Vol.  49.] 
OF  THE  ISLAHD  OP  CAPRAJA. 
133 
sists  of  alternating  breccias  and  andesites,  with  a  small  dyke  of 
grey  andesite  near  the  headland.  It  is  interesting  to  notice  that 
the  inclination  of  the  main  fault-lines  here  coincides  appreciably, 
not  only  with  the  small  dyke  at  this  point,  but  also  with  most  of 
the  other  dykes  along  the  western  coast.  And  it  is  not  improbable 
that  these,  dykes — which  are  petrographically  so  similar — all  owe 
their  origin  to  the  same  period,  viz.  that  of  the  development  of  the 
plane  of  weakness  corresponding  with  the  faults. 
Prom  Punta  della  Saccatoja  all  round  the  northern  coast  as  far  the 
harbour  of  Capraja,  there  is  perhaps  less  to  arrest  the  attention  of 
the  geologist.  Thick  masses  of  andesite  rest  on  breccia,  or  project 
into  the  sea.  Apophyses  and  ramifications  of  andesite  have  forced 
their  way  into  the  breccia ;  and  in  places  the  latter  has  been  eaten 
into  by  the  waves,  forming  caverns.  Worthy  of  notice  are  the  thin 
bands  and  patches  of  bright-red  and  yellow  tuff  which  occur  spo¬ 
radically  between  the  andesite  and  the  breccia.  One  band  runs 
uninterruptedly  from  La  Mortola  to  Scalo  della  Teja,  and  another 
along  the  coast  by  Punta  delle  Scaffe.  Other  patches  may  be 
found  just  south  of  Punta  della  Pica,  and  under  Mounts  Campanile 
and  Majone. 
The  profile  sketched  on  the  following  page  will  suffice  to  give  an 
idea  of  the  geological  structure  of  the  eastern  coast,  southwards 
from  the  harbour  of  Capraja  as  far  as  Cala  Rossa. 
As  to  the  field  geology  iuland,  there  is  not  very  much  to  be  said. 
Almost  everywhere  andesite  may  be  found,  and  in  the  valley- 
bottoms  are  seen  patches  of  the  underlying  breccia,  especially  in  the 
Vado  del  Porto. 
Except  for  what  may  be  called  a  small  parasitical  cone  at  Punta 
del  Zenobito,  as  before  mentioned,  there  are  no  traces  of  any  centre 
of  volcanic  activity  to  be  found  on  the  island.  An  ‘  extinct  crater  ’ 
is  marked  on  the  Admiralty  chart ;  but  there  is  no  confirmatory 
evidence  to  be  gathered  on  the  spot.  I  suspect  that  the  so-called 
4  crater 7  is  merely  the  saddle  between  the  peaks  of  Monte  delle 
Cancelle  and  Monte  Porcone.  The  rocks  here  are  as  compact  as 
anywhere  on  the  island  ;  that  would  hardly  be  the  case  if  we 
were  dealing  with  an  extinct  crater.  The  fact  that  the  underlying 
breccias  at  the  northern  end  of  the  island  dip  northward  and 
appear  to  strike  eastward,  while  at  the  southern  end  they  dip 
southward,  would  seem  to  indicate  that  the  chief  centre  of  activity 
lay  west  of  the  centre  of  the  island.  Moreover,  the  fact  that  the 
beds  of  tuff  are  both  thin  and  sparse  goes  to  prove  that  the  present 
island  is  a  part  of  the  outermost  rim  of  the  parent  volcano — other¬ 
wise  we  should  expect  to  find  the  tuffs  thicker  and  more  frequent. 
Evidence  of  a  more  definite  character  I  was  unable  to  obtain. 
3.  Macroscopic  Characters  of  the  Rocks. 
Macroscopically  the  rocks  of  Capraja  present  great  differences, 
in  texture,  in  colour,  and  in  porphyritic  constituents  -r  but,  as  will 
be  seen  later,  they  may  be  classified  microscopically  under  two 
heads,  namely  : — andesite  and  anamesite. 
