﻿214 
  PROF. 
  E. 
  HULL 
  ON 
  THE 
  TWO 
  BEITISfl. 
  

  

  Fig. 
  2. 
  — 
  Diagram 
  showing 
  Present 
  and 
  Original 
  Positions 
  of 
  Strata. 
  

  

  X 
  X. 
  Approximate 
  sea-level 
  or 
  horizontal 
  line. 
  

  

  A 
  Z. 
  Present 
  base 
  of 
  the 
  Lower 
  Silurian 
  beds. 
  

  

  A' 
  Z'. 
  Original 
  position 
  of 
  ditto. 
  

  

  B 
  B. 
  Present 
  basement 
  floor 
  of 
  the 
  Cambrian 
  sandstone. 
  

  

  B' 
  P/. 
  Original 
  position 
  of 
  ditto. 
  

  

  It 
  will 
  thus 
  be 
  seen 
  that 
  the 
  floor 
  of 
  the 
  Cambrian 
  sandstones, 
  

   formed 
  of 
  Laurentian 
  rocks, 
  must 
  have 
  originally 
  sloped 
  upwards 
  

   towards 
  the 
  central 
  Highlands, 
  and 
  in 
  that 
  direction 
  probably 
  

   formed 
  a 
  ridge 
  during 
  a 
  portion, 
  or 
  the 
  whole 
  of 
  the 
  period 
  in 
  which 
  

   the 
  Cambrian 
  beds 
  were 
  being 
  deposited. 
  This 
  ridge 
  would 
  form 
  

   the 
  eastern 
  margin 
  while 
  that 
  of 
  the 
  outer 
  Hebrides 
  would, 
  as 
  sug- 
  

   gested 
  by 
  Professor 
  Ramsay, 
  form 
  the 
  western 
  margin, 
  of 
  the 
  basin 
  

   in 
  which 
  the 
  Cambrian 
  beds 
  of 
  the 
  Scottish 
  type 
  were 
  deposited. 
  

  

  On 
  the 
  other 
  side 
  of 
  this 
  ridge, 
  which 
  embraced 
  the 
  Scottish 
  

   Highlands 
  and 
  the 
  north 
  and 
  west 
  of 
  Ireland, 
  the 
  Cambrian 
  beds 
  

   of 
  the 
  Welsh 
  and 
  Irish 
  type 
  were 
  deposited 
  in 
  a 
  much 
  larger 
  basin*, 
  

   into 
  which 
  the 
  ocean 
  waters 
  gained 
  access 
  at 
  intervals, 
  if 
  indeed, 
  as 
  

   seems 
  to 
  me 
  more 
  probable, 
  they 
  did 
  not 
  prevail 
  throughout 
  the 
  

   entire 
  period 
  f. 
  

  

  What 
  may 
  have 
  been 
  the 
  eastern 
  and 
  southern 
  limit 
  to 
  the 
  Cam- 
  

   brian 
  beds 
  of 
  the 
  Hiberno- 
  Cambrian 
  type 
  it 
  is 
  less 
  easy 
  to 
  indicate. 
  

   The 
  floor 
  of 
  these 
  beds 
  crops 
  up 
  in 
  Bohemia, 
  and 
  probably 
  in 
  Central 
  

   France 
  and 
  Brittany 
  ; 
  but 
  it 
  would 
  be 
  hazardous 
  to 
  assert 
  that 
  the 
  

   old 
  crystalline 
  rocks 
  of 
  these 
  regions 
  were 
  never 
  covered 
  by 
  the 
  Cam- 
  

   brian 
  beds 
  of 
  the 
  Ardennes. 
  

  

  Thus 
  it 
  is 
  that 
  we 
  are 
  in 
  possession 
  of 
  two 
  kinds 
  of 
  evidence, 
  per- 
  

   fectly 
  distinct, 
  but 
  both 
  pointing 
  to 
  the 
  conclusion 
  with 
  which 
  I 
  

   commenced, 
  viz. 
  that 
  of 
  the 
  existence 
  of 
  two 
  distinct 
  basins 
  in 
  the 
  

   Cambrian 
  period, 
  one 
  lacustrine 
  and 
  the 
  other 
  marine, 
  lying 
  on 
  either 
  

   side 
  of 
  a 
  ridge 
  of 
  Archaean 
  metamorphic 
  rocks. 
  

  

  * 
  Prof. 
  Kamsay, 
  judging 
  by 
  their 
  mineral 
  characters, 
  considers 
  that 
  the 
  Cam- 
  

   brian 
  beds 
  of 
  Wales 
  were 
  deposited 
  in 
  proximity 
  to 
  land 
  (Phys. 
  G-eol. 
  Great 
  

   Brit. 
  5th 
  edit. 
  p. 
  67). 
  

  

  t 
  I 
  include 
  in 
  the 
  second 
  (Hiberno-Cambrian) 
  type 
  of 
  Cambrian 
  beds 
  the 
  

   rocks 
  of 
  Charnwood 
  Forest, 
  which 
  were 
  originally 
  referred 
  by 
  Jukes 
  to 
  this 
  for- 
  

   mation 
  ; 
  and 
  I 
  have 
  not 
  seen 
  sufficient 
  eridence, 
  notwithstanding 
  all 
  that 
  has 
  been 
  

   since 
  written, 
  that 
  he 
  was 
  in 
  error. 
  

  

  