In Jackson county, however, the matter of mining has become an enterprise of some magnitude, and we are enabled to give some facts and figures which exhibit in some measure the importance to the State of this new branch of industry. There are several "workings" of coal in the vicinity of Jackson, and several companies have been formed for the purpose of mining coal. Considerable coal has been mined and sold from these different workings and mines. The principal mine, and one which in all its arrangements and provisions is equal to any mine in the country, is that of the Detroit and Jackson Coal and Mining Company. The works of this Company are at Woodville station on the line of the Michigan Central Railroad, about three and a half miles west of Jackson city. The mine is situated on the north side of the Railroad and about half a mile from the main track. The Coal Company have built a side track from the Central Road to the mouth of their shaft. The shaft from which the coal is taken is ninety feet deep, and at the bottom passes through a vein of coal about four feet in thickness. This vein has been opened in different directions for several hundred feet from the shaft, and with a tram-road through the different entries the coal is reached and brought from the rooms to the shaft, and then lifted by steam to the surface. This coal has been transported to different points in the State and is rapidly coming into use for all ordinary purposes, taking the place of many of the Ohio coals and at a reduced cost. The mine to which reference is made is within _four hours'_ ride of Detroit, on the Central Road, and a visit of two hours (which can be accomplished any day, by taking the morning train, leaving the city at 9 45 and returning so as to reach here at half past six in the evening,) will repay any one for the trouble. The station is called Woodville, and is only three and a half miles west of Jackson. Michigan, hitherto a heavy importer of salt, is in a fair way not only to have amply sufficient for her own wants, but something perhaps to spare. To aid in developing our saline resources, the Legislature wisely provided a bounty upon the production, which has already brought forth good fruits. At Grand Rapids, salt water has been discovered much stronger than that of the Syracuse springs, requiring only twenty-nine gallons to produce a bushel.--Arrangements have been almost perfected for commencing the manufacture upon a very extensive scale. At Saginaw, within a few days, at the depth of 620 feet, copious volumes of brine were revealed. This is also stronger than any in New York. From some cause, it is sought to keep this information a secret, but it is fair to presume it would soon have leaked out. The salt both at Grand Rapids and Saginaw, is a beautiful article, of great purity.