6o8 THE PLIOCENE PERIOD 



late igneous formations of the Sierras, and perhaps of northern 

 California, 1 belong to this time, and probably some of those of 

 nearly or quite every other state west of the Rocky Mountains. 

 Many of the prominent volcanic peaks of the west date from this 

 time or later, and represent the later phases of the prolonged period 

 of volcanic activity, just as the great lava flows and intrusions 

 represent the earlier. Many lesser cones belong to the same period. 



Foreign 



From considerable areas of Europe covered by water during the 

 Miocene, the waters retreated late in the period or at its close; but 

 the sea covered southern and southeastern England, Belgium, and 

 parts of France during at least some portion of the Pliocene, and 

 still more extensive areas of the present continent about the Medi- 

 terranean. Beyond the inland margins of the marine Pliocene, there 

 are contemporaneous beds of terrestrial origin. In southeastern 

 Europe, brackish and salt lakes came into existence, as shown by 

 the fossils and the local deposits of salt and gypsum. In some 

 places, as in the Vienna basin, brackish water beds below grade up 

 into fluviatile beds above. 



In Italy only do Pliocene beds attain massive development. 

 Along the Apennines their thickness has been estimated at from 

 i, 600 to 3,000 feet, and in Sicily*2,ooo feet. Limestone as well as 

 clastic beds enter into the system, which occurs up to heights of 

 3,000 feet. 



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

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

 of the Red Sea and the Gulf of Suez has been assigned to this 

 period. These depressions have been thought to be down-faulted 

 blocks. 



LIFE 



Land plants. During the Pliocene there was a further sort- 

 ing out of the mixed flora of previous periods, and the southerly 

 segregation of what are now tropical and subtropical plants contin- 

 ued; but in Europe generally there was still much commingling of 

 species now separated geographically. 



Land animals. Three important features characterized the 

 Pliocene history of mammals: (i) A notable intermigration between 

 the continents, including North and South America; (2) the begin- 



1 Hershey, Jour. Geol., Vol. X, pp. 377~392. 



