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  Geological 
  Society 
  : 
  — 
  

  

  December 
  1st. 
  — 
  Dr. 
  Henry 
  Hicks, 
  F.R.S., 
  President, 
  

   in 
  the 
  Chair. 
  

   The 
  following 
  communications 
  were 
  read 
  : 
  — 
  

  

  1. 
  'A 
  Revindication 
  of 
  the 
  Llanberis 
  Unconformity.' 
  By 
  the 
  

   Rev. 
  J. 
  F. 
  Blake, 
  M.A., 
  F.G.S. 
  

  

  In 
  a 
  paper 
  published 
  in 
  the 
  Quarterly 
  Journal 
  of 
  the 
  Society 
  

   for 
  1893, 
  the 
  author 
  of 
  the 
  present 
  paper 
  maintained 
  that 
  certain 
  

   conglomerates 
  and 
  associated 
  rocks 
  occurring 
  for 
  some 
  distance 
  

   north-east 
  and 
  south-west 
  of 
  Llanberis, 
  which 
  had 
  hitherto 
  been 
  

   considered 
  to 
  lie 
  below 
  the 
  workable 
  slates 
  of 
  the 
  Cambrian 
  rocks 
  

   of 
  that 
  area, 
  were 
  in 
  reality 
  unconformable 
  deposits 
  of 
  later 
  date 
  

   than 
  those 
  slates. 
  In 
  the 
  year 
  1 
  894 
  a 
  paper 
  appeared 
  in 
  the 
  same 
  

   Journal, 
  in 
  which 
  the 
  authors 
  maintained 
  that 
  in 
  no 
  case 
  which 
  

   had 
  been 
  examined 
  could 
  any 
  valid 
  evidence 
  be 
  found 
  in 
  favour 
  of 
  

   the 
  alleged 
  unconformity, 
  and 
  that 
  in 
  one 
  (on 
  the 
  north-east 
  side 
  of 
  

   Llyn 
  Padaru) 
  which 
  they 
  supposed 
  to 
  afford 
  the 
  most 
  satisfactory 
  

   proof 
  of 
  it, 
  the 
  facts 
  were 
  wholly 
  opposed 
  to 
  the 
  notion. 
  

  

  The 
  present 
  paper 
  is 
  a 
  reply 
  to 
  these 
  authors, 
  in 
  which 
  their 
  

   objections, 
  founded 
  on 
  general 
  considerations, 
  on 
  field 
  observations, 
  

   and 
  on 
  microscopic 
  examination 
  of 
  rock-specimens, 
  are 
  discussed, 
  

   and 
  the 
  author 
  gives 
  the 
  results 
  of 
  further 
  observations 
  on 
  the 
  

   rocks 
  of 
  the 
  district. 
  The 
  Moel 
  Tryfaen 
  sections, 
  and 
  those 
  on 
  each 
  

   side 
  of 
  Llyn 
  Padarn 
  in 
  the 
  Llanberis 
  district 
  are 
  considered, 
  and 
  

   he 
  maintains 
  that 
  the 
  post-Llanberis 
  (using 
  this 
  term 
  in 
  the 
  sense 
  

   of 
  being 
  after 
  the 
  deposition 
  of 
  the 
  main 
  workable 
  slates) 
  age 
  

   of 
  the 
  conglomerates 
  which 
  are 
  under 
  discussion 
  is 
  established 
  ; 
  

   though 
  the 
  more 
  he 
  considers 
  the 
  correlation 
  of 
  these 
  conglomerates 
  

   with 
  the 
  Bronllwyd 
  Grits 
  the 
  less 
  he 
  likes 
  it, 
  and 
  as 
  far 
  as 
  the 
  

   stratigraphy 
  is 
  concerned, 
  they 
  may 
  be 
  much 
  newer, 
  — 
  their 
  age 
  is 
  

   at 
  present 
  an 
  open 
  question 
  ; 
  but 
  of 
  their 
  unconformable 
  position 
  

   he 
  has 
  no 
  doubt. 
  

  

  2. 
  ' 
  The 
  Geology 
  of 
  Lambay 
  Island, 
  Co. 
  Dublin.' 
  By 
  Messrs. 
  C. 
  

   I. 
  Gardiner, 
  M.A., 
  F.G.S., 
  and 
  S. 
  H. 
  Reynolds, 
  M.A., 
  F.G.S. 
  

  

  The 
  authors, 
  who 
  have 
  previously 
  described 
  the 
  neighbouring 
  

   district 
  of 
  Portraine 
  (Quart. 
  Journ. 
  Geol. 
  Soc, 
  Dec. 
  1897), 
  undertook 
  

   an 
  examination 
  of 
  this 
  island, 
  with 
  the 
  intention 
  of 
  comparing 
  the 
  

   rocks 
  with 
  those 
  of 
  Portraine, 
  and 
  of 
  investigating 
  the 
  nature 
  of 
  the 
  

   rock 
  familiar 
  to 
  geologists 
  under 
  the 
  name 
  of 
  ' 
  Lambay 
  porphyry.' 
  

   The 
  sedimentary 
  rocks 
  are 
  similar 
  to 
  some 
  of 
  those 
  of 
  Portraine, 
  and 
  

   are 
  of 
  Middle 
  or 
  Upper 
  Bala 
  age. 
  Associated 
  with 
  them 
  are 
  pyro- 
  

   clastic 
  rocks 
  and 
  andesitic 
  lava 
  flows, 
  some 
  of 
  the 
  lavas 
  having 
  flowed 
  

   beneath 
  the 
  sea. 
  The 
  sediments 
  and 
  volcanic 
  rocks 
  were 
  exposed 
  

   to 
  denudation, 
  and 
  a 
  conglomerate 
  composed 
  of 
  their 
  fragments 
  

   was 
  accumulated 
  round 
  the 
  volcano. 
  The 
  ' 
  Lambay 
  porphyry,' 
  

   which 
  has 
  been 
  determined 
  as 
  a 
  diabase-porphyry 
  by 
  Dr. 
  von 
  Lasaulx, 
  

   is 
  partly 
  intrusive 
  in 
  the 
  other 
  rocks, 
  but 
  has 
  in 
  places 
  come 
  to 
  the 
  

   surface 
  as 
  a 
  lava-flow. 
  

  

  Petrographical 
  descriptions 
  of 
  the 
  various 
  rocks 
  are 
  given 
  by 
  the 
  

   authors. 
  

  

  