638 GEOLOGY OP CENTRAL WISCONSIN. 



766. Granite. Hueonian? Xear Spring Lalce, Waushara county, N. E. qr. Sec. 

 27, T. IS, E. 11 E. Similar to 757 froin MonteUo. The felspar is more or less decom- 

 posed; but tliis is probably local or accidentiil. 



8.59 1-2. Hornblende Schist. Laurbntian. Grand Rapids of the Wisconsin, 

 Wood countfj, S. W. qr. Sec. 8, T. 25, R. 6 E. Bright greenish-black sprinlded with gi-ay; 

 fine-grained, highly crystaUine texture; oonchoidal fracture; the fresh surface having a 

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

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

 grains of quartz and several fluid inclusions, or smaE liquid-fUled cavities. The speci- 

 men resembles the hornblende-scliist of the Marquette ii-on district. 



897. Hornblende Rock.. LAURENTiA^vr. Little Bull Falls, Marathon county, Sec. 

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

 even fracture and somewhat jointed. The mineral ingredients 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 fev/ 

 grains of qaartz. 



898. Syenite. Laukentian. lAttle Bull Falls, Marathon county. Sec. 29, T. 27, 

 R. 7 E. Greyish-wliite, 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 quaitz may be seen; also a little chlorite. The former contains fluid in- 

 clusions. 



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

 29, T. 27, R. 7 E. Greenish-black, mottled vidth 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 .clctu- and limpid. 

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



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

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

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

 •structure. Under the microscope, the section appears composed of clilorite, small 

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



905. Chloritic Hornblende Rock. Laukentian. Little Bull Falls, Marathon 

 county, Sec. 29, T. 27, R. IE. Greenish-black; aphauitic texture; very jointed and ap- 

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

 phibole and quartz. The felspai- 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 tlierefore passing 

 into a silicious chloritic scliist. 



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

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

 rough, uneven fi-acture. The felspar is easily recognized. The amphibole and black 

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

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

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

 The former, however, is in excess of the latter. The felspai-s are mostly twinned, after 

 the Carlsbad fonn; some of thorn appear, in tlie polai-ized Ught, to be uregularly band- 

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

 quartz are present. The rook is evidently metaraorphic. 



908. Syenite. Laukentian. Big Bull -Falls, Marathon county. Sec. 26, T. 20, 



