Girba 20 (?) Kheiba 40 (?) Shiyata 20 (?) Melfa (including Shebat, 260 18 (?) Exabia, and Gagub) As will be seen from the figures in the table, by far the largest and deepest depression in this series—seven times as large, in fact, as all the others put together—is that of Qattara, which has not been shown on any previous map, and of which the existence was proved only last year. That so deep a depression should exist comparatively near to the Mediterranean and to Cairo, and have remained undiscovered until now, is striking evidence of how much has still to be learned concerning the configuration of the desert surface. The manner in which the discovery was made is perhaps worth placing on record. Hearing early in 1917 that a military patrol was about to operate in the Qattara region, I lent a small aneroid to the officer in charge of the patrol, and asked him to take readings with it at various points along his route, with the object of getting some idea of the altitudes in that region. It was, of course, certain that low-lying country existed along the foot of the Qattara escarpment, but no idea was entertained that any great part of it might be below the level of the sea. The officer brought back aneroid-readings which seemed to indicate that the spring at the foot of the scarp at Qattara was about 60 metres below sea-level; but the aneroid itself was unfortunately lost during the return journey. The result was too surprising for it to be accepted without evidence that the readings of the instrument had not been vitiated by accidental rough treatment, and consequently I refrained at the time from placing the levels found on the maps. But I resolved to confirm them or otherwise on the first opportunity. That opportunity came last year, when it was possible to send a survey- party to triangulate westwards from the Wadi Natrun so as to cross the place where the aneroid readings had been taken. The work was entrusted to Mr. G. F. Walpole, of the Survey of Egypt, who had already distinguished himself by successfully carrying out a difficult triangulation from the Nile across some 500 kilometres of the Libyan Desert _viâ_ Baharia to Siwa. The result of Mr. Walpole’s work was not only to confirm the substantial accuracy of the previous estimation of the level of the Qattara spring, but to bring to light the existence of a vast hollow, thousands of square kilometres of whose floor lie at even lower levels, and which at one place descends to a depth of no less than 134 metres below the level of the sea.[4] This last-mentioned spot, some 100 kilometres south-south-west of the Qattara spring, is probably the lowest-lying point on the land-surface of the African continent.