﻿i66 
  

  

  XEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Helderberg 
  regions. 
  There 
  are, 
  however, 
  good 
  instances 
  of 
  the 
  

   formation 
  of 
  such 
  inHers, 
  still 
  going 
  on, 
  seen 
  in 
  the 
  islands 
  of 
  our 
  

   large 
  fresh-water 
  lakes, 
  especially 
  in 
  Lake 
  Champlain, 
  where 
  the 
  

   islands 
  composed 
  of 
  Paleozoic 
  rocks 
  are 
  being 
  surrounded 
  and 
  grad- 
  

   ually 
  buried 
  by 
  the 
  deep 
  alluvial 
  deposits 
  filling 
  up 
  the 
  lake. 
  This 
  

   is 
  for 
  instance 
  well 
  shown 
  in 
  the 
  case 
  of 
  A^alcour 
  island, 
  near 
  

   the 
  mouth 
  of 
  Ausable 
  river 
  which 
  is 
  rapidly 
  pushing 
  a 
  delta 
  into 
  

   the 
  lake. 
  

  

  Another 
  group 
  of 
  depositional 
  inHers, 
  however, 
  is 
  well 
  repre- 
  

   sented 
  in 
  this 
  State. 
  The 
  best 
  instances 
  of 
  this 
  are 
  the 
  numerous 
  

   hummocks 
  of 
  Grenville 
  and 
  other 
  Precambric 
  rocks 
  protruding 
  

  

  through 
  the 
  Potsdam 
  sandstone 
  on 
  

   the 
  north 
  and 
  especially 
  on 
  the 
  

   northwest 
  side 
  of 
  the 
  Adirondacks. 
  

   These 
  are 
  especially 
  well 
  seen 
  in 
  

   the 
  region 
  south 
  of 
  Alexandria 
  

   bay 
  [^sec 
  fig. 
  i, 
  2]. 
  They 
  orig- 
  

   inated 
  from 
  the 
  irregular 
  surface 
  

   of 
  the 
  Precambric 
  floor 
  result- 
  

   ing 
  'from 
  'the 
  differing 
  hardness 
  

   of 
  the 
  rocks. 
  The 
  mostly 
  small, 
  

   elongate 
  hills 
  emerge 
  now 
  from 
  

   beds 
  of 
  Potsdam 
  sandstone 
  which 
  

   by 
  their 
  position 
  and 
  the 
  coarser 
  

   texture 
  of 
  their 
  basal- 
  portions, 
  

   clearly 
  show 
  deposition 
  upon 
  and 
  against 
  these 
  hills. 
  The 
  latter 
  

   v/ere 
  not 
  true 
  outliers 
  in 
  Potsdam 
  time, 
  since 
  their 
  strata 
  were 
  

   still 
  in 
  connection 
  with 
  the 
  Adirondack 
  mass, 
  but 
  they 
  have 
  

  

  >^ 
  >A. 
  y\ 
  

  

  ^ 
  /\ 
  /\ 
  /I 
  

  

  Inliers 
  of 
  P/e 
  cambr 
  ic 
  rocks 
  

   in 
  Potsdam 
  sandstone 
  : 
  

  

  near 
  Alexandria, 
  X. 
  V 
  

   I 
  in. 
  

  

  Scale 
  15 
  m. 
  =^ 
  

  

  ^^ 
  y^. 
  ^ 
  'v 
  ^ 
  

  

  Fig. 
  2 
  Diagrammatic 
  section 
  of 
  Precambric 
  inliers 
  near 
  Alexandria, 
  X. 
  Y, 
  

   E^ 
  Precambric 
  P-'-:*:'*:';-*-'.-;^ 
  Potsdam 
  sandstone 
  

  

  y\ 
  y\ 
  y\ 
  

  

  become 
  true 
  inliers 
  in 
  the 
  Potsdam 
  formation 
  because 
  exposed 
  

   again 
  through 
  the 
  agency 
  of 
  erosion. 
  It 
  is 
  then 
  illogical 
  to 
  term 
  

   these 
  outcrops 
  outliers 
  as 
  is 
  generally 
  done, 
  since 
  they 
  do 
  

   not 
  fulfil 
  the 
  conditions 
  of 
  an 
  outlier 
  which 
  according 
  to 
  the 
  cur- 
  

   rent 
  conception 
  is 
  a 
  detached 
  mass 
  of 
  rock, 
  resting 
  upon 
  and 
  sur- 
  

   rounded 
  on 
  all 
  sides 
  by 
  older 
  rocks. 
  These 
  supposed 
  outliers 
  are 
  

   only 
  " 
  detached 
  " 
  on 
  the 
  surface, 
  but 
  still 
  connected 
  w^ith 
  the 
  

  

  