_ 264 Formation of Crystals in Geodes. 
‘This was true not only of the spongy matter, but of the 
separate crystals, which we are entitled to consider us 
crystals of quartz, almost instantaneously deposited, from 
a rich siliceous solution. These crystals were of a rather 
dull white, without much lustre or transparency. Their 
diameter was that of fine sewing silk, and their length not - 
exceeding one sixth of an inch. It is much to be regret- 
ted, that no opportunity was afforded, of examining this 
fluid, so that it is impossible to say, whether it were some 
modification of water, or a distinct fluid. The earthy de- 
posit and the crystals were tasteless, and proved to be a 
very sharp grit between the teeth. Mr. N. was so fortu- 
nate as to break another pebble, whose diameter was five 
inches by three,and consisting of a mixture of hornstone and 
chalcedony,in whose centre wasa cavity ofan inch anda half 
by one inch, This cavity, although strictly speaking not 
occupied by a fluid, was nearly filled with the spongy sili- 
ceous deposite already described, but 1 was still morst, to 
such a degree as to form a pulpy or gelatinous mass, very 
soft and impressible ; this mass was also soon dried by 
the intense heat of the weather. As there was less fluid to 
evaporate, so, as might have been expected,there were but 
few crystals formed; still, they shot, here and there, 
as in the other cavity. The spongy mass in the 
cavity of the largerstone admits a knife to penetrate 
it more than an inch, and portions of its surface have 
a mammillary and stalactical appearance. It 1s silex like 
the other. Many pebbles, from the same heap of ballast 
stones, have been broken for the purpose of discovering 
more of the fluid, but none has yet been found. Nume- 
rous cavities have, however, been observed, some lined 
with the spongy siliceous deposite already mentioned, in- 
termixed with minute prismatic crystals, which last have 
however rather more lustre than those which were so rap- 
idly formed; and it is observable that the stone, forming 
most of the immediate walls of the interior of the cavities, 
is of an opaque enamel white, as if it had been penetrated 
by a fluid, and in some measure softened, by incipient so- 
lution. Other cavities were lined with distinct and beauti- 
ful crystals of transparent quartz of the usual form, per- 
fectly well defined, but exhibiting little more than the 
pyramidal termination. In a few cavities, the siliceous 
