side of Mont Blanc. The thermal water rises near the junction of mica-slate and limestone. The temperature 94° to 98°. This spring was discovered about the year 1806: it is very copious. Baths have lately been erected, and are much frequented.

AIX LES BAINS, in Savoy; the temperature from 112° to 117°. The thermal waters rise in great abundance from two springs, situated at the foot of a lofty calcareous mountain, and are near the bottom of the great calcareous formation that forms the outer range of the Alps: there are also numerous hot springs in the vicinity, which the Sardinian government will not allow to be opened. Of the mode of douching at these baths, I have given a particular account in the first volume of my Travels in Savoy, Switzerland, and Auvergne. The thermal waters of Aix were well known to the Romans.

MOUTIERS, in the Tarentaise.-The thermal waters rise in great abundance from the bottom of a nearly perpendicular mass of limestone. From the position of this rock, and its connection with those on the opposite side of the valley, in which the hot springs rise, I have no doubt that it is the lowest calcareous bed in that part of the Alps; but its junction with mica or talcose slate is not here seen. The thermal waters of Moutiers, contain about two per cent. of saline matter, chiefly common salt. The process of extracting it, I have described in the Philosophical Magazine, vol. lxiii. p. 86.

BRIDA, in the Tarentaise. -The thermal waters of Brida were noticed in the ancient records of Savoy, but they were covered during a sudden inundation of the valley, and their situation was concealed for many years. In the summer of 1819, another inundation, occasioned by the breaking down of the side of the glacier, laid open the spring again. The rock from which the spring rises is a greenish talcose slate, passing into mica-slate: it is in junction with limestone. The temperature of the water is from 93° to 97° Fahrenheit. The geological position of this spring, is more obvious than that of any of the other thermal waters which I visited, being situated close to the steep bank of the river Doron, where both the rocks are laid bare. There are some warm springs on the opposite bank of the river, which rise in limestone; but the temperature is lower, owing to an intermixture with

common water.

SAUTE DE PUCELLE, or Virgin's Leap.-There is a very copious thermal spring rising from the bottom of a perpendi

cular rock near the Isère, between the town of Moutiers and St. Maurice, at the foot of the Little St. Bernard; but, owing to the difficulty of access to it, I did not visit it, to ascertain its temperature.

Beside the above thermal waters in the Pennine Alps, various thermal springs were discovered in the adjacent Alps, near Grenoble, in the year 1820; and it seems probable, that a series of these springs might be found, were proper search made, extending westward to the thermal waters of the Pyrenees; for in this line we should approach the southern border of the volcanic district of France. On the Italian side of the Pennine Alps there are also thermal waters: the warm baths of Cormayeur and of St. Didier are situated almost immediately under the southern escarpment of Mont Blanc. I was prevented by the weather, from examining the geological position of these springs: their temperature is stated to be 94° of Fahrenheit.*

The inference that may be drawn from the geological position of these thermal waters near the junction of the calcareous beds with mica-slate, or the dark schist which passes into mica-slate, is, that the waters do not rise from the upper strata, but spring out of the lower or primary rocks; and as they break out near the feet of the highest range of the Alps, that extend from the northern side of the Simplon through the Valais and Savoy into France, we may with much probability infer, that these mountains are situated over or near to one common source of heat, by the agency of which they were originally elevated, and their beds placed in a position nearly vertical. This inference is in some degree supported by the well-attested fact, that the districts where the hot springs are situated, are subject to great and frequent convulsions, particularly in the upper valley of the Rhone. In the year 1755, at Brieg, Naters, and Leuk, the ground was agitated by earthquakes every day from the 1st of November to the 27th of February; some of the shocks were so violent, that the steeples of the churches were thrown down, the walls split, and many houses rendered uninhabitable: many of the springs were dried up, and the waters of the Rhone were observed to boil. At three different times the inhabitants abandoned their houses, and fled for safety into the fields.

been before mentioned, that the mountain above the warm spring at Naters, opened during the time of the great earth

Nearly all the thermal waters in the Alps, emit sulphureous vapours, and are slightly saline, except the waters of Leuk, which have the highest temperature, and are inodorous, and free from saline impregnation.

quake at Lisbon, and threw out hot water; at the same period the warm saline springs at Moutiers ceased to flow for fortyeight hours. When the water returned, the quantity was said to be increased, and the saline impregnation was weaker. Former and more formidable agitations of the earth are recorded in the Haut Valais, particularly in the district where the principal hot springs are situated. The last earthquake of consequence in the Valais took place in January, 1803.

