Tin- extinction is of course parallel to the length o!' Mir prism. 

 Apatite occurs in IOIIL; colourless prisms, as inclusions in nil the other 

 minerals. It, is especially conspicuous in the hiotil.e. 



Hocks of a diorilic character are extensively <|eve|o|>ei| iii the northern 

 portion of the Mahern ran-e They consist of felspar, <;reen hornblende, 

 biotile, titaniferous iron ore, sphene, quart/, apatite, chlorite and epidole. 

 The felspars are generally more or less turhid. I'nder crossed nicols the 

 t.urhidily is often seen !< l>e due t,o minute scales of a vividly polari/in^ 

 mineral. In some cases I. In- felspars ha\e lieeii replaced by inl erlacni", 

 a<rorcn-a.tes of while mica a,nd a colourless granular mineral of hi-h 

 retract ive and double-refractive power (epidole.') Yellowish pleoehroie 

 epidole is usually present and sometimes one and the same individual may 

 he seen to he coloured in one part and colourless in another. The 

 pleoehroism of the common liornhlende is as follows a, brownish yellow ; 



(9 and 7, rich deep green. The hornblende often passes into chlorite \\iih 



which epidole rauules, opacile and terrile are associated. The spheiie 

 rarely shows j^ood form. I n some slides I, he grains or imperfect, crystals of 

 phene contain nuclei of iron-ore, the relations of the two minerals hem- 



similar to those described by YKI.AIN (l) as occurring in a hornblende -neiss 

 from Siberia, (^uart/ is present in variable ipiaiilily in the form of Bruins. 

 Apal ile is sometimes very abundant in tolerably thick prisms. Strongly 

 pleochroic Inoi ile is sometimes present, sometimes absent. Kpidole not 

 only occurs in the rock, as already mentioned, but. also in I he form of veins 

 The rocks are often ^neissose in si rud ure and they exhibit, a consider 

 able amount of variability so far as the ivlali\e proportions of the 



constituents are concerned. Some are thoroughly basic in ohftraoter owing 



1,0 tile preilolllllialiee of t lie ferro I : la- liesia 1 1 constituents, others form a 



kind of transition between the intermediate plulonic and the acid plulnjc 



ell'ei't thill, is with its HIM jnr Mliil lililiur IIM-S u!' <lepnhiri/.Ml inn nl nutrli <! I < In the phine-, if 



polarization of the polarizer and inmlyNer. \W then slide in tin- c|iiari/,-wcil^c between the 



:m.-||\ -ier Mini the e\ i pi. , < , I iikillX' rare In IT|I it s li'iltfl li ini'li III! l> lu I lir en IMN \viri-M. If 



ii'lr il III HIM \\;i\ We llliMCI \ ( llllll, I lie rll'rrl \H, 1,1) TIMNC tlic (illls lit' I III' Ml -rl.il III III N I'.WTl P.N ' )> 

 Mill I it' V\r si I ilr it ill 11 UlIT WIIV (lit ri^llt, Illl^li-'. I" I III' t'nr ') \\r nliMiTVr I li:ll (1 1C I'tl'l'c), 



is (,IP ili-jirr.sM tlif lint.M. Iii tin' Iii II IT ni MC 1 1 will not. lie ih Mi in 1 1 Iii II 111 1 ii i ii >'. 1 1 111 \\-liirli rompm 



:I!MIII |,II|< ( 'M pla(!0 and l.lir Mivliuii npprni-H il:irl\. Nnw ill thin |iiiMili<in lln- nmjur :i\in 111 I!M< 



iredgG li |i:ii:illrl Iii I In- iiiinur :i \JM in (In- .'-IT! inn :iml \ irr \ n ,i , I In- ilin-rl i I III. i . 



ill tin' Wi'il^' 1 lirill^ UlUiWIl, (.llii.sr ill ill.- Mi'i-liuli lilliy In- lit, iilli'i- ill d IIMMM .1 



II ire make thil ODMrration 00 ;m\ iini:i\inl minrnil lyin^- witli HH iipliit iixin |iunillil u i 



approximately pnrallcl to the stage of Uie miorocoope we can at oiu'r hinic wliriln-r ilm <i.,ni,i. 



n-i'nii'ii.ui ni' the mineral ii positive or negative, ir tin- HIUMM- U\JK in tin- i-ryMini \\,->< |,M,II,I 



With the Optic ax in fas in <|inirt/, I lir i Inn I ! n l'r:n linn IM | , ulur ; it' tin- niiijnr IIXJH licw |..n ill. I 

 Iflth the Optic :i\in (MM in n|i:ilili-j lln- ilnnhli- ivt'i'Mi-l inn i.-, nc^nl i vr. AMHUIIHIIK the Mtrnn>fly 

 refracting and .strnn^ly double-refracting minrnil inrnliniii-il nlinvr In In- nnin\i;il, \\i' I-MII hditi' 

 tteflnitely tint li ' dnnl.li icI'i'Mi-linn in positive mill this IIKI'ees willi /iri'iili. 



I In i-lninii-ler of I ln< ilonhlr rcl'nicl ion in liin \iiil niinenilH c.Mniiol. lie ilrli-r'niin-il in lliiM wn\ 

 1 1 II less we Know Ih.'ll t lie M-rlinn in (|lli'Hlion eon III ins I lie Mi'llte Iii MI 'i -I ri \ MIII I null ! u e ;il o lvim\\ 

 '" Vhioh direction the in-nle liisee||-i\ lies. TIlIlM we eiimiot. ll isl in^lliNll eliHljilili limn 



ayperntheno by thiM method, although we e:m i-;<i\\ |im\. il i:i i in lon^itmliiiMl MeetimiH of the 



rhombic [>yroXOIIO the minor M\is of ilejioliiii/.nlion M|WII\.< eoineiilen wild the len;..||i of the 

 Motion tlinl is with t.he vert,ie.nl M\i.n of tin- eryntMl. In other wonln we I-MII prove I hut r '/. 



(1) B.8.G., :;r,l S,.., Ton,,- \IV. nsH.'i). p. n.. 



