234 ^ KOTö. 



tnkeii from siicli ;i spot give scarcely a clue as fo their true nature, 

 especially hy examining them on a fractured surface, (îorresponrling to 

 the ]>Jane of scliistosity ; hut on a face hroken across that plane, the 

 hlack components sliow a taint indication of ai'rangement in a 

 definite plane. Fn small chips, even tliis structure can not 1)e dis- 

 cerned. 



Under the microsco|)e with thin ])reparations, however, nianv 

 ])roofs of its heing affected l)y a media nical deformation l)ecome 

 evident. First of all. the uninjure<l quart:-grains a Ireadv show a so- 

 called undulatory extinction ; dixerse net-works of the hands of liquid- 

 inclusions gTov7 numerous ; and adjoining faces of quartzes among 

 themselves get more and more irregular, dis])lavinü' vivid mosaic 

 colours under ])olarized light l)etween crossed Niçois, hut not so the 

 faces adjacent to other components. Tlie innate hut latent twinning 

 lameliation of felihpars hecomes visihle l)y tliis time througli the 

 mass-jnotion of mountaiiis. The feldspars polarize in hrilliant colours, 

 and show also undulatorv extinctions akin to the connate quartz. Biotite 

 in normal granite has usually a regular outline, hut iji this transi- 

 tional rock the original form is now more or less ohliierated, showing 

 wavy l)ands, and its characteristic nacreous lustre hetween crcjssed 

 Xicols. The l)iotite is loosened and fihrillated on the side in direct 

 contact with the feldspars, and the latter specially kaolinize at the 

 adjacent portion of the mica. C(^iise((uently, the cause of alteration hoth 

 of feldsp:irs and mica is )iot mcrelij iiimospheric, hut mast he ascrihal to .some 

 inner movement of the rock. It is particuhu'ly noticeahle to find frequentlv 

 the secondary epidote (Fig. 4, XXiri). ivi conjunction with degeneration 

 of hotli mineruls, and the suhstratum necess;u'v for the formation of 

 epidote may prcjhahly have heen contrihuted hy hiotite and feldspars, just 

 as in tlie case of other react ionari' mineraU. The usual alternation of the 

 üTcen, hleached hands v^ith the fresh lamellai of hiotite makes here its 



