RECENT AND POST-PLIOCENE VOLCANIC ROCKS. 525 
at the earth’s surface, and we can sometimes prove that those 
areas which are now the great theatres of volcanic action 
were in a state of perfect tranquillity at remote geological 
epochs, and that, on the other hand, in places where at for¬ 
mer periods the most violent eruptions took place at the sur¬ 
face and continued for a great length of time, there has been 
an entire suspension of igneous action in historical times, and 
even, as in the British Isles, throughout a large part of the 
antecedent Tertiary Period. 
In the absence of British examples of volcanic rocks new¬ 
er than the Upper Miocene, I may state that in other parts 
of the world, especially in those where volcanic eruptions are 
now taking place from time to time, there are tulFs and lavas 
belonging to that part of the Tertiary era the antiquity of 
which is proved by the presence of the bones of extinct 
quadrupeds which co-existed with terrestrial, fresh-water, 
and marine mollusca of species still living. One portion of 
the lavas, tulfs, and trap-dikes of Etna, Vesuvius, and the 
island of Ischia has been produced within the historical era; 
another and a far more considerable part originated at times 
immediately antecedent, when the waters of the Mediterra¬ 
nean were already inhabited by the existing testacea, but 
when certain species of elephant, rhinoceros, and other quad¬ 
rupeds now extinct, inhabited Europe. 
Vesuvius .—I have traced in the “Principles of Geology” 
the history of the changes which the volcanic region of Cam¬ 
pania is known to have undergone during the last 2000 years. 
The aggregate effect of igneous operations during that pe¬ 
riod is far from insignificant, comprising as it does the forma¬ 
tion of the modern cone of Vesuvius since the year 79, and 
the production of several minor cones in Ischia, together with 
that of Monte Nuovo in the year 1538. Lava-currents have 
also fiowed upon the land and along the bottom of the sea— 
volcanic sand, pumice, and scoriae have been showered down 
so abundantly that whole cities were buried—tracts of the 
sea have been filled up or converted into shoals—and tufa- 
ceous sediment has been transported by rivers and land- 
floods to the sea. There are also proofs, during the same re¬ 
cent period, of a permanent alteration of the relative levels 
of the land and sea in several places, and of the same tract 
having, near Puzzuoli, been alternately upheaved and de¬ 
pressed to the amount of more than twenty feet. In con¬ 
nection with these convulsions, there are found, on the shores 
of the Bay of Baiae, recent tufaceous strata, filled with ar¬ 
ticles fabricated by the hands of man, and mingled wfith ma¬ 
rine shells. 
