﻿540 
  MAJOR-GENERAL 
  C. 
  A. 
  M'MAHON 
  ON 
  THE 
  HORNBLENDE-SCHISTS 
  

  

  dyke. 
  Similarly 
  trie 
  two 
  granite 
  dykes 
  (G 
  1 
  , 
  G 
  2 
  ) 
  had 
  probably 
  an 
  

   underground 
  connexion 
  with 
  each 
  other 
  at 
  the 
  time 
  of 
  eruption. 
  

   This, 
  however, 
  is 
  a 
  mere 
  matter 
  of 
  inference, 
  as 
  owing 
  to 
  shingle 
  

   and 
  boulders 
  on 
  the 
  sea-shore 
  (not 
  to 
  mention 
  the 
  two 
  faults) 
  their 
  

   onward 
  course 
  cannot 
  be 
  traced, 
  nor 
  can 
  they 
  be 
  directly 
  connected 
  

   with 
  the 
  outcrop 
  of 
  the 
  " 
  granulitic 
  " 
  group 
  on 
  the 
  foreshore. 
  

  

  Fig. 
  12. 
  — 
  Diorite- 
  and 
  Granite-dykes 
  intrusive 
  in 
  Serpentine, 
  

   Kennack 
  Cove. 
  

  

  D 
  * 
  f 
  f 
  Q 
  s 
  G' 
  D> 
  

  

  S, 
  serpentine 
  ; 
  c, 
  c, 
  gabbro 
  ; 
  D 
  1 
  , 
  D 
  2 
  , 
  diorite 
  ; 
  G 
  1 
  , 
  G 
  2 
  , 
  granite 
  ; 
  /, 
  /, 
  faults. 
  

  

  At 
  G 
  2 
  , 
  D 
  2 
  we 
  see 
  the 
  diorite 
  and 
  granite 
  running 
  separate 
  courses 
  

   through 
  the 
  serpentine 
  ; 
  at 
  D 
  1 
  , 
  G 
  1 
  the 
  granite 
  has 
  followed 
  the 
  

   diorite, 
  and 
  for 
  a 
  short 
  distance 
  they 
  have 
  held 
  a 
  common 
  course. 
  

   This 
  circumstance, 
  taken 
  alone, 
  is 
  insufficient 
  to 
  justify 
  our 
  calling 
  

   D 
  1 
  , 
  G 
  1 
  an 
  intrusive 
  dyke 
  of 
  " 
  granulite." 
  

  

  Mr. 
  Somervail 
  states 
  that 
  at 
  the 
  west 
  end 
  of 
  Kennack 
  Cove 
  " 
  the 
  

   dykes 
  cutting 
  the 
  serpentine 
  are 
  seen 
  to 
  coalesce 
  with 
  the 
  ' 
  granu- 
  

   litic 
  ' 
  rocks 
  forming 
  the 
  foreshore." 
  My 
  last 
  visit 
  to 
  the 
  cove 
  was 
  

   made 
  at 
  a 
  time 
  particularly 
  favourable 
  for 
  observation. 
  It 
  was 
  at 
  

   low 
  water 
  at 
  spring- 
  tide, 
  and 
  recent 
  storms 
  had 
  swept 
  away 
  accumu- 
  

   lations 
  of 
  sand 
  and 
  shingle 
  to 
  such 
  an 
  extent 
  that 
  Mr. 
  Pox 
  saw 
  for 
  

   the 
  first 
  time 
  rocks 
  in 
  situ 
  that 
  on 
  every 
  previous 
  visit 
  had 
  been 
  buried 
  

   six 
  feet 
  deep 
  under 
  sand. 
  I 
  saw 
  that 
  the 
  porphyritic 
  diorite 
  had 
  

   intruded 
  profusely 
  into 
  ordinary 
  diorites 
  (presumably 
  the 
  dioritic 
  

   rocks 
  of 
  the 
  "granulitic" 
  group) 
  and 
  that 
  both 
  had 
  been 
  invaded 
  

   and 
  injected 
  by 
  intrusive 
  granite. 
  Granite-veins 
  may 
  be 
  seen 
  darting 
  

   about 
  in 
  all 
  directions, 
  crossing 
  and 
  recrossing 
  each 
  other 
  at 
  every 
  

   angle, 
  in 
  the 
  porphyritic 
  diorite 
  of 
  the 
  foreshore 
  ; 
  but 
  I 
  could 
  not 
  

   directly 
  connect 
  the 
  diorite 
  and 
  granite 
  of 
  the 
  foreshore 
  with 
  the 
  

   diorite 
  and 
  granite 
  of 
  the 
  serpentine-cliffs. 
  The 
  question 
  then 
  arises, 
  

   Are 
  they 
  portions 
  of 
  the 
  same 
  intrusions, 
  or 
  do 
  the 
  diorite 
  and 
  granite 
  

   in 
  the 
  cliffs 
  represent 
  intrusions 
  of 
  one 
  period, 
  and 
  the 
  diorite 
  and 
  

   granite 
  in 
  the 
  '• 
  granulitic 
  " 
  group 
  on 
  the 
  foreshore 
  those 
  of 
  another 
  

   age 
  ? 
  This 
  question 
  will 
  best 
  be 
  answered 
  after 
  the 
  consideration 
  of 
  

   two 
  other 
  sections. 
  

  

  On 
  the 
  occasion 
  of 
  my 
  last 
  visit 
  I 
  was 
  able, 
  thanks 
  to 
  Mr. 
  Fox's 
  

   able 
  guidance, 
  to 
  reach 
  a 
  very 
  interesting 
  spot, 
  only 
  exposed 
  for 
  a 
  

   short 
  time 
  at 
  spring-tide, 
  on 
  the 
  west 
  coast, 
  about 
  200 
  yards 
  east 
  of 
  

  

  