For this long digression we feel conscious that some apology is necessary; the extreme interest as well as novelty of the phenomenon will at once suggest a sufficient excuse to the geologist; and to other observers it may at least be pleaded in extenuation, that they have lost nothing by the delay, for it has been in a district which offers but few objects of amusement or instruction.
About a mile and a half south-east of Hayle is Huel Alfred, which was some years ago one of the richest and most profitable Copper mines in the county. The adventurers gained a clear profit of nearly £130,000 during the period in which it was wrought. In the year 1816, from various causes, this mine was stopped, but about six months ago a company of London gentlemen embarked in the concern, and commenced their operations in a very spirited manner. Before Midsummer 1824, they expect to set at work two steam-engines with cylinders of the immense size of 90 inches in diameter, and one of less dimensions. This mine will undoubtedly prove attractive and interesting to the mineralogist, as, during the last period of working, several curious and rare minerals were discovered, as Stalactitic, swimming, and cubic quartz; carbonate, and phosphate of Lead; stalactitic, botryoidal, and investing Calcedony, &c. The lodes of this mine are so large that should the stranger intend to visit the interior of the earth, he cannot select a better opportunity.
About a mile east of Huel Alfred are situated the Herland Mines, which, after an interval of twenty years, have been lately set at work again. The adventurers in these mines are also principally London capitalists, who have erected two steam-engines of which the cylinders are 80 inches in diameter. The mineralogist will not fail to visit mines which were celebrated for the beautiful specimens of Native Silver, Vitreous Silver ore, and black oxide of Silver, found there during the last period of its working, an account of which, by the Rev. M. Hitchins, was published in the Philosophical Transactions for the year 1801.
There is a remarkable contrast between the lodes of Huel Alfred and those of Herland. The former being few, but very large; the latter, small but very numerous, and the ore peculiarly rich.
The stranger may now proceed to Redruth, between which place and Hayle, there is a regular line of rich Copper mines, but as we propose to examine this metalliferous district in a future excursion, we shall return by Saint Erth to Penzance.
The desolate and barren appearance of the country in the neighbourhood of Hayle Sands, is much relieved by the woodland scenery of Trevethoe, the seat of the family of Praed; the father of the present possessor first introduced the Pineaster Fir, as a nurse for the growth of forest trees, and the estate of Trevethoe, as well as many others in the county, affords a striking evidence of the expediency of the plan. To the same gentleman we are indebted for the introduction of the Arundo arenaria, above mentioned.
Arriving at the bridge of Saint Erth, the traveller will perceive that a considerable portion of the breadth of the peninsula is here penetrated by an arm of the sea, and that the land which succeeds it in a direction towards the south is so low, that a canal might easily be cut along the hills which terminate at Marazion, and a communication be thus opened between the English and Irish Channels; or that an iron rail-way for the conveyance of coals, sand, &c. might be constructed at a comparatively small expense.
At Saint Erth, were formerly situated the "Rolling Mills" for reducing blocks, or bars of Copper, into flat sheets, as described in the first edition of this "Guide;" since, however, the Copper-works at Hayle have been abandoned, these mills have been used for rolling and hammering iron.
In the neighbourhood of Saint Erth is Tredrea, the Cornish residence of Davies Gilbert, Esq. M. P.
On our return to Penzance an opportunity occurs of witnessing the operation of smelting Tin ore.[81] It consists in first heating the ore, with about an eighth part of Culm,[82] in a reverbatory furnace for six hours, during which period the sulphur and arsenic are volatilized, and the ore is reduced to its metallic state; the furnace is then tapped, and the liquid metal run out; a second melting, however, is necessary before it is sufficiently pure to be cast into blocks,[83] and assayed at the Coinage. After this last melting, and before the Tin is poured into the moulds, a piece of green apple-tree wood is thrown into the liquid metal, and kept under its surface; the effect of which is to throw up the scoria with rapidity; it would seem to act merely in producing a violent ebullition by the sudden disengagement of steam. One hundred parts of the oxide of Tin ("Black Tin") at an average will yield about 65 parts of metal, or White Tin, as it is technically termed.