76 
numerable; and there are some hair-like appearances on 
the tops of some of them, which are bending or otherwise 
modified: in the point of one is a little black speck like 
soot. The specimen has broken rather conchoidally, but 
not far from the primitive fracture. The somewhat zigzag 
line is interruptedly six-sided, depending on the particular 
interruption of the primitive molecules, and is chiefly filled 
with the same powder as the others; whence its opacity. 
It is not much unlike in the angles to che bottom figure of 
tab. 72, and is remarkable for its contrary and prostrate ap- 
pearance; and the combination of the two might lead the 
imagination very far, of any one who had not attended to 
Crystallography. I mentioned in the description of tah. 71 
the water or liquid in the little hollows of this substance. 
I add an outline or sketch of them at the bottom of this 
plate, as hitherto they appear to be a great curiosity. The 
hollows are rather irregular, a little angular, and have 
sometimes more or less tendency to the form of crystalli- 
zation. The air bubbles of course upwards, in whatever 
position they are held; but in the long one it only moves 
the space marked with dots. 
I have specimens of solid crystals of Sulphate of Barytes 
covered with, and passing into one another; and so it 
happens with different substances; but these I thought 
sufficiently remarkable to illustrate the present pheno- 
menon, which may be very useful. . Both these specimens 
serve to show the double refraction completely through the 
columnar sides. Thus the bubbles and hollows are seen 
double as in the bottom specimen—see the magnified figure. 
And where we can look into the upper specimen, the py- 
ramids and odd forms may be seen double. 
These specimens are from near Alstone Moor, Cumber- 
land, and are in the possession of Walker, Esq. I have 
specimens with Copper Pyrites in spicule, hair-formed, &c., 
in them. 
