﻿566 
  DR. 
  W. 
  ERASER 
  HUME 
  ON 
  [Dec. 
  1897, 
  

  

  Formerly 
  there 
  appears 
  to 
  have 
  also 
  been 
  an 
  important 
  exposure 
  

   at 
  Tamlaght, 
  near 
  Coagh, 
  Portlock 
  recording 
  it 
  thus 
  : 
  — 
  ' 
  The 
  lower 
  

   portion 
  of 
  the 
  chalk 
  is 
  here 
  a 
  very 
  curious 
  pebbly 
  or 
  conglomeratic 
  

   bed, 
  with 
  much 
  green 
  matter, 
  but 
  still 
  containing 
  many 
  fossils 
  of 
  

   the 
  lower 
  chalk 
  or 
  grey 
  marl, 
  such 
  as 
  Ammonites 
  leivesiensis, 
  Nau- 
  

   tilus 
  elegans, 
  var., 
  N. 
  radiatus, 
  d'Orb., 
  1 
  Baculites 
  Faujasii, 
  Hamites 
  

   sp., 
  Inoceramus 
  Cripsii, 
  Cardium 
  decussatum, 
  etc. 
  Its 
  total 
  thickness 
  

   is 
  about 
  30 
  feet, 
  and 
  it 
  rests 
  on 
  the 
  variegated 
  shales 
  or 
  marls 
  of 
  the 
  

   New 
  Bed 
  Sandstone/ 
  2 
  In 
  addition, 
  he 
  mentions 
  Ventriculites 
  radi- 
  

   atus, 
  Mant., 
  and 
  Holaster 
  planus 
  (Mant.), 
  (small 
  specimens 
  -6 
  inch 
  

   long). 
  Echinocorys 
  ovatus, 
  Lam., 
  Catopygus 
  columbarius 
  an 
  2 
  ., 
  and 
  

   Belemnitella 
  mucronata, 
  Schloth., 
  have 
  also 
  been 
  recorded. 
  

  

  Eespecting 
  Ammonites 
  leivesiensis, 
  Sowerby 
  remarked, 
  ' 
  These 
  

   specimens 
  lead 
  me 
  to 
  suspect 
  that 
  A. 
  lewesiensis 
  is 
  only 
  a 
  com- 
  

   pressed 
  variety 
  of 
  A. 
  peramplus.' 
  Those 
  obtained 
  at 
  Tamlaght 
  

   very 
  closely 
  resemble 
  MantelPs 
  original 
  examples. 
  This 
  species 
  is 
  

   said 
  to 
  be 
  abundant 
  in 
  the 
  lower 
  or 
  glauconitic 
  portion 
  of 
  the 
  

   western 
  chalk, 
  aud 
  seems 
  to 
  mark 
  a 
  distinct 
  bed 
  along 
  its 
  escarp- 
  

   ment. 
  The 
  rock 
  itself 
  consists 
  of 
  a 
  pink 
  chalk, 
  with 
  a 
  few 
  glauco- 
  

   nitic 
  grains 
  scattered 
  through 
  it. 
  

  

  Slieve 
  Gallion. 
  

  

  In 
  this 
  district 
  the 
  Chalk 
  beds 
  overlie 
  the 
  Keuper 
  marls, 
  being 
  about 
  

   30 
  feet 
  thick 
  near 
  Coagh. 
  The 
  Geological 
  Survey 
  Memoir, 
  Expl. 
  

   Sheet 
  26, 
  p. 
  28, 
  states 
  that, 
  in 
  a 
  stream 
  south 
  of 
  the 
  large 
  quarry 
  N.W, 
  

   of 
  Spring 
  Hill, 
  the 
  lower 
  part 
  of 
  the 
  Chalk 
  is 
  a 
  compact 
  white 
  lime- 
  

   stone 
  speckled 
  with 
  minute 
  grains 
  of 
  quartz, 
  and 
  containing 
  water- 
  

   worn 
  pebbles 
  of 
  quartz, 
  quartzite, 
  and 
  quartz-porphyry. 
  The 
  arena- 
  

   ceous 
  portion 
  is 
  confined 
  to 
  a 
  depth 
  of 
  about 
  6 
  inches, 
  but 
  scattered 
  

   pebbles 
  occur 
  for 
  some 
  distance 
  higher 
  up, 
  embedded 
  in 
  the 
  ordinary 
  

   compact 
  chalk, 
  into 
  which 
  the 
  former 
  seems 
  gradually 
  to 
  pass. 
  In 
  

   the 
  adjacent 
  quarry 
  the 
  chalk-rock 
  is 
  found 
  to 
  reach 
  a 
  thickness 
  of 
  

   about 
  30 
  feet 
  above 
  the 
  Triassic 
  strata. 
  

  

  At 
  Slieve 
  Gallion 
  Cam 
  (3 
  miles 
  from 
  the 
  main 
  summit 
  of 
  

   Slieve 
  Gallion) 
  the 
  Chalk 
  is 
  seen 
  to 
  rest 
  directly 
  on 
  Carboniferous 
  

   sandstone. 
  The 
  lower 
  part 
  is 
  a 
  faint 
  pink 
  limestone 
  dotted 
  with 
  a 
  

   few 
  glauconitic 
  grains, 
  but 
  containing 
  numerous 
  pebbles 
  and 
  frag- 
  

   ments 
  of 
  quartz. 
  The 
  officers 
  of 
  the 
  Geological 
  Survey 
  regard 
  this 
  

   bed 
  as 
  a 
  connecting-link 
  between 
  the 
  Chalk 
  and 
  Upper 
  Greensand, 
  

   classing 
  it 
  with 
  the 
  former 
  on 
  account 
  of 
  the 
  abundance 
  of 
  Chalk 
  

   fossils 
  which 
  it 
  contains. 
  So 
  far 
  as 
  can 
  be 
  judged, 
  this 
  deposit 
  must 
  

   be 
  very 
  similar 
  in 
  its 
  fossil 
  contents 
  to 
  that 
  at 
  Moneymore. 
  

  

  Benbradagh, 
  Dungiven, 
  and 
  Keady 
  Hill. 
  

  

  The 
  White 
  Chalk 
  of 
  these 
  localities 
  is 
  particularly 
  interesting, 
  on 
  

   account 
  of 
  the 
  character 
  and 
  abundance 
  of 
  the 
  fauna 
  that 
  it 
  contains. 
  

  

  1 
  One 
  labelled 
  thus 
  in 
  the 
  Jerniyn 
  Street 
  Museum 
  appears 
  to 
  me 
  to 
  b& 
  

   N. 
  Deslongchampsianus. 
  

  

  2 
  'Keport 
  Geol. 
  Londonderry, 
  etc.,' 
  Dublin, 
  1843, 
  pp. 
  115-116. 
  

  

  