In a former part of this work, we gave a list of the principal Tin and Copper Mines in this county; but as we apprehended the limits of it would not allow a particular description of them, we have since, at the suggestion of some of our subscribers, curtailed the historical and topographical notices, with the view to enable us to present our readers with some little particulars as to the situation and nature of the most valuable mines now working. In passing through the county according to the plan of our several Excursions, there are not any mines deserving of particular attention, until the traveller arrives at St. Austell; here it is necessary that he should make some stay, as the vicinity of the town possesses many attractions, and the numerous works now in progress will amply gratify his curiosity.
The most considerable Tin Mine in the county is Polgooth, which is situated about two miles south-west of St. Austell; and even in Borlase’s time, is said to have yielded to its proprietors a profit of £20,000 annually for some years. Owing, however, to some unfortunate disputes, the operations have been suspended for nearly 20 years, but have lately been resumed with increased vigour. From the extensive nature of the works carried on in this mine, the whole surface of the country in its vicinity, has been completely disfigured, and presents a very gloomy aspect. The quantity of ore which has been raised from this mine, during the progress of its workings, is far beyond calculation: the immense piles of earth, which have been excavated and thrown up, have quite a mountainous appearance: roads have been formed in several directions leading to the places or shafts, where the miners are at work; and the dreariness of the scene is only enlivened by the humble cottages, which have been erected for their residence. The number of shafts which have been sunk in this mine, amount to near 50, and the greater part of them are mostly working; but since the introduction of steam engines, the operations have been considerably increased, as the water is now raised to the level of the adits, and which before had in some cases overflowed certain parts of the mine.
The introduction of steam engines for drawing off the water from the mines in Cornwall, is one of the most valuable discoveries imaginable; and the greatest advantages have attended these powerful machines, while on the other hand few accidents have been occasioned by their adoption.[[48]]
In Dr. Maton’s Observations on the Western Counties, is the following description of a Steam Engine; but since that time, their powers of acting have been considerably augmented; and on some occasions they are now made on a very large scale, with cylinders even 90 inches in diameter.
“The Steam Engine is one of the most curious, and perhaps most useful machines that owe their origin to the discoveries of philosophy; without it many of the mines in Cornwall must long ago have ceased to have been worked; and among other purposes to which it has elsewhere been most advantageously applied, should be mentioned, the supplying of towns with water, the grinding of corn, the turning of the wheels of machines in woollen manufactories, and the blowing of bellows to fuse ores and metals; we have to boast of this grand machine, being invented, as well as perfected, in our own country: Captain Savery is said to have first discovered the method of raising water by the pressure of air, in consequence of the condensation of steam; or at least he was the first person that put any method of this sort into practice: he obtained a patent, in the year 1698, for a machine contrived in the following manner; the air was expelled from a vessel by steam, and the steam condensed by the admission of cold water, which causing a vacuum, the pressure of the atmosphere forced the water to ascend into the steam vessel through a pipe 24 or 26 feet high: by dense steam brought from the boiler, the water in the steam vessel was elevated to the requisite height. This construction, however, did not answer, because very strong vessels were wanted to resist the expansive violence of the steam; an enormous quantity of which was, besides, condensed by coming in contact with the cold water in the steam vessel. The danger of bursting the vessels was avoided soon afterwards by the invention of Messrs. Newcomen and Cawley, of Dartmouth. These gentlemen employed for the steam vessel a hollow cylinder, shut at the bottom and open at the top, and furnished with a piston sliding easily up and down in it, but made tight by oakum or hemp, and covered with water: the piston was suspended by chains from one end of a beam moveable on an axis in the middle of its length; to the other end of this beam hung the pump rods. Some imperfections still remained; but the most important were at length wholly removed by the discoveries of Mr. Watt, and the construction made use of by that gentleman and Mr. Bolton, of Soho, near Birmingham; who obtained a patent for 25 years, in addition to the term granted to Mr. Watt alone, in the year 1768. One of these machines will work a pump of 18 inches in diameter, and upwards of 100 fathoms in height, at the rate of 10 or 12 strokes, of seven feet long each, in one minute. It will raise to the height of 80 feet, in that same space of time, a weight equal to 18,000 pounds; the combined action of 200 horses could not effect more. In Newcomen’s engine this would have required a cylinder 10 feet in diameter; but as, in the new engine, the steam acts, and a vacuum is made, alternately above and below the piston, the power exerted is double to what the same cylinder would otherwise produce; and is farther augmented by an inequality in the length of the two ends of the lever. It must be considered too, that one-third part only of the coals which the old engine would have required, is used for the same portion of work.” The expense of erecting the first steam engine in the Polgooth Mine, amounted to nearly £20,000; and the quantity of coals consumed by it, in the short space of 24 hours, is stated to amount to 144 bushels.
According to Borlase, the main vein of ore in this mine, was about six feet thick, running from east to west, and dipping to the north, at the rate of about six feet in a fathom; towards the east it divides into two branches, and there is another that cuts the former nearly at a right angle, and consequently runs north and south, but dipping to the east. The ore is disseminated in general through a matrix of Caple,[[49]] accompanied with a yellow cupreous pyrites, and sometimes a ferrugineous ochre; it is of the vitreous kind, but rarely found in crystals, the colour for the most part being of a greyish brown.
Crennis Copper Mine, which is situated about two miles east of St. Austell, is highly deserving of notice: here also steam engines have been introduced with the most beneficial effects; but although the ore found in this mine is extremely rich, it was not discovered till within the last few years, but is stated in some instances to have yielded a clear profit to its proprietors of £84,000 in one year.
The several Tin Stream Works also in the neighbourhood of St. Austell, are particularly deserving of notice; the one on the left of the road near Pentuan, has proved a considerable benefit to the adventurers concerned in it. In Luxilian parish, through which the road leading from St. Austell to Bodmin has been formed, there are several works of a similar nature; but owing to the number of excavations which have been made for the discovery of ore, it is desirable that strangers should avoid travelling in this direction after dusk. The celebrated Wood Tin, as it is called, is mostly found in the Stream Works, and which although extremely valuable, appears far from prepossessing in the minds of those persons who are unacquainted with mineralogy.
Small particles of gold are frequently found in the Stream Works, but they are mostly incorporated with tin crystals in streaks.