﻿270 
  JOURNAL 
  OF 
  THE 
  WASHINGTON 
  ACADEMY 
  OF 
  SCIENCES 
  VOL. 
  12, 
  NO. 
  11 
  

  

  lead 
  us 
  to 
  believe 
  that 
  the 
  theory 
  of 
  isostasy 
  is 
  substantially 
  true 
  and 
  that 
  the 
  

   amount 
  of 
  matter 
  in 
  blocks 
  of 
  the 
  crust 
  of 
  equal 
  cross 
  section 
  at 
  the 
  depth 
  

   of 
  compensation 
  is 
  very 
  nearly 
  equal 
  in 
  various 
  parts 
  of 
  the 
  earth. 
  

  

  Since 
  the 
  earth's 
  crust 
  is 
  in 
  hydrostatic 
  or 
  isostatic 
  equilibrium 
  now 
  it 
  is 
  

   a 
  logical 
  conclusion 
  that 
  it 
  has 
  been 
  so 
  during 
  the 
  earlier 
  geological 
  periods 
  

   and 
  therefore 
  we 
  must 
  conclude 
  that 
  movements 
  within 
  the 
  earth's 
  crust 
  which 
  

   are 
  recorded 
  in 
  geological 
  strata 
  and 
  structures 
  did 
  not 
  materially 
  increase 
  

   the 
  amount 
  of 
  matter 
  in 
  any 
  block 
  of 
  the 
  crust. 
  

  

  There 
  are 
  four 
  rather 
  distinct 
  movements 
  of 
  material 
  within 
  the 
  earth's 
  

   crust 
  or 
  at 
  its 
  surface. 
  First 
  the 
  transportation 
  of 
  material 
  by 
  wind 
  and 
  water 
  

   from 
  one 
  place 
  to 
  another 
  over 
  the 
  surface. 
  Second, 
  a 
  downward 
  movement 
  

   of 
  the 
  material 
  of 
  the 
  earth's 
  crust 
  under 
  the 
  area 
  of 
  sedimentation, 
  some 
  of 
  

   this 
  movement 
  being 
  due 
  to 
  a 
  yielding 
  under 
  the 
  load 
  of 
  the 
  sediment 
  and 
  the 
  

   remainder 
  to 
  thermal 
  contraction 
  and 
  a 
  contraction 
  due 
  to 
  physical 
  or 
  chem- 
  

   ical 
  action. 
  Third, 
  a 
  movement 
  below 
  the 
  earth's 
  crust, 
  in 
  a 
  more 
  or 
  less 
  

   horizontal 
  direction, 
  of 
  material 
  which 
  is 
  yielding 
  to 
  long 
  continued 
  horizon- 
  

   tal 
  stress. 
  This 
  material 
  flows 
  from 
  the 
  block 
  of 
  the 
  earth's 
  crust 
  on 
  which 
  

   sediments 
  are 
  placed 
  toward 
  the 
  block 
  from 
  whose 
  surface 
  material 
  was 
  

   eroded. 
  The 
  fourth 
  is 
  the 
  upward 
  movement 
  of 
  the 
  material 
  in 
  a 
  block 
  of 
  

   the 
  earth's 
  crust 
  under 
  the 
  area 
  of 
  erosion. 
  As 
  the 
  material 
  is 
  eroded 
  from 
  

   the 
  surface, 
  the 
  isostatic 
  balance 
  is 
  restored 
  by 
  the 
  entering 
  of 
  material 
  at 
  the 
  

   bottom 
  of 
  the 
  block, 
  thus 
  causing 
  the 
  block 
  to 
  rise. 
  

