406 C. T. Jackson on Crystals 
brown spar and quartz. "The crystals of argentiferous galena 
are in the forms of octahedra, having their solid angles re- 
placed by single planes, and rhombic dodecahedra with their 
surfaces rounded and dimmed by decrystallization, or by ir- 
regular deposits of minute particles of the ore. There are 
also some cubic crystals which have their surfaces much al- 
tered, and their angles effaced or blunted, and which present 
depressions in the planes of the cube, as if the ore had sunk, 
in a semi-fluid state, into a cavity. 
Some of the crystals exhibit the most decisive proof of their 
igneous origin, and have undergone a sort of eliquation, the in- 
terior of its mass having flowed out, and left the exterior crust 
in the form which the crystal originally assumed on cooling of 
its surface. Some of these crystals are somewhat larger than 
a hen's egg, and form very beautiful specimens to illustrate 
the origin of the ore, and would ornament the cabinet of a 
mineralogist. 
We may suppose that the cavern in which these crystals 
occur, was originally filled with molten galena, and that the 
ore ran out from it into other crevices, and left the cooled and 
crystallized ore on the walls; or that an open crevice allowed 
the vapor of lead ore to sublime into the chamber, and that the 
crystals were deposited on its surface by their cooling action. 
The appearance of the walls seem to indicate the latter 
theory as the most reasonable; for the crystals of lead de 
were deposited upon the quartz and brown spar crystals; which 
do not appear to have been bathed in the molten ore. I 
should assign“the same origin to the resplendent octahedral 
crystals of black cupriferous blende, which are sprinkled over 
the surface of this cavern, and to the crystals of copper PY rites 
which are associated with the lead ore. 
Assay of a Specimen of the Crystallized Argentiferous 
Galena from the Cavern in Shelburne Mine. ~ 
Two hundred grains of the ore, reduced with carbonate of 
soda and the iron of an iron crucible, yielded 147 grains 
metallic lead, or 73.5 per cent. 
