﻿Geological 
  Societi/. 
  819- 
  

  

  results 
  are 
  reduced 
  to 
  July 
  1, 
  1903, 
  by 
  means 
  o£ 
  secular 
  change 
  

   data 
  derived 
  from 
  the 
  repetition 
  of 
  the 
  observations 
  at 
  a 
  selected 
  

   number 
  of 
  the 
  stations. 
  Details 
  as 
  to 
  the 
  geographical 
  position 
  of 
  

   the 
  stations 
  and 
  the 
  observed 
  values 
  of 
  the 
  magnetic 
  elements 
  are 
  

   reserved 
  for 
  Appendix 
  E 
  (215 
  pages). 
  In 
  the 
  body 
  of 
  the 
  work 
  

   are 
  a 
  number 
  of 
  tables 
  showing 
  the 
  values 
  of 
  the 
  magnetic 
  elements^ 
  

   for 
  July 
  1, 
  1903, 
  as 
  observed 
  and 
  as 
  calculated 
  by 
  methods 
  intended 
  

   to 
  eliminate 
  local 
  disturbances. 
  Deductions 
  are 
  made 
  as 
  to 
  the 
  

   disturbances, 
  "ridge" 
  and 
  "valley" 
  lines, 
  &c., 
  after 
  the 
  method 
  of 
  

   Eiicker 
  and 
  Thorpe, 
  and 
  these 
  are 
  illustrated 
  by 
  a 
  number 
  of 
  small 
  

   maps 
  in 
  the 
  text. 
  The 
  large 
  charts 
  at 
  the 
  end 
  of 
  the 
  volume 
  show 
  

   the 
  position 
  of 
  the 
  stations, 
  isogonal 
  lines, 
  isoclinal 
  lines, 
  and 
  iso- 
  

   magnetics 
  for 
  the 
  total 
  intensity 
  and 
  a 
  variety 
  of 
  its 
  components. 
  

   They 
  also 
  include 
  a 
  geological 
  map 
  prepared 
  by 
  Mr. 
  A. 
  W. 
  Eogers. 
  

  

  LXXXYIII. 
  Proceedings 
  of 
  Learned 
  Societies. 
  

  

  GEOLOGICAL 
  SOCIETY. 
  

  

  [Continued 
  from 
  p. 
  680.] 
  

  

  March 
  24th, 
  1909.— 
  Prof. 
  W. 
  J. 
  Sollas, 
  LL.D., 
  Sc.D., 
  F.E.S., 
  

   President, 
  in 
  the 
  Chair. 
  

  

  HE 
  followino: 
  communication 
  was 
  read 
  : 
  — 
  

  

  T 
  

  

  Glacial 
  Erosion 
  in 
  Xorth 
  Wales.' 
  By 
  Prof. 
  William 
  Morris- 
  

   Davis, 
  For.Corr.G.S. 
  

  

  An 
  excursion 
  around 
  Snowdon 
  in 
  September 
  1907, 
  followed 
  by 
  

   a 
  further 
  visit 
  in 
  1908, 
  led 
  the 
  author 
  to 
  the 
  conclusion 
  that 
  a. 
  

   large-featured, 
  round-shouldered, 
  full-bodied 
  mountain 
  of 
  pre-Glacial 
  

   time, 
  had 
  been 
  converted 
  by 
  erosion 
  during 
  the 
  Glacial 
  Period 
  — 
  

   and 
  chiefly 
  by 
  glacial 
  erosion 
  — 
  into 
  the 
  sharp-featured, 
  hollow 
  - 
  

   chested, 
  narrow-spurred 
  mountain 
  of 
  to-day. 
  The 
  peculiar 
  in- 
  

   difference 
  of 
  topographic 
  form 
  to 
  the 
  trend 
  of 
  formation-boundaries 
  

   and 
  the 
  insequent 
  stream-arrangement, 
  are 
  what 
  might 
  be 
  expected 
  

   as 
  the 
  result 
  of 
  prolonged 
  erosion 
  upon 
  a 
  mass 
  of 
  complicated 
  and 
  

   resistant 
  structure. 
  The 
  author 
  discusses 
  Ramsay's 
  theory 
  of 
  a 
  

   plain 
  of 
  marine 
  denudation, 
  and 
  is 
  of 
  opinion 
  that 
  the 
  upland 
  

   seems 
  to 
  deserve 
  classification 
  rather 
  with 
  peneplains 
  ; 
  he 
  suggests 
  

   for 
  it 
  a 
  Tertiary 
  date, 
  which 
  would 
  not 
  be 
  inconsistent 
  with 
  the 
  

   erosion 
  of 
  open 
  valleys 
  in 
  the 
  uplifted 
  peneplain 
  after 
  its 
  elevation, 
  

   and 
  argues 
  that 
  Snowdon 
  and 
  its 
  high 
  neighbours 
  had 
  a 
  relief 
  of 
  

   some 
  2000 
  feet 
  above 
  the 
  plain. 
  As 
  the 
  result 
  of 
  a 
  comparison 
  

   with 
  the 
  non-glaciated 
  regions 
  of 
  Devon, 
  it 
  is 
  considered 
  that 
  

   the 
  dissection 
  of 
  North 
  Wales 
  must 
  liave 
  been 
  somewhat 
  less 
  

   developed 
  in 
  pre-Glacial 
  times 
  than 
  in 
  Devon 
  to-day. 
  On 
  this 
  

   assumption 
  it 
  is 
  possible 
  to 
  make 
  a 
  tentative 
  restoration 
  of 
  the 
  

   pre-Glacial 
  form 
  of 
  Snowdon 
  : 
  subdued 
  mountains, 
  with 
  dome-like 
  

   summits 
  and 
  rounded 
  spurs, 
  drained 
  by 
  prevailingly 
  graded 
  streams 
  

   of 
  accordant 
  levels 
  at 
  their 
  junctions. 
  In 
  fact, 
  the 
  characters 
  were 
  

  

  