During pliocene times especially, the northern parts of the Balkan peninsula were occupied by a series of freshwater lakes, while Greece was joined to Southern Italy, Sicily, and Tunis. Central and Northern Italy were represented by a long narrow peninsula connected in the north with the Alps. Corsica and Sardinia were joined to Sicily, and the Straits of Gibraltar did not exist. When I first published my views regarding these geographical conditions of the Mediterranean area, Professor Depéret was good enough to send me his criticisms from a purely geological standpoint. He is of opinion that though Sicily and Sardinia might at this time have still been connected with Tunis, the Straits of Messina must already have been formed--in other words, Southern Italy and Sicily could no longer have been connected with one another. This opinion is based upon the fact that in the upper strata of the enormously thick Sicilian pliocene deposits are found a number of arctic or subarctic species of mollusca which are entirely foreign to the Mediterranean fauna. It is generally supposed that these reached the Mediterranean area by the newly opened Straits of Gibraltar in later pliocene times, and that the lower Sicilian deposits must therefore have been laid down earlier. So far the deductions are perfectly correct, if we assume the northern mollusca to have arrived in the Atlantic at the time stated. However, they must have reached the Atlantic much later--not till pleistocene times--if we adopt the above-stated suggestions as to the age of the Forest-Bed (cf. p. 125). Moreover, the great similarity between the faunas of Southern Spain and North-western Africa indicate that the formation of the Straits of Gibraltar is of very recent date. The northern mollusca, of course, could not have reached Sicily till later. To suppose that the Sicilian deposits have been uplifted 7000 feet since then is no doubt contrary to all our geological teaching, but we must remember that this is altogether an exceptional case. The area in question has probably ever since been in the immediate neighbourhood of an active volcano, and the rate of the uplift has therefore been immeasurably greater than at other localities with which this one might be compared. The disconnection between Tunis, Sicily, and Southern Italy was evidently produced by a subsidence of the tract of land uniting these countries. If we suppose that this happened in early pliocene times, we have either to take for granted that the terrestrial fauna and flora of these countries are of miocene origin, or that they were joined again during the Pleistocene Epoch. The range of a very large number of animals and plants is such as can only be explained by assuming that Tunis, Sicily, Sardinia, Corsica, and Southern Italy were connected with one another. Of such extensive land-connections subsequent to the arrival of the northern marine mollusca we possess,