Doge! BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
section. The nepheline and leucite phenocrysts are evidently somewhat 
vicarious, for zones of the rock rich in one are poor in the other. 
Microscopically the rock is composed of the following minerals : 
Phenocrysts of nepheline and pseudo-leucite ; few crystals of augite 
and occasional plates of biotite. 
Ground mass: aegirine-augite needles, orthoclase, nepheline as essen- 
tials, with a little analcite, biotite, calcite, ete. 
The nepheline phenocrysts are glassy and fresh, bounded by base and 
prism. The pseudo-leucites are composed of an aggregate of orthoclase, 
partly in irregular grains, more often in radiating prisms, forming even 
imperfect sphero-crystals, several of which may occupy one original 
leucite. Between the orthoclase there is a comparatively small amount 
of nepheline, usually in irregular patches, rarely in prisms, and this 
nepheline lies between the orthoclase rays. The space in the centre of 
the original leucite, especially that between the curving boundaries of 
two opposite spheroids of orthoclase is filled with a clear isotropic sub- 
stance with refractive index lower than the feldspar, traces of cubic 
cleavage, gelatinizing with HCl, and determined as analcite. Into this 
the square ends of the orthoclase rays sometimes project with a struc- 
ture curiously analogous to that described by Iddings (‘‘ Obsidian 
Cliff’) in the obsidian spherulites, where rays of orthoclase project 
into a quartz or tridymite paste. Associated with the analcite there 
occurs an undetermined zeolite with equally low index, good double 
cleavage and distinct though feeble birefringence. The very early period 
of formation of the leucites is shown by their penetration by tongues of 
the rock carrying nepheline and augite phenocrysts. 
The pyroxene phenocrysts are a deep green, slightly pleochroic, aegir- 
ine-augite, with the direction of negative extinction about 38° to c’. 
They sometimes have a centre of colorless or reddish augite and an 
aegirine border. Small masses of purple fluorite are deposited within 
or around them and they are frequently filled with secondary biotite. 
Associated with them are a few melanite crystals, titanite masses, areas 
of colorless fluorite and astrophyllite(?). 
The ground mass comprises a fine net work of slender pyroxene crystals 
in a background of colorless minerals. These acicular pyroxenes are 
pale to deep grass green in color, slightly pleochroic, parallel c’ grass 
green perpendicular to e! olive green; most of them extinguish nearly 
parallel to c’, others as high as 19° ; in either case this is the negative 
optical direction and they would pass for aegirine or aegirine-augite. 
The colorless background is resolved in polarized light into irregular 
