236 The American Geologist. April, 1896 
La Capucin n.g (C) is perpendicular to the "hexagonal" base. 
This grain is quite similar in all characters to Nos. 5 and (>. 
No. '.) has a large inclusion which adheres to one corner. Its 
interference figure is also a branch of a black cross. In No. 
10 the same part of the interference figure is visible in con- 
vergent light. Its colors show two orders of red. Figs. 11 
and 12 resemble each other in their manner between crossed 
nicols, but as No. If shows an axis of elasticity of which the 
index is np (a) and reveals a very small measure for 'IE, it 
may be allied to the group No. 4. They both polarize in low 
tints of the first order. These grains all have a strongly con- 
choidal fracture. They are not soluble in hydrofluosilicic 
acid. 
4. A mineral which shows no evident cleavage, has a rusty 
yellowish yet clear transparency when free from inclusions, 
in form roundish-angular, polarizing in the tints of the first 
order even when rather thick. Represented by the following 
figures (13 and 14). The grain represented by fig. 13 lies so 
as to show the axis np vertical ; the ar- 
row shows the direction of the axial 
^ \f\-M plane. The optic axial angle is very 
14 small. It may be estimated at 10° to 15°. 
In the grain figured this axis seen in the 
upper half is not parallel with the same 
seen in the lower half, indicating theex- 
istence of a twinned individual. Fig. 14 shows white polar- 
ization tints of the first order. The central portion of fig. 
No. 13 shows a yellow color, but in parallel light it is rather 
obscure throughout. Fig. 14 seems also to lie so as to show 
an elasticity axis, but the grain is so thick that it cannot be 
identified with certainty. It is possible that fig. 11 should be 
removed to this group. 
5. Water-clear grains with sharp or eonchoidal fracture, 
which have not disclosed any cleavages. On an oblique sur- 
face fig. 15 transmits light between crossed nicols, but other- 
wise it is wholly isotropic. The whole central portion (a) 
remains dark, while the edges (b) which are obliquely frac- 
tured, transmit light, and darken at four points in rotation, 
the arrow showing the direction of extinction. The two little 
grains shown in fig. 16 have no optical characters except that 
