We see by the Cincinnatti papers that their great tunnel is advertised for letting. The hillson the north side of the- city rise about 200 feet above the upper plains of the town; obstructing, except in one direction, the free access of railways to the uppsr' part of the town. A company has been formed to tunnel the hill, for the benefit of all the railways approaching from the Ohio side. This tunnel will be 6,000feet in length, and will have 2,000 feet of side cuttings. It is intended to lay it with four tracks, and thus provide free and safe entrance into the city for six or eight di fferent railways, who will each contribute to its receipts, and thus make it very profitable stock., The enterprise, is a great one, and will prove eminently useful.