322 THE PENUKEB lEON-BEAlUNG SERIES. 



Tlie two siiecimens differ in appearance. The first is almost black, fine grained, 

 and finely laminated. The second is srsiyi coarser grained, and massive. Both 

 contain shining fiakes of white mica. 



In slide 5403 rather snuill fragmcntal particles ot quartz and feldspar, with 

 a few flakes of white mica, compose two-thirds of the section. The quartz grains 

 arc often enlarged. The feldspar comprises orthoclasc, microcline, and plagioclase, 

 the latter very ])lentifnl. All the feldspars have altered considerably to chlorite, 

 sericitc, biotite, and qnartz, chlorite being the most abundant. The remaining one- 

 third of the section is api)arent]y composed of the same minerals as the coarser jiarts, 

 with the addition of pyrite, opaque iron oxide, and a little of some carbonate. Slide 

 5402 differs fnmi 540.3 in that its fragmental quartz and feldsjiar are in much 

 smaller particles, in that the latter is more altered; and in containing more ferru- 

 ginous and perhaps some carbonaceous material. 



3.'3. Chlorite graywacke-slate, from a middle horizon. Specimen 12770 (slide 

 5400), near center SW. i of SE. i Sec. 29, T. 45 N., R. 1 W., Wisconsin, on 

 Wisconsin Central Eailroad. 



The rock is precisely like 12773 in 32. 



The thin section is in no important point different from 5403 in 32. 



34. Chloritic graywackes, from a middle horizon. Specimens 2108 Wis. (slide 

 387), 1000 N., 7S4 W.; 9011 (slide 3341), 1000 N., SOO W.; 2104 Wis. (slide 300), 1000 

 N., 784 W.; 9013 (slide 3342), 11.50 N., 775 W., Sec. 28, T. 45 N., E. 1 W., Wisconsin. 



The rocks are light gray, rather fine grained, and cleave most readily along the 

 jdane of stratification, although easily breaking across this plane with a conchoidal 

 or subconchoidal fracture. 



In thin sections, well louudcd clastic particles of quartz and feldspar are set in 

 a fine matrix, consisting generally of quartz aud chh>rite, but containing some kaolin, 

 biotite, and brown and black material which is taken to be ferritc, mingled perhaps 

 with pyrite and organic matter. The fraginents of ijuartz are frc(iucntly enlarged. 

 The feldspars are often quite fresh, but nuich of this mineral is altejed to chlorite, 

 kaolin, and biotite, with simultaneous separation of silica. 



35. Biotitic graywacke-slate, from a middle horizon. Specimen 9(527 (slide 3343), 

 15.50 N., W., Sec. 29, T. 45 N., II. 1 W., W^isconsin. 



A dark gray aphanitic banded rock. 



The thin section is exceedingly fine grained. It consists of a confused mass of 

 quai'tz, feldspar, chlorite, biotite, and ferrite, with jicrhaps some sericite. 



.30. Chloritic biotite slates, from an upper middle hori/.on. Si)ecinieiis 0000 (slide 

 4428), 100 N., 1525 W.; 9010 (slide 4429), 140 N., 1540 W.; 2098, Wis. (slide 304), 

 «outh line Sec. 21, at point where intersected by Tylers fr>rk. Sec. 21, T. 45 N., K. 

 1 W., Wisconsin. 



