76 
SUBTERRANEAN VOLCANIC ACTION 
BOOK I 
existence of some volcanic vent in the neighbourhood, but without further 
evidence he would be unable to tell whether it lay to right or left, whether 
it was now at the surface or lay still buried under cover of the stratified 
deposits which were laid down upon it. 
In the second or central example (B) we have a pipe and cone which 
have been similarly disturbed. But in tbis case denudation has proceeded 
so far as to reveal the cone and even to cut away a portion of it, as shown 
by the dotted lines to the right hand. Owing, however, to the general 
inclination of the rocks towards the left, that side of the cone, together with 
the tuffs or lavas connected with it, still lies buried and protected under 
cover of the sedimentary formations (s, s). 
The third example (0) shows a much more advanced stage of destruction. 
Here the whole of the cone has been worn away. All the lavas and tuffs 
which w’ere ejected from it towards the right have likewise disappeared, 
and strata older than the eruptions of this vent now come to the surface 
there. To the left, however, a little portion of its lavas still remains at I, 
though all the intervening volcanic material has been removed. That 
solitary fragment of tlie outpourings of this volcano once extended further 
to the left hand, but the occurrence of the large dislocation (/) has carried 
this extension far down below the surface. The vent in this instance, 
owing to its position, has suffered more from denudation tlian the other two. 
Yet, judged by the size of its neck, it was probably larger than either 
of them, and threw out a more extensive pile of volcanic material. Its 
funnel has been filled with agglomerate (a), through wliich a central plug 
of lava {f) has ascended, and into which dykes or veins {d, d), the last efforts 
of eruption, have been injected. 
This diagram will serve to illustrate the fact already so often insisted on, 
that although denudation may entirely remove a volcanic cone, and also all 
tlie lavas and tuffs which issued from it, the actual filled-up pipe cannot be 
so effaced, but is practically permanent. 
