132 
MR.  H.  EMMORS  OR  THE  PETROGRAPHY  [May  1893* 
than  the  andesite,  for  the  faults  run  through  breccia  and  andesite 
alike,  proving  them  to  have  been  in  situ  when  the  southern  erup¬ 
tion  took  place.  < 
No  evidence  could  be  gathered  regarding  the  relative  ages  ot 
the  anamesite  and  the  andesite-dykes  of  the  western  coast,  because 
nowhere  do  they  come  in  contact  with  each  other.  From  a  chemical 
point  of  view  such  evidence  would  have  been  particularly  interesting. 
The  next  feature  of  interest  is  a  stretch  of  about  1  kilometre 
(|  mile)  on  the  western  coast,  including  the  Seno  della  Peruccia 
and  Cala  del  Eucciso.  Here  the  breccia  and  overlying  andesite 
have  been  pierced  by  dykes  of  grey  andesite,1  the  salbands  of  which 
have  developed  a  columnar  structure  perpendicular  to  the  walls  of 
the  dyke.  These  salbands  also  offer  greater  resistance  to  weather¬ 
ing  than  the  centre  of  the  dyke,  a  circumstance  undoubtedly  due  to 
the  larger  quantity  of  porphyritic  constituents  in  the  latter. 
In  Eucciso  Bay  we  have  three  dykes.  The  main  dyke,  starting 
opposite  the  Scoglio  del  Eucciso,  cuts  through  the  headland  and 
reappears  in  the  Seno  della  Peruccia.  Thence  it  is  easily  traceable 
with  the  naked  eye,  thanks  to  its  salband-columns,  up  over  the 
ridge  of  Le  Penne  in  a  north-north-easterly  direction.  ^Measured 
with  a  clinometer,  from  the  boat,  it  seems  to  strike  IS  .N.E.  and 
S.S.W.,  and  to  have  a  dip  of  58°  to  the  N.N.W. 
The  second  dyke,  which  I  consider  to  be  an  offshoot  of  the  larger 
one,  strikes  almost  due  north-and-south,  and  dips  40°  E.  It  is  first 
easily  visible  on  the  northern  side  of  Eucciso  Bay  ;  appears  again  on 
the  southern  side ;  and,  cutting  through  the  headland  of  II  Fondo, 
reappears  for  the  last  time  in  the  angle  of  II  Fondo  Bay.  The  third 
dyke  starts  in  the  northern  indentation  of  Eucciso  Bay,,  and  is 
traceable  a  short  distance  inland  in  an  east-south-easterly  direction, 
A  small  apophysis  is  visible,  high  up  in  the  cliff,  near  by. 
Following  the  coast  northward  from  here  for  about  1  kilometre 
(|  mile)  along  cliffs  consisting  mostly  of  breccia,  we  come  to  a 
little  bay  bounded  on  the  north  by  Punta  della  Manza.  Here 
again  we  meet  with  two  dykes  of  grey  andesite  in  the  breccia, 
besides  other  masses  of  the  same  rock  in  different  parts  of  the  bay. 
The  first  dyke  runs  northward  through  the  headland  and  appears  in 
the  angle  on  the  other  side,  but  seems  to  go  no  farther.  It  resembles 
very  closely,  both  in  the  direction  of  its  course  and  angle  of  inclina¬ 
tion,  the  second  dyke  already  described  in  Eucciso  Bay. 
The  second  Punta  della  Manza  dyke,  situated  a  little  to  the  east¬ 
ward  of  the  first,  is  traceable  only  a  short  distance  inland.  The 
two  islets  and  the  masses  opposite  them  on  the  shore  may  belong  to 
a  third  dyke  ;  petrographically,  at  any  rate,  they  belong  to  these 
dykes,  and  not  to  the  original  andesite-eruptions. 
From  Punta  della  Manza  the  coast  bends  slightly  eastwaid, 
showing  sections  of  breccia  with  thin  beds  and  injected  masses  of 
andesite.  On  reaching  Cala  della  Saccatoja  we  come  upon  a  fine 
example  of  complex  faulting  on  a  miniature  scale.  The  bluff  con- 
1  In  order  to  distinguish  the  massive  andesite  of  the  island  from  die 
andesite-dykes,  which  are  younger,  I  shall  call  the  latter  ‘  grey  andesite,  as 
that  colour  is  macroscopically  its  chief  characteristic. 
