200 Mr. G. P. Scrope on the Formation of Craters, 
to carry their wavings still further, and at the throat of the 
fissure, where the squeeze and jam of the protruded matters 
must be at its maximum, to occasion those enormous and repeated 
zigzag foldings of the laminated beds, so frequently observed in 
mica- and chlorite-schists in such positions. 
Meantime another influence would be similarly affecting the 
overlying stratified rocks above, or on the outer flanks of the 
elevated axis, namely their own specific gravity, urging them to 
slide or slip laterally when tilted up at (perhaps) a considerable 
angle on either side. The more compact and indurated strata 
would be partly fractured into cliffy masses, partly broken up 
into breccias and conglomerates by this movement; but the 
softer beds, especially those which were saturated with water 
(perhaps even yet under the sea), or which contained interstra- 
tified beds of silt, shale or clay, permeated with water, would 
glide laterally away from the axis in extensive landslips, and be 
wrinkled up into vast foldings under the intense pressure com- 
pounded of their own weight, and that perhaps of portions of the 
protruded matter thrust against them,—in a manner very similar 
to the contortions produced in the more crystalline laminated 
rocks by the violent squeeze which accompanied thezr protrusion. 
It may even be difficult to draw a line between the effects of 
these two replicating and fracturing forces. But, together, they 
seem to me sufficient to account for most of the phenomena of 
the kind observable in mountain-chains. 
These were the ideas on this subject which I endeavoured to 
develope, though very imperfectly I am aware, in the more theo- 
retic portion of my work on volcanoes, so often referred to, and 
they were illustrated by a rude ideal section of an elevated 
mountain-chain in the frontispiece to the volume. I still think 
they will be found a not improbable solution of this the greatest 
problem in the dynamics of geology. It appears to me that the 
results would be much the same, whether we suppose this eleva- 
tory action to have been paroxysmal and simultaneous or gradual, 
taking place by minor and successive expansive throes or shocks, 
or even still more slowly in the manner of a creep, as Sir Charles 
Lyell would probably conceive it to have operated, and to be 
still continuing. On these last assumptions, the earthquake- 
shocks which certamly accompany at present every effort of 
elevation, and appear to be propagated in waves through the 
substance of the earth’s crust, in directions usually at right 
angles to the principal axes of elevation, or fissures of erystal- 
line protrusion, may indicate the force by which the extreme 
replications and slaty cleavage of the laminated beds are occa- 
sioned. 
