﻿1XV1 
  PROCEEDINGS 
  OP 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  [May 
  1897, 
  

  

  a 
  fairly 
  connected 
  history 
  of 
  the 
  main 
  results 
  which 
  have 
  been 
  

   obtained 
  during 
  an 
  extended 
  period 
  might 
  not 
  be 
  altogether 
  

   unacceptable 
  to 
  the 
  Fellows 
  of 
  the 
  Society. 
  

  

  After 
  describing 
  the 
  structure 
  and 
  order 
  of 
  the 
  rocks 
  in 
  various 
  

   areas, 
  Sir 
  R. 
  Murchison 
  in 
  the 
  edition 
  quoted 
  proceeds 
  to 
  say 
  : 
  — 
  

   ' 
  Observation 
  has 
  now 
  taught 
  us 
  of 
  what 
  materials 
  the 
  fundamental 
  

   rocks 
  of 
  different 
  countries 
  consist. 
  In 
  Scandinavia, 
  particularly 
  in 
  

   the 
  central 
  and 
  northern 
  parts 
  of 
  Norway, 
  there 
  is 
  every 
  reason 
  to 
  

   believe 
  that, 
  as 
  in 
  British 
  North 
  America, 
  Bohemia, 
  and 
  the 
  North- 
  

   west 
  of 
  Scotland, 
  crystalline 
  rocks 
  of 
  Laurentian 
  age 
  underlie 
  all 
  the 
  

   deposits 
  to 
  which 
  the 
  terms 
  Cambrian 
  and 
  Silurian 
  can 
  be 
  applied. 
  

   In 
  Bohemia, 
  however, 
  as 
  in 
  Great 
  Britain 
  and 
  portions 
  of 
  North 
  

   America, 
  the 
  lowest 
  zone 
  containing 
  Silurian 
  remains 
  (" 
  Zone 
  pri- 
  

   mordiale 
  " 
  of 
  Barrande) 
  is 
  underlain 
  by 
  very 
  thick 
  basements 
  of 
  

   earlier 
  sedimentary 
  accumulations 
  of 
  Cambrian 
  age, 
  whether 
  sand- 
  

   stone, 
  schist, 
  or 
  slate, 
  which, 
  though 
  occasionally 
  not 
  more 
  crystalline 
  

   than 
  the 
  fossiliferous 
  beds 
  above 
  them, 
  have 
  as 
  yet 
  afforded 
  only 
  rare 
  

   indications 
  of 
  former 
  beings. 
  This 
  is 
  the 
  important 
  fact 
  to 
  which 
  

   attention 
  is 
  now 
  directed 
  ; 
  for 
  in 
  such 
  instances 
  the 
  geologist 
  

   appeals 
  to 
  strata 
  which 
  have 
  undergone 
  little 
  or 
  no 
  alteration. 
  

   In 
  this 
  enormous 
  pile 
  or 
  series 
  of 
  early 
  subaqueous 
  sediment, 
  com- 
  

   posed 
  of 
  mud, 
  sand, 
  or 
  pebbles, 
  the 
  successive 
  bottoms 
  or 
  shores 
  of 
  

   a 
  former 
  sea, 
  all 
  of 
  which 
  had 
  been 
  derived 
  from 
  pre-existing 
  

   rocks, 
  he 
  has 
  been 
  unable, 
  after 
  many 
  years 
  of 
  research, 
  to 
  detect 
  

   more 
  than 
  a 
  very 
  few 
  traces 
  of 
  former 
  creatures. 
  But 
  lying 
  upon 
  

   them, 
  and 
  therefore 
  evolved 
  after 
  them, 
  other 
  strata 
  succeed, 
  in 
  

   which 
  clear 
  relics 
  of 
  a 
  primeval 
  ocean 
  are 
  discernible 
  ; 
  whilst 
  these 
  

   again 
  are 
  everywhere 
  succeeded 
  by 
  deposits 
  containing 
  many 
  

   organic 
  remains 
  of 
  a 
  more 
  advanced 
  nature. 
  In 
  this 
  way, 
  evi- 
  

   dences 
  have 
  been 
  fairly 
  obtained 
  to 
  show 
  that 
  the 
  rocks 
  bearing 
  

   the 
  name 
  of 
  Laurentian 
  and 
  Cambrian 
  constitute 
  the 
  sterile 
  natural 
  

   bases 
  of 
  the 
  rich 
  deposits 
  termed 
  Silurian.' 
  

  

  It 
  will 
  of 
  course 
  be 
  understood 
  that 
  the 
  term 
  Cambrian 
  was 
  

   restricted 
  by 
  Sir 
  R. 
  Murchison 
  to 
  the 
  rocks 
  which 
  were 
  older 
  

   than 
  the 
  Lingula-Fl&ga, 
  including 
  the 
  Menevian 
  beds, 
  in 
  which 
  

   Salter 
  and 
  myself 
  had 
  previously 
  discovered 
  a 
  very 
  rich 
  fauna 
  in 
  

   Wales. 
  The 
  actual 
  line 
  of 
  division 
  which 
  was 
  adopted 
  in 
  the 
  

   colouring 
  of 
  the 
  Survey 
  maps 
  was 
  first 
  traced 
  out 
  at 
  St. 
  David's 
  

   by 
  Sir 
  A. 
  Ramsay 
  in 
  1841, 
  who 
  refers 
  to 
  the 
  fact 
  in 
  vol. 
  iii. 
  

   Mem. 
  Geol. 
  Surv. 
  (1866) 
  p. 
  7, 
  as 
  follows 
  : 
  — 
  ' 
  In 
  the 
  same 
  year, 
  at 
  

   St. 
  David's, 
  I 
  traced 
  a 
  provisional 
  line 
  between 
  the 
  black 
  and 
  the 
  

  

  