A HISTORY OF CUMBERLAND 
tured and crumpled at one stage was soon after that covered by other 
layers of fine dust which had, of course, not shared in the disturbance. 
The ‘green slates’ of Tilberthwaite and of many other localities in 
the Lake district show these interesting records of contemporaneous 
disturbance very beautifully, and museum specimens, or even specimens 
that will go into a waistcoat pocket, may easily be obtained which will 
show these features well. 
Another set of features of general interest connected with the tuffs 
has been produced by the action of rain, or of aqueous vapour from the 
volcano, chilled by its upward passage into the air. Such vapour 
condenses readily upon the cooler and finer fragments of volcanic dust 
in the upper part of the column shot out from the volcano during erup- 
tion. Once such a nucleus is formed it tends to enlarge by the addition 
of more water and more dust as the pellet descends. Finally it reaches 
the surface as a small ball of mud, and may plump down into the fine 
dust and there become entombed. There are many examples of this 
kind, especially near Ambleside. 
Also it often happens that the torrential rains precipitated from the 
column during an eruption wash vast quantities of the finer material 
down the slopes of the cone, and give rise to such floods of volcanic 
mud as those (/ava @agua) which overwhelmed Herculaneum during 
the Plinian eruption of Vesuvius. Many beds of rock of origin similar 
to this occur in connection with the Cumberland volcanoes. 
It is from the combined results of these explosive eruptions, violent 
or gentle, from the outpourings of the floods of lava, from the action of 
surface causes, and from the forcible injection of materials underground 
derived from the volcanic focus, that the great pile of rocks was formed, 
out of whose much-altered remains the finest scenery of the Lake dis- 
trict has since been carved. It may be remarked here that these rocks 
underwent many changes and modifications long before they were finally 
exposed. These will have to be considered in chronological order, and 
will be therefore referred to again. 
The volcanic eruptions were by no means continuous, but were 
often separated by long periods of repose, during which surface agencies 
modified the slopes of the volcanoes. Furthermore, it is very unlikely 
that the volcanoes attained their maturity without the episodes of des- 
truction which almost every other volcano, ancient or modern, seems at 
some time or other in its history to have undergone. 
The length of time required for the growth of this stage of the 
Cumberland volcano must have been very great indeed. Notwithstand- 
ing the apparent evidence to the contrary, the growth of a volcano is b 
no means rapid. Taking one volcano with another, it would seem a 
fair estimate of their rate of growth if it is set at one foot in 300 
years. The Cumberland volcano certainly rivalled Etna in dimensions ; 
and Mr. Ward’s estimate of 12,000 feet as the maximum thickness of 
these rocks is, if anything, below, rather than above, the actual thick- 
ness to be found. 
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