Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/102

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Dr. Kidd on the Mineralogy of St. David's.

it would be improper on the present occasion to enter into the particulars or on the defence of those grounds, I think it respectful to the Society to be silent on those points.

I may however with propriety add, that from communications with very competent judges, aided by the inspection of specimens which they had themselves collected, it is clear to me that the geological phenomena above described are of very extensive occurrence. In Jersey and Guernsey for instance, in various parts of Devonshire and Cornwall, in North Wales and Cumberland, in the neighbourhood of Mount Sorrel in Leicestershire, in all these places severally, is found an assemblage of rocks of a decidedly crystalline character, and consisting of hornblende and felspar, associated with rocks either of a schistose structure or resembling a more or less fine-grained conglomerate, intersected not infrequently by masses of a porphyritic character, and sometimes passing into serpentine.[1]

In the decidedly crystallized rocks of these suites, consisting of hornblende and felspar, the felspar sometimes predominates and is of a red colour, in which case the compound is usually, I believe, called sienite; but the same term seems justly applicable where the hornblende predominates and the compound is of a black or of a green colour, for the two varieties insensibly pass into each other.

The opinion which I have here ventured to express of the natural alliance between the various rocks above described is strongly supported by its correspondence with the opinion entertained by M. Godon respecting a similar class of rocks occurring in the

  1. The transition of the natural compound of hornblende and feldspar into serpentine has been observed in Cornwall, and is satisfactorily shewn in specimens brought from thence and deposited in the Ashmole Museum; and the opinion of the natural alliance of these two rocks is strongly confirmed by the inspection of numerous specimens brought from the coast of Labrador and deposited in the same Museum.