Mr Brooke on Crystallisation. S 
from which we may infer that they have been sometimes slowly 
formed, and that accompanying crystals of different minerals 
have been deposited at very different periods. 
The crystals of carbonate of lime which are found at Ecton 
in Staffordshire^ frequently contain numerous minute crystals of 
copper-pyrites, apparently first deposited on small crystals of the 
carbonate of lime. This substance has then formed over the 
pyrites, and produced a larger crystal of the carbonate of lime, 
upon which a second deposit of copper-pyrites has taken place. 
This has been again enclosed within a still larger crystal of the 
calcareous matter, upon which other crystals of pyrites have 
been again deposited. And we may discover, when the crystals 
are large, several alternations of these two minerals successively 
covering each other. 
The crystals which are termed yseudomoryhous.^ afford very 
distinct evidence of successive formation, as the period at which 
these were produced must have been posterior to that of the 
crystal whose form they imitate. I have observed in one in- 
stance a mould in preparation, if I may so term it, for a pseudo- 
morphous crystal, from which a part only of the model, a crys- 
tal of fluate of lime, had been removed. 
The mould itself was crystallised quartz, which had coated 
the crystal of fluor. The size of this crystal was originally more 
than a cubic inch ; but it had been subsequently reduced to a 
rounded mass^ loose within the mould, of about half that bulk, 
with an irregular and smooth surface, like that of partially dis- 
solved salts. 
Hollows of various forms, contained within crystallised quartz^ 
are not uncommon ; but I do not recollect any other instance 
of the crystal, whose removal had produced the vacuity, being 
only in part destroyed, as if its dissolution had been recently 
going on. Numerous other examples might be cited as evi- 
dences of the gradual and the successive formation of crystals, 
by processes which are probably still’ in operation, although we 
are uninformed with respect to their nature. 
There are circumstances which render it almost certain that 
some crystals have been produced from solution in a fluid. The 
water found in the ca\ ities of certain crystals of quartz, would 
seem to refer their oiigin to solution in that fluid; and we 
