18: Rutilated Quartz Cry wisill from ¥ Vermont. 
of these substances could have produced it. The. ssi while ‘ied p 
Pee | 
spn itself around either of them, would have taken the ex-° - 
ct form of either, precisely.as we see such impress of their forms. 
in bi crystals of subsequent formation, as for exariple, in the 
quartz crystals from Herkimer, New York. So it is.evident, that 
if any substance ever occupied the cavity, it must have received 
its form from the cavity, without communicating any to pi and — 
thus a anne tag crystal may have been produced in a man-' 
ner somewhat different from usual: viz., by filling up a pera, 4 
which had never been occupied by any crystallized substance, — 
‘ 
whatever. Should such pseudo-crystals of infiltration or deposition, S 
be met with in similar cavities of the quartz from this locality, it 
will become an interesting enquiry to determine whether they 
have the same composition, or are various depending upon acci 
dental circumstances. If the view here taken of them be correct, 
they cannot come under the desieciallia of any of the pseudo- 
morphs hitherto described, (as they do not eo the form of 
any other crystal which has disappeared,) and we must accept 
such explanation of them as is afforded by be quartz itself. It 
is not easy to trace in these cavities, as it is in those before spo- 
ken of, any certain relation between them and the crystalline 
structure of the quartz whose surfaces they impress; their sides 
are not parallel with any of the striz as seen upon the faces of 
the crystals; they indicate an interruption in the process of crys- 
tallization, and we have only to. suppose a successive retrocession 
or withdrawal of particles in such parallel directions, thus enlarg- 
ing the cavity outwardly, as the crystal itself inereased in size. 
They do not appear to have been produced by the irregular com- 
bination of two or more crystals or by the union of different 
crystalline planes leaving spaces between them, because the stria- 
tions which mark the faces of the crystal, and which have been 
intercepted by the eavity, appear opposite to each other on both 
sides of the cavity. This is shown by the figure. It therefore 
appears to belong to one crystal. The cavity intended to be rep- 
resented by the large figure measures one inch on a side, an 
half an inch in depth; the striations at bottom are parallel with 
those upon the face of the crystal. It is more accurately shown 
by the following drawings taken from a cast of it in wax, which 
presents it in opposite positions.* The crystal itself, has a rhom- 
5. . 
" * The deep bevelment on the broadest surface of these casts, (not shown in n the 
euts,) gives the true angle at which the plane r of the erystal sat 
an? 
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a ge ee 
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ae. ie * 
Pn ee 
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