SKETCH OF “GINA AND METHANA. 43 
brown groundmass, the base being colorless glass which is filled 
with an infinite number of grains of ‘dust’? and small microlites, 
generally short, stout and rarely long (as usual). These micro- 
lites are chiefly augite and hypersthene, little plagioclase being 
represented. Besides these microlitic constituents there are small 
lathes and rectangular sections of plagioclase, small augite and 
hypersthene crystals and some magnetite. 
The hornblende phenocrysts in these rocks are yellowish 
brown in color, and often altered on the outer edges to an augite 
opacite aggregate. Hypersthene crystals are common, but not 
as large asin the preceding type. In one specimen, which shows 
signs of decomposition, they are either entirely or partially 
changed to rusty or reddish brown secondary products. The 
plagioclase, whose sections are generally rhombic or rectangular, 
is similar to that of the preceding. A few clear, corroded and 
cracked quartz grains are seen. 
The third type is only represented by the Panagia specimen, 
which also differs from the others megascopically. The ground- 
mass here seems to be chiefly microfelsite with little or no glass. 
In the microfelsitic base are many minute magnetite grains, and 
flecks and microlites of feldspar, part of which may be ortho- 
clase, as indicated by the parallel extinctions. As the per- 
centage of K,O is small, however, it seems more probable that 
this is labradorite, or oligoclase.. Hypersthene is not abundant 
in the groundmass. 
The phenocrysts are not numerous and consist of brown horn- 
blende, altered as before described, with some plagioclase and 
hypersthene, which call for no special comment. There are 
numerous spots of tridymite, which seem to be an essential and 
not a secondary constituent. 
It must be remarked that the position of this Panagia rock is 
an uncertain one on the whole, and I would call it a trachyte 
were its percentage of K,O not so very much lower than that of 
any other trachyte analysis. 
Liotite-Dacite.—This dacite, whose occurrence is described on 
page 806, Vol. II., is only found on the mainland, and all the 
