APPENDIX MICROSCOPIC LITHOLOGY. (839 



R.7E. Gray, thickly speckled with black; fine to medium-grained; rough, uneven 

 fracture; the felspar and hornblende are plainly visible to the naked eye. Under the 

 microscope, each of the above minerals is easily recognized. The felspar fragments 

 are chiefly plain, though a few of them are beautifully striated in one direction. Very 

 little quartz is contained. 



910. Syenite. LATJRENTIAN. Big Bull Falls, Marathon county, Sec. 35, T. 29, R. 

 7 E. Same as 908, but coarser grained, and some of the grains of quartz contain cavi- 

 ties filled with a salt solution, out of which have crystallized small, transparent cubes of 

 salt. The small bubble and crystals are easily distinguished from each other, even 

 when the comers of the cube are rounded, by the difference of their refractive indices. 

 Scarcely any motion is perceptible in the bubbles, even when heated to 130 C. 



915. Silicions Hornblende-Schist. LAURENTIAX. West bank of Wisconsin 

 river, north line Sec. 26, T. 29, B. 7 E. Grayish-black; very fine-grained, arenaceous 

 texture; jointed and irregular fracture. Under the microscope, in the polarized light, 

 the section appears composed of a silicious base, interspersed with fragments of am- 

 phibole, felspar, and dark colored mica. The felspar is of two varieties, one in small 

 striated fragments, and the other in large plain ones, which are very much altered, fre- 

 quently so much so that only an indistinct outline remains. 



932. Chloro-Silicious-Schist (provisional). LAURENTIAN. East Bank Wis- 

 consin river, S. W. (jr. Sec. 1, T. 29, R. 7 E. Grayish-green; aphanitic texture; 

 conchoidal fracture; slightly banded. Under the microscope the greenish chloritic 

 base is interspersed with small angular grains of felspar and silica. An occasional patch 

 of ealcite may be recognized. 



9 32 a. Very Silicious Marble 1 (provisional.) LAURENTIAN. East bank Wis- 

 consin river, S. W. qr. Sec. 1, T. 29, R. 7 E. Grayish-green; aphanitic texture; 

 conchoidal fracture; slightly banded. A fragment thrown into acid effervesces briskly, 

 for a time, without disintegrating. Under the microscope it presents an indefinite 

 fringy base, strewn with small crystals of felspar, grains of quartz, and greenish leaves 

 of chlorite. 



948. Chloro-Silicious-Schist (provisional). LAURENTIAN. Falls of Big Rib riter, 

 Marathon county, N. E. qr. Sec. 28, T. 29, R. 5 E. Resembles 932. Under the 

 microscope the base of the rock is composed largely of decomposed crystals of felspar; 

 scattered in this are numerous fragments of amphibole and leaves of chlorite. The rock 

 is apparently an altered hornblende-schist. 



948a. Chloro-Silicious-Scuist (provisional). Same place as 948, to which it is 

 closely similar. 



950. Syenite. LAURENTIAN. Falls of Biff Rib river, Marathon county, N. E. qr. 

 Sec. 28, T. 29, R. 5 E. Light- pinkish-gray, mixed with dark-gray and black; medi- 

 um to coarse-grained, indefinite texture. A few crystal- facets of felspar may be recog- 

 nized, but they are mostly too much altered to have preserved their cleavage. This 

 altered condition is very apparent under the microscope, where the section appears 

 thickly strewn with indistinct outlines of the altered crystals, though some are quite 

 fresh. The amplibole is also somewhat changed. A few angular grains of quartz are 

 present, and they show liquid inclusions. 



952. Granite. LAUREXTIAX. Falls of the Big Rib riter, Marathon county, N. E. 

 qr. Sec. 28, T. 29, R. 5 E. Grayish-white, spotted with dark-green; medium-grained. 

 With the loupe, small, glassy grains of quartz may .be recognized. The felspar is so 

 much decomposed that it shows but little signs of cleavage. Under the microscope the 

 crystals of felspar are grayish and indistinctly outlined. A greenish chlorite is contained, 



i This rock is merely a phase of the preceding one (932) moat specimens of which show no 

 effervescence with acid. it. D. I. 



