vious to it. In these instances, at least, there are no grounds for supposing that any chemical decomposition of the sulphur ores in the lode has caused the high temperature of the water, or contributed to it in any degree, seeing that it contains no metallic, and scarcely any sulphate salt.

The difference in the heat of the two springs may perhaps, in part, be attributed to the tendency of the warmer currents to rise towards the upper wall of the lode; and still more to that of water at a much lower temperature passing from superior strata down upon the inclined surface of the lower wall, where, mixing with the water rising from below, the temperature becomes modified, as well as the proportion of the saline contents.

It cannot be doubted that ascending and descending currents of water, more or less copious, and at different degrees of temperature, abound in the veins and fissures of the earth, and often at the junctions of different rocks, and that they must have a great influence in modifying the subterranean temperature, and in different degrees in different places.

Common salt is of rare occurrence in our mines; its presence in the water in question cannot well be attributed to the flowing of sea-water into the excavation, in consequence of its local or direct pressure; for if some miles of distance from the coasts did not render this highly improbable, the considerable streams at very high temperatures, and very constant too (as appears from observations made at different times), are facts not consistent with such an explanation. If the subterranean jets of water were caused by the inroads of a neighbouring sea, we should expect to find them at comparatively low temperatures, aud these diminishing in proportion to the duration and amount of the influx.

The salt may, however, have been derived from the ocean, in consequence of the latter penetrating into the earth at its greater depths, or even at its lesser ones, which, under different given circumstances, it may be supposed to do. In either case, the salt water would, from its superior specific gravity, have a tendency to descend through the heated and less saline water in the veins, fissures, &c., where the fluids becoming gradually more or less mixed and extended in dif

ferent directions, might ultimately appear in some of our mines, brought up, perhaps, in the largest proportions, by the upward tendency of the more heated currents of water. -The Fourteenth Annual Report of the Royal Cornwall Polytechnic Society, 1847.

On the High Temperature of the Water at the United Mines. By Captain W. FRANCIS.

Whitehall, 2d September 1846. DEAR SIR,-In fulfilment of my promise to you yesterday, I now give you some facts which have come under my notice relative to the temperature of water in our mines, especially in reference to the great difference in the heat of water issuing from different parts of the same level; remarkable instances of which are now observed in the United Mines.

The United Mines on the south are traversed from west to east throughout their whole extent by two large elvan courses, which are of considerable thickness, and whose direction is almost parallel with the principal lodes. At the surface, the distance from the south lode to the first elvan course is about 200 fathoms, and to the second about 230 fathoms. By the dip or underlie, northward, of the elvan courses being so much faster than that of the lodes, the former intersect and pass through the latter at depths which vary in different parts of the mines; but the 155 fathom level may be taken as the average depth at which the south lode passes through the first elvan course; the middle lode passes through it at the 170 fathom level; and the north lode at the 194 fathom level; whilst the second elvan course, as yet, has only been seen at the 220 fathom level, where the south lode is in it, and the other two lodes can only be intersected by it at a greater depth. These elvan courses are distinctly traceable for several miles, and are so jointed and open, especially near the surface, as to become ready conductors of large quantities of water; and to this circumstance is to be mainly attributed the unusual quantity of water which we have to contend with in these mines,

The quantity lifted being, in the dry season, about 1400 gallons per minute, and, in the rainy season, about 2400 gallons. The greatest difference in the temperature of the water is when we have most to lift, and the mean temperature of the whole is then at the lowest. In every instance the water issuing from the south side of the level is colder than that from the north side, and the water from the south lode is colder than that from the middle and north lodes. The elvan courses, as I have before said, are, at all seasons of the year, the channels through which a considerable portion of the water is conveyed into the mines, and I believe nearly all the additional water in the wet season is brought in by them. This water finds its way into the mines rapidly, and without having passed through the lodes to the same extent as that portion of the water which is always flowing, and which may be considered as the permanent source of supply to the engines.

