on this fubject Mr. Kirwan's opinions are well known. He has proved that we have little reason to afcribe mountains to volcanos, fince even Ætna and Vefuvius do not owe their whole elevations to fubterraneous fires, but were mountains before they burst into flame. The marks to diftinguish old volcanos from mountains of a different kind are accurately detailed.

In all cafes where doubts may be entertained, whether a hill, or mountain, is volcanic, or Neptunian, our judgment may, in my opinion, be governed by the following maxims:

1°. Where trap, or bafaltic columns, appear on, or form the body of the hill or mountain, of their usual black, bluish, or greyish black colour, there the hill or mountain may be deemed Neptunian, at least so far as concerns thefe; fuch as are found on actual ignivomous mountains must have been thrown out with other Neptunian stones, but in that cafe they are never erect, and commonly bear fome marks of heat.

2. Where maffes of fhiftofe porphyry occur, of a greyifl black, afh grey, blackish blue, or greenish colour, and the felfpar appear uninjured by heat, they, and the parts they repose on, are. Neptunian.

3. Difintegrated, or decayed, porphyries, or traps, wacken, and amygdaloids, may be diftinguished from indurated volcanic fand and afhes, piperino, pouzzolana, porous lava, respectively, by local circumstances, and the changes which low degrees of heat produce in them, compared with the changes which the fame variations of heat occafion in the real volcanic products that refemble them. Wacken containing mica can never be ambiguous. Beds of real volcanic ashes, if ancient, are always interrupted or interceded by beds of earth, which fome, without any proof, would have to be vegetable earth; and if, by this appellation, they mean no more than earth fit for vegetation, the appellation is just; but if they mean that fuch earth was in all inftances such as had produced vegetables, they are certainly mistaken, as Dolomieu has already noticed; this earth having been merely washed down by rain from the cinders and fragments of lava, with which it was originally mixed; wacken prefents no fuch appearance.' P.274.

Yet let us add fome limitations. If a mountain be in fhape conical; if it rife infulated in a comparative plain, or at least be not connected with any neighbouring chain; if the subftance of that mountain differ from the furrounding ftrata, whatever may be its compofition, if not evidently primæval, it must have been volcanic. Even our author's characteristics, to which he afterwards adds decompofed pyrites, may have been fubfequent and fecondary formations. Pfeudo-volcanic hills are thofe which have experienced flighter or accidental fires from the neighbourhood of coal.

The fixth effay is on the internal arrangement of mountains. Our author's great object is to fhow that the ftrata are com monly and naturally horizontal. He has adduced, however, fomewhat too anxioufly, the facts for this purpose: they appear to be felected, though the probable caufes of their change, from the horizontal to the vertical fituation, are well explained. In the fact on this fubject, quoted above from Sauffure, we meant not to infinuate that the alteration was volcanic. It may have been from accidental expanfions from below, independently of actual fire, or from the finking on one fide in confequence of alluvial causes. From a ftrict and continued attention to beds of granite, we have not feen verticle ftrata but where the latter cause was at least probable if not evident.

The feventh effay is on coal-mines, and, as ufual, Mr. Kirwan adduces a vaft extent of information from travellers of every kind. His great object is to fhow that petrol and carbon were primordial fubftances, entered into the compofition of primitive mountains, and, on their decompofition, were washed into the veins of fecondary rocks, where they hardened into coal. We have more than once offered our opinion that coal was produced from decayed vegetables, and we do not yet fee fufficient reafon to refign that opinion; yet, on the whole, we can add that Mr. Kirwan's fyftem is well fupported; nor will it be eafy to invalidate it entirely: the foliated structure, the polifhed furface, and the fmall earthy refiduum of coal, will ftrongly fupport it. Our author's mineralogical arguments are peculiarly ftriking.

The practical inferences from this theory are,

1°. That coal is never to be expected in primeval mountains, as granite, gneifs, &c. but that on the fides of thefe, particularly if very high, or in the hanging level that flopes from them to fome river or valley, it may be fought.

