dered as a certain fign of an impending eruption. Befides this, the mountains of Myvatn and Kattlegia are known in this century, on account of the violent eruptions of the former, between the year 1730 and 1740, and of the latter in 1756.

But permit me, Sir, to omit a farther account of the volcano at this time, in order to fpeak of another effect of the fire, which is more curious and as wonderful as the, firft, therefore must be the more remarkable, as there is not in any part of the known world any thing that refembles it; I mean the hot fprings of water which abound in Iceland †.

They have different degrees of warmth, and are on that account divided by the inhabitants themfelves into lauger, or warm baths, and huerer, or fprings that throw up the water to a confiderable height; the firft are found in feveral other parts of Europe, though I do not believe that they are employed to the fame purposes in any other place; that is to fay, the inhabitants do not bathe in them here merely for their health, but they are likewise the occafion for a fcene of gallantry. Poverty prevents here the lover from making prefents to his fair one, and nature prefents no flowers of which garlands elsewhere are made it is therefore customary, that instead of all this the fwain perfectly cleanses one of these baths, which is to be afterwards honoured with the visits of his bride. The other kind of springs mentioned above deserves

:

more attention. I have seen a great number of them; but will only fay fomething of three of the moft remarkable. Near Laugervatn, a small lake of about a mile in circumference, which is about two days journey diftant from Heckla, I faw the first hot spouting fprings; and I mult confefs that it was one of the most beautiful fights I ever beheld. The morning was uncommonly clear, and the fun had already begun to gild the tops of the neighbouring mountains; it was fo perfect a calm, that the lake on which fome swans were fwimming was as fmooth as a looking glafs, and round about it arofe, in eight different places, the fteam of the hot fprings, which loft itself high in the air.

Water was fpouting from all these springs; but one in particular continually threw up in the air a column, from 18 to 24 feet high, and from 6 to 8 feet diameter; the water was extremely hot. A piece of mutton, and some falmon trouts, as likewife a ptarmigan, were almoft boiled to pieces in fix minutes, and tafted excellently. I wish it was in my power, Sir, to give you a defcrip tion of this place as it deferves; but I fear it would always remain inferior in point of expreffion. So much is certain at least, nature never drew from any one a more chearful homage to her great Creator than I here paid him.

At Reikom was another fpont of the fame fort; the water of which, I was affured, rofe to 60 or 70 feet perpendicular height fome years

3

ago

ago; but a fall of earth having almoft covered the whole opening, it now spouted only between 54 and 60 feet fideways. We found here a great many petrified leaves in this place, as likewife fome native fulphur, of which alfo the water had a much stronger taste than any where else.

I have referved the most remarkable water spout for the end; the defcription of which will appear as incredible to you as it did to me, could I not affure you that it is all perfectly true, for I would not aver any thing but what I have feen myself. At Geyfer, not far from Skallholt, one of the epifcopal fees in Iceland, a moft extraordinary large fpouting fountain is to be feen, with which the celebrated water-works at Marley and St. Cloud, and at Caffel, and Herren hausen near Hanover, can hardly be compared. One fees here, within the circumference of half a mile*, 40 or 50 boiling fprings together, which, I believe, all proceed from one and the fame refervoir. In fome the water is perfectly clear, in others thick and clayey; in fome, where it paffes through a fine ochre, it is tinged red as fcarlet; and in others, where it flows over a paler clay, it is white as milk.

The water spouts up from all, from fome continually, from others only at intervals. The largeft fpring, which is in the middle, particularly engaged our attention the whole day that we spent here, from fix in the morning till feven at night. The aperture through which the water arofe, and the depth of which I cannot deter

mine, was 19 feet in diameter; round the top of it is a bafon, which, together with the pipe, has the form of a cauldron; the margin of the bafon is upwards of nine feet one inch higher than the conduit, and its diameter is of fifty-fix feet. Here the water does not spout continually, but only by intervals feveral times a day; and, as I was informed by the people in the neighbourhood, in bad rainy weather, higher than at other times.

On the day that we were there, the water fpouted at ten different times, from fix in the morning till eleven A. M. each time, to the height of between five and ten fathoms; till then the water had not rifen above the margin of the pipe, but now it began by degrees to fill the upper balon, and at laft ran over. The people who were with us told us, that the water would foon fpout up much higher than it had done till then, and this appeared very credible to us. To determine its height therefore, with the utmost accuracy, Dr. Lind, who had accompanied us on this voyage in the capacity of an aftronomer, fet up his quadrant.

Soon after four o'clock we obferved that the earth began to tremble in three different places, as likewife the top of a mountain, which was about three hundred fathoms diftant from the mouth of the fpring. We also frequently heard a fubterraneous noife like the difcharge of a cannon; and immediately after a column of water fpouted from the opening, which at a great height divided

itself into several rays, and, according to the obfervations made with the quadrant, was ninety-two feet high. Our great furprize at this uncommon force of the air and fire was yet increafed, when many ftones, which we had flung into the aperture, were thrown up again with the fpouting water. You can eafily conceive, Sir, with how much pleasure we spent the day here; and indeed, I am not much furprized, that a people fo much inclined to fuperftition as the Icelanders are, imagine this to be the entrance of hell; for this reafon they feldom pafs one of these openings without fpitting into it; or, as they fay, uti fandens man, into the devil's mouth.

