﻿TYPES 
  OF 
  THE 
  CAMBEIAN 
  BEDS. 
  215 
  

  

  Discussion. 
  

  

  Dr. 
  Hicks 
  congratulated 
  Prof. 
  Hull 
  on 
  the 
  change 
  which 
  this 
  

   and 
  other 
  recent 
  papers 
  of 
  his 
  showed 
  in 
  his 
  views 
  with 
  regard 
  

   to 
  the 
  pre-Cambrian 
  rocks. 
  It 
  was 
  quite 
  clear 
  that 
  the 
  acknowledg- 
  

   ment 
  of 
  a 
  pre-Cambrian 
  ridge 
  in 
  the 
  central 
  part 
  of 
  Scotland 
  up 
  to 
  a 
  

   late 
  period 
  in 
  the 
  Silurian 
  was 
  a 
  step 
  towards 
  the 
  view 
  of 
  Dr. 
  Hicks, 
  

   that 
  this 
  ridge, 
  which 
  was 
  at 
  the 
  close 
  of 
  the 
  Cambrian 
  the 
  highest 
  

   point, 
  and 
  the 
  last 
  submerged 
  and 
  overlapped 
  by 
  sediments, 
  has 
  

   become 
  reexposed 
  during 
  the 
  elevation 
  and 
  denudation 
  of 
  the 
  more 
  

   deeply 
  buried 
  adjoining 
  portion 
  of 
  the 
  old 
  floor 
  on 
  the 
  west 
  coast. 
  

   He 
  was 
  pleased 
  also 
  to 
  find 
  that 
  Prof. 
  Hull 
  now 
  accepted 
  the 
  

   pre-Cambrian 
  age 
  of 
  some 
  rocks 
  in 
  Wales 
  and 
  Ireland. 
  Dr. 
  

   Hicks 
  did 
  not, 
  however, 
  believe 
  . 
  that 
  the 
  Torridon 
  Sandstone 
  was 
  a 
  

   lacustrine 
  deposit, 
  more 
  than 
  other 
  sandstones 
  and 
  conglomerates 
  ; 
  

   but 
  he 
  believed 
  that 
  the 
  differences 
  in 
  the 
  materials 
  and 
  in 
  the 
  

   thicknesses 
  of 
  these 
  early 
  deposits 
  was 
  due 
  to 
  their 
  being 
  thrown 
  

   down 
  over 
  a 
  gradually 
  subsiding 
  area, 
  and 
  that 
  the 
  old 
  floor 
  was 
  in 
  

   a 
  very 
  uneven 
  condition 
  at 
  the 
  time. 
  He 
  agreed 
  with 
  the 
  main 
  line 
  

   of 
  depression 
  indicated 
  ; 
  and 
  it 
  was 
  the 
  one 
  he 
  had 
  himself 
  pointed 
  out 
  

   in 
  a 
  paper 
  read 
  to 
  the 
  Society 
  in 
  1875. 
  

  

  Prof. 
  Jttdd 
  said 
  that 
  Prof. 
  Hull 
  had 
  certainly 
  not 
  committed 
  

   himself 
  to 
  the 
  view 
  that 
  the 
  whole 
  of 
  the 
  existing 
  surface 
  of 
  Central 
  

   Scotland 
  was 
  to 
  be 
  regarded 
  as 
  belonging 
  to 
  the 
  Archaean. 
  

  

  Prof. 
  Hughes 
  pointed 
  out 
  that 
  there 
  was 
  some 
  confusion 
  between 
  

   overlap 
  and 
  unconformity. 
  He 
  thought 
  that 
  there 
  was 
  no 
  break 
  

   between 
  the 
  Cambrian 
  of 
  the 
  Survey 
  and 
  the 
  Silurian, 
  nor 
  at 
  the 
  

   base 
  of 
  the 
  Llandeilo 
  beds. 
  As 
  submergence 
  went 
  on, 
  the 
  newer 
  

   overlapped 
  the 
  older 
  and 
  lay 
  directly 
  on 
  that 
  portion 
  of 
  the 
  Archaean 
  

   rocks 
  which 
  happened 
  to 
  be 
  the 
  shore. 
  He 
  did 
  not 
  think 
  the 
  exact 
  

   position 
  of 
  the 
  Olclhamia 
  beds 
  was 
  established. 
  

  

  Prof. 
  Bonistey 
  said 
  that 
  Prof. 
  Hull, 
  in 
  still 
  claiming 
  the 
  Charnwood- 
  

   Forest 
  rocks 
  as 
  Cambrian, 
  appeared 
  to 
  be 
  inconsistent 
  with 
  himself, 
  

   since 
  a 
  main 
  argument 
  of 
  his 
  paper, 
  for 
  the 
  identification 
  of 
  beds, 
  

   was 
  lithological 
  similarity. 
  Further, 
  Prof. 
  Hull 
  had 
  assumed 
  

   that 
  the 
  Torridon 
  Sandstone 
  was 
  Cambrian. 
  Prof. 
  Bonney, 
  however, 
  

   thought 
  the 
  age 
  of 
  that 
  deposit 
  was 
  so 
  uncertain 
  that 
  this 
  was 
  an 
  

   unsafe 
  foundation 
  for 
  the 
  superstructure 
  of 
  an 
  argument. 
  

  

  Mr. 
  Httdlestojst 
  agreed 
  with 
  Prof. 
  Bonney, 
  and 
  thought 
  that 
  Prof. 
  

   Hull 
  was 
  driven 
  to 
  his 
  hypothesis 
  in 
  order 
  to 
  account 
  for 
  the 
  

   differences 
  in 
  the 
  two 
  basins. 
  He 
  thought, 
  also, 
  that 
  Dr. 
  Hicks 
  

   had 
  hardly 
  understood 
  Prof. 
  Hull's 
  map. 
  

  

  Mr. 
  Deew 
  also 
  thought 
  that 
  the 
  map 
  was 
  not 
  intended 
  to 
  refer 
  

   to 
  any 
  thing 
  post-Cambrian. 
  

  

  Mr. 
  Champeknowne 
  said 
  certainly 
  Prof. 
  Hull 
  at 
  York 
  spoke 
  of 
  

   the 
  Archsean 
  ridge 
  as 
  being 
  a 
  concealed 
  barrier, 
  and 
  did 
  not 
  suppose 
  

   it 
  to 
  consist 
  of 
  the 
  flaggy 
  gneisses 
  of 
  the 
  Central 
  Highlands. 
  

  

  Q.J.G.S. 
  tfo.150. 
  

  

  