LODE. 



•tker diftriAl, «rV>ere probably » later formation has ex- 

 hibited different plienomeiia, might conjcHiire. 



Lead-mines, jndotd, exill in many parts of England, in 

 various rock, and under various ciicmnftances ; but no ge- 

 neral rules of minin;T c;in be formed from det'ofits of a metal, 

 which appears to have taken its place at a pi'riod compara- 

 tively late. Such rules cnn only be applicable to feparate 

 diftrifts, where the circumllances attending the depofits are 

 fimilar. 



There are two general clalTea of rock which claim the 

 dillliiftion of metalliferous above all others. Thele arc the 

 iiUai of the Cornilh miner, or grauwacke or tranfitioii flate 

 of Werner ; and granitic rocks, including porphyry, gneifs, 

 and other varieties, known in Cornwall by the general name 

 of groiuan. 



Of thefe the great m^ijority of mines are in kilias, or graii- 

 Avacke, not only in Cornwall and Devon, but in Scotland, 

 in the Hartz, in the Saxon Erzgebirge, on the 'Uiine, in 

 Bohemia, Siielia, Moravia, Salzburg, and other diftrifts im- 

 portant for their mineral produces. 



Granitic rocks are not fo metalliferous as the ii.'/as, but 

 produc'five veins are found in them ; and, as Dr. Bcrger has 

 well obferved in his account of Devon and Cornwall, in the 

 (irft volume of the Tranlaclions of the Geological Society, 

 even the kilias is not a depot of metallic veins to any extent, 

 hut near its juniftion with the granite: and this oblervation 

 had been made, as he fays, by baron Born and Fcrber on 

 the mines of the continenr. 



This fail of moll mines being in one prevai ing rock, 

 would leem to iimplify the exerciie of judgment in a miner 

 fpeculating on the effecfl of the rock upon the contents of a 

 lode. But though kilias is fo univerfal, it is tar from being 

 all alike: on the contrary, it confifts of many varieties. 

 Thefe varieties do not alternate according to certain rules, 

 like the bed* of fecondarv rocks ; but exhibit changes in 

 pofition and extent, more or lefs frequent, and moll uncer- 

 tain and capricious; 



The varieties of kilias, \vhi( li are efteemed the mod kindly 

 for copper, are the blue and the white, more efpecially if of 

 a tender, flaty texture. Tin often is found in abundance in 

 harder kilias, more irregular in its llrufture, and of a darker 

 colour, indicating the prefence of iron. Pratlice alone can 

 enable men to iudge of the fliades of difference in thele re- 

 fpefls, which l«ng experience has pointed out as eflcnticil to 

 be attended to : and even then, allowance n^.uft be made for 

 exceptions which frequently occur ; rules wliicli feem to 

 hold good, when applied to one mine, being often inap- 

 plicable to another. 



111. The third thing to be confidered is 7 he iv'tdth and 

 regularity of the vein, and its direiiion and dip. 



Thefe are important circumllances. If the lode be fmall, 

 it cannot be expeded that abundant depofits of metal can be 

 found ; and if it has not the characters belonging to a re- 

 gular filTure, it is probable that the m.iner will foon be dif- 

 appoi.ited, by finding it dwindle to a trifling branch, or 

 fplit into feveral infignificant ramifications. 



Every large and productive li-diis accompanied by other 

 ▼eins running parallel to it, or nearly fo, which often fall , 

 into the main lode, and geaeraily enrich it by their junc- 

 tion. 



Thefe muft be carefully attended to, and fought after, as 

 the changes that they produce are often molt important, 

 and the quantity of ore which they yield is frequently very 

 great. It has indeed been aderted, that there is hardly a 

 mine working on a finglc vein only, which has been profitable 

 to any great degree. 



The diredlion of the lode (hould be carefully afcertained ; 



becaufe certain ores are only found in ^elns which ha^e their 

 courfe in common with others having fimilar depofits in the 

 dillria. 



Thus the writer of the prefent article has obferved that 

 copper and tin, in Cornwall, mud only be expetted in lodes 

 running eall and wefl: ; while lead is raifed from Inch as 

 have a direftion at right angles to them, or from north to 

 fouth. 



The more ufual dip or underlay, in copper mines parti- 

 cularly, is to the north ; but fome lodes that underlay to 

 the fouth have been very produdtive. In either cafe, it is 

 ro favourable fymptom to find the inclination from the per- 

 pcndicular to be great ; and it may be faid to be fo, tf it 

 exceed four feet in the fathom. 



When a lode often fplits or divides into two or more 

 branches, it is fnbjeft to fludluation in its produce; and 

 thele occurrences are important to be noticed with atten- 

 tion, as they afford prognoftics as to the future fuccefs of 

 working. 



IV. The fourth and lail head, under which we have ar- 

 ran-ijed the appearances of produiliyc lodes, is that relating 

 to 1 he JlruBure of the vein, li'hclhcr open or porout, nnd thui 

 pervious to ivater ; or, on the other hunJ, denje and clofe, and 

 conjt-quently dry. 



All miners agree in this, that water being found to be 

 abnnd.int io a lode is an omen of a very favourable nature; 

 and it is often confidently alferted, that no larg.e returns of 

 ore have been made from dry veins. As far as tlie ex- 

 perience of the writer of this article goes, it ferves to confirm 

 the oblervation. 



Water, indeed, may be found pafTing freely through crofs- 

 courfes, and other veins, from which metallic depofits are 

 ablent ; but then fuch veins will be found to have all the 

 charafters which are adduced as proofs of a later forma- 

 tion, and are therefore eafily dillinguilhed from metallic 

 veins. 



Large lodes acl as natural underdrains, and are channel* 

 through which water percolates ; fo that the rock lying.on 

 either fide may often be fimk upon with but httle inter- 

 ruption from water- until the vein is cut into, and then 

 abundant llivnms flow out, and would put an end to fur- 

 ther labour, if it were not for the aid of proper engines to 

 get rid of it. 



The quantity of water will of courfe be, in fome degree, 

 proportioned to the extent tif the wide and porous parts of 

 the lode ; and, as it is from thefe parts only that much ore 

 can be expefted, the water forms in the firll inftance a 

 pretty good prognollic. 



If, in driving upon the courfe of a fmall, clofe, and un- 

 produftive lode, a llream of water be ftiddenly met with, it 

 indicates the approach to an enlargement in the vein, and is 

 a mofl favourable fymptom ; and it is, in point of fatt, aU 

 moil always obferved before a good courfe of ore is feen. 



1'he mines of Devon and Cornwall abound with water in 

 a much greater degree than perhaps any others ; and a» 

 evidence of this, we may adduce the number of vaft lleam- 

 engiaes and overfhot waier-wheels employed for the fole 

 purpofe of draining them. We believe, likev.ife, that when 

 the quantities of ores raifed in this diftrift be compared 

 with thofe of any other which yield them from trve veins, 

 they will be found abundant iu the fame proportion. 



Under the head of the internal ftruilure of lodes,may be 

 noticed the cavities, called by the Germans drufes, and by 

 the Cornifh miners voogs : thefe are obferved moll frequently 

 in large veins, and in iuch, of courfe, aflift in the jjaffage 

 of water, and may be claffed in the fame place as a favour- 

 able indication. In thefe voogs are found all the varieties 



