﻿EOCKS 
  OE 
  SHKOPSHIKE. 
  121 
  

  

  from 
  north 
  to 
  south, 
  and 
  is 
  coloured 
  on 
  the 
  Survey 
  Map 
  as 
  " 
  green- 
  

   stone." 
  At 
  the 
  north 
  end, 
  there 
  are 
  good 
  exposures 
  of 
  purple 
  rhy- 
  

   olite, 
  banded 
  and 
  spherulitic 
  (no. 
  56, 
  p. 
  124). 
  The 
  resemblance 
  of 
  

   this 
  rock 
  to 
  the 
  Wrekin 
  lavas, 
  and 
  especially 
  to 
  the 
  type 
  at 
  Lea 
  

   Rock, 
  near 
  Wrockwardine, 
  is 
  unmistakable. 
  In 
  the 
  quarry 
  below 
  

   the 
  road, 
  there 
  is 
  apparent 
  bedding 
  with 
  a 
  south-west 
  dip 
  and 
  some 
  

   contortion. 
  Above 
  the 
  road, 
  a 
  highly 
  spherulitic 
  variety 
  is 
  well 
  seen 
  

   in 
  the 
  hill-slope. 
  The 
  spherules 
  are 
  frequently 
  of 
  chalcedony. 
  

   Similar 
  concretions, 
  together 
  with 
  a 
  smaller 
  proportion 
  of 
  agate, 
  are 
  

   found 
  as 
  derived 
  fragments 
  in 
  the 
  Lower 
  Cambrian 
  conglomerates 
  of 
  

   Haughmond 
  Hill, 
  near 
  Shrewsbury. 
  A 
  little 
  higher 
  than 
  the 
  sphe- 
  

   rulitic 
  type, 
  the 
  rhyolite 
  is 
  clearly 
  banded, 
  the 
  flow-lines 
  dipping 
  to 
  

   the 
  south-south-west 
  at 
  45°. 
  

  

  The 
  summit 
  of 
  the 
  northern 
  spur 
  of 
  the 
  hill 
  is 
  occupied 
  by 
  com- 
  

   pact 
  dolerite 
  (basalt) 
  (no. 
  57, 
  p. 
  124) 
  ; 
  and 
  similar 
  rock 
  is 
  to 
  be 
  traced 
  

   along 
  the 
  ridge 
  to 
  the 
  top 
  of 
  the 
  mountain. 
  This 
  mass 
  is 
  apparently 
  

   intrusive 
  ; 
  and 
  as 
  it 
  is 
  not 
  found 
  in 
  the 
  neighbouring 
  Cambrian 
  con- 
  

   glomerates, 
  it 
  is 
  probably 
  Postcambrian. 
  Doleritic 
  rocks, 
  some 
  

   highly 
  altered, 
  are 
  also 
  exposed 
  on 
  the 
  western 
  slope 
  of 
  the 
  ridge. 
  

   On 
  this 
  side 
  of 
  the 
  hill 
  I 
  also 
  noticed 
  compact 
  felsite 
  and 
  hornstone 
  

   of 
  ordinary 
  Archaean 
  types. 
  

  

  The 
  structure 
  just 
  described, 
  a 
  plagioclinal 
  ridge 
  broken 
  through 
  

   by 
  intrusive 
  greenstone, 
  agrees 
  with 
  the 
  formation 
  of 
  the 
  Wrekin, 
  

   the 
  Lawley, 
  Caer 
  Caradoc, 
  and 
  other 
  elevations 
  of 
  the 
  eastern 
  axis. 
  

  

  At 
  Lyd's 
  Hole, 
  a 
  picturesque 
  ravine, 
  with 
  a 
  cascade, 
  situated 
  

   about 
  half 
  a 
  mile 
  east 
  of 
  the 
  north 
  end 
  of 
  the 
  hill, 
  the 
  purple 
  rhy- 
  

   olites 
  (no. 
  55, 
  p. 
  124), 
  banded 
  and 
  highly 
  spherulitic, 
  are 
  finely 
  ex- 
  

   posed 
  in 
  the 
  crags 
  overhanging 
  the 
  stream. 
  The 
  flow-lines 
  dip 
  

   south-easterly 
  at 
  80°. 
  Just 
  above 
  the 
  fall 
  is 
  a 
  junction 
  of 
  the 
  

   Archaeans 
  with 
  purple 
  sandstones 
  and 
  shales 
  of 
  Lower 
  Cambrian 
  age, 
  

   which 
  dip 
  as 
  if 
  in 
  conformable 
  succession. 
  I 
  believe, 
  however, 
  for 
  

   reasons 
  which 
  cannot 
  here 
  be 
  enumerated, 
  that 
  the 
  two 
  groups 
  are 
  

   faulted 
  together, 
  so 
  that 
  the 
  conformity 
  of 
  dip 
  is 
  merely 
  a 
  coincidence. 
  

   Following 
  up 
  the 
  stream 
  to 
  the 
  south-east, 
  we 
  pass 
  over 
  several 
  

   hundred 
  feet 
  of 
  the 
  Cambrian 
  ; 
  and 
  west 
  of 
  Eatcliff 
  we 
  come 
  to 
  a 
  

   conglomerate 
  dipping 
  at 
  a 
  high 
  angle 
  to 
  south-south-east. 
  Pebbles 
  

   of 
  quartzite 
  and 
  purple 
  rhyolite 
  predominate 
  ; 
  but 
  green 
  slate 
  and 
  

   mica-schist 
  also 
  occur. 
  A 
  little 
  higher 
  in 
  the 
  series, 
  there 
  is 
  a 
  

   second 
  conglomerate, 
  dipping 
  at 
  a 
  lower 
  angle, 
  from 
  50° 
  to 
  60°. 
  

   The 
  composition 
  is 
  similar; 
  but 
  the 
  pebbles 
  are 
  larger, 
  some 
  of 
  

   them 
  reaching 
  the 
  size 
  of 
  a 
  child's 
  head. 
  The 
  purple 
  felsite 
  of 
  

   this 
  conglomerate 
  is 
  very 
  characteristic, 
  and 
  is 
  undoubtedly 
  derived 
  

   from 
  the 
  Archaean 
  volcanic 
  group. 
  

  

  A 
  short 
  distance 
  north 
  of 
  Lyd's 
  Hole, 
  there 
  occur 
  stream-sections 
  

   of 
  greenish 
  shale 
  containing 
  Trinudeus 
  concentricus, 
  Orthis 
  testudi- 
  

   naria, 
  Diplograjptus 
  pristis, 
  and 
  Beyrichia 
  complicata, 
  an 
  assemblage 
  

   characteristic 
  of 
  the 
  Harnage 
  Shales 
  (Lower 
  Caradoc), 
  with 
  which 
  

   these 
  rocks 
  agree 
  also 
  in 
  their 
  lithology. 
  In 
  Murchison's 
  i 
  Silurian 
  

   System 
  ' 
  it 
  is 
  stated 
  that 
  at 
  this 
  spot 
  intrusive 
  " 
  greenstone 
  " 
  has 
  

   " 
  caught 
  up 
  fragments 
  of 
  shale," 
  a 
  singular 
  reversal 
  of 
  the 
  true 
  facts. 
  

  

  k2 
  

  

  