31 



rtititra {\), There is a souwc less remote of motion in tins upper portion of volcanic and pi u- 

 tonic fluid or semi-fluid masses which 1 have liot sren noticed by geoloniHts. When the s uperin- 

 ctircibent strata were fractured in NW. ~ SE. lines ^ and the fluid mass preyed into the 

 opening*, the adjoining pari torn would acquire a temporary motion towards the opening or 

 ii n-;ljr n [jles lo the I tries of fracture. In all eases of pin Ionic elevation there must either 

 be a slow continued motion upwards as the ilrala insensibly gire way to tlic pressure F or an 

 accelerated motion when great rcnls in the ft rata are abruptly produced, In most cases the 

 xUcid gran i 1 ic m;i.-yi lias probably been of too great extent, and the motion too slow and uni- 

 form, la vc rise to any van jbkijf£> of sS mi:E lite. 



If a motion , however induced f of I he iffneons fluid from SW, to SE, be assumed t ihis 

 iiljcrmilitms which we £iud in tlie Palo Uhin recks ^ in band* running SW, - BE, , might 

 perhaps be explained on the same principle by which Professor Fo&n&a accounts for the viscid 

 mass coTiHtilul in^ .t ^ladtf be- In;* j.rjm-d in lliu dl reel ion of its length > — an explanation which 

 Mr. D.iiiivrj has applied to the lamination of volcanic rocks or the trachylic series. Jn the 

 case of the PWa roeirs^ the general agreement hi direction between the zones of 



vadable mineral character and the principal joints , renders it in a ln;r,li drrjrnc proba- 

 ble f if not certain! that, ir not contemporaneous in origin , the continual action of the 

 uimc cause superinduced holh. This cause must hare beyun to operate when the mnss 

 was in rt fluid or viscous slafe. Xow as name toned fjlt£d&r$ are of great bulk as many 

 exposed rrraniiJe masses , such as those of Cornwall or that of Puto Ettm« we may safely 

 consider that the* influx of a viscous body of granite into feu res (rradually enlarging into 

 Great taviliea 3 would , at least seme I vines , under a certain range or motion , and where the 

 conditions n^irnilaied to those of (jlaeieT motion f ho attended with mechanical structural 

 effect* somewhat similar to those observed in glaciers, and repeated in the experiments 

 made by Profcsscr Fo&«(ta on other iri*eid mbriidtot** The condition* under which pi u tonic 

 m.w rile must Tary very greatly f but there is no difficulty in believing that they some- 

 times , fiml particularly in raissi'S of no great bulk, approximate: HUnkieully, lo LtnsHc whieh , 

 in glaciers , produce parallel bands of variance tension j vertical towards the surface. 



Reverting now to the analogies between the roots of Pulo Ukin and rock* of a decided 

 rrncisso&c structure (2) J let mc request that , in reference to this subject f the proceeding dis- 

 cussion be kept in view* Mr, D^swis remark* \hat such facts as the vertical vt highly in- 

 clined lamination of fclspalhie rocks, such as be observed at the island of jisccttjieti, and 

 which exist elsewhere , a are manifestly of importance with relation to the structural origin 



rt) Jo tlifr neii rtetil iniianra- sf un tnrlaqnik* of rithI ji^mtr , — thtl *ipi?ri#D*ad ca lb* wtui cvul of 



Svuih JjA+Pica iu Jft35 fib |iUin«n<<fi4 ef irbieb elMrlr pr»TflJ |b& iAdnliL^ t?f fUrLomc and T*fcwic psv«r ■ — 

 ihe uTidubl ii>:n jspfiejr la tavd> (if^ccd ii ?4 froiv I kg S\T. nJiti g ebBMqacflilr ia HWi . > SE» HfHi Mr, 

 Dakvij uyi: ■ TJifr fiuprr* ia Die gr«nnd g*iieraLEr„ ibonijli oat uaiTor mlj . citta^cd in a SE. aad NW. 

 diratliaa and tbtrt/dre cot i m| ...iiddil to Jjr.ci of umjuliliitu m of principal Jt. iu-*. M Dipwii i JvurKai pi 3|1 

 (2d. «tL] 



