Tol.  49.] 
THE  PETBOGBAPHY  OE  THE  ISLAND  OF  CAPBAJA. 
131 
The  accompanying  map  indicates  roughly  the  results  of  my 
geological  observations  during  a  three  weeks’  stay  on  the  island 
in  the  year  1S92,  but  is  not  put  forth  as  complete.  The  short 
time  at  my  disposal  rendered  it  impossible  to  follow  out  in  detail 
every  andesitic  outflow,  or  to  trace  all  the  dykes  with  which  the 
western  coast  in  particular  is  seamed.  The  main  object  of  my  visit 
was  petrographical ;  and  I  must  leave  the  special  geological  details 
to  some  future  observer  who  may  have  more  time  at  his  command. 
I  may  remark  here  that  I  have  purposely  omitted  a  number  of 
small  patches  of  breccia  inland :  in  a  map  on  this  scale  they 
would  hardly  appear  so  large  as  a  pin’s  head,  and  their  insertion 
would  in  all  probability  only  tend  to  create  confusion. 
2.  Geological  Peatuees  of  the  Island. 
Without  entering  into  a  detailed  description  of  the  geology  of 
Capraja,  it  will  perhaps  be  advisable  to  mention  some  of  its  most 
interesting  features — and  firstly  the  southern  end.  Here  seems 
to  have  been  situated  a  distinct  centre  of  volcanic  activity,  whose 
products  are  younger  in  age  and  more  basic  in  character  than  the 
rest  of  the  Caprajan  rocks.  Its  various  phases  may  be  briefly 
summarized  as  follows  :  — 
(a)  Breccias,  which  in  Cala  il  Moreto  seem  to  rest  unconform- 
ably  on  the  northern  breccias  (the  strata  are  inclined  at  about  45° 
from  the  vertical  at  the  line  of  contact). 
( h )  One  or  two  lava-streams  of  anamesite. 
(c)  Highly  scoriaceous  ejectamenta ;  these  in  Cala  Rossa  are 
piled  up  in  such  a  way  as  to  give  the  impression  that  here  was  a 
small  cone  or  parasitical  crater. 
(cl)  Wore  than  forty  thin  lava-streams ;  each  one  separated  from 
the  other  by  a  few  inches  of  scoriae  similar  to  those  of  phase  (c). 
(e)  A  mass  of  anamesite,  which  has  forced  its  way  up,  cutting 
through  the  cone,  and  sending  out  apophyses  into  the  lava-streams. 
It  is  worthy  of  note  that  these  lava-streams  everywhere  lie 
horizontally,  even  when  in  contact  with  the  cone.  This  would  seem  to 
indicate  that  they  must  have  flowed  from  a  distance.  They  cannot 
have  issued  from  the  same  vent  as  the  scoriae ;  for  otherwise  there 
would  be  more  evidence  of  interbedding  than  is  the  case,  and  the 
lava- streams  would  have  the  same  inclination  as  the  beds  of 
scoriae.  Prom  the  fact  that  the  lava-streams  seem  thicker  in  Cala  il 
Aloreto  than  in  Cala  Rossa  I  am  inclined  to  locate  this  vent  to  the 
westward. 
The  unconformity  above  mentioned  in  Cala  Rossa  proves  that 
the  southern  breccias  are  younger  than  the  northern.  Absolute  proof 
that  they  are  also  younger  than  the  andesite  is  wanting ;  we  have, 
however,  evidence  of  a  less  positive  character.  There  are  a 
number  of  faults  at  this  end  of  the  island,  whose  upthrows  lie  to 
the  south.  If,  as  is  reasonable  to  suppose,  this  upheaval  of  the 
southern  end  was  caused  by  the  formation  of  the  cone  or  outburst 
of  anamesite,  then  we  must  also  conclude  the  latter  to  be  younger 
k  2 
