582 METALLIFEROUS DEPOSITS. 



In Somersetshire it is chiefly the refuse and slag left by the ' old miners ' that is 

 now smelted ; and the material has been dug near Priddy and East Harptree. 

 Type-metal is made of an alloy of lead and antimony. 



Zinc Ores. 



Zinc has not been found native. The ores include blende or ' Black Jack ' 

 (sulphide), calamine (carbonate), and smithsonite (hydrous silicate). 



Zinc-ores are met with in the Triassic, Carboniferous, Devonian, and Cambrian 

 rocks; and they have been worked in Cornwall, on tlie Mendip Hills in Somerset- 

 shire, at Holywell in Flintshire, in Denbighshire, Cardiganshire, the Isle of Man, 

 at Alston Moor and various other localities in Cumberland, Westmoreland, and 

 north-west Yorkshire. Brass is an alloy of zinc and copper. 



Copper Ores. 



Copper is found native in Anglesey and in the Devonian and other rocks of 

 Devon and Cornwall : and has been in use since prehistoric times, especially in the 

 form of bronze, an alloy of copper and tin. (See p. 480.) Copper-pyrites or 

 chalcopyrite (sulphide of copper and iron), copper glance or redruthite (sulphide 

 of copper), cuprite (red oxide), and malachite (green carbonate), are among the 

 principal ores of Copper. 



Copper-ores are worked in the neighbourhood of Tavistock (Devon Great 

 Consols), Redruth (Dolcoath, and Fowey Consols), Caradon, Callington, and 

 other places in Devon and Cornwall ; at the Parys Mountain and Mona mines 

 near Amlwch, in Anglesey ; and they have also been met with at Ecton on 

 the borders of Staffordshire, at Alderley Edge in Cheshire, and near Ulverston. 



Tin Ore. 



Tin is not known in a native state. The principal ore is tin-stone or 

 cassiterite, sometimes known as black-tin (binoxide). Wood-tin is a fibrous 

 form of it. Tin, like copper, has been known from very early times ; but the term 

 Cassiterides or Tin Islands, applied sometimes to the Scilly Isles, was probably 

 used in very early times for the Land's End district, as no productive veins of 

 tin-ore, and no old workings, are to be found in those isles.' Thus, a tin-trade 

 was carried on by the Phoenicians upwards of 2000 years ago, and it is considered 

 probable that up to the eleventh century the whole of the tin-ore was derived from 

 the 'stream- works' and the washings of stanniferous sands and clays.- The stream- 

 works are in alluvial or estuarine deposits, which contain rounded fragments of 

 tin-ore (stream-tin) derived from the rocks of the district.'' (See p. 526.) 



Tin-ore occurs in the ' Devonian ' rocks and granite of Cornwall, and has been 

 largely worked near Redruth, Camborne, St. Ives, etc. At the Botallack mine 

 both tin- and copper-ores are obtained. Britannia metal and pewter are alloys of 

 tin with antimony. 



Gold. 



Gold occurs native, or alloyed with other metals.'' According to Mr. W. W. 

 Smyth, it was worked by the Romans at Gogofau, near Pumpsant, west of Llan- 

 dovery, in the Arenig rocks, where it occurred in quartz-veins.^ It is now worked 



^ Ussher, G. Mag. 1879, p. 35. 



'^ D. C. Davies, Treatise on Metalliferous Minerals, etc. 



2 W. J. Kenwood, Journ. R. Inst. Cornwall, 1S73 ; G. Mag. 1873, p. 317. 



* A. G. Lock, Gold : its occurrence and extraction, 1SS2, p. 726. 



* Smyth, Mem. Geol. Surv. i. 4S0. 



