﻿E. 
  R. 
  Perkins 
  — 
  Dighton 
  Conglomerate. 
  65 
  

  

  marine 
  deposition, 
  and 
  speaks 
  of 
  deposition 
  by 
  currents 
  

   changing 
  in 
  direction 
  and 
  velocity. 
  

  

  Lenses 
  indicate 
  the 
  same 
  thing. 
  These 
  are 
  very 
  com- 
  

   mon 
  throughout 
  the 
  Dighton 
  formation 
  and 
  its 
  associated 
  

   beds. 
  Sandstone 
  lenses 
  in 
  conglomerate 
  were 
  noted 
  in 
  

   about 
  30 
  per 
  cent 
  of 
  the 
  outcrops. 
  Gray 
  shale 
  lenses 
  

   were 
  found 
  in 
  two 
  localities, 
  while 
  coaly 
  shales 
  were 
  

   found 
  in 
  four 
  outcrops. 
  The 
  finer 
  beds 
  may 
  also 
  hold 
  

   conglomerate 
  lenses. 
  These 
  occur 
  in 
  seven 
  different 
  

   localities. 
  Marine 
  beds 
  may 
  contain 
  lenses 
  of 
  different 
  

   material 
  from 
  the 
  surrounding 
  rock. 
  These 
  beds 
  will 
  be 
  

   formed 
  parallel 
  to 
  the 
  coast 
  line. 
  In 
  streams, 
  on 
  the 
  

   other 
  hand, 
  the 
  lenses 
  will 
  be 
  parallel 
  to 
  the 
  course 
  of 
  

   the 
  stream. 
  The 
  lenses 
  of 
  the 
  Dighton 
  are 
  interfingered 
  

   in 
  various 
  directions 
  and 
  so 
  indicate 
  changes 
  in 
  the 
  

   depositing 
  currents. 
  

  

  Both 
  the 
  interstratified 
  beds 
  and 
  the 
  lenses 
  show 
  cross- 
  

   bedding, 
  this 
  feature 
  being 
  especially 
  well 
  developed 
  in 
  

   the 
  finer 
  beds. 
  The 
  conglomerates 
  themselves, 
  as 
  a 
  rule, 
  

   give 
  no 
  indications 
  of 
  bedding. 
  The 
  cross-bedding 
  is 
  

   extremely 
  irregular 
  and 
  is 
  of 
  the 
  same 
  type 
  as 
  that 
  shown 
  

   in 
  glacial 
  flood-plains. 
  Both 
  the 
  angle 
  and 
  the 
  strike 
  of 
  

   the 
  laminations 
  change 
  repeatedly 
  in 
  a 
  small 
  exposure. 
  

   The 
  best 
  exposures 
  to 
  study 
  are 
  along 
  the 
  coast, 
  as 
  

   inland 
  the 
  weaker 
  beds 
  which 
  show 
  cross-bedding 
  are 
  

   eroded 
  out. 
  

  

  Associated 
  with 
  cross-bedding 
  were 
  found 
  a 
  few 
  cases 
  

   of 
  contemporaneous 
  erosion. 
  The 
  best 
  examples 
  were 
  

   in 
  the 
  Coal 
  Measures 
  at 
  the 
  Thatcher 
  Road 
  bridge 
  near 
  

   Attleboro 
  and 
  on 
  the 
  Newport 
  cliffs. 
  In 
  both 
  cases 
  

   streams 
  have 
  cut 
  into 
  the 
  underlying 
  beds 
  and 
  the 
  chan- 
  

   nels 
  later 
  filled 
  in. 
  At 
  the 
  Attleboro 
  location 
  the 
  new 
  

   deposits 
  are 
  gray 
  and 
  contain 
  fragments 
  of 
  the 
  under- 
  

   lying 
  red 
  beds. 
  

  

  At 
  three 
  inland 
  localities 
  and 
  at 
  various 
  places 
  along 
  

   the 
  Newport 
  cliffs, 
  shale 
  pebbles 
  were 
  found 
  in 
  the 
  con- 
  

   glomerate. 
  These 
  appear 
  to 
  be 
  of 
  the 
  same 
  material 
  as 
  

   the 
  neighboring 
  shale 
  beds 
  and 
  may 
  indicate 
  contempo- 
  

   raneous 
  erosion. 
  

  

  At 
  various 
  places 
  in 
  the 
  basin 
  and 
  especially 
  along 
  the 
  

   Sakonnet 
  River 
  cliffs, 
  pebble 
  bands 
  occur 
  in 
  the 
  finer 
  

   beds. 
  These 
  bands 
  often 
  cross 
  each 
  other 
  and 
  form 
  an 
  

   irregular 
  network 
  over 
  the 
  surface 
  of 
  the 
  exposure. 
  

   The 
  pebbles 
  of 
  a 
  band 
  may 
  be 
  close-set, 
  or 
  they 
  may 
  be 
  

  

  Am. 
  Jour. 
  Sci.— 
  Fourth 
  Series, 
  Vol. 
  XLIX, 
  No. 
  289— 
  January, 
  1920. 
  

   5 
  

  

  