The Botanic Garden Volume I Part 23

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 Derbyshire 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 Lordship 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 washing 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.

STEEL.

It is probably owing to a total deprivation of vital air which it holds with so great avidity, that iron on being kept many hours or days in ignited charcoal becomes converted into steel, and thence acquires the faculty of being welded when red hot long before it melts, and also the power of becoming hard when immersed in cold water; both which I suppose depend on the same cause, that is, on its being a worse conductor of heat than other metals; and hence the surface both acquires heat much sooner, and loses it much sooner, than the internal parts of it, in this circ.u.mstance resembling gla.s.s.

When steel is made very hot, and suddenly immerged in very cold water, and moved about in it, the surface of the steel becomes cooled first, and thus producing a kind of case or arch over the internal part, prevents that internal part from contracting quite so much as it otherwise would do, whence it becomes brittler and harder, like the gla.s.s-drops called Prince Rupert's drops, which are made by dropping melted gla.s.s into cold water. This idea is countenanced by the circ.u.mstance that hardened steel is specifically lighter than steel which is more gradually cooled. (Nicholson's Chemistry, p. 313.) Why the brittleness and hardness of steel or gla.s.s should keep pace or be companions to each other may be difficult to conceive.

When a steel spring is forcibly bent till it break, it requires less power to bend it through the first inch than the second, and less through the second than the third; the same I suppose to happen if a wire be distended till it break by hanging weights to it; this shews that the particles may be forced from each other to a small distance by less power, than is necessary to make them recede to a greater distance; in this circ.u.mstance perhaps the attraction of cohesion differs from that of gravitation, which exerts its power inversely as the squares of the distance. Hence it appears that if the innermost particles of a steel bar, by cooling the external surface first, are kept from approaching each other so nearly as they otherwise would do, that they become in the situation of the particles on the convex side of a bent spring, and can not be forced further from each other except by a greater power than would have been necessary to have made them recede thus far. And secondly, that if they be forced a little further from each other they separate; this may be exemplified by laying two magnetic needles parallel to each other, the contrary poles together, then drawing them longitudinally from each other, they will slide with small force till they begin to separate, and will then require a stronger force to really separate them. Hence it appears, that hardness and brittleness depend on the same circ.u.mstance, that the particles are removed to a greater distance from each other and thus resist any power more forcibly which is applied to displace them further, this const.i.tutes hardness. And secondly, if they are displaced by such applied force they immediately separate, and this const.i.tutes brittleness.

Steel may be thus rendered too brittle for many purposes, on which account artists have means of softening it again, by exposing it to certain degrees of heat, for the construction of different kinds of tools, which is called tempering it. Some artists plunge large tools in very cold water as soon as they are compleatly ignited, and moving it about, take it out as soon as it ceases to be luminous beneath the water; it is then rubbed quickly with a file or on sand to clean the surface, the heat which the metal still retains soon begins to produce a succession of colours; if a hard temper be required, the piece is dipped again and stirred about in cold water as soon as the yellow tinge appears, if it be cooled when the purple tinge appears it becomes fit for gravers' tools used in working upon metals; if cooled while blue it is proper for springs. Nicholson's Chemistry, p. 313. Keir's Chemical Dictionary.

MODERN PRODUCTION OF IRON.

The recent production of iron is evinced from the chalybeate waters which flow from mora.s.ses which lie upon gravel-beds, and which must therefore have produced iron after those gravel-beds were raised out of the sea. On the south side of the road between Cheadle and Okeymoor in Staffordshire, yellow stains of iron are seen to penetrate the gravel from a thin mora.s.s on its surface. There is a fissure eight or ten feet wide, in a gravel-bed on the eastern side of the hollow road ascending the hill about a mile from Trentham in Staffordshire, leading toward Drayton in Shropshire, which fissure is filled up with nodules of iron- ore. A bank of sods is now raised against this fissure to prevent the loose iron nodules from falling into the turnpike road, and thus this natural curiosity is at present concealed from travellers. A similar fissure in a bed of marl, and filled up with iron nodules and with some large pieces of flint, is seen on the eastern side of the hollow road ascending the hill from the turnpike house about a mile from Derby in the road towards Burton. And another such fissure filled with iron nodes, appears about half a mile from Newton-Solney in Derbyshire, in the road to Burton, near the summit of the hill. These collections of iron and of flint must have been produced posterior to the elevation of all those hills, and were thence evidently of vegetable or animal origin. To which should be added, that iron is found in general in beds either near the surface of the earth, or stratified with clay coals or argillaceous grit, which are themselves productions of the modern world, that is, from the recrements of vegetables and air-breathing animals.

Not only iron but manganese, calamy, and even copper and lead appear in some instances to have been of recent production. Iron and manganese are detected in all vegetable productions, and it is probable other metallic bodies might be found to exist in vegetable or animal matters, if we had tests to detect them in very minute quant.i.ties. Manganese and calamy are found in beds like iron near the surface of the earth, and in a calciform state, which countenances their modern production. The recent production of calamy, one of the ores of zinc, appears from its frequently incrusting calcareous spar in its descent from the surface of the earth into the uppermost fissures of the limestone mountains of Derbyshire. That the calamy has been carried by its solution or diffusion in water into these cavities, and not by its ascent from below in form of steam, is evinced from its not only forming a crust over the dogtooth spar, but by its afterwards dissolving or destroying the sparry crystal. I have specimens of calamy in the form of dogtooth spar, two inches high, which are hollow, and stand half an inch above the diminished sparry crystal on which they were formed, like a sheath a great deal too big for it; this seems to shew, that this process was carried on in water, otherwise after the calamy had incrusted its spar, and dissolved its surface, so as to form a hollow cavern over it, it could not act further upon it except by the interposition of some medium. As these spars and calamy are formed in the fissures of mountains they must both have been formed after the elevation of those mountains.

