north side of Loch Chloney, where some granite mountains rise from under the schistus. In travelling near this place, Lord Webb Seymour and myself were advertised of our approach to a junction of granite and schistus, by finding among the loose stones on the road many pieces of schistus, intersected with veins of feldspar and granite. We walked along this junction for more than a mile; and toward the east end, where the road leaves it, we saw, in the bed of a stream that runs into Loch Chloney, many beautiful specimens of granitic veins pervading the schistus, and branching out into very minute ramifications.

285. The last instance I have to mention from my own observation, is at St Michael's Mount in Cornwall. That mount is entirely of granite, thrust up from under a very hard micaceous schistus, which surrounds it on all sides. At the base of it, on the west side, a great number of veins run off from the granite, and spread themselves like so many roots fixed in the schistus: they are seen at low water. In the smaller veins, the granite is of very minute, though distinct parts; in the larger, it is more highly crystallized, and is undistinguishable from the mass of the hill.

Besides the above, Cornwall probably affords many other instances of the same kind, which I have not had an opportunity to examine. Such instances may in particular be looked for at the

Land's End, where a promontory, consisting of a central part of granite, and covered by a micaceous schistus on both sides of it, is cut transversely by the sea coast, and the contact of the granite and schistus of course twice exposed to view.

286. Scotland also affords other examples of granite veins, and some of them have been actually described. Mr Jameson has taken notice of some which he saw in the bottom of the river Spey, at Glen Drummond, in Badenoch, and has represented them in an engraving. They traverse the strata in various directions, and inclose pieces of the micaceous schistus; and, from the great number of loose blocks which he found, exhibiting portions of such veins, it is probable, that they are very numerous in this quarter. The same mineralogist mentions some instances of similar veins in the Shetland Isles. †

In Ross-shire, Sir George Mackenzie has observed a great variety of granite veins, some of them of large size. One of them, in particular, not far from Coul, when first discovered, was supposed to be a single mass, rising from under the schistus; but, on a more careful examination, has been found to be a part of a great system of veins,

Mineralogy of the Scottish Isles, Vol. II. p. 173. + Ibid. p. 216.

which intersects the micaceous schistus of this tract in various directions.

287. The granite veins are not the only proof that this stone is more recent than some other productions of the mineral kingdom. Specimens of granite are often found, containing round nodules of other stones, as, for example, of gneiss or micaceous schistus. Such is the specimen of granite containing gneiss, which Werner himself is said to be in possession of, and to consider as a proof, that the schistus is of greater antiquity than the granite. Such also seemed to me some pieces of granite, which I met with in Cornwall, near the Land's End; and others which I saw in Ayrshire, in loose blocks, on the sea coast between Ayr and Girvan. It is impossible to deny that the containing stone is more modern than the contained. The Neptunists indeed admit this to be true, but allege, that all granite is not of the same formation; and that, though some granite is recent, the greater part boasts of the highest antiquity which belongs to any thing in the fossil kingdom. This distinction, however, is purely hypothetical; it is a fiction contrived on purpose to reconcile the fact here mentioned with the general system of aqueous deposi tion, and has no support from any other phenome

non.

2. Granite of Portsoy.

288. The granite of Portsoy is one of the most singular varieties of this stone, and is remarkable for this circumstance, that the feldspar is the substance which has assumed the figure of its proper crystal, and has given its form to the quartz, so that the latter is impressed both with the acute and obtuse angles belonging to the rhombic figure of the former. The angular pieces of quartz thus moulded on the feldspar, and ranged by means of it in rows, give to this stone the appearance of rude alphabetical writing.

Now, Dr Hutton argued, that substances precipitated from a solution, and crystallizing at liberty, cannot be supposed to impress one another in the manner here exemplified; and that they could do so only when the whole mass acquired solidity at the same time, or at the same time nearly.* Such simultaneous consolidation can be produced in no way that we know of, but by the cooling of a mass that has been in fusion.

289. A granite, brought from Daouria by M. Patrin, and described by him in the Journal de Physique for 1791, p. 295, under the name of pierre graphique, seemed to Dr Hutton to have

VOL. I.

Theory of the Earth, Vol. I. p. 104.

X

so great a resemblance to the granite of Portsoy, that he ventured to consider them both as the same stone, and as both containing quartz moulded on feldspar.* It should seem, however, from further explanations, which M. Patrin has since given, that Dr Hutton was mistaken in his conjecture, and that, in the pierre graphique of the former mineralogist, the quartz gives its form to the feldspar, preserving in its crystals their natural angle of 120 degrees. It is impossible, I think, to doubt of the accuracy of this statement; and the graphical stone of Portsoy must therefore be admitted to differ materially from that of Daouria. They are not, however, without some considerable affinity, besides that of their outward appearance; for, though the quartz in the former is generally moulded on the feldspar, the feldspar is also occasionally impressed by the quartz, and sometimes even included in it. They may be considered as varieties of the same species of granite; and the pierre graphique of Corsica is probably a third variety, different from

them both.

290. It would seem, however, that all these stones lead exactly to the same conclusion. M. Patrin describes his specimen as containing quartz

* Trans. Royal Society Edin. Vol. III. p. 83.

Bibliothèque Britannique, (of Geneva,) 1798, Vol. VIII. Sciences et Arts, p. 78.