638 GEOLOGY OF CENTRAL WISCONSIN. 



766. Granite. HUROXIAN? Near Spring Lake, Waushara county, N. E.qr. Sec. 

 27, T. IS, R. 11 E. Similar to 757 from Montello. The felspar is more or less decom- 

 posed; but this is probably local or accidental. 



859 1-2. Hornblende Schist. LAURENTIAN. Grand Rapids of Hie Wisconsin, 

 Wood count//, S. W. qr. Sec. 8, T. 22, R. 6 E. Bright greenish- black sprinkled with gray; 

 fine-grained, highly crystalline texture; conchoidal fracture; the fresh surface having a 

 raspy feel ; several specks of iron pyrites are strewn along the joints ; under the microscope 

 can be easily recognized the amphibole, and considerable orthoclase felspar; also angular 

 grains of quartz and several fluid inclusions, or small liquid-filled cavities. The speci- 

 men resembles the hornblende- schist of the Marquette iron district. 



897. Hornblende Rock. LAURENTIAX. Little Bull Falls, Marathon county, Sec. 

 29, T. 27, R. 7 E. Dark grayish- green; medium to fine-grained, crystalline texture; un- 

 even fracture and somewhat jointed. The mineral ingredieuts can not well be distin- 

 guished with the lens. Under the microscope, however, the amphibole, and plain and 

 striated fragments of felspar, are easily recognized; also, a little chlorite, and a few 

 grains of quartz. 



898. Syenite. LAURENTIAN. Little Bull Falls, Marathon county, Sec. 29, T. 27, 

 R. 7 E. Greyish-white, spotted with greenish-black; coarse-grained texture; the amphi- 

 bole and felspar are plainly visible to the naked eye. Under the microscope the felspar 

 appears to be somewhat altered, and a few of the crystals are striated. An occasional 

 fragment of quartz may be seen; also a little chlorite. The former contains fluid in- 

 clusions. 



898 a. Hornblende Rock. LAURENTIAN. Little Bull Falls, Marathon county, Sec. 

 29, T. 27, R. 7 E. Greenish-black, mottled with grayish- white; medium to coarse- 

 grained; uneven fracture; the felspar and amphibole are plainly visible. It resembles 

 very much a diorite. Under the microscope, the essential minerals are easily recognized. 

 The felspar, owing to the partial decomposition, presents a milky texture, which fre- 

 quently renders it nearly opaque. The grains of quartz, however, are clear and limpid. 

 The specimen, no doubt, is a coarser variety of 897. 



902. Silicions Chloritic Schist (provisional). LAURENTIAN. Little Bull Falls, 

 Marathon county, Sec. 29, T. 27, R, 7 E. Very dark greenish-gray, and slightly 

 tinged with bluish-black; weathers to a light drab; fine-grained texture and schistose 

 structure. Under the microscope, the section appears composed of chlorite, small 

 grains of silica, brownish leaves of mica, and a few fragments of amphibole. 



905. Chloritic Hornblende Rock. LAURENT-IAN. Little Bull Falls, Marathon 

 county, Sec. 29, T. 27, R. 7 E. Greenish-black; aphanitic texture; very jointed and ap- 

 parently schistose; weathers to a dirty drab. Under the microscope can be seen the am- 

 phibole and quartz. The felspar is very much altered, but may be recognized by a mo- 

 ment's careful observation. Considerable chlorite is contained, also an occasional scale of 

 mica. It is possible that this rock is a less altered variety of 902, and therefore passing 

 into a silicious chloritic schist. 



907. Syenitic Granite. LAURENTIAN. Big Bull Falls, Marathon county, Sec. 

 26, T. 29, R. 7 E. Pinkish, speckled with greenish-black; medium-grained texture; 

 rough, uneven fracture. The felspar is easily recognized. The amphibole and black 

 mica are scarcely to be distinguished from each other, even with a strong lens. Under 

 the microscope this similarity still exists, but the position of the optical bisectrix to the 

 principal crystallographic axis in the hornblende readily separates it from the mica. 

 The former, however, is in excess of the latter. The felspars are mostly twinned, after 

 the Carlsbad form; some of them appear, in the polarized light, to be irregularly band- 

 ed, which is probably due to an unequal decomposition. Numerous angular grains of 

 quartz are present. The rock is evidently metamorphic. 



908. Syenite. LAURENTIAN. Bic/ Bull Falls, Marathon county, Sec. 26, T. 29, 



