Volume I Part 23 (1/2)
Another mode in which limestone appears is in the form of round granulated particles, but slightly cohering together; of this kind a bed extends over Lincoln heath, perhaps twenty miles long by ten wide. The form of this calcareous sand, its angles having been rubbed off, and the flatness of its bed, evinces that that part of the country was so formed under water, the particles of sand having thus been rounded, like all other rounded pebbles. This round form of calcareous sand and of other larger pebbles is produced under water, partly by their being more or less soluble in water, and hence the angular parts become dissolved, first, by their exposing a larger surface to the action of the menstruum, and secondly, from their attrition against each other by the streams or tides, for a great length of time, successively as they were collected, and perhaps when some of them had not acquired their hardest state.
This calcareous sand has generally been called ketton-stone and believed to resemble the sp.a.w.n of fish, it has acquired a form so much rounder than siliceous sand from its being of so much softer a texture and also much more soluble in water. There are other soft calcareous stones called tupha which are deposited from water on mosses, as at Matlock, from which moss it is probable the water may receive something which induces it the readier to part with its earth.
In some lime-stones the living animals seem to have been buried as well as their sh.e.l.ls during some great convulsion of nature, these sh.e.l.ls contain a black coaly substance within them, in others some phlogiston or volatile alcali from the bodies of the dead animals remains mixed with the stone, which is then called liver-stone as it emits a sulphurous smell on being struck, and there is a stratum about six inches thick extends a considerable way over the iron ore at Wingerworth near Chesterfield in Derbys.h.i.+re which seems evidently to have been formed from the sh.e.l.ls of fresh-water muscles.
There is however another source of calcareous earth besides the aquatic one above described and that is from the recrements of land animals and vegetables as found in marls, which consist of various mixtures of calcareous earth, sand, and clay, all of them perhaps princ.i.p.ally from vegetable origin.
Dr. Hutton is of opinion that the rocks of marble have been softened by fire into a fluid ma.s.s, which he thinks under immense pressure might be done without the escape of their carbonic acid or fixed air. Edinb.
Transact. Vol. I. If this ingenious idea be allowed it might account for the purity of some white marbles, as during their fluid state there might be time for their partial impurities, whether from the bodies of the animals which produced the sh.e.l.ls or from other extraneous matter, either to sublime to the uppermost part of the stratum or to subside to the lowermost part of it. As a confirmation of this theory of Dr.
Hutton's it may be added that some calcareous stones are found mixed with lime, and have thence lost a part of their fixed air or carbonic gas, as the bath-stone, and on that account hardens on being exposed to the air, and mixed with sulphur produces calcareous liver of sulphur.
Falconer on Bath-water. Vol. I. p. 156. and p. 257. Mr. Monnet found lime in powder in the mountains of Auvergne, and suspected it of volcanic origin. Kirwan's Min. p. 22.
NOTE XVII.--MORa.s.sES.
_Gnomes! you then taught transuding dews to pa.s.s Through time-fallen woods, and root-inwove mora.s.s_.
CANTO II. l. 115.
Where woods have repeatedly grown and perished mora.s.ses are in process of time produced, and by their long roots fill up the interstices till the whole becomes for many yards deep a ma.s.s of vegetation. This fact is curiously verified by an account given many years ago by the Earl of Cromartie, of which the following is a short abstract.
In the year 1651 the EARL OF CROMARTIE being then nineteen years of age saw a plain in the parish of Lockburn covered over with a firm standing wood, which was so old that not only the trees had no green leaves upon them but the bark was totally thrown off, which he was there informed by the old countrymen was the universal manner in which fir-woods terminated, and that in twenty or thirty years the trees would cast themselves up by the roots. About fifteen years after he had occasion to travel the same way and observed that there was not a tree nor the appearance of a root of any of them; but in their place the whole plain where the wood stood was covered with a flat green moss or mora.s.s, and on asking the country people what was become of the wood he was informed that no one had been at the trouble to carry it away, but that it had all been overturned by the wind, that the trees lay thick over each other, and that the moss or bog had overgrown the whole timber, which they added was occasioned by the moisture which came down from the high hills above it and stagnated upon the plain, and that n.o.body could yet pa.s.s over it, which however his Lords.h.i.+p was so incautious as to attempt and slipt up to the arm-pits. Before the year 1699 that whole piece of ground was become a solid moss wherein the peasants then dug turf or peat, which however was not yet of the best sort. Philos. Trans. No.
