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LXXXIV. [1]But if Glaſs be made, as
- ↑ All Earths are vitrifiable by extreme Degrees of Heat. Nothing is more certain, than that the Vitrification, or converting the Subſtances of which Glaſs is made, into that Form,
thouſand Kinds; and is, diſtinctly ſpeaking, no genuine Foſſil.
In order to the rightly underſtanding what is meant by the calling any Subſtance by either of the other Names, it may not be improper briefly to give their ſeveral Diſtinctions, ſo far as the general Uncertainty of the Foſſile Kingdom will permit:
1. Clays are Earths compoſed of very fine Parts, ſmooth, heavy, not eaſily mixing with Water; and when mixed, not readily ſubſiding in it; compact, viſcid, and leaving a fatty Impreflion on the Tongue: ſoft while in the Stratum, and hardening by Fire into a kind of ſtony Texture.
2. Ochres are ponderous earthy Subſtances, more fat than Chalk, and leſs ſo than Clay, readily diffuſible in Water, and friable when dry, ſtaining the Fingers in handling, and principally differing from the Boles, in that they are of a looſer Texture.
3. Boles are ponderous earthy Subſtances, more fat than Chalk or Marle, but leſs ſo than Clay; ponderous, of an aſtringent Taſte, melting in the Mouth, ſtaining the Fingers; and generally partaking more or leſs of the Nature of Iron; as indeed, in ſome Degree, do moſt, if not all, the other Earths, but the Boles generally more than any.
4. Marles are light friable Subſtances, of a middle Nature between Clay and Chalk, not ſo fatty as the former, nor ſo denſe as the latter, eaſily diffuſible in Water, and, when taſted, dry, inſipid, and adhering to the Tongue.
5. Chalks are earthy Subſtances, denſe, brittle, readily diffuſible in Water, and quickly ſeparating themſelves from it by Subſidence, ſtaining the Fingers in handling, and, in taſting, ſticking to the Tongue.6. And Loams are earthy Bodies, of a denſe, rough Texture, conſiſting of clayey or ochreous Matter, with arenaceous Particles of various Figures, Sizes, and Colours, immerſed in and intimately mixed with it.
Much more might be ſaid on this Occaſion, were this a proper Place for it; but a general and ſuccint Account of what is meant by the general Names of Clays, &c. may be ſufficient for what is intended in this Place; which is only to give ſomething of a determinate Idea of what is meant by the Words Chalk, Bole, &c. when there ſhall be Occaſion hereafter to ſay any of the Bodies deſcribed by this Author is of the Nature of one or other of theſe Subſtances.
