as may feem likely to give our readers an adequate idea of the author's style, as well as of the nature of the fubject, and his mode of treating it.

In the letter, number 4, Mr. P. fpeaking of the nomenclature generally adopted by the mineralogical writers, men tions his objections to the term Petrifaction; for as this means only the conversion into flone, it cannot of course be generally applied to denote the objects of his examination, fince these are found in various other flates of existence, fuch as the pyritous, and the bituminous.

The epithets, extraneous or adventitious, are ftill more objectionable, for they convey opinions refpecting those subftances, which a close examination of the facts will fhow to be ill founded.

"The term fofil," he fays, "fo often vaguely employed, is, in fact, the term, defcribing all thofe mineral fubftances, which have been dug out of the earth. Thefe I divide into primary and fecondary, agreeable to the generally accepted divifion of mountains. Under the PRIMARY FOSSILS, I place all those substances, which may be fuppofed to be natives of, and to have exifted pri mitively in, the fubterranean regions: fuch are the metals, ftones of the granitic clafs, and moft of the various fubftances, of which the primitive mountains are formed. Under the SECONDARY FOSSILS, I place thofe fubftances, which bear indifputable testimony, in their structure and form, of their having existed in an organized state; and which are therefore known to have had an animal or vegetable origin; but which have afterwards entered into, and become fabjects of, the mineral kingdom.

"SECONDARY FOSSILS, which are alone intended to be the fubjects of our inveftigation, may, according to their origin, be divided into two claffes, VEGETABLE OR ANIMAL FOSSILS. Each clafs will be found alfo capable of a further divifion, into orders, genera, and fpecies; which claffification, although impoffible to be made correfpondent with that of their recent analogues, will certainly, however, yield fome degree of perfpicuity to the ob fervations offered in this work. The varieties of the fpecies can feldom be expected to be difcoverable in our fpecimens; this term, therefore, may be adopted for thofe varieties dependent on compofition; and which may be diftinguished by the epithets, appropriated to the feveral kinds of matter of which they are formed: fuch as filiceous, calcareous, aluminous, bituminous, &c. Thus, I hope, without adopting any harsh or offenfive change, all confufion of terms may be avoided, and an intelligi. ble mode of expreffion fecured.

Tranfubftantiata, Linnæi.

་་ t

"It is proper to obferve here, that I fhall confider as foffil bodies, fome fubftances, which, by writers of confiderable autho rity, have been deemed unfit to come under that denomination. The fubftances which I here allude to, are thofe which, having loft, by the decompofing powers of certain fubterranean proceffes, not only all the fofter parts, but almoft the whole of those principles which are peculiar to animal or vegetable fubftances, feem to retain only the earth of the bony lamelle, or of the ligneous fibre. Thefe are the feffilia, vulgo dicta, of Linnæus. But, fince it is indubitable, that the remaining principles have not only entered into intirely new combinations; but that new matter, as carbonic acid, &c. is fuper-added, it must be allowed, that a degree of change, in the nature of the fubftance, must have taken place. Other bodies have been confidered as fecondary foffils, which, a flight examination will fuffice to fhew, ought not to be thus claffed. These are-ft. IMPRESSIONS*. These are certain hard, but once foft, mineral fubftances; which retain the figure which has been impreffed on them, by fome fecondary fofil. 2dly. CASTS +. These are formed by the depofition o mineral matter in the vacuities, left by the decay of organized bodies, involved in fome folid matrix. 3dly. INCRUSTATIONS . Thefe are formed by fuch an appofition of mineral matter, generally by precipitation or depofition, as effects the envelopement of fome vegetable or animal body, in a mineral cruft." P. 36.

The fifth letter contains the following elegant epitome of Geology :

"Mountains are, with propriety, divided into primitive, or primeval; and fecondary, or epizootic. The primitive and fecondary mountains differ, not only in their compofition, but even their form.

