GEOLOGY 
Carrock Fell is a striking example of the feature referred to. It 
was described at some length by the late Mr. Ward, and has since 
formed the subject of an important memoir by Messrs. Marr and 
Harker. Another area of the same general nature occurs around the 
foot of Thirlmere.’ 
There are several other areas in the Lake district which are of the 
complicated nature here referred to, and as most of these give rise to 
striking scenery, the subject can hardly be passed over without some 
kind of reference, even though that reference involves certain technic- 
alities. 
There is another set of phenomena which originated soon 
after the close of the Silurian Period, and which gives rise to effects of 
considerable commercial importance, as well as being largely concerned 
in the evolution of the scenery. This is the phenomenon known as 
cLEAVAGE. Under its influence rocks of various kinds split with more 
or less facility in parallel directions, which bear no necessary relation to 
any of the original planes of structure. All true slates split solely under 
the influence of this structure. The exact origin of slaty cleavage has 
not yet been quite satisfactorily explained; but it will suffice for the 
purpose at present in view to state that it is certainly due to a slight 
rearrangement of the particles composing the rock affected, which has 
been brought about by intense lateral pressure exerted under certain 
special conditions at present imperfectly understood. ‘The true nature 
of cleavage does not strike one so much in connection with the slates 
of Wales as it does with those of the Lake district, because in this 
latter case the bands which mark the original bedding of the rock are 
much more prominently displayed, and because slate in one form or 
another is largely quarried and is so extensively used, in Cumberland 
especially, for building purposes. It may be remarked here that the 
slates of the Lake district do not quite accord with the definition laid 
down in text-books, inasmuch as most of them consist of rocks of vol- 
canic origin ; and these are not, and never were, rocks of argillaceous 
composition, to which, judging by the statements copied into text-books, 
cleavage is supposed to be confined. 
In whatever way slaty cleavage may have originated, the date when 
the structure was impressed upon the rocks is clearly one shortly after 
the close of the Silurian Period. It affects the rocks in different degrees, 
in accordance with their composition. Tuffs and fine-grained rocks of 
argillaceous composition cleave to the highest degree of perfection. 
1 The explanation generally given of the plutonic phenomena referred to in the last 
paragraph is that they are due to the effects of heat given off by incandescent molten rock, 
which has been bodily and violently transferred from a lower level to a higher from some zone 
of fusion within the earth’s crust. It will be seen that the writer of this article regards them 
primarily as manifestations of the effects of superheated alkaline waters, which have effected a 
gradual transformation of rocks im situ, in the case of metamorphic rock, and an equally 
gradual replacement in the case of the so-called ‘igneous’ rock. - According to this view, 
therefore, all eruptive rocks represent the products of consolidation from aqueous solutions ; 
and water, not dry heat, is the chief agent concerned. 
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