I am informed that several of the retired valleys on the Italian side of the Alps, at the foot of the central chain, are subject to earthquakes, during which the ground has opened or sunk down in various parts, though these effects have been too local, to excite attention at a distance. From these facts, it seems as reasonable to infer that the thermal waters of the Alps owe their high temperature to subterranean fire, as that the hot springs in countries that have formerly been volcanic, derive their warmth from an internal, unextinguished, but quiescent, source of heat. No person who has attentively examined the lofty granitic plain to the west of Clermont Ferrand in France, and observed the granite in various parts pierced through by ancient volcanoes that have poured currents of lava over its surface, or seen other parts, where the granite itself has been changed by its contiguity to subterranean fire, or upheaved and intermixed with volcanic rocks;

a cause

no one, I say, who has observed this, can doubt that the hot springs of Mont d'Or and Vichy, derive their high temperature from a source of heat situated beneath the granite mountains, though ages have passed away since the volcanoes of that country have been in an active state, and the only proof of the present existence of subterranean fire in Auvergne, is to be found in the hot springs themselves. Nor can any adequate reason be assigned, for attributing the high temperature of the thermal waters in the Alps, to any other cause than to a source of subterranean fire under these mountains, which is sufficient also to have produced their original elevation. It is, however, proper to state, that in some of the mountains of the Alps, the temperature may be slightly increased by a cause hitherto unnoticed. In the upper part of the secondary formations covering the granite, there are beds of gypsum, and this gypsum is anhydrous; but when exposed to air and moisture, it combines with water, and passes to the state of common gypsum: during this combination we may suppose heat to be evolved; but the process must be extremely slow, and the heat evolved, must be totally inadequate to raise the temperature of powerful streams to 126°. Saussure found

the temperature of the water in the lower part of the salt mines of Bex, which are situated in the vicinity of gypsum, to be four degrees of Reaumur higher than the mean temperature of the earth. It is not improbable, though Saussure was not aware of the circumstance, that this small increase of temperature in the mines of Bex, might be partly owing to the combination of water with gypsum: however, an increase of temperature, it is well known, is observed in deep mines, far removed from the gypsum formation.

In reply to what I have advanced respecting the thermal waters in the Pennine Alps, it may be said, that few thermal springs have been yet discovered in the northern range of the Alps which form the Bernese Oberland; but the difference in the geological structure of the two ranges will, I conceive, be sufficient to explain, why hot springs are more rare in the latter than in the southern range. Most of the highest mountains in the Bernese Alps are covered with secondary strata; and the valleys are chiefly excavated in these strata, or in enormous beds of sandstone and conglomerate, that form a thick intervening mass between the surface and the primary rocks, sufficient to obstruct the rise of thermal waters; for it has before been stated, that all the thermal waters in the Pennine Alps, issue from the primary rocks, or near their junction with the lowest calcareous strata.

ON THE TEMPERATURE OF MINES AND WELLS.

It was stated in Chap. XXIV. that the temperature of the water in Artesian wells (or those wells formed by boring) had been found in France to increase about 1° centigrade for 25 metres in depth. But this increase of temperature is sometimes variable in different situations. France has been the seat of active volcanoes at no remote geological epoch; and, in the volcanic districts, there are numerous hot springs remaining it is, therefore, not improbable that, in the southern and central departments, the increase of temperature with the increase of depth in Artesian wells, may be derived from the remains of volcanic heat. In England, many borings for water have been executed; but I am not aware of any experiments having been made on the water to ascertain the temperature. At Boston, in Lincolnshire, water was bored for to the extraordinary depth of 600 feet: the boring, during the whole depth, was in clay; and the experiment was unsuc cessful, no good water being obtained. It is to be regretted that the temperature of the water at that depth had not been ascertained.

Many experiments have been made on the temperature both of the air, the water, and the rocks in mines, at different depths; and the general results of each have indicated a considerable increase of heat with the increase of depth. In Dolcoath copper mine, Mr. Fox found the temperature of the water (at about 480 yards from the surface) to be more than 30° of Fahrenheit above the mean temperature of the country. A thermometer, plunged into the earthy matter, at the bottom of another mine in the same county, 400 yards deep, and which had been inundated for two days, was raised 38° above the mean temperature. I apprehend that in these instances, and in many others that have been stated, one source of error has not been sufficiently attended to, viz. the increase of heat by chemical changes that are taking place in the mineral substances in mines, from access to water or the atmosphere. I was informed by working miners in Cornwall, that they could generally tell when they were approaching to a copper lode, by the increased warmth of the water; but this was not the case when they came to a lode of tin ore. The cause of this warmth seems very intelligible: the copper ore of Cornwall