﻿ROCKS 
  OP 
  SHROPSHIRE. 
  123 
  

  

  southward, 
  approaches 
  more 
  and 
  more 
  closely 
  to 
  the 
  Archaean 
  axis 
  ; 
  

   and 
  at 
  Knolls 
  Eidge 
  and 
  Cold 
  Hill 
  it 
  is 
  almost 
  in 
  contact. 
  This 
  is 
  

   one 
  evidence 
  of 
  the 
  want 
  of 
  conformity 
  previously 
  suggested. 
  The 
  

   conglomerate 
  does 
  not 
  materially 
  vary 
  towards 
  the 
  south, 
  being 
  still 
  

   composed 
  of 
  quartzite 
  and 
  purple 
  felsite, 
  and 
  nowhere 
  containing, 
  

   so 
  far 
  as 
  I 
  have 
  observed, 
  fragments 
  derived 
  from 
  the 
  hornstone. 
  

   This 
  is 
  not 
  what 
  we 
  should 
  expect 
  if, 
  as 
  might 
  at 
  first 
  be 
  inferred, 
  

   the 
  conglomerate 
  were 
  the 
  base 
  of 
  the 
  Cambrian, 
  and 
  formed 
  as 
  a 
  

   shore-deposit 
  along 
  the 
  Archaean 
  axis. 
  

  

  I 
  have 
  stated 
  that 
  the 
  strike 
  of 
  the 
  Archaean, 
  wherever 
  observed, 
  

   except 
  at 
  Lyd's 
  Hole, 
  is 
  east 
  and 
  west 
  or 
  south-east 
  and 
  north- 
  

   west, 
  while 
  the 
  adjoining 
  Cambrians, 
  Upper 
  and 
  Lower, 
  strike 
  

   south-south-west, 
  tbe 
  great 
  fault 
  and 
  the 
  Archaean 
  ridges 
  also 
  trend- 
  

   ing 
  in 
  the 
  same 
  direction. 
  The 
  formation 
  of 
  the 
  fault 
  and 
  the 
  

   upthrust 
  of 
  the 
  Archaeans 
  would 
  therefore 
  seem 
  to 
  be 
  connected 
  

   with 
  the 
  forces 
  which 
  at 
  the 
  close 
  of 
  the 
  Ordovician 
  epoch 
  threw 
  the 
  

   Ordovician 
  and 
  Cambrian 
  deposits 
  into 
  folds, 
  and 
  determined 
  the 
  

   direction 
  of 
  the 
  older 
  mountain 
  ridges 
  of 
  Shropshire. 
  I 
  cannot, 
  how- 
  

   ever, 
  speak 
  positively 
  on 
  this 
  point, 
  since 
  powerful 
  earth- 
  movements 
  

   have 
  taken 
  place 
  in 
  this 
  district 
  along 
  the 
  same 
  lines 
  at 
  different 
  

   epochs. 
  

  

  It 
  will 
  have 
  been 
  noted 
  that, 
  as 
  is 
  so 
  frequently 
  the 
  case 
  with 
  

   Archaean 
  elevations, 
  the 
  structure 
  of 
  the 
  ridges 
  described 
  is 
  plagio- 
  

   clinal. 
  

  

  Summary 
  of 
  Results. 
  

  

  1. 
  On 
  a 
  south-south-west 
  line 
  running 
  between 
  Pontesbury 
  and 
  

   Linley 
  Hall 
  are 
  seven 
  distinct 
  elevations, 
  composed 
  wholly 
  or 
  in 
  

   part 
  of 
  Archaean 
  rocks. 
  

  

  2. 
  This 
  line 
  corresponds 
  with 
  a 
  great 
  fault, 
  on 
  the 
  east 
  side 
  of 
  

   which 
  Longmynd 
  rocks 
  dip 
  easterly, 
  and 
  on 
  the 
  west 
  Tremadoc 
  

   shales 
  dip 
  westerly. 
  

  

  3. 
  The 
  prevailing 
  rock-types 
  are 
  purple 
  rhyolites 
  at 
  the 
  north 
  

   end 
  of 
  the 
  chain, 
  purple 
  hornstone 
  (or 
  halleninta) 
  in 
  the 
  middle, 
  

   and 
  purple 
  and 
  green 
  hornstone 
  (or 
  halleflinta), 
  with 
  some 
  indurated 
  

   grits, 
  partly 
  derived 
  from 
  a 
  gneissic 
  series, 
  at 
  the 
  south. 
  

  

  4. 
  The 
  Precambrian 
  age 
  of 
  these 
  rocks 
  is 
  proved 
  by 
  their 
  close 
  

   lithological 
  affinities 
  with 
  known 
  Salopian 
  types, 
  and 
  by 
  the 
  almost 
  

   universal 
  occurrence 
  of 
  fragments 
  of 
  the 
  purple 
  rhyolites 
  in 
  the 
  

   Longmynd 
  series. 
  The 
  strike, 
  also, 
  is 
  usually 
  more 
  or 
  less 
  trans- 
  

   verse 
  to 
  the 
  strike 
  of 
  the 
  Cambrian 
  deposits. 
  

  

  5. 
  The 
  rocks 
  of 
  this 
  axis 
  belong 
  exclusively 
  to 
  the 
  younger 
  of 
  the 
  

   two 
  Salopian 
  Archaean 
  groups, 
  no 
  traces 
  of 
  granitoid 
  or 
  gneissic 
  

   rocks, 
  except 
  as 
  included 
  fragments, 
  having 
  been 
  detected. 
  

  

  