﻿430 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  county 
  has 
  an 
  average 
  thickness 
  of 
  65 
  feet. 
  It 
  is 
  a 
  well 
  known 
  for- 
  

   mation 
  and 
  has 
  been 
  quarried 
  for 
  lime 
  at 
  numerous 
  points 
  

   throughout 
  the 
  state. 
  One 
  of 
  the 
  best 
  exposures 
  of 
  this 
  stone 
  is 
  at 
  

   The 
  Indian 
  Ladder. 
  Underlying 
  the 
  Pentamerus 
  bed 
  is 
  a 
  series 
  of 
  

   thin 
  bedded 
  dark 
  blue 
  limestones, 
  which 
  generally 
  crop 
  out 
  at 
  

   the 
  base 
  of 
  the 
  Helderberg 
  escarpment 
  but 
  are 
  frequently 
  hidden 
  

   by 
  the 
  talus 
  at 
  the 
  base 
  of 
  the 
  cliff. 
  These 
  Tentaculite 
  lime- 
  

   stones 
  are 
  often 
  of 
  a 
  shaly 
  nature. 
  Their 
  thickness 
  along 
  the 
  

   eastern 
  face 
  of 
  Helderberg 
  mountain 
  according 
  to 
  Darton 
  is 
  

   about 
  30 
  feet. 
  They 
  are 
  also 
  exposed 
  at 
  the 
  Indian 
  Ladder 
  and 
  

   at 
  South 
  Bethlehem. 
  An 
  excellent 
  section 
  of 
  both 
  Pentamerus 
  

   and 
  the 
  Tentaculite 
  bed 
  is 
  seen 
  in 
  Callanan's 
  quarry 
  southwest 
  of 
  

   South 
  Bethlehem, 
  analyses 
  of 
  which 
  are 
  given 
  below. 
  Under- 
  

   lying 
  the 
  Tentaculite 
  are 
  the 
  waterlime 
  beds, 
  also 
  exposed 
  at 
  

   Indian 
  Ladder 
  and 
  in 
  the 
  floor 
  of 
  the 
  quarry 
  at 
  South 
  Bethlehem, 
  

   and 
  at 
  both 
  localities 
  they 
  are 
  about 
  four 
  feet 
  thick 
  and 
  represent 
  

   impure 
  magnesian 
  limestones.® 
  

  

  The 
  following 
  analyses 
  made 
  for 
  this 
  report 
  will 
  indicate 
  the 
  

   character 
  of 
  limestones 
  of 
  the 
  Helderberg 
  series 
  in 
  Callanan's 
  

   quarry 
  at 
  South 
  Bethlehem: 
  

  

  Lower 
  third 
  of 
  quarry 
  

  

  Silica 
  9.05 
  

  

  Ferric 
  oxid 
  .99 
  

  

  Alumina 
  6 
  . 
  66 
  

  

  Lime 
  carbonate 
  . 
  . 
  . 
  79.86 
  

  

  Magnesia 
  carbonate 
  4 
  . 
  17 
  

  

  100.73 
  

   Middle 
  third 
  

  

  Silica 
  5 
  . 
  12 
  

  

  Alumina 
  1 
  . 
  45 
  

  

  Ferric 
  oxid 
  .74 
  

  

  Lime 
  48.34 
  

  

  Magnesia 
  2 
  . 
  93 
  

  

  Carbon 
  dioxid 
  41 
  .22 
  

  

  99.80 
  

  

  ^Darton's 
  geology 
  of 
  Albany 
  county, 
  N. 
  Y. 
  state 
  geol. 
  rep't 
  1893. 
  

  

  