144 THE JOURNAL OF GEOLOGY. 
the groundmass is vitreous. The groundmass is composed 
largely of a perfectly clear and colorless glass base, showing no 
perlitic cracks, in which lie small water-clear plagioclase crystals 
and skeleton crystals, either forked at each end or forming a hol- 
low square, with some small hornblendes, apatite needles and, in 
the case of the Methana segregations, some small hypersthene 
prisms. Round vesicles or gas pores are also not uncommon. 
In a few cases this base is brownish in streaks and. patches, the 
color being due to the presence of minute brown dust grains, and 
associated with these (in one specimen ) are very many straight 
black trichites or minute club-shaped microlites often arranged 
radially. One segregation from Kakoperato, which is especially 
rich is these brown streaks, contains also many rounded 
granospherites, which have little or no action on polarized light. 
These frequently contain, as seen only under the highest powers, 
extremely small straight black trichites, in fan-shaped aggre- 
gates. As in the preceding variety there is no evidence of flow 
structure either in the groundmass or among the phenocrysts. 
The hornblende phenocrysts are in the shape of needle-like 
crystals or prisms, elongated parallel to ¢. When embedded in 
the groundmass they are automorphic, but are on the other hand 
generally xenomorphic in respect to the plagioclase, though the 
converse also occurs. Their color is, it has been said, olive 
green, and they show no signs of alteration. An exception to 
this must be noted inthe case of one Kaimeni segregation, where 
they are yellowish brown and generally have an altered border.* 
This specimen shows the dust and black trichites in the ground- 
mass in the greatest perfection, and the small hypersthene prisms 
are almost entirely altered to a brown or black substance. Large 
phenocrysts of colorless augite occur in small quantity in one or 
two of the specimens, but they are rare and call for no special 
mention except that they are always xenomorphic in respect to 
the hornblende. 
The plagioclase phenocrysts are all automorphic, generally 
tThis enclosure, it must be remarked, is in a scoriaceous lava which shows many 
signs of decomposition, perhaps due to fumarole action. 
