﻿294 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1927 
  

  

  River. 
  During 
  the 
  long 
  earlier 
  history 
  of 
  the 
  north-flowing 
  rivers, 
  

   with 
  lower 
  and 
  more 
  steady 
  position 
  of 
  the 
  land, 
  the 
  valleys 
  were 
  

   greatly 
  widened. 
  Later, 
  by 
  the 
  Tertiary 
  uplift, 
  the 
  rivers 
  were 
  en- 
  

   livened 
  or 
  rejuvenated, 
  and 
  they 
  sawed 
  down 
  more 
  rapidly, 
  produc- 
  

   ing 
  the 
  narrower, 
  and 
  steeper-walled, 
  bottom 
  sections 
  of 
  the 
  valleys. 
  

  

  Rivers 
  are 
  the 
  valley 
  makers. 
  Mountain 
  or 
  Alpine 
  glaciers 
  modify 
  

   the 
  valleys 
  which 
  they 
  occupy. 
  They 
  are 
  chiefly 
  agents 
  of 
  trans- 
  

   portation. 
  Their 
  minor 
  work 
  of 
  erosion 
  tends 
  to 
  widen 
  rather 
  than 
  

   deepen 
  their 
  channels. 
  They 
  change 
  stream, 
  or 
  V-shaped 
  valleys, 
  

   into 
  U-shaped. 
  But 
  the 
  ice 
  work 
  in 
  New 
  York 
  was 
  not 
  that 
  of 
  stream 
  

   glaciers 
  but 
  that 
  of 
  a 
  widespread 
  or 
  continental 
  ice 
  sheet. 
  It 
  had 
  

   little 
  power 
  of 
  deepening 
  valleys, 
  but 
  was 
  effective 
  rather 
  in 
  filling 
  and 
  

   damming 
  the 
  valleys. 
  Lobations 
  of 
  the 
  ice 
  margin 
  pushed 
  into 
  the 
  

   old 
  valleys, 
  during 
  both 
  the 
  oncoming 
  and 
  the 
  recession 
  of 
  the 
  

   glacier. 
  But 
  the 
  lobes, 
  pushing 
  up 
  the 
  valleys, 
  with 
  imprisoned 
  

   lakes 
  facing 
  them, 
  were 
  heavily 
  loaded 
  with 
  rock-rubbish 
  (glacial 
  

   drift), 
  and 
  had 
  little 
  power 
  of 
  erosion. 
  Moreover, 
  the 
  bottom 
  ice 
  in 
  

   the 
  deep 
  valleys 
  is 
  believed 
  to 
  have 
  been 
  comparatively 
  stagnant, 
  

   serving 
  as 
  the 
  bridge 
  for 
  the 
  flow 
  of 
  the 
  plastic 
  upper 
  ice. 
  When 
  

   the 
  ice 
  sheet 
  was 
  thick 
  it 
  moved 
  south 
  westward, 
  or 
  diagonally 
  across 
  

   the 
  central 
  valleys. 
  And, 
  as 
  noted 
  above, 
  the 
  later 
  lobations 
  were 
  

   too 
  heavily 
  loaded 
  with 
  bottom 
  drift 
  to 
  do 
  effective 
  cutting. 
  They 
  

   piled 
  their 
  drift 
  burden 
  mostly 
  in 
  the 
  hummocky 
  deposits 
  that 
  now 
  

   make 
  the 
  divides 
  or 
  water 
  parting 
  south 
  of 
  the 
  lakes. 
  (See 
  fig. 
  2.) 
  

  

  In 
  general 
  the 
  jce 
  sheet 
  had 
  only 
  a 
  smoothing 
  or 
  sandpapering 
  

   effect 
  on 
  the 
  land 
  surfaces. 
  It 
  rubbed 
  down 
  the 
  projections 
  and 
  filled 
  

   the 
  depressions, 
  thus 
  producing 
  the 
  remarkably 
  uniform 
  curving 
  sur- 
  

   faces 
  whicli 
  give 
  the 
  slopes 
  of 
  the 
  Finger 
  Lakes 
  valleys 
  their 
  grace- 
  

   ful 
  outlines. 
  

  

  During 
  the 
  later 
  stand 
  of 
  the 
  Quebec 
  ice 
  sheet 
  it 
  completely 
  filled 
  

   the 
  northern 
  ends 
  of 
  the 
  valleys 
  with 
  i'ts 
  drift 
  deposit, 
  forming 
  the 
  

   wide 
  plains 
  north 
  of 
  the 
  lakes. 
  This 
  drift 
  filling 
  makes 
  the 
  dams 
  

   that 
  hold 
  the 
  lakes. 
  

  

  In 
  addition 
  to 
  this 
  northern 
  blocking 
  of 
  the 
  valleys 
  another 
  agency 
  

   has 
  helped 
  to 
  make 
  the 
  basins. 
  This 
  is 
  the 
  tilting 
  uplift 
  of 
  the 
  

   land. 
  The 
  weight 
  of 
  the 
  Quebec 
  ice 
  cap, 
  many 
  thousand 
  feet 
  thick, 
  

   depressed 
  the 
  land. 
  When 
  the 
  ice 
  was 
  removed 
  the 
  land 
  rose, 
  slant- 
  

   ingly 
  in 
  New 
  York. 
  The 
  amount 
  of 
  slant, 
  or 
  uptilting, 
  has 
  raised 
  

   the 
  north 
  ends 
  of 
  Cayuga 
  and 
  Seneca 
  Lakes 
  about 
  80 
  feet 
  more 
  

   than 
  the 
  south 
  ends. 
  As 
  the 
  outlets 
  are 
  at 
  the 
  north 
  ends, 
  it 
  is 
  evi- 
  

   dent 
  that 
  the 
  land 
  movement 
  is 
  partly 
  responsible 
  for 
  the 
  lake 
  

   basins. 
  

  

  However, 
  the 
  "basin" 
  character 
  has 
  been 
  overemphasized. 
  A 
  

   true 
  vertical 
  profile 
  of 
  the 
  basins 
  shows 
  that 
  they 
  are 
  comparatively 
  

  

  