Of the Bafaltic Pillars. From Profeffor Bergman's Letter to Dr. Troil.

F all the mountains hitherto

to

thefe pillars is a problem which we have hitherto been unable to folve fatisfactorily. This difficulty has appeared fo infurmountable fome, that they have thought it impoffible to be the effects of nature, and have confidered them as works made by human hands: this idea betrays the utmoft ignorance in regard to the true nature of thefe mountains of pillars, and does not even deferve a refutation.

As far as we know, nature makes use of three methods to produce regular forms in the mineral kingdom, namely, that of cryftallization or precipitation 2dly, the crufting or fettling of the external furface of a liquid mafs whilft it is cooling and, 3dly, the bursting of a moift fubftance whilft it is drying.

The first method is the moft common, but to all appearance nature has not made ufe of this in the prefent cafe. Crystals are feldom or never found in any confiderable quantity running in the

doubt not any more remarkable than those that are compofed of angular pillars. A few years ago only one or two of this kind were known; but new ones are daily discovered, which is a plain proof how much our attention requires being rouzed to prevent it from flumbering, on the most important occafions.

It cannot be much doubted that there has been fome connections between thefe pillars, and the effects of a fubterraneous fire, as they are found in places where the figns of fire are yet visible; and as they are even found mixed with lava, tuff, and other fubftances produced by fire.

The cause of the regular form of

from one another, or, what is still more common, placed towards one another in feveral floping directions. They are alfo generally separated a little from one another, when they are regular; the nature of the thing likewife requires this; becaufe the feveral particles, of which the cryftals are compofed, muft have the liberty of following that power which affects their regular difpofition.

The bafalt columns, on the contrary, whofe height are frequently from thirty to forty feet, are placed parallel to one another in confiderable numbers, and fo close together that the point of a knife can hardly be introduced between them. Befides, in mott

places

places, each pillar is divided into feveral parts or joints, that feem to be placed upon one another; and indeed it is not uncommon for crystals to be formed above one another in different layers, when the folvent has been vifibly diminished at different times; but then the upper cryftals never fit fo exactly upon the lower ones as to produce connected prifms of the fame length and depth as all the ftrata taken together, but each ftratum feparately forms its own crystals.

How then can the Giant's Caufeway, in the county of Antrim, Fingal's Cave at Staffa, and all other affemblages of pillars of the fame kind, be confidered as crystallizations? Precipitation, both in the wet and dry manner, requires that the particles fhould be free enough to fix themselves in a certain order; and as this is not practicable in a large melted mafs, no cryftallizations appear in it, except on its furface, or in its cavities.

Add to this, that the bafalts in a fresh fracture do not fhew a plain fmooth furface under the microfcope, but appear fometimes like grains of different magnitude, and at other times refemble fine rays Fanning in different directions, that do not correfpond with the internal structure of the cryftals, which I have endeavoured to examine in another place.

From what I have hitherto mentioned, the opinion that the bafalts have been produced by cryftallization, becomes at leaft lefs probable, whether we admit the wet or dry method. But I must not omit that the spars exhibit a kind of cryftallization, which at first fight refemVOL. XXIII.

bles a heap of b falts; but, upon a closer examination, a very great difference is obferved. The form of the fpar is every where alike, but the bafalis differ from one another in point of fize and number of fides; the former, when broken, confits of many fmall unequal cubes, but the bafalt does not feparate in regular parts, &c.

Nature's fecond method to produce regular forms is that of crusting the outer furface of a melted mafs, by a fudden refrigeration. Nature, to effect this purpofe, makes ufe of polyedrous and irregular forms. if we fuppofe a confiderable bed, which is become fluid by fire, and fpread over a plain, it evidently appears that the furface must first of all lofe the degree of heat requifite for melting, and begin to congeal; but the cold requifite for this purpofe likewife contracts the uppermot congealed ftratum into a narrower pace, and confequently caufes it to feparatę from the remaining liquid mafs, as the fide expoted to the air is already too ftiff to give way. In this manner a ftratum is produced running in a parallel direction with the whole mafs, others ftill are produced by the fame caufe, in proportion as the refrigeration pene trates deeper.

*

Hence we may, in my opinion, very plainly fee how a bed may be divided into ftrata. In the fame manner the refrigeration advances on the fides, and confequently divides the ftrata into polyed rous pieces of pillars, that can hardly ever be exactly fquare, as the ftrongest refrigeration into the inner parts of the mafs advances almost in a diagonal line from the corners. If we add to this, that a H

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