One of the greatest and most significant laws which modern palæontology has unfolded to us, is that principle by which it is definitively ascertained that, as a general rule, the animals of the Post-Pliocene, and indeed all the later Tertiary ages, were restricted to the same great geographical provinces as their representatives in the existing fauna. Amongst the Pliocene Mammalia of South America, we find the same preponderance of the Edentata, the same family of prehensile-tailed Monkeys, and the same typical Llamas and Vicuñas, as we find in the present pampas of La Plata, forests of Brazil, or elevations of the Andes.

But we also find animals which, from all our previous pre-conceived associations, we had considered peculiar to the old world. The Elephants, of which one species (E. Africanus) now exists in Africa, a second (E. Indicus) in India, and a third (E. Sumatranus) in Sumatra and Ceylon, apart from the extensive and widely-distributed evidences which we find of their fossil remains in Europe, India, China, and Australia, extended their geographical province in the later Tertiary age over the whole of North America. The species of elephant which we find in Siberia (E. primigenius) has also been found over the whole of the space lately marked on our maps as the United States. South of the 30th degree of N. Iatitude it however gives place to a totally different species of true Elephant (Elephas Texianus, Owen, E. Columbi? Falconer), the molars of which, by their less degree of complexity, were more adapted to triturate the soft succulent herbage of Texas and Mexico. Besides these true Elephants, there existed in North America many individuals of the genus Mastodon, to which the present communication more particularly alludes.