﻿ECONOMIC 
  GEOLOGY 
  211 
  

  

  the 
  last 
  two, 
  the 
  clay 
  is 
  overlaid 
  by 
  the 
  delta 
  deposits 
  of 
  rivers 
  

   tributary 
  to 
  the 
  Hudson, 
  and 
  the 
  alternation 
  of 
  layers 
  may 
  be 
  due 
  

   to 
  variations 
  in 
  the 
  flow 
  of 
  the 
  rivers 
  emptying 
  at 
  those 
  points, 
  

   the 
  sandy 
  layers 
  being 
  deposited 
  during 
  periods 
  of 
  floods. 
  Iso- 
  

   lated 
  ice-scratched 
  bowlders 
  are 
  not 
  uncommonly 
  found 
  in 
  the 
  

   clay. 
  

  

  There 
  is 
  often 
  a 
  sharp 
  line 
  of 
  division 
  between 
  the 
  yellow 
  

   weathered 
  portion 
  and 
  the 
  blue 
  or 
  unweathered 
  part 
  of 
  the 
  clay. 
  

   The 
  line 
  of 
  separation 
  between 
  the 
  clay 
  and 
  overlying 
  sand 
  is 
  

   also 
  quite 
  distinct 
  in 
  most 
  cases. 
  Of 
  the 
  blue 
  and 
  the 
  yellow 
  clay 
  

   the 
  former 
  is 
  the 
  more 
  plastic, 
  but 
  both 
  effervesce 
  readily 
  with 
  

   acid, 
  .due 
  to 
  the 
  presence 
  of 
  3 
  to 
  6% 
  of 
  carbonate 
  of 
  lime, 
  and 
  

   are, 
  therefore, 
  properly 
  speaking, 
  marly 
  clays. 
  The 
  clay 
  is 
  

   underlaid 
  by 
  a 
  bed 
  of 
  gravel, 
  sand, 
  hardpan, 
  bowlder, 
  till 
  or 
  

   bed 
  rock. 
  From 
  Albany 
  to 
  Catskill 
  the 
  underlying 
  material 
  

   is 
  a 
  dark 
  gray 
  or 
  black 
  sand 
  with 
  pebbles 
  of 
  shale 
  and 
  quartz. 
  

   The 
  sand 
  grains 
  are 
  chiefly 
  of 
  pulverized 
  shale, 
  the 
  rest 
  being 
  

   silicious 
  and 
  calcareous 
  with 
  a 
  few 
  grains 
  of 
  feldspar 
  and 
  garnet. 
  

   This 
  sand 
  can 
  often 
  be 
  used 
  for 
  tempering, 
  but 
  at 
  Catskill 
  con- 
  

   tains 
  too 
  much 
  lime 
  for 
  this 
  purpose. 
  

  

  From 
  Catskill 
  northward 
  the 
  clay 
  is 
  in 
  most 
  cases 
  covered 
  by 
  

   but 
  a 
  foot 
  or 
  tw^o 
  of 
  loam. 
  South 
  of 
  Catskill 
  the 
  character 
  of 
  

   the 
  overlying 
  material 
  varies. 
  

  

  THE 
  CLAYS 
  OF 
  THE 
  CHAMPLAIN 
  VALLEY 
  

  

  The 
  clays 
  of 
  the 
  Champlain 
  valley 
  are 
  estuary 
  formations 
  and 
  

   of 
  the 
  same 
  age 
  as 
  the 
  Hudson 
  river 
  clays. 
  They 
  underlie 
  ter- 
  

   races 
  along 
  the 
  lake 
  which 
  have 
  been 
  elevated 
  to 
  a 
  height 
  of 
  400 
  

   feet 
  above 
  the 
  lake 
  surface. 
  These 
  terraces 
  may 
  be 
  traced 
  almost 
  

   continuously 
  from 
  Whitehall, 
  at 
  the 
  head 
  of 
  Lake 
  Champlain, 
  to 
  

   the 
  northern 
  end 
  of 
  the 
  lake 
  and 
  beyond 
  it, 
  but 
  on 
  account 
  of 
  the 
  

   extensive 
  erosion 
  which 
  has 
  taken 
  place, 
  they 
  are 
  usually 
  narrow, 
  

   and 
  it 
  is 
  O'uly 
  at 
  sheltered 
  points, 
  like 
  Port 
  Kent 
  and 
  Beauport, 
  

   thiat 
  they 
  are 
  especially 
  prominent. 
  The 
  section 
  involved 
  is 
  yel- 
  

   lowish 
  brown 
  sand, 
  yellowish 
  brown 
  clay 
  and 
  stiff 
  blue 
  clay, 
  the 
  

   latter 
  being 
  rather 
  calcareous. 
  The 
  upper 
  clay 
  is 
  somewhat 
  

  

  