These plains are much more extensive than I supposed yesterday, and many new plants were found on them.  The river rose upwards of a foot during the night, and still continues to rise; a circumstance which appears very singular to me, there having been no rains of any magnitude for the last five weeks, and none at all for the last ten days.  We are also certain that no waters fall into it or join it easterly for nearly one hundred and fifty miles.  This rise must therefore be occasioned by heavy rains in the mountains, whence the river derives its source; but it is not the less singular, that during its whole course, as far as it is hitherto known, it does not receive a single tributary stream.  Observed the latitude 33. 16. 33.  S.

May 11.—­The river rose about four feet during the night, and still continues to rise.  Set forward on our journey down the river.  About four miles and a half from this morning’s station. the river began to wash the immediate edge of the plain, and so continued to do all along.  My astonishment was extreme at finding the banks of the river not more than six feet from the water:  it at once confirmed my supposition that the whole of this extensive country is frequently inundated; the river was here about thirty yards broad.  Mount Cunningham was at this time distant about two miles, and Mount Melville four miles; the plains winding immediately under the base of each.  At twelve o’clock ascended the south end of Mount Cunningham, a small branch of the river running close under it.  From this elevation our view was very extensive in every direction, particularly in the west quarter.  The whole country in that direction was so low, that it might not improperly be termed a swamp, the spaces which were bare of trees being more constantly under water than those where they grew.  A remarkable peaked hill bearing W. 27 1/4.  N. was named Hurd’s Peak [Note:  After Captain Hurd, Hydrographer to the Admiralty.], and a lofty hummock S. 83 1/2.  W, Mount Meyrick:  these were the only elevations of any consequence in the western direction.  To the north, low ranges of rocky hills bounded the swamps, which on the south had a similar boundary, except that occasionally a bolder rocky projection would obtrude itself on the flat.

On descending from the hill, we proceeded to the point where the north-west arm is separated from the main branch, but apparently to join it in water, bearing from Mount Cunningham W. 40.  N.:  on arriving there we found the boats and horses.  The crew of the former reported, that an equally considerable branch of the river, with that down which they had come, had turned off to the south-west, about two miles below the place where we stopped last night.  After directing the horses and baggage to be got over the north-west arm, I returned to examine the branch passed by the boats, and found it at least as considerable as that which we were pursuing.  I am in hopes that when again joined, the width and depth of the river will be considerably increased.  At half past four returned to the tents on the north-west arm.  The river (from whatever cause) was still rising, and no part of the banks was more than four feet above the level of the water.  I consider that the river may have from eight to ten feet more water in it than usual:  its present average depth is about eighteen feet.