2. That there is ftill a greater probability of finding it in the neighbourhood of mountains of argillaceous porphyry, as thofe are ftill more fubject to difintegration.

3. That it may be fought with probability of fuccefs in fandftone mountains, if fandftone and clay alternate, or fandftone, clay, and argillaceous iron ore.

4°. That in any elevated land in which fandstone and shale, with vegetable impreffions, or indurated clay and shale, or bituminous fhale, form diftinct ftrata, or clay, iron ore, and shale, with or without ftrata of fand, coal may well be expected.

5°. That if fandstone be found under limeftone, or if they alternate with each other, and, particularly, if indurated city and fhale form any of the ftrata, they afford a probable indication of coal; otherwife coal is very rarely found in, or under, limestone.

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6°. That coal is very feldom found with argillite, and such as has been is of the uninflammable kind,

7°. That where trap, or whin and clay, alternate, and more efpecially trap and fandstone, coal may be expected; it is often, but not regularly, found under bafalt :-Wood coal is fometimes found under both.

Laftly, that coal frequently burfts out on the furface, or on the fides of hills, in a withered state, which diffuses itself to a diftance from its origin, and requires an experienced miner to trace it truly to the feam to which it belongs.' P. 347.

The feventh effay is on common falt and its mines. The vaft mine of common falt is the fea, which prefents a fource of much curious fpeculation. Of the different proportions of falt in the ocean, from fea-water taken up in various latitudes, Mr. Kirwan gives a very particular account, though the faltnefs of the fea he does not derive from the mountains of rock falt, but the latter from the fubfidence of the former. This pofition is well fupported, and, as we think, verified. Whence then is the falt derived? It cannot have escaped even a fuperficial obferver that foda muft be a primæval fubftance. If it fhould be proved a compound, we know that magnefia, hydrogen, and carbon, are,fuch; and that carbon is at least contemporaneous, perhaps very ftrictly fo, with the production of granite, long previous to the fea being the habitation of fishes. The fea then was perhaps, at first, an alkaline fluid, but the caufe of its being faturated with marine acid is not known. It is faid, in a foreign journal, that the radical of the muriatic acid is difcovered in this country; but we are acquainted only with the unfuccefsful attempts recorded in the Philofophical Tranfactions to afcertain it. Should that gentleman, or any fubfequent chemift, have fucceeded, we can only regret that no journal in England is honoured with his philofophical communications; and that, in this as in other inftances, we catch the firft glimpse of the fuccefsful labours of English philofophers from foreign publications. But to return, Mr. Kirwan has fhown, from chemical affinities, what we fhould à priori have fufpected, that the marine was the acid firft formed; and indeed we fee in finall quantities the formation ftill go on in the air, as condenfed froft always contains a portion of it, even at a distance from the fea. The various mines of rock-falt, and their extent, are particularly defcribed, chiefly with a view to eftablish our author's opinion of their origin. Salt lakes are noticed with equal care; and as thefe have not hitherto been fufficiently examined, we may remark that they differ from the water of the ocean, by containing generally lefs common falt and a larger proportion of Glauber's.

The ninth effay is on metallic mines, noticing the metals found native, fulphurated, in calciform ores, metallic veins, and ores as occurring in primæval or fecondary mountains. Our author's great object is to prove that metals are primeval

fubftances, found native from the deftruction of mountains, and, in other forms, from meeting the different mineralifers. It may perhaps contribute to fupport his opinion, if we add, that manganefe, which contains fo large a proportion of oxygen, is generally difcovered near the furface, in broad and fhallow patches, not without fufpicion that the foil over it is of recent formation from the detritus of neighbouring hills.

