SKETCH OF 47GINA AND METHANA. 143 
prior to that of the consolidation at a great depth of the magma 
forming the segregations. This seems at first sight to be at vari- 
ance with the fact already noted in the case of the hornblende- 
augite-andesites, that many of the small groundmass crystals are 
still fresh ; so that we seem driven to the conclusion that not 
only are the conditions under which the alteration may take place 
extremely variable, but that after hornblende has been formed 
and altered, a subsequent formation of fresh hornblende may 
occur. The final stage of the process is similar in physical 
structure, though chemically and genetically quite different from 
the final stage of the uralitization of augite, which we know to be 
due to the action of moisture, and it might be said that instead 
of hornblende being the stable form of augite, augite is the stable 
form of hornblende, at least of the basaltic variety. 
In one of the segregations of Mt. Pagoni accessory olivine is 
present in large colorless crystals’, of a bright yellow on the 
edges. While the crystals are of irregular shape they have been 
formed, as was to have been expected, prior to the formation of 
the hornblende or augite, both of which are xenomorphic with 
respect to it. Few of these segregations differ from the type 
just described. One from Mt. Pagoni seems to have solidified 
rather more rapidly than the above, as the groundmass is a color- 
less glass base, hyalopilitic through the presence of numerous 
plagioclase microlites. In this segregation the bearded horn- 
blende pseudomorphs are especially well shown, and the plagio- 
clase phenocrysts, which are very clear and show few twinning 
lamella, are much more numerous. The other (from Mt. 
Gaiapha) seems to have been originally very similar, but the 
groundmass is replaced by colorless calcite, which entirely 
replaces the glass and acts as mesostasis for the large crystals. 
Neither the hornblende nor the plagioclase phenocrysts of this 
segregation nor the surrounding rock in general show signs of 
decomposition, and it is possible that the calcite is rather a pri- 
mary than a secondary constituent. 
The second variety of segregations differs from those just 
described in two important respects; the hornblende is green and 