"The primitive mountains are compofed of granites, and of ftones of the granitic clafs; of porphyry, jafper, ferpentine, fand. ftone, trap, and fometimes, but more rarely, of lime-stone, Auors, gypfum, &c. Thefe fubftances, fometimes, lay [lie] in ftrata; but, moft frequently, they are found in huge block; thus a granite mountain, about thirty miles from the Cape of Good Hope, called the PEARL DIAMOND, rifes out of the ground, to the height of about 400 feet, being half a mile in circumference; and formed of a fingle block of granite. Thefe mountains never cover fecondary mountains, but are often covered by them. They are commonly the highest ridges in any chain, and terminate, generally, more narrow and sharp, than the fecondary.

Impreffa, Linnæi; Typolithi, Wailerii; Type and Ectype, Breynii; Figuratorum Lapidom Matrices, of others.

+ Redintegrata, Linnæi; Petrificata fpoliata, Luidii; Noyau, Gallorum.

Incruftata, Linnæi,

A 4

"The

"The most diftinguishing character of these mountains, açcording to Mr. Kirwan, is a circumftance which particularly demands your attention-no organic remains, he fays, are to be found, in the interior part of the fubftance of the ftones of which they are compofed.

:

"Secondary mountains are, generally, marked by a fofter outline and poffefs the diftinctive character, of being compofed of, or at least, of containing within them, the foffil remains of organized fubftances. They always reft on, and cover primary mountains and very commonly, alfo, they lean on their fides, or inveft them. The fecondary mountains are formed, like the primitive; of either one fpecies of stone, or of ftrata of different fpecies. Some are faid to be derivative, being fupposed to have originated from the difintegration of primitive mountains.

"The fubftances, of which the fecondary mountains are chiefly compofed, are lime-ftone, fwine-ftone, marlite, chalk, and gypfum. They are alfo, fometimes, formed of indurated clay and lithomarga, jafper, porphyry, trap, filiceous fand-ftone, and other fubftances, which belong alfo to the primitive mountains.

"The various ftrata of which the earth is compofed, as deep as the curiofity, and the neceffities of man, have induced him to explore them, manifeft, in a moft ftriking manner, the wifdom. difplayed in the arrangement of the materials which compofe the prefent world. The first layer, generally confifting of a rich black mould, is formed almoft entirely of the remains of innumerable animals and vegetables, which, having lived through their destined periods, have been refolved into their first principles. This fubftance, laying [lying] at the furface, where alone it would be of utility, yields fuftenance to the vegetable kingdom; and, thereby, becomes the actual, though not the immediate, fupport of man, and of the rest of the animal creation. Beneath this, is most commonly found, a thick bed of clay, which furnishes the matter of which bricks and tiles, with the various fpecies of pottery, and innumerable other articles, adapted to promote the comforts of focial life, are formed. Next to this, in general, vaft beds of gravel appear, compofed of pebbles; varying much in their fize and form and with this is alfo commonly found the finer gravel; which likewife varies, in different parts, in its degree of fineness, and in its colour. Underneath thefe are the infinitely varying ftrata of fand-ftone, lime-ftone, &c. which ferve, with the trunks of trees, which have grown in, and which have been nourished by, the firft layer; and with the bricks and tiles, made from the fecond layer, to fupply the materials, of which the dwellings of man may be compofed. They alfo ferve, with the fand and gravel of the third ftratum, to fupply that kind of furface to the earth, in those parts which are moit inhabited by the civilized part of mankind, as may best contribute to the comfort and expedition of the intercourfe, which muft, neceffarily, zake place between the inhabitants of diftant parts. Thefe ftrata

:

of

of ftone, varying perpetually in their colour, folidity, and texture, form, in fome places, the ceilings and floors of the vaft fubterranean caverns, which are found in various parts of the world; and which often contain, as do thofe, particularly, in the principality of Bayreuth, and in the Hercynian forefts, very interefting fpecimens of thofe remains, which are the objects of par particular research. They also form the furrounding parts of thofe mines, which contain the valuable metals, which civilized man forms into innumerable articles of utility, and of ornament. Beneath fchiftofe or flaty ftrata, are, generally, found the immenfe beds of coal, fo neceffary to the comfort, and, in fome fituations, even to the existence of man. These ftrata do not always follow each other in regular order; fince fand and gravel are, fometimes, found at a confiderable depth, and trap, or ragftone, is often interpofed between them, in various directions.

