There are two circumstances upon which the magnitude, and velocity of a river, more immediately depend.  The first is the abundance of its sources, the other the dip of its bed.  If a stream has constant fountains at its head, and numerous tributaries joining it in its course, and flows withal through a country of gradual descent, such a stream will never fail; but if the supplies do not exceed the evaporation and absorption, to which every river is subject, if a river dependant on its head alone, falls rapidly into a level country, without receiving a single addition to its waters to assist the first impulse acquired in their descent, it must necessarily cease to flow at one point or other.  Such is the case with the Lachlan, the Macquarie, the Castlereagh, and the Darling.  Whence the latter originates, still remains to be ascertained; but most undoubtedly its sources have been influenced by the same drought that has exhausted the fountains of the three first mentioned streams.

In supporting his opinion of the probable discharge of the interior waters of Australia upon its north-west coast, Mr. Cunningham thus remarks in the publication from which I have already made an extract.

“To those remarkable parts of the north-west coast above referred to in the parallel of 16 degrees south, the Macquarie river, which rises in lat. 33 degrees, and under the meridian of 150 degrees east, would have a course of 2045 statute miles throughout, while the elevation of its source, being 3500 feet above the level of the sea as shown by the barometer, would give its waters an average descent of twenty inches to the mile, supposing the bed of the river to be an inclined plane.

“The Gwydir originating in elevated land, lying in 31 degrees south, and long. 151 degrees east, at a mean height of 3000 feet, would have to flow 2020 miles, its elevated sources giving to each a mean fall of seventeen inches.

“Dumaresq’s river falling 2970 feet from granite mountains, in 28 1/4 degrees under the meridian of 152 degrees, would have to pursue its course for 2969 miles, its average fall being eighteen inches to a mile.”

As I have never been upon the banks either of the Gwydir or the Dumaresq, I cannot speak of those two rivers; but in estimating the sources of the Macquarie at 3500 feet above the level of the sea, Mr. Cunningham has lost sight of, or overlooked the fact, that the fall of its bed in the first two hundred miles, is more than 2800 feet, since the cataract, which is midway between Wellington Valley and the marshes, was ascertained by barometrical admeasurement, to be 680 feet only above the ocean.  The country, therefore, through which the Macquarie would have to flow during the remainder of its course of 1700 miles, in order to gain the N.W. coast, would not be a gradually inclined plain, but for the most part a dead level, and the fact of its failure is a sufficient proof in itself how short the course of a river so circumstanced must necessarily be.