﻿ON 
  THE 
  NORTHERN 
  SLOPES 
  OF 
  CADER 
  IDRIS. 
  439 
  

  

  Tremadoc 
  fossils 
  which 
  had 
  been 
  discovered 
  were 
  rather 
  Upper 
  than 
  

   Lower 
  Tremadoc. 
  He 
  had 
  published 
  a 
  paper 
  in 
  which 
  he 
  maintained 
  

   that 
  the 
  so-called 
  Upper 
  Tremadoc 
  rocks 
  of 
  Caernarvonshire 
  should 
  be 
  

   classed 
  as 
  Arenig. 
  In 
  these 
  there 
  was 
  a 
  considerable 
  amount 
  of 
  

   volcanic 
  material. 
  It 
  was 
  yet 
  doubtful 
  how 
  frequently 
  volcanic 
  

   outbursts 
  had 
  occurred 
  in 
  the 
  region 
  ; 
  the 
  Harlech 
  Beds 
  of 
  the 
  

   Harlech 
  anticlinal 
  and 
  the 
  Menevian 
  beds 
  contained 
  materials 
  

   indicative 
  of 
  contemporaneous 
  volcanic 
  action, 
  and 
  similar 
  conditions 
  

   to 
  those 
  of 
  North 
  Wales 
  occurred 
  in 
  the 
  St. 
  David's 
  region. 
  The 
  same 
  

   was 
  the 
  case 
  in 
  the 
  succeeding 
  series. 
  In 
  the 
  rocks 
  of 
  the 
  Arenig 
  

   mountains 
  there 
  was 
  a 
  climax 
  to 
  the 
  volcanic 
  action. 
  

  

  Prof. 
  Blake 
  hinted 
  at 
  the 
  occurrence 
  of 
  lavas 
  in 
  the 
  Cader 
  Idris 
  

   district, 
  from 
  evidence 
  derived 
  from 
  an 
  examination 
  of 
  loose 
  blocks. 
  

   Mr. 
  Rutley 
  commented 
  on 
  the 
  difficulty 
  of 
  distinguishing 
  between 
  

   lavas 
  and 
  ashes 
  after 
  induration. 
  He 
  referred 
  to 
  Daubeny's 
  obser- 
  

   vations 
  on 
  submarine 
  volcanoes 
  ; 
  that 
  author 
  considered 
  such 
  lavas 
  

   could 
  never 
  be 
  glassy 
  and 
  never 
  vesicular. 
  Nevertheless, 
  such 
  had 
  

   actually 
  been 
  found 
  so 
  formed. 
  

  

  Mr. 
  Cole 
  replied 
  to 
  Dr. 
  Hicks 
  that 
  there 
  were 
  undoubted 
  tuffs 
  at 
  

   tke 
  lower 
  levels 
  of 
  the 
  mountain. 
  Their 
  age 
  must 
  be 
  left 
  to 
  future 
  

   investigation 
  into 
  the 
  stratigraphical 
  geology 
  of 
  the 
  area 
  ; 
  but 
  the 
  

   statements 
  made 
  in 
  the 
  paper 
  were 
  founded 
  on 
  prevailing 
  opinion. 
  It 
  

   was 
  possible 
  that 
  the 
  Tremadoc 
  Beds 
  might 
  be 
  faulted 
  out. 
  The 
  

   old 
  Survey 
  sections 
  were 
  fairly 
  accurate. 
  The 
  scoriaceous 
  rocks 
  were 
  

   sometimes 
  intrusive, 
  though 
  many 
  of 
  the 
  tuffs 
  were 
  also 
  scoriaceous. 
  

   Nowhere 
  on 
  Cader 
  Idris 
  were 
  there 
  such 
  coarse 
  tuffs 
  as 
  in 
  the 
  

   Snowdoiian 
  district. 
  

  

  