On fhe Cri/stixUim- Slruvltin' of /Ac 



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case, l\(is(' ooiicl ^ul^^^ {\\c\ imoht \o bo liH)ko(l upon as iho s;mu\ ;iuil in. 

 ohuleil in Olio class; of (lio propriol y of \\hicli slop, tlio prccodinL;- re- 

 marks soem to leave but liltle tloubt. These experiinenis are luosi, int(M-- 

 cstiiig-, wlien viewed as furnishing us with a stantlarJ of comparison, by 

 which we may form some idea, of the dirterent times retpiired for I lie 

 production of ditierent minerals in nature. The rate of coolino- may also 

 be estimated, from the peculiar forms assumed by the minerals produced, 

 as for instance, in the sienite, so frequently mentioned in this paper, the 

 ingredients of wliich, the quartz, felspar, and hornblende, are all known 

 to require slow cooling for their production ; and, therefore, we conclude 

 the sienite to liave passed very gradually, from its highest point of tem- 

 perature, down to its present state— similarly, with reference to the tr.q> 

 dykes under con^^idcration, in wliiidi hornblende and mica prevail, sub- 

 stances also requiring slow and gradual cooling for their production. 

 Tlie earliest experiments on rc -ord, by which the connection between 

 the ciystalline structure, and the application of heat was exhibited, are 

 those of Sir James Hall, in i/98: in 1801, Mr. Walt pursued the same 

 subject in greater detail, while in our own diy, WoUastone, Millen, and 

 Haidenger, have been occupied in the sime train of research. T do not 

 intend to enter farther on this point, since enough has been addui ed to 

 prove the analogy subsisting between these operations of men in their 

 laboratories, and those due to the action of the general laws by whicdi 

 God governs the material world, and which arc included in the three 

 first classes. 



Now, the general and connecting link of the whole series of pheno- 

 mena above described, is their dependance on the application of tem- 

 perature, but, it will readily be observed, it is not so much on the abso- 

 lute degree of this, to which the substances exhibiting them have been 

 subjected, that the phenomena depend, as iipon the fact, that the original 

 temperature has undergone variations of greater, or less, extent. Had 

 the original heat appHed, remained the same, only the effects due to this 

 would have been exhibited; as, for instance, if the heat had continued at 

 the points of fusion, or of viscidity, the bodies, of course, would ever 

 have remained in a fluid or viscous state : but, the gradual diminution of 

 the temperature has given rise to new, and striking phenomena, depend- 

 ant on it for their development, and following it invariably, as effects fol- 

 low their cause. Assuming then for the present, that, as a natural law, 

 including a certain series of phenomena, provided disturbing causes are 

 not in operation, " signs of crystallization will follow on a body, kept 

 in a fluid or partially fluid state by the action of heat, again becoming 

 solid," it is natural for us to enquire if the law can be extended further, 

 and be rendered more general in its expression, and application. And 



