﻿REPORT 
  OF 
  THE 
  DIRECTOR 
  r79 
  

  

  or 
  structure. 
  The 
  glacial-derived 
  material 
  always 
  forms 
  the 
  frontal 
  

   aud 
  frontal-basal 
  portions 
  of 
  the 
  . 
  terrace. 
  If 
  no 
  erosion 
  of 
  the 
  

   terrace 
  takes 
  place 
  it 
  can 
  usually 
  be 
  recognized 
  from 
  its 
  composite 
  

   character. 
  Gilbert* 
  further 
  states 
  that 
  this 
  form 
  so 
  closely 
  simulates 
  

   the 
  stream 
  terrace 
  as 
  to 
  be 
  in 
  many 
  cases 
  indistinguishable. 
  

  

  As 
  in 
  the 
  case 
  of 
  moraines 
  two 
  types 
  of 
  moraine 
  terrace?, 
  frontal 
  

   and 
  lateral, 
  are 
  recognized. 
  (^Figures 
  12 
  and 
  13) 
  — 
  (Figures 
  14 
  

   and 
  15). 
  Gilbert 
  says 
  : 
  ** 
  "The 
  lateral 
  type 
  is 
  identical 
  in 
  cross 
  

   profile 
  and 
  in 
  longitudinal 
  profile, 
  and, 
  unless 
  portions 
  of 
  the 
  

   morainic 
  ridge 
  remain, 
  has 
  but 
  one 
  formal 
  difference; 
  the 
  contour 
  

   of 
  its 
  outer 
  face 
  being 
  determined 
  by 
  the 
  side 
  of 
  an 
  ice 
  stream 
  are 
  

   smooth 
  curves 
  of 
  gentle 
  flexure." 
  

  

  Clearly, 
  all 
  of 
  the 
  terraces 
  dotting 
  the 
  east 
  and 
  west 
  sides 
  of 
  the 
  

   Finger-lake 
  valleys 
  are 
  lateral 
  terraces, 
  and 
  in 
  no 
  way 
  do 
  they 
  

   resemble 
  stream 
  terraces 
  ; 
  but, 
  as 
  has 
  been 
  shown, 
  represent 
  true 
  

   deltas 
  deposited 
  by 
  streams, 
  with 
  their 
  mouths 
  at 
  that 
  eleva- 
  

   tion 
  and 
  their 
  entrance 
  into 
  a 
  static 
  body 
  of 
  water. 
  If 
  these 
  

   represented 
  moraine 
  terraces 
  we 
  should 
  expect 
  to 
  find 
  in 
  some 
  of 
  

   them 
  at 
  least 
  evidence 
  of 
  glacial 
  or 
  morainal 
  material 
  ; 
  on 
  the 
  

   contrary, 
  not 
  a 
  single 
  terrace 
  examined 
  has 
  offered 
  much 
  doubt 
  as 
  

   to 
  the 
  kind 
  of 
  naaterial 
  of 
  which 
  it 
  is 
  composed. 
  The 
  absence 
  of 
  

   such 
  material 
  can 
  not 
  be 
  accredited 
  to 
  erosion, 
  as 
  the 
  majority 
  

   of 
  these 
  terraces 
  are 
  almost 
  as 
  fresh 
  as 
  the 
  day 
  they 
  were 
  con- 
  

   structed. 
  Apparently, 
  therefore, 
  they 
  have 
  suffered 
  no 
  erosion 
  save 
  

   that 
  of 
  the 
  streams 
  which 
  built 
  them, 
  which 
  has 
  been 
  in 
  the 
  nature 
  

   of 
  a 
  bisection 
  when 
  the 
  waters 
  fell 
  to 
  a 
  lower 
  level 
  and 
  the 
  con- 
  

   struction 
  of 
  the 
  ne:xt 
  lower 
  delta 
  began. 
  As 
  has 
  been 
  shown, 
  the 
  

   morainal 
  terrace 
  is 
  characterized 
  either 
  by 
  a 
  smooth 
  flowing 
  

   frontal 
  outline 
  or 
  by 
  an 
  irregular 
  morainal 
  or 
  hummocky 
  frontal 
  

   outline. 
  The 
  majority 
  of 
  the 
  terraces 
  so 
  far 
  examined 
  in 
  the 
  

   valleys 
  have 
  distinctly 
  serrated 
  fronts, 
  and 
  with 
  no 
  structural 
  

   resemblance 
  whatever 
  to 
  the 
  morainal 
  type. 
  

  

  After 
  the 
  deposition 
  of 
  the 
  terrace 
  material 
  against 
  the 
  front 
  or 
  

   lateral 
  edge 
  of 
  the 
  ice, 
  and 
  the 
  withdrawal 
  of 
  the 
  ice, 
  the 
  material 
  

   which 
  has 
  been 
  held 
  up 
  at 
  its 
  front 
  by 
  the 
  supporting 
  ice 
  tongue, 
  must 
  

  

  a 
  Gilbert, 
  G 
  K., 
  Lake 
  Bonneville. 
  Monograph 
  1, 
  U. 
  S. 
  G 
  S., 
  p. 
  83. 
  

  

  