A HISTORY OF CUMBERLAND 
Next to these in this respect come argillaceous limestones, as, for 
example, some of the beds of Coniston Limestone. Lavas in Cum- 
berland show only faint traces of cleavage, while grits and greywackes 
hardly show any cleavage at all. It may be remarked that in North 
Wales Pre-Carboniferous rocks of all kinds are cleaved more or less ; 
while in Scotland the same rocks, even where most intensely com- 
pressed and contorted, rarely show any trace of cleavage. In Ireland 
cleavage affects rocks of Carboniferous age, asin the case of the Carboni- 
ferous Slate near Cork. Cleavage affects these rocks in Cumberland to 
a decreasing extent as we go northward, and it ceases to produce any 
marked effect north of an east and west line through Cross Fell. It is 
hardly discernible in the northern part of the Caldbeck Fells, where, by 
the way, true bedding has been mistaken for cleavage. 
(g) After this digression we are in a better position to understand 
the events which took place in Cumberland in Devonian times. The 
period of upheaval crumpling and cleavage of the strata, added to that 
of their subsequent waste and removal by surface agencies, which fol- 
lowed the Silurian Period, must have been one of prolonged duration, if 
we may judge by the amount of disturbance and the enormous thickness 
of rock removed. It seems probable that mountains of considerable 
elevation and consisting of these Silurian rocks had arisen, and that it 
was in connection with these upheavals that the later set of volcanoes had 
arisen to which previous reference has been made. There is good reason 
to believe that a considerable mass of these Devonian volcanic rocks 
accumulated here, and that they formerly extended, with a marked un- 
conformity, over all the Lake district rocks, and have been subsequently 
removed by denudation. But although the volcanic rocks themselves 
have disappeared, the volcanoes have left their mark in other ways, for 
there is reason to believe that several of the granite masses, such as those 
of Shap, Skiddaw, and Eskdale, not to mention smaller areas less well 
known, mark the site of former volcanoes belonging to the period under 
consideration. The granites of Cumberland are therefore of two ages, 
Ordovician and Devonian. 
In connection with these Devonian volcanoes there was a repetition 
of the phenomena already noticed under the Ordovician Period. Con- 
tact alteration took place around the granite areas, and the more ancient 
lavas and tuffs, more or less altered by changes due to the long-continued 
circulation of underground waters, underwent considerable change in 
lithological character. It is important to remember in studying this 
set of facts that the contact-alteration of rocks which have lost part of 
their alkalies and have suffered chemical change in other ways, must 
necessarily give rise to a kind of rock quite different from what resulted 
from contact-alteration before they were so changed. The effects have 
been very remarkable in some cases, and were described many years 
ago by Mr. Ward, and more recently, by the light of much fuller 
knowledge, by Mr. Harker in the case of the tuffs, etc., around the Shap 
granite. 
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