﻿ALDERNEY 
  AND 
  THE 
  CASQT7ETS. 
  385 
  

  

  some 
  grains 
  of 
  felspar, 
  so 
  far 
  as 
  can 
  be 
  seen 
  plagioclase, 
  but 
  as 
  a 
  

   rule 
  much 
  decomposed, 
  some 
  flakes 
  of 
  rich-brown 
  mica, 
  and 
  iron 
  

   oxides 
  as 
  usual. 
  The 
  rock 
  may 
  be 
  called 
  a 
  picrite, 
  though, 
  like 
  some 
  

   of 
  those 
  in 
  Anglesey 
  and 
  at 
  Little 
  Knot, 
  it 
  has 
  rather 
  too 
  much 
  

   felspar 
  to 
  be 
  a 
  typical 
  example. 
  

  

  This 
  occurrence 
  is 
  to 
  me 
  of 
  interest 
  as 
  being 
  my 
  first 
  case 
  from 
  

   these 
  islands 
  of 
  an 
  olivine-bearing 
  rock. 
  The 
  scyelite 
  from 
  Sark, 
  

   described 
  by 
  Prof. 
  Bonney 
  in 
  the 
  ' 
  Geol. 
  Mag/ 
  of 
  March 
  1889 
  (p. 
  109), 
  

   was 
  collected 
  at 
  a 
  later 
  elate. 
  

  

  4. 
  The 
  Grits. 
  

  

  The 
  igneous 
  rocks 
  hitherto 
  described 
  occupy 
  the 
  greater 
  part 
  of 
  

   Alderney, 
  but 
  not 
  the 
  whole. 
  A 
  divisional 
  line 
  (very 
  possibly 
  a 
  

   line 
  of 
  fault) 
  runs 
  north-east 
  and 
  nearly 
  straight 
  from 
  the 
  cliff-foot 
  

   opposite 
  L'Etac 
  de 
  la 
  Quoire 
  to 
  the 
  middle 
  of 
  Corblet's 
  Bay. 
  The 
  

   igneous 
  rocks 
  lie 
  west 
  of 
  this 
  ; 
  to 
  the 
  east 
  is 
  a 
  series 
  differing 
  from 
  

   everything 
  in 
  Guernsey, 
  Sark, 
  or 
  Herm, 
  a 
  sedimentary 
  series, 
  a 
  series 
  

   of 
  grits. 
  An 
  outlying 
  patch 
  of 
  these 
  about 
  | 
  mile 
  long 
  occurs 
  on 
  the 
  

   southern 
  cliffs, 
  opposite 
  the 
  islet 
  called 
  Coque 
  Lihou. 
  But 
  they 
  are 
  

   not 
  confined 
  to 
  Alderney. 
  Of 
  them 
  consist 
  Burhou 
  and 
  Ortac, 
  and 
  

   the 
  whole 
  of 
  the 
  Archipelago 
  between 
  the 
  Swinge 
  and 
  the 
  Ortac 
  

   Channel 
  ; 
  of 
  them 
  also 
  consist 
  the 
  Casquets, 
  and 
  all 
  their 
  satellite 
  

   reefs. 
  Beds 
  absolutely 
  undistinguishable 
  I 
  discovered 
  on 
  the 
  mainland 
  

   of 
  France, 
  at 
  Omonville 
  la 
  Eogue, 
  east 
  of 
  Cap 
  La 
  Hague 
  *. 
  "With 
  

   these 
  last 
  M. 
  Bigot 
  identifies 
  some 
  beds 
  which 
  he 
  calls 
  " 
  steaschistes 
  

   noduleux 
  " 
  at 
  Tourlaville, 
  east 
  of 
  Cherbourg; 
  and 
  having 
  seen 
  both, 
  

   I 
  entirely 
  agree 
  with 
  him. 
  From 
  the 
  Casquets 
  on 
  the 
  west 
  to 
  

   Tourlaville 
  in 
  the 
  east 
  is 
  a 
  distance 
  of 
  thirty 
  miles, 
  accordingly 
  the 
  

   series 
  we 
  are 
  considering 
  is 
  one 
  of 
  no 
  little 
  extent 
  and 
  importance. 
  

  

  Both 
  Macculloch 
  and 
  Ansted 
  were 
  unable 
  to 
  visit 
  Burhou 
  or 
  the 
  

   Casquets. 
  The 
  pilot-boat 
  which 
  conveyed 
  me 
  to 
  the 
  Casquets 
  took 
  

   me 
  within 
  50 
  feet 
  of 
  Ortac, 
  and 
  also 
  threaded 
  devious 
  channels 
  of 
  

   the 
  reefs, 
  so 
  as 
  to 
  give 
  me 
  a 
  good 
  view 
  of 
  the 
  greater 
  number 
  ; 
  on 
  a 
  

   later 
  visit 
  I 
  was 
  able 
  to 
  land 
  on 
  Burhou. 
  

  

  There 
  are 
  ample 
  means 
  for 
  studying 
  the 
  group, 
  since, 
  besides 
  the 
  

   clean 
  surfaces 
  shown 
  along 
  the 
  shores 
  and 
  in 
  the 
  reefs, 
  there 
  is 
  the 
  

   range 
  of 
  quarries 
  now 
  or 
  formerly 
  worked 
  to 
  obtain 
  materials 
  for 
  

   the 
  breakwater. 
  The 
  group 
  is 
  thus 
  seen 
  to 
  be 
  a 
  series 
  of 
  sand- 
  

   stones 
  and 
  grits, 
  consisting 
  primarily 
  of 
  quartz, 
  but 
  with 
  an 
  ad- 
  

   mixture 
  of 
  felspathic 
  material, 
  which, 
  though 
  variable 
  in 
  quantity, 
  

   is 
  always 
  too 
  much 
  for 
  a 
  quartzite. 
  Occasionally 
  there 
  are 
  thin 
  

   beds 
  of 
  a 
  micaceous 
  sandstone. 
  The 
  colour, 
  though 
  generally 
  a 
  

   greyish 
  white 
  or 
  cream-colour, 
  has 
  often 
  a 
  pinker 
  tinge, 
  reaching 
  

   even 
  to 
  a 
  deep 
  rusty 
  red 
  ; 
  as, 
  for 
  instance, 
  in 
  a 
  quarry 
  north-west 
  of 
  

   Essex 
  Castle. 
  Every 
  variety 
  occurs 
  of 
  fineness 
  and 
  coarseness, 
  

   ranging 
  from 
  the 
  above-mentioned 
  mudstones 
  through 
  sandstones 
  

   and 
  coarser 
  grits 
  up 
  to 
  constituent 
  grains 
  J 
  of 
  an 
  inch 
  across. 
  As 
  

  

  * 
  M. 
  Bigot 
  had 
  previously 
  made 
  the 
  same 
  identification 
  in 
  the 
  paper 
  referred 
  

   to 
  above. 
  

  

  Q. 
  J. 
  G. 
  S. 
  No. 
  179. 
  2 
  f 
  

  

  