From some of the foregoing observations it is obvious that the chalk formation at one time must have covered a very great tract of the surrounding country, and we may very reasonably conclude that it was during the gradual elevation of the land, that the action of the waves of the ocean as gradually destroyed the soft materials of which it had been fabricated. But long after this had been accomplished, and at a comparatively recent geological period, the whole country seems again to have been covered with water,—not only the nearly level country between the shores of the present sea and the elevated table-land, but even the highest parts of the table-land itself. This is proved by the thick stratum which exists on both, of a deep red-coloured diluvial clay, similar to that which I have observed to cover nearly the whole surface of Brazil, from the sea-shore to the summits nearly of the highest mountains, and which is often more than forty feet in thickness. When this is cut through it is found to consist of various layers of clay and sandy gravel, in which are imbedded rounded stones of different sizes. These have evidently been deposited from water; and in that part of the country in which we are now speaking, this deposition of clay must have taken place at a period subsequent to the inundation of the country to the east and west of the table-land. This could only have been accomplished by the sinking of the land again beneath the level of the sea, which will account for the nearly total destruction of the white chalk, as well as for those small cones of it which remain imbedded in the red clay,—that deposit having been laid down before the whole of the chalk could be washed away; since then this part of the continent must have gradually emerged a second time from the bosom of the ocean.