27 



bra. Sir II. sr, it Bztina stemi to consider that the joints^ and the change in Uic m LoLrraln^ical 

 character of the reel at their side*, must hare been produce) I subsequent to the consolida- 

 iion of lhe prariilc, since id many places lite flame joints traverse ih.: hdji rocks* Would 

 iH not be a simpler ci pollution est' Iht'se phenomena to suppose that the schistose reeks 

 were hralcd and consequently cTjMHidcd by the fluid Frranilc* — that the cm I alligation 

 and solidification of the granite commenced in a band or layer next tha surface where 

 it wuld sooner cool t and where the contact of the solid schist* the immersion of froclnred 

 portions of it in the granitic fluid „ and tlie greater di^Lurbinfj motions (I) would favour 

 rry;-!,iliinf ; — that, m -l-r such Co-mLr ioi l-s . r ■ i . i r v *cv] schfirl are 1 1 1- v i - F 1 1 j *« ■ = 1 .it the sur- 

 face; — f lial T as the Ileal escaped, or crystallization advanced^ plan en of minor tension, u]« 

 tintatcly (jiving rise fo the join c* nr plants of diseomiily, were produced by contraction, vari- 

 liTjIc motion, polar set ion, or (lie mutual action of regularly arranged spheroid*; tint [hey travers- 

 ed the sehiitoHo mass immediately ak?i: p because, Hcinjj heated by the adjacent nraniEe, any 

 effect poduccd by contraction on rcfrigeralion, the forces of crystalliialinn , or polar action, 

 would, |o n ci-rlaiiL extent , be common to bulb, and e* fended through tire superjacent 

 ftcfcist* to sonic distance because a splitting of a solid mass fcudi la extend itself 

 mechanically and the schist W&& probably in a stale of tension from the upward 

 pressure of the granitic bubble j — thai, finally, the granite bein« still in a viscid 

 s-latc when the join to Were formed t the surface of the joints became quarfcoge and 

 jichorlaceousP Why ihc granite towards the join Is should hare an excess of rru.irlx .it snmo 

 places and of nunrlz end tcharl at other places, is a question *i difficult ps it is important. 

 It may be considered under two hypotheses., either that forcirrn ingredients were not intro- 

 duced on live opening of the joints or that they were* If wo believe lhe joints fo hare 

 been formed at a period in the gradual cooling- of the fluid mass, some time prior to com* 

 plete solidification a:i<] while the crystals^ whether incipient or uiJiiiiaEe, were in a ris- 

 ■ L (.iatf rami mliHi'treiJ of motion amongst themselves (2), we shall then have a separation of 

 the mass into ^eomelriepl cubes* pri&ms a:\z, t in each of which cryntallij.aii-nn womSd proceed 

 scparalcly. if in these cubes we suppose Ihe nonsiUceous elements to hare united first with 

 the proportion* nf ftleX neoo-iry for Lhe formation of felxpar, imra otn. -in J the cry.ifals 

 ibus formed to be then attracted together lea? injj a base of vilcx for u J teriour consolidation, (us 

 seems to have been- the case, from the ifuarlx in common granite filling the iiiler^tico between 

 the other ingredients) then, if Ihrre he a considerable surplusage of i(unrti, we should ex- 

 pect to find it accumulated towards Lhe surfaces of the cubes. In llipsc eases where Schorl 

 arcompiiiiiui ih>; <ju irlx, some of the ingredients necessary to the schorl, such as boracie aeia% 



( I ) It ii trident Lfajil iWb th* %uwfm£& of a giapitjj: Uubli'i! , ■nrcULdg- up fr*m ■ rut tlniJ n-ipiflia, cim« in 

 toBtftcl wilb iriB-fCHJl ro-ck*. p*rbap« uf UCm^U*.! iriiitaniq , ihern tfiU.il Lira b*ntt greater U.J toot* f u [ablfl ffidebo- 

 nttil Ji i hi r banco- I bun id Ihi bedr at lb* bub bit, 



fS) Wi unit tuitions | bat granite txiiltJ far i e&niintcr&l-Ce p-eri-Dii in m trnuiiliaa itatt brlrwD flwEJilj islU 

 dily i- ?* m i f'ueld ar pailj iubilu» , md LLil ibd uNiajiCtt cryitik vbieb ioli^i&*i irtra n«t produced Jw-ring- 



