On the 23rd of April, about a week after the departure of Warburton, William Christie Gosse, Deputy Surveyor-General of South Australia, also left Alice Springs on an exploring expedition, having been appointed by the South Australian Government to take charge of the Central and Western Exploring Expedition. Like Warburton, he was frustrated by dry country in his endeavour to reach Perth. He had with him both white men and Afghan camel drivers, and a mixed outfit of horses and camels. He left the telegraph line and struck westward, soon finding himself in very dry country, where he lost one horse on a dry stage. He made a depot camp on a creek which he called the Warburton, and while on an excursion from this camp he had the singular experience of riding all day through heavy rain and camping at night without water, the sandy soil having quickly absorbed the downpour. On his return he found that the creek at the camp was running, and though repeated attempts had been made by the Afghans to goad one of the camels over, the animal obstinately refused to cross. Probably the leader thought that it was fortunate for the progress of the expedition that they were not likely to meet with many more running streams. After passing both Warburton's tracks and those of Giles, Gosse reached the extreme western point of the Macdonnell Ranges, where another stationary camp was pitched. The leader made a long excursion to the south-west, and at 84 miles, after passing over sand-ridges and spinifex country, caught sight of a remarkable hill, that on a nearer approach proved to be of singular limestone formation. "When I got clear of the sandhills, and was only two miles distant, and the hill, for the first time coming fairly in view, what was my astonishment to find it was one immense rock rising abruptly from the plain; the holes I had noticed were caused by the water in some places causing immense caves." This hill, which Gosse made an ineffectual attempt to ascend, he called Ayer's Rock. He returned to his depot camp, crossing an arm of Lake Amadeus as he did so, and moved the main body on to Ayer's Rock. Rain having set in heavily for some days, he pushed some distance into Western Australia, but soon reached the limit of the rainfall. After many attempts to penetrate the sand-hill region which confronted him, the heat and aridity compelled him to turn back. His homeward course was by way of the Musgrave Ranges, where he found a greater extent of pastoral country than had been thought to exist there. He discovered and christened the Marryat, and followed down the Alberga to within sixty miles of the Overland Line, when he turned north-eastward to the Charlotte Waters station. Although Gosse's exploration did not add any important new features, he filled in many details in the central map, and was able correctly to lay down the position of some of the discoveries of Ernest Giles.