The tenth effay is on Dr. Hutton's fyftem, which our author has enthrined in his work. We very early gave our opinion. of it, an opinion which the matureft confideration has confirmed; nor have the modifications it has received in two fucceffive impreffions changed our fentiments. Yet this little con troverfy, as managed in the effay before us, is neither unentertaining nor uninftructive.

On the whole, we ought not to conclude without the warmeft commendations of this work, which we have in general cheerfully praised, and from which we have occafionally diffented, we truft with caution and refpect; for few who can appreciate the extent of our author's knowledge, particularly developed in the effays before us, will differ from him but with diffidence, and, while differing, acknowledge his merits.

Letters from a Father to his Son, on various Topics relative to Literature and the Conduct of Life. Written in the Years 1798 and 1799. By J. Aikin, M. D. Vol. II. 8vo. 55. Boards. Johnfon. 1800.

WHEN the reviewer turns from the perufal of multitu dinous pages of affectation and dullness to the examination of volumes like the prefent, he experiences fenfations fimilar to thofe of the traveller, who, in the courfe of his journey through the Defert of Syria, arrives unexpectedly at fome infulated fpot of verdure, whofe charms are heightened by the contraft of furrounding fterility.

The name of Aikin ftands high in the records of genuine tafte; and in his literary labours he has exemplified the truth of the poet's obfervation,

Omne tulit punctum qui mifcuit utile dulci.'

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From the favourable reception which the public gave to the first volume of his Letters from a Father to his Son,' it may be prefumed that the annunciation of a fecond volume would rife confiderable expectations. We will venture to predict that thefe expectations will not be disappointed. The Jetters now under our confideration exhibit the fame maturity

* See our Xth Vol. New Arr. p. 273.

of thought, and correct practical judgement of men and things, which rendered their precurfors fo truly interesting and inftructive. They are eighteen in number, and treat of the following fubjects.

On party. On the estimate of morals.-On a criterion of perfection in writing.-On authority in matter of opinion.~ On Milton's garden of Eden.-On the character of Ajax.— On evidence in matter of fact.-On the character of Cicero. -On the value of life.-On the refpect due to fuperiors.. On the tafte for farming.-Hiftory and biography estimated. -On openness and fincerity.-On the advantages of a tafte for poetry. On the best mode of encountering the evils of life. On the comparative value of different ftudies.-On the experience of life.

The introductory letter commences in a ftrain of benevolent ferenity, which irrefiftibly winds its way into the feelings of every affectionate mind.

My dear Arthur,

I resume the pen to you under circumstances that may make my correfpondence more interefting than formerly, though, perhaps, lefs inftructive. The illness under which I have long laboured, and which feems to have fapped all the principles of vigour in my frame, may well be fuppofed to have incapacitated me from efforts which require clofeness of thinking, or depth of research, But the delightful retreat into which it has compelled me, has thed fuch a tranquillity over my mind, and even furnifhed it with fuch new fubjects of pleafing contemplation, that I feel better tuned, as it were, for epiftolary converfe, than I could be in the midft of the buftle and cares of the metropolis. I may add, that I think myfelf able to fpeculate more freely and impartially concerning the affairs of a world, my connexion with which promifes to be of no long duration.

I reckon myself in no fmall degree obliged to my indifpofition for the occafion it has given me, in a more varied and delicious spot than I ever before inhabited, of once more obferving the progress of thofe rural phenomena, all beautiful in themfelves, by which fpring infenfibly flides into fummer, and the youth of the year grows up to its full maturity. Amid the wooded hills and fequeftered vallies of this charming country, I have witnessed the earliest notes of the returning nightingale and its migratory companions, and the fucceffive expanfion of leaves, bloffoms, and wild flowers, not more grateful to the fenfes, than interefting to the reflection. I have here again in fome degree renewed the botanical ardour, which I recollect to have been a fource of delightful fenfations when firft kindled in my breast, and which I ftill find to beftow peculiar intereft on every ride and walk. In this manner I have been enabled to pafs with confiderable enjoyment through fome months of an in