THE SOUTHERN COMPLEX, 107 



this is secondary saturating quartz. If the latter is true it becomes not 

 impossible, although hardly probable, that the independent (juartz in tlie 

 interstices of the feldspar is a secondary material, in which case the original 

 rock would have been a syenite. 



All of the minerals are more or less altered. A kaolinitic decom- 

 position has widely affected the feldspar. Less frequently chlorite and 

 mica have developed within it, and the chlorite has further partly chang-ed 

 to epidote. But the most interesting decomposition shown by the feldspar 

 is an alteration into quartz and l)iotite. This alteration has occurred to 

 some extent in quite a number of the rocks, and is verv clearly shown by 

 the gneiss a short distance west of the south quarter post of Sec. 23, T. 44 

 N., R. f) W., Wisconsin (PI. xiv. Fig. 2) on Marengo river. Here the large 

 individuals of feldspar have each decomposed in a great measure to the 

 more basic mineral biotite, the excess of silica apparently separating as 

 finely crystalline quartz, so that a single feldspar contains many score folia 

 of biotite and grains of quartz. In certain parts of the section this decompo- 

 sition has gone on until little or no feldspar remains, the result being a 

 finely cr^'stalline interlocking aggregate of quartz and biotite in place of a 

 single grain of feldsi)ar. In other words, a somewhat coarsely crystalline 

 strongly feldspathic rock — the normal phase of granite — has changed to a 

 finely crystalline gneissoid biotitic quartz rock. It is interesting to note in 

 this connection that these are the identical changes which have, in the tipper 

 belt of the Penokee series, changed a feldspathic fragmental rock to a 

 crystalline mica-schist. 



The Western qreen schist. — The exposures within this area are com- 

 paratively few in number, particularly in its western half The rocks are 

 quite finely laminated, dark colored, fine grained, crystalline schists. 

 They are, then, in strong contrast to the coarse grained granites and gneis- 

 soid granites to the westward. In different parts of the area they huve 

 very different characters, so that they can not be descrilied together. 



At Bad river the schistose rocks are technically all gneisses. T]ie>' 

 have a strike which is nearly conformable to the strike of the overlying 

 Penokee series ; but their dip is south instead of north, and hence they 



