THE ARCILEAN ROCKS. 483 



Ft In. 



6. Granite (995) : similar to No. 4; holding veins .and masses of quartz 10 



7. Decomposed gneiss : similar to No. 5 20 . . 



8. Granite : light- pinkish, felspathic 4 



9. Decomposed gneiss : similar to No. 7 30 



JO. Red felspathic seam : altered; standing vertical 2 



11. Dark-green rock (997) : composed almost entirely of a fine, flaky mineral, 



which appears like an altered amphibole 5 



12. Granite: reddish; resembling No. G 6 



13. Decomposed gneiss: contorted ; holding seams of quartz and partly altered, 



fine-grained granite 75 



Total.. 204 10 



At the south end of the railroad bridge at Knowlton, in the north part of Sec. 29, T. 

 26, R. 7 E., is a cutting 100 feet long, and 5 to 10 feet deep, through rock. The northern 

 portion of the cut exposes a fine-grained, blackish, hornblende schist (890), having a 

 distinct crystalline texture, and resembling much some of the hornblendic beds of the 

 section at Grand Rapids. The apparent strike of this rock is N. 55 W., and the dip 

 60 N. E. Its horizontal width at right angles to this strike direction is about 40 feet. 

 The remainder of the cut is in modi um* grained, highly crystalline, grayish, granitoid 

 rock (889), which -weathers white. Quartz, white felspar, and dark-colored, small-flaked 

 mica, the latter showing a slight stringy arrangement, can be seen with a Ions. Some 

 of the dark-colored mineral may be amphibole. The apparent bedding of this rock co- 

 incides with that of the preceding; and its horizontal width is also about 40 feet. 



On the wagon road between Knowlton and Mosinee, on the east side of the Wis- 

 consin, several small and indefinite exposures occur of decomposing fine-grained rocks, 

 resembling those observed on the line of the Wisconsin Valley Railroad. Two miles 

 north of Knowlton, where the road ascends a high ridge, exposures occur of a fine- 

 grained to aphanitic, dark colored, slaty rock (892.) This rock is pyritiferous, and dis- 

 tinctly attracted by the magnet in coarse powder; it weathers with a dirty- white, earthy 

 surface. At 3.7 miles north of Knowlton, another exposure, of a similar rock, occurs in 

 the road. This rock (968), according to Mr. Wright's microscopic examination, is com- 

 posed of chlorite, altered felspar and magnetite. These exposures were all too poor to 

 show any definite bedding structure. 



At Little Bui) falls, on the Wisconsin rivor, at Mosinee, Sec. 29, T. 27, R. 7 E., 

 Marathon county, are quite large rock exposures. The river here is divided into twa 

 widely separated channels by a high rocky island about a quarter of a mile in width. 

 On its northeast end tins island is itself cut by several smaller channels, dry at low water, 

 which show high walls of bare rock. Most of the water of the river passes through tho 

 easternmost channel, which in one place, for a distance of 130 feet, is a gorge only 35 

 feet wide. The main fall of the river was formerly in this gorge, but has lately been 

 moved down stream by a dam erected below. The rocks of the various' exposures at 

 this place aie all closely allied and may be designated by the general term of syenite. 

 They axe all characterized by the presence of much greenish-black amphibole, and white 

 striated felspar, the quartz, though present, being always subordinate. Two general 

 kinds were noted. The prevailing rock (8%, 898, 900) is a moderately coarse-grained, 

 highly crystalline, syenite, with a greenish-gray, mottled appearance, and without 

 any sign of parallel arrangement of the various ingredients, which are uniformly 

 intermingled. On a weathered surface this rock appears greenish to white, the 

 latter color being due to a kaolinization of the felspar. On a fresh fracture the two 

 main ingredients are readily perceptible to the naked eye. The hornblende is usually 

 of a bright-knitted, greenish- black color; the felspar facets are commonly white 



