VEIN. 



The crofs courfes or veins which interfeft the metalliferous 

 veins, frequently occafion a confiderable derangement in the 

 pofition of metalliferous vems, and, what is ftill more re- 

 markable, occafion a change in the quantity or quality of 

 their contents. When a vein is cut through by another, 

 either in its line of beai-ing along a countr)^, or croffes it by 

 declining in a different direAion, the vein which is cut 

 through is fuppofcd to be of more ancient formation than 

 the vein which crofles and cuts through it ; but it may be 

 doubted, from vajious circumftances, whether many of thefe 

 veins were not formed at the fame time with the rock itfelf, 

 or were fiffures palling through the rock in different direc- 

 tions, into which the various metallic fubftances were fe- 

 creted, during its confolidation. To form a more diftinft 

 idea of the flrufture of a vein and its interfeftion by crofs 

 courfes, we refer to Plate IV. Geology. Fig. ^. a a repre- 

 fent a rake-vein defcending obliquely ; b i, the rock ; c, c, 

 the walls or cheeks of the vein ; d, an interpoling piece of 

 rock, called the rider ; e, e, e, the divifion of the vein into 

 numerous fmall veins or firings of ore. If the fpacc at d, 

 which is fuppofed to be filled with rock, were empty, or 

 filled with water, it would conditute what is called a drufe ; 

 and it is in thefe cavities or drufes that all the moll beautiful 

 and regular cryftalliz.ationa of the mine occur. Fig. 5. re- 

 prefents the feClion of a rock containing a metallic vem cut 

 through, and dilplaced by crofs courfes or veins of another 

 metal ; a a a is a vein which appears to have been once con- 

 tinuous, and contains tin ; b, I, b, reprefent different veins of 

 copper, which cut through the former, and have upheaved 

 the lower part, and brought them nearer the furface. In 

 Plate II. Geology, Jig. 10. reprefents the ground plan or 

 horizontal fedion of a plot of ground traverled by a vein 

 and a crofs courfe ; E. W. reprefent the eatl and weft fides of 

 the ground. It is in this direftion the vein a a pafTes, but 

 it is cut through by the crofs vein b b, which has carried the 

 weftern fide of the vein and tlie ground along with it confi- 

 derably to the north of its original pofition. Such a frafture 

 and removal of the vein can only be conceived to have taken 

 place by a lateral or horizontal motion of a portion of the 

 ground. Such a motion has been frequently obferved during 

 violent earthquakes. For though the ground is heaved up- 

 wards, the greater refiftance which certain parts offer to this 

 motion mufl occafion a lateral preffure on other parts of the 

 earth's furface, and to fuch a preffure we mufl alfo refer the 

 remarkable contortions of the coal llrata near Valenciennes. 

 See Plate U.fg. 9. 



MetaUic veins frequently occafion a difplacement of 

 the ilrata when they pafs through regularly ttratified 

 rocks ; and it is obferved, that when this difplacement 

 is confiderable, fo as to bring a bed of lime-ftone on 

 the fame level with a bed of fand-flone or (hale, the vein 

 is never fo produttive as when the oppofite fides or walls 

 of the vein are in the fame kind of rock. See Plate II. 

 Geology, Jig. 8. where the different ttrata a, b, c, d, e,f, g, 

 reprefent different ftrata on each fide of a vein or fault. 

 If d, d, are fuppofed to reprefent parts of a bed of lime- 

 ftone broken by the vein, and g g ^ bed of fand-ftone 

 below the lime-ftone, but brought on the fame level with 

 it by the upheaving of the ftrata, — in that part of the 

 vein where the Ume-flone, d, and the fand-ftone, g, form the 

 walls oppofite to each other, the vein will be unprodutlive, 

 though in other parts of the diftrift, when the vein pnffes 

 through the fame bed of lime-ftone, on each fide of it, at 

 the fame level, it will be remarkably produiftive. Thefe 

 fafts may be commonly obferved in the mining diftrifts of 

 the weftern parts of Northumberland and Durham, where 

 the ftrata confift of different beds of mountain lime-ftone, 



fand-ftone, and fhale. See Strata, under which article 

 the fucceflion of the different beds is enumerated. 



