﻿138 
  PROCEEDINGS 
  OF 
  THE 
  GEOLOGICAL 
  SOCIETY. 
  [Jail. 
  20, 
  

  

  on 
  the 
  coast 
  subjected 
  to 
  the 
  long-continued 
  cleansing 
  action 
  of 
  the 
  

   waves 
  above 
  described, 
  thus 
  converting 
  it 
  into 
  clean 
  sand 
  and 
  rounded 
  

   shingle. 
  

  

  "With 
  regard 
  to 
  drift 
  clay-beds, 
  rapid 
  submergence 
  would 
  con- 
  

   tinually 
  present 
  fresh 
  points 
  of 
  approach 
  for 
  the 
  eroding 
  waters, 
  and 
  

   might 
  tend 
  to 
  the 
  accumulation 
  of 
  debris 
  at 
  a 
  greater 
  rate 
  than 
  the 
  

   finer 
  matters 
  could 
  be 
  cleansed 
  away 
  by 
  repeated 
  tidal 
  action. 
  The 
  

   Strethill 
  clay-bed, 
  which 
  was 
  probably 
  deposited 
  in 
  deeper 
  water, 
  

   contains 
  a 
  much 
  larger 
  proportion 
  of 
  angular 
  and 
  unworn 
  fragments 
  

   than 
  the 
  shingle 
  accompanying 
  the 
  clean 
  sand, 
  and 
  also 
  lumps 
  of 
  soft 
  

   Wenlock 
  shale, 
  which, 
  had 
  they 
  been 
  subjected 
  to 
  long 
  coast-action, 
  

   must 
  soon 
  have 
  been 
  broken 
  up. 
  I 
  would 
  submit, 
  therefore, 
  that 
  

   the 
  alternating 
  strata 
  of 
  Strethill 
  present 
  us 
  with 
  evidence 
  of 
  un- 
  

   equal 
  or 
  interrupted 
  action 
  in 
  the 
  submergence 
  of 
  the 
  land, 
  in 
  the 
  

   same 
  way 
  that 
  the 
  Bridgnorth 
  terraces 
  prove 
  an 
  irregularity 
  in 
  the 
  

   rate 
  of 
  upheaval. 
  

  

  I 
  believe 
  that 
  the 
  whole 
  of 
  the 
  drift-strata 
  I 
  have 
  described, 
  ex- 
  

   cepting, 
  perhaps, 
  the 
  flat 
  valley- 
  alluvium, 
  were 
  deposited 
  in 
  the 
  

   interval 
  between 
  a 
  single 
  period 
  of 
  depression 
  and 
  re-elevation, 
  but 
  

   that 
  subsequent 
  oscillations 
  of 
  level, 
  represented 
  by 
  a 
  separate 
  series 
  

   of 
  drifts 
  of 
  a 
  different 
  character 
  at 
  a 
  lower 
  level, 
  are 
  also 
  evident. 
  

  

  The 
  lowest 
  beds 
  of 
  the 
  Shropshire 
  drift 
  are 
  nearly 
  100 
  feet 
  above 
  

   the 
  sea-level; 
  they 
  are,*excepting 
  the 
  flat 
  alluvium 
  bordering 
  the 
  river, 
  

   exclusively 
  of 
  marine 
  origin, 
  entirely 
  devoid 
  of 
  Mammalian 
  remains, 
  

   and, 
  considering 
  their 
  immense 
  thickness 
  and 
  range 
  of 
  altitude, 
  their 
  

   monotonous 
  character 
  and 
  paucity 
  of 
  organic 
  remains 
  contrast 
  

   strikingly 
  with 
  the 
  drifts 
  of 
  lower 
  levels, 
  such 
  as 
  those 
  of 
  the 
  valleys 
  

   of 
  the 
  Somme, 
  the 
  Avon, 
  and 
  the 
  lower 
  part 
  of 
  the 
  Severn 
  Valley. 
  

   All 
  of 
  these, 
  from 
  the 
  smaller 
  scale 
  of 
  their 
  constituent 
  strata 
  and 
  

   close 
  alternation 
  of 
  marine 
  and 
  freshwater 
  beds, 
  appear 
  to 
  have 
  been 
  

   the 
  result 
  of 
  less 
  extensive 
  variations 
  of 
  level 
  than 
  that 
  involved 
  in 
  

   the 
  formation 
  of 
  the 
  Strethill 
  drift, 
  and 
  may 
  have 
  gone 
  on 
  during 
  

   comparatively 
  short 
  periods 
  within 
  the 
  100 
  feet 
  separating 
  the 
  pre- 
  

   sent 
  sea-level 
  from 
  our 
  lowest 
  Shropshire 
  drift, 
  and 
  subsequently 
  to 
  

   its 
  last 
  denudation. 
  They 
  would 
  be 
  more 
  essentially 
  valley-drifts 
  

   than 
  those 
  now 
  described, 
  which 
  belong 
  to 
  an 
  epoch 
  in 
  which 
  nearly 
  

   the 
  whole 
  land-surface 
  of 
  Great 
  Britain 
  was 
  probably 
  submerged. 
  

  

  In 
  the 
  valley 
  about 
  Bridgnorth, 
  and 
  on 
  the 
  terraces 
  of 
  drift 
  before 
  

   described, 
  there 
  here 
  and 
  there 
  occur 
  large 
  boulders 
  of 
  grey 
  granite, 
  

   Cambrian 
  slate, 
  Llandovery 
  sandstone, 
  Coal-measure 
  rocks, 
  Car- 
  

   boniferous 
  limestone, 
  New 
  Red 
  sandstone, 
  New 
  Red 
  conglomerate, 
  

   Devonian 
  sandstone, 
  and 
  a 
  volcanic 
  rock, 
  probably 
  from 
  N. 
  Wales. 
  

   They 
  are 
  for 
  the 
  most 
  part 
  subangular, 
  and, 
  although 
  they 
  do 
  not 
  

   exhibit 
  any 
  well-marked 
  glacial 
  striae, 
  the 
  large 
  weight 
  of 
  some 
  of 
  

   them 
  (from 
  one 
  to 
  two 
  tons) 
  clearly 
  implies 
  some 
  form 
  of 
  ice- 
  

   action 
  as 
  a 
  means 
  of 
  transport. 
  These 
  erratic 
  blocks 
  occur 
  sparingly 
  

   amongst 
  the 
  drift 
  all 
  up 
  the 
  valley 
  to 
  Shrewsbury, 
  but 
  much 
  more 
  

   abundantly 
  on 
  the 
  higher 
  ground 
  at 
  altitudes 
  of 
  from 
  400 
  to 
  800 
  

   feet 
  above 
  the 
  sea, 
  where 
  they 
  are 
  not 
  always 
  accompanied 
  by 
  the 
  

   ordinary 
  drift. 
  

  

  