THE ARCHiEAN ROCKS. 483 



Ft In. 



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



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



S. Granite: light- pinkish, felspathic 4 



9. Decomposed gneiss: similar to No. 7 30 . . 



10. Red felspathic seam : altered; standing vertical 2 . . 



11. Dark-green rock (991): composed almost entirely of a fine, flaky mineral, 



which appears like an altered amphibole 5 . . 



12. Granite : reddish; resembling No. 6 6 



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



fine-grained gramte , 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 crystaUine texture, and resembling much some of the hornblendic beds of the 

 section at Grand Rapids. The apparent strike of this rook 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 medium- grained, highly crystalline, grayish, granitoid 

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

 mica, the latter showing a shght stringy arrangement, can be seen with a lens. Some 

 of the dark-colored mineral may be a,mphibole. The apparent l)edding 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 mUea 

 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, eartliy 

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

 the road. Tliis 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 Bull falls, on the Wisconsm river, at Mosinee, Sec. 29, T. 27, R. 7 E., 

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

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

 On its northeast end tliis 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 tinrough 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 m tliis gorge, but has lately been 

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

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

 They are all characterized by the presence of much greenish-bla^k amphibole, and wliite 

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

 kinds were noted. The prevailing rock (896, 898, 900) is a moderately coarse-gi-amed, 

 liighly crystaUine, 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 kaoUnization 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-lustred, greenish-black color; the felspar facets are commonly whitev 



