The purpose of the last Expedition was to conclude the labours begun, during the spring of 1877, in a mining country unknown, or rather, fallen into oblivion. Hence its primary "objective" was mineralogical. The twenty-five tons of specimens, brought back to Cairo, were inspected by good judges from South Africa, Australia, and California; and all recognized familiar metalliferous rocks. The collection enabled me to distribute the mining industry into two great branches--(1) the rich silicates and carbonates of copper smelted by the Ancients in North Midian; and (2) the auriferous veins worked, but not worked out, by comparatively modern races in South Midian, the region lying below the parallel of El-Muwaylah. It is, indeed, still my conviction that "tailings" have been washed for gold, even by men still living. We also brought notices and specimens of three several deposits of sulphur; of a turquoise-mine behind Ziba; of salt and saltpetre, and of vast deposits of gypsum. These are sources of wealth which the nineteenth century is not likely to leave wasted and unworked. In geography the principal novelties are the identification of certain ruined cities mentioned by Ptolemy, and the "Harrahs" or plutonic centres scattered over the seaboard and the interior. I venture to solicit the attention of experts for my notes on El-Harrah, that great volcanic chain whose fair proportions have been so much mutilated by its only explorer, the late Dr. Wallin. Beginning with Damascan Trachonitis, and situated, in the parallel of north lat. 28 degrees, about sixty direct miles east of the Red Sea, it is reported to subtend the whole coast of North-Western Arabia, between El-Muwaylah (north lat. 27 degrees 39') and El-Yambu' (north lat. 24 degrees 5'). Equally noticeable are the items of information concerning the Wady Hamz, the "Land's End" of Egypt, and the most important feature of its kind in North-Western Arabia. Its name, wrongly given by Wallin, is unknown to the Hydrographic Chart, and to the erudite pages of my friend Professor Aloys Sprenger, who, however, suspects with me that it may be the mouth of the celebrated Wady el-Kura. For further topographical details the reader is referred to the "Itineraries" of the Expedition, offered to the Royal Geographical Society of London.