CHAP. VI MOUNTAINS 2438 
Though long extinct, volcanoes once existed 
in the British Isles; Arthur’s Seat, near 
Edinburgh, for instance, appears to be the 
funnel of a small volcano, belonging to the 
Carboniferous period. 
The summit of a volcanic mountain is 
sometimes entirely blown away. Between 
my first two visits to Vesuvius 200 feet of the 
mountain had thus disappeared. Vesuvius 
itself stands in a more ancient crater, part 
of which still remains, and is now known as 
Somma, the greater portion having disap- 
peared in the great eruption of 79, when the 
mountain, waking from its long sleep, de- 
stroyed Herculaneum and Pompeii. 
As regards the origin of volcanoes there 
have been two main theories. Impressed by 
the magnitude and grandeur of the phenom- 
ena, enhanced as they are by their destruc- 
tive character, many have been disposed to 
regard the craters of volcanoes as gigantic 
chimneys, passing right through the solid 
crust of the globe, and communicating with 
a central fire. Recent researches, however, 
have indicated that, grand and imposing as 
