Many fountains rose in the courses of the ancient river beds, and the outflow was always in the direction of the current of the parent stream.  Many of these ancient fountains still contain water, and form the stages on a journey, but the primitive waters seem generally to have been laden with lime in solution:  this lime was deposited in vast lakes, which are now covered with calcareous tufa.  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.  The Zambesi flows above the Kebrabasa, through great beds of the same formation, and generally they are of hard crystalline rocks; and it is impossible to conjecture what the condition of the country was when the large pot-holes were formed up the hillsides, and the prodigious attrition that rounded the shingle was going on.  The land does not seem to have been submerged, because marine limestones (save in the exceptional cases noted) are wanting; and torrents cutting across the ancient river beds reveal fresh-water shells identical with those that now inhabit its fresh waters.  The calcareous tufa seems to be the most recent rock formed.  At the point of junction of the great southern prehistoric Nile with an ancient fresh-water lake near Buchap, and a few miles from Likatlong, a mound was formed in an eddy caused by some conical lias towards the east bank of this rent within its bed, and the dead animals were floated into the eddy and sank; their bones crop out of the white tufa, and they are so well preserved that even the black tartar on buffalo and zebra’s teeth remain:  they are of the present species of animals that now inhabit Africa.  This is the only case of fossils of these animals being found in situ.  In 1855 I observed similar fossils in banks of gravel in transitu all down the Zambesi above Kebrabasa; and about 1862 a bed of gravel was found in the delta with many of the same fossils that had come to rest in the great deposit of that river, but where the Zambesi digs them out is not known.  In its course below