In order to collect the various minerals of the county the stranger must apply to the different dealers,[118] (rapax et sordidum pecus) and make the best bargain he is able; he may also occasionally purchase some good specimens of the miners at the various mines he may happen to visit. In his rambles we recommend him to visit Saint Agnes, where are the Trevaunance, and Seal Hole mines, from which have been raised the most beautiful specimens of crystallized Tin in the world, accompanied occasionally with Topazes, and twenty-four-sided Fluor. Here too may be seen a geological phenomenon of considerable interest,—the slate of the coast intersected with Porphyry Dykes, Saint Agnes' Beacon is also well worthy of observation; it is an insulated eminence of a pyramidal form, entirely covered with debris, and is composed of Slate, although it rises 664 feet above the level of the sea. Saint Agnes is the birth place of the celebrated artist Opie,[119] and the tourist may be gratified by inspecting many of the earlier productions of his pencil. But we now take our leave of the Mineralogist, and shall attend the Antiquary in order to inspect Carn-breh hill, which rises a little to the south-west of Redruth, to an elevation of 697 feet; its principal interest is derived from the lucubrations of Dr. Borlase, who regarded it as having been the grand centre of Druidical worship, and he asserts that, in his time, the remains of the monuments which were peculiar to that priesthood were to be easily recognized, such as Rock Basins; Circles; Cromlechs; Rock Idols; Karns; Caves; religious enclosures; Logan Stones; a Gorseddau, or place of elevation, whence the Druids pronounced their decrees; and the traces of a Grove of Oaks!—this is all very ingenious and imposing, but is there any rational testimony in support of such an hypothesis? are there any just grounds for considering the objects to which he alludes as the works of art?—most certainly none, they are unquestionably the results of the operation of time and the elements, and have never been formed by any agents except those which Nature employs in the decomposition of granitic masses; but the age of Antiquarian illusion is past; the light of geological science dispels the phantoms which the wizard fancy had created, just as the rising sun dissolves the mystic forms which the most common object assumes in twilight, when viewed through the medium of credulity and superstition. The rock basins of Antiquaries are rounded cavities on the surface of rocks, and are occasionally as spheroidal, internally, as if they had been actually shaped by a turning lathe; it was this artificial appearance which first suggested the hypothesis concerning their origin, and induced the Antiquary to regard them as pools of lustration. Dr. Mac Culloch,[120] however, very justly observes, that their true nature is very easily traced by inspecting the rocks themselves; on examining the excavations they will be always found to contain distinct grains of Quartz, and fragments of the other constituent parts of the granite; a small force is sufficient to detach from the sides of these cavities additional fragments, shewing beyond doubt, that a process of decomposition is still going on under favourable circumstances; these circumstances are the presence of water, or rather the alternate action of air and moisture; if a drop of water can only make an effectual lodgement on a surface of this granite a small cavity must be sooner or later produced, this insensibly enlarges as it becomes capable of holding more water, and the sides as they continue to waste necessarily retain an even and rounded cavity, on account of the uniform texture of the granite. This explanation is sufficiently satisfactory; in addition to which it may be further stated, that these very basins not unfrequently occur on the perpendicular sides of rocks,[121] which at once excludes the idea of their artificial origin.
The other grotesque and whimsical appearances of rocky masses, such as "rock idols, logan stones," &c. are to be explained upon the tendency which granite possesses of wearing more rapidly on the parts which are most exposed to the action of the weather, as already explained at page [104]. There occurs upon the western part of the ridge of Carn-breh an equipoised stone, about 20 feet in diameter, affording a very singular illustration of these views, and of which we shall here present a sketch to our readers.
Thus upon simple and philosophical principles are such appearances to be easily explained, and this Phantasmagoria of the learned antiquary vanishes.
For the information of the Geologist who may visit this spot, we shall state, that in a porphyritic granite on the summit, Mr. W. Phillips has lately discovered that some of the crystals formerly considered as Felspar, were Cleavelandite;[122] and we have little doubt that this curious discovery might be extended to many of the granitic masses in Western Cornwall.
At the eastern end of the hill is Carn-breh Castle; the rocks upon which this building stands, not being contiguous, are connected by arches turned over the cavities; one part of the fortress pierced with loopholes is evidently very ancient, and is supposed to have been of British work; the other is of modern construction, and was probably erected as an ornamental object from the grounds of Tehidy. There were formerly some outworks to the north-west; and, near the summit of the hill is a circular fortification called the Old Castle, which appears to have been included within a strong wall. The hill itself, on which the spectator stands, is quite in unison with the scene around him; its silence and desolation,—the awful vestiges of its convulsion,—and the immense rocky fragments which lie scattered on its brow, are well calculated to harmonize with an extended and barren tract of country, every where broken up by mining operations, and whose horizon is bounded by the ocean.
FOOTNOTES:
[84] The Phœnicians traded upon the western coasts of Cornwall, for at least six hundred years before the birth of our Saviour, and that for the sake of Tin;—so that the antiquity of our tin trade has been established upon mercantile principles for not less than twenty-four centuries. But in the earlier ages this metal was all procured from Stream Works, the method of working mines not having been known and practised for more than seven hundred years.
[85] In the year 1822, the produce of the Copper mines in Cornwall amounted to 106,723 tons of ore, which produced 9,331 tons in Copper, and £676,285 in money. Whereas the quantity of Tin Ore raised did not exceed 20,000 tons.