﻿Reelevation 
  of 
  the 
  St. 
  Lawrence 
  river 
  basin. 
  17 
  

  

  with 
  the 
  marine 
  fauna 
  which 
  is 
  preserved 
  in 
  the 
  Leda 
  clays 
  

   and 
  Saxicava 
  sands. 
  

  

  The 
  Champlain 
  Marine 
  Submergence. 
  

  

  That 
  the 
  land 
  northward 
  from 
  Boston 
  was 
  lower 
  than 
  now 
  

   while 
  the 
  ice-sheet 
  was 
  being 
  melted 
  away, 
  is 
  proved 
  by 
  the 
  

   occurrence 
  of 
  fossil 
  mollusks 
  of 
  far 
  northern 
  range, 
  including 
  

   Leda 
  arctica 
  Gray, 
  which 
  is 
  now 
  found 
  living 
  only 
  in 
  the 
  

   Arctic 
  seas, 
  preferring 
  localities 
  which 
  receive 
  muddy 
  streams 
  

   from 
  existing 
  glaciers 
  and 
  from 
  the 
  Greenland 
  ice-sheet. 
  This 
  

   species 
  is 
  plentiful 
  in 
  the 
  stratified 
  clays 
  resting 
  on 
  the 
  till 
  in 
  

   the 
  St. 
  Lawrence 
  valley 
  and 
  in 
  New 
  Brunswick 
  and 
  Maine, 
  

   extending 
  southward 
  to 
  Portsmouth, 
  N. 
  H. 
  But 
  it 
  is 
  known 
  

   that 
  the 
  land 
  was 
  elevated 
  from 
  this 
  depression 
  to 
  about 
  its 
  

   present 
  height 
  before 
  the 
  sea 
  here 
  became 
  warm 
  and 
  the 
  

   southern 
  mollusks, 
  which 
  exist 
  as 
  colonies 
  in 
  the 
  Gulf 
  of 
  St. 
  

   Lawrence, 
  migrated 
  thither, 
  for 
  these 
  southern 
  species 
  are 
  not 
  

   included 
  in 
  the 
  extensive 
  lists 
  of 
  the 
  fossil 
  fauna 
  found 
  in 
  the 
  

   beds 
  overlying 
  the 
  till. 
  

  

  In 
  the 
  St. 
  Lawrence 
  basin 
  these 
  marine 
  deposits 
  reach 
  to 
  the 
  

   southern 
  end 
  of 
  Lake 
  Champlain, 
  to 
  Ogdensburgh 
  and 
  Brock- 
  

   ville, 
  and 
  at 
  least 
  to 
  Pembroke 
  and 
  Allumette 
  island, 
  in 
  the 
  

   Ottawa 
  river, 
  about 
  75 
  miles 
  above 
  the 
  city 
  of 
  Ottawa. 
  The 
  

   isthmus 
  of 
  Chiegnecto, 
  connecting 
  Nova 
  Scotia 
  with 
  New 
  

   Brunswick, 
  was 
  submerged, 
  and 
  the 
  sea 
  extended 
  50 
  to 
  100 
  

   miles 
  up 
  the 
  valleys 
  of 
  the 
  chief 
  rivers 
  of 
  Maine 
  and 
  New 
  

   Brunswick. 
  The 
  uplift 
  of 
  this 
  region 
  from 
  the 
  Champlain 
  sea 
  

   level 
  was 
  10 
  to 
  25 
  feet 
  in 
  the 
  vicinity 
  of 
  Boston 
  and 
  northeast- 
  

   ward 
  to 
  Cape 
  Ann 
  ; 
  about 
  150 
  feet 
  near 
  Portsmouth, 
  N. 
  H. 
  ; 
  

   from 
  150 
  to 
  about 
  300 
  feet 
  along 
  the 
  coast 
  of 
  Maine 
  and 
  

   southern 
  New 
  Brunswick 
  ; 
  about 
  40 
  feet 
  on 
  the 
  northwestern 
  

   shore 
  of 
  Nova 
  Scotia 
  ; 
  thence 
  increasing 
  westward 
  to 
  200 
  feet 
  

   in 
  the 
  Bay 
  of 
  Chaleurs, 
  375 
  feet 
  in 
  the 
  St. 
  Lawrence 
  valley 
  

   opposite 
  the 
  Saguenay, 
  and 
  about 
  560 
  feet 
  at 
  Montreal 
  ; 
  150 
  to 
  

   400 
  or 
  500 
  feet, 
  increasing 
  from 
  south 
  to 
  north, 
  along 
  the 
  basin 
  

   of 
  Lake 
  Champlain 
  ; 
  about 
  275 
  feet 
  at 
  Ogdensburgh, 
  and 
  450 
  

   feet 
  near 
  the 
  city 
  of 
  Ottawa. 
  The 
  differential 
  elevation 
  was 
  

   practically 
  completed, 
  as 
  we 
  have 
  seen 
  from 
  the 
  boreal 
  charac- 
  

   ter 
  of 
  the 
  Champlain 
  marine 
  molluscan 
  fauna, 
  shortly 
  after 
  

   the 
  departure 
  of 
  the 
  ice 
  sheet. 
  With 
  the 
  areas 
  of 
  the 
  glacial 
  

   Lakes 
  Agassiz, 
  Warren, 
  and 
  Iroquois, 
  in 
  the 
  interior 
  of 
  the 
  

   continent, 
  this 
  coastal 
  region 
  gives 
  testimony 
  of 
  a 
  wave-like 
  

   epeirogenic 
  elevation 
  of 
  the 
  formerly 
  ice-laden 
  portion 
  of 
  the 
  

   earth's 
  crust, 
  proportionate 
  with 
  the 
  glacial 
  melting 
  and 
  closely 
  

   following 
  the 
  retreat 
  of 
  the 
  ice 
  from 
  its 
  boundaries 
  of 
  greatest 
  

  

  Am. 
  Jour. 
  Sci.— 
  Third 
  Series, 
  Vol. 
  XLIX, 
  No. 
  289.— 
  Jan., 
  1895. 
  

   2 
  

  

  