I Was Not Then Aware That Any One Else
Had Discovered The Elevated Trough Form Of The Centre Of Africa.
I had observed that the old schistose rocks on the sides dipped in
toward the centre of the country,
And their strike nearly corresponded
with the major axis of the continent; and also that where
the later erupted trap rocks had been spread out in tabular masses
over the central plateau, they had borne angular fragments of the older rocks
in their substance; but the partial generalization which the observations
led to was, that great volcanic action had taken place in ancient times,
somewhat in the same way it does now, at distances of not more than
three hundred miles from the sea, and that this igneous action,
extending along both sides of the continent, had tilted up the lateral rocks
in the manner they are now seen to lie. The greater energy
and more extended range of igneous action in those very remote periods
when Africa was formed, embracing all the flanks, imparted to it
its present very simple literal outline. This was the length
to which I had come.
The trap rocks, which now constitute the "filling up" of the great valley,
were always a puzzle to me till favored with Sir Roderick Murchison's
explanation of the original form of the continent, for then
I could see clearly why these trap rocks, which still lie
in a perfectly horizontal position on extensive areas, held in their substance
angular fragments, containing algae of the old schists,
which form the bottom of the original lacustrine basin:
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