﻿70 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  rests 
  either 
  on 
  the 
  Potsdam 
  or 
  on 
  the 
  Precambric. 
  In 
  the 
  upper 
  

   Black 
  river 
  valley 
  it 
  lies 
  on 
  the 
  Precambric. 
  xMl 
  these 
  formations 
  

   are 
  capable 
  of 
  furnishing 
  sandy 
  material 
  and 
  hence 
  the 
  sandstone 
  

   base 
  of 
  the 
  formation 
  is 
  but 
  natural. 
  The 
  Theresa, 
  however, 
  is 
  less 
  

   capable 
  in 
  this 
  respect 
  than 
  are 
  the 
  other 
  formations, 
  thus 
  account- 
  

   ing 
  for 
  the 
  fact 
  that 
  this 
  sandy 
  base 
  is 
  a 
  less 
  prominent 
  feature 
  of 
  

   our 
  area 
  here 
  than 
  it 
  is 
  in 
  the 
  others. 
  

  

  Hereabout, 
  the 
  best 
  section 
  of. 
  this 
  basal 
  material 
  seen 
  is 
  at 
  the 
  

   foot 
  of 
  the 
  Pamelia 
  inface, 
  2 
  miles 
  east 
  of 
  Perch 
  lake, 
  Theresa 
  

   sheet. 
  The 
  small 
  creek 
  there 
  runs 
  over 
  a 
  massive, 
  bared 
  layer 
  of 
  

   Theresa 
  dolomite, 
  above 
  which 
  a 
  14 
  inch 
  layer 
  of 
  the 
  same 
  shows 
  in 
  

   the 
  bank. 
  Above 
  this 
  lie 
  weak, 
  greenish 
  sands 
  and 
  sandy 
  shales, 
  

   with 
  an 
  exposed 
  thickness 
  of 
  some 
  7^/^ 
  feet, 
  the 
  basal 
  layer 
  some- 
  

   what 
  pebbly 
  and 
  more 
  massive 
  than 
  the 
  rernainder. 
  The 
  cement 
  is 
  

   calcareous 
  and 
  abundant. 
  The 
  rock 
  is 
  therefore 
  weak 
  and 
  seldom 
  

   exposed, 
  yet 
  in 
  a 
  sufficient 
  number 
  of. 
  places, 
  and 
  sufficiently 
  well 
  

   to 
  show 
  that 
  it 
  everywhere 
  underlies 
  the 
  limestone 
  throughout 
  the 
  

   district 
  with 
  a 
  thickness 
  of 
  from 
  10 
  to 
  15 
  feet, 
  much 
  of 
  which 
  is 
  

   shaily. 
  It 
  is 
  a 
  more 
  calcareous, 
  and 
  vastly 
  w^eaker 
  rock 
  than 
  even 
  

   the 
  most 
  calcareous 
  beds 
  of 
  the 
  Potsdam, 
  and 
  quite 
  different 
  from 
  

   it 
  lithologically 
  ; 
  so 
  unlike 
  in 
  fact 
  that 
  the 
  two 
  rocks 
  can 
  be 
  readily 
  

   distinguished 
  from 
  one 
  another 
  by 
  lithologic 
  character 
  alone 
  through- 
  

   out 
  the 
  whole 
  region. 
  This 
  becomes 
  of 
  importance 
  in 
  the 
  region 
  

   around 
  Kingston, 
  where 
  in 
  our 
  opinion 
  both 
  sandstones 
  are 
  pres- 
  

   ent 
  but 
  without 
  the 
  separating 
  Theresa 
  formation. 
  The 
  Pamelia 
  

   basal 
  sandstone 
  rests, 
  now 
  on 
  the 
  Potsdam 
  and 
  now 
  on 
  the 
  Pre- 
  

   cambric, 
  is 
  less 
  shaly 
  and 
  attains 
  greater 
  thickness 
  than 
  on 
  the 
  

   New 
  York 
  side, 
  and 
  shows 
  at 
  times 
  astonishingly 
  coarse 
  basal 
  

   conglomerate. 
  In 
  its 
  green 
  color, 
  weathering 
  to 
  a 
  red 
  mottling, 
  

   in 
  its 
  abundant 
  calcareous 
  cement, 
  and 
  in 
  its 
  weakness, 
  it 
  corre- 
  

   sponds 
  exactly 
  with 
  the 
  New 
  York 
  rock, 
  while 
  the 
  silicious 
  Pots- 
  

   dam 
  beneath 
  also 
  corresponds 
  with 
  the 
  Potsdam 
  across 
  the 
  river 
  in 
  

   every 
  minute 
  lithologic 
  detail, 
  even 
  in 
  the 
  '' 
  tree 
  " 
  concretions. 
  

  

  In 
  the 
  upper 
  Black 
  river 
  valley 
  both 
  Potsdam 
  and 
  Theresa 
  are 
  

   absent 
  and 
  the 
  Pamelia 
  rests 
  on 
  the 
  Precambric. 
  At 
  Martinsburg 
  

   the 
  wonderfully 
  complete 
  section 
  shows 
  a 
  thickness 
  of 
  19 
  feet 
  for 
  

   the 
  basal 
  sandy 
  portion, 
  weak 
  green 
  sandstone, 
  blotched 
  with 
  red, 
  

   abundant 
  calcareous 
  cement 
  and 
  with 
  thin 
  conglomerate 
  at 
  the 
  base. 
  

  

  Where 
  thickest, 
  the 
  limestones 
  of 
  the 
  lower 
  division 
  show, 
  above 
  

   the 
  basal 
  sandstones, 
  beds 
  of 
  gray, 
  magnesian 
  limestone 
  with 
  fre- 
  

   quent 
  shale 
  partings; 
  these 
  are 
  followed 
  upward 
  by 
  black, 
  fos- 
  

   silif 
  erous 
  limestones, 
  holding 
  a 
  rather 
  abundant 
  marine 
  fauna 
  ; 
  then 
  

  

  