Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/441

 water. “ Puteolanus pulvis,” says, “ si aquam attigit, Saxum est.”—It was a property so well known to the ancients, that the ashes of Putéoli were exported to very distant parts of the Roman Empire, to be used in the preparation of mortar for all public works, such as moles, bridges, and ramparts, situate in rivers, lakes, or in bays, and upon the borders of the sea. The excavations carried on in search of it, caused the spacious caverns and extensive subterraneous galleries, afterwards used as catacombs, in the neighbourhood of Naples and of Rome; and the same arenaceous substance has sometimes been brought even into Great Britain, to be used in the fabrication of mortar, both in ancient and in modern times. It may therefore be considered as a discovery of some importance, that we possess, in this country, a species of limestone which, when used for purposes of extracting lime, and in the preparation of mortar, is capable of communicating to the cement all the properties of the pulvis Puteolanus.

This species of limestone is found in North Wales, in the parish of Whitford, in Flintshire. Some specimens of it were sent to me by my friend David Pennant, Esq. son of the celebrated naturalist of the same name. Its specific gravity, estimated in pump water, at a temperature of 50° of Farenheit, equals 2.670. It is of a dark brown colour, and, when breathed upon, it exhales an earthy odour, denoting the presence of iron oxide, in combination with, alumine; but its colour is owing to bitumen, rather than to iron, as will appear by the following analysis, undertaken at the request of Mr. Pennant, for ascertaining the chemical constituents of this limestone.