﻿Report 
  of 
  the 
  State 
  Geologist. 
  703 
  

  

  relief, 
  and 
  there 
  can 
  be 
  no 
  doubt 
  that 
  then, 
  as 
  now, 
  the 
  gneiss 
  

   formed 
  the 
  higher 
  and 
  the 
  limestone 
  the 
  lower 
  areas. 
  That 
  this 
  

   was 
  so 
  is 
  not 
  only 
  inferred, 
  but 
  is 
  shown 
  by 
  direct 
  evidence 
  

   in 
  the 
  present 
  relation 
  of 
  sandstone 
  beds 
  to 
  gneiss 
  and 
  limestone. 
  

   Now, 
  in 
  this 
  limestone, 
  the 
  ore 
  was 
  forming 
  by 
  the 
  process 
  out- 
  

   lined 
  above. 
  As 
  the 
  country 
  approached 
  more 
  closely 
  to 
  a 
  base- 
  

   level 
  any 
  deposits 
  formed 
  at 
  elevated 
  points 
  would 
  be 
  destroyed, 
  

   being 
  in 
  part 
  removed 
  by 
  erosion 
  and 
  in 
  part 
  working 
  down 
  to 
  

   form 
  deeper-^ 
  ated 
  accumulations. 
  Thus, 
  when 
  the 
  Potsdam 
  sea 
  

   spread 
  over 
  the 
  region 
  there 
  would 
  be 
  left 
  only 
  such 
  deposits 
  as 
  

   had 
  been 
  formed 
  below 
  the 
  last 
  land 
  surface, 
  and 
  these 
  would 
  all 
  

   be 
  in 
  depressions. 
  Being 
  covered 
  by 
  the 
  sea, 
  the 
  whole 
  area 
  

   received 
  a 
  thick 
  coating 
  of 
  sandstone, 
  which 
  filled 
  up 
  all 
  depres- 
  

   sions 
  and 
  produced 
  a 
  surface 
  approximately 
  fiat. 
  Were 
  there 
  

   had 
  previously 
  been 
  a 
  depression 
  the 
  sandstone 
  would 
  be 
  thickest, 
  

   and 
  where 
  there 
  had 
  been 
  an 
  elevation 
  it 
  would 
  be 
  thinnest. 
  

  

  The 
  region 
  being 
  again 
  elevated, 
  denudation 
  began. 
  As 
  a 
  

   result 
  of 
  this 
  denudation 
  the 
  once 
  extensive 
  and 
  continuous 
  sheet 
  

   of 
  sandstone 
  is 
  reduced 
  to 
  a 
  number 
  of 
  scattered 
  patches. 
  It 
  is 
  

   only 
  natural 
  that 
  these 
  patches 
  should 
  be 
  left 
  where 
  the 
  sandstone 
  

   was 
  originally 
  thickest 
  ; 
  in 
  other 
  words, 
  where 
  it 
  had 
  to 
  fill 
  up 
  

   depressions. 
  As 
  the 
  ore 
  was 
  deposited 
  in 
  such 
  depressions 
  it 
  is 
  

   not 
  surprising 
  that 
  sandstone 
  should 
  be 
  found 
  resting 
  upon 
  it. 
  A 
  

   further 
  agency 
  which 
  would 
  tend 
  to 
  produce 
  the 
  same 
  result 
  is 
  

   underground 
  drainage. 
  After 
  the 
  sandstone 
  was 
  cut 
  down 
  to 
  

   the 
  limestone, 
  at 
  many 
  points 
  water 
  would 
  be 
  removed 
  through 
  

   underground 
  channels, 
  and 
  would 
  have 
  little 
  erosive 
  effect 
  upon 
  

   the 
  scattered 
  patches 
  of 
  sandstone. 
  The 
  fact 
  that 
  the 
  lower 
  

   layers 
  of 
  sandstone 
  become 
  ferruginous 
  and 
  grade 
  into 
  the 
  ore, 
  

   is 
  what 
  would 
  necessarily 
  result 
  from 
  the 
  deposition 
  of 
  the 
  former 
  

   upon 
  the 
  latter, 
  the 
  sandstone 
  deriving 
  a 
  portion 
  of 
  its 
  material 
  

   from 
  the 
  ore. 
  In 
  fact, 
  at 
  the 
  Old 
  Sterling 
  mine 
  the 
  sandstone 
  

   just 
  above 
  the 
  ore 
  contains 
  distinct 
  pebbles 
  of 
  the 
  latter. 
  

  

  If 
  this 
  explanation 
  of 
  the 
  cause 
  of 
  association 
  of 
  sandstone 
  

   and 
  ore 
  is 
  correct, 
  it 
  would 
  be 
  expected 
  that 
  sandstone 
  would 
  be 
  

   less 
  common 
  in 
  gneissic 
  areas 
  than 
  in 
  limestone 
  areas, 
  the 
  gneiss 
  

   being 
  assumed 
  to 
  have 
  formed 
  the 
  elevated 
  portions 
  of 
  the 
  sea 
  

   bottom 
  upon 
  which 
  the 
  sandstone 
  was 
  deposited, 
  and 
  hence 
  to 
  

   have 
  received 
  a 
  thinner 
  layer. 
  As 
  a 
  matter 
  of 
  fact 
  this 
  is 
  pre- 
  

  

  