I 



B 



l heir Taryinrj mmrnlnjrieal eharador, and, in foci, to h* an effect of the same tmuw. At 

 the Tomnjy crp-Eallii-alian of ilia rocks icemcd to reject the distinction of pluEonic and *c|- 

 canic so their striuM n m not only flpproiitnalog to Hist of bolh those divisions ^ but even 

 partake*, often in a striking manner , of iWt winch cbar acteriars same of the principal 

 members pf what Mr. Li&ll term* Ihe I amorphic M)rieft The ailcraiitLori of bed* or zones 

 of different compost* ion , and the approach,, where mica abounds., to the structure of j^ieix^ 

 frequently ossirnilnto I hem to rocks uf thnt series while Ihe predominance of granitic types, 

 aed the general character of the whole rocks ^ demonstrate llicir direct origin from igneous- 

 fusion. The clone approiimntion of this develop i.*mcnl of Ejj neons icckd u£ Nome of it* points 

 to certain point* in ^ticiissosc developments will be mora parlkukrly considered iu the 

 -qneJ (I), 



Sonic Geologists appear still la doubt whether {jranalc em-r has nn original concretionary 

 structure. Tliuv Sir If. ns 1A lkcm in hi« valuable Import on the Geology of Comma U t 

 Dwan and VKmJ S&mcr*ct (p. 4iM>) In reference to the del ached block a, protruding rocks t 

 and hollow* called rock bruins, which abound in the rjramlic ItqcI* of (U.kt district f says 

 that, after I]qyi]mj Jjiven milch attention to ibe subject, ho in- far from perceiving good evidence 

 in favour of UiEf opinion that, the fllobulnr blocks are owing to ml original cone rcf inn ary 

 arrangement of the granite. He adds, that after ranch careful ohscrvajion be is inclined to 

 refer the rounded character of a lor^e proportion of the blocks t either ecatlrred oror the 

 surface or still enisling in the tors of the granitic district* , more to the doftompotiJion of 

 surface* produced by divisional planes Ihau to any oilier cause. Many or the exposed jjroflite- 

 blocks Oii llio Pinany mountains aro rounded at Hie edges, and this is undoubtedly lliero 

 ihe result of mere weathering. That eut ori(j i nally an^uLr block must disintegrate more 

 j-- 1 1 ■ : - J I v oti ihe eiljj&s than elsewhere is evident j for 5 here two fnce* both subjected Iti inelccK 

 rie aelion approximate and meet f rd that the edfle decomposes quite through, and being in, 

 every fall of rain eonrcrtcd into the summit of a pelly waterfall, the name mechanical pro- 

 cqi* which, on a grand seals, \s wasting the clilEs of Niagara, wears down the diH.:o-m po- 

 sing ed^o lul such an operation would not eiplain the occurrence of really ftlobub* blocks, 

 and oi these arc aecn on Palo Ukin in the very act of iejtarnl fjrom the ore^inoJ compaoi 

 raa&es in whieli they Itad brcrn formed t and eipostn^ I ha concentric co^l5 of wliicb tliey 

 const >1 F the fact of granite assuming this structure under certain condition! in mailer of 

 ocular demonstration. Tlic factj itowever, is not new, for aUhou^h it not noJictMj by- 

 Lt«. frfiLun, or any other of our recenl En^ii^li writers on ihe plntonk rocU wiih 

 woom tmprks I am acquainted K and Sup l| h m m llnona i« cYidetittv nor u^arc thnl a concen- 

 tric laminar structure had ever been dclujHy cU'rTcd in ([ranite f it it distinctly mentioned 

 by one of WKftMit^ pupils, the matt able and learned of out few minerulopati, Professor 

 Jimmm of Edinburgh, in his article on mineralogy nnd neology m the EiHnhunjk Ency- 

 rfopwitifi f and j| sterns lo be aSso well known to many coniin^iiUd [jco1i>[[lsSs Hrofestor 

 liHKoa ki^- p Some fjraniiis arc dUposcd in rounded balls or cnucreLiaus , wlikh are from 



