Dana and Wells — New mineral, Beryllonite. 29 



and merit a more detailed study than our limited time has 

 permitted us to give them. They are most distinct on the 

 basal plane, where they appear as nearly square depressions 

 closely crowded together, at first sight suggesting tetragonal 

 symmetry. Figure 12 will give some idea of the appearance 

 of a portion of the surface ; in some cases these pittings run 

 across the basal face in diagonal lines. A more careful exami- 

 nation shows that while square or nearly so in outline the sym- 

 metry is rhombic. The little pits ai*e bounded within by two 

 surfaces in the zone he, making an angle of 22° with each 

 other, and in the zone ac the prominent surfaces are inclined 

 about 11°, while occasionally other deeper faces inclined 21° 

 are also noted. The angles can be only roughly measured, but 

 they suggest 013(/9) and 1-0 10, 105 as probable symbols for the 

 faces in question. The planes in the two series of domes also 

 show at times distinct etching figures, especially e (101) and 

 £ (Oil), but the form is less distinct, though in general acute 

 trowel-shaped with the vertex pointed upward. In some cases 

 those on e appear to vary slightly from the symmetry about 



the plane of the axes b e which the crystallographic relations of 

 the form demands. The b faces often show longitudinal fig- 

 ures ( [| c) and others transverse, but their form is not distinct ; 

 this is also true to some extent of the prismatic faces. The 

 other planes are almost always slightly roughened, but distinct 

 figures are not often to be made out. Not infrequently the 

 solvent action on the crystals has gone so far as to leave only 

 rounded angles with indistinct planes. 



Inclusions. — Another interesting feature of this mineral is 

 the presence of great numbers of fluid inclusions. A superfi- 

 cial examination shows the common existence of a columnar 

 structure normal to the cleavage plane. This is seen in thin 

 sections to be due to great numbers of slender canals parallel 

 to the vertical axis. In some cases these seem to be hollow 

 or filled with earthy matter, but in others they appear as 

 fluid cavities with long bubbles. These vertical canals and 

 fluid cavities are often thickly crowded together, sometimes 

 extending from base to base and again starting from a sharply 

 defined plane within the crystal parallel to the base. The 

 forms of some of these are shown in fig. 9 (X90). Not infre- 

 quently, instead of a long cavity, we have a line of them present 

 all lying in the same direction. Besides these regular cavities 

 there are also groups of fine parallel or wavy lines inclined 

 sharply to c and giving rise to a peculiar sheen ; these are prob- 

 ably also hollow canals. 



There are, further, multitudes of other fluid cavities, often so 

 small as to require a high power of the microscope, either 



