﻿296 
  

  

  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1927 
  

  

  As 
  stated 
  above, 
  the 
  east 
  and 
  west 
  Ontario-Mohawk 
  depression 
  was 
  

   initiated 
  on 
  the 
  outcropping 
  belt 
  of 
  weak 
  strata, 
  and 
  it 
  became 
  the 
  

   master 
  valley 
  because 
  of 
  the 
  great 
  thickness 
  of 
  these 
  nonresistant 
  

   strata. 
  In 
  New 
  York 
  these 
  weak 
  strata 
  are 
  thickest 
  on 
  the 
  meridian 
  

   of 
  Seneca 
  and 
  Cayuga 
  Lakes, 
  where 
  in 
  the 
  vertical 
  series 
  of 
  5,150 
  

   feet 
  of 
  strata, 
  between 
  the 
  Trenton 
  limestone 
  below 
  and 
  the 
  Portage 
  

   sandstone 
  above, 
  4,500 
  feet 
  are 
  weak 
  shales, 
  350 
  feet 
  soluble 
  lime- 
  

   stone 
  and 
  only 
  250 
  feet 
  sandstone. 
  Consequently 
  the 
  south 
  wall 
  of 
  

   the 
  great 
  Ontario 
  Valley 
  in 
  the 
  district 
  of 
  the 
  Cayuga 
  and 
  Seneca 
  

   tributaries 
  receded 
  rapidly 
  producing 
  the 
  decided 
  concavity 
  as 
  shown 
  

   by 
  the 
  south 
  shore 
  of 
  the 
  present 
  lake. 
  Naturally 
  the 
  northward 
  

   stream 
  flow 
  was 
  directed 
  by 
  the 
  prevailing 
  land 
  slopes 
  and 
  converged 
  

   toward 
  the 
  district 
  of 
  more 
  rapid 
  erosion. 
  

  

  The 
  complex 
  history 
  of 
  the 
  Finger 
  Lakes 
  may 
  be 
  summarized 
  as 
  

   follows 
  : 
  

  

  (1) 
  The 
  original 
  drainage 
  on 
  the 
  uplifted 
  sea 
  bottom, 
  or 
  coastal 
  

   plain, 
  was 
  southward 
  across 
  New 
  York 
  from 
  Canada. 
  Only 
  a 
  few 
  

  

  KEUKA-KCLKA 
  

  

  SKA^£A^ZWE^ 
  

  

  Fig. 
  3. 
  — 
  Profile 
  of 
  lake 
  region 
  showing 
  depth 
  and 
  greatest 
  width 
  of 
  lakes. 
  Base 
  line 
  is 
  

  

  sea 
  level 
  

  

  remnants 
  of 
  that 
  primitive 
  flow 
  now 
  exist 
  in 
  western 
  New 
  York, 
  

   Avith 
  the 
  upper 
  Susquehanna 
  and 
  its 
  tributaries 
  in 
  the 
  eastern 
  district. 
  

  

  (2) 
  Evolution 
  of 
  the 
  great 
  east-and-west 
  Ontario 
  Valley, 
  in 
  a 
  wide 
  

   belt 
  of 
  weak 
  rocks, 
  shales, 
  and 
  limestone, 
  by 
  the 
  Ontarian 
  River, 
  

   beheaded 
  the 
  Canadian 
  rivers. 
  

  

  (3) 
  Northward 
  tributaries 
  of 
  the 
  Ontarian 
  River, 
  on 
  the 
  south 
  

   side 
  of 
  the 
  expanding 
  valley, 
  ate 
  back 
  (southward), 
  by 
  headwaters 
  

   erosion, 
  into 
  the 
  Allegany 
  Plateau, 
  even 
  to 
  Pennsjdvania. 
  In 
  this 
  

   way 
  was 
  developed 
  the 
  remarkable 
  series 
  of 
  parallel 
  valleys; 
  the 
  

   reverse, 
  in 
  direction, 
  of 
  the 
  original 
  drainage. 
  (Fig. 
  1.) 
  

  

  (4) 
  High 
  elevation 
  of 
  eastern 
  America, 
  in 
  later 
  Tertiary 
  time, 
  

   enlivened 
  the 
  rivers 
  by 
  increasing 
  their 
  fall 
  to 
  the 
  sea, 
  and 
  hence 
  

   their 
  velocity. 
  This 
  caused 
  rapid 
  doAvn-cutting 
  of 
  the 
  valleys 
  (fig. 
  

   3), 
  so 
  producing 
  the 
  steeper 
  lower 
  walls 
  of 
  the 
  central 
  lakes, 
  and 
  the 
  

   convex 
  it}^ 
  of 
  the 
  slopes. 
  

  

  (5) 
  The 
  high 
  elevation 
  of 
  eastern 
  America, 
  possibly 
  accompanied 
  

   by 
  a 
  slight 
  lowering 
  of 
  world 
  climate, 
  produced 
  vast 
  and 
  deep 
  ice 
  

   sheets. 
  The 
  latest 
  one, 
  the 
  Quebec 
  Glacier, 
  overspread 
  New 
  York, 
  

  

  