198 Mr. G. P. Serope on the Formation of: Craters, 
deserve the attention of geologists engaged in investigating the 
origin of the so-called “ plutonic” and ‘ metamorphic” rocks. 
It seems to me more probable that some process of this kind 
may have metamorphosed granite into the laminated rocks of 
plutonic origin, gneiss and mica-schist, than that these rocks 
should have been formed by the mere fusion and reconsolidation 
or crystallization in place of sedimentary strata already laminated, 
according to the usual “metamorphic” doctrine. I can under- 
stand the clay-slates and other fine-grained schists to have been 
formed through the mechanical disintegration of mica-schist, but 
not mica-schist by the baking or melting and cooling of the clay- 
slates in place, in the manner suggested by Sir C. Lyell. 
In the formation of the clay-slates, perhaps, the action of heat 
was not concerned (except as engendering the pressure to which 
they have evidently been subjected), but that of water or an 
aqueous silicaté only. Still in thei case also internal move- 
ments and mutual friction of the component particles under 
extreme and irregular opposing pressures have, I am convinced, 
had a primary influence in occasioning that parallel arrangement 
of the scaly and flaky micaceous particles to which their slaty 
cleavage is due. This, at least, was the conviction forced upon 
my mind by a close examination of the fissile clinkstone of the 
Mont Dor and Mezen, which is used for roofing-slate, and is in 
its lamination and cleavage undistinguishable from many clay- 
slates. And that opinion I recorded at the time in my ‘ Consi- 
derations on Volcanoes*.’ 
I have since found this view of the origin of slaty cleavage 
supported by Mr. Darwin in his work ‘On Volcanic Islands,’ 
and by Mr. Sorby in his paper on slaty cleavage in the Edin- 
burgh Philosophical Journal for 1853. I need not say that such 
support affords strong confirmation of its correctness. 
Of course we are led to connect the movements under extreme 
pressure, to which this peculiar texture of the laminated rocks 
is here attributed, with the action of those same forces by which 
their beds have been so generally bent and contorted into a 
series of folds or wrinkles, more or less at right angles to the 
general strike. 
If we seek to discover under what circumstances these flexures 
were brought about, we can hardly be wrong in ascribing them 
to the same violent process by which they have been elevated, 
usually on the flanks of some protruded mdge or enormous dyke 
of crystalline rock, which is seen to form the axis of the moun- 
tain range to which they belong. 
Now what may we suppose to have been the character of this 
elevatory process ? 
* See pp. 103, 144 and 202. 
