﻿of 
  the 
  Northern 
  Appalachians. 
  329 
  

  

  General 
  Indications 
  of 
  Wide 
  Oscillations 
  of 
  the 
  Strand-line. 
  

  

  The 
  views 
  respecting 
  oscillations 
  of 
  the 
  strand-lines, 
  

   entertained 
  by 
  leading 
  geologists 
  up 
  to 
  the 
  close 
  of 
  the 
  

   nineteenth 
  century, 
  are 
  expressed 
  in 
  Dana's 
  Manual 
  of 
  

   Geology 
  of 
  which 
  the 
  first 
  edition 
  was 
  published 
  in 
  1863, 
  

   the 
  fourth 
  and 
  thoroughly 
  revised 
  edition 
  in 
  1895. 
  And 
  

   various 
  other 
  text 
  books 
  in 
  this 
  country 
  express 
  the 
  

   same 
  ideas. 
  From 
  these 
  volumes 
  it 
  is 
  learned 
  that 
  at 
  

   the 
  opening 
  of 
  the 
  Paleozoic 
  era 
  a 
  sea 
  covered 
  the 
  greater 
  

   part 
  of 
  North 
  America, 
  the 
  principal 
  land 
  area 
  being 
  a 
  

   large 
  V-shaped 
  mass 
  surrounding 
  Hudson 
  Bay. 
  During 
  

   the 
  Paleozoic 
  successive 
  belts 
  of 
  land 
  were 
  added, 
  repre- 
  

   senting 
  roughly 
  the 
  present 
  outcrops 
  of 
  rocks 
  of 
  the 
  suc- 
  

   cessive 
  periods. 
  The 
  Paleozoic 
  interior 
  sea 
  was 
  thus 
  

   regarded 
  as 
  continuously 
  in 
  existence, 
  but 
  as 
  periodically 
  

   diminishing 
  in 
  area. 
  Occasional 
  marginal 
  expansions 
  

   were 
  granted 
  on 
  the 
  evidence 
  of 
  younger 
  strata 
  overlap- 
  

   ping 
  beyond 
  immediately 
  older 
  strata, 
  but 
  such 
  expan- 
  

   sions 
  were 
  regarded 
  as 
  minor 
  features 
  not 
  affecting 
  the 
  

   general 
  progress 
  of 
  continental 
  growth. 
  

  

  On 
  the 
  Atlantic 
  border 
  the 
  Coastal 
  Plain 
  deposits 
  

   begin 
  with 
  the 
  Potomac 
  group 
  of 
  the 
  Comanchian 
  period, 
  

   fresh 
  water 
  in 
  origin 
  and 
  regarded 
  as 
  deposited 
  in 
  estu- 
  

   aries. 
  The 
  shore-line 
  was 
  drawn 
  as 
  following 
  the 
  

   present 
  landward 
  boundary 
  of 
  the 
  Potomac. 
  With 
  the 
  

   opening 
  of 
  the 
  Upper 
  Cretaceous 
  the 
  sea 
  advanced 
  

   inland 
  but 
  the 
  shore-line 
  is 
  not 
  shown 
  as 
  extending 
  be- 
  

   yond 
  the 
  previous 
  limit 
  fixed 
  by 
  the 
  Potomac. 
  This 
  

   marked 
  the 
  maximum 
  submergence. 
  During 
  the 
  Ter- 
  

   tiary 
  a 
  progressive 
  emergence 
  of 
  the 
  Atlantic 
  Coastal 
  

   Plain 
  was 
  held 
  to 
  have 
  taken 
  place, 
  the 
  parts 
  under 
  water 
  

   being 
  limited 
  by 
  the 
  present 
  outcrops. 
  16 
  

  

  During 
  the 
  fifteen 
  years 
  following 
  the 
  last 
  edition 
  of 
  

   Dana's 
  Manual 
  the 
  general 
  progress 
  of 
  geologic 
  thought 
  

   may 
  be 
  measured 
  by 
  the 
  ' 
  ' 
  Outlines 
  of 
  Geologic 
  History 
  

   with 
  special 
  reference 
  to 
  North 
  America," 
  a 
  volume 
  

   written 
  by 
  many 
  contributors 
  and 
  presenting 
  a 
  series 
  of 
  

   paleogeographic 
  maps 
  constructed 
  by 
  Willis. 
  In 
  this 
  

   volume 
  the 
  character 
  of 
  the 
  interior 
  Paleozoic 
  sea 
  shows 
  

   a 
  marked 
  change. 
  Wide 
  advances 
  and 
  retreats 
  are 
  

   shown. 
  Large 
  areas 
  are 
  indicated 
  as 
  doubtfully 
  land 
  or 
  

   sea. 
  Grabau, 
  writing 
  on 
  Ordovic, 
  Siluric, 
  and 
  early 
  

  

  10 
  J. 
  D. 
  Dana, 
  Manual 
  of 
  Geology, 
  1895, 
  pp. 
  813 
  and 
  881. 
  

  

  