This estimate only embraces the deposits since the river ran in its present channel. The bluffs along the river rise in many places two hundred and fifty feet, and contain shells, with the remains of the mastodon, elephant, tapir, megalonyx, and other huge animals. It is evident that these bluffs must have belonged to an ancient plain or valley long anterior to the present level. In several sections of the valley as it now exists, excavations have been made deeper than the Gulf of Mexico, and successive growths of cypress-timber found, to the number of four or five distinct growths, the lowest lying at the depth of six hundred feet. Some of these trees are ten feet in diameter, and have from five to six thousand annual rings of growth. As the valley of the river from age to age grew in elevation by deposits of sediment, a new growth of cypress was produced, and is now supervened by the live-oak plain, so called, which has had an existence, as estimated by the annual rings of the oaks, of fourteen thousand years. In excavating for gas-works at New Orleans, a human skull was found beneath the roots of a cypress belonging to the fourth-forest level, in a good state of preservation, while the other bones of the skeleton crumbled to dust on exposure to the air. The type of the cranium was that of the aboriginal American. Now, if we take the period required to form the live-oak level, and add it to the time required to produce the next three subterranean growths of cypress, which overlie the fourth growth, in which the cranium was found, it clearly proves that the human race existed in the great valley of the Mississippi more than fifty-seven thousand years ago. Not only in the valley of the Mississippi have fossil remains of man and animals been discovered at depths and in formations that prove their remote antiquity, but in many other parts of the world. Not many years ago, a human skull was found in Brazil, embedded in a sandstone rock overgrown with lofty trees. There is still preserved, in the museum at Quebec, a human skull which was excavated from the solid schist-rock on which the citadel now stands. Human skeletons have also been found in the island of Guadeloupe, embedded in a rock said to be as hard as the finest statuary marble. Even so recently as the year 1868, while sinking a well at the Antelope station, on the Union Pacific Railroad, the workmen penetrated a rock six feet thick, and at eighty feet below the rock discovered a human skeleton in such a state of preservation as to be readily recognized as such.