APPENDIX -MICROSCOPIC LITHOLOGY. ' 637 



APPEl^^DIX. 



MICEOSCOPIC LITHOLOGY. 



BY CHARLES E. WRIGHT. 



[Note. — The following deacriptions are of a small number of crystalline rocks selected from the 

 large mass of material on hand, as most difllcnlt to determine, or as having a special importance. 

 The numljers are the same as given in the hody of the report, and the original specimens will be 

 found in the survey collections, when distributed. A few of Mr. Wright's descriptions have been 

 made use of in the foregoing pages, but the descriptions of crystalline roclis there given are 

 nearly always wholly my own. It is a matter of regret that the funds were not available for micro- 

 scopic examination of a full suite of the Central Wisconsin rocks. R. D. I.] 



501. Sllicious Hornblende-Schist. Hueonian? Black river, Jackson county, 

 north line Sec. 14, T. 21, E. 4 W. Light-greenish-black; very fine-grained; crystalline 

 texture; conchoidal fracture; hard and compact. Witli the lens, niinute grains of silica 

 are plainly visible, bu£ the ingredient tninorals cannot be distinguished. Under the mi- 

 croscope, in the polarized light, a thin section of the rock presents a very pretty field, 

 and is composed of small fragments of ampliibole, minute grains of quartz, and a few- 

 scattered leaves of chlorite. From the structure it is evident that the amphibole formed 

 after the quartz, since the fonner encloses grains of the latter. 



7.57. Granite. Huronian? Village of Montelln, Marquette county, S. W. qr. 

 Sec. 9, T. 15, R. 10 E. Pale flesh-color, dotted vrith a few dark patches of mica. The 

 facets of felspar gre easily recognized. Traversing the specimen is a tliin, light-green- 

 ish seam of what appears to be epidote. Under the microscope, in the polarized hght, 

 the coarse fragments of orthoclase apparently constitute more than one-half the en- 

 tu-e section. An occasional twin crystal of felspar after . the Carlsbad form may , bo 

 seen. The ^auis of quartz are mostly very small and angular, and are frequently 

 enclosed vrithin the felspar. "With a power of 500 diameters are visible, in the quartz, 

 fluid inclusions; the absence, however, of any glass or stone-fiUed cavities wiU no doubt 

 refer the rock to a metamoiphic origin. 



758. Argillo-chloritic Schist. Huronian? Village of Montello, Marquette County; 

 S. W. qr. Sec. 9, T. 15, R. 10 E. Grayish-green; fine-grained texture; partially decom- 

 posed; cleaves readily into irregular plates; in the joints it is often ocherous; under the 

 microscope the pale greenish leaves of chlorite are plainly visible; also minute grains of 

 silica and a few scales of hematite. 



