Page:Transactions of the Geological Society, 1st series, vol. 1.djvu/190

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From these several facts we may conclude, that although quartz is the oldest vein-stone, it has nevertheless been produced at different periods under various forms.

Spathose iron, though scares, is however one of the vein-stones at Beer-alston.

But fluor appears to be by far the most common vein-stone in both Devonshire and Cornwall. it is more generally disseminated in particles, than occurring massive: it belongs almost entirely to the green variety, and differs in intensity of colour from a greenish white to a bluish-green with a dull aspect. It is of a brittle texture, and slightly coherent: it is found, I believe, in the middle parts of the vein, and is therefore of the most recent formation. It chiefly occurs in the copper mines.

Perhaps the different colours of the fluor may, to a certain extent, have some connection with the different periods of its formation. Red or pink fluor, as far as I know, has never been found but in primitive countries : it has been met within the valley of Chamouni, near the glacier of Talcul, in the valley of Urseren, not far from Mont St. Gothard, &c. The violet or blackish-green fluor is chiefly peculiar to the stratified limestone of Derbyshire, and the green variety would seem to characterize that of Devonshire and Cornwall.

Dr. Kidd mentions a bivalve shell in the mineralogical cabinet of Oxford, the interior of which is lined with imperfect crystals of transparent fluor, showing undeniably, that fluor is in some cases