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northern and weftern parts of England, the in-dependent coal-formation is generally obfervedwithin a little diftance of the limeftone on theoppofite fide to the flate-rock, and therefore di-vided from it by the limeftone. The extenfivecollieries of Flint, Ruabon and Chirk in NorthWales , of Glamorganfhire in South Wales, ofCoalbrook-dale in Shropfhire, and Kingfwood,near Briftol, are all examples of this, all of themcommencing immediately in the vicinity of fe-condary limeftone, which itfelf on the oppofitefide may be traced into flate: in fome of thefe in-ftances the limeftone does not exceed a few hun-dred yards in width, while in others it amountsto feveral miles. Among the ftrata of whichthe coal-formation itfelf is compofed, limeftone,clay, and marl, are the leaft certain indications,as thefe are met with moft frequently in form-ations unconnected with coal. White mica-ceous fandftone, efpecially when in thin, layersis a promifing fign: argillaceous iron is ftillmore fo; but fhale with vegetable impreffions,or the tenacious blue clay into which it de-compofes, is the ftrongeft indication of all:there are few fituations in which this fhale orclay occurs where an accurate fearch will notdifcover detached fragments of coal, and oftenthe crop or outburft of the feam itfelf; andeven fhould thefe be wanting, it will be wellworth while to employ the borer and piercethrough the fhale, immediately beneath whicha feam will be found, if it belongs to the coal-formation.

Front the vegetable remains with which thefhale that lies upon coal is always filled, fromthe ligneous texture which may be traced hereand there, even in the moft compact fpecies ofcoal, and from the regular and gradual tran-fition of bituminized wood through pitch coal,and flate coal, into glance coal, it is now gene-rally fuppofed that all coal (plumbago excepted)is of vegetable origin. As to the precife modeand agent by which the procefs of bitumini-zation has been brought about, the manner inwhich, and the period when the fucceflive ftrataof the coal-formations have been depofited, thereexifts and probably ever will exift, various theo-ries more or lefs ingenious and confiftent, whichalthough in all likelihood very remote from thetruth are valuable as exciting to further enquiry,and as convenient methods of arranging aridcolle&ing many very curious and importantfafts. To enter into the detail of thefe, how-ever, would be deviating too far from the prac-tical objedls of the prefent work.

The great ufe of coal is as a material for

fuel, and it i3 ufed either in its . flate, orafter it has been converted it.vc co..k by a pro-cefs analogous to that by which wood is madeinto charcoal.

Unprepared coal is employed in all manu-factures in which liquids are to be boiled orevaporated, fuch as brewing, falt-making, dif-tilling, and dying; it is ufed alfo in this ftateby glafsmakers, blackfmiths, and limeburners,and in all metallurgical precedes in the largeway, where fufion is performed in a reverbe-rating furnace. As a domeftic fuel alfo it isufed for the moft part without any preparation;but in fome places where coal cannot readilybe procured, it is reduced by pounding, to theconfidence of fmall gravel, and worked up withan equal weight of tenacious clay, and mouldedinto balls of the fize of the fill. Thefe beingfirft well dried in the air are made ufe of asfuel, and are found to burn longer and give outmore heat than the coal would do without thisaddition. The only inconvenience attendingthefe balls is, that they do not readily inflame,and therefore it is neceflary at the kindling thefire to employ common coal, and not to addthe balls till a fufficient body of fire has beencollected.

In blall furnaces, and the upright fmeltingfurnaces for iron and copper, coal cannot be ufedin its crude ftate, both becaufe its fulphureousvapours would injure the quality and dimi-nilh the quantity of metal, and becaufe by itscaking the current of air would be obftrufled,and the whole procefs thrown into diforder: nei-ther can this combuftible be employed, exceptin the ftate of coak, for drying malt and otherfimilar procefles in which fmoaky fuel wouldbe extremely prejudicial. Coal is deprived ofits bitumen and other volatile parts, or in otherwords is made into coak, in various ways. Thefimpleft mode is to difpol'e it in beds, from 40to 60 yards long about fix feet wide and threefeet high, in the open air, and kindling it in va-rious parts, to allow the combuftion to proceedtill the mafs is of a glowing red and ceafes tofmoke: being now taken to pieces and fpreadabroad the fire foon goes out, and the refidue isfound to be a light fpungy fcoriform fubftance(technically called coak or cinders) not fo eafilyinflammable as coal, but when once kindledgiving out an intenfe heat without either cakingor fmoaking. The above is apparently a verywafteful procefs, not only becaufe the volatilematters are allowed to efcape, but by this freecxpofure to the air a confiderable portion of thecarbonaceous part is alfo loft: it has however