230 
ORGANIC  ROCKS  FROM  THE  NEW  HEBRIDES.  [May  1893, 
andesites.  Inclusions  of  glassy  matter  are  common.  The  augite 
is  monoclinic  and  faintly  pleochroic  in  greenish  and  brownish  tints. 
The  groundmass  is  thickly  crowded  with  minute,  ill-defined  grannies, 
and  contains  a  few  acicular  microlites  of  felspar.  Iron  ores  occur 
as  grains,  and  also  as  extremely  minute  granules  scattered  through 
the  groundmass. 
The  rock  is  an  augite-andesite.  Similar  rocks  are  common  in  the 
volcanic  regions  surrounding  the  Pacific. 
Tongoa  Island.  Lava  from  summit,  1584  feet  above  sea-level. — • 
A  dark  brown,  massive  rock,  containing  a  few  small  porphyritic 
felspars. 
Microscopic  characters. — The  porphyritic  constituents  consist  of 
basic  plagioclase,  often  honeycombed  with  inclusions,  pseudomorphs 
after  olivine,  and  augite  (scarce).  The  groundmass  is  an  aggregate 
of  lath-shaped  plagioclase,  granular  augite,  and  magnetite. 
The  rock  is  a  basalt. 
Makura  Island. — A  dark,  medium-grained,  massive,  crystalline 
rock. 
Microscopic  characters. — Basic  plagioclase,  a  pale  green  augite, 
dark  brown  pseudomorphs  after  olivine  (?),  and  opaque  iron-ores. 
The  rock  is  a  dolerite. 
Appendix  II. 
\_The  Microscopic  Structure  of  some  of  the  Organic  Bocks  from  the 
New  Hebrides.  By  George  Jennings  Hinde,  Ph.D.,  Y.P.G.S. 
Efate ,  Havannah  Harbour.  Prom  the  summit  of  a  peak  at  1274 
feet  above  sea-level. — The  rock  is  a  brownish,  porous  or  cavernous 
limestone,  consisting  principally  of  nullipore  ( Litliothamnion ),  appa¬ 
rently  in  its  position  of  growth,  with  a  few  foraminifera  ( Amphi - 
stegina)  and,  rarely,  fragments  of  polyzoa.  The  spaces  between  these 
organisms  are  partly  occupied  by  finely-comminuted  organic  debris 
cemented  by  calcite. 
Erradaka.  Prom  the  summit  of  the  island,  at  345  feet  above 
sea-level. — A  white,  hard  limestone  consisting  of  Litliothamnion 
and  corals,  apparently  in  their  position  of  growth.  The  interspaces 
are  filled  in  with  calcite.  The  minute  structure,  both  of  the  nulli¬ 
pore  and  of  the  corals,  is  well  preserved. 
Mallicolo  or  Malekula  Island ,  Sasun  Bay.  Prom  Bocky  Point, 
about  3  feet  above  sea-level. — A  brownish  compact  claystone,  in 
which  are  scattered  a  few  specimens  of  Globigerina.  The  matrix 
consists  of  very  minute  mineral  particles,  some  of  which  can  be 
recognized  as  volcanic.  The  slight  reaction  which  the  rock  gives 
with  acid  is  probably  due  to  the  foraminifera  present  therein. 
Prom  the  shores  of  the  same  Bay,  about  10  feet  above  sea-level, 
there  is  a  greyish,  granular,  soft  limestone-rock,  consisting  almost 
entirely  of  foraminifera,  with  a  few  fragments  of  nullipore,  cemented 
by  calcite.  The  greater  portion  of  the  foraminifera  belong  to 
Globigerina ,  and  there  are  also  forms  of  Amphistegina  and  Poly ~ 
stomella. 
