Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/444

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Dr. Mac Culloch on the Geology of

crystal. It is perfectly evident, that whatever is true of the above cited granite veins, must also be true of this rock, that the schorl has been crystallized, then broken, and penetrated by quartz in a state of fluidity. Nor is there any intermixture of the matter of quartz, with the matter of schorl, but the line of separation is most accurately drawn between them. It follows then from these circumstances, that the rock in question is not a simultaneous formation from a state of fusion, nor can we readily understand how it can be the effect of fusion at all, consistently with the chemical principles we acknowledge. Had such a mass of fused quartz invaded the minute fragments of schorl which the specimen exhibits, the latter must either have been fused into a shapeless mass, or at least the asperities of fracture could not have remained in a substance whose fusibility is so much lower than that of quartz. Those who attribute the formation of this rock to aqueous solution, will perhaps in the above mentioned specimens find arguments in favour of their hypothesis. I will not repeat the often quoted difficulties which attend this theory also, but request from it an explanation of the remaining specimens.

The first of these is from the same vein at Portsoy, and contains an acicular and detached crystal of schorl, which is bent without fracture, so as to form a considerable curvature.

As chemistry produces no examples of incurvated crystallization, I may safely conclude that this crystal has been bent by external force after its formation. The noted fragility of schorl will not allow us to suppose that it could be bent without breaking, unless it had been previously rendered flexible by some chemical agent possessed of powers which we have not hitherto discovered in water.

The other specimens are not from Portsoy, but from an interior part of the country, and exhibit appearances equally irreconcilable