﻿Brigham 
  — 
  Drift 
  Bowlders 
  in 
  Central 
  New 
  York. 
  227 
  

  

  If 
  to 
  any 
  extent 
  the 
  movement 
  of 
  the 
  bowlders 
  was 
  by 
  rota- 
  

   tion* 
  in 
  the 
  ice 
  mass, 
  the 
  larger 
  and 
  more 
  eqnidimensional 
  

   sandstones 
  would 
  have 
  the 
  advantage 
  in 
  the 
  race. 
  The 
  angu- 
  

   larity 
  of 
  many 
  of 
  the 
  sandstone 
  blocks, 
  however, 
  renders 
  rota- 
  

   tion 
  for 
  this 
  case 
  doubtful. 
  

  

  To 
  sum 
  up 
  briefly 
  the 
  facts 
  of 
  distribution 
  : 
  We 
  find 
  the 
  

   Archaean 
  and 
  more 
  northern 
  Paleozoic 
  fragments 
  strewn 
  over 
  

   the 
  whole 
  district 
  at 
  all 
  altitudes, 
  but 
  diminishing 
  southward 
  

   in 
  size, 
  and 
  sparse 
  in 
  amount 
  on 
  the 
  highest 
  hills, 
  especially 
  to 
  

   the 
  southward, 
  where 
  the 
  tops 
  of 
  the 
  ranges 
  are 
  often 
  surpris- 
  

   ingly 
  free 
  from 
  transported 
  material. 
  f 
  The 
  Oriskany 
  sand- 
  

   stone 
  drops 
  off 
  from 
  the 
  hilltops 
  after 
  about 
  25 
  miles 
  and 
  dis- 
  

   appears, 
  so 
  far 
  as 
  observation 
  goes, 
  at 
  40 
  miles. 
  The 
  Lower 
  

   Helderberg 
  and 
  Corniferous 
  limestones 
  appear 
  only 
  for 
  six 
  or 
  

   eight 
  miles 
  at 
  high 
  levels, 
  but 
  continue 
  far 
  down 
  in 
  the 
  valley 
  

   drift. 
  As 
  a 
  rule 
  local 
  material 
  far 
  exceeds 
  the 
  imported, 
  at 
  a 
  

   given 
  point.;}; 
  Exceptions 
  to 
  this 
  rule 
  are 
  due 
  to 
  special 
  local 
  

   conditions. 
  We 
  may 
  note 
  as 
  factors 
  on 
  which 
  the 
  local 
  distri- 
  

   bution 
  and 
  southward 
  extension 
  depend 
  : 
  accessibility 
  of 
  the 
  

   preglacial 
  ledges 
  for 
  plucking 
  ; 
  the 
  bedding 
  and 
  joint 
  planes 
  

   and 
  power 
  of 
  current, 
  as 
  controlling 
  size 
  and 
  number 
  of 
  frag- 
  

   ments 
  plucked; 
  surrounding 
  topography 
  as 
  related 
  to 
  removal; 
  

   southward 
  extension 
  and 
  limit 
  of 
  the 
  current 
  doing 
  the 
  pluck- 
  

   ing 
  ; 
  lithological 
  character 
  as 
  controlling 
  change 
  of 
  form 
  and 
  

   reduction 
  of 
  size 
  during 
  carriage 
  ; 
  zone 
  of 
  carriage 
  and 
  mode 
  

   of 
  transport 
  as 
  affecting 
  form, 
  size 
  and 
  manner 
  of 
  deposition. 
  

   This 
  is 
  doubtless 
  a 
  partial 
  statement, 
  and 
  the 
  several 
  factors 
  

   will 
  be 
  found 
  in 
  combinations 
  of 
  endless 
  variety. 
  

  

  Whatever 
  may 
  be 
  said 
  of 
  the 
  more 
  northern 
  material, 
  it 
  

   seems 
  plain 
  that 
  that 
  from 
  the 
  Oriskany 
  Falls 
  region 
  was 
  carried 
  

   in 
  the 
  basal 
  portions 
  of 
  the 
  ice. 
  The 
  position 
  of 
  the 
  ledges 
  

   and 
  the 
  combing 
  out 
  of 
  the 
  greater 
  number 
  of 
  large 
  blocks 
  by 
  

   the 
  hill 
  range, 
  seem 
  to 
  assure 
  this 
  view. 
  A 
  valley 
  tongue, 
  

   whose 
  top 
  barely 
  reached 
  and 
  caught 
  away 
  the 
  blocks, 
  does 
  not 
  

   satisfy 
  the 
  case. 
  It 
  could 
  not 
  have 
  grappled 
  the 
  masses 
  with 
  

   sufficient 
  power. 
  It 
  certainly 
  could 
  not 
  have 
  wrought 
  the 
  very 
  

   considerable 
  elevation 
  which 
  their 
  present 
  situation 
  demon- 
  

   strates. 
  Had 
  the 
  bowlders 
  risen 
  to 
  the 
  upper 
  zones 
  of 
  the 
  

   ice 
  while 
  it 
  was 
  at 
  its 
  greatest 
  thickness, 
  the 
  hilltops 
  should 
  

   show 
  more 
  of 
  far 
  travelled 
  material. 
  It 
  is 
  to 
  be 
  added 
  that 
  

   while 
  some 
  of 
  the 
  bowlders 
  are 
  rounded, 
  others 
  in 
  the 
  same 
  

   groups 
  are 
  notably 
  angular, 
  joint 
  blocks 
  carried 
  from 
  5 
  to 
  12 
  

   miles 
  with 
  almost 
  no 
  reduction 
  of 
  angles. 
  

  

  * 
  T. 
  C. 
  Chamberlin, 
  Rock 
  Scorings 
  of 
  the 
  Great 
  Ice 
  Invasions, 
  7th 
  Ann. 
  Rep. 
  

   U. 
  S. 
  G. 
  S.. 
  pp. 
  232-233. 
  

  

  + 
  See 
  ref. 
  to 
  Rep. 
  Z., 
  Pa. 
  Surv. 
  already 
  cited; 
  also, 
  J. 
  C. 
  Branner, 
  this 
  Journal, 
  

   III. 
  vol. 
  xixii, 
  p. 
  365. 
  

  

  % 
  Cf. 
  R. 
  D 
  Salisbury, 
  Ann. 
  Rep. 
  Geol. 
  Surv. 
  X. 
  J., 
  1891, 
  pp. 
  6S-70. 
  

  

  