﻿Taylor 
  — 
  Scoured 
  Bowlders 
  of 
  the 
  Mattawa 
  Valley. 
  209 
  

  

  The 
  bowlders 
  which 
  show 
  these 
  modifications 
  are 
  almost 
  all 
  

   large, 
  ranging 
  from 
  about 
  two 
  to 
  twenty-five 
  or 
  thirty 
  feet 
  in 
  

   diameter. 
  Bowlders 
  of 
  large 
  size 
  are 
  extremely 
  numerous 
  on 
  

   the 
  areas 
  where 
  these 
  forms 
  are 
  found, 
  completely 
  covering 
  

   over 
  the 
  surface 
  of 
  the 
  ground. 
  They 
  are 
  all 
  of 
  very 
  hard 
  

   crystalline 
  rock; 
  some 
  are 
  red 
  or 
  gray 
  granite, 
  and 
  some 
  are 
  

   greenstones, 
  but 
  by 
  far 
  the 
  greater 
  number 
  are 
  of 
  the 
  hard 
  

   foliated 
  gneiss 
  which 
  is 
  so 
  common 
  in 
  the 
  surrounding 
  region. 
  

   Many 
  of 
  the 
  large 
  bowlders 
  of 
  gneiss, 
  even 
  after 
  the 
  long 
  

   exposure 
  to 
  weather 
  which 
  they 
  have 
  undergone, 
  show 
  no 
  

   signs 
  of 
  fracture 
  or 
  breaking. 
  So 
  far 
  as 
  observed 
  the 
  bowl- 
  

   dery 
  areas 
  of 
  the 
  former 
  rapids 
  of 
  the 
  river 
  appear 
  to 
  be 
  asso- 
  

   ciated 
  with 
  belts 
  of 
  morainic 
  accumulation.' 
  

  

  Varieties. 
  

  

  One 
  may 
  best 
  learn 
  the 
  processes 
  by 
  which 
  scoured 
  bowlders 
  

   are 
  made 
  by 
  studying 
  the 
  action 
  of 
  the 
  current 
  in 
  bowldery 
  

   rapids 
  of 
  the 
  modern 
  river 
  at 
  a 
  time 
  of 
  low 
  water. 
  In 
  passing 
  

   over 
  and 
  among 
  the 
  bowlders 
  the 
  current 
  is 
  very 
  much 
  dis- 
  

   turbed. 
  It 
  is 
  turned 
  aside 
  suddenly 
  and 
  thrown 
  this 
  way 
  and 
  

   that 
  ; 
  it 
  strikes 
  against 
  the 
  front 
  or 
  the 
  sides 
  of 
  some 
  bowlders 
  

   and 
  passes 
  through 
  narrow 
  passages 
  between 
  others 
  ; 
  it 
  glides 
  

   smoothly 
  over 
  the 
  tops 
  of 
  some 
  and 
  falls 
  heavily 
  on 
  the 
  tops 
  

   of 
  others, 
  and 
  in 
  a 
  few 
  cases 
  it 
  is 
  thrown 
  into 
  a 
  vortex 
  whirl 
  

   in 
  an 
  angle 
  or 
  slight 
  depression 
  on 
  the 
  surface 
  of 
  a 
  bowlder. 
  

   Just 
  as 
  the 
  billows 
  in 
  a 
  rocky 
  rapid 
  remain 
  constant 
  in 
  posi- 
  

   tion, 
  so 
  these 
  various 
  turns 
  and 
  whirls 
  in 
  the 
  current 
  beneath 
  

   the 
  surface 
  remain 
  constant 
  in 
  place 
  and 
  action 
  so 
  long 
  as 
  the 
  

   bowlders 
  lie 
  unmoved. 
  Thus 
  the 
  currents 
  that 
  play 
  upon 
  a 
  

   bowlder 
  are 
  generally 
  constant 
  in 
  the 
  particular 
  manner 
  of 
  

   their 
  action. 
  Where 
  sand 
  and 
  small 
  pebbles 
  are 
  being 
  borne 
  

   along 
  in 
  small 
  or 
  moderate 
  quantities, 
  they 
  follow 
  the 
  devia- 
  

   tions 
  of 
  the 
  current 
  from 
  bowlder 
  to 
  bowlder, 
  and 
  each 
  sand- 
  

   grain 
  and 
  pebble 
  does 
  a 
  little 
  work 
  of 
  abrasion 
  as 
  it 
  goes 
  along. 
  

   Every 
  one 
  that 
  follows 
  the 
  same 
  course 
  among 
  the 
  bowlders 
  

   performs 
  its 
  iota 
  of 
  work 
  upon 
  the 
  same 
  part, 
  so 
  that 
  the 
  wear 
  

   on 
  each 
  bowlder 
  comes 
  where 
  the 
  current 
  impinges 
  upon 
  it. 
  

   In 
  the 
  course 
  of 
  time, 
  but 
  very 
  slowly, 
  the 
  bowlders 
  are 
  worn 
  

   into 
  the 
  fantastic 
  shapes 
  which 
  are 
  here 
  called 
  scoured 
  bowlders. 
  

   The 
  forms 
  which 
  the 
  bowlders 
  take 
  under 
  the 
  scour 
  of 
  the 
  

   sand- 
  and 
  pebble-bearing 
  current 
  are 
  quite 
  varied. 
  But 
  after 
  

   examining 
  several 
  hundreds 
  of 
  specimens 
  it 
  became 
  apparent 
  

   that 
  all 
  could 
  be 
  classified 
  according 
  to 
  their 
  forms 
  under 
  a 
  few 
  

   heads, 
  although 
  a 
  few 
  individual 
  cases 
  would 
  have 
  to 
  stand 
  as 
  

   intermediate 
  forms. 
  Six 
  varieties 
  may 
  be 
  distinguished 
  as 
  

   follows 
  : 
  

  

  