A HISTORY OF CUMBERLAND 
that author called attention to the fact that where this rock occurred an 
equivalent thickness of sedimentary rock was missing. Mr. Clough 
explained this as due to the assimilation of the sedimentary rock by the 
magma from which the Whin Sill was derived. Mr. Clough’s views 
were too advanced to meet with acceptance at the time, though the case 
is different now. 
The present author has put forward a modification of Mr. Clough’s 
view, in which it is suggested that the Whin Sill (as well as every other 
eruptive rock) owes its origin to the slow solution of pre-existent rocks 
by heated waters containing alkalies, and the subsequent crystallization 
of the new compound when the temperature fell and the aqueous solvent 
escaped. 
Beyond the fact that the Whin Sill is of later date than some of 
the disturbances which affect the Carboniferous rocks, its age is un- 
known. But it may be contemporaneous with the volcanic rocks of New 
Red age in Scotland. 
VII. Ruatic Beps.—Near the close of the New Red Period the 
subsidence to which reference has been made was continued until it 
eventually carried the surface nearer and nearer to the sea level; con- 
sequently the desert conditions came to an end and have not affected 
Britain since. The change was a very gradual one, extending over a 
period of very great length, as is shown by the vast and important 
changes which took place on the continent in the meantime. In Britain 
these changes gave rise to a set of rocks very similar in many respects to 
those which were formed at a previous period, when the desert condi- 
tions which prevailed when the Old Red Sandstone was formed were 
gradually giving way before the humid conditions which characterized 
Carboniferous times. The strata formed at the period now under notice 
probably extended far and wide over western Europe. In Cumberland 
they may be represented only by a small patch, which has survived 
denudation, and occurs at Orton, west of Carlisle, it alone having been 
left between Arran and the midland counties of England. The strata 
usually consist, in their lower parts, of reddish and greenish clays with 
cornstones, and in their upper parts of dark shales. The total thick- 
ness in Britain nowhere much exceeds 100 feet. On the Continent 
strata of the same age range to several thousand feet, including impor- 
tant masses of limestone, chiefly formed by the agency of plants (Alga). 
VIII. Jurassic Rocks.—With the commencement of the subsidence 
which ushered in the Rhetic period there set in a repetition of condi- 
tions very similar to those which prevailed during Carboniferous times. 
The Lias and Oolites everywhere succeed the New Red, so that where 
the one occurs, or can be proved to have existed, there also was the 
other. This is another way of stating the fact that not only the New 
Red extended continuously across the whole of what is now Cumberland, 
but that the whole district was formerly buried also beneath a great pile 
of the Lias and the Oolite. Of this vast accumulation all that is left 
now is a tiny patch at Orton, west of Carlisle, which is shown upon the 
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