The good fortune which had followed Sir Thomas Mitchell throughout his three earlier expeditions did not forsake him during this one, which proved to be the last and most arduous of the series. It was his ambition this time to cross the continent and open an overland route to the distant Carpentaria. Of all men living, he was the most likely to accomplish this task. He did not, indeed, attain the desire of his heart, but in all other respects his expedition was eminently successful, and forms a memorable epoch in the history of exploration. The party mustered at the old rendezvous of Buree, in the Western District, which, though no longer the outpost of settlement, was yet a convenient starting-point. Mitchell chose for his second in command Mr. Edmund B. Kennedy, the unfortunate explorer who, several years later, was killed by the blacks when leading a disastrous expedition in Cape York Peninsula. The rest of the party were mostly convicts from Port Jackson, who had volunteered their services in the hope of obtaining their freedom. The little army, consisting of two dozen able-bodied men, amply provisioned, left Buree on the 15th of December, 1845. The old route was followed for a considerable way, and in a short time the Hervey Range, containing the sources of the Bogan, was crossed without serious difficulty. For a long distance westward the country was now occupied by squatters, but many of the outsiders had already succumbed to the hostility of the Darling blacks, who had speared their cattle and otherwise harassed them beyond the limit of human endurance. Ten years had now passed away since Mitchell led his preceding expedition through these parts, and the abortive attempts at settlement were the principal changes observable in the general aspect of the country. One very remarkable minor feature was the appearance of couch-grass and horehound, which had sprung up around the stockyards. Mitchell was quite positive in asserting that no specimen of these plants could have been found in the district before the white men settled there.
The party suffered from want of water till Nyngan was reached, on the 16th January, and then one difficulty was quickly followed by another. Most of the men were seized with eye-blight, and compelled to remain in camp longer than was convenient for the object of the expedition. But they were again on the move as soon as circumstances would permit, the march being now directed towards the Macquarie. Meanwhile an encampment was made on the Canonbar, a tributary of the Bogan. While resting here the saltbush became an object of curiosity, and some interesting experiments were made with this singular plant of the interior plains. The tiny leaves were found to be a tolerable substitute for vegetables after boiling, by which process a yield of pure salt was obtained in the proportion of one ounce to the pound. The condition of the stock also bore witness to the fattening quality of the same plant.
After a few days of eventful travel by way of Sturt's Duck Ponds, the Macquarie River was struck a few miles below Mount Harris, which had been an important landmark for explorers since the time of Oxley. The channel was dry, but the blacks reported a heavy flood as near at hand. Mitchell had often heard of sudden inundations appearing in an arid part of the country, and was anxious to witness so singular a visitation. Late in the still evening there fell upon his ear a dull murmur as of distant thunder, speedily followed by a cracking and crashing of trees, and in a few minutes more the river was overflowing its banks in a wide-spreading flood. The phenomenon is described as being grand in the extreme, and of so improbable a character as scarcely to be credited unless it had been witnessed.
On the 27th the Castlereagh was reached, and the next day the party found themselves on the banks of the Darling. For many miles in both directions the river at this period was studded with pastoral settlements. Having crossed at Warley, near one of the stations, Mitchell now struck out for the Narran, the nearest point of which was reckoned to be about 35 miles distant. The intervening space was found to consist of choice pastoral country, covered with tall kangaroo grass. Commissioner Mitchell, son of the explorer, had previously traversed these parts, and this expedition soon "pulled up" his tracks. The line of the Narran River having thus been already explored, it was traversed as expeditiously as possible, and this part of the journey was over by the beginning of April, when the Balonne (pronounced Baloon) was sighted. Mitchell described it as the finest river he had seen in Australia, with the exception of the Murray. The current was very slight, but the water stretched out in long and beautiful reaches. The march was once more resumed, and the party moved along the line of this river till St. George's Bridge was reached, where the width expanded to 120 yards. At this point there is a chain of rocks stretching from bank to bank, which has always the appearance, and sometimes the convenience, of a natural bridge. It was this circumstance which led to its being called St. George's Bridge, a name which it still retains in common with the flourishing township that has sprung up in the vicinity.
While enjoying a short interval of repose in this enchanting situation, Mitchell had the pleasure of receiving a despatch from headquarters containing a brief account of Leichhardt's successful journey to Port Essington. Being somewhat jealous of his rival, and, it may be, concerned for his own laurels, he determined on making a redoubled effort to cross the continent and discover a more practicable route than Leichhardt had been able to find. Leaving Kennedy in charge of the depôt at St. George, he took a light party and pushed forward, having given instructions to the rest to follow his tracks when the stock should be sufficiently recruited for travel. One day's march brought the advance party to the junction of another important river, which was afterwards found to be the Maranoa. But they still kept the line of the Balonne as far as the Cogoon, a considerable tributary, which was now followed. This led the explorers into a splendid district, known afterwards as the Fitzroy Downs, near the centre of which the town of Roma now stands. This fine region was studded with isolated mountain-peaks, one of which Mitchell hastened to ascend. The prospect obtained from its summit was magnificent, and the pasture so abundant on this height as to suggest the name of Mount Abundance, which it has ever since retained. At a short distance the three-peaked Bindango, standing near its fellow, Bindeygo, formed most picturesque features in the landscape. It was on Mount Abundance that the first bottle-tree was discovered. This is the strangest product of the Australian forest, and Sir Thomas was disposed to regard it as a lusus naturæ in the vegetable kingdom.
