We came to some low hills, of coarse sandstone, and on crossing these we could see, by looking back, that for many days we had been travelling over a perfectly level valley, clothed with a mantle of forest.

The barometers had shown no difference of level from about 1800 feet above the sea.

We began our descent into this great valley when we left the source of the Bua; and now these low hills, called Ngale or Ngaloa, though only 100 feet or so above the level we had left, showed that we had come to the shore of an ancient lake, which probably was let off when the rent of Kebra-basa on the Zambesi was made, for we found immense banks of well-rounded shingle above--or, rather, they may be called mounds of shingle--all of hard silicious schist with a few pieces of fossil-wood among them.

The gullies reveal a stratum of this well-rounded shingle, lying on a soft greenish sandstone, which again lies on the coarse sandstone first observed.

This formation is identical with that observed formerly below the Victoria Falls.