Such conclusions throw a new light on the adaptation of the attributes and migratory habits of animals and plants to the changes which are unceasingly in progress in the physical geography of the globe. It is clear that the duration of species is so great, that they are destined to outlive many important revolutions in the configuration of the earth's surface; and hence those innumerable contrivances for enabling the subjects of the animal and vegetable creation to extend their range; the inhabitants of the land being often carried across the ocean, and the aquatic tribes over great continental spaces. It is obviously expedient that the terrestrial and fluviatile species should not only be fitted for the rivers, valleys, plains, and mountains which exist at the era of their creation, but for others that are destined to be formed before the species shall become extinct; and, in like manner, the marine species are not only made for the deep and shallow regions of the ocean existing at the time when they are called into being, but for tracts that may be submerged or variously altered in depth during the time that is allotted for their continuance on the globe. OSSEOUS BRECCIAS AND DEPOSITS IN CAVES OF THE PLIOCENE PERIOD. _Sicily._--Caverns filled with marine breccias, at the base of ancient sea-cliffs, have been already mentioned in the sixth chapter; and it was noticed, respecting the cave of San Ciro, near Palermo (p. 75.), that upon a bed of sand filled with sea-shells, almost all of recent species, rests a breccia (_b_, fig. 93.), composed of fragments of calcareous rock, and the bones of animals. In the sand at the bottom of that cave, Dr. Philippi found about forty-five marine shells, all clearly identical with recent species, except two or three. The bones in the incumbent breccia are chiefly those of the mammoth (_E. primigenius_), with some belonging to an hippopotamus, distinct from the recent species, and smaller than that usually found fossil. (See fig. 132.) Several species of deer also, and, according to some accounts, the remains of a bear, were discovered. These mammalia are probably referable to the Post-Pliocene period. The Newer Pliocene tertiary limestone of the south of Sicily, already described, is sometimes full of caverns; and the student will at once perceive that all the quadrupeds of which the remains are found in the stalactite of these caverns, being of later origin than the rocks, must be referable to the close of the tertiary epoch, if not of still later date. The situation of one of these caves, in the valley of Sortino, is represented in the annexed section. [Illustration: Fig. 125. Cross section. _a_. Alluvium, } containing the remains of quadrupeds _b_, _b_. Deposits in caves, } for the most part extinct. C. Limestone, containing the remains of shells, of which between 70 and 80 per cent. are recent.]