Page:Africa by Élisée Reclus, Volume 4.djvu/424

 enormous dimensions. They also speak of another remarkable pit in the neighbourhood, in which animals are immediately suffocated if by any chance they happen to full into it. This is doubt!ess due to an emanation of carbonic acid gas.

Lake Naivasha, also first explored by Thomson, is a shallow island-studded basin standing at an elevation of about 6,000 feet above the sea. It has no outflow,

evaporation balancing the contributions of several small affluents; yet its waters are sweet, which seems to indicate that this lacustrine basin is of recent origin. Its formation may perhaps be due to the damming up of the fluvial valley by some eruptions of lavas and ashes accumulating on the north and cast sides and separating the plain from the Upper Tana basin. In this reservoir there are no fish, which have probably been destroyed by the escape of mephitic gases.

The underground forces elsewhere quiescent or extinct, are still active in the district to the north-east of Naivasha. Tere rises the Dunye Buru, or "Steam