214 ACTIVE VOLCANOES OF THE EARTH 
ejected from them. But if we include mountains which exhibit the 
external conical form, crater-like hollows, and other features of 
volcanoes, yet concerning the activity of which we have no record 
or tradition, the number will fall little, if anything, short of 1,000. 
The mountains composed of volcanic materials, but which have 
lost through denudation the external form of volcanoes, are still 
more numerous, and the smaller temporary openings which are 
usually subordinate to the habitual vents that have been active dur- 
ing the periods covered by history and tradition, must be numbered 
by thousands. There are still feebler manifestations of the volcanic 
forces—such as steam-jets, geysers, thermal and mineral waters, 
spouting saline and muddy springs, and mud volcanoes—that may 
be reckoned by millions. It is not improbable that these less pow- 
erful manifestations of the volcanic forces to a great extent make 
up in number what they want in individual energy ; and the relief 
which they afford to the imprisoned activities within the earth’s 
crust may be almost equal to that which results from the occasional 
outbursts at the great habitual volcanic vents. 
In taking a general survey of the volcanic phenomena of the 
globe, no facts come out more strikingly than that of the very un- 
equal distribution, both of the great volcanoes, and of the minor 
exhibitions of subterranean energy. 
Thus, on the whole of the continent of Europe, there is but 
one habitual volcanic vent—that of Vesuvius—and this is situated 
upon the shores of the Mediterranean. In the islands of that sea, 
however, there are no less than six volcanoes: namely, Stromboli, 
and Vulcano, in the Lipari Islands; Etna, in Sicily ; Grahaim’s Isle, 
a submarine volcano, off the Sicilian coast; and Santorin and Ni- 
syros, in the Aigean Sea,