Charles Lyell's argument in this classic volume is that the processes of nature are slow and uniform, and that the Earth is in consequence hundreds of millions of years old. This work includes his prediction that if our nearest relatives are great apes, then the places to look for human fossils will be central Africa and Indonesia.

As important to modern world views as any work of Darwin, Marx, or Freud, Lyell's" Principles of Geology "has never before been available in paperback. In this third and final volume, Charles Lyell (1797-1875) devotes much attention to the "syntax of geology," that is, to a way of reconstructing the geological past on the basis of the "grammar" of the present processes he has described in the earlier volumes. He defines four periods of the Tertiary--Newer Pliocene, Older Pliocene, Miocene, and Eocene--and argues that the deposits dating from each period demonstrate the uniformity of processes and environments throughout the Tertiary, and indeed in earlier periods of earth history.
Martin J. S. Rudwick has compiled a bibliography giving full references for the sources Lyell cites in all three volumes of the "Principles."