﻿1 
  62 
  

  

  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  amples 
  of 
  the 
  effect 
  of 
  the 
  dragging 
  pressure 
  and 
  the 
  pei 
  

   force 
  of 
  the 
  boulder-shod 
  ice. 
  The 
  rock 
  is 
  too 
  hard 
  to 
  accep 
  

   furrowing 
  or 
  mass 
  removal 
  on 
  the 
  flat 
  surfaces, 
  but 
  its 
  bri 
  cleness 
  

   favors 
  the 
  production 
  of 
  fractures 
  due 
  to 
  compression 
  and 
  t 
  ■ 
  " 
  

   ing 
  force. 
  Of 
  these 
  features 
  two 
  classes 
  will 
  be 
  briefly 
  des 
  i'^i 
  

  

  The 
  hard 
  boulders 
  held 
  as 
  planes 
  and 
  hammers 
  in 
  the 
  bott 
  n 
  ice 
  

   have 
  produced 
  two 
  kinds 
  of 
  curving 
  fractures, 
  one 
  class 
  conv 
  

   stream 
  or 
  toward 
  the 
  boulder, 
  the 
  other 
  convex 
  downstream 
  c 
  

   cave 
  toward 
  the 
  boulder. 
  Those 
  with 
  the 
  concavity 
  facing 
  

   stream, 
  that 
  is 
  to 
  say, 
  with 
  the 
  convexity 
  toward 
  the 
  producing 
  ccoi, 
  

   fall 
  under 
  the 
  category 
  of 
  " 
  cones 
  of 
  percussion 
  " 
  or 
  " 
  chnttcr 
  

   marks." 
  Many 
  excellent 
  examples 
  of 
  these 
  concentric 
  fractur 
  re 
  

   seen, 
  some 
  of 
  large 
  size 
  or 
  up 
  to 
  lo 
  inches 
  of 
  arc 
  and 
  forming 
  iiom 
  

   one 
  quarter 
  to 
  one 
  third 
  of 
  the 
  circle. 
  Sometimes 
  the 
  parallel 
  r. 
  >n- 
  

   centric 
  fractures 
  are 
  closely 
  crowded, 
  several 
  within 
  an 
  inch 
  

   are 
  usually 
  somewhat 
  more 
  open, 
  three 
  or 
  four 
  or 
  less 
  to 
  the 
  inch. 
  

   Figure 
  13 
  is 
  traced 
  from 
  a 
  " 
  rub 
  " 
  taken 
  by 
  the 
  road 
  near 
  the 
  house 
  

  

  Six 
  I 
  n 
  che5 
  

  

  Fig. 
  13 
  Chatter 
  fractuies 
  

  

  of 
  William 
  Northrup, 
  3 
  miles 
  northwest 
  of 
  Redwood 
  and 
  3 
  miles 
  

   east 
  of 
  Alexandria 
  Bay, 
  and 
  about 
  ^ 
  of 
  a 
  mile 
  northeast 
  of 
  thq 
  

   curved 
  scorings 
  described 
  above. 
  In 
  this 
  case 
  11 
  fracture 
  lines 
  lie! 
  

   within 
  4 
  inches 
  along 
  the 
  axis 
  of 
  the 
  curvature, 
  most 
  of 
  them 
  beinfi 
  

  

  