SKIBINCIE! (OU? ZIAGIINA BUND) Nie MW abaliNal 29 
less well preserved specimens of a reddish brown or brilliant 
orange. Some of them are bent and show frayed ends. The 
plagioclase calls for no special remarks; twinning lamelle are 
common and the extinction angles of nearly 30° show that it isa 
bytownite, A few clear colorless augite crystals are also present. 
The rock from this locality has been described by R. Lepsius* 
_who states that the feldspar is orthoclase, does not mention the 
very abundant hornblende, states that the rock contains 60.21 per 
cent. of SiO,, and calls it a trachyte and the same rock as that 
which occurs at Kalamaki and Kolautziki, which last, as we shall 
see later is not the fact. He seems to have examined but one hand 
specimen, and that more or less weathered. My study of the 
rock zz situ and of the three specimens brought back with me 
does not bear out his view that it is a biotite-trachyte. The 
feldspar is all, with scarcely an exception, undoubtedly plagio- 
clase, hornblende is abundantly present, and the slightest com- 
parison of the specimens in my possession show that the Poros 
and the Kolautziki rocks are quite different. It is possible that 
Philippson may have collected a specimen quite different from 
mine, but if so it must be of a subordinate facies and not from 
the main mass of the Poros dome. In the few hours which we 
spent at Poros I went over most of the small hill and found only 
the rocks such as have been described above. The main body 
of the rock of Poros must then be with certainty regarded as a 
biotite-hornblende-andesite and not as a trachyte. 
Hornblende-Augite-Andesite—TVhe chief rocks of the central 
part of the island of Aigina belong to this group as it makes up 
the main part of Mts. Chondos, Pagoni, Dendros and Gaiapha, 
with probably many of their outlying spurs. 
Megascopically they differ considerably from the rocks to the 
north and south of them, showing a highly porphyritic structure 
with very numerous ‘phenocrysts, the latter being in some cases 
so abundant as to give the rock almost a granitic appearance. 
The phenocrysts are almost entirely plagioclase, with few horn- 
blende prisms and still fewer biotite tables, no quartz grains 
1 PHILIPPSON. Op. cit. p 604, cf ZIRKEL, Petr. p. 258. 
