At the commencement of the passage by which the waters entered the Fayûm, the highest Nile deposit is at R.L. 26·00. At Hawârah it is at R.L. 24·50, and along the ridge reaching out towards Medineh, R.L. 23·50. Probably, therefore, the water in the Lake reached about R.L. 26·50 at the commencement of the gorge, but the level of the Lake itself rarely, if ever, exceeded R.L. 25·00. [Illustration: PLATE XIX. CONTOURED DIAGRAM OF THE FAYÛM DEPRESSION. _Note._—This being a diagram only, all minor folds and indentations of contours have been suppressed, so as to show more clearly the general shape. The upper contours along the north-west side of the Lake must not be considered to be accurately represented, as no surveys of this side have been made.] It will be as well to determine, before going further, whether the present volumes of the Nile flood would suffice to fill the Lake Fayûm to the level of R.L. 25·00, which I have assumed it must have reached to account for the Nile deposits on its borders at R.L. 24·50. At the time we are considering, no artificial works existed for controlling the inflow and outflow of the Lake. We have first to determine the lowest level to which the Lake would have been lowered by the outflow and evaporation at the end of the summer, and before the next rise of the river commenced. The Nile may have flowed at a lower level then (that is, in very early prehistoric times) than now, the summer volume was probably greater then than now, as the unbreached barriers in the upper reaches would have ponded up the water into reservoirs, which, slowly emptying themselves, would have helped to raise the summer level; the flow-out also from the Fayûm Lake would have raised at its exit the level of the summer Nile, at least during the winter months, but not necessarily during the summer months, as it may have expended itself sooner. There are thus three unknown elements in the problem, and nothing to witness to the former _minimum_ levels in the same way that the Nile deposit does to the maximum levels. We are therefore forced to base the calculations on existing levels, and to suppose that the effect on the water surface of the former lower level of the Nile bed was counterbalanced by the increased volume of water flowing in the river bed. At any rate at some period sooner or later the present minimum level of the Nile must have been reached. The probability is that the exit channel of the lake joined the Nile at or near Wâstah. Up to the end of April the rate of fall of the river exceeds the rate at which evaporation would lower a lake surface, but in May the river falls about 15 centimetres, and not at all on an average in June. Hence, up to the end of April the fall of the river would determine the rate of fall of the lake, but in May and June the fall due to evaporation would rule the rate. R.L.