47 
more or less oblique angle. Apart from the cleavage, the effect 
produced on the two formations has been very different, the 
Skiddaw Slates, being less able to resist the pressure, are much 
contorted and crumpled, except where the soft beds are interstrat- 
ified with beds of grit; while the hard volcanic rocks have merely 
been thrown into a series of low curves. Most of the dykes and 
masses of igneous rock probably owe their origin to the earth 
movements which caused the contortion and cleavage. There is, 
however, a notable exception in the case of the quartz felsite dyke on 
the summit of Kirkfell, which is highly cleaved, while the adjoining 
ash beds are not so. Cleavage is very highly developed in some of 
the beds of ash and breccia, while in others, with which the highly 
cleaved beds are in contact above and beneath, it is very imperfect, 
This difference appears to be due in some cases to the finer quality 
of the material of which the highly cleaved beds are formed, but it 
is not always so, because the beds that are made up chiefly of fine 
materials are not uniform throughout, but have in them, here and 
there, portions that are very coarse, and in these coarse portions 
the cleavage is often as perfect as where the material is of the finest 
quality. There is, moreover, a marked want of uniformity in the 
cleavage in beds where it is most perfectly developed. The beds may 
sometimes be traced for a great distance by certain well defined 
bands of colour, and in some parts of their course cleavage has 
been developed in its greatest intensity, and large quantities of 
slate of the best quality are obtained from it, while in the adjacent 
parts, on each side, the cleavage is so imperfect, that it will not 
yield slate at all. ‘The same irregularity would, no doubt, be found 
in following the beds downwards that has already been proved to 
exist in tracing them horizontally, but it has yet to be ascertained. 
On the surface, the highly cleaved portions of a bed occur at 
uncertain intervals, and measure from fifty to two hundred and 
fifty feet in diameter, the vertical and horizontal measurement 
_ being much the same; and if a series of bore-holes were put down 
on the dip of the bed, by means of the diamond borer, they would 
in all probability reveal the same irregular succession of perfectly 
and imperfectly cleaved patches in following it downwards. The 