In respect to the recent production of copper, it was before observed in note on Canto II. l. 394, that the summit of the grit-stone mountain at Hawkstone in Shropshire, is tinged with copper, which from the appearance of the blue stains seems to have descended to the parts of the rock beneath. I have a calciform ore of copper consisting of the hollow crusts of cubic cells, which has evidently been formed on crystals of fluor, which it has eroded in the same manner as the calamy erodes the calcareous crystals, from whence may be deduced in the same manner, the aqueous solution or diffusion, as well as the recent production of this calciform ore of copper.

Lead in small quant.i.ties is sometimes found in the fissures of coal- beds, which fissures are previously covered with spar; and sometimes in nodules of iron-ore. Of the former I have a specimen from near Caulk in Derbyshire, and of the latter from Colebrook Dale in Shropshire. Though all these facts shew that some metallic bodies are formed from vegetable or animal recrements, as iron, and perhaps manganese and calamy, all which are found near the surface of the earth; yet as the other metals are found only in fissures of rocks, which penetrate to unknown depths, they may be wholly or in part produced by ascending steams from subterraneous fires, as mentioned in note on Canto II. l. 398.

SEPTARIA OF IRON-STONE.

Over some lime works at Walsall in Staffordshire, I observed some years ago a stratum of iron earth about six inches thick, full of very large cavities; these cavities were evidently produced when the material pa.s.sed from a semifluid state into a solid one; as the frit of the potters, or a mixture of clay and water is liable to crack in drying; which is owing to the further contraction of the internal part, after the crust is become hard. These hollows are liable to receive extraneous matter, as I believe gypsum, and sometimes spar, and even lead; a curious specimen of the last was presented to me by Mr. Darby of Colebrook Dale, which contains in its cavity some ounces of lead-ore.

But there are other septaria of iron-stone which seem to have had a very different origin, their cavities having been formed in cooling or congealing from an ignited state, as is ingeniously deduced by Dr.

Hutton from their internal structure. Edinb. Transact. Vol. I. p. 246.

The volcanic origin of these curious septaria appears to me to be further evinced from their form and the places where they are found.

They consist of oblate spheroids and are found in many parts of the earth totally detached from the beds in which they lie, as at East Lothian in Scotland. Two of these, which now lie before me, were found with many others immersed in argillaceous shale or shiver, surrounded by broken limestone mountains at Bradbourn near Ashbourn in Derbyshire, and were presented to me by Mr. Buxton, a gentleman of that town. One of these is about fifteen inches in its equatorial diameter, and about six inches in its polar one, and contains beautiful star-like septaria incrusted and in part filled with calcareous spar. The other is about eight inches in its equatorial diameter, and about four inches in its polar diameter, and is quite solid, but shews on its internal surface marks of different colours, as if a beginning separation had taken place. Now as these septaria contain fifty per cent, of iron, according to Dr. Hutton, they would soften or melt into a semifluid globule by subterraneous fire by less heat than the limestone in their vicinity; and if they were ejected through a hole or fissure would gain a circular motion along with their progressive one by their greater friction or adhesion to one side of the hole. This whirling motion would produce the oblate spheroidical form which they possess, and which as far as I know can not in any other way be accounted for. They would then harden in the air as they rose into the colder parts of the atmosphere; and as they descended into so soft a material as shale or shiver, their forms would not be injured in their fall; and their presence in materials so different from themselves becomes accounted for.

About the tropics of the large septarium above mentioned, are circular eminent lines, such as might have been left if it had been coa.r.s.ely turned in a lathe. These lines seem to consist of a fluid matter, which seems to have exsuded in circular zones, as their edges appear blunted or retracted; and the septarium seems to have split easier in such sections parallel to its equator. Now as the crust would first begin to cool and harden after its ejection in a semifluid state, and the equatorial diameter would become gradually enlarged as it rose in the air; the internal parts being softer would slide beneath the polar crust, which might crack and permit part of the semifluid to exsude, and it is probable the adhesion would thus become less in sections parallel to the equator. Which further confirms this idea of the production of these curious septaria. A new-cast cannon ball red-hot with its crust only solid, if it were shot into the air would probably burst in its pa.s.sage; as it would consist of a more fluid material than these septaria; and thus by discharging a shower of liquid iron would produce more dreadful combustion, if used in war, than could be effected by a ball, which had been cooled and was heated again: since in the latter case the ball could not have its internal parts made hotter than the crust of it, without first loosing its form.

NOTE XIX.--FLINT.

_Trans.m.u.te to glittering flints her chalky lands, Or sink on Ocean's bed in countless sands._

CANTO II. l. 217.

1. SILICEOUS ROCKS.

The great ma.s.ses of siliceous sand which lie in rocks upon the beds of limestone, or which are stratified with clay, coal, and iron-ore, are evidently produced in the decomposition of vegetable or animal matters, as explained in the note on mora.s.ses. Hence the impressions of vegetable roots and even whole trees are often found in sand-stone, as well as in coals and iron-ore. In these sand-rocks both the siliceous acid and the calcareous base seem to be produced from the materials of the mora.s.s; for though the presence of a siliceous acid and of a calcareous base have not yet been separately exhibited from flints, yet from the a.n.a.logy of flint to fluor, and gypsum, and marble, and from the conversion of the latter into flint, there can be little doubt of their existence.