128 NEWER PLIOCENE PERIOD. 



[Ch. X. 



scribed. Masses of alternating lava and tuff, the products of 

 submarine eruptions, might on their emergence become hills 

 and islands; the level intervening plains might afterwards ap- 

 pear, covered partly by the ashes drifted and deposited by 

 water, and partly by those which would fall after the laying 

 dry of the tract. The last features imparted to the physical 

 geography would be derived from such eruptions in the open 

 air as those of Monte Nuovo and the minor cones of Ischia. 



No signs of diluvial waves. Such a conversion of a large 

 tract of sea into land might possibly take place while the sur- 

 face of the contiguous country underwent but slight modifica- 

 tion. No great wave was caused by the permanent rise of the 

 coast near Puzzuoli in the year 1538, because the upheaving 

 operation appears to have been effected by a long succession of 

 minor shocks *. A series of such movements, therefore, might 

 produce an island like Ischia without throwing a diluvial rush 

 of waters upon low parts of the neighbouring continent. The 

 advocates of paroxysmal elevations may, perhaps, contend that 

 the rise of Ischia must have been anterior to the birth of all 

 the cones of loose scoriae scattered over the Phlegrasan Fields, 

 for, according to them, the sudden rise of marine strata causes 

 inundations which devastate adjoining continents. But the 

 absence of any signs of such floods in the volcanic region of 

 Campania does not appear to us to warrant the conclusion, 

 either that Ischia was raised previously to the production of 

 the volcanic cones, or that it may not have been rising during 

 the whole period of their formation. 



We learn from the study of the mutations now in progress, 

 that one part of the earth's surface may, for an indefinite 

 period, be the scene of continued change, while another, in the 

 immediate vicinity, remains stationary. We need go no far- 

 ther than our own country to illustrate this principle ; for, 

 reasoning from what has taken place in the last ten centuries, 

 we must anticipate that in the course of the next 4000 or 5000 

 years, a long strip of land, skirting the line of our eastern 

 * See vol. i. p. 457, first edition j p. 527, second edition. 



