. British Central Africa; an attempt to give some account of a portion of the territories under British influence north of the Zambezi. Natural history. 3« BRITISH CENTRAL AFRICA a deep valley with abrupt cliffs ; though this condition of course restricts its area of growth. Still, although we must, I think, admit a certain diminution in rainfall owing to the decrease of forest or other causes, the rate at which this decrease is going on has been exaggerated, and as we come to know the country better and our records grow with years of occupation, we see that there are signs of cycles of greate
. British Central Africa; an attempt to give some account of a portion of the territories under British influence north of the Zambezi. Natural history. 3« BRITISH CENTRAL AFRICA a deep valley with abrupt cliffs ; though this condition of course restricts its area of growth. Still, although we must, I think, admit a certain diminution in rainfall owing to the decrease of forest or other causes, the rate at which this decrease is going on has been exaggerated, and as we come to know the country better and our records grow with years of occupation, we see that there are signs of cycles of greater and less rain dependent on atmospheric conditions which we have not yet realised. The marks on the rocks show that during some ages there has been a slight—but a very slight—fall in Lake Nyasa, varied by periods of extraordinary diminution as for instance some seventy years ago when according to the natives' traditions the north end of the lake became so shallow between Deep Bay and Amelia Bay that a chief and his men waded across where it is now many fathoms deep. The highest watermark on these polished rocks is perhaps at most six feet above the present high levels of the lake in good rainy seasons. In years of relative drought Lake Nyasa may be as much as six feet below its best rain)- season average. This means, of course, that instead of there being nine feet of water on the bar of the Shire where that river quits the lake there are only three feet; consequently the navigability of the Shire in the dry season becomes much embarrassed and in these bad years it can only be navigated all the year round by vessels not drawing more than one and a half feet. Yet we know that in the later " fifties " and early " sixties " Livingstone constantly travelled up and down the Shire on a vessel drawing five feet. Even in the year 1889 the James Stevenson which draws about three feet of water was able to navigate the Shire through al- most all the year up to th
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
