﻿210 
  Taylor 
  — 
  Scoured 
  Bowlders 
  of 
  the 
  Mattawa 
  Valley. 
  

  

  Scoured 
  Bowlders. 
  

  

  1. 
  Pierced 
  (Ring-bowlders). 
  

  

  2. 
  Basined. 
  

  

  3. 
  Niched. 
  

  

  4. 
  Guttered. 
  

  

  5. 
  Facetted. 
  

  

  6. 
  Smoothed. 
  

  

  The 
  table 
  of 
  varieties 
  of 
  form 
  as 
  given 
  above 
  is 
  offered 
  

   only 
  provisionally. 
  For 
  it 
  is 
  quite 
  probable 
  that 
  a 
  more 
  

   extended 
  study 
  of 
  the 
  subject 
  would 
  suggest 
  some 
  modifica- 
  

   tions. 
  In 
  forming 
  the 
  table, 
  however, 
  the 
  writer 
  has 
  had 
  the 
  

   advantage 
  of 
  discussion 
  and 
  joint 
  observation 
  with 
  Dr. 
  Robert 
  

   Bell, 
  Assistant 
  Director 
  of 
  the 
  Geological 
  Survey 
  of 
  Canada. 
  

   Shortly 
  after 
  the 
  beginning 
  of 
  the 
  study 
  of 
  the 
  bowlders 
  at 
  

   Mattaw 
  T 
  a, 
  Dr. 
  Bell 
  arrived 
  from 
  James 
  Bay 
  and 
  during 
  three 
  or 
  

   four 
  days 
  delay 
  from 
  other 
  causes, 
  gave 
  a 
  part 
  of 
  his 
  time 
  to 
  

   the 
  study 
  of 
  the 
  scoured 
  bowlders. 
  The. 
  names 
  of 
  some 
  of 
  the 
  

   varieties 
  as 
  presented 
  in 
  the 
  table 
  were 
  suggested 
  by 
  him. 
  

   These 
  names 
  are 
  based 
  mainly 
  on 
  forms 
  of 
  scoured 
  bowlders 
  

   found 
  on 
  the 
  terraces 
  at 
  Mattawa 
  and 
  in 
  the 
  modern 
  rapids 
  of 
  

   the 
  Mattawa 
  and 
  Ottawa 
  rivers. 
  The 
  observations 
  of 
  this 
  

   season, 
  however, 
  are 
  not 
  the 
  only 
  ones 
  that 
  the 
  writer 
  has 
  

   made. 
  Basined 
  bowlders 
  were 
  observed 
  in 
  1895 
  in 
  the 
  rapids 
  

   of 
  the 
  Ottawa 
  both 
  above 
  and 
  below 
  Mattawa 
  and 
  also 
  in 
  the 
  

   rapids 
  of 
  the 
  Nipigon. 
  Some 
  of 
  the 
  less 
  pronounced 
  forms 
  

   were 
  found 
  in 
  1894 
  in 
  several 
  of 
  the 
  streams 
  that 
  course 
  down 
  

   the 
  slopes 
  of 
  the 
  Alps, 
  in 
  the 
  Maggia 
  especially, 
  and 
  to 
  some 
  

   extent 
  also 
  in 
  the 
  Toce 
  and 
  Ticino. 
  In 
  1893 
  a 
  few 
  basined 
  

   bowlders 
  were 
  seen 
  in 
  the 
  Au 
  Sable 
  and 
  Saranac 
  rivers 
  in 
  the 
  

   Adirondacks. 
  The 
  first 
  bowlders 
  of 
  this 
  kind 
  noted 
  by 
  the 
  

   writer 
  were 
  seen 
  in 
  1888 
  and 
  1889 
  in 
  some 
  of 
  the 
  rapids 
  of 
  

   Grand 
  river 
  above 
  Hot 
  Sulphur 
  Springs 
  in 
  Middle 
  Park, 
  Colo- 
  

   rado, 
  and 
  they 
  were 
  also 
  seen 
  in 
  several 
  other 
  rivers 
  in 
  the 
  

   same 
  state. 
  Some 
  of 
  those 
  in 
  Grand 
  river 
  show 
  well-developed 
  

   potholes. 
  

  

  Distribution. 
  

  

  Scoured 
  bowlders 
  of 
  the 
  more 
  pronounced 
  types 
  may 
  be 
  pro- 
  

   duced 
  in 
  almost 
  any 
  stream 
  of 
  large 
  or 
  moderate 
  size 
  provided 
  

   certain 
  conditions 
  of 
  stability 
  obtain. 
  The 
  bowlders 
  must 
  be 
  

   permanent 
  in 
  position 
  for 
  a 
  long 
  period, 
  and 
  the 
  general 
  direc- 
  

   tion 
  of 
  the 
  current 
  must 
  not 
  change. 
  There 
  must 
  also 
  be 
  a 
  

   fairly 
  constant 
  supply 
  of 
  sand 
  and 
  gravel, 
  moderate 
  in 
  amount, 
  

   for 
  the 
  current 
  to 
  roll 
  along 
  as 
  it 
  moves 
  over 
  the 
  bowlders. 
  

   Streams 
  meandering 
  in 
  alluvial 
  plains 
  are 
  not 
  likely 
  to 
  show 
  

   effects 
  of 
  this 
  kind. 
  Even 
  streams 
  flowing 
  in 
  drift 
  beds 
  suffer 
  

   so 
  many 
  alterations 
  of 
  their 
  courses, 
  due 
  to 
  caving 
  banks 
  and 
  

  

  