My remarks in reference to the manner in which the elvan courses intersect the lodes, will at once shew you how any water passing through them will, in every instance, make its appearance on the south side of the levels, and that the south lode will drain a larger portion of the water thus brought into the mines than either of the others; hence it is clear that the temperature of the water depends on the time which it requires to pass from its source to the different parts of the mines, and also to the medium by which it is conveyed. Several circumstances exist to shew that what I have termed the permanent supply of water to the engines, must be derived from sources at a considerable distance from the mines, and that its course through the lodes is at a depth from the surface little short of that at which it comes into the shafts, and which varies from 200 to 260 fathoms.

I am aware that it may be urged that, in other mines, when a difference in the temperature of the water is observed, the same causes to produce it do not exist as I have described in the United Mines; but, notwithstanding such mines may not have large elvan courses running through them, it will be found that other means of letting down water freely do exist, such as large cross-courses, changes of

strata, &c.; and the water so discharged into the mines will be found to be of lower temperature than the usual coming stream.

Having endeavoured to account for the difference in the temperature of the water, I should be glad were I able to advance some facts illustrative of the source of heat itself; but although I have watched narrowly the various circumstances under which the highest temperatures have been observed, I am still in some doubt as to the causes by which they are produced.

It is a commonly received notion that the highest degrees of temperature are indications of large bodies of ores being contiguous, if not actually open to sight; but at the United Mines, and in others also, the lodes in those levels where the heat is greatest, are almost without ores, and both the lodes the rock about them are hard and very compact. At the same time I admit, that such lodes have been found, somewhere, to contain large quantities of copper ore; but my object in making the preceding remark is rather to shew that the presence of great heat is not to be considered an infallible indication of large masses of ores being near at hand.

It should also be observed, that those lodes which yield the most copper ores generally hold considerable quantities of other minerals, such as iron-pyrites, arsenic, &c.; and it becomes a question, whether these may not account for much, if not the whole, of the heat in the mines.

That most of the lodes, and especially those which have yielded large quantities of copper ores, have, at some period, been under the influence of great heat, there can be no doubt, and to such an extent as to fuse their contents; and I see no reason for believing otherwise than that intense heat still exists in them at a distance from where they have been penetrated: but it should be remembered that the symptoms indicating the action of heat are not so frequent or strong in the deepest parts of those mines which have been worked to the greatest depths, as they are at higher levels, and especially near the surface, where gosson, at the depth of a few fathoms, or even a few feet, usually exhibit this fact in the clearest manner. I have had numerous opportunities of

witnessing the fact just named in the deep mines in the Gwennap district, and in almost every case the lodes at the lowest points are composed of hard compact quartz, almost free from the presence of minerals, and yet the water issuing from those parts is of the highest temperature, which certainly strengthens the opinion that the source of heat is from a still greater depth; and its effects not being so evident in those places may be accounted for by the absence of those substances in the lodes on which the action of heat would manifest itself. But whilst it is admitted that the temperature increases with the depth, it should be observed, that it is not found to be the same at the same depth, even in parts of the same mine which are only a few fathoms' distance from each other. In different mines in the same locality, and in precisely similar formations, the result is often very different. As instances of this, I will refer to the Consolidated Mines, which adjoin the United Mines, and the lodes in each bear the same direction, and run parallel to each other. The former have been worked to the depth of 316 fathoms from the surface, whereas the latter have only been worked 260 fathoms, or 56 fathoms less than the first. The highest temperature in the Consolidated Mines has been 98° Fahrenheit, whilst in the United Mines it is 106°. Again at Tresavean, the depth of which is 320 fathoms from the surface, the highest temperature yet observed is about 95°. It should, however, be noticed, that the deepest part of Tresavean is in granite formation, and that the Consolidated and United Mines are in slate.

These circumstances go to shew that there must be other causes producing heat, apart from the mere depth of the mines; and, without being prepared with conclusive evidence as to its origin, or the source from whence it proceeds, I cannot help remarking that the degree of heat is very much increased by its passing through immense bodies of mineralized matter powerfully acted on by galvanic agency.

I feel that I have now carried these hasty remarks as far as it is safe to go, without entering upon ground which it would be dangerous for me to venture on; and I will bring them to a close, by expressing a hope that they may serve,