TUESDAY, DEC. 12. The quicksilver mines of California constitute one of the most important elements in her mineral wealth. Only one vein has as yet been fully developed; this lies a few miles from San José, and is owned by Hon. Alexander Forbes, British consul at Typé, in Mexico—a gentleman of vast means and enterprise—and who has a heart as full of generous impulses as his mine is of wealth. Many of our countrymen, in misfortune, have shared his munificent liberality. His mine, in the absence of suitable machinery, has been worked to great disadvantage; and yet, with two whaling-kettles for furnaces, he has driven off a hundred and fifty pounds a day of the pure metal. If this can be done with an apparatus intended only for trying blubber, a ton may be rolled from a capacious retort constructed for the purpose. The title of Mr. Forbes to this mine has excited some inquiry, but it will be found among the soundest in California. Instead of attempting to shake this title, a more wise and profitable course will be to open a fresh vein. They lie in the contiguous spurs of the same mountain range, and only require a small outlay of labor and capital to develop their untold wealth. The metal need not travel from California to find a market; vast quantities will be required in the gold mines: the cradle and bowl must give place to more complicated machinery; the sands of the river pass through a more delicate process; and the quartz of the steep rock, crumbled under the stamper, surrender its gold to the embrace of quicksilver. This stupendous issue is close at hand; and they who anticipate it, will find the fruits of their sagacity and enterprise in sudden fortunes. MONDAY, DEC. 25. The multitudes who are in the mines, suffer in health and constitution from the extreme changes of temperature which follow day and night. In some of the ravines in which we camped, these variations vibrated through thirty and forty degrees. In mid-day we were driven into the shade to keep cool, and in the night into two or three blankets to keep warm. The heat is ascribable in part to the nature of the soil, its naked sandy features, its power of radiation, and the absence of circulation in the glens. But the cold comes with the visits of the night-wind from the frosty slopes of the Sierra Nevada.