﻿74 
  E. 
  H. 
  Perkins 
  — 
  Dighton 
  Conglomerate. 
  

  

  been 
  located 
  to 
  the 
  east 
  of 
  our 
  present 
  coast-line. 
  The 
  

   streams 
  which 
  deposited 
  the 
  Dighton 
  flowed 
  to 
  the 
  west. 
  

  

  4. 
  The 
  stream 
  or 
  streams 
  to 
  the 
  sonth 
  flowed 
  from 
  a 
  

   country 
  where 
  the 
  bed-rock 
  was 
  npper 
  Cambrian 
  quartz- 
  

   ite, 
  while 
  the 
  streams 
  to 
  the 
  north 
  flowed 
  from 
  a 
  more 
  

   granitic 
  country. 
  It 
  might 
  be 
  argued 
  that 
  the 
  granite 
  

   pebbles 
  to 
  the 
  north, 
  being 
  smaller, 
  might 
  be 
  deposited 
  

   along 
  the 
  lower 
  courses 
  of 
  the 
  streams 
  which 
  deposited 
  

   the 
  Purgatory 
  quartzite 
  conglomerate. 
  The 
  quartzite 
  

   nature 
  of 
  the 
  southern 
  beds, 
  however, 
  extends 
  down 
  into 
  

   the 
  finer 
  basal 
  conglomerates 
  and 
  even 
  into 
  the 
  Sakonnet 
  

   sandstone. 
  In 
  the 
  same 
  way 
  the 
  finer 
  conglomerates 
  to 
  

   the 
  north 
  are 
  as 
  granitic 
  as 
  the 
  upper 
  beds. 
  

  

  5. 
  The 
  production 
  of 
  the 
  coarse 
  material 
  of 
  the 
  New- 
  

   port 
  region 
  seems 
  to 
  require 
  some 
  stronger 
  erosive 
  agent 
  

   than 
  normal 
  river 
  and 
  atmospheric 
  action 
  in 
  a 
  temperate 
  

   climate. 
  Vigorous 
  frost 
  action 
  with 
  the 
  possible 
  assist- 
  

   ance 
  of 
  glaciers 
  would 
  furnish 
  the 
  material 
  to 
  the 
  

   streams. 
  The 
  great 
  abundance 
  of 
  angular 
  pebbles, 
  with 
  

   a 
  consistent 
  percentage 
  of 
  rhombic 
  and 
  blunted 
  and 
  

   pointed 
  pebbles, 
  as 
  well 
  as 
  concave 
  fractures 
  in 
  the 
  least 
  

   metamorphosed 
  parts 
  of 
  the 
  basin, 
  also 
  point 
  to 
  ice 
  ac- 
  

   tion. 
  There 
  is 
  no 
  evidence 
  that 
  the 
  ice-sheets 
  ever 
  

   reached 
  the 
  plain 
  in 
  the 
  Narragansett 
  Basin. 
  It 
  is 
  

   entirely 
  possible 
  that 
  the 
  Newport 
  beds 
  were 
  deposited 
  

   in 
  front 
  of 
  an 
  advancing 
  glacier 
  which 
  later 
  covered 
  the 
  

   region. 
  If 
  such 
  a 
  thing 
  ever 
  happened, 
  its 
  beds 
  have 
  

   been 
  entirely 
  lost 
  through 
  erosion. 
  

  

  6. 
  When 
  the 
  Dighton 
  conglomerate 
  is 
  considered 
  in 
  

   connection 
  with 
  the 
  entire 
  Carboniferous 
  series 
  of 
  the 
  

   basin, 
  it 
  is 
  seen 
  to 
  be 
  at 
  the 
  end 
  of 
  a 
  more 
  or 
  less 
  gradual 
  

   climatic 
  change. 
  A 
  broad 
  area 
  of 
  country 
  was 
  so 
  situ- 
  

   ated 
  through 
  a 
  long 
  period 
  of 
  time 
  that 
  disintegration 
  

   covered 
  the 
  surface 
  with 
  a 
  deep 
  mantle 
  of 
  arkose 
  and 
  

   broken 
  rock. 
  Locally 
  conditions 
  permitted 
  the 
  forma- 
  

   tion 
  of 
  red 
  rocks. 
  Toward 
  the 
  latter 
  part 
  of 
  the 
  Penn- 
  

   sylvanian 
  the 
  climate 
  became 
  more 
  moist, 
  perhaps 
  

   accompanied 
  by 
  an 
  upheaval 
  of 
  the 
  old 
  land 
  mass. 
  The 
  

   increased 
  run-off 
  swept 
  the 
  arkose 
  and 
  broken 
  rock 
  into 
  

   the 
  valleys 
  and 
  started 
  the 
  series 
  of 
  basin 
  beds. 
  As 
  the 
  

   climate 
  became 
  more 
  moist 
  and 
  cooler, 
  erosion 
  continued, 
  

   and 
  a 
  broad 
  alluvial 
  fan 
  or 
  series 
  of 
  fans 
  was 
  built 
  out 
  

   to 
  the 
  west. 
  Over 
  these 
  fans 
  were 
  scattered 
  wooded 
  

   swamps 
  which 
  were 
  buried 
  by 
  the 
  ever-increasing 
  debris 
  

   from 
  the 
  mountains, 
  only 
  to 
  be 
  replaced 
  by 
  new 
  swamps. 
  

  

  