﻿ON 
  THE 
  NORTHERN 
  SLOPES 
  OP 
  CADER 
  IDRIS. 
  425 
  

  

  or 
  more 
  across. 
  In 
  thoir 
  cracked 
  and 
  scoriaceous 
  interior 
  calcite 
  has 
  

   developed 
  freely, 
  so 
  much 
  so 
  as 
  to 
  suggest 
  at 
  first 
  the 
  presence 
  of 
  

   ejected 
  limestone 
  blocks. 
  After 
  boiling 
  this 
  crystalline 
  alteration- 
  

   product 
  in 
  hydrochloric 
  acid, 
  the 
  residue 
  yields 
  little 
  of 
  interest, 
  

   quartz 
  and 
  a 
  few 
  brown 
  flakes 
  of 
  mica 
  being 
  the 
  only 
  identifiable 
  

   minerals. 
  

  

  Prof. 
  Ramsay 
  * 
  has 
  commented 
  on 
  the 
  difficulty 
  of 
  distinguishing 
  

   between 
  the 
  compacter 
  intrusive 
  sheets, 
  themselves 
  often 
  scoriaceous, 
  

   and 
  the 
  soft 
  grey-green 
  ash-beds. 
  On 
  the 
  broken 
  slopes 
  between 
  

   Llyn-y-Gafr 
  and 
  Llyn-y-Gader 
  the 
  cleavage 
  of 
  the 
  district 
  has 
  affected 
  

   some 
  of 
  the 
  igneous 
  layers, 
  while 
  every 
  crack 
  and 
  hollow 
  is 
  filled 
  

   with 
  secondary 
  calcite. 
  Hence 
  the 
  rocks 
  afford, 
  when 
  considered 
  in 
  

   the 
  laboratory, 
  excellent 
  hand-specimens 
  of 
  " 
  Schalstein 
  ; 
  " 
  but 
  to 
  

   designate 
  them 
  by 
  such 
  a 
  name 
  is 
  to 
  admit 
  that 
  we 
  are 
  baffled 
  in 
  

   the 
  field. 
  

  

  Some 
  of 
  the 
  undoubted 
  ash-beds, 
  even 
  when 
  soft 
  and 
  calcareous, 
  

   are 
  divided 
  by 
  jointing 
  into 
  spike-like 
  columns 
  ; 
  while 
  the 
  compacter 
  

   and 
  more 
  metamorphosed 
  ashes 
  at 
  the 
  base 
  of 
  the 
  cliff 
  of 
  Mynydd 
  

  

  Fig. 
  2. 
  — 
  Beds 
  beneath 
  the 
  Eurite 
  on 
  Mynydd 
  Moel. 
  

  

  1. 
  Black 
  Slates, 
  with 
  cleavage 
  practically 
  coincident 
  with 
  bedding. 
  

  

  2. 
  Altered 
  flinty 
  slates, 
  with 
  well-marked 
  bedding. 
  

  

  3. 
  Greenish 
  softer 
  laver. 
  

  

  4. 
  Bedded 
  Ash, 
  altered 
  and 
  jointed 
  into 
  columns, 
  

  

  5. 
  The 
  Massive 
  Eurite. 
  

  

  Moel 
  imitate 
  closely 
  the 
  columnar 
  eurite 
  of 
  the 
  wall 
  (fig. 
  2). 
  The 
  fine 
  

   layers 
  of 
  the 
  bedding, 
  however, 
  frequently 
  weather 
  out, 
  and 
  give 
  a 
  

   clue 
  to 
  the 
  origin 
  of 
  the 
  rock 
  ; 
  while 
  microscopic 
  examination 
  removes 
  

   many 
  of 
  the 
  difficulties 
  presented 
  by 
  the 
  porcellaneous 
  varieties 
  f 
  . 
  

  

  * 
  Memoirs 
  of 
  theGeol. 
  Surv. 
  of 
  Gt. 
  Britain, 
  vol. 
  iii. 
  2nd 
  edition, 
  p. 
  31. 
  

  

  t 
  Mr. 
  J. 
  Clifton 
  Ward 
  discussed 
  the 
  microscopic 
  characters 
  of 
  somewhat 
  

   similar 
  ashes 
  in 
  his 
  paper 
  on 
  the 
  " 
  Structure 
  of 
  Ancient 
  and 
  Modern 
  Volcanic 
  

   Rocks," 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  xxxi. 
  (1875) 
  p. 
  403. 
  

  

  