﻿240 
  

  

  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  [Mar. 
  23, 
  

  

  the 
  one 
  to 
  the 
  other. 
  Even 
  of 
  these 
  genera 
  that 
  do 
  transgress 
  the 
  

   line, 
  the 
  Primordial 
  and 
  Silurian 
  rocks 
  contain 
  distinct 
  species 
  ; 
  while 
  

   the 
  intervention 
  of 
  the 
  whole 
  of 
  the 
  Tremadoc 
  rocks, 
  containing 
  a 
  

   remarkable 
  assemblage 
  of 
  fossils 
  distinct 
  from 
  both, 
  easily 
  explains 
  

   the 
  meaning 
  of 
  this 
  wide 
  difference 
  in 
  the 
  fossils, 
  and 
  indicates 
  that 
  

   the 
  epochs 
  of 
  the 
  Llandeilo 
  and 
  Lingula-flags 
  were 
  separated 
  by 
  an 
  

   enormous 
  period 
  of 
  time. 
  

  

  Fig. 
  2. 
  — 
  Geological 
  Sketch-map 
  of 
  Porth-y-Rhaw 
  Harbour. 
  

  

  

  9 
  <2 
  

  

  Cj 
  

  

  N.N.E. 
  

   Mill. 
  

  

  Fig. 
  3. 
  — 
  Section 
  of 
  the 
  East 
  Side 
  of 
  Porth-y-Rhaw. 
  

   (By 
  H. 
  Hicks, 
  Esq.) 
  

  

  Hedge. 
  Camp. 
  

  

  S.S.W. 
  

  

  a. 
  Cambrian 
  rocks. 
  

   h. 
  Transition 
  beds. 
  

  

  e 
  d 
  e 
  f 
  g 
  

  

  c, 
  c, 
  g. 
  Lower 
  Lingula-flags 
  * 
  Cavern. 
  

  

  (fossiliferous). 
  d, 
  f. 
  Volcanic 
  tuff. 
  

  

  In 
  addition 
  to 
  the 
  general 
  section 
  on 
  page 
  239, 
  which 
  is 
  not 
  true 
  

   to 
  scale, 
  I 
  have 
  given 
  above 
  a 
  measured 
  map 
  and 
  section 
  of 
  the 
  fossili- 
  

  

  