tides in the Harlem River," says General John Newton, in a report to the War Department, " are chiefly due to the propagated Hellgate wave, while the latter is the result of the contact of the Sound and Sandy Hook tides. The tides in the Hudson River and Spuyten Duyvil are produced by the propagation of the sea. tide through the Upper and Lower bays." The mean rise of the tide in the Harlem is from Ave and one-half to six feet; in the Spuyten Duyvil Creek it is three and eight-tenths feet. The mean high water level in the Hudson River at Spuyten Duyvil Creek is nearly a foot lower and an hour and forty minutes earlier than in the Harlem, and the mean duration of the rise of tide in the former is thirty-six minutes shorter than in the latter. The westerly current, from Hellgate, is swifter than the easterly, from the Hudson. The place of " divide " between the Harlem River and the Spuyten Duyvil Creek is usually located at Kingsbridge. In early times the Harlem was navigable for most of its length, but owing to artificial obstructions (notably that of Macomb's Dam), which were begun in the first part of the present century, the channel above the present Central Bridge became both shallow and contracted. The mean natural depth of Spuyten Duyvil Creek has always been comparatively slight. Owing to the importance of this waterway as a means of short transit for craft plying between the Hudson River and ports on the Sound and in New England, the United States Government has in our own time dredged a channel, which, from the Hudson to Hellgate, has a depth of from twelve to fifteen feet. This improvement, known as the Harlem Ship Canal, was opened to commerce on the 17th of June, 1805.