level of the water-surface of the Nile, and the water occurs on both sides of the river, it is certain that the water-bearing bed is cut through by the Nile channel itself; the seepage into the river along the stretch of 16 kilometres must therefore be very considerable. It seems evident that the water is not derived from the bed of the Wadi Alagi, great drainage-channel though that wadi is; for we could not then account for the temperature of the water, nor for its appearing to a larger extent on the west bank than on the east, with the river in between. Moreover, the water appeared to be much more free from salts than we should expect it to be if it were merely drainage from the Wadi Alagi. It strongly resembles, in fact, both in temperature and character, the artesian water of the greater oases, and there can hardly be the smallest doubt that at Dakka the Nile is not only continually abstracting artesian water from the same underground water-sheet that feeds the oases, but is abstracting it in far larger quantities than those yielded by all the oasis wells and springs put together.[22] It is certainly remarkable that the place where considerable supplies of warm underground water enter the Nile should coincide with the embouchure of what is perhaps the greatest drainage channel of the Eastern Desert of Egypt; but I think it is likely that the explanation of the coincidence may be a tectonic one; the water-bearing beds may have been brought up by a local fold in the strata, and the same fold may in some way have conditioned the formation of the primitive drainage-line which was ultimately to become the Wadi Alagi. Having now indicated briefly the grounds for their acceptance, I give below a table showing the various points which I have adopted as furnishing data for constructing the contours of the static water- surface underlying the Libyan Desert, together with the altitudes of the points above or below sea, and the sources of these level-data. The levels are doubtless in some cases slightly inaccurate; but a few metres of error are immaterial to the object in view, and it is believed that even those levels which rest on barometric determinations are sufficiently accurate for our purpose. LIST OF ADOPTED POINTS ON THE STATIC WATER-SURFACE _Place._ _Level _Determined by._ (metres)._ Wadi Natrun, surface of − 23 Ball, Trigonometric lakes levelling, 1914. Birket el Qarun, surface of − 45 Survey of Egypt, 1926. lake Based on spirit levelling from Alexandria. Moghara, surface of lake − 23 Walpole, Trigonometric levelling, 1924. Qattara Depression, various − 80[23] „ „ „ points on salt-marsh, the lowest being Sittra, surface of lake − 16 „ „ „