Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/54

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Dr. Berger on the Isle of Man.

turn quite brown before the blowpipe, The texture of the lamellar variety is not so close as that of the other. The specific variety of the latter is 2.777, and that of the first 2.820.

The magnesian limestone that appears along Castle-town river from Ball-Fhallack towards Athol-bridge, is remarkable for a circumstance that has not as far as I can remember been yet noticed. I mean the occurrence of quartz-nodules, sometimes above the size of a pea and even of a bean. The quartz is quite glassy, and the concretions perfectly distinct, as if they had been water-worn and subsequently imbedded in the limestone itself. This is not however a conclusion I should adopt, as it seems to me that their existence may be better accounted for by way of crystallization. The colour of this magnesian limestone varies from bluish-grey to dirty-yellow; it makes a very slow effervescence with diluted muriatic acid, contains rhomb spar either in lumps or on the seams of stratification, and sometimes sparry iron ore; the latter before the blowpipe assumes the character of a slag, which acts sensibly on the magnet, whereas the bitterspath, though it turns brown, is not attractable. The powder of the sparry iron ore of a brown colour effervesces briskly with diluted muriatic acid. The specific gravity from three specimens is 2.81.

At Scarlet point the magnesian limestone has a yellowish-grey colour, and is close in its texture. Patches of compact greyish lime-stone are imbedded in it.

A dyke occurs in the limestone formation at Scarlet point, upon which I shall say no more for the present, as it is a subject which I intend at some future period to bring before the attention of the Society.

In the little bay of Purl-Keill-Moirrey, the limestone on account of its low retreating strata, imitates a sort of causeway, ending towards the high land of Spanish head.