52 IDO Ricketts—Changes in the Earth’s Crust. 
is concerned, the result is the formation of alluvial and marine plains, 
occurring about or below the level of the sea; it is only on the 
conditions being altogether changed they become raised, chiefly 
in consequence of the removal of weight, consequent on the great 
denudation they have undergone, and thus help to form mountains. 
The flanks of mountains are frequently composed of rocks whose 
strata have undergone disturbance and contortion, and are oftentimes 
affected by cleavage. These foldings have been referred to as 
essential features in the formation and “building” of mountains ; 
but they extend as frequently to low ground, and pass beneath 
deltas and estuaries, and form the base upon which the strata con- 
stituting the bed of the sea rest. Geological inquiry shows that 
after having been raised above the sea-level and become weathered 
and eroded, the valleys and channels formed may again be sub- 
merged, and have their weathered surfaces buried beneath sediments 
to a depth of several thousand feet. 
Contortions have been attributed to the forcing of wedge-shaped 
masses of metamorphic rock upwards so as to penetrate and protrude 
through sedimentary strata; but in a general elevation affecting a 
district the whole thickness of the’ earth’s crust must be lifted 
together, and from a depth which would render such an occurrence 
impossible. In no instance would it appear more probable that 
such has taken place than on the flanks of the Malvern Range, had 
not Miss Annie Phillips’ (sister to the Oxford Professor) found 
Silurian organisms embedded in a breccia derived from the dis- 
integration of the metamorphic rock. Her discovery was most 
important, more so than is generally recognized; proving that during 
the deposition of the Upper Silurians the Malvern Hills formed an 
Island, in all probability the summit of a former mountain, buried 
beneath a great accumulation of strata then in process of deposition, 
the margins of which consisted of fragments of the metamorphic 
rock which had fallen down from its sides into the Silurian sea.? 
The contortions in these Silurian strata, or the power that caused 
them, could not have given origin to the mountain, for its summit 
was situated above the sea-level during the time of their deposition ; 
on the contrary, its presence may have influenced but not caused, 
that action by which they are thrown into extensive folds. The rudder 
does not cause the ship to sail, but determines the direction of 
its course. 
Any movement by which the crust of the earth is compressed 
into a less lateral space must, to an extent commensurate with the 
size of the area effected, have a tendency to cause the strata to 
become bent and contorted. This may result in some degree from 
the weight of accumulations causing subsidence, and, by thus pressing 
downwards the earth’s crust, cause it also to be compressed within 
less lateral dimensions, but the lateral pressure thus developed can 
only be considered as inducing a tendency to form flexures ; its 
1 Memoirs of the Geological Survey, vol. ii. p. i. p. 66. 
2 Fragments derived from the hills also enter into the composition of the Holly- 
bush Sandstone (Lower Silurian). 
