If we calculate this amount by twenty-four, the years of the existence of the gold-mines of California, and in which they have produced $1,000,000,000, we will have the aggregate sum of $4,230,456,000 worth of iron, lead, copper, tin, and coal in Great Britain, against $1,000,000,000 of gold produced from all the mines of California within the same period. A feature worthy of notice in connection with this subject is that, while the yield of the precious metals in California is steadily on the decrease, the production of the mines of the British islands is steadily on the increase. But it is doubtless only a question of time when the supply from the earth must give out.

The minerals raised from the earth in the United Kingdom, in 1869, were of the value of no less than $176,269,000. This amount exceeds that of the preceding year by upwards of $8,000,000. The coal produced in 1869 was 107,427,557 tons. The returns for 1868 showed only 103,141,157 tons produced, being less than in 1869 by above four million tons. The production of iron ore in 1869 advanced to 11,508,525 tons, of the value of $16,000,000; the quantity is about 1,340,000 tons more than the year preceding. The great increase is in North Staffordshire and in Scotland. The tin ore amounted to 14,720 tons, and copper ore, 129.953 tons.

CHAPTER XXI.

Tunnel-mining-Sutro tunnel-Canals- Ditches-Asphaltum— Cement-Coal-Copper-Cobalt-Nickle-Diamonds-Electrosilicon-Gypsum-Iron-Lead-Petroleum-Quicksilver-Salt -Sulphur-Tin-Marble-Granite-Caves-Mining laws-Mining laws of Spain and Mexico-Geology and mineralogy-Great mines of the world.

TUNNEL-MINING.-Tunnel-mining is carried on to a considerable extent in California: mountains are pierced through granite and slate, for great distances and at great expenditure of time and money, in order to reach quartz veins; the object being to strike the lode as low down as possible, so as to drain the mine of water and extract ore: when the lode is reached, drifts and branch tunnels enable the miner to quarry the quartz, which finds its way through the main tunnel to the surface or the mill, where it is ground and the metal extracted. Mountains are also often pierced in order to reach the deposits of gold dust in the beds of ancient rivers and basins, which in many instances have proven very rich.

SUTRO TUNNEL.-The grandest project in tunnelmining in America is the Sutro tunnel, at Virginia City, in the State of Nevada, intended to cut the famous Comstock lode, and pass under Mount Davidson at a depth of 7,827 feet from its top, which is 1,622 feet above Virginia City.

The Comstock lode will be reached by this tunnel at a distance of twenty thousand feet, or three and onefourth miles, from its mouth, and be cut at a perpendicular depth of 1,900 feet--or 2,900, following the dip

of the lode. At the beginning of the year 1872, the Crown Point, Belcher, and other mines on this lode had reached a depth of 1,700 feet, developing marvellous richness. The present working of all the mines on this lode is done by the tedious and expensive process of hoisting through shafts and pumping out water. The tunnel when completed will drain the mines to a great depth, and open a wide avenue for transporting ores from the vein on cars. It is estimated that three and a-half years from January 1, 1872, will be necessary to reach the lode by this tunnel, involving an outlay of four and a-half million dollars.

Congress, by act of July 25, 1866, has made liberal donations to this project, granting in perpetuity a belt of rich mineral land through which the tunnel passes, seven miles in length and four thousand feet in width5,080 acres; also, 1,280 acres of land at the mouth of the tunnel, the exclusive ownership of all mines dis covered by the tunnel, and a royalty forever of two dollars on each ton of ore extracted from any part of the Comstock lode after the vein is reached by the tunnel. The payment of this amount is made compulsory by the same act. From this tax the tunnel company will derive a large revenue. Work on the tunnel is being vigorously pushed.

Deep mining, on true silver veins such as the Comstock, has proved most successful. The shafts now down three thousand feet on the Sampson mine, in Germany-the deepest in the world-demonstrate continued and improving richness.

Beyond all doubt the Comstock lode is the most extensive and the richest quartz mine in the world, far surpassing any thing in Mexico, South and Central

America, and Europe. Granada, in Spain; Kongsberg, in Norway; Pasco, in Peru; Potosi, in Bolivia; Chañarcillo, in Chili; Valenciana, Veta Granda, Real del Monte, of Mexico; the Schemnitz and Felsobanya, of Hungary-although representing the great silver supply fountains of the world-all pale before the magnitude of the Comstock, of Nevada.

The lode proper, as developed in the Comstock, extends five miles in length, and has a width of from fifty to five hundred feet. Fifty steam-engines and three thousand men are employed in working the various mines, which were opened in 1859, and have yielded, up to January, 1872, an aggregate of one hundred and forty million dollars-of which ninety million dollars was silver and fifty million dollars gold.

With the present mode of working, rock yielding less than twenty dollars a ton is not worked, because it will not pay.

The annual yield from the Comstock is now about sixteen million dollars, and of the State of Nevada twenty-five million dollars.

The Austrian government has but recently completed the adit-level of Joseph II, commenced in 1782, leading from the valley of the river Gran to the mining district at Schemnitz, a distance of ten miles, cutting the veins at a depth of fourteen hundred feet. It is ten feet wide and twelve high, used both as a railway and canal, and was constructed partly to explore for new veins and partly to drain mines already in operation. The Schemnitz mines, in the northern part of Hungary, furnish gold, silver, iron, lead, copper, and sulphurgold to the value of about seventy-five thousand dollars, silver seven hundred thousand dollars—the annual

value of all the metals not exceeding one million five hundred thousand dollars.

The celebrated silver mines at Freiberg, in operation since the commencement of the thirteenth century, are at present drained by an adit beginning on a tributary of the river Elbe, extending something over eight miles, so as to communicate with all the mines in the upper part of the district, being over eight feet wide and nearly ten feet high, securing a drainage at a depth of sixteen hundred feet. But, as the ore of these mines continues to increase in richness with the depth, it has been proposed by eminent engineers, and the government of Saxony it is said has in contemplation the construction of an adit-level of the extraordinary length of twenty-two miles, opening in the river Elbe, and cutting the veins of the Freiberg district at the average depth of two thousand feet. Should this bold conception ever be carried into practical effect, it will constitute one of the grandest enterprises of the present age, and the most extensive mining tunnel in the world.

The Freiberg mines, to which so much talent, energy, and such vast expenditures of money are being devoted in contriving works to operate and improve them, yield a silver product of the annual value of about one million dollars, and in a period of nearly three hundred and fifty years have produced an aggregate value not exceeding one hundred and twenty million dollars.

The Harz mines, in the district of Clausthal, in the former kingdom of Hanover, are drained by a tunnel penetrating the mountains for a distance of six and one-half miles, nine hundred feet beneath the town of Clausthal, commenced in 1777 and completed about the beginning of the present century. The first tunnel