A HISTORY OF CUMBERLAND 
changes which affected the rocks of Cumberland at this period, and which 
have left vestiges at many places, both within the county and around it. 
These will be stated in historical order, even though doing so involves 
a reference to events that took place prior to the period under notice. 
(2) During the later history of the Cumberland volcanoes, the gran- 
itic zones beneath the focus of each gradually ate their way upwards 
through the sedimentary rocks and into the material of the volcano itself; 
so that the lavas, tuffs, and intrusive masses of the inner parts of some of 
the volcanoes were gradually replaced by, or perhaps transformed into, 
material which afterwards consolidated as granitic masses. Furthermore, 
with the enlargement of the granitic zones, the zones of thermo-meta- 
morphism also extended farther and farther into the overlying rocks, so 
that the lately formed volcanic rocks themselves were in some few cases 
reduced to a softened state, and kept in that condition long enough to 
permit of a certain amount of rearrangement of their constituents. As 
the temperature of the whole mass gradually fell, this process finally led 
to the crystallization of some of these rearranged materials. The reader 
who wishes to understand the geology of the country around Keswick, 
Ambleside, Buttermere, etc., should try to comprehend this, for a large 
proportion of what was at one time loose fragmentary tuff has been altered 
by these changes into rock which, in many cases, can only be distin- 
guished from lava by patient investigation in the field, supplemented by 
the careful study of thin sections of the rock under the microscope. The 
rocks in question were referred to by the Geological Survey officers who 
mapped the ground (and who, therefore, had an intimate knowledge of 
the true relations of these rocks) as ‘ altered ashes.’ The late Mr. Clifton 
Ward very rightly laid great stress upon this point, the importance of 
which in the present connection, can hardly be overestimated. It was 
not only the tuffs which were altered in this way, but the lavas them- 
selves also underwent a certain amount of change by the same process ; 
while the sedimentary rocks were first softened and subsequently re- 
crystallized to such an extent that they are hardly any longer recognizable 
as sediments. A fine series of these altered rocks was placed by Mr. Ward 
in the Keswick Museum, the Museum of Practical Geology in London, 
and in the Carlisle Museum, and they were admirably described by him 
in the Geological Survey Memoir on the ‘ Northern Part of the English 
Lake District.’ 
(e) Complicated alterations of also the earlier-formed volcanic 
rocks later originated as a further consequence of the growth of the vol- 
cano and the progressive uprise of the granitic zone at its base. The 
lava streams, beds of tuff, dykes and sills, of which the volcano was 
built, gradually passed through every stage of conversion into crystalline 
masses, and became more and more interlaced with, and traversed b 
rocks which had been crystalline from their first stage of consolidation, 
until these inner zones of the old volcano assumed the structure of a 
complex mass, whose details seem at first sight to offer endless difficulties 
to the geologist. 
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