266 Geological Excursion into Central Wisconsin— Hall. 



varied in places by a tendency to form chlorite to a greenish hue. 

 Joints are in two groups; at Trapp city the major one showing a 

 direction N. 85*^ E. mag., and at Kickbusch N. 15° W., and in 

 both places nearly vertical. 



Judging from lithologic evidence all these granites arepoorin 

 lime and magnesia. While there is a fair proportion of triclinic 

 feldspars they seem to have the low extinction angle of the al- 

 bite-oiigoclase end of the series. In the mineral changes going on 

 some small, fresh, secondary areas have been formed which are 

 seen lying in the quartz mosaic fringing the large and primary 

 individuals. In a few cases an enlargement of these old albite in- 

 dividuals was seen where fresh limpid material was added to them 

 in crystal continuity and apparently at the expense of the micro- 

 clines and orthoclases. If this observation be a valid one, its ex- 

 planation would doubtless presume the disappearance of the potash 

 from the potash feldspars and its replacement by the soda lime 

 constituents of the albite-oligoclase members.* Prof. Van Hise 

 some time ago noticed the enlargement of feldspar fragments in 

 certain clastic rocks of northern Michigan and Wisconsin.f 



These granites are highly silicious. Large areas of clear 

 quartz can anywhere be seen and much in the form of microcrys- 

 talline aggregates also occurs. The basic constituents, hornblende 

 and biotite, are far from abundant, yet they occur in about equal 

 proportion. Occasionally, and particularly in the quarry at Kick- 

 busch, there are thin seams or veins of segregated mineral matter. 

 While it is suspected that most of this matter is chlorite still horn- 

 blende is present as is altered pyrite and a uniaxial mineral which 

 is possibly zircon. 



There were some evidences of pressure noted among these 

 granites such as bent feldspars and lines of fluid inclusions. The 

 latter are particularly noticeable as they extend entirely across the 

 slide, through quartzes and feldspars alike. No marked lamina- 

 tion was noted in the exposures visited. 



The Schists. — Under this name are grouped rocks of quite 

 diverse characters, both macrocrystalline and microcrystalline. 

 There are, on the one hand, rocks which, although squeezed and 



^Compare Sauer A., * * * sowie ueber Neubildung von Albit in 

 granitischen orthoklasen, Neues Jahrbach, 1889, Band I, Referat, S. 203. 



IBulletin No. 8, U. S. Geol. Survey, p. 44; also Amer. Jour. Sci., 

 May, 1884. 



