The Tigris is often 250 yards wide at Diarbekr, which is not a hundred miles from its source, and is navigable in the flood time from the bridge of Diarbekr to Mosul, from which place it is descended at all seasons to Baghdad, and thence to the sea.  Its average width below Mosul is 200 yards, with a depth which allows the ascent of light steamers, unless when there is an artificial obstruction.  Above Mosul the width rarely exceeds 150 yards, and the depth is not more in places than three or four feet.  The Euphrates is 250 yards wide at Balbi, and averages 350 yards from its junction with the Khabour to Hit:  its depth is commonly from fifteen to twenty feet.  Small steamers have descended its entire course from Bir to the sea.  The volume of the Euphrates in places is, however, somewhat less than that of the Tigris, which is a swifter and in its latter course a deeper stream.  It has been calculated that the quantity of water discharged every second by the Tigris at Baghdad is 164,103 cubic feet, while that discharged by the Euphrates at Hit is 72,804 feet.

The Tigris and Euphrates are very differently circumstanced with respect to tributaries.  So long as it runs among the Armenian mountains, the Euphrates has indeed no lack of affluents; but these, except the Kara Su, or northern Euphrates, are streams of no great volume, being chiefly mountain-torrents which collect the drainage of very limited basins.  After it leaves the mountains and enters upon a low country at Sumefsat, the affluents almost entirely cease; one, the river of Sajur, is received from the right, in about lat. 36 deg. 40’; and two of more importance flow in from the left-the Belik (ancient Bilichus), which joins it in long. 39 deg. 9’; and the Khabour (ancient Habor or Chaboras), which effects a junction in long. 40 deg. 30’, lat. 35 deg. 7’.  The Belik and Khabour collect the waters which flow from the southern flank of the mountain range above Orfa, Mardin, and Nisibin, best known as the “Mons Masius” of Strabo.  They are not, however, streams of equal importance.  The Belik has a course which is nearly straight, and does not much exceed 120 miles.  The Khabour, on the contrary, is sufficiently sinuous, and its course may be reckoned at fully 200 miles.  It is navigable by rafts from the junction of its two main branches near the volcanic cone of Koukab, and adds a considerable body of water to the Euphrates.  Below its confluence with this stream, or during the last 800 miles of its course, the Euphrates does not receive a single tributary.  On the contrary, it soon begins to give off its waters right and left, throwing out branches, which either terminate in marshes, or else empty themselves into the Tigris.  After awhile, indeed, it receives compensation, by means of the Shat-el-Hie and other branch streams, which bring back to it from the Tigris, between Mugheir and Kurnah, the greater portion of the borrowed fluid.  The Tigris, on the contrary,