It has already been remarked that the hydrographical system of the South Downs is a peculiar one, that the rivers of Sussex are in no way determined as to their courses by that range of hills, and that the heights themselves are devoid of water, because all that falls upon them percolates through the chalk and does not spring out again until it finds the clay at their base. But there is upon the Downs a traditional method of water-getting handed down, perhaps, from prehistoric times when the camps of refuge, of which we shall speak in a moment, were hard put to it to water their garrisons. This method is the formation of dew pans. A space is hollowed out, preferably towards the summit of a hill. It is circular and shallow in form, and is coated with some impermeable substance--to-day, usually, with concrete. In a very short time this pan will fill with the dew and the rain, and in such a pond, if its dimensions are sufficiently large, there will but rarely be lack of water after it is once formed. It is true that no great strain is laid upon them, though the present writer does know of one case, outside the boundaries of the county, where a large one has been constructed to supply all the needs of a considerable household. A further matter which every one who is familiar with them must have remarked upon the Downs, is the presence of numerous earthworks raised apparently for defence, and often of very great size. The classical instances of these and the most perfect examples are upon Mount Caburn and Cissbury, one of the foot-hills towards the sea, upon which research has proved that the prehistoric, the Roman, and the barbarian pirate inhabitants have lived in succession. Here was discovered that regular manufactory of flint instruments which is among the most curious prizes of modern prehistoric research, and here also Roman and Saxon ornaments have been found succeeding those of the neolithic men. But though Cissbury is the most perfect, it is but one of very many similar camps. There is hardly one of the greater summits of the Downs that does not bear traces of these enclosures, and upon some of the hills, notably east of Ambery and again east of Bramber, they are as perfect as they are enormous. There can be little doubt that they were created for the purposes of defence, and the late General Pitt-Rivers conducted an [Sidenote: THE TUMULI]