﻿68 
  E. 
  H. 
  Perkins 
  — 
  Dighton 
  Conglomerate. 
  

  

  ary 
  origin. 
  The 
  matrix 
  was 
  apparently 
  formed 
  nnder 
  

   conditions 
  which 
  did 
  not 
  permit 
  the 
  chemical 
  decomposi- 
  

   tion 
  of 
  snch 
  minerals 
  as 
  feldspar. 
  Two 
  kinds 
  of 
  climate 
  

   are 
  characterized 
  by 
  snch 
  a 
  condition: 
  a 
  warm 
  arid 
  

   climate 
  and 
  a 
  cold 
  moist 
  one. 
  The 
  evidence 
  of 
  the 
  

   matrix 
  is 
  therefore 
  in 
  favor 
  of 
  flnviatile 
  origin 
  nnder 
  one 
  

   of 
  the 
  above 
  climatic 
  conditions. 
  

  

  Larger 
  Fragments. 
  

  

  The 
  larger 
  fragments 
  of 
  the 
  Dighton 
  conglomerate 
  

   consist 
  of 
  quartzite, 
  granite, 
  vein 
  qnartz 
  and 
  small 
  

   amounts 
  of 
  shale, 
  sandstone 
  and 
  felsite. 
  The 
  first 
  

   greatly 
  predominates. 
  The 
  percentages 
  of 
  qnartzite 
  in 
  

   the 
  various 
  areas 
  going 
  north 
  through 
  the 
  basin 
  are 
  as 
  

   follows 
  : 
  Newport 
  95, 
  Dighton 
  88, 
  Taunton 
  80, 
  and 
  Attle- 
  

   boro 
  58. 
  The 
  percentages 
  for 
  granite 
  in 
  the 
  same 
  areas 
  

   are 
  : 
  Newport 
  5, 
  Dighton 
  12, 
  Taunton 
  11, 
  and 
  Attleboro 
  

   23. 
  Thus 
  granite 
  increases 
  in 
  amount 
  as 
  one 
  goes 
  north, 
  

   while 
  the 
  qnartzite 
  decreases. 
  

  

  There 
  is 
  also 
  a 
  decrease 
  in 
  size 
  of 
  the 
  fragments 
  as 
  one 
  

   goes 
  north 
  and 
  west. 
  This 
  is 
  shown 
  in 
  both 
  granite 
  and 
  

   quartzite 
  but 
  is 
  most 
  noticeable 
  in 
  the 
  latter. 
  About 
  

   Newport, 
  bowlders 
  one 
  and 
  two 
  feet 
  in 
  diameter 
  are 
  not 
  

   uncommon 
  while 
  specimens 
  may 
  be 
  found 
  five 
  or 
  six 
  feet 
  

   through. 
  It 
  is 
  this 
  great 
  size 
  of 
  the 
  fragments 
  which 
  is 
  

   the 
  most 
  impressive 
  thing 
  about 
  the 
  Newport 
  exposures. 
  

   At 
  the 
  northern 
  edge 
  of 
  the 
  basin 
  about 
  Attleboro 
  few 
  

   cobbles 
  over 
  six 
  inches 
  and 
  none 
  over 
  a 
  foot 
  in 
  diameter 
  

   were 
  found. 
  Many 
  of 
  the 
  fragments 
  contain 
  Upper 
  

   Cambrian 
  brachiopods 
  (Obolus). 
  No 
  outcrops 
  of 
  simi- 
  

   lar 
  quartzites 
  have 
  been 
  found 
  nearer 
  than 
  Newfound- 
  

   land. 
  It 
  seems 
  probable 
  that 
  there 
  was 
  an 
  area 
  of 
  

   Upper 
  Cambrian 
  quartzite 
  exposed 
  to 
  erosion 
  a 
  very 
  

   short 
  distance 
  to 
  the 
  southeast. 
  

  

  The 
  granite 
  and 
  other 
  pebbles 
  to 
  the 
  north 
  might 
  be 
  

   derived 
  as 
  readily 
  from 
  the 
  west 
  as 
  from 
  the 
  east 
  as 
  far 
  

   as 
  their 
  composition 
  is 
  concerned. 
  However, 
  the 
  in- 
  

   crease 
  in 
  size 
  toward 
  the 
  eastern 
  side 
  of 
  the 
  basin 
  indi- 
  

   cates 
  a 
  source 
  in 
  that 
  direction. 
  

  

  The 
  characteristics 
  of 
  the 
  larger 
  fragments 
  of 
  the 
  

   Dighton 
  formation 
  and 
  other 
  conglomerates 
  and 
  gravels 
  

   were 
  studied. 
  The 
  points 
  noted 
  which 
  seem 
  of 
  value 
  in 
  

   the 
  determination 
  of 
  the 
  origin 
  were 
  the 
  following 
  : 
  pres- 
  

  

  