The streams of the South African plateau, whether river, spruit, sluit, or donga, have, in addition to their extreme variability, another marked and almost universal peculiarity. Running in deep beds, of which the banks are usually level with the surrounding country, and the sides terraced from the highest to the lowest water-mark, they constitute natural entrenchments which are generally invisible, except where rarely defined by a line of bushes, and, owing to the dead uniformity of the surrounding country, are almost impossible to reconnoitre. Nor, in 1899, were their defensive capabilities lessened by the dearth of bridges, by the dangers of the drifts, and by the absence of defined approaches to all crossing-places away from the main roads. The "drifts," or fords, especially rendered the laying out of a line of operations in South Africa a complex problem. Their depth varied with the weather of the day; they were known by many names even to local residents, and were of many types; but all alike were so liable to sudden change or even destruction, that any information concerning them, except the most recent, was practically useless. [Sidenote: Effect of winds on climate.] [Sidenote: The velds.] To comprehend broadly the salient physiological features of a region so enormous as South Africa, the causes of the climatic influences which affect them must be understood. These causes on are simplicity itself. The warm winds blow from the east, and the cold from the west; the former, from the warm Mozambique current, skirting the eastern seaboard, the latter, from the frigid Antarctic stream, setting from south to north, and striking the western coast about Cape St. Martin. It follows, therefore, that the climate and country become more genial and fertile the further they are removed from the desiccating influence emanating from the western seaboard. The dreariness of the solitudes between Little Namaqualand and Griqualand West, the latter slightly more smiling than the former, attests this fact. But the comparative inhospitality of the Boer States--comparative, that is, to what might be expected from their proximity to the warm Indian Ocean--demands further explanation. From the Atlantic to the eastern frontiers of these States no mountain ranges of any elevation intervene to break the progress of the dry, cold breezes; from the mouth of the Orange river to the Drakensberg the country is subject almost uninterruptedly to their influence. But it is not so with the milder winds from the east. The great screen of the Drakensberg meets and turns them from end to end of South Africa; no country west of this range profits by their moisture, whereas the regions east of it receive it to the full. Hence the almost tropical fertility of Natal and eastern Cape Colony, with their high rainfall, their luxuriance of vegetation, indigo, figs, and coffee, and the jungles of cactus and mimosa which choke their torrid kloofs. Hence, equally, the more