"In almost all these ftrata, even to a very confiderable depth, the remains of vegetables and animals, which have existed in for. mer remote periods, are frequently found: and, in general, poffefs the fame phyfical and chemical properties, and are compofed of fimilar conftituent parts, with the ftrata themselves. What thefe constituent parts are, becomes, therefore, an object of ne ceffary examination." P, 40,

Among the various objects of mineralogical investigation, the nature, origin, and formation of coals, or of bituminous fubftances in general, have long exercised the industry of fcientific perfons. Their extenfive ufe in civil economy, befides other obvious and weighty confiderations, renders that fpecies of bodies an article not of mere curiofity, but of the utmost importance to the human fpecies; and, therefore, no pains ought to be fpared in the inveftigation of whatever relates to them.

It has been a queftion long difcuffed, whether coals were, or were not of a vegetable origin; for though evident parts of vegetables have often been found imbedded in coal, yet their general appearance, as every body knows, is far from exhibiting the forms of vegetable bodies. However, the prefent flate of knowledge feems to admit that coals truly have a vegetable origin; as fuch therefore they come within the limits of Mr. Parkinson's plan, and accordingly the nature of coals and of bituminous fubftances in general occupies a great part of his work.

After the preliminary illuftration of the first transformation of vegetable matter, Mr. P. begins by giving the hif tory of the difcovery of coals; he then ftates the principal facts, that have been recorded, concerning their fituation, extent, and variety; their different ingredients, as deter

1

mined

mined by chemical analysis; their use, and other parti

culars.

In the 18th letter he enters on the most difficult part of the fubject; namely, the transformation of vegetable matter into coal. This he endeavours to explain in a modest and ingenious manner; and we muft acknowledge that his explanation feems, at left for the prefent, to be quite fatiffactory. For the information of our readers we fhall fub. join it in his own words.

"The refolution," he fays, "of vegetable matter into mould, fit for the future growth of vegetables, is the refult of a defign, the end of which is evident. But when vegetable matter is depofited at depths lower than the roots of vegetables ever reach, a converfion into a fubftance of this kind would be ufelefs; and nature, it must be remembered, does nothing in vain. procefs is therefore inftituted; and instead of a fubftance being produced, calculated to promote vegetation, where vegetation never takes place, a fubftance is formed, differing in its nature, and varying in its properties, from all others.

Another

"The process by which this fubftance is formed I fhall take the liberty to confider as of the fermentative kind, and shall distinguish it by the name of BITUMINOUS FERMENTATION; defining it-A fermentation peculiar to vegetable matter placed in fuch fituations, as not only exclude the external air, and fecure the prefence of meifture, but prevent the escape of the more volatile principles; and which terminates in the formation of those fubftances termed bitumens.

Soon after, he fays, "Almost all vegetable matters manifeft a strong difpofition to decompofition, when the feparation of their integrant molecules is aided by the interpofition of the par. ticles of water; and particularly if, with this, is combined the powerful energy of caloric. If this latter agent be employed, only in a low degree, an inteftine motion among the integrant molecules takes place, the equilibrium by which that particular mode of compofition was preferved is broken, a feparation of the conftituent principles takes place, they become influenced by new attractions, and then enter into new combinations and modes of existence. Thus a refolution of the original compound is effect. ed, and new fubftances are formed, differing much in their phy. fical, as well as their chemical properties, from the fubftance from which they have proceeded. One particular point in which they almoft always differ may be here very properly noticed. The combinations refulting from thefe fpontaneous changes, occafioned by the inteftine motions of the conftituent principles, regu larly produce fubftances lefs compounded than thofe which thefe principles previously formed. Before the final change, however, is completed, certain regular periods in the process must be paffed

through;