GEOLOGY AND :MINERAL RESOURCES. The 11101111 tain ranges are formed chiefly of plutonic and volcanic rocks such as granites, gneiss, syenites, mineral-bearing trachytes, basalts, porphyries, obsidian, sulphur. pumice, lavas. and tufa. Sedi mentary formations are also represented especial ly by a carboniferous limestone interspersed with deposits of anthracite. The land consists mainly of metamorphic formations largely penetrated and overlaid by volcanic outpourings and the d'bris resulting from mountain denudation. The most valuable rocks thus far known are the argentiferous porphyries and schists of Sinaloa and the central plateau. It has not yet been re vealed whether the auriferous deposits of Sonora are destined to equal them in economic value. The sandstones of the northern States have pro duced the sandy plains of North Mexico, but none of the horizontal layers is rich in ores. which are found chiefly in metamorphic rocks of Durango, Chihuahua, and the south.
Mexico is one of the richest mining countries in the world. Excepting Sinaloa and Sonora, which contain vast stores of the precious metals, nearly all the historic mines lie on the south central plateau at elevations of from 5500 to 9500 feet. A line drawn from the City of Mexico to Guanajuato. thence north to Chihuahua and south to Oaxaca, incloses a silver-yielding zone that is unsurpassed in richness. The central group of mines in the districts of Guanajuato, Zacatecas, and Catorce in the States of Guana juato. Zacatecas, and San Luis Potosi have thus far yielded over half of the silver mined in Mex ico. The Veta Madre lode of Guanajuato alone produced 8252.000.000 between 1556 and 1803. Gold is found chiefly, not on the plateau, but on the slopes facing the Pacific. It is believed to be in greatest abundance in Sonora, but the gold mining industry may be said as yet to b almost in its infancy, and the production is compara tively small. The inferior development of gold mining is due to the fact that it is far more dillienit and expensive to mine and reduce gold than silver; and most of the gold Mexico pro duces is that obtained in association with silver mining. Copper in a pure stale is found Dear the City of Guanajuato and associated with gold in several States. Iron is in vast abundance in Michoacan, Jalisco. and Durango, but until the coal fields found at various points are developed there is little prospect that iron-mining will be come very important. The famous Cerro del Mercado in Durango. discovered in 1562, is a hill of magnetic iron ore. 4800 feet long, 1100 feet in width, and 640 feet high. averaging about 70 per cent, of metal and estimated to contain over 300.000.000 tons of ore above the plain, beneath
which it may extend to a great depth. Fuel is one of the most pressing needs of Fire wood costs in the City of Mexico $14 it cord. Coal ranges from $16 to $22 a ton. and is brought from England and the United States. The diffi culty is that most of the coal is remote from lines of transportation. and the fields cannot he developed till means of cheap carriage are pro vided. Sonora has a carboniferous area with veins from 5 to 16 feet in thickness of hard clean anthracite carrying :is high a per centage of fixed carbon as the best coal of Wales. 1Vhen it can be transported the anthracite of this field will supply the Pacific Coast of North Amer ica with anthracite of the first quality for years to come. The coal measures of Michoacan and Oaxaca are also undeveloped. Many of the in habitants of the northern State of Coahuila burn mesquite bush, straw, and cotton bushes because they cannot procure the coal mined at Salinas in their State, which now supplies fuel for the International Railroad Company. a part of the Southern Pacific Railroad, and the factories in Monterey.
Much lead is associated with silver, and tin, sulphur. salt, marble, and the building stones are in abundance. All other mining enterprises, however, are dwarfed by the colossal develop ment of silver production. The value of the pre cious metals presented at the Mexicali] mints and assay offices in the year 1898.99 was: Silver, $57. 985.400; gold, $4,043,374. In 1899 there were in Mexico 1142 mines including: Silver. 256; silver and lead, 171; silver and other metals, 114; gold. 84: gold and silver, 27S; gold and other metals. 117: copper, 31. The total output of ore was valued at $89,000,000, and the number of persons employed was 106.536.
Three mints and eight Government assay offices are maintained. and producers of gold and silver may have their bullion coined at small cost. The total coinage of :Mexican silver from the time of its discovery by the Spaniards to 1895 amounted to $3,398,664,400, which is more than one-third of the world's production of silver from 1493 to 1S95. As a large amount of silver is not• coined, but is used in the arts, it is estimated that 'Mex ico has produced nearly one-half of the world's silver mined in the past four centuries. The larger part of the gold and silver is exported. In the twenty-two years ending in 1896 the silver exports amounted to $429.057,100 in coin, $143. 418.595 in bullion, $85,898,933 in ores, and $30. 102.15] in other forms. Europe is the principal market for the export silver and the United States for the export gold.