eee ed ig 
ae 
140. | “On Certain Cavities in Quartz, §c. - 
formly rhombic, than in any other that I have seen. 'The gene- —— 
ral figure of, this specimen is oblong. It is compressed upon two 
opposite surfaces, and possesses additional interest by having two 
translucent crystallized surfaces capping the one end. ‘These 
faces incline at an angle of about 120°, are 8 inches long, and 
32 wide, having a ragged periphery, as if broken, and constituting 
two of the planes of an hexagonal prism. pee smaller speci- 
men has two sides of the prism and two sides of the - -pyramid 
extending across the centre of the mass; while a third is com- 
pletely surrounded by innumerable cells, with acicular ee of 
actynolite pervading one end. 
In order to ascertain the particular cd of sleien cavition 
several casts were made for me by my friend Dr. E. Parry. 'Tak- 
ing these as correct models of the crystals that preoccupied these 
cavities, it will be easy to ascertain their exact figure. The fol- 
lowing diagrams will represent the angles of several of the casts, 
ar 
These angular and tabular impressions vary in size from the 
smallest pyramidal point and rhombic table, to rhombic cavities 
of three inches parallel diameter, and two inches in depth. And. 
you will perceive that the above diagrams are all portions of 
rhombic figures. 
A geological inquiry naturally arises as to the cause sof the pe- 
culiar cellular structure of these specimens. Before inquiring 
into the particular agents -which prepared the quartz to receive 
these impressions, and caused the dispersion of the crystals that 
produced them, it will be necessary to examine into the character 
of the solids, which, at one time, were encased by these peculiar 
cavities. “Your attention has been called above to the rhombic 
form of the casts. Now there are no mineralogical specimens, of 
ee ed saosin in our vicinity, that so exactly 
