240 BULLETIN OF THE 
and a fine groundmass. Among the phenocrysts augite greatly exceeds 
hornblende, biotite is rare. The hornblende crystals are brown and 
strongly plechroic; they have lost their crystal angles and show rounded 
resorption outlines. The same is the case with the few pieces of biotite 
seen. With the augite, however, it is different ; this mineral appears 
commonly with complete or partial crystal outlines, though some show 
the rounded resorption form. It is evident that most of the augite 
crystals were formerly rounded and have gained the angular form by 
a later growth in the magma, for irregularly rounded cores can be dis- 
tinguished surrounded by portions having different extinction angles. 
The structure thus given closely resembles zonal structure; zonal 
structure does sometimes occur in these secondary borders. The older 
portions of the crystals are pale green in color, the borders are pinkish; 
in one case the pink border is pleochroic, pink to greenish yellow. 
The phenocrysts of hornblende and augite may each contain rounded 
inclusions of the other mineral, inclusions of the augite in the hornblende 
being much more common. Thus there seem to have been five stages 
in the crystallization of this magma: first, a time when hornblende and 
augite formed in good-sized crystals ; second, these crystals were resorbed 
until they became rounded grains ; third, another separation of large 
crystals of augite and hornblende, which often enclosed indiscriminately 
and without crystallographic relation the grains above mentioned; fourth, 
this second generation of augite and hornblende underwent resorption 
sufficient to destroy the crystal outlines; fifth, a final separation of 
augite, renewing the crystalline form of the augite phenocrysts, and 
probably taking place at the same time as the crystallization of the 
groundmass. The inclusion of hornblende crystals in augite, as well as 
the converse, has been noted before,’ but the peculiar association above 
noted is perhaps new. The accompanying plate shows the essential 
points above mentioned. Both varieties of phenocryst also contain 
inclusions of calcite; the frequent occurrence of iron oxide with this 
calcite may indicate that the calcite fills cavities left by the solution of 
the iron oxide. 
The groundmass is composed chiefly of minute augite crystals of a 
pale pink or green color, closely compacted together. Magnetite in fine 
crystals is abundant, perhaps composing a third of the bulk of the 
groundmass. Small crystals of brown hornblende are common, but 
compose no considerable percentage of the mass. 
1 J. F. Kemp and V. F. Marsters, Amer. Geol., August, 1889. Also J. F. Kemp, 
Amer. Geol., March, 1890. 
