320 GEOLOGY, 



in thickness, and in Sicily 2000 feet. Limestone as well as clastic- 

 beds enter into the system, and they occur up to heights of 3000 feet. 

 Sedimentation was brought to an end by the movements which culmi- 

 nated in the outbreak of Vesuvius, Etna, and other Italian volcanoes. 

 Etna at least, was first submarine, for its older tuffs are interstratified 

 with marine beds. Later, by elevation, or by the upward growth of the 

 volcanic cones, or both, the eruptions became subaerial. 



Marine Pliocene is known in Egypt, where the sea is thought to 

 have extended up the Nile to Assuan. The formation of the rifts of the 

 Red Sea and the Gulf of Suez, has been assigned to the Pliocene period, 1 

 though the rift origin of these depressions has not been universally 

 accepted. 2 Pliocene beds have also been reported from Tibet 3 (non- 

 marine), India, 4 Borneo, 5 and the Philippines. 6 



The Life of the Pliocene. 



The land plants. — The Pliocene was characterized by a still fur- 

 ther sorting out of the mixed flora of previous periods, and by the 

 southerly migration of what are now tropical and sub- tropical plants. 

 Whether there was a northerly shifting of the opposite class of plants 

 has not been determined. In southern France there were still some 

 species identical with those now living in the Canaries. In Europe 

 generally also, there was still much commingling of species that have 

 since become geographically separated. Some of this was separation 

 in longitude, and does not carry climatic suggestiveness. There were 

 some genera that have since been driven eastward to the Caucasus, 

 and some that are now characteristic types in North America, and so 

 the flora had a somewhat American aspect. The tenor of available 

 evidence, however, indicates not only a general differentiation, but a 

 movement in latitude antecedent to the present distribution and 

 adaptations of the plants. This has usually been interpreted as sig- 

 nifying a progressive refrigeration of the earth's climate, consonant 

 with the conception of a progressive cooling of the globe, and an approach 

 to a permanent condition of refrigeration; but other lines of evidence 



i Barron and Hume, Geol. Mag., 1901, p. 156. 

 2 Mennell, Geol. Mag., 1903, p. 548. 

 'Lydekker, Q. J. G. S., Vol. LVI1, p. 292 

 * Oldham, Geology of India. 



5 Molengraaf, Geol. Expl. in Central Borneo, Rev. Ceol. Mag., 1903, p. 170. 



6 Becker, 21st Ann. Rept. U. S. Geol. Surv., Pt. III. 



