One of the tunnels on the Pennsylvania Railroad now constructing, is to be 3,670 feet in length. Its area at the widest space within the lines of the masonry will be about 24 feet, and the spring of the arch will begin 16 feet from the crown of the arch. The arch itself, of the tunnel, will be rather of an oval form, one ot the most beautiful curvatures which Conic Sections can afford. The greater part of the vast arched excavation will be inlaid with strong and substantial masonry. More than half of this masonry will be composed of sandstone well laid in hydraulic cement j and the remainder will be hard burnt brick. This whole masonry will be 22 inches thick. The tunnel passes the Allegheny Mountain in Sugar Run Gap, and lies partly in Blair and partly in Cambria County. Taking into account the length of the Tunnel and its interi-or breadth, and the quantity and solidity of its masonry, it may be regarded as the largest work of the kind in the United States.— About 400 men are employed upon it. The Seminole Indians have again entered into hostilities against the United Sttaes.