Book II. QUARRIES, LIME-KILNS, &c. 561 



duct, and to incur great expense in making abortive trials. To ascertain the nature and 

 value of the minerals of an estate of any magnitude, or one of small size, but of peculiar 

 exterior organization, it will always-be worth while for the proprietor to have a mi- 

 neral survey, map, and description, made out by a professional man. 



3580. Coal is perhaps the most valuable British mineral, because, among other reasons, 

 it does not appear to abound in any other country in such quantity and quality, as ever to 

 lessen by importation the home produce. There are three species of coal, the brown, 

 the black, and the uninflammable. To the first belongs the Bovey coal or Ijitumenised 

 wood, found chiefly at Bovey, near Exeter ; to the second the slate coal, which includes 

 the pit and sea-coal, and all the kinds in common use, and also the canal coal, which 

 occurs only occasionally in the coal pits of Newcastle, Ayrshire, and Wigan, in Lanca- 

 shire ; to the third belongs the Kilkenny coal, and Welsh culm, or stone coal which burns 

 to ashes without flaming. 



3581. The indications of coal are different in different coal districts. In general the 

 surface is argillaceous or slaty, and limestone commonly forms an accompanying strata. 

 In some collieries near Newcastle, however, limestone is wanting, but whinstone, sand- 

 stone, and others of secondary formation, are present in a great variety of forms. 



3582. The discovery of coal is made by bonng, and that operation is generally per- 

 formed in coal districts as a guide for sinking new shafts. By this means the owners 

 procure most essential data on which to proceed, being informed beforehand of the na- 

 ture of the earth, minerals, and waters through which they have to pass; and knowing, 

 to an inch or so, how deep the coal lies, as well as the quahty and tliickness of the stratum 

 bored. It is confessedly of the first importance, either to the inhabitants of a district in 

 general, or to the owners of the soil in particular, to be able to detect and work such 

 veins of coal as may exist under their soil ; and hence, we find, on enquiry in the neigh- 

 borhood, that almost every common, moor, heath, or piece of bad land, in parts where 

 coals are scarce, have at onetime or otherbeenreportedby ignorant coal -finders to contain 

 coal : how many times, for instance, have our grandmothers, and nurses, repeating their 

 stories, told us, that plenty of coals might be dug at such and such a place, if government 

 had not prohibited their being dug, for encouraging the nursery for seamen, SiC. ? Farcy's 

 inquiries, and those of Smith, have brought to light hundreds of instances, where borings 

 and sinkings for coals have been undertaken in situations, and on advice, in the southern 

 and eastern parts of England; attended with heavy, and sometimes almost ruinous ex- 

 penses to the parties, though a source of profit to the pretended coal-finders. These 

 attempts a very slight degree of geological knowledge would have shown to be vain. 



3583. The coal fields of Britain will be found scientifically described in Outlines of 

 Geology, by Conybeare and Philips, and also in BakewelVs Geology. 



3584. Limestone, chalk, and building or other stone, are found in strata either on or 

 near the surface. At a great depth it is seldom found worth while to work them. 

 When stones of any kind are procured by uncovering the earth, and then working them 

 out, they are said to be quarried ; but when a pit or shaft is sunk, and the materials are 

 procured by working under ground, they are said to be mined. 



3585. Gravel, chalk, clay, marl, and other loose matters, when worked from the surface, 

 are said to be worked from a pit, and hence the terms stone, quarry, gravel, clay, or 

 marl pit. Little knowledge of geology is in general required for the discovery of gra- 

 vel or marl ; but still, even a little would be found of the greatest advantage. 



3586. The working of quarries is a simple operation, and one depending more on 

 strength than skill. In quarrying sandstone, consisting of regular layers, the work is 

 performed chiefly by means of the pick, the wedge, the hammer, and the pinch or lever ; 

 recourse being seldom had to the more violent and irregular effects of gunpowder. But 

 for many kinds of limestone, and for greenstone and basalt, blasting with gunpowder 

 is always resorted to ; and some of the rocks called primitive, such as granite, gneiss, 

 and sienite, could scarcely be torn asunder by any other means. 



3587. The burning of lime may be considered as belonging to the subject of quarrying. 

 This operation is performed in what are called draw kilns, or perpetual kilns. Tliese 



should always be close to or near the quarry, and either situated at a bank, or furnished 

 with a ramp or inclined plane of earth for carting up the coal and lime to the top of the. 

 kiln. Lime-kilns may he built either of stone or brick ; but the latter, as being better 

 adapted to stand excessive degrees of heatj, is considered as preferable. The outside 

 form of such kilns is sometimes cylindrical, but more generally square. The inside 

 should be formed in the shape of a hogshead, or an egg, opened a little at both ends, and 

 set on the smallest ; being small in circumference at the bottom, gradually wider to- 

 wards the middle, and then contracting again towards the top. In kilns constructed in 

 this way, it is observed, fewer coals are necessary in consequence of the great degree of 

 reverberation, which is created above that which takes place in kilns formed in the shape 

 of a sugar loaf reversed. Near the bottom, in large kilns, two or more apertures are 



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