﻿GEOLOGICAL 
  CLIMATES 
  SCOTT 
  285 
  

  

  the 
  weather 
  is 
  always 
  cold, 
  though 
  never 
  extremely 
  so. 
  In 
  this 
  in- 
  

   stance 
  the 
  modifying 
  effects 
  of 
  solar 
  changes 
  are 
  produced 
  by 
  the 
  

   distribution 
  of 
  the 
  marine 
  and 
  continental 
  areas. 
  In 
  the 
  Northern 
  

   Hemisphere, 
  there 
  is 
  much 
  reason 
  to 
  believe, 
  diastrophic 
  movements, 
  

   both 
  the 
  orogenic 
  folding 
  and 
  the 
  epeirogenic 
  warping 
  of 
  broad 
  areas, 
  

   have 
  had 
  an 
  in)portant 
  bearing 
  on 
  the 
  effects 
  of 
  solar 
  changes, 
  now 
  

   opposing 
  and 
  reducing 
  those 
  effects, 
  now 
  assisting 
  and 
  increasing 
  

   them. 
  

  

  VARIATIONS 
  IN 
  RAINFALL 
  AND 
  THEIR 
  CAUSES 
  

  

  The 
  second 
  great 
  factor 
  in 
  the 
  determining 
  of 
  climates 
  is 
  moisture 
  

   and 
  its 
  resulting 
  precipitation 
  in 
  the 
  form 
  of 
  rain 
  or 
  snow. 
  Even 
  more 
  

   than 
  temperature, 
  precipitation 
  is 
  affected 
  by 
  topography 
  and 
  pre- 
  

   vailing 
  winds. 
  High 
  m.ountain 
  ranges, 
  which 
  cut 
  off 
  moisture-laden 
  

   winds, 
  may 
  throw 
  a 
  " 
  rain 
  shadow 
  " 
  far 
  across 
  the 
  continent, 
  as 
  do 
  

   the 
  ranges 
  of 
  the 
  Pacific 
  coast 
  region. 
  The 
  remarkable 
  monsoons 
  

   of 
  the 
  Indian 
  Ocean, 
  a 
  reversible 
  system 
  of 
  winds, 
  bring 
  the 
  rains 
  to 
  

   India 
  when 
  blowing 
  from 
  the 
  southwest. 
  Many 
  similar 
  instances 
  of 
  

   the 
  effects 
  of 
  topography 
  and 
  prevalent 
  winds 
  might 
  be 
  mentioned, 
  

   if 
  it 
  were 
  worth 
  while 
  to 
  do 
  so; 
  but 
  these 
  are 
  well 
  understood 
  and 
  

   it 
  is 
  not 
  necessary 
  to 
  recapitulate 
  them. 
  

  

  Evidences 
  of 
  arid 
  climates 
  in 
  ancient 
  geological 
  times 
  where 
  now 
  

   are 
  regions 
  of 
  pluvial 
  conditions, 
  are 
  abundant, 
  and 
  such 
  evidences 
  

   are 
  for 
  the 
  most 
  part 
  independent 
  of 
  fossils 
  and 
  are 
  contained 
  in 
  the 
  

   rocks 
  themselves, 
  Beds 
  of 
  gypsum 
  and 
  rock 
  salt 
  are 
  indicative 
  of 
  

   ai'idity, 
  for 
  they 
  are 
  accumulated 
  in 
  salt 
  lakes, 
  which 
  can 
  not 
  be 
  

   maintained 
  in 
  regions 
  of 
  normal 
  rainfall; 
  and 
  the 
  distribution 
  of 
  

   such 
  deposits 
  in 
  time 
  and 
  space, 
  their 
  geological 
  and 
  geographic 
  

   arrangement, 
  frequently 
  enable 
  us 
  to 
  demarcate 
  the 
  regions 
  of 
  special 
  

   aridity. 
  No 
  doubt 
  there 
  were 
  many 
  others 
  of 
  which 
  we 
  do 
  not 
  know, 
  

   the 
  proofs 
  of 
  which 
  have 
  been 
  swept 
  away 
  by 
  denudation. 
  The 
  

   changes 
  from 
  pluvial 
  to 
  arid 
  conditions, 
  and 
  vice 
  versa, 
  would 
  seem 
  

   to 
  have 
  been 
  local 
  in 
  some 
  instances, 
  of 
  immense 
  geographical 
  extent 
  

   in 
  others. 
  

  

  The 
  Ordovician 
  of 
  Siberia 
  and 
  the 
  lower 
  Carboniferous 
  of 
  eastern 
  

   North 
  America 
  were, 
  so 
  far 
  as 
  we 
  can 
  judge, 
  instances 
  of 
  locally 
  re- 
  

   stricted 
  changes 
  to 
  more 
  or 
  less 
  arid 
  conditions, 
  while 
  nearly 
  the 
  

   whole 
  of 
  the 
  Permian 
  and 
  Triassic 
  periods 
  show 
  a 
  belt 
  all 
  around 
  the 
  

   Northern 
  Hemisphere 
  of 
  extreme 
  aridity. 
  Under 
  the 
  north 
  German 
  

   plain 
  lies 
  a 
  vast 
  body 
  of 
  rock 
  salt 
  of 
  unknown 
  thickness, 
  for 
  none 
  of 
  

   the 
  very 
  deep 
  bore 
  holes, 
  which 
  have 
  been 
  put 
  down, 
  reach 
  the 
  

   bottom 
  of 
  the 
  salt. 
  Making 
  a 
  reasonable 
  allowance 
  for 
  the 
  thickness 
  

   of 
  the 
  salt 
  body, 
  it 
  has 
  been 
  estimated 
  that 
  it 
  represents 
  the 
  evapo- 
  

   ration 
  of 
  a 
  body 
  of 
  sea 
  water 
  three 
  times 
  as 
  great 
  in 
  cubic 
  content 
  as 
  

  

  