In former years a large quantity of quicksilver was exported, but for some time this mineral product has ceased to appear as an item in the exports, the large deposit of cinnabar at Tegora having apparently been worked out. The existence of this mineral in other parts of the state is proved by traces found in several places, and the same may be said of antimony, of which there are indications of rich deposits; but the discovery of these minerals in paying quantities is a matter of chance. Antimony is still worked by the Borneo Company, Ltd., and a recent rise in the price has been an inducement to Chinese and Malay miners to increase the production, and the export of 1906 was more in quantity than it was in 1905, though small as compared with what it used to be. Black bituminous coal, which occurs in the Tertiary strata, has been found in different parts, and two collieries are owned and worked by the Government, at Semunjan in the Sadong district, and at Brooketon. Several hundred Chinese are employed as miners under European supervision, and large sums have been expended upon machinery, etc. Oil, a crude petroleum, has been discovered in two places; it is of good quality, and is an excellent lubricant. It is not impossible, or indeed improbable, that diamond deposits in Sarawak will be found and exploited. No systematic operations in search of these precious stones have been attempted, the dense jungle which covers the country being an obstacle. The only people who wash for diamonds are the Malays, and these carry on their work in a very desultory and imperfect manner. But agriculture and jungle produce have been, and will be, the main source of revenue to Sarawak, and prosperity to the country. We shall deal with these products, as well as with those that are mineral, more fully in a subsequent chapter. The Bornean forest is so varied and so different at different hours and seasons that no description can possibly convey an adequate idea of it to those who have not known it. Infinite and ever changing are its aspects, as are the treasures it hides. Its beauties are as inexhaustible as the varieties of its productions. In the forest man feels singularly free. The more one wanders in it, the greater grows the sense of profound admiration before nature in one of its grandest aspects. The more one endeavours to study it, the more one finds in it to study. Its deep shades are sacred to the devotee of Science. Yet they afford ample food for the mind of the believer, not less than to that of the philosopher.[10] And we would add, to the superstitious native, to whom the jungles teem with ghosts and spirits.