74 
SUBTERRANEAN VOLCANIC ACTION 
BOOK I 
crater, or if they reached at least a higher level in the funnel than the sur- 
rounding water-bottom or land-surface, the destruction of the cone might 
leave a projecting knob or neck to he surrounded and covered by the accu- 
mulating sediments of the time. It is thus evident that the levelling of a 
cone of loose ashes during gradual subsidence, and the deposition of a con- 
temporary series of sedimentary deposits, might give rise to a true neck, 
which would be coeval with the geological period of the volcano itself. 
In practice it is extremely difficult to decide how far any now visible 
neck may have been reduced to the condition of a mere stump or core of a 
volcano before being buried under the stratified accumulations of its time. 
In every case the e.xistence of the neck is a proof of denudation, and per- 
haps, in most cases, the chief amount of that denudation is to be ascribed 
not to the era of the original volcano, but to the comparatively recent 
interval that has elapsed since, in the progress of degradation, the volcanic 
rocks, after being long buried within the crust, were once more laid bare by 
the continuous waste and lowering of the level of the land. 
vii. Stages in the History of old Volcanic Vents 
Let us now try to follow the successive stages in the history of a 
volcano after its fires had quite burnt out, and when, slowly sinking in the 
waters of the sea or lake wherein it had burst forth, it was buried under an 
ever-growing accumulation of sedimentary material. The sand, mud, cal- 
careous ooze, shell-banks, or whatever may have been the sediment that was 
gathering there, gradually crept over the submerged cone or neck, and 
would no doubt be more or less mixed with any volcanic detritus which 
waves or cuirents could stir up. If the cone escaped being levelled, or if 
it left a projecting neck, this subaqueous feature would be entombed and 
preserved beneath these detrital deposits. Hundreds or thousands of feet of 
strata might be laid down over the site of the volcano, which would then 
remain hidden and preserved for an indefinite period, until in the course of 
geological revolutions it might once again be brouglit to the surface. 
These successive changes involve no theory or supposition. They must 
obviously have taken place again and again in past time. That they 
actually did occur is demonstrated by many examples in the British Isles. 
I need only refer here to the interesting cases brought to light by mining 
operations in the Dairy coalfields of Ayrshire, which are more fully described 
in Chapter xxvii. (p. 433). In that district a number of cones of tuff, one 
of which is 700 feet in height, have been met with in the corirse of boring 
and raining for ironstone and coal. The well-known mineral seams of the 
coalfield can be followed up to and over these hidden hills of volcanic tuff 
which in the progress of denudation have not yet been laid bare (Fig. 146). 
The subsidence which carried down the water-bottom and allowed the 
volcanic vents to be entombed in sedimentary deposits 'may have been in 
most cases tolerably equable, so that at any given point these deposits 
would be sensibly horizontal. But subsequent terrestrial disturbances 