330. Abridg. Vol. V. p. 272.
Mora.s.ses in great length of time undergo variety of changes, first by elutriation, and afterwards by fermentation, and the consequent heat. 1.
By water perpetually oozing through them the most soluble parts are first washed away, as the essential salts, these together with the salts from animal recrements are carried down the rivers into the sea, where all of them seem to decompose each other except the marine salt. Hence the ashes of peat contain little or no vegetable alcali and are not used in the countries, where peat const.i.tutes the fuel of the lower people, for the purpose of was.h.i.+ng linen. The second thing which is always seen oozing from mora.s.ses is iron in solution, which produces chalybeate springs, from whence depositions of ochre and variety of iron ores. The third elutriation seems to consist of vegetable acid, which by means unknown appears to be converted into all other acids. 1. Into marine and nitrous acids as mentioned above. 2. Into vitriolic acid which is found in some mora.s.ses so plentifully as to preserve the bodies of animals from putrefaction which have been buried in them, and this acid carried away by rain and dews and meeting with calcareous earth produces gypsum or alabaster, with clay it produces alum, and deprived of its vital air produces sulphur. 3. Fluor acid which being washed away and meeting with calcareous earth produces fluor or cubic spar. 4. The siliceous acid which seems to have been disseminated in great quant.i.ty either by solution in water or by solution in air, and appears to have produced the sand in the sea uniting with calcareous earth previously dissolved in that element, from which were afterwards formed some of the grit- stone rocks by means of a siliceous or calcareous cement. By its union with the calcareous earth of the mora.s.s other strata of siliceous sand have been produced; and by the mixture of this with clay and lime arose the beds of marl.
In other circ.u.mstances, probably where less moisture has prevailed, mora.s.ses seem to have undergone a fermentation, as other vegetable matter, new hay for instance is liable to do from the great quant.i.ty of sugar it contains. From the great heat thus produced in the lower parts of immense beds of mora.s.s the phlogistic part, or oil, or asphaltum, becomes distilled, and rising into higher strata becomes again condensed forming coal-beds of greater or less purity according to their greater or less quant.i.ty of inflammable matter; at the same time the clay beds become purer or less so, as the phlogistic part is more or less completely exhaled from them. Though coal and clay are frequently produced in this manner, yet I have no doubt, but that they are likewise often produced by elutriation; in situations on declivities the clay is washed away down into the valleys, and the phlogistic part or coal left behind; this circ.u.mstance is seen in many valleys near the beds of rivers, which are covered recently by a whitish impure clay, called water-clay. See note XIX. XX. and XXIII.
LORD CROMARTIE has furnished another curious observation on mora.s.ses in the paper above referred to. In a moss near the town of Eglin in Murray, though there is no river or water which communicates with the moss, yet for three or four feet of depth in the moss there are little sh.e.l.l-fish resembling oysters with living fish in them in great quant.i.ties, though no such fish are found in the adjacent rivers, nor even in the water pits in the moss, but only in the solid substance of the moss. This curious fact not only accounts for the sh.e.l.ls sometimes found on the surface of coals, and in the clay above them; but also for a thin stratum of sh.e.l.ls which sometimes exists over iron-ore.
NOTE XVIII.--IRON.
_Cold waves, immerged, the glowing ma.s.s congeal, And turn to adamant the hissing Steel._
CANTO II. l. 191.
As iron is formed near the surface of the earth, it becomes exposed to streams of water and of air more than most other metallic bodies, and thence becomes combined with oxygene, or vital air, and appears very frequently in its calciform state, as in variety of ochres. Manganese, and zinc, and sometimes lead, are also found near the surface of the earth, and on that account become combined with vital air and are exhibited in their calciform state.
The avidity with which iron unites with oxygene, or vital air, in which process much heat is given out from the combining materials, is shewn by a curious experiment of M. Ingenhouz. A fine iron wire twisted spirally is fixed to a cork, on the point of the spire is fixed a match made of agaric dipped in solution of nitre; the match is then ignited, and the wire with the cork put immediately into a bottle full of vital air, the match first burns vividly, and the iron soon takes fire and consumes with brilliant sparks till it is reduced to small brittle globules, gaining an addition of about one third of its weight by its union, with vital air. Annales de Chymie. Traite de Chimie, per Lavoisier, c. iii.