﻿MAR. 
  4, 
  1922 
  PARIS 
  : 
  some 
  problems 
  of 
  the 
  sea 
  127 
  

  

  It 
  is 
  therefore 
  important 
  that 
  the 
  relation 
  of 
  the 
  land 
  elevations 
  to 
  sea 
  

   level 
  be 
  studied 
  and 
  accurately 
  known. 
  A 
  knowledge 
  of 
  this 
  relation 
  

   is 
  vital 
  to 
  the 
  study 
  of 
  the 
  subsidence 
  or 
  emergence 
  of 
  land 
  areas. 
  

  

  That 
  there 
  have 
  been 
  great 
  uplifts 
  and 
  subsidences 
  in 
  the 
  surface 
  

   materials 
  of 
  the 
  earth 
  in 
  past 
  ages 
  is 
  well 
  known. 
  How 
  long 
  these 
  

   were 
  in 
  being 
  accomplished, 
  especially 
  the 
  uplifts, 
  is 
  not 
  so 
  well 
  known. 
  

   Adjustments 
  of 
  the 
  material 
  of 
  the 
  lithosphere 
  have 
  not 
  ceased, 
  and 
  

   these 
  adjustments 
  generahy 
  result 
  in 
  some 
  changes 
  in 
  reference 
  to 
  

   sea 
  level. 
  

  

  Of 
  course 
  the 
  duration 
  of 
  one 
  generation 
  is 
  a 
  short 
  time 
  in 
  which 
  

   to 
  study 
  by 
  physical 
  observations 
  any 
  facts 
  of 
  subsidence 
  now 
  in 
  

   operation, 
  but 
  the 
  observations 
  should 
  be 
  arranged 
  by 
  this 
  generation 
  

   and 
  carried 
  out 
  systematically 
  and 
  handed 
  on 
  to 
  the 
  next, 
  so 
  that 
  

   cumulative 
  evidence 
  may 
  later 
  establish 
  what 
  the 
  facts 
  are 
  relative 
  

   to 
  changes 
  in 
  land 
  elevations. 
  

  

  These 
  observed 
  facts 
  must 
  be 
  closely 
  related 
  to 
  tidal 
  observations 
  

   of 
  one 
  or 
  two 
  years' 
  duration 
  all 
  along 
  the 
  coasts, 
  connected 
  by 
  lines 
  

   of 
  precise 
  levels. 
  These 
  tidal 
  observations 
  must 
  be 
  simultaneous 
  

   with 
  tidal 
  observations 
  at 
  standard 
  base 
  tidal 
  stations 
  where 
  a 
  long 
  

   series 
  of 
  observations 
  have 
  already 
  been 
  or 
  are 
  being 
  secured. 
  

  

  No 
  systematic 
  work 
  for 
  accurate 
  subsidence 
  determinations 
  has 
  

   been 
  carried 
  out 
  anywhere, 
  as 
  far 
  as 
  I 
  know, 
  though 
  there 
  are 
  a 
  few 
  

   cases 
  where 
  precise 
  levels 
  were 
  run 
  between 
  bench 
  marks 
  after 
  inter- 
  

   vals 
  of 
  from 
  25 
  to 
  78 
  years. 
  ^ 
  Our 
  present 
  knowledge 
  of 
  the 
  changes 
  in 
  

   the 
  relation 
  of 
  sea 
  and 
  land 
  elevations 
  (except 
  those 
  due 
  to 
  sudden 
  

   changes) 
  depends 
  almost 
  entirely 
  upon 
  deductions 
  from 
  geologic 
  

   evidence 
  found 
  in 
  the 
  fossil 
  remains 
  of 
  sedimentary 
  rocks, 
  studies 
  of 
  

   coastal 
  erosion, 
  and 
  perhaps 
  in 
  the 
  study 
  of 
  coral 
  reef 
  formation 
  

   about 
  the 
  coasts 
  and 
  around 
  the 
  islands 
  of 
  tropical 
  seas. 
  

  

  In 
  this 
  connection 
  it 
  seems 
  proper 
  to 
  emphasize 
  the 
  importance 
  of 
  

   having 
  hydrographic 
  surveys 
  about 
  the 
  islands 
  of 
  the 
  tropical 
  seas 
  

   especially, 
  not 
  only 
  for 
  geographical 
  reasons 
  and 
  for 
  purposes 
  of 
  safer 
  

   navigation 
  but 
  also 
  for 
  the 
  use 
  in 
  the 
  study 
  of 
  coral 
  formation 
  and 
  also 
  

   to 
  afford 
  us 
  information 
  of 
  shore 
  line 
  changes 
  effected 
  through 
  sub- 
  

   sidence, 
  uplift, 
  and 
  erosion. 
  

  

  Terrestrial 
  magnetism. 
  — 
  The 
  problem 
  of 
  the 
  earth's 
  magnetism 
  

   is 
  about 
  the 
  most 
  difficult 
  of 
  all 
  the 
  unsolved 
  problems 
  of 
  geophysics. 
  

   The 
  data 
  requisite 
  for 
  the 
  study 
  of 
  this 
  problem 
  include 
  magnetic 
  

   observations 
  over 
  the 
  ocean 
  areas, 
  not 
  only 
  to 
  measure 
  the 
  magnetic 
  

  

  ^Geograph. 
  Rev. 
  3: 
  136-137. 
  1917. 
  

  

  