One enormous fresh-water lake, in which probably sported the Dyconodon, was let off when the remarkable rent was made in the basalt which now constitutes the Victoria Falls.
Another seems to have gone to the sea when a similar fissure was made at the falls of the Orange River.

It is in this calcareous tufa alone that fossil animal remains have yet been found.

There are no marine limestones except in friths which the elevation of the west and east coasts have placed far inland in the Coanza and Somauli country, and these contain the same shells as now live in the adjacent seas.
Antecedently to the river system, which seems to have been a great southern Nile flowing from the sources of the Zambesi away south to the Orange River, there existed a state of fluvial action of greater activity than any we see now: it produced prodigious beds of well-rounded shingle and gravel.

It is impossible to form an idea of their extent.

The Loangwa flows through the bed of an ancient lake, whose banks are sixty feet thick, of well-rounded shingle.