﻿GEOLOGICAL 
  CLIMATES 
  SCOTT 
  277 
  

  

  subsequently 
  confirmed 
  by 
  very 
  widespread 
  observations 
  in 
  other 
  

   continents. 
  Even 
  in 
  the 
  Tropics 
  the 
  same 
  rule 
  would 
  seem 
  to 
  apply. 
  

   Mount 
  Kilimanjaro, 
  the 
  highest 
  mountain 
  in 
  Africa, 
  which 
  stands 
  

   very 
  near 
  the 
  Equator 
  (3° 
  south 
  latitude), 
  still 
  has 
  snow 
  fields 
  and 
  

   glaciers 
  near 
  the 
  summit, 
  while 
  the 
  unmistakable 
  ice 
  marks 
  of 
  polish- 
  

   ing 
  and 
  striation 
  extend 
  more 
  than 
  5,000 
  feet 
  below 
  the 
  present 
  limit 
  

   of 
  the 
  glaciers 
  — 
  a 
  very 
  different 
  thing 
  from 
  the 
  snow 
  line. 
  To 
  pro- 
  

   duce 
  such 
  climatic 
  conditions, 
  Penck 
  has 
  calculated 
  that 
  a 
  lowering 
  

   of 
  the 
  annual 
  average 
  temperature 
  of 
  about 
  9° 
  F. 
  below 
  the 
  existing 
  

   standard 
  would 
  suffice. 
  That 
  amount, 
  9° 
  F., 
  is 
  all 
  that 
  stands 
  be- 
  

   tween 
  us 
  and 
  a 
  recurrence 
  of 
  glacial 
  conditions. 
  

  

  In 
  brief, 
  therefore, 
  what 
  we 
  must 
  account 
  for 
  is 
  the 
  long 
  contin- 
  

   uance, 
  throughout 
  the 
  Mesozoic 
  and 
  earlier 
  Tertiary 
  times, 
  of 
  genial, 
  

   nearly 
  uniform 
  conditions 
  of 
  climate, 
  with 
  zones 
  only 
  obscurely 
  

   demarcated. 
  There 
  was 
  then, 
  and 
  probably 
  always 
  has 
  been, 
  a 
  dif- 
  

   ference 
  of 
  temperature 
  between 
  the 
  Equator 
  and 
  the 
  poles, 
  as 
  is 
  indi- 
  

   cated 
  by 
  the 
  distribution 
  of 
  fossil 
  floras, 
  but 
  a 
  difference 
  far 
  less 
  in 
  

   amount 
  than 
  that 
  which 
  now 
  obtains. 
  In 
  the 
  latter 
  half 
  of 
  the 
  

   Tertiary 
  period 
  began 
  a 
  slow 
  and 
  gradual 
  refrigeration, 
  which 
  had 
  

   brought 
  severe 
  conditions 
  in 
  high 
  latitudes 
  in 
  the 
  early 
  Pliocene 
  — 
  

   conditions 
  in 
  which 
  the 
  typically 
  Arctic 
  fauna 
  of 
  mammals 
  had 
  been 
  

   differentiated. 
  The 
  increasing 
  cold 
  finally 
  culminated 
  in 
  the 
  wide- 
  

   spread 
  glaciation 
  of 
  the 
  Pleistocene; 
  but 
  this 
  was 
  itself 
  highly 
  com- 
  

   plex, 
  from 
  the 
  climatic 
  point 
  of 
  view. 
  Within 
  a 
  short 
  space 
  of 
  time, 
  

   as 
  geological 
  time 
  is 
  measured, 
  there 
  were 
  many 
  extreme 
  fluctuations 
  

   of 
  climate, 
  four 
  or 
  more 
  glacial, 
  alternating 
  with 
  interglacial 
  stages. 
  

   It 
  would 
  be 
  going 
  beyond 
  the 
  evidence 
  to 
  say 
  that 
  in 
  all 
  the 
  inter- 
  

   glacial 
  stages 
  the 
  climate 
  was 
  milder 
  than 
  at 
  present, 
  but 
  it 
  may 
  have 
  

   been 
  so 
  in 
  all, 
  and 
  certainly 
  was 
  in 
  some. 
  Finally, 
  the 
  conditions 
  

   were 
  once 
  more 
  ameliorated, 
  bringing 
  about 
  the 
  present 
  order 
  of 
  

   things. 
  

  

  This 
  is 
  far 
  from 
  being 
  a 
  complete 
  statement 
  of 
  the 
  problem 
  of 
  

   geological 
  climates, 
  or 
  even 
  of 
  the 
  temperature 
  factor 
  in 
  climates, 
  

   but 
  in 
  this 
  abbreviated 
  and 
  simplified 
  form 
  it 
  will 
  suffice 
  for 
  our 
  

   present 
  purposes. 
  The 
  solution 
  of 
  the 
  problem 
  in 
  this 
  form 
  will 
  

   offer 
  quite 
  sufficient 
  difficulty 
  for 
  an 
  evening's 
  consideration. 
  Only 
  

   a 
  brief 
  mention 
  of 
  the 
  cognate 
  climatic 
  factors 
  — 
  moisture, 
  precipita- 
  

   tion, 
  and 
  prevailing 
  winds 
  — 
  is 
  permissible 
  because 
  of 
  the 
  limitations 
  

   of 
  our 
  time. 
  

  

  THEORIES 
  TO 
  EXPLAIN 
  GLACIAL 
  EPOCHS 
  

  

  Wlierever 
  it 
  is 
  feasible, 
  I 
  have 
  always 
  thought 
  that 
  there 
  is 
  an 
  

   especial 
  charm 
  in 
  presenting 
  scientific 
  theories 
  historically, 
  as 
  this 
  

   method 
  records 
  the 
  progress 
  of 
  discovery 
  and 
  interpretation, 
  the 
  

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