﻿152 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  tinguish 
  the 
  ice-heaped 
  blocks 
  from 
  the 
  frost 
  fracture 
  piles; 
  the 
  

   frost 
  work 
  having, 
  of 
  course, 
  also 
  affected 
  the 
  ice 
  deposits. 
  

  

  In 
  some 
  places 
  the 
  morainal 
  character 
  of 
  the 
  drift 
  is 
  clearly 
  ex- 
  

   pressed 
  by 
  the 
  well 
  known 
  features 
  of 
  irregular 
  surface, 
  mound 
  

   and 
  basin 
  topography, 
  but 
  over 
  most 
  of 
  the 
  area 
  the 
  morainal 
  ele- 
  

   ment 
  has 
  been 
  discriminated 
  by 
  one 
  or 
  the 
  other 
  of 
  two 
  features 
  ; 
  

   unusually 
  stony 
  patches 
  or 
  kettles. 
  Very 
  stony 
  fields 
  with 
  heaps 
  of 
  

   boulders 
  and 
  stone 
  fences, 
  specially 
  if 
  containing 
  considerable 
  per- 
  

   centage 
  of 
  nonlocal 
  rock, 
  have 
  been 
  diagnosed 
  as 
  moraine. 
  Dis- 
  

   crimination 
  is 
  needed, 
  for 
  in 
  a 
  district 
  of 
  ledges, 
  scarps 
  or 
  cliffs, 
  

   specially 
  of 
  the 
  quartzitic 
  Potsdam^ 
  the 
  ground 
  may 
  be 
  strewn 
  with 
  

   rubbish 
  from 
  the 
  native 
  rocks 
  which 
  is 
  not 
  strictly 
  morainal, 
  or 
  

   peripheral 
  to 
  the 
  ice 
  sheet, 
  even 
  if 
  glacial. 
  This 
  criterion 
  of 
  stoni- 
  

   ness 
  is 
  often 
  equivocal 
  and 
  in 
  such 
  cases 
  is 
  usually 
  disregarded. 
  

  

  In 
  districts 
  of 
  clayey 
  till 
  the 
  occurrence 
  of 
  kettles 
  or 
  inclosed 
  

   l.iasins 
  in 
  the 
  drift 
  is 
  interpreted 
  as 
  indicating 
  ice 
  margin 
  deposits, 
  

   and 
  sometimes 
  they 
  may 
  correlate 
  with 
  stony 
  tracts. 
  Over 
  lime- 
  

   stone 
  floors 
  small 
  sinks 
  may 
  simulate 
  kettles, 
  but 
  over 
  the 
  sand- 
  

   stone 
  and 
  crystallines 
  this 
  deception 
  can 
  not 
  occur. 
  

  

  The 
  above 
  description 
  will 
  suggest 
  how 
  difficult 
  if 
  not 
  quite 
  

   impossible 
  it 
  would 
  be 
  to 
  accurately 
  map 
  the 
  morainal 
  deposits 
  over 
  

   the 
  entire 
  area, 
  and 
  this 
  is 
  not 
  attempted. 
  The 
  heavier 
  morainic 
  

   masses 
  are 
  shown 
  in 
  plates 
  44-47. 
  

  

  Boulder 
  moraines. 
  Plate 
  47 
  shows 
  the 
  larger 
  portion 
  of 
  the 
  

   Black 
  river 
  moraine, 
  which 
  continues 
  southwest 
  to 
  and 
  beyond 
  

   Watertown. 
  On 
  this 
  map 
  conventional 
  signs 
  indicate 
  lines 
  and 
  

   ridges 
  of 
  block 
  moraine. 
  Some 
  of 
  these 
  have 
  high 
  rehef 
  and 
  are 
  

   striking 
  features 
  in 
  the 
  landscape. 
  One 
  photograph 
  is 
  given 
  in 
  plate 
  

   56. 
  The 
  character 
  of 
  the 
  ridges 
  as 
  bare 
  limestone 
  blocks 
  is 
  partly 
  

   the 
  result 
  of 
  wave 
  work 
  of 
  the 
  falling 
  waters 
  of 
  Lake 
  Iroquois. 
  

   The 
  Black 
  river 
  delta 
  built 
  in 
  the 
  lake 
  was 
  banked 
  against 
  the 
  

   moraine 
  and 
  partly 
  buried 
  its 
  southeastern 
  border. 
  From 
  the 
  trend 
  

   of 
  these 
  ridges 
  it 
  is 
  apparent 
  that 
  the 
  ice 
  flow 
  constructing 
  them 
  

   was 
  from 
  the 
  northwest, 
  and 
  that 
  the 
  ice 
  margin 
  was 
  spreading 
  

   or 
  deploying 
  on 
  the 
  plain. 
  

  

  The 
  great 
  massing 
  of 
  limestone 
  blocks 
  with 
  very 
  few 
  crystallines 
  

   could 
  hardly 
  have 
  been 
  effected 
  by 
  the 
  earlier 
  ice 
  movement 
  from 
  

   the 
  northeast 
  or 
  north, 
  as 
  the 
  limestone 
  formations 
  do 
  not 
  extend 
  

   far 
  in 
  that 
  direction. 
  The 
  change 
  in 
  direction 
  of 
  flow 
  enabled 
  the 
  

   ice 
  to 
  sweep 
  up 
  the 
  rubbish 
  left 
  on 
  the 
  limestone 
  tract 
  on 
  the 
  north- 
  

   west, 
  and 
  perhaps 
  the 
  new 
  direction 
  of 
  impact, 
  changing 
  from 
  south- 
  

   westv/ard 
  to 
  southeastward, 
  gave 
  the 
  ice 
  a 
  more 
  effective 
  grip 
  for 
  

  

  