Geological research and chemical investigation are requisite to account for the appearance of this stone, which is generally as if it had undergone a burning process. The specimens were sent me by Mr. Pennant himself some years since, and are labelled from near Mosetyn, mentioned in his account of Whitford, p. 136. I hope this plate will be acceptable as a specimen of the pseudo-volcanic nature of some rocks or remains of rocks. I would only hint that it may be pseudo-volcanic, but do not mean to venture an opinion, hoping that its history will come from more conversant hands than myself. Sir H. C. Englefield favoured me some years since with specimens from near Leeds, in Yorkshire, that have some similar signs of heat and fusion apparently having acted upon an irony schistose rock or clay, which has become like dull red Jasper; it is full of cracks, and has a cinder-like bubbled appearance which he could not then account for.
The natural Coak, tab. 192, much resembles a pseudo-volcanic production; this is, however, I think, sufficiently explained there as caused by the decomposition of the pyrites by water and air.
The Kizen-kiesel Jasper, tab. 219, nearest resembles these pseudo-volcanic changes; the hollows, however, are generally sufficiently characterized to show something like impressions of crystals having passed out of them, and the crystals of quartz are perfect and shining red, transparent, &c.