Calcedony or Agate. (Argilliferous Silex)
This beautiful specimen was found near the surface of the ground at Churchills, near Lanford, Somersetshire; and is part of one double the size, belonging to my kind friend, C. John Harford, Esq. It is instructive in as much as it appeared not to have been long from the rock in which it probably originated, as it has no such marks of violence* as many agates and separate siliceous stones have, thus implying a rock beneath, from which it had been detached. Richard Wilding, Esq. was so kind as to send me a year ago, specimens from Llanrhaiadr, near Denbigh, of a dark grey Limestone, including a great variety of siliceous, coated, hollow, tuberose masses, now I conceive it must be a similar rock that has produced this, a circumstance which may be worthy the attention of those whose leisure will allow them to indulge a desire of forwarding geological knowledge.
The boldness of the circles and the variety of the depositions is superior to any Agate I ever met with, either British or Foreign. The surface of each layer has small rounding risings all over it, which are more or less conspicuous in the section, but rather more so in the first or smaller circles; the distinctness or facility of separation intimates a cessation or interval between the layers, thus marking dryer or wetter and more or less copious deposits, and a sort of seasons.
- * On the fresh cut side it was observably that the exposed part of the whiter coats was more opaque than the interior, as if the little exposure it had had caused a difference by dissipating the water or loosening the particles, as in common flints, &c.