INTROD UCTION 
BOOK I 
signs of ■volcanic action in the more prominent rocky features of landscape. 
A bold crag, a deep and precipitous ravine, a chasm in the side of a mount- 
ain, have been unhesitatingly set down as proof of volcanic disturbance. 
IMany a cauldron-shaped recess, like the corries of Scotland or the cwms 
of Wales, has been cited as an actual crater, with its encircling walls still 
standing ’almost complete. 
The relics of former volcanoes in this country furnish ample i)roofs to 
dispel these common misconceptions. They show that not a single crater 
anywhere remains, save where it has been buried under lava ; that^ no trace 
of the original cones has survived, except in a few doubtful cases where 
they may have been preserved under subsequent accumulations of material ; 
that in the rugged tracts, where volcanic action has been thought to have 
been most rife, there may be not a vestige of it, while, on the^^other hand, 
where the uneducated eye would never suspect the presence of any remnant 
of volcanic energy, lavas and ashes may abound. We are thus presented 
with some of the most impressive contrasts in geological history, while, at 
the same time, this momentous lesson is borne in upon the mind, that the 
existing inequalities in the configuration of a landscape are generally due 
far less to the influence of subterranean force than to the action of the 
superficial agents which are ceaselessly carving tlie face of the land. 
I hose rocks which from their liardness or structure are best aide to with- 
stand that destruction rise into prominence, while the softer material around 
them is worn away. Volcanic rocks are no exception to this rule, as the 
geological structure of Britain amply proves. 
In the following chapters, forming Book I. of this work, I propose to 
begin by offering some general remarks regarding the nature and causes of 
volcanic action, so far as these are known to us. I shall then proceed to 
consider the character of the evidence that may be expected to be met with 
respecting the former prevalence of that action at any particular locality 
where volcanic disturbances have long since ceased. Tlie most telling evi- 
dence of old volcanoes is naturally to Ije found in the materials whicirthey 
have left behind them, and the reader’s attention will be asked to the special 
characteristics of these materials, in so far as they give evidence of former 
volcanic activity. 
As has been already remarked, many of the most prominent phenomena 
of a modern volcano aie only of transient importance. The earthquakes 
and tremors, and the constant disengagement of steam and gases, that play so 
conspicuous a part in an eruption, may leave no sensible record behind them. 
But even the cones of ashes and lava, which are piled up into mountainous 
masses, have no true permanence : they are liable to ceaseless erosion by 
the meteoric agencies of waste, and every stage in their degradation may be 
traced. In successive examples we can follow them as they are cut down 
to the very core, until in the end they are entirely effaced. 
We may well, therefore, ask at the outset by what more endurino- 
records W'e may hope to detect the traces of fonner volcanic action. The 
following introductory chapters will be devoted to an attempt to answer 
