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MESSES.  H.  FOX  AND  J.  J.  H.  TEALL  ON 
[May  1893, 
for  every  tongue  of  serpentine  into  schist  there  is  a  corresponding 
tongue  of  schist  iuto  serpentine.  The  relations  of  the  two  rocks 
are  further  complicated  by  small  faults,  some  of  which  are  repre¬ 
sented  in  the  Map.  As  these  are  in  no  way  remarkable,  it  is 
unnecessary  to  do  more  than  refer  to  them. 
We  have  examined  other  localities  on  the  western  coast  where 
hornblende,  schist,  and  serpentine  are  in  juxtaposition,  and  in  no 
case  have  we  found  appearances  which  were  incompatible  with  the 
view  suggested  by  the  facts  above  described. 
III.  Basic  Dykes,  and  the  Conveesion  of  Doleeite  into 
Hoenblende-schist. 
In  concluding  this  part  of  our  paper,  we  desire  to  offer  some 
additional  remarks  on  the  porphyritic  and  non-porphyritic  dykes 
which  are  so  well  seen  in  this  part  of  the  coast.  Starting  from 
Ogo  Dour  on  the  north,  and  walking  over  the  boulders  and  rocks 
to  Potstone  Point,  at  low  water,  we  find  both  coarse  and  fine-grained 
porphyritic  epidiorites 1  cutting  the  hornblende-schist  and  them¬ 
selves  passing  into  hornblende-schist,  which  closely  resembles  that 
of  the  district.  Extremely  coarse-grained  gabbros,  or  gabbro- 
pegmatites  as  they  may  be  termed,  also  occur.  Crossing  a  ridge, 
we  reach  the  narrow  gully  on  the  northern  side  of  Potstone  Point. 
The  cliffs  on  the  north-east  are  formed  of  well-banded  serpentine 
with  a  south-westerly  dip  of  about  60°,  and  the  face  of  the  cliff  is 
determined  by  the  slope  of  the  banding.  The  floor  of  the  gully  is 
formed  of  porphyritic  epidiorite  and  dolerites,  which  are  here 
intimately  interblended  with  white  and  grey,  banded,  saussuritic 
rocks. 
The  porphyritic  epidiorite  varies,  from  the  massive  variety 
with  well-marked  idiomorphic  crystals  of  felspar,  to  a  fissile  variety 
in  which  the  crystals  appear  merely  as  narrow  white  streaks. 
Every  intermediate  phase  may  be  observed  within  a  few  feet.  The 
south-western  face  of  the  gully  is  formed  in  its  lower  part  of  por¬ 
phyritic  epidiorite  with  large  and  very  numerous  porphyritic 
felspars,  and  in  its  upper  part  of  a  more  compact  non-porphyritic 
variety  of  the  same  rock.  The  junction  between  the  intrusive 
igneous  rock  and  the  schist  of  the  country  may  be  observed  near 
the  top.  Two  gabbro-dykes  containing  pseudophite,  from  6  to  12 
inches  thick,  traverse  the  serpentine  on  the  north-eastern  side  of 
the  gully.  The  head  of  the  gully  is  crossed  by  a  small  fault,  pro¬ 
ducing  a  shift  of  about  10  feet  in  one  of  the  gabbro-dykes. 
We  now  come  to  Potstone  Point.  Here  the  porphyritic  epidio¬ 
rite,  containing  numerous  large  white  crystals  of  felspar,  has  on  its 
western  side  a  ‘  chilled  ’  margin  in  which  very  few  crystals  are 
seen.  The  dykes  c  and  cl,  and  the  coarse  porphyritic  epidiorite 
P  D,  which  is  merely  a  thicker  dyke  of  the  same  age  and  character, 
1  We  use  the  term  ‘  epidiorite/  because  there  is  reason  to  believe  that  all 
these  rocks  were  once  dolerites.  Some  portions  are  dolerites  even  now,  but  it 
is  impossible  to  distinguish  the  dolerite  from  the  epidiorite  in  the  field. 
