carrying the remaining constituents of the 

 rock. See p 262. 



Fig. 5. A corroded individual of plagioclastic feldspar in the midst of 

 segregated microcrystalline quartz granules and feldspars, the eye structure 

 very common in the valley. See p. 264. 



Fig. Q. A reproduction of almost an entire thin section (author's 

 slide No. 884) to show the eye structure so common in these gneissic rocks. 

 The finely granular matrix here carries the biotite and hornblende, which 

 minerals are arranged with considerable parallelism of position. The 

 feldspars, which are plagioclastic, are considerably more altered than is 

 shown in the slightly magnified figure. See p. 265. 



