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on; others may be ſhaped by the Turner's Tools; others may be cut or ſawed: Some alſo there are which no Iron Inſtruments will touch; and others which are very difficultly, or ſcarce at all to be cut by them[1].
- ↑ I cannot but obſerve from this, Paſſage of our Author, that, ſo early as in his Time, not only very many Species of precious Stones were in Uſe, and their different Degrees of Hardneſs familiarly known, but that the various
terwards; and the Maſs formed of the whole appeared a Flint, or Pebble, of regular and ſimilar Subſtance: and if, laſtly, this Matter, before its Application, had received other various-coloured Affluxes into it, they are ſeen in the Concrete, in irregular Lines and Striæ, and it becomes an Agate, or other ſuch Stone. In all theſe Caſes the Matter firſt formed into a Maſs, yet remains in Form of a central Nucleus, in or near the Middle of the Stone, according to the equal or irregular Quantity of the'additional Matter which formed each Cruſt; this being ſometimes all of the ſame Colour with that Nucleus, remains unperceivable, but ſometimes, as before obſerved, being of different Colours, is evident to the Eye.
This Nucleus in ſome, indeed moſt of theſe Maſſes, being of the ſame Texture with the reſt, has remained in its Place, and become a viſible Spot of equal Hardneſs and Beauty with the reſt of the Stone: in others, after the Application of ſome, or all the outer Cruſts, it has ſhrunk into a ſmaller Compaſs, detached itſelf from the inner Cruſt, and become a looſe, ſeparate Stone, rolling about in the Cavity, now too large for it; and rattling in it when ſhaken. This is our Ætites; and the central Nucleus ſo detached, and ſhrunk, is its Callimus. In others, this central Nucleus has crumbled into looſe, ſandy, or earthy Matter, and remaining in that Form, looſe in its Cavity, has made what is called the Geodes, or baſtard Eagle Stone. The Geodes, and the Eagle Stone, ſo much renowned for Virtues, and ſo fabulouſly talked of as to their Origin, are therefore no other than common Pebbles, the central Nuclei of which have, from the different Nature and Texture of the Matter of which they were formed, detached themſelves from the ſuperadded Cruſts, and either ſhrunk, on becoming more dry, into ſmaller Dimenſions; or fallen into the original Grit, or ſandy Matter, of which they were firſt compoſed.
