5/8 MINERAL VEINS. 



Gabbro occurs at Coverack Cove, and extends to Manacle Point, and Crousa 

 Down. In places it penetrates tlie serpentine in veins and dykes, and is also itself 

 traversed by veins of granite and diorite. Mr. Teall has pointed out that the 

 foliation of the gabbros in this district is due to pressure- or regional-metamorphism.^ 



The Clickertor Rock, near Menheniot, is an intrusive serpentine with veins of 

 carbonate of lime and chrysolite. It is described by Mr. Allport as an interest- 

 ing example of the conversion of an intrusive olivine-dolerite into a mass of 

 imperfectly formed serpentine.^ 



Soapstone or steatite is a variety of talc, and it has been used at Swansea in 

 the manufacture of porcelain, and in other places for various ornamental purposes. 

 It is found associated with serpentine in the Soapstone Rock near Mullion, in the 

 Lizard district ; and is also met with in Caernarvonshire, Anglesey, Cumberland, 

 and Herefordshire. 



MINERAL VEINS AND METALLIFEROUS DEPOSITS. 



Mineral veins are deposits of mineral matter that usually occur 

 in faults, but sometimes in other fissures, or joints in stratified 

 and eruptive rocks. Those only which yield valuable ores are termed 

 Lodes or Metalliferous veins ; for the veins of quartz that frequently 

 traverse the older strata are appropriately termed Rock veins. The 

 term "ore" is applied to the metals when found in combination 

 with other substances ; and metalliferous deposits occur not only 

 in lodes, but also in beds, seams, and pockets, as nodules, and as 

 detritus in the stratified rocks. The ores worked in England and 

 Wales are chiefly those of Lead, Zinc, Tin, Copper, and Iron.^ 



The material forming the greater part of the lode or vein apart from the ore 

 worked, composed of quartz, calc-spar, or other non-metallic substances, is called 

 the Gangue, Matrix, or Vein-stuff; the material at or near the outcrop of the lode 

 is called the Gossan ; the surrounding rock is known as the Country ; and certain 

 siliceous bands bordering the lode are sometimes termed the Capel (or Caple). 

 The Gossan (or Gozzan) is usually of an ochreous nature, as it is much charged 

 with iron-ores, derived from pyrites. In different parts of the country, however, 

 many local terms are used, and the same term may be applied in different senses. 



Veins vary in width from one to twenty-four feet and upwards, 

 and they take various directions, spoken of sometimes by the 

 miners as running at different hours, as nine or twelve o'clock, 

 according to the sun-dial. 



Metalliferous deposits occur in rocks of all ages, but lodes are 

 more abundant in eruptive and metamorphic rocks, and especially 

 near the junction of Pali^ozoic and intrusive rocks. Thus, mountain 

 reo-ions possess greater mineral wealth as a rule than low-lying 

 countries. 



1 Bonney, Q. J. xxxiii. 884, xxxix. 23 ; F. T. S. Houghton, G. Mag. 1879, 

 p. 504 ; Teall, G. Mag. 18S6, p. 4S1, Brit. Petrogr. PI. xviii. 



- Q. J. xxxii. 423 ; De la Beche, Report, pp. 79, 96. 



•' See J. A. Phillips, Treatise on Ore Deposits, 18S4 ; R. Hunt, British Mining, 

 1884 ; D. C. Davies, Treatise on Metalliferous Minerals and Mining, ed. 3 ; J. H. 

 Collins, Principles of Metal Mining, 1875; C. Le N. Foster, Article 'Mining' 

 in Encylop. Brit. vol. xvi. 1883. 



