April. The variation of the weather this month has been equalled by the uncommon variation of the needle.

Between noon of the 1st Apr..

Rain fallen Between noon of the 1st May 1735 inch.

Evaporation during the same period

.1.90

ARTICLE X.

ANALYSES OF BOOKS.

Transactions of the Geological Society, Volume 2d. London, William Phillips, 1814.

This volume contains 24 papers, and is accompanied by afvolume of plates.

I. On certain Products obtained in the Distillation of Wood, with some Account of Bituminous Substances, and Remarks on Coal. By J. Macculloch, M. D. F. L. S., Chemist to the Ordnance, and Lecturer on Chemistry at the Royal Military Academy at Woolwich, and Vice President of the Geological Society.

When wood is exposed to destructive distillation there comes over a thick black fluid like tar. Great quantities of this substance are obtained at the powder works from the distillation of willow and alder. It was this substance that Dr. Macculloch examined. It is very inflammable, and may be burnt like oil in a lamp. When it is washed in water, that liquid separates a considerable proportion of acetic acid, coloured by an oily matter, which has an empyreumatic smell and taste. When triturated, or boiled with carbonate of potash, it acquires a pitchy consistence; but does not seem to combine fully with the alkali. It is soluble in alcohol, ether, caustic fixed alkaline lees, acetic acid, and the mineral acids. Fat oils and fresh essential oils dissolve it imperfectly; but the drying oils and inspissated essential oils act on it more readily. Coloured oil of turpentine dissolves a good deal of it. Naphtha has scarcely any action on it. When exposed to a heat just sufficient to keep it boiling, an oil comes over, at first light coloured, but becoming darker as the process advances. If the heat of the retort be gradually increased to redness, nothing remains but a spongy charcoal. There is found in the receiver an oil and acetic acid, combined with a little ammonia. No gas is evolved in this process, if the heat be carefully managed. When a gas is formed, the oil has been exposed to too high a temperature, by letting the fire act too much on the upper part of the retort. If the heat be continued for a certain time, what remains in the retort resembles petroleum; if longer, maltha; if longer, bitumen; and if still longer, only coal remains. But these resemblances are merely external. Bitumen and our substance are different in their composition; since the first is soluble in naphta, the second insoluble. Dr. Macculloch conceives it probable that vegetables may have been converted into bitumen or jet, by the action of water, and the bitumen afterwards converted into coal by heat. He shows that heat is incapable of bituminizing wood, but that it converts jet into coal. Many other very ingenious hypotheses respecting the origin of the various species of coal and plumbago occur in this paper; but they are of so bold a nature, and so little supported by the present state of our knowledge, that I am afraid to enter upon them, least they should lead to a tedious controversy about a subject, the decision of which is at present obviously beyond the reach of our faculties. The valuable part of the paper is the chemical description of the new substance obtained by distilling vegetables, which Dr. M. proposes to distinguish by the name of

bistre.

II. Mineralogical Account of the Isle of Man. By I. F. Berger, M. D. M.G. S.-The Isle of Man, the situation of which is too well known to require specification here, is rather more than 30 miles long from north to south, while its breadth varies from 15 to eight miles. The northern extremity is tolerably low for about five miles, where a range of mountains commence that proceed to the southern extremity. This group of mountains consists of three

chains, separated from each other by high table lands. Three very narrow openings cross the group from east to west. The furthest north of which lies between Douglas Town and Peel Town; and the furthest south is the narrow channel between the island and Calf of Man. The first of these is highest, and the last lowest, being under the level of the sea. The highest mountain in Man is Snowfield, which is 2000 feet above the level of the sea. Dr. Berger has given the elevation of 89 mountains and spots of this island, which has enabled him to give interesting sections of the island in various directions. The Calf of Man is 206 feet high. The mean annual temperature he reckons from the heat of 31 springs, at 49.99°, or 50°, Fahrenheit.

Very little granite has been observed in Man. It occurs, however, in two or three spots; but most likely only forming beds in the clay-slate, which constitutes the central and highest part of the island. Grey-wacke covers the lower parts of this clay-slate, almost surrounds it, and constitutes the sea-coast both on the east and west side of Man. This grey-wacke sometimes contains beds of grey-wacke slate and flinty slate. It has not been observed to contain any animal remains. A floetz lime-stone containing madreporites, and some univalve shells, occupies the south-east coast; except a peninsula of old red sand-stone, which occurs likewise at Peel Town. The Calf of Man is grey-wacke. Veins containing galena occur in three different parts of the island, and always in the grey-wacke. Sulphuret of copper likewise occurs. These veins have been wrought more than once, but are at present abandoned. Dr. Berger thinks that the southern part of the island has at some former period subsided. Hence he accounts for the gradual declivity, the dip, and the narrow valleys. The population is reckoned at 28,000; but Mr. Curwen thinks it does not exceed 23,000.

