﻿ALDERNEY 
  AND 
  THE 
  CASQJJETS. 
  383 
  

  

  granite 
  and 
  the 
  normal 
  darker 
  rock 
  may 
  be 
  seen 
  sharply 
  defined 
  in 
  

   the 
  bay 
  south 
  of 
  JBibette 
  Head. 
  

  

  A 
  granite 
  similar 
  to 
  the 
  pink 
  decomposing 
  form 
  of 
  this 
  occurs 
  in 
  

   outcrops 
  on 
  the 
  southern 
  cliffs 
  ; 
  as, 
  for 
  instance, 
  on 
  a 
  slope 
  north 
  of 
  

   the 
  islet 
  called 
  Coque 
  Lihou, 
  where 
  a 
  pink 
  and 
  a 
  bluish 
  rock 
  may 
  be 
  

   seen 
  in 
  intrusive 
  contact. 
  Some 
  of 
  this 
  pink 
  rock 
  recalls 
  the 
  L'Eree 
  

   gneiss 
  in 
  Guernsey, 
  and 
  itself 
  shows 
  under 
  the 
  microscope 
  signs 
  of 
  

   disturbance. 
  A 
  specimen 
  collected 
  from 
  somewhere 
  on 
  these 
  cliffs 
  

   of 
  this 
  circle 
  shows 
  a 
  very 
  large 
  orthoclase 
  crystal 
  | 
  of 
  an 
  inch 
  long, 
  

   such 
  as 
  characterizes 
  the 
  granite 
  of 
  Cap 
  La 
  Hague, 
  on 
  the 
  neigh- 
  

   bouring 
  coast 
  of 
  France 
  ; 
  such 
  crystals 
  also 
  characterize 
  a 
  rock 
  at 
  

   L'Eree. 
  The 
  perpendicular 
  cliffs 
  of 
  this 
  coast, 
  even 
  more 
  inaccessible 
  

   than 
  those 
  of 
  Sark, 
  swept 
  at 
  their 
  base 
  by 
  some 
  of 
  the 
  most 
  violent 
  

   tides 
  in 
  Europe, 
  offer 
  serious 
  obstacles 
  to 
  examination. 
  

  

  The 
  only 
  locality 
  where 
  I 
  have 
  noticed 
  crush-structure 
  on 
  a 
  scale 
  

   visible 
  to 
  the 
  eye 
  is 
  on 
  the 
  shore 
  under 
  Eort 
  Tourgis. 
  Here 
  are 
  

   seen 
  many 
  dark 
  node-like 
  patches, 
  some 
  narrow 
  and 
  lenticular, 
  and 
  

   of 
  these 
  the 
  axes 
  lie 
  with 
  a 
  certain 
  amount 
  of 
  parallelism, 
  while 
  the 
  

   rock 
  itself 
  has 
  a 
  rude 
  appearance 
  of 
  a 
  structure 
  which 
  is 
  directed 
  

   N.E. 
  to 
  S.W. 
  and 
  vertical. 
  

  

  The 
  general 
  appearance 
  of 
  the 
  normal 
  Alderney 
  rock 
  recalls 
  the 
  

   diorites 
  and 
  syenites 
  of 
  Guernsey, 
  and 
  some 
  specimens 
  can 
  scarcely 
  

   be 
  distinguished 
  from 
  some 
  of 
  the 
  quartzose 
  varieties 
  of 
  that 
  group. 
  

   But 
  the 
  abundance 
  of 
  mica, 
  and 
  the 
  smaller 
  amount 
  of 
  hornblende, 
  

   would 
  connect 
  it 
  rather 
  with 
  the 
  granites 
  of 
  Jethou 
  and 
  Sark. 
  The 
  

   microscopic 
  study 
  has 
  resulted 
  in 
  a 
  similar 
  opinion. 
  

  

  3. 
  Minor 
  Igneous 
  Rocks. 
  

  

  The 
  minor 
  intrusive 
  rocks 
  of 
  Alderney 
  do 
  not 
  equal 
  in 
  interest 
  

   and 
  variety 
  those 
  of 
  Guernsey, 
  still 
  less 
  do 
  they 
  rival 
  the 
  singu- 
  

   larities 
  which 
  Jersey 
  presents. 
  Nevertheless, 
  they 
  are 
  numerous 
  

   and 
  interesting. 
  Most 
  of 
  the 
  families 
  found 
  in 
  the 
  other 
  islands 
  

   are 
  represented. 
  Granites 
  occur 
  here 
  and 
  there 
  : 
  one, 
  for 
  instance, 
  

   about 
  a 
  yard 
  thick 
  in 
  the 
  sides 
  of 
  a 
  chasm 
  in 
  the 
  crags 
  north 
  of 
  

   Port 
  Albert. 
  Pink 
  micro-crystalline 
  quartz-felspar 
  dykes 
  are 
  most 
  

   abundant 
  ; 
  the 
  western 
  headlands 
  are 
  cut 
  by 
  many 
  so 
  parallel 
  that 
  

   an 
  observer 
  from 
  a 
  boat 
  might 
  even 
  think 
  the 
  rock 
  stratified, 
  and 
  

   so 
  abundant, 
  that 
  I 
  estimated 
  them 
  to 
  occupy 
  more 
  than 
  one 
  tenth 
  

   of 
  the 
  cliff-face. 
  They 
  appear 
  to 
  be 
  identical 
  with 
  the 
  Guernsey 
  

   quartz-felspar 
  dykes 
  (Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xl. 
  p. 
  416). 
  

  

  Compacter 
  pink 
  dykes 
  occur 
  from 
  Braye 
  Harbour 
  westwards, 
  

   which 
  may 
  represent 
  the 
  pink 
  felsites 
  of 
  Guernsey. 
  A 
  remarkable 
  

   purple 
  intrusion, 
  several 
  feet 
  thick, 
  may 
  be 
  followed 
  some 
  hundreds 
  

   of 
  feet 
  along 
  the 
  shore 
  west 
  of 
  the 
  causeway 
  leading 
  to 
  Eort 
  Clonque, 
  

   and 
  ultimately 
  appears 
  to 
  transform 
  itself 
  into 
  a 
  variety 
  of 
  the 
  last- 
  

   named 
  group. 
  Under 
  the 
  microscope 
  this 
  shows 
  a 
  very 
  compact 
  

   matrix 
  speckled 
  with 
  opacite, 
  and 
  containing 
  small 
  crystals 
  of 
  

   felspar. 
  The 
  matrix 
  exhibits 
  a 
  minute 
  devitrification, 
  and 
  the 
  rock 
  

   might 
  perhaps 
  be 
  called 
  a 
  porphyrite. 
  Basic 
  intrusions 
  are 
  less 
  

  

  