The telescope again brought into view a range of hills. Mitchell, bent on reaching Carpentaria, had for some time been disappointed in not finding the division of the northern waters, and fervently hoped this distant range would prove to be the dividing line. This watershed was to him, through the whole journey, what the horizon is to the traveller—always appearing near and ever receding. Many a weary day did he toil on, sustained by this expectation, but it kept mocking him to the last, and he went to his grave without having crossed the coveted watershed. But for the present he enjoyed the pleasures of hope. Leaving Mount Abundance he soon discovered the Amby, which, being followed, led on to the Maranoa, whose junction with the Balonne he had previously discovered. Here he established another depôt and waited for Kennedy, making in the meantime several short excursions in various directions. Not far from this depôt a squatting station was subsequently formed, and more recently an important town has been built, in both of which the name of Mitchell has been perpetuated. Kennedy having brought up his party in excellent condition, the experiment which had been so successfully made at St. George's Bridge was repeated here—the leader again setting out for the north with a small equipment and a four months' supply of provisions. The natives in this quarter were not disposed to stand on friendly terms with the strangers, and usually kept at a safe distance. One inconvenience only Mitchell regretted. Many interesting natural features were observed, especially mountain-peaks, which he would gladly have made known under the aboriginal names. Failing in this, his favourite custom, he called them after some of the leading men of the time, as Owen, Faraday, Buckland, and P. P. King. As an exception, he named one of the heights Mount Aquarius, in remembrance of a very seasonable supply of water it had furnished for his party. This difficulty now seemed to be overcome for some time by the discovery of the Nive and the Nivelle, important tributaries of a large river. This was the Warrego, which would have been followed had it not persisted in taking a course which would have led them in the opposite direction to Carpentaria.
The country to the northward continued to rise till it reached an elevation of something like 1,500 feet. Being also of a mountainous character, it was fondly hoped that here, at least, would be found the long-sought watershed. This anticipation was rather confirmed by the discovery of a beautiful stream, now called Salvator Rosa, which flowed northward with a clear and musical current. This pleasing delusion lasted only one day, for on the morrow the lovely river ended its course in a reedy lake, on the opposite side of which a channel was found, but it contained no water at that time. This is one of the heads of the Nogoa, a river trending too much to the east to suit Sir Thomas's purpose. Other discoveries of streams or watercourses were made soon afterwards, two of the principal being named the Claude and the Balmy Creek. These designations are suggestive of pleasant associations, and, while speaking well for the country, sufficiently prove that the expedition had its share of enjoyment as well as the usual experience of toil and fatigue.
The 21st of July was rendered memorable by the discovery of the Belyando, a fine river, heading towards the north, and offering a better promise of leading to the Gulf. In this expectation, it was eagerly followed, and in four days conducted the explorers across the Tropic of Capricorn. In many parts the country was excellent, stretching out in splendid downs, which squatters have long since applied to a lucrative purpose, but in other places the axe had to be used to clear a path through the brigalow scrubs. In common with other explorers, Mitchell has noticed that "the Australian rivers have all distinguishing characteristics, which they seem to possess from their source to their termination." The Belyando was no exception. It was found throughout its course to have an unfortunate propensity for splitting into channels, which were often difficult to trace through the thick scrub; but, as a compensation, these branches afforded excellent facilities for storage of water against dry seasons. Many days of persevering travel gave the party a good northing, but, after passing over three and a half degrees of latitude, it began to be evident that the Belyando also was going to deceive them. It had been steadily, and latterly very decisively, making for the east, thus leaving no hope of conducting the expedition to Carpentaria. Mitchell rightly conjectured that it must be the tributary which Leichhardt had seen joining the Suttor, and, with a crushing feeling of disappointment, determined to change his front and return home.
Having still a sufficient store of provisions, he was unwilling to continue his homeward track, and resolved to follow up a river to the westward, which took its rise in the high ground previously mentioned. It was found to lead through first-class pasture land, and this excursion resulted in opening up a large area of squatting country. Many tributaries were noticed to fall in on either side, particularly the Alice, which came from the north. The main river was followed till it, too, left no hope of leading to the coveted north. Soon after Sir Thomas gave up the search altogether, and set his face in earnest for the settled districts, which he reached, after no long interval, by way of the Mooni River and the Liverpool Plains. Having failed to enter into communication with the aborigines, he was unable to ascertain the native name of the river which had led him so far to the west. It was the last of his great discoveries, and he called it after the name of the Queen, an unfortunate designation, as there is another Victoria River on the west coast. About the same period Captain Sturt was exploring on another part of this river, and gave it the name of Cooper's Creek. The natives called it the Barcoo, and by this name it is now generally known throughout its whole course.