﻿474 
  W. 
  Boioie 
  — 
  Distribution 
  of 
  Isostatic 
  Compensation. 
  

  

  compare 
  these 
  average 
  anomalies 
  with 
  those 
  bj 
  the 
  Bouguer 
  

   reduction 
  which 
  postulates 
  an 
  entire 
  absence 
  of 
  isostasy. 
  The 
  

   Bouguer 
  anomalies 
  without 
  regard 
  to 
  sign 
  for 
  217 
  stations 
  in 
  

   the 
  United 
  States 
  are 
  given 
  below 
  for 
  the 
  five 
  classes 
  of 
  topog- 
  

   raphy 
  used 
  in 
  the 
  investigations. 
  

  

  Bouguer 
  

   Mean 
  Anomaly 
  

   without 
  regard 
  

   to 
  sign 
  

  

  Dyne 
  

  

  27 
  coast 
  stations 
  0*02 
  1 
  

  

  46 
  stations 
  near 
  the 
  coast 
  ._ 
  0*025 
  

  

  88 
  stations 
  in 
  the 
  interior, 
  not 
  in 
  mountainous 
  regions 
  0-033 
  

   36 
  stations 
  in 
  mountainous 
  regions, 
  below 
  the 
  general 
  

  

  level.- 
  0-108 
  

  

  20 
  stations 
  in 
  mountainous 
  regions, 
  above 
  the 
  general 
  

  

  level 
  0-111 
  

  

  217 
  stations, 
  all 
  classes 
  of 
  topography 
  0'049 
  

  

  These 
  mean 
  anomalies 
  show 
  a 
  very 
  decided 
  relation 
  to 
  the 
  

   topography. 
  

  

  While 
  the 
  isostatic 
  anomalies 
  without 
  regard 
  to 
  sign 
  show 
  

   no 
  relation 
  to 
  the 
  topography, 
  even 
  for 
  various 
  methods 
  of 
  dis- 
  

   tributing 
  the 
  compensation, 
  yet 
  there 
  is 
  shown 
  some 
  relation 
  to 
  

   the 
  character 
  of 
  the 
  topography 
  when 
  we 
  consider 
  the 
  sign 
  of 
  

   the 
  anomalies. 
  Each 
  method 
  of 
  distribution 
  shows 
  a 
  negative 
  

   mean 
  anomaly 
  with 
  regard 
  to 
  sign 
  for 
  the 
  18 
  coast 
  stations. 
  

   This 
  can 
  probably 
  be 
  explained 
  by 
  the 
  presence 
  of 
  light 
  Ceno- 
  

   zoic 
  material 
  near 
  the 
  coasts.* 
  This 
  subject 
  need 
  not 
  be 
  dis- 
  

   cussed 
  here 
  and 
  we 
  may 
  leave 
  these 
  stations 
  out 
  of 
  consideration. 
  

  

  For 
  the 
  remainder 
  of 
  the 
  topographic 
  groups 
  the 
  means 
  with 
  

   regard 
  to 
  sign 
  show 
  no 
  decided 
  relation 
  to 
  the 
  character 
  of 
  the 
  

   topography 
  for 
  the 
  local 
  and 
  the 
  regional 
  distribution 
  of 
  com- 
  

   pensation 
  out 
  to 
  the 
  limits 
  of 
  zones 
  K 
  (18*8 
  kms.) 
  and 
  M 
  

   (58*8 
  kms.). 
  The 
  ranges 
  in 
  the 
  means 
  are 
  *005, 
  '001 
  and 
  "004, 
  

   respectively, 
  for 
  the 
  three 
  methods. 
  But 
  there 
  is 
  a 
  decided 
  

   relation 
  shown 
  bv 
  the 
  means 
  with 
  regard 
  to 
  sign 
  for 
  the 
  

   regional 
  distribution 
  to 
  the 
  outer 
  limit 
  of 
  zone 
  O 
  (166*7 
  kms.). 
  

   For 
  the 
  22 
  stations 
  in 
  mountain 
  regions 
  below 
  the 
  general 
  

   level 
  the 
  mean 
  is 
  +0*006 
  and 
  for 
  the 
  18 
  stations 
  in 
  mountain- 
  

   ous 
  regions 
  above 
  the 
  general 
  level, 
  the 
  mean 
  with 
  regard 
  to 
  

   sign 
  is 
  — 
  0*010. 
  The 
  range 
  in 
  values 
  is 
  therefore 
  *016, 
  which 
  

   is 
  nearly 
  as 
  great 
  as 
  the 
  average 
  anomaly, 
  without 
  regard 
  to 
  

   sign, 
  by 
  the 
  various 
  methods 
  of 
  distribution 
  for 
  all 
  stations. 
  

  

  If 
  we 
  make 
  the 
  reasonable 
  assumption, 
  that 
  the 
  method 
  

   which 
  shows 
  no 
  deviation 
  from 
  normal 
  with 
  changed 
  topo- 
  

   graphic 
  conditions 
  is 
  nearest 
  the 
  truth, 
  we 
  may 
  conclude 
  that 
  the 
  

  

  * 
  See 
  page 
  76 
  of 
  Special 
  Publication 
  No. 
  40 
  of 
  the 
  U. 
  S. 
  Coast 
  and 
  Geodetic 
  

   Suryey, 
  Investigations 
  of 
  Gravity 
  and 
  Isostasy. 
  

  

  