III. On the Granite Tors of Cornwall. By Dr. Macculloch.— The Logging Rock, and Cheese Wring in Cornwall, and the Vixen Tor in Dartmoor, exhibiting curious configurations of granite rocks, are described and figured; and Dr. Macculloch shows very clearly that they have resulted from the natural effects of the disintegration of the rock, and that they have not, as some supposed, been formed artificially. He terminates the paper with some speculations on the origin of granite, and rather inclines to its igneous origin. Into these speculations I think it unnecessary to enter; because I conceive them to be entirely beyond the reach of the human faculties. Supposing a man to spend his life in guessing how the Almighty brought the earth into its present state, and supposing him even to guess right, (no very probable supposition) Task by what means he could prove his conjecture? The only conclusive evidence in such a case is historical evidence, and where could it be found? Geology does not consist in speculating about the origin or creation of the earth, it consists simply in determining the number, nature, and position of all the rocks

which constitute the surface of the earth; and till it is confined to this, it can never become a useful nor correct science. If you can demonstrate by petrifactions the epochs of the formation of rocks, or the changes they must have undergone, do so; but never reason or speculate from the mere love of hypothesis.

I may just observe for the consideration of Dr. M., that nothing is more common than to find sand-stone having exactly the structure of his Cornish granite, I mean decaying ultimately into balls. As examples, I may mention a sand-stone in the Isle of Skye, a sand-stone in Fifeshire, and another in Dumfries-shire. It follows, therefore, that if the Doctor's reasoning about the igneous origin of granite be accurate, he must admit likewise the igneous origin of sand-stone.

IV. Notes on the Mineralogy of the Neighbourhood of St. David's Pembrokeshire. By John Kidd, M. D. Prof. Chem. in the University of Oxford, M. G. S.-It would appear from Dr. Kidd's description, that the fundamental rock of this district is a syenite, which seems in some cases to pass into granite, in others to porphyry; but, unfortunately, the descriptions are not sufficiently minute to make us sure of these transitions. Beds or rocks of these three different species, however, occur here. Over the syenite, and, in general, covering the flat country, lie beds of clay-slate, which vary a good deal in their appearance. This slate is often black, has little lustre, and contains quartz veins running through it; hence it is probably a transition slate. Dr. Kidd calls it grey-wacke; but that term never can be applied correctly to a slate. Indeed it is quite obvious from Dr. Kidd's observations, that the term grey-wacke has no fixed meaning in his mind: yet it is as well defined a rock as any other, and any mineralogist in five minutes might make himself so well acquainted with its characters, as afterwards to run no risk of confounding it with any other. The following definition may be of some use.

"Grey-wacke of Werner is a conglomerated rock with a basis of clay-slate. It contains portions or fragments of clay-slate, flinty-slate, quartz; and sometimes grains of felspar and scales of mica."

If Dr. Kidd dislikes the term grey-wacke, he may substitute transition sand-stone. The word grey-wacke was invented by the miners at Freyberg, where the rock abounds. Werner adopted it from them, and drew up an accurate description of the rock. Very good specimens of it are to be found in the Pentlands and Lamermuirs, near Edinburgh. About 100 yards east of the fourth milestone from Truro in Cornwall, there is a quarry of excellent grey-wacke, which is employed in mending the road. Many other British localities might be given; but from either of these two it would be easy to bring up a sufficient number of specimens to London, to make every mineralogist familiar with the appearance of this rock. I conceive that the structure of the country described in this paper by Dr. Kidd is similar to that of the

Crifle in Galloway, of which an account will be found in the Annals of Philosophy, vol. iii. p. 465.

V. An Account of the Brine Springs at Droitwich. By Leonard Horner, F. R.S. M.G.S.--Salt has been made at Droitwich in Worcester for above a thousand years. The structure of the country, as far as it has been ascertained, is this. Uppermost a bed of sand-stone, usually red, but sometimes greenish, and then containing veins of gypsum. Mr. Aikin and Mr. Horner consider it as old red sand-stone. Under this lies a bed of gypsum about 150 feet thick: below this a river of brine 22 inches deep. Lastly, there lies a bed of rock salt which has never been penetrated. If the sand-stone be old red sand-stone, the position of the gypsum and rock salt is uncommon, as these beds have hitherto been observed only above the red sand-stone and never below it. There are four pits at present used at Droitwich, and the quantity of brine which flows out is much greater than can be consumed. The quantity of salt manufactured annually is about 16,000 tons. This is chiefly consumed in England, and pays a duty of 320,000l. The present market price of the salt is 317. per ton, 301. of which is duty.

The specific gravity of the brines of the different pits is as follows::

The last pit is not at present in use, and is probably somewhat mixed with surface water. None of them are perfectly saturated; for water saturated with salt at 55 is of the specific gravity 1-21. Walker's pit ought to contain, by my experiments, 28-88 per cent. of salt; or three ounces of it hold in solution 470 grains of salt. Mr. Horner, however, obtained by evaporation only 431 86 grains; but it is well known to chemists, that the whole of the salt dissolved in water cannot be recovered by evaporation. However carefully the evaporation be conducted, a portion of the salt always makes its escape. The quantity of salt obtained by evaporation from four cubic inches of each of the pits, by Mr. Horner, was as follows:

The salt was dried in the temperature of 180°. The constituents of this salt Mr. Horner found as follows: