A letter dated Nevada, Oct. 24, says that the continued dry weather has given unusual opportunities and facilities to miners now working in the river channels. At the best these operations are very precarious in their nature--necessarily attended with a vast outlay, and frequently, where the most sanguine hopes were entertained, the results have been most unfortunate. The time for working in the rivers is usually confined to a very limited period, the water being seldom or never sufficiently low to work to advantage earlier than September; it follows, therefore, that every additional week of dry weather is of the utmost value to such as are thus engaged. Luckily for them, the present dry season has been unusually protracted, consequent upon which, the rivers are at an exceedingly low stage, and the success of the miner proportionate to this advantage. On the other hand, those interested in ravine and hill mining (by far the greater proportion of the miners,) are anxiously awaiting the wet season for a supply of water--without which, all their labor is fruitless. The Bear River and Auburn Water Company's canal is so far completed as to be available to the miners by the first rains, notwithstanding the great expense and time attending its construction, arising from a want of experience, and so far beyond the calculations of its projectors. This work traverses an extensive and rich mining country, totally dependent upon the canal for water, which cannot be exhausted for many years. The discovery of a continuation of the celebrated Coyote lead, in Nevada, from which so many millions of the precious metals were extracted in '50 and '51, is now established beyond a doubt. As yet it is not developed to any great extent, but enough, however, to give employment to a goodly number of miners. The character of the lead continues to be similar to the old mines, in appearance and productiveness. A few weeks' further investigation of the locality will no doubt give a new impetus to mining operations here, which have latterly been somewhat stagnant. The Sacramento Journal says:--We have been shown a lot of the gold taken out of the Mokelumne run, valued at $2,500, which was superior to any thing we ever examined before. The pieces of glittering ore were of sizes varying from a cucumber seed up to a pumpkin seed, and all in that flat, oval shape so peculiarly characteristic of Mokelumne gold. It was sent down from the store of D. L. Angier, in Calaveras county, and we are informed that the same company of six men that disposed of it, have taken out of the claim $36,000 of the same kind of specimens. Gold has been found in considerable quantities in the mountains back of San Buenaventura. The existence of the gold was made known by the Indians to some white men, who, on visiting the spot indicated, were rewarded with six ounces of the precious metal. The prospect is said to be good.