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are diſtinct Kinds; as are alſo thoſe which ſupply Nouriſhment to Plants[1].
LXXXVII. Nor ought thoſe to be leſs conſidered which are ſingular and remarkable in their Colours, and for that Reaſon uſed by Painters.
LXXXVIII. The Production of theſe, as was obſerved in the Beginning of this Treatiſe, is from the mere Afflux or Percolation of their conſtituent Particles,
LXXXIX. Some of theſe ſeem burnt,
- ↑ Vegetable Mould, I have before obſerved, is no genuine Foſſil.
and ſeveral other Springs in Northamptonſhire, Chedworth, and Norleach Springs in Glouceſterſhire, and many other petrifying Springs, as they are called, in England, and elſewhere, that this is denying Things for which they have the Evidence of their Senſes: But ſuch Perſons are to be taught, that what they eſteem Petrifactions, are no other than Incruſtations of ſparry, argillaceous, and other Matter, brought away with theſe Waters in their Paſſage through the Strata, and ſettling from them again. There is great Difference between changing the Subſtance, and only covering the Surface of a Body. Theſe Petrifactions, as they are called, being no other than Precipitations of Matter too heavy to be longer ſuſtained in the Water; and which, being very fine, adapts itſelf to every Prominence and Cavity of the Body it ſettles upon, and exactly aſſumes its Shape. The firſt Proceſs in theſe Operations of Nature forms only an extremely thin Cruſt over the Body; on which there after ſettle at Times many more, often to a Covering of conſiderable Thickneſs in the whole, but always giving evident Proofs of the Manner in which it was ſucceſſively formed, by the Number of thin Strata of which it is compoſed.
