﻿Diastrophism 
  in 
  Atlantic- 
  Arctic 
  Region. 
  5 
  

  

  Middle 
  Cambrian 
  time 
  passes 
  quietly 
  into 
  that 
  of 
  the 
  

   Upper 
  Cambrian, 
  and 
  the 
  distribution 
  of 
  the 
  sea 
  seems 
  

   to 
  remain 
  much 
  the 
  same, 
  along 
  with 
  continued 
  deposi- 
  

   tion 
  of 
  the 
  black 
  (alum) 
  shales 
  so 
  characteristic 
  of 
  the 
  

   sea 
  shown 
  in 
  the 
  map. 
  

  

  Ordovician 
  Time 
  (see 
  figs. 
  3 
  and 
  4). 
  — 
  While 
  in 
  a 
  larger 
  

   part 
  of 
  the 
  region 
  considered 
  in 
  the 
  previous 
  maps 
  the 
  

   Cambrian 
  seems 
  to 
  pass 
  very 
  gently 
  and 
  with 
  much 
  

   the 
  same 
  kind 
  of 
  sediments 
  into 
  the 
  Ordovician, 
  yet 
  the 
  

   conditions 
  in 
  the 
  most 
  northern 
  part 
  of 
  Norway 
  are 
  

   very 
  different. 
  The 
  present 
  author, 
  in 
  the 
  February 
  

   1919 
  number 
  of 
  this 
  Journal, 
  indicated 
  the 
  presence 
  here 
  

   of 
  a 
  large 
  northern 
  land 
  that 
  has 
  yielded 
  the 
  material 
  of 
  

   the 
  thick 
  sandstones 
  of 
  Finmarken, 
  presumably 
  depos- 
  

   ited 
  in 
  Ozarkian 
  and 
  Canadian 
  time. 
  This 
  fact, 
  then, 
  

   may 
  have 
  some 
  connection 
  with 
  the 
  rapid 
  movement 
  of 
  

   the 
  shore-line 
  in 
  the 
  Cambrian-Ordovician 
  transition 
  

   time. 
  

  

  The 
  earliest 
  Ordovician 
  was 
  not 
  a 
  very 
  quiet 
  time 
  

   throughout 
  the 
  more 
  southern 
  parts 
  of 
  the 
  British- 
  

   Scandinavian 
  region. 
  In 
  Carnarvonshire, 
  northern 
  

   Wales, 
  a 
  considerable 
  uplift 
  took 
  place, 
  causing 
  a 
  very 
  

   powerful 
  denudation 
  between 
  Tremadoc 
  and 
  Arenig 
  

   time, 
  and 
  in 
  the 
  most 
  southern 
  part 
  of 
  the 
  Kristiania 
  

   region, 
  the 
  absence 
  of 
  lowest 
  Ordovician 
  sediments 
  tells 
  

   the 
  same 
  story 
  of 
  crustal 
  upheaval. 
  

  

  With 
  the 
  beginning 
  of 
  Ordovician 
  time, 
  we 
  have 
  a 
  

   better 
  knowledge 
  of 
  the 
  distribution 
  of 
  the 
  sea 
  also 
  in 
  

   the 
  Arctic 
  region, 
  and 
  therefore 
  in 
  the 
  accompanying 
  

   map 
  showing 
  Lower 
  Ordovician 
  (Canadian) 
  geography, 
  

   it 
  is 
  possible 
  to 
  consider 
  a 
  much 
  larger 
  area 
  of 
  the 
  earth. 
  

   The 
  most 
  significant 
  geographic 
  feature 
  is 
  the 
  existence 
  

   now 
  of 
  two 
  ocean 
  basins 
  (the 
  characters 
  of 
  which 
  have 
  

   been 
  treated 
  by 
  the 
  author 
  in 
  several 
  recent 
  publica- 
  

   tions), 
  water-ways 
  that 
  were 
  very 
  effectively 
  separated 
  

   by 
  a 
  narrow 
  Scandinavian-Scottish 
  land 
  barrier. 
  

  

  A 
  similar 
  land 
  barrier, 
  but 
  of 
  somewhat 
  different 
  

   shape, 
  must 
  be 
  assumed 
  also 
  for 
  Middle 
  Ordovician 
  time, 
  

   if 
  one 
  may 
  depend 
  upon 
  the 
  present 
  stratigraphic 
  and 
  

   faunal 
  knowledge. 
  

  

  In 
  the 
  northwestern 
  part 
  of 
  the 
  British-Scandinavian 
  

   geosyncline 
  there 
  was 
  considerable, 
  and 
  in 
  places 
  exceed- 
  

   ingly 
  strong, 
  volcanic 
  activity 
  in 
  several 
  districts 
  as 
  

   early 
  as 
  the 
  Lower 
  Ordovician; 
  in 
  Middle 
  Ordovician 
  

   time 
  we 
  notice 
  in 
  the 
  northwest 
  important 
  crustal 
  defor- 
  

  

  