Notwithstanding we had been thus forced to a partial retreat, both Mr. Hume and myself were unwilling to quit the pursuit of the river, in so unsatisfactory a manner. There was no difference in the appearance of the country to the westward of it; but a seeming interminable flat stretched away in that direction. A journey across it was not likely, therefore, to be attended with any favorable results, since it was improbable that any other leading feature was within our reach. I proposed, therefore, to take the most serviceable of the horses with me down the river, that, in the event of our finding fresh water, we might again push forward. Mr. Hume requesting to be permitted to accompany me, it was arranged that we should start on the 8th, thereby giving the animals a day's rest. We had not seen any natives since our parting with the chief horde; and as we were stationed at some little distance from the river, I hoped that they would not visit the camp during my absence. This was the only circumstance that gave me uneasiness, but the men had generally been behaving so well that I relied a great deal upon them. EXTRAORDINARY SOUND. About 3 p.m. on the 7th, Mr. Hume and I were occupied tracing the chart upon the ground. The day had been remarkably fine, not a cloud was there in the heavens, nor a breath of air to be felt. On a sudden we heard what seemed to be the report of a gun fired at the distance of between five and six miles. It was not the hollow sound of an earthly explosion, or the sharp cracking noise of falling timber, but in every way resembled a discharge of a heavy piece of ordnance. On this all were agreed, but no one was certain whence the sound proceeded. Both Mr. Hume and myself had been too attentive to our occupation to form a satisfactory opinion; but we both thought it came from the N.W. I sent one of the men immediately up a tree, but he could observe nothing unusual. The country around him appeared to be equally flat on all sides, and to be thickly wooded: whatever occasioned the report, it made a strong impression on all of us; and to this day, the singularity of such a sound, in such a situation, is a matter of mystery to me. FURTHER ATTEMPT TO EXPLORE THE RIVER.