4 
INTRODUCTION 
BOOK I 
Wliat is here predicted as probable or certain in the future has 
undoubtedly happened again and again in the past. Over many districts of 
Europe and Western America extinct volcanoes may be seen in every stage 
of decay. The youngest may still show, perfect and bare of vegetation, their 
cones and their craters, with the streams of lava that escaped from them. 
Those of older date have been worn down into mere low rounded hills, or 
the whole cone has been cleared away, and there is only left the hard core 
of material that solidified in the funnel below the surface. The lava-sheets 
have been cut through by streams, and now remain in mere scattered patches 
capping detached hills, which only a trained eye can recognize as relics of 
a once continuous level sheet of solid rock. 
By this resistless degradation, a volcanic district is step by step stripped 
of every trace of its original surface. All that the eruptions did to change 
the face of the landscape may be entirely obliterated. Cones and craters, 
ashes and lavas, may be gradually efiaced. And yet enough may be left to 
enable a geologist to make sure that volcanic action was once rife there. 
As the volcano rnarics a channel of direct communication between the 
interior of the earth and the atmo.sphere outside, there are subterranean as 
well as superficial manifestations of its activity, and while the latter are 
removed by denudation, the former are one by one brought into light. Tlie 
progress of denudation is a process of dissection, whereby every detail in the 
structure of a volcano is successively cut down and laid bare. But for this 
process, our knowledge of the mechanism and history of volcanic action 
would be much less full and definite than happily it is. In active volcanoes 
the internal and subterranean structure can only be conjectured ; in those 
of ancient date, which have been deeply eroded, this underground structure 
is open to the closest examination. 
By gathering together evidence of this nature over the surface of the 
globe, we learn that abundantly as still active volcanoes are distributed bn 
that surface, they form but a small fraction of the total number of vents 
which have at various times been in eruption. In Italy, for example, while 
Vesuvius is active on the mainland, and Etna, Stromboli and Volcano 
display their vigour among the islands, there are scores of old volcanoes that 
have been silent and cold ever since the beginning of history, yet show by 
their cones of cinders and streams of bristling lava that they were energetic 
enough in their day. But the Italian volcanic region is only one of many 
to be found on the European Continent. If we travel eastward into Hun- 
gary, or northward into the Eifel, or into the heart of France, we encounter 
abundant cones and craters, many of them so fresh that, though there is no 
historical record of their activity, they look as if they had been in eruption 
only a few generations ago. 
But when the geologist begins to search among rocks of still older date 
than these comparatively recent volcanic memorials, he meets with abund- 
ant relics of fiir earlier eruptions. And as he arranges the chronicles of the 
earth’s history, he discovers that each section of the long cycle of geological 
ages has preserved its records of former volcanoes. In a research of this 
