﻿422 
  MESSRS. 
  G. 
  A. 
  J. 
  COLE 
  AKD 
  A. 
  V. 
  JENNINGS 
  

  

  28. 
  The 
  Northern 
  Slopes 
  o/Cader 
  Idris. 
  By 
  Grenville 
  A. 
  J. 
  Cole, 
  

   Esq., 
  F.G.S., 
  and 
  A. 
  Vattghan 
  Jennings, 
  Esq., 
  F.L.S. 
  (Read 
  

  

  April 
  17, 
  1889.) 
  

  

  I. 
  The 
  General 
  Features 
  of 
  the 
  Surface 
  (Fig. 
  1). 
  

  

  Since 
  the 
  year 
  1829, 
  when 
  Mr. 
  Aikin 
  published 
  in 
  the 
  Transactions 
  

   of 
  the 
  Geological 
  Society 
  of 
  London 
  his 
  " 
  Notes 
  on 
  the 
  Geological 
  

   Structure 
  of 
  Cader 
  Idris 
  " 
  *, 
  much 
  attention 
  has 
  been 
  called 
  to 
  the 
  

   stratigraphy 
  of 
  the 
  district, 
  while 
  the 
  maps 
  and 
  memoir 
  of 
  the 
  

   Government 
  Survey 
  have 
  guided 
  numerous 
  workers 
  and 
  have 
  pointed 
  

   out 
  the 
  relics 
  of 
  eruptive 
  activity 
  in 
  which 
  Merionethshire 
  abounds. 
  

  

  Mr. 
  Aikin, 
  while 
  describing 
  the 
  general 
  features 
  presented 
  by 
  the 
  

   rock-masses 
  as 
  they 
  succeed 
  one 
  another 
  on 
  the 
  mountain-side, 
  notes 
  

   also 
  many 
  of 
  their 
  mineral 
  peculiarities, 
  combining 
  in 
  his 
  paper 
  the 
  

   breadth 
  of 
  view 
  and 
  accuracy 
  of 
  detail 
  that 
  characterize 
  so 
  markedly 
  

   the 
  works 
  of 
  many 
  early 
  observers, 
  pioneers 
  whose 
  knowledge 
  was 
  

   largely 
  dependent 
  upon 
  personal 
  researches 
  in 
  the 
  field. 
  

  

  Sir 
  A. 
  C. 
  Ramsay, 
  in 
  the 
  first 
  and 
  second 
  editions 
  of 
  his 
  " 
  Geology 
  

   of 
  North 
  Wales 
  " 
  t, 
  deals 
  fully 
  with 
  the 
  physical 
  structure 
  and 
  rela- 
  

   tions 
  of 
  the 
  slate-beds, 
  the 
  ashes, 
  and 
  the 
  intrusive 
  sheets 
  that 
  rise 
  

   tier 
  upon 
  tier 
  above 
  Dolgelley. 
  We 
  have 
  thought, 
  however, 
  that 
  

   some 
  further 
  investigation 
  into 
  the 
  nature 
  of 
  the 
  eruptions 
  in 
  this 
  

   area, 
  and 
  the 
  characters 
  of 
  their 
  products 
  at 
  successive 
  stratigraphical 
  

   horizons, 
  might 
  even 
  now 
  add 
  somewhat 
  to 
  the 
  interest 
  with 
  which 
  

   all 
  geologists, 
  in 
  common 
  with 
  all 
  lovers 
  of 
  scenery, 
  regard 
  the 
  

   heights 
  of 
  Cader 
  Idris. 
  The 
  publication 
  of 
  the 
  six-inch 
  Ordnance 
  

   map, 
  though 
  too 
  late 
  to 
  be 
  of 
  service 
  in 
  our 
  earlier 
  observations, 
  

   has 
  enabled 
  us 
  to 
  ascertain 
  the 
  height 
  of 
  many 
  points 
  with 
  precision, 
  

   and 
  to 
  better 
  estimate 
  the 
  thickness 
  of 
  the 
  various 
  groups 
  of 
  

   rocks 
  j. 
  

  

  Despite 
  the 
  fine 
  valley 
  descending 
  to 
  Tal-y-llyn, 
  and 
  the 
  cliffs 
  of 
  

   Cwm-ammarch 
  and 
  Pen-coed, 
  the 
  northern 
  slopes 
  of 
  the 
  mountain 
  

   are 
  by 
  far 
  the 
  most 
  attractive 
  from 
  a 
  structural 
  and 
  geological 
  point 
  

   of 
  view. 
  The 
  strata 
  and 
  their 
  intercalated 
  igneous 
  material 
  dip 
  to 
  

   the 
  south 
  and 
  to 
  the 
  south-east, 
  forming 
  one 
  flank 
  of 
  Sedgwick's 
  

   " 
  Merionethshire 
  anticlinal 
  ; 
  " 
  and 
  their 
  denuded 
  edges 
  form 
  a 
  series 
  

   of 
  bold 
  escarpments 
  that 
  face 
  the 
  Harlech 
  plateaux 
  on 
  the 
  north. 
  

   Aided 
  by 
  these 
  exposures, 
  Prof. 
  Sedgwick, 
  in 
  a 
  memorable 
  paper 
  in 
  

   1847 
  §, 
  traced 
  the 
  succession 
  of 
  " 
  fossiliferous 
  slates 
  " 
  and 
  " 
  con- 
  

  

  * 
  Trans. 
  Geol. 
  Soc. 
  ser. 
  2, 
  vol. 
  ii. 
  p. 
  273. 
  

  

  t 
  Memoirs 
  of 
  Geol. 
  Survey 
  of 
  Gt. 
  Britain, 
  vol. 
  iii. 
  2nd 
  edition, 
  1881. 
  

  

  J 
  We 
  have 
  followed 
  this 
  map 
  in 
  the 
  spelling 
  of 
  names, 
  in 
  the 
  hope 
  of 
  

   securing 
  uniformity. 
  

  

  § 
  " 
  On 
  the 
  Classification 
  of 
  the 
  Fossiliferous 
  Slates 
  of 
  North 
  Wales, 
  Cumber- 
  

   land, 
  Westmoreland, 
  and 
  Lancashire," 
  Quart. 
  Journ. 
  Geol. 
  Soc. 
  vol. 
  iii. 
  pp. 
  133- 
  

   1,64. 
  

  

  