The depth of the wells varies from 200 to 1,600 metres, according to the region. The duration of the flow is essentially variable, depending upon the magnitude of the deposit of oil. But it goes without saying that when a spring has flowed for seven years more or less, like the first one exploited by the _Mexican Eagle_, it gives out, yielding salt water. The fact is quite ordinary, and is known in all competent circles, although it is sometimes brandished as a warning by interested people in order to lower the value of certain oil shares. One often hears of "pools," "rivers," or "veritable lakes of oil." These expressions are most inaccurate. Apart from certain exceptions, such as the famous well of the _Colombia_ in Rumania in 1913, the deposits of oil are neither rivers nor pools. They are _actually solid layers of sandstone, often very hard, impregnated, saturated with oil_. This sandstone is very porous and contains thousands of cavities or pockets enclosing the precious "rock-oil." Its thickness varies from the usual 30 or 50 metres (giving wells of a yield of 200, 500, or 1,000 barrels a day) to _one kilometre_ in certain wells of the _Eagle_ (yielding 70,000 to 100,000 barrels a day, instead of 200 to 1,000). The _Eagle_ is lucky, it must be admitted, and its history is unique in the annals of oil. Only its sister company, the _Mexican Oil_, which works in the same field, but for the _Standard Oil_ group, can be compared with it. Even a superficial examination of the chemical composition of oil, a hydrocarbon, in which the carbon, in a proportion of 80 to 88 per cent., is combined with hydrogen, and sometimes with a little oxygen, reveals in this compound a marvellous source of thermal energy, which may manifest itself in various ways. For, from the greenish-brown oil which is lighter than water, no less than 128 chemical compounds are obtained, which are used in forty different industries. From the retort in which the crude oil is distilled comes an infinity of substances of basic importance in modern industry. * * * * * Although the intensive use of oil and its industrial applications are of comparatively recent date, the discovery of deposits of petroleum goes back to remote antiquity. The history of oil is as old as the world, since there is already mention of it in the Book of Genesis. The wells of Baku were known long before the Christian era. In the peninsula of Apsheron, where they are situated, arose the cult of Zoroaster and the fire-worshippers. According to the latter, the flames which escaped from the soil would burn until the end of the world. They were, at any rate, famed throughout the world nearly three thousand years ago.