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Places, indeed, in which Ptimices are produced, ſeem to teſtify the Manner of their Formation; for they are principally found about the Craters of the burning Mountains. On the whole, ſome Kinds of them, perhaps, may be formed by the Action of Fire on Stones of a proper Texture, and others in ſome other Manner: for there are in Nature many different Ways of Production[1].
XXXVI. The Pumices in the Iſland of [2]Niſuros ſeem an Inſtance of this,
- ↑ That all true genuine Pumices are formed by the Action of Fire, I believe, is an unqueſtionable Certainty; but as the antient as well as modern Naturaliſts have often confuſedly placed among them, and under their Names, other Stones of different Kinds, and abſolutely different Origin, though ſomething reſembling them in external Figure, the Author does very judiciouſly here in alloting a different Proceſs of Nature for the Formation of ſuch.
- ↑ Theſe Pumices, as they are called, of Niſuros, ſeem not only an Inſtance of the different Operations of Nature uſed in the Formation of the different Pumices; but of there having been Stones of wholly different Kinds and Origin ranked among them. The Deſcription the Author gives of them, proves them to be no genuine Pumices, but Tophi; natural and original Nodules, or looſe Maſſes of Matter; covered with a Cruſt, as moſt of the natural Nodules are, but none of the Pumices ever are ſeen to be; nor, indeed, is it eaſy to be conceived, from their manner of Formation, how they ſhould: Theſe were foſſile Subſtances, therefore, of ſome other Claſs, which, as they in a ſuperficial Manner reſembled the Pumice, the indeterminate Man-
ſpeaking of it, ſays, Ὁδόντων δὲ σμῆγμα γίνεται καυθεὶς άλλιστον. and Ὀ δὲ Ἀραβικὸς λεγόμενος λιθος ἔοικεν ἐλέφαντος ἀσπέλου. Pliny, Arabicus Lapis Ebori ſimilis dentifrictis accommodatur crematus. And this was ſo early as in thoſe Times, and even continues yet to be one principal Uſe of all the Pumice Kind,
