considerable portions of gneiss and mica-slate. This being the case, it is probable the topaz will be found in one, or possibly in all these different rocks. It may, however, be alleged, that probably the topaz-rock also occurs there, and that the topaz may be derived from it. be derived from it. But the topaz-rock is one of the rarest of the mountain-rocks, and the topaz which it contains has always a yellow colour, and differs somewhat in regular form from the topaz of Scotland; it is also smaller, and is never accompanied with rock-crystal or precious beryl. Hence it is not probable, that the topazrock occurs in the district of which we are treating. If, then, the topaz-rock is wanting, it will be inquired, in which of the primitive rocks already mentioned we are to look for it? Some may be of opinion that it occurs in veins, in gneiss or mica-slate, as is the case with the Bohemian, and certain varieties of the Saxon topaz. The want of all the accompanying minerals, as tin-stone, arsenic pyrites, copper pyrites, fluor-spar, &c. render this supposition improbable. But the topaz of Siberia agrees with that found in Aberdeenshire, in having green and white as its most frequent colour; in opalescence; in figure, being generally bevelled at the extremity; in size, the largest topazes being found in Siberia; and in accompanying minerals, which are usually rock-crystal and precious beryl.

Lastly, the Siberian topaz is said to occur in drusy cavities or veins in granite, and in considerable quantity. If this account be correct, we may infer that the Aberdeenshire topaz will be found in drusy cavities or veins in granite, and in considerable quantity,

I trust the conjecture I have now suggested, will induce mineralogists to examine the tract of country where this interesting mineral is found.*

* Since this paper was read to the Society, I have been informed by my friend Colonel Imrie, that the large fragment of topaz in the possession of Mr. Farquharson of Invercauld, was broken from a mass of granite.

Another topaz has been found near Invercauld, in Aberdeenshire. Its weight, as communicated to me by Colonel Imrie, is 3420 grains, or 7 ounces 2 pennyweights and 12 grains: Its specific gravity 3.56. It is said, that a distinct crystal, heavier than the preceding one, has been found in the same county, and is now in the possession of a gentleman in Aberdeen.

INTELLIGENCE.

GALVANIC BATTERY.

ON Saturday, July 2d, 1813, J. G. Children, Esq. put in action the greatest galvanic battery that has ever been constructed. It consisted of 20 pair of copper and zinc plates, each plate 6 feet in length, 2 feet 8 inches in breadth. Each pair was fixed together at the top by pieces of lead cut into ribbons. A separate wooden cell was constructed for each pair. The plates were suspended from a wooden beam fixed at the ceiling, and were so hung by means of counterpoises that they could be easily raised or let down into the cells. The cells were filled with water, containing a mixture of sulphuric and nitric acids. At first the acids amounted to 1-60th of the water; but more was gradually added till it amounted to the 30th. Leaden pipes were attached to the two extremities of the battery, and conveyed the electricity out of doors to an adjoining shade, where the experiments were made. The power of this battery was very great; though I am not certain whether it increased in proportion to the size of the plates. It ignited about 6 feet in length of thick platinum wire. The heat produced was very intense, It melted platinum with great facility. Iridium was likewise melted into a globule, and proved to be a brittle metal.

The ore of iridium and osmium was likewise melted, but not so completely. Charcoal was kept in a white heat in chlorine gas, and in phosgene gas; but no change took place in either of these gases.

Neither tungsten nor uranium underwent any change. A very singular fact was pointed out by the sagacity of Dr. Wollaston, and succeeded upon trial. A greater length of thick platinum wire was ignited than of platinum wire of a much smaller size. This Dr. Wollaston had previously ascertained in his own minute galvanic batteries, consisting of a single pair of small plates.

Annals of Philosophy, No. VIII.

THE FAROE ISLANDS,

THESE Islands have long been considered as highly worthy the attention of naturalists, particularly as regards their geology and mineralogy; and as every information respecting them will be deemed interesting, we beg leave to present to our readers, the following extract of a letter, which we have received from our learned friend and correspondent Thomas Allan, Esq. of Edinburgh.

"You will naturally be anxious to know what we saw in Faroe; of this I shall try to give you a sketch in as few words as possible. Sir George Mackenzie having been offered accommodations in one of his majesty's vessels, in case he had any inclination to visit the Faroe Islands, asked me to accompany him, which I most readily consented to do. About the end of May (1812) we sailed from Leith in the Clio, and after clearing the Firth, reached Thorshaven the capital in 60 hours; the distance is 500 miles, so that we were very fortunate in our run.

The Islands are 18 in number inhabited, besides several small ones uninhabited. They extend about 60 miles from N. to S. The largest is Stromoe, 25 miles long, by about & in the widest part.

From one end to the other they are completely composed of trap-rocks, greenstone, basalt, amygdaloid and tuff. These are arranged in beds wonderfully regular, and rising to the north and west. The highest mountain is in Stromoe, and may be about 3000 feet. We measured one in Osterve which is 2825 feet. On the north west side, the coast presents some of the most tremendous cliffs I ever saw : one I measured and found it to be 1134 feet. This cliff is in Osterve, and is called the Kodlen; there is another near it in Stromoe called the Mylling, which is considered the highest in Faroe, and may be about one third loftier than the one I measured. These are entirely composed of trap; I did not see an atom of stratification in the country.

In Suderoe there is coal. We did not visit that Island, but, from the similarity of its structure, as seen from a distance, it in every probability is essentially the same as the other islands, the coal resembling that of Ballintory in Antrim, as also that which occurs in Skye. These traprocks are intersected in every direction with dykes which are generally nearly perpendicular, sometimes perfectly so.

in

Upon the zeolitic amygdaloid we saw some of the most evident marks of fusion. Of minerals we got none but zeolites, calcedonies, and some native copper. Of the former I have got some mezotype far finer than any I ever saw, groups of transparent diverging needles from one to two inches long, perfectly crystallized and terminated. Of the stilbite I also got some magnificent specimens, one I think new in large cubes; these are sometimes elongated, forming the rectangular prism, sometimes they are truncated on all the solid angles so as to present the cube octaedre. They are semi-transparent, and where they have been affected by the weather, are snow-white. One of the crystals I got of this is an inch long, and about thick. The calcedonies are difficult to procure, but are some of them magnificent. I saw in the rock the remains of one that had been four feet

in length and about two in the widest part. In the cavity of one of them I found the mezotype finely crystallized. The situation of the copper is the most singular, it occurs disseminated in a bed of trap and zeolitic amygdaloid beauttifully crystallized, and sometimes forming the centre of a very fine zeolite. This is a curious fact, it was on this variety of trap that we saw such evident marks of fusion, and no copper from the veins of Cornwall can present crystallizations more perfect.

We remained five weeks in the Islands, and had as rapid a voyage home as we had out."

ZIRCON FOUND IN SCOTLAND.

PROFESSOR JAMESON of Edinburgh, in a letter to the Editor, mentions his having discovered this rare mineral in Galloway imbedded in gneiss.

GEOLOGY OF LONG ISLAND.

WE have received a Letter from the Hon. Professor Mitchill, containing the following additional facts illustrating the modern and alluvial character of Long Island.

"In the third number of the American Mineralogical Journal, you published a paper of mine, shewing that the whole of Nassau or Long Island, in the State of NewYork, was alluvial, and not one half alluvial and the other primitive, as Messrs. Volney and Maclure have taught. I have additional facts, which I have now the pleasure to make known to you.

1. North Hempstead in Queen's County.-A well was dug during the summer of 1813, at Great Neck, for Messrs. William and John Mott. The place is, at least, three miles north of the ridge of hills at Success. They penetrated the