452 Umiversity Geological Survey of Kansas. 
figures. Whatever their nature, they serve our purpose.) 
These consist of etch-pits,’ isosceles triangles with the two 
sides which meet at right angles parallel to the cubic edges, 
as figure 3 shows. The position of the etch-pits is different 
on the different faces under consideration. The right angle 
in each case points toward the solid angle of the crystal on 
the face adjacent to that angle. Now, if twinning were re- 
sponsible for this structure these different areas would all be 
faces of a cube, and accordingly the etch-figures would all be 
alike, and would moreover possess a higher grade of sym- 
metry. Itis then evident that the faces are those of a vici- 
nal trigonal trisoctahedron. 
Some peculiar crystals of galena were found at the Gracie 
Clark mines, northwest of Galena. The faces of the cube are 
hollowed out similar to those of the hopper-shaped crystals 
of halite or rock salt. The planes bounding the hopper- 
shaped depressions are apparently those of the octahedron 
or a tetragonal trisoctahedron. They are really oscillatory 
combinations of the cube with one of the above-mentioned 
forms. The cavities present an appearance of having been 
formed by solution, although this is not at allcertain. Itisa 
well-known fact that certain crystalline planes are produced 
by the action of solvents, and it seems probable that to such 
a category the formation of these planes, or pseudo-planes, 
should be assigned. Still, they may be a variety of skeleton 
crystals, or cystals only partially formed, like the hopper- 
shaped salt crystals. 
Peculiar reticulate forms consisting of octahedral crystals, 
with a number of individual plates parallel to the face of the 
octahedron superimposed upon one another, with intervening 
spaces, are found associated with wurtzite, which is described 
later on. 
A fine-grained galena very closely resembling the ‘‘bleisch- 
weif’’ from Clausthal is found at Granby. This so-called 
short-grained variety is commonly thought to indicate silver, 
but, as far as known, no galena from the district contains 
more than a trace of silver. 
3. For a recent discussion of the nomenclature of etch-figure, see R. A. Daly: A Compara- 
tive Study of Etch-Figures; the Amphiboles and Pyroxenes, Proc. Amer. Acad. of Arts and 
Sciences, vol. xxxIv, p. 175, et seq. 
