182 Lamplugh : On Movements in Rocks. 
of like to like from masses of mixed composition. The par- 
ticles of silica scattered by the decay of silica-secreting or- 
ganisms through the calcareous mud of our Carboniferous and 
Cretaceous seas could not stay where they were cast, but must 
creep from all directions to their rallying-points, around which 
they have combined into lumps of chert and flint. Similarly, 
the lime-particles scattered among clay have clustered them- 
selves into nodules which have often energetically pushed aside 
the layers of the clay in their gradual expansion. Thus, also, 
the particles of iron, of phosphate, of magnesia, and of other 
rarer ingredients among sediments have shown intolerance of 
isolation, and have responded to the mysterious bonds of 
kinship. (See Plate XI., fig. a). 
Into the nature of the subtle all-pervading forces implied by 
this kind of movement, I shall not attempt to enter. We know 
that they are akin to the wonderful forces of crystallization 
which are, as yet, indifferently understood at the best. Most 
of the movements, but probably not all, are performed through 
the agency of solution; the restless particles, in obeying the 
call of kinship, take advantage of the water circulating through 
all the pores of the rock as a medium to carry them from place 
to place. Be the agency what it may, the fact remains that 
there is ceaseless activity among the rocks, not only near the 
surface, but deep down in the earth—an activity that is concealed 
from our senses. Often it happens that, like the march ofa 
relief-guard, as a particle of one kind is taken up into solution, 
a particle of another kind drops out exactly in its place; and 
so we get the singular phenomenon of replacement, by which 
the shape of a body remains unchanged while its substance 
is completely altered. For example, we may have a shell 
originally of lime, which has been converted into flint, or 
into pyrites, with all its minute and delicate sculpturing 
unimpaired. 
Then there is the allied but more intense display of activity 
known as metamorphism to be reckoned with. In this case 
heat and pressure have so greatly facilitated the movement of 
particles in sedimentary rocks that the ingredients have partly 
or wholly re-arranged themselves according to their affinities 
into true crystals, and the original aspect of the rock is more 
or less completely lost. This kind of alteration has usually 
been effected when the strata were buried deeply in the earth’s 
crust, and we cannot discover it until very long afterwards, 
when the elevated parts of the land have been worn down so 
far that the once deep-seated layers are revealed. But we 
are reminded by such rocks that the same processes are almost 
certainly in operation at the present time in the depths beneath 
our feet, and that the transformation of the strata in the crust 
of the earth by solution, pressure and heat is never in abeyance. 
Naturalist, 