As crofs veins generally difplace and injure the quality of 

 veins, on the contrary, when eaft and well veins in a diftridi 

 meet, by a flight variation in their direftion or dip, the part 

 where they join is frequently very rich in ore ; and vi'here 

 a number of metallic veins crofs each other at the fame 

 place, they frequently produce a large irregular conical m.afs 

 of ore of vaft extent, from which the different veins diverge, 

 like radii from a common centre. The main (haft of fucli 

 a vein, which Mr. WiUiams, in his Mineral Kingdom, calls asi 

 accumulated vein, " refembles," he fays, " tlie infide of a 

 glafs-houfie ; and the vaft ca|)acity of this vein is frequently 

 ftored with a rich body of metallic ore, often imbeddtJ 

 in foft mineral foils ; but the veins and branches which join 

 and diverge refemble rake-veins, or perpendicular minera. 

 fiffures. When the ore is wqiked out of an accumulated 

 vein, it exhibits a frightful gulf, fometimes fifty or fixtj 

 feet wade below, and is often worked down to a great deptlx 

 from the furface." A number of thefe accumulated veins 

 have been worked at Pike-Law, m the countv of Durham . 

 Crofs coui-fes fometimes contain ore to a fmall diftance froni 

 their junftion with metalhc veins, and in other fituatione 

 they become fo rich as to be worked with advantage. Th; 

 Botallock mine, on the fea-coaft near St. Juft, in Coniwall, 

 offers a ilriking illuftration of this, though we believe itf 

 ftruAure has not been generally known or underftood. The 

 vein which is worked is a north and fouth vein, varying in 

 width from nine to twelve feet, and extending under the fea. 

 The vein-ftone is quartz, with a fmaU quantity of fluor fpar. 

 It is found to contain ore of copper and tin only in thofe 

 parts where the eaft and weft veins enter it, and for thirty 

 or forty fathoms on each fide of the juniElion. This mine 

 produces the richeft ore of copper in Cornwall, the grey 

 fulphuret yielding twenty per cent, of this metal. It is de- 

 ferving notice, that the metalliferous veins which enter this 

 lode on the eaft fide and render it produdive, have never 

 been found on the weft fide, fo that they appear to termi- 

 nate in it. The rock near the great north and fouth vein is 

 a foft killas or fiate, but beyond this it is a very indurated 

 flinty flate. This vein may properly be confidered as a crofs 

 courfe, rendered ricli in ore in various parts by a number of 

 fmall veins which fall into it, like brooks into a large river 

 where they are loft. The fituation of this mine is truly re- 

 markable, at the foot of a precipitous chff that overhangs 

 the Atlantic ocean. If ever a fpot feemed to bid defiance 

 to the efforts of the miner, it v/as this. At the very com- 

 mencement of his labours, he was required to lower an im- 

 menfe fteam-engine down a precipice of more than two 

 hundi-ed feet, with a view of extending his operations under 

 the bed of the fea, where the workings are at prefent con- 

 tinned for feventy fathoms in length and fixty-five fathoms 

 in depth. In thefe caverns of darknefs, many human beings 

 for a fmall pittance, and that even of an uncertain amount, 

 are conftantly digging for ore, regardlefs of the horrors 

 wliich furround them, and of the roar of the Atlantic ocean, 

 vvhofe boifterous waves are incelfantly rolling over their 

 heads. In fome places the fea actually penetrates through ; 

 and it is worthy of obfervation, that the water is deprived of 

 a great portion of its falts ; but whether this arifes from fil- 

 tration, or whether fome portion of the frefh water from the 

 land percolated through fnbterranean fiffures in the rocks, 

 we could not afcertain when we vifited this Angular mine. 

 If the filtration be more abundant after heavy rains, it 

 would prove the intermixture of rain-water. The thin crofs 

 courfes filled with clay called flucan, heave the eaft and weft 

 venjs, and alfo hold up the water. The vein which is jiich 



in 



