MODIFIED ty COMPRESSION. 129 
fhell had fhrank upon itfelf, fo as to ftand detached from 
the fides, and bore very ftrong marks of fufion. The exter- 
nal furface was quite fmooth, and fhining like an enamel. 
The internal part confifted of a mixture of large bubbles 
and folid parts: the infide of the bubbles had a luftre much 
fuperior to that of the outfide, and equal to that of glafs. _ The 
general mafs was femitranfparent ; but {mall parts were vifible 
by the lens, which were completely tranfparent and colour- 
lefs. In feveral places this fmooth furface had cryftallized, 
fo as to prefent brilliant facettes, fteadily fhining in certain 
afpects.. | Lobferved one of thefe facettes on the infide of an 
-air-bubble, in which it interrupted the fpherical form as if 
the little {phere had been preffed inwards at that fpot, by the 
contact of a plane furface. In fome chalk near the mouth of 
the large'tube, which lay upon a ftratum of filex, another very 
anterefting circumftance occurred. Connected with its lower 
‘end, a fubftance'was vifible, which had undoubtedly refulted 
from the union of the carbonate with the filex. This fubftance 
was white and femitranfparent, and bore the appearance of 
chalcedony. ‘The mafs of chalk having attached itfelf to that 
above it, had fhrunk upwards, leaving an. interval between it 
and the filex, and carrying fome of the compound up with it. 
From thence this’ laft had been in the act of dropping in a 
vifcid ftate of fufion, as evidently appeared when the {peci- 
‘men was entire; having a ftalactite and ftalagmite corre- 
{ponding accurately to each.other.. Unluckily I broke off the 
ftalactite, but the ftalagmite continues entire, in the form of a 
little cone. This new fubftance effervefced in acid, but not 
brifkly..: Dbiwatched its entire folution ; a fet of light clouds 
aemained! undiffolved, and’ probably fome jeliy was, farmed ; 
for: 1 obferved, that a feries of air-bubbles. remained «in. the 
form: of the fragment, and moved together without any vifible 
connection; thus feeming to indicate a chemical. union be- 
VVor. VI.—P.L ; R veer 
