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bres. Sir H. de la. Beche seems to consider that the joints, and the change in the mineralogical 

 character of the rock at their sides must have been produced subsequent to the consolida- 

 tion of the granite, since in many places the same joints traverse the schistose rocks. Would 

 it not be a simpler explanation of these phcnomena to suppose that the schistose rocks 

 were heated and consequently expandcd by the fluid granite, — that the crystallization 

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

 it would sooner cool, and where the contact of the solid schist, the immersion of fractured 

 portions of it in the granitic fluid, and the greatcr disturbing motions (1) would favour 

 crystallization; — that, under such conditions, quartz and schorl are developed at the sur- 

 face; — that, as the heat escaped, or crystallization ad vaneed, planes of minor tension, ul- 

 timately giving rise to the joints or planes of disconuity, were produced by contraction, vari- 

 able motion, polar action, or the mutual action of regularly arranged spheroids ; that they travers- 

 ed the schistose mass immediately above, because, being heated by the adjacent granite, any 

 effect poduced by contraction on refrigeration, the forces of crystallization, or polar action, 

 would, to a cerlain extent, be common to both, and extended through the superjacent 

 schists to some distancc because a splitting of a solid mass tends to extend itself 

 mechanically and the schist was probably in a state of tension from the upward 

 pressure of the granitic bubble; — that, finally, the granite being still in a viscid 

 state when the joints were formed, the surfaces of the joints became quartzose and 

 schorlaceous? Why the granite towards the joints should have an excess of quartz at some 

 places and of quartz and schorl at other places, is a question as diflficult as it is important. 

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

 duced on the opening of the joints, or that they were. If we believe the joints to have 

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

 plete solidification and while the crystals, whether incipient or ultimate, were in a vis- 

 cid state and admitted of motion amongst themselves (2), we shall then have aseparation of 

 the mass into geometrical cubes, prisms etc. , in each of which crystallization would proceed 

 separately. If in these cubes we suppose the nonsiliceous elements to have united first with 

 the proportions of silex necessary for the formation of felspar, mica etc. and the crystals 

 thus formed to bethen attracted together leaving a base of silex for ulteriour consolidation, (as 

 seems to have been the case, from the quartz in common granite filling the interstices between 

 the other ingredients) then, if there be a considerable surplusage of quartz, we should ex- 

 peet to find it accumulated towards the surfaces of the cubes. In those cases where schorl 

 accompanies the quartz, some of the ingredients necessary to the schorl, such as boracic acid, 



(1) It is evident that where the surface of a granitic bubble , swelling up from a vast fluid expanse, came in 

 contact with aqueous rocks, perhaps of unequal resistaace , there must have been greater aud more variable mecha- 

 nical disturbance than in the body of the bubble. 



(2) We must believe that granite existed for a considerable period iu a transition state between fluidity nnd soli- 

 dity i. f. as a viscid or pasty substance, and that the ultimate crystals which solidified were not produced during 

 the early slages of this period. 



