﻿236 
  Crosby 
  — 
  Geology 
  of 
  Newport 
  Neck 
  and 
  Conanicut 
  Is. 
  

  

  regular 
  member 
  of 
  the 
  Carboniferous 
  series, 
  seems 
  to 
  be 
  proved 
  

   by 
  the 
  following 
  considerations 
  : 
  First, 
  it 
  is 
  composed 
  chiefly 
  

   of 
  granite 
  debris 
  and 
  not 
  of 
  fragments 
  of 
  shale, 
  as 
  it 
  undoubt- 
  

   edly 
  would 
  be 
  if 
  due 
  to 
  the 
  mutual 
  friction 
  of 
  the 
  granite 
  and 
  

   shale. 
  Second, 
  it 
  is 
  essentially 
  identical 
  with 
  the 
  arkose 
  which 
  

   elsewhere 
  in 
  the 
  Narragansett 
  Basin 
  clearly 
  underlies 
  the 
  green 
  

   and 
  gray 
  shales, 
  as 
  on 
  Rose 
  Island, 
  Coasters 
  Harbor 
  Island, 
  and 
  

   Sachuest 
  Neck, 
  and 
  on 
  the 
  mainland 
  at 
  Tiverton 
  and 
  Fall 
  

   River 
  ; 
  and 
  is 
  quite 
  certainly, 
  as 
  held 
  by 
  Dale, 
  Collie, 
  and 
  

   others, 
  the 
  basal 
  member 
  of 
  the 
  Carboniferous 
  series. 
  Collie 
  

   says, 
  " 
  the 
  arkose 
  (of 
  Conanicut 
  Island) 
  is 
  not 
  a 
  local 
  exposure. 
  

   It 
  is 
  everywhere 
  present, 
  lying 
  between 
  the 
  granite 
  and 
  the 
  

   overlying 
  schist 
  (shale). 
  Well-diggers 
  state 
  that 
  in 
  all 
  parts 
  of 
  

   the 
  island 
  they 
  invariably 
  come 
  upon 
  a 
  layer 
  of 
  rotten 
  granite 
  

   before 
  the 
  hard 
  granite 
  is 
  reached." 
  

  

  The 
  arkose 
  clearly 
  follows 
  the 
  northern 
  border 
  of 
  the 
  granite 
  

   and 
  flinty 
  slate, 
  cutting 
  across 
  the 
  north-south 
  strike 
  of 
  the 
  

   shales. 
  This 
  marked 
  discordance 
  of 
  the 
  arkose 
  and 
  shales 
  sug- 
  

   gests 
  a 
  northeast-southwest 
  fault 
  between 
  them, 
  with 
  the 
  down- 
  

   throw 
  on 
  the 
  northwest. 
  Of 
  this 
  fault 
  we 
  have 
  abundant 
  

   evidence 
  on 
  the 
  shores, 
  and 
  especially 
  on 
  the 
  eastern 
  shore, 
  

   where 
  we 
  find 
  between 
  the 
  arkose 
  and 
  shale 
  a 
  magnificent 
  

   development 
  of 
  fault 
  breccia. 
  For 
  a 
  breadth 
  of 
  about 
  fifty 
  

   feet 
  the 
  green 
  and 
  black 
  shales 
  are 
  completely 
  brecciated, 
  the 
  

   fragments 
  being 
  cemented 
  by 
  an 
  imperfectly 
  lithified 
  argilla- 
  

   ceous 
  paste 
  ; 
  and 
  north 
  of 
  this 
  crushed 
  zone 
  are 
  many 
  minor 
  

   shear 
  planes 
  approximately 
  parallel 
  to 
  the 
  main 
  fault 
  and 
  trans- 
  

   verse 
  to 
  the 
  strike 
  of 
  the 
  shales. 
  This 
  great 
  fault 
  evidently 
  

   belongs 
  to 
  the 
  same 
  system 
  as 
  those 
  on 
  Newport 
  Neck, 
  the 
  

   chief 
  difference 
  being 
  that 
  in 
  the 
  case 
  of 
  the 
  latter 
  the 
  upthrow 
  

   has 
  been 
  sufficient 
  to 
  carry 
  the 
  arkose 
  wholly 
  above 
  the 
  present 
  

   plane 
  of 
  erosion. 
  The 
  relations 
  of 
  the 
  arkose 
  on 
  Conanicut 
  

   Island 
  point 
  distinctly 
  to 
  the 
  conclusion 
  that 
  the 
  faults 
  date 
  

   from 
  the 
  time 
  when 
  the 
  Carboniferous 
  strata 
  were 
  folded 
  and 
  

   the 
  rigid 
  floor 
  of 
  granite 
  and 
  flinty 
  slate 
  was 
  upheaved, 
  that 
  is, 
  

   during 
  the 
  Appalachian 
  revolution. 
  

  

  Concerning 
  the 
  southwest 
  extension 
  of 
  this 
  fault 
  nothing 
  

   can 
  be 
  positively 
  asserted. 
  The 
  non-occurrence 
  of 
  the 
  ancient 
  

   slate 
  and 
  granite 
  on 
  the 
  Beaver 
  tail 
  portion 
  of 
  the 
  island 
  sug- 
  

   gests 
  a 
  fault 
  parallel 
  with 
  the 
  major 
  axis 
  of 
  Mackerel 
  Cove. 
  

   The 
  trap 
  (minette) 
  dikes 
  (fig. 
  1), 
  as 
  Collie 
  has 
  pointed 
  out, 
  cut 
  

   both 
  the 
  granite 
  and 
  the 
  shales, 
  and 
  must 
  be 
  post-Carboniferous, 
  

   probably 
  dating, 
  like 
  the 
  great 
  dikes 
  of 
  the 
  Paradise 
  Rocks, 
  

   from 
  the 
  folding 
  and 
  faulting 
  of 
  the 
  strata, 
  This 
  completes 
  

   the 
  parallelism 
  with 
  the 
  geology 
  of 
  the 
  Boston 
  Basin, 
  where 
  

   the 
  granitic 
  rocks 
  — 
  granite, 
  diorite, 
  and 
  felsite 
  — 
  are 
  clearly 
  

   newer 
  than 
  the 
  Cambrian 
  slates 
  and 
  older 
  than 
  the 
  Carbonifer- 
  

   ous 
  strata, 
  and 
  the 
  trap 
  dikes 
  are 
  post-Carboniferous, 
  except 
  a 
  

   few 
  which 
  antedate 
  the 
  granite. 
  

  

  