  

  It 
  seems 
  to 
  be 
  reasonably 
  certain 
  that 
  mountain 
  systems 
  are 
  caused 
  by 
  

   a 
  vertical 
  uplift 
  due 
  to 
  local 
  causes 
  rather 
  than 
  to 
  horizontal 
  thrusts 
  result- 
  

   ing 
  from 
  forces 
  acting 
  from 
  great 
  distances. 
  The 
  distortions 
  of 
  sedimentary 
  

   rocks 
  which 
  are 
  visible 
  in 
  most 
  elevated 
  regions 
  appear 
  to 
  be 
  incidents 
  to 
  the 
  

   sinking 
  of 
  an 
  area 
  under 
  sedimentation 
  and 
  to 
  subsequent 
  uplifting 
  of 
  the 
  

   area. 
  As 
  an 
  area 
  once 
  subject 
  to 
  sedimentation 
  is 
  uplifted, 
  and 
  since 
  this 
  

   uplift 
  must 
  be 
  a 
  result 
  of 
  a 
  change 
  in 
  density 
  within 
  the 
  block, 
  the 
  upward 
  

   movement 
  would 
  follow 
  lines 
  of 
  least 
  resistance. 
  The 
  direction 
  of 
  such 
  lines 
  

   would 
  frequently 
  be 
  inclined 
  to 
  the 
  vertical 
  and 
  at 
  times 
  be 
  almost 
  or 
  quite 
  

   horizontal. 
  

  

  The 
  change 
  in 
  density 
  in 
  a 
  block 
  of 
  the 
  earth's 
  crust 
  which 
  has 
  undergone 
  

   heavy 
  sedimentation 
  may 
  be 
  due 
  to 
  the 
  fact 
  that 
  the 
  material 
  of 
  the 
  block 
  has 
  

   been 
  pushed 
  down 
  into 
  regions 
  hotter 
  than 
  that 
  originally 
  occupied. 
  The 
  shrink- 
  

   ing 
  and 
  increase 
  of 
  density 
  of 
  a 
  block 
  under 
  an 
  area 
  of 
  erosion 
  may 
  be 
  due 
  to 
  

   the 
  fact 
  that 
  many 
  thousands 
  of 
  feet 
  of 
  material 
  had 
  been 
  eroded, 
  thus 
  re- 
  

   sulting 
  in 
  the 
  raising 
  of 
  the 
  material 
  of 
  the 
  block 
  below 
  the 
  area 
  into 
  regions 
  

   that 
  were 
  much 
  cooler 
  than 
  that 
  which 
  the 
  material 
  had 
  originally 
  occupied. 
  

   This 
  change 
  in 
  temperature, 
  which 
  may 
  be 
  as 
  much 
  as 
  200 
  or 
  300 
  degrees 
  

   Centigrade, 
  may 
  cause 
  a 
  thermal 
  contraction 
  as 
  well 
  as 
  an 
  increase 
  in 
  density 
  

   due 
  to 
  physical 
  or 
  chemical 
  changes 
  other 
  than 
  the 
  thermal 
  expansion. 
  

  

  It 
  is 
  certain 
  that 
  the 
  theory 
  of 
  isostasy 
  must 
  be 
  taken 
  into 
  consideration 
  

   in 
  geological 
  investigations, 
  especially 
  those 
  having 
  to 
  do 
  with 
  dynamic 
  and 
  

   structural 
  geology. 
  

  

  H. 
  V. 
  Sverdrup: 
  The 
  scientific 
  work 
  of 
  the 
  present 
  Amundsen 
  Arctic 
  Expe- 
  

   dition 
  (illustrated). 
  It 
  was 
  discussed 
  by 
  Messrs. 
  Marmer 
  and 
  Beall. 
  

  

  (Author's 
  abstract.) 
  Captain 
  Amundsen's 
  Expedition 
  left 
  Norway 
  

   in 
  July, 
  1918, 
  with 
  the 
  intention 
  to 
  follow 
  the 
  coast 
  of 
  Siberia 
  eastward 
  to 
  the 
  

   vicinity 
  of 
  Bering 
  Strait, 
  proceed 
  thence 
  towards 
  the 
  north, 
  let 
  the 
  vessel, 
  

   the 
  "Maud," 
  freeze 
  in 
  and 
  drift 
  with 
  the 
  ice 
  fields 
  across 
  the 
  Polar 
  Seas 
  back 
  

  

  