^38 



CORNWALL. 



Cornwall, also directed to be held by four stewards, appointed by 

 2^~p / ~ w the lord warden, where causes are decided by juries of 

 ei ' six persons. 



As the copper mines of Cornwall, though numerous 

 and productive, are not peculiar to it, they do net re- 

 quire particular description. We shall, therefore, pro- 

 ceed to notice those appearances and productions of 

 this county,^ which are most interesting to the geolo- 

 gist, the mineralogist, the botanist, and the natural 

 historian. This county may be considered as formed 

 of a chain of low mountains, stretching from E.N.E. 

 to W.S.W. The central and highest part of this cliain 

 is granite, extending into a narrow mountain plain at 

 the north-eastern extremity, and, at the other extremi- 

 ty, gradually contracting into a ridge ; on each side of 

 the granite, grauwacke is found : both sides of this 

 chain have nearly the same inclination, the rivers on 

 the one side running into the British, and on the other 

 into the Bristol Channel. The grauwacke formation 

 occupies a very considerable extent in Cornwall : on 

 the southern side of the chain, it is found from the 

 mouth of the Hamoaze to that of the Huel, a space of 

 about 40 miles from east to west. The Cornish miners 

 give the name of killas to a variety of grauwacke slate, 

 which is very abundant in tins county, which is smooth 

 to the touch, though not unctuous ,• the colour varying 

 from dark-grey to white ; the lustre silvery, and the 

 structure schistose : it is very rich in ore. The grau- 

 wacke continues uninterrupted from Lynhercreek to 

 the north, till we approach Kelt-hill, near Callington, 

 where its termination is indicated, by the quantities of 

 quartz lying on the road. In the neighbourhood of 

 Kelt-hill, an adventitious mass of tourmaline, of a cy- 

 lindrical form, has been found, which the Count de 

 JBournon considers a new variety of form. In the neigh- 

 bourhood of St Stephen's church, the killas, or grau- 

 wacke slate, passes into the slate of common grau- 

 wacke ; and its termination, on this side, is indicated, 

 by its being stained with oxide of iron, and mixed with 

 numerous veins and pebbles of quartz. Near this place, 

 decomposed granite, in the state of kaolin, or China- 

 stone, as it is here called, is found : its qualities were 

 accidentally discovered about 50 years ago, by a gen- 

 tleman who was present at the founding of some bells 

 at Fowey, and noticed the appearance of some of the 

 earth, which had been contained in the mould. Great 

 quantities of kaolin are sent by sea from Charlestown, 

 for the use of the Worcestershire and Staffordshire pot- 

 teries. It has also been manufactured at Truro, into 

 retorts and crucibles, of an excellent nature for resist- 

 ing fire. The next formation of importance, which 

 succeeds the grauwacke in Cornwall, is the serpentine, 

 which stretches from the neighbourhood of Treelevor, 

 by Ruan Mager, as far as Corner Pradanack, including 

 the promontory called the Lizard Point : in this space, 

 there are two formations of rocks, in subordinate beds, 

 and of different natures, the one mica slate, to the 

 S.S.W. of the village of Lizard; and the other the 

 soap-rock, to the north of Kinance Cove. The colour 

 of the latter is whitish, or straw-yellow, streaked with 

 red, green, and purple : it is soft and wet when first 

 taken out, but soon becomes hardened : it is found of 

 three degrees of pm-ity ; the first, called the best-best, 

 is uncommonly white. This kind is used in the ma- 

 nufacture of porcelain, as it contains, naturally, the 

 same proportions of magnesian and argillaceous earth, 

 which are artificially mixed, for the purpose of manu- 

 facturing the finest Worcester China. The whole soap- 



rock is rented by the proprietors of the porcelain ma- Cornwall, 

 nufactory in that city. v — v^* 1 ' 



The mineralogist will find manyrare and curious M > nes - 

 specimens in this county : some of them have been al- 

 ready incidentally mentioned. The following also de- 

 serve notice : Green carbonate of lead and apatite, near 

 Heslton ; blende, in twenty sided crystals, and greeft 

 fluor, in twenty-four sided crystals, at St Agnes ; cry- 

 stallized antimony, with red blende on quartz, at Huel 

 Bays ; yellow copper ore and opal, near Roskier ; and 

 arseniate of copper, in cubes of a bright grass-green 

 colour, from Huel Carpenter. Formerly ivood tin, as 

 it is called, was found at Poth in great abundance, but 

 it is now scarce : in colour it resembles hwmatiles, and 

 is finely streaked like radiated zeolite. It is so hard as 

 to emit sparks with steel, and, when broken, has a fi- 

 brous appearance. According to Klaproth, it yields 

 more than sixty-three parts of tin in a hundred. The , 

 clvan stone of the Cornish miners is akso found at Pol- 

 goth : it is a greenish, or cineraceous granite, with some 

 steatites intimately blended with the quartz, mica, and. 

 felspar. Under some of the granite rocks, which pro- 

 ject from the shore near Pengerswick, there is an ex- 

 tremely hard, black, schistose substance, apparently a 

 species of hornslate : a similar species, with their veins, 

 of a whitish colour, between the laminae, may be seen 

 near St Roche. The Cornish moor-stone, a very close 

 species of granite, that takes a good polish, and is ap- 

 plied to a great variety of purposes, is found abundant 

 near the Land's End : it is split, by applying several 

 wedges to holes made on the -surface of the stone, about 

 three or four inches from each other ; and it is remark- 

 ed, that the harder the mass, the more easily and re- 

 gularly it is cut : it is sometimes used for posts, instead 

 of wood, in pieces of from 14 to 15 feet in length, and 

 not more than six inches thick. In the Gwennap 

 mines, to the south-east of Redruth, the substance 

 called gossati abounds : it is of a reddish or yellowish 

 brown colour, amorphous, and principally composed 

 of oxide of iron, mixed with argillaceous particles : it is 

 regarded by the miners as indicative of the neighbour- 

 hood of a rich vein. In Caharrack mine, red, vitreous 

 copper ore, with octahedral crystals, and some varie- 

 ties of arseniate of copper, are found. It is also said, 

 that asphaltum has been found in this mine, at the 

 depth of 90 yards. At Huel Unity, black fuliginous 

 copper ore, a very rare mineral in other countries, is 

 found; and at Huel Jewel, the substance called growan 

 by the miners. It is now, however 1 , become extremely 

 -scarce : it is a granite, consisting of transparent glassy 

 quartz, a small portion of felspar, and mica in a de- 

 caying state. The crystals of tin which this substance 

 contains are in tetrahedral pyramids, and of a colour 

 like rosin ; wolfram is also distributed through the 

 mass. In one of the mines near St Agnes, the sul- 

 phurated ore, discovered by Raspe, was dug. He pro- 

 posed to call it bell-metal ore : according to Klaproth, 

 it contains, out of 1 19 grains, SO of pure sulphur,. 41 

 of tin, 43 of copper, 2 of iron, and 3 of the stony ma- 

 trix. Its colour is like that of the grey copper ore, its 

 texture lamellar, and it is extremely brittle. In one of 

 the tin lodes of Polgoth mine, the schiefer spar of Wer- 

 ner was discovered some years ago. On this circum- 

 stance, Dr Maton remarks, " calcareous substances are 

 very scarce in Cornwall ; and I was not a little surpri- 

 sed to hear, that the schiefer spar (which is one of the 

 scarcest species, and had never been before found, but 

 at K'enigsberg, in Norway, and in Saxony) was a na» 



