Coal has been discovered in California, in various places, and is reported to abound in considerable quantities in the neighborhood of San Francisco. Every day developes some new wealth of this land of treasure, and we regard the discovery of the abundance of coal as in the highest degree important to the residents of California. Even amid the news of the extraordinary yield of the gold region during the present year, 1850, when a single vessel, in one trip, brings $2,000,000 worth of gold dust to the United States we can pause to notice the discovery of the more useful substances. The Trinity River and Humboldt Harbor, in the north-western part of California, have lately become a resort for the superfluous population of the Sacramento and San Joaquin regions. The harbor is pronounced a very good one, and the discovery of abundance of gold on the branches of Trinity River, will, doubtless, contribute to the building of a large town upon its shores. In the middle of June, there was much excitement in San Francisco, caused by the reported discovery of a gold lake, among the mountains between the South Fork of Feather River and the Yuba. One man was said to have got $7000 in four days, and a party of ten Kanakas were reported to have got $75,000 in a week. A vast number of people were by this means attracted to the sources of the Feather and Yuba Rivers, and though they found the lake story a hoax of a vile character, they found tolerably fair diggings, which would console them for their disappointment. The following extract from the Placer Times of the 17th of July, 1850, under the head of "Great Discoveries of Gold--Gold Lake," will afford the reader a lively conception of the degree of excitement caused in California by every new announcement of a newly discovered locality abounding in gold: