GRANITIC BOOKS. 49 



rocks adjacent to the granitic, have suffered mechanical displacement, and such chemical 

 changes as heat only could produce. 



JS"ow all these statements are to some extent true ; and they show the presence of a 

 considerable amount of heat, and some mechanical action by the granitic rocks. But more 

 careful examination shows that granite does not generally form the axis of mountains, nor 

 do the stratified rocks dip away from it on opposite sides, but often the granite lies between 

 the strata, and instead of having been the agent by which they have been lifted up, it has 

 only partaken of the general movement, which has resulted from some other and more 

 general cause. Moreover the heat requisite to keep granite in a melted state, must be 

 higher than it seems to have possessed ; for Bischof says he could not melt it perfectly 

 in the most powerful blast furnace. Again, if it crystallized from such fusion, the quartz 

 would be first consolidated, because least fusible ; whereas it is found to have been the last. 

 Granite, also, contains not a few hydrated minerals, or such as must have been produced 

 in the wet way, and its own ingredients can hardly have had any other origin. If now we 

 admit the foliated rocks to have been brought into a plastic state by the joint action of heat 

 and water, why not admit the same as to the granitic rocks ; for often we cannot draw the 

 line between them between gneiss and granite, for instance. Their composition is the 

 same and they differ only in the schistose or foliated structure, which often is so nearly 

 obliterated in gneiss that we are in doubt whether it be present. What can granite be, 

 then, but an example of metamorphism Carried to its utmost limit ? carried far enough to 

 obliterate all traces of stratification, lamination and foliation ? If water be admitted as a 

 principal agent, heated by caloric from the earth's interior, and prevented from escaping 

 by thousands of feet of superincumbent rock, complete plasticity would result at a temper- 

 ature far below that required to melt granite in a dry state. 



By this view a large proportion of granitic rocks may be only metamorphosed schists. 

 If so, it explains why they have disturbed or changed the adjacent strata so little the 

 chemical influence rarely being traceable more than a quarter or half of a mile. In some 

 instances they may have been thrown up from the melted interior of the earth, and pos- 

 sibly in a state of fusion without water. If only five or ten per cent, of water be present, 

 it is calculated that the heat need not be so high as redness to produce the requisite 

 plasticity. 



If it be doubted whether water penetrates so deep into the earth's crust as we know 

 granite to extend, it should be recollected that the stratified rocks all of whi6h were orig- 

 inally deposited from water, and, so far as we can judge, retain more or less of it still are 

 from ten to twenty miles thick. But, if even lava owes its fluidity in a measure to water, 

 it may be supposed to be present in liquid granite with equal reason. In short, whoever 

 admits the aqueo-igneous origin of the crystalline foliated rocks, will feel compelled to 

 admit the granitic rocks to have resulted from essentially the same causes. Nor is this 

 theory very different, after all, from that which has usually prevailed. It admits fluidity 

 from heat in the materials, and only introduces water as an important auxiliary in the 

 work. It is by no means the old Wernerian theory revived ; for that made granite a 

 deposit from an ocean. 



7. Metamorphism throws lir/Jd upon the formation of dikes and veins, whether they belong to 

 iJie f/fftiiifir, trappean, or volcanic (jrovp of rocks. It does this by introducing water along 



