﻿1864.] 
  MAW 
  SEVERN-VALLEY 
  DRIFT. 
  137 
  

  

  List 
  of 
  Bocks, 
  <$fc, 
  from 
  the 
  Drift 
  in 
  the 
  Valley 
  of 
  the 
  Severn 
  at 
  

  

  Bridgnorth. 
  

  

  Llandovery 
  sandstone. 
  

  

  Wenloek 
  limestone. 
  

  

  Drift 
  coal. 
  Coal-measure 
  rocks 
  and 
  Penneystone 
  ironstone. 
  

  

  Carboniferous 
  limestone. 
  

  

  Red 
  and 
  grey 
  Permian 
  sandstone. 
  

  

  Bunter 
  sandstone. 
  

  

  Basalts 
  and 
  greenstones. 
  

  

  Red, 
  grey, 
  and 
  white 
  granites. 
  

  

  Quartz-rock. 
  

  

  Elvan 
  or 
  compact 
  granite-rock. 
  

  

  Flints 
  and 
  hard 
  chalk, 
  and 
  

  

  A 
  Lias 
  fossil 
  (Gryphcea 
  incurva). 
  

   The 
  composition 
  of 
  the 
  whole 
  of 
  these 
  Severn- 
  Valley 
  gravels 
  is 
  

   very 
  similar, 
  and 
  only 
  differs 
  in 
  respect 
  of 
  the 
  formation 
  upon 
  

   which 
  they 
  immediately 
  rest, 
  which 
  always 
  preponderates 
  ; 
  thus, 
  

   the 
  Bridgnorth 
  drift 
  partakes 
  largely 
  of 
  the 
  components 
  of 
  the 
  New 
  

   Red 
  Sandstone, 
  especially 
  the 
  beds 
  at 
  Quatford, 
  about 
  two 
  miles 
  below 
  

   the 
  town, 
  which 
  are 
  almost 
  entirely 
  composed 
  of 
  the 
  detritus 
  of 
  the 
  

   Bunter 
  sandstone, 
  and 
  contrast 
  strikingly 
  with 
  the 
  tough 
  clays 
  of 
  

   the 
  Strethill 
  deposit, 
  which 
  I 
  cannot 
  help 
  thinking 
  have 
  been 
  largely 
  

   derived 
  from 
  the 
  waste 
  of 
  the 
  Coal-measure 
  clays 
  and 
  Wenloek 
  shale 
  

   in 
  its 
  immediate 
  neighbourhood. 
  

  

  The 
  cuttings 
  of 
  the 
  Severn-Valley 
  Railway 
  below 
  Bridgnorth, 
  on 
  

   the 
  west 
  side 
  of 
  the 
  valley, 
  expose 
  several 
  sections 
  of 
  drift 
  ; 
  gravels 
  

   and 
  sands, 
  containing 
  a 
  few 
  broken 
  fragments 
  of 
  Shells, 
  generally 
  

   rest 
  on 
  the 
  older 
  formation, 
  and 
  in 
  some 
  places 
  these 
  are 
  again 
  over- 
  

   lain 
  by 
  a 
  more 
  clayey 
  deposit, 
  which 
  may 
  possibly 
  be 
  related 
  to 
  the 
  

   clay-beds 
  of 
  the 
  Strethill 
  drift 
  ; 
  but 
  as 
  the 
  whole 
  of 
  the 
  drift-beds 
  

   exhibit 
  so 
  much 
  variety 
  of 
  character, 
  the 
  correlation 
  of 
  their 
  con- 
  

   stituent 
  strata 
  in 
  different 
  localities 
  is 
  most 
  difficult 
  and 
  uncertain. 
  

  

  In 
  describing 
  the 
  strata 
  of 
  Strethill, 
  I 
  mentioned 
  that 
  the 
  larger 
  

   constituent 
  materials 
  were 
  the 
  same 
  throughout, 
  but 
  that 
  the 
  cha- 
  

   racter 
  and 
  aspect 
  of 
  the 
  strata 
  differ 
  considerably, 
  the 
  middle 
  beds 
  

   being 
  composed 
  of 
  unstratified 
  clay, 
  silt, 
  and 
  muddy 
  gravel, 
  whilst 
  

   the 
  upper 
  and 
  lower 
  strata 
  consist 
  of 
  clean 
  sand 
  and 
  water-worn 
  

   shingle, 
  evenly 
  stratified, 
  and 
  without 
  the 
  slightest 
  trace 
  of 
  mud. 
  

  

  That 
  the 
  whole 
  mass 
  was 
  derived 
  from 
  similar 
  sources 
  appears 
  

   probable 
  from 
  the 
  identity 
  of 
  the 
  constituent 
  rocks 
  and 
  boulders, 
  and 
  

   its 
  variety 
  of 
  character 
  and 
  aspect 
  must 
  be 
  attributable 
  to 
  the 
  different 
  

   circumstances 
  under 
  which 
  its 
  component 
  strata 
  were 
  deposited. 
  

  

  The 
  long-continued 
  action 
  of 
  the 
  tide 
  upon 
  a 
  particular 
  level 
  will 
  

   tend 
  to 
  the 
  removal 
  of 
  all 
  fine 
  matter 
  capable 
  of 
  being 
  held 
  in 
  watery 
  

   suspension, 
  and 
  leave 
  the 
  coarser 
  particles 
  as 
  clean 
  sand 
  and 
  shingle 
  

   similar 
  to 
  what 
  we 
  find 
  on 
  our 
  more 
  exposed 
  coasts 
  ; 
  and 
  I 
  would 
  

   suggest 
  that 
  such 
  beds, 
  forming 
  the 
  base 
  and 
  summit 
  of 
  the 
  Strethill 
  

   drift, 
  may 
  represent 
  periods 
  of 
  comparative 
  cessation 
  in 
  the 
  sub- 
  

   mergence 
  of 
  the 
  land, 
  during 
  which 
  fresh 
  erosion 
  and 
  accession 
  of 
  

   new 
  materials 
  would 
  be 
  checked, 
  and 
  the 
  debris 
  already 
  accumulated 
  

  

  