﻿E. 
  H. 
  Perkins 
  — 
  Dighton 
  Conglomerate. 
  69 
  

  

  ence 
  of 
  bevelled 
  surfaces 
  ; 
  amount 
  of 
  rounding 
  ; 
  shape, 
  

   either 
  blunted 
  or 
  pointed 
  or 
  rhombic 
  ; 
  and 
  concave 
  frac- 
  

   tures. 
  The 
  results 
  are 
  shown 
  as 
  percentages 
  in 
  Table 
  

   II. 
  

  

  Table 
  II. 
  Characteristics 
  of 
  Conglomerate 
  Pebbles. 
  

  

  A 
  BCD 
  E 
  

  

  Beveled 
  surfaces 
  83 
  93 
  98 
  31 
  58 
  

  

  Well 
  rounded 
  23 
  11 
  5 
  19 
  48 
  

  

  Moderately 
  rounded 
  57 
  48 
  53 
  39 
  32 
  

  

  Slightly 
  rounded 
  20 
  41 
  42 
  42 
  20 
  

  

  Blunted 
  and 
  pointed 
  pebbles 
  7-6 
  24 
  29 
  0-6 
  8-3 
  

  

  Rhombic 
  pebbles 
  6-2 
  15 
  14 
  1-2 
  5-5 
  

  

  Concave 
  fractures 
  58 
  81 
  92 
  6-8 
  24 
  

  

  A, 
  Dighton 
  conglomerate; 
  B, 
  Tills; 
  C, 
  Aqueoglacial 
  grav- 
  

   els; 
  D, 
  Fluviatile 
  gravels; 
  E, 
  Marine 
  beaches. 
  

  

  Under 
  the 
  head 
  of 
  beveled 
  surfaces 
  are 
  classed 
  frag- 
  

   ments 
  having 
  one 
  or 
  more 
  flattened 
  surfaces. 
  These 
  

   may 
  have 
  been 
  formed 
  either 
  as 
  a 
  result 
  of 
  wear 
  or 
  from 
  

   joints 
  or 
  other 
  planes 
  of 
  weakness 
  in 
  the 
  parent 
  rock. 
  

  

  It 
  will 
  be 
  seen 
  that 
  the 
  Narragansett 
  Basin 
  conglom- 
  

   erates 
  have 
  a 
  higher 
  percentage 
  of 
  flat 
  surfaces 
  than 
  

   marine 
  or 
  fluviatile 
  deposits 
  and 
  tills. 
  The 
  percentage 
  

   for 
  marine 
  deposits 
  is 
  high 
  from 
  the 
  fact 
  that 
  many 
  of 
  

   the 
  marine 
  beaches 
  studied 
  were 
  formed 
  of 
  glaciated 
  

   pebbles. 
  The 
  average 
  for 
  the 
  fluviatile 
  deposits 
  is 
  low, 
  

   due 
  to 
  the 
  fact 
  that 
  the 
  coastal 
  plain 
  deposits 
  which 
  were 
  

   studied 
  were 
  made 
  up 
  of 
  fragments 
  which 
  had 
  travelled 
  

   a 
  considerable 
  distance 
  and 
  had 
  suffered 
  a 
  proportionate 
  

   amount 
  of 
  wear. 
  The 
  evidence 
  from 
  the 
  beveled 
  sur- 
  

   faces 
  indicates 
  an 
  erosive 
  agency 
  which 
  furnished 
  a 
  

   large 
  number 
  of 
  angular 
  fragments, 
  and 
  also 
  a 
  moderate 
  

   amount 
  of 
  transportation. 
  

  

  The 
  amount 
  of 
  rounding 
  in 
  the 
  fragments 
  of 
  the 
  

   Dighton 
  conglomerates 
  seems 
  to 
  be 
  less 
  than 
  that 
  found 
  

   in 
  the 
  marine 
  gravels, 
  and 
  more 
  than 
  the 
  average 
  for 
  

   tills. 
  However, 
  the 
  degree 
  of 
  rounding 
  is 
  more 
  depend- 
  

   ent 
  on 
  the 
  nature 
  of 
  the 
  fragments 
  and 
  the 
  amount 
  of 
  

   erosion 
  than 
  on 
  the 
  agent. 
  Hence 
  the 
  degree 
  of 
  round- 
  

   ing 
  is 
  not 
  decisive 
  evidence 
  in 
  determining 
  the 
  method 
  of 
  

   origin 
  of 
  a 
  conglomerate. 
  

  

  Two 
  types 
  of 
  pebbles 
  have 
  been 
  found 
  to 
  occur 
  in 
  all 
  

   tills 
  and 
  aqueoglacial 
  deposits 
  examined: 
  rhombic, 
  and 
  

  

  