A stream of the Atlantic slope of the United States, meeting tide-water at Trenton, New Jersey,130 m. above its mouth. Its total length, from the head of the longest branch to the capes, is 410 m., and above the head of the bay its length is 360 m. It constitutes in part the boundary between Pennsylvania and New York, the boundary between New Jersey and Pennsylvania, and, for a few miles, the boundary between Delaware and New Jersey. The main, west or Mohawk branch rises in Schoharie county, N.Y., about 1886 ft. above the sea, and flows tortuously through the plateau in a deep trough until it emerges from the Catskills. Other branches rise in Greene and Delaware counties. In the upper portion of its course the varied scenery of its hilly and wooded banks is exquisitely beautiful. After leaving the mountains and plateau, the river flows down broad Appalachian valleys, skirts the Kittatinny range, which it crosses at Delaware Water-Gap, between nearly vertical walls of sandstone, and passes through a quiet and charming country of farm and forest, diversified with plateaus and escarpments, until it crosses the Appalachian plain and enters the hills again at Easton, Pa. From this point it is flanked at intervals by fine hills, and in places by cliffs, of which the finest are the Hockamixon Rocks, 3 m. long and above zoo ft. high. At Trenton there is a fall of 8 ft. Below Trenton the river becomes a broad, sluggish inlet of the sea, with many marshes along its side, widening steadily into its great estuary, Delaware Bay. Its main tributaries in New York are Mongaup and Neversink rivers and Callicoon Creek; from Pennsylvania, Lackawaxen, Lehigh and Schuylkill rivers; and from New Jersey, Rancocas Creek and Musconetcong and Maurice rivers. Commerce was once important on the upper river, but only before the beginning of railway competition (1857). The Delaware division of the Pennsylvania canal, running parallel with the river from Easton to Bristol, was opened in 1830. A canal from Trenton to New Brunswick unites the waters of the Delaware and Raritan rivers; the Morris and the Delaware and Hudson canals connect the Delaware and Hudson rivers; and the Delaware and Chesapeake canal joins the waters of the Delaware with those of the Chesapeake Bay. The mean tides below Philadelphia are about 6 ft. The magnitude of the commerce of Philadelphia has made the improvements of the river below that port of great importance. Small improvements were attempted by Pennsylvania as early as 1771, but apparently never by New Jersey. The ice floods at Easton are normally Io to 20 ft., and in 1841 attained a height of 35 ft. These floods constitute a serious difficulty in the improvement of the lower river. In the "project of 1885" the United States government undertook systematically the formation of a 26-ft. channel 600 ft. wide from Philadelphia to deep water in Delaware Bay; $1,532,688.81 was expended - about $200,000 of that amount for maintenance - before the 1885 project was superseded by a paragraph of the River and Harbor Act of the 3rd of March 1899, which provided for a 30-ft. channel 600 ft. wide from Philadelphia to the deep water of the bay. In 1899 the project of 1885 had been completed except for three shoal stretches, whose total length, measured on the range lines, was 42m. The project of 1899, estimated to cost $5,810,000, was not completed at the close of the fiscal year (June 30) 1907, when $4,93 6 ,55 0.6 3 had been expended by the Federal government on the work; in 1905 the state of Pennsylvania appropriated $75 0, 000 for improvement of the river in Pennsylvania, south of Philadelphia.