Important as mining has been in the past history of Mexico, it is, and must remain, the most important of the industries of the country--in the sense of wealth produced. This does not mean, of course, that it is the most beneficial to the interests of the country and its inhabitants at large, for agriculture is that by which the bulk of the native Mexicans earn their means of subsistence. The mineral-bearing zone of the country is a very extensive one, and includes all that portion of the Republic traversed by the Sierra Madres and their offshoots. From the State of Sonora in the north, the boundary with the United States, to that of Chiapas in the south--bordering upon the neighbouring Republic of Guatemala--minerals are found. The region in which the most important mining districts exist, and in which the historic mines of Mexico lie, forms a great zone 1,600 miles long--between the States of Sonora in the north to Oaxaca in the south--and 250 miles wide. These more famous and largely-worked mines are chiefly upon the western slope of the Eastern Sierra, and their elevations above sea-level range from 3,000 feet to 9,000 feet, and more. The minerals which are found throughout this great region include almost all those known to commerce, and, more or less in relative order of their importance, are as follows:-- Silver, copper, gold, lead, quicksilver, iron, coal, zinc, salt, antimony, petroleum, sulphur, tin, bismuth, platinum; and others more rarely, as nickel, cobalt, &c. Onyx, marble, opals, emeralds, sapphires, topazes, rubies, are found, and other precious stones, whilst diamonds are said to exist in certain localities. Agates, cornelians, obsidian, are also among the products of this nature. The following table shows the principal distribution of minerals in the various states:--