CORNWALL. Copper and tin are the most important minerals of Cornwall. The extent of the metalliferous veins is unknown, as well as the depth to which they extend no miner has yet seen the end or bottom of a vein. Their width varies much, from the thickness of a sheet of paper to 30 feet; but they are usually from 1 to 3 feet in thickness. The ores of copper .or tin do not often occur together in the same vein at any great depth. If tin be discovered first, it sometimes disap pears, after sinking 100 feet more, and is suc ceeded by copper; in others, tin is found at the depth of 1000 feet beneath the surface, almost without a trace of copper ; if copper be first discovered, it is very rarely, if ever, succeeded by tin. It is seldom that either ore is found nearer to the surface than 80 or 100 feet.
The copper and tin mines, excepting a few near Callington, are south-west of the rivers Alan and Fowey. The chief mining district extends from St. Agnes on the north coast by Redruth to the neighbourhood of Helston and Marazion; and some mines are worked west of Marazion. St. Austell is in the centre of another but less extensive mining district near the south coast.
The lead mines of Cornwall are not nu. merons, though the ore has been discovered in many parts of the county. Silver ores have been obtained from several mines in Corn wall, chiefly in lodes or cross courses in the graywacke. Gold has been found in the tin streams. Iron ore is also obtained, and shipped to Wales. Zinc, antimony, cobalt and arsenic are procured, as well as some other of the semi-metals. Freestone of dif ferent qualities is quarried.
During the 30 years from 1815 to 1845, there were 220 copper mines in the county, the produce of which was sold at the public ticketings. In the year 1845, 35 of these mines had been worked upwards of 20 years ; 40 had been worked between 10 and 20 years; 31 had been worked between 5 and 10 years ; and 114 had been worked less than 5 years.
The average percentage of copper from all the mines during the 30 years was 7i ; the highest average from any one mine was 261; and the lowest average from any mine was 21. The quantity and value of Cornish ores are briefly alluded, to in another article [COPPER].
The following demands for space at the Great Exhibition, whether fully adhered to or not, will serve to illustrate the products and resources of Cornwall :—In the first section (raw materials and produce) for the mineral kingdom will bo required—for ores, 398 super ficial feet ; for models of machinery, illus trating the preparation of the ore for the smelter and tin smelting, 70 feet ; ochres, clays, and china stone, including a model of a clay work, 94 feet ; building and road stones, sand, hone stones, &c., 171 feet; ornamental stones and slates, 202 feet. Animal and vegetable kingdoms—for hides, 100 feet ; pilchards, 4 feet ; Normal guano, 3 feet; wheat, 2 feet 109 feet ; for nets illustrating tho Cornish fisheries, 150 feet; making a total required in section 1, 1,194 feet. In the second section (machinery) are required for steam-engines and instruments connected with steam ma 1 chinery, 781 superficial feet ; miscellaneous machines, models, and tools, 204 superficial feet; naval architecture, 70 superficial feet; total in second section, 1,058 superficial feet. For the display of manufactures 412 feet of space have been demanded, 336 feet of which are required for ornamental manufactures in granite, porphyry, serpentine, rib and slate, &c., the remainder being wanted for crucibles, safety fuze, chairs, embroidery, &c. Making a total of space required for the county of 2,604 superficial feet.