﻿40 
  ECONOMICAL 
  GEOLOGY. 
  

  

  river 
  from 
  its 
  mouth 
  to 
  the 
  vicinity 
  of 
  Indian 
  Creek, 
  a 
  distance 
  of 
  

   about 
  ten 
  miles. 
  This 
  sandstone 
  will 
  furnish 
  an 
  inexhaustible 
  sup- 
  

   ply 
  of 
  the 
  best 
  glass 
  sand 
  to 
  be 
  found 
  in 
  the 
  Mississiypi 
  Valley, 
  and 
  

   in 
  its 
  economical 
  importance 
  it 
  is 
  second 
  only 
  to 
  the 
  Coal 
  Measures 
  

   in 
  the 
  value 
  of 
  its 
  products. 
  It 
  is 
  found 
  at 
  only 
  two 
  points 
  in 
  the 
  

   State 
  outside 
  of 
  LaSalle 
  county, 
  viz 
  : 
  at 
  Grand 
  de 
  Tour, 
  in 
  Lee, 
  and 
  

   at 
  Cap 
  au 
  Gres 
  in 
  Calhoun, 
  counties. 
  Its 
  maximum 
  thickness 
  is 
  

   probably 
  about 
  225 
  feet 
  in 
  the 
  southern 
  part 
  of 
  this 
  county, 
  but 
  it 
  

   thins 
  out 
  to 
  the 
  northward, 
  so 
  that 
  in 
  the 
  northern 
  portion 
  it 
  does 
  

   not 
  much 
  exceed 
  150 
  feet. 
  Its 
  extensive 
  out-rnps 
  in 
  the 
  bluffs 
  of 
  

   the 
  Illinois 
  river 
  make 
  its 
  economical 
  products 
  easily 
  accessible 
  to 
  

   both 
  railroad 
  and 
  water 
  transportation, 
  and 
  the 
  abundance 
  of 
  coal 
  

   to 
  be 
  obtained 
  in 
  close 
  proximity 
  to 
  this 
  sandstone 
  indicates 
  that 
  

   this 
  is 
  one 
  of 
  the 
  most 
  favorable 
  points 
  in 
  the 
  State, 
  or 
  in 
  the 
  United 
  

   States, 
  for 
  the 
  manufacture 
  of 
  all 
  kinds 
  of 
  glassware, 
  and 
  several 
  

   extensive 
  factories 
  of 
  this 
  kind 
  have 
  already 
  been 
  established 
  in 
  this 
  

   county. 
  

  

  The 
  Trenton 
  limestone, 
  which 
  is 
  the 
  next 
  formation 
  above 
  the 
  

   St. 
  Peter's 
  sandstone, 
  has 
  been 
  so 
  much 
  eroded 
  where 
  it 
  appears 
  in 
  

   natural 
  outcrops 
  in 
  this 
  county, 
  that 
  no 
  accurate 
  estimate 
  of 
  its 
  

   original 
  thickness 
  could 
  be 
  made 
  from 
  an 
  examination 
  of 
  its 
  sur- 
  

   face 
  exposures, 
  but 
  in 
  boring 
  at 
  Streator 
  for 
  artesian 
  water, 
  its 
  thick- 
  

   ness 
  was 
  found 
  to 
  be 
  a 
  little 
  over 
  203 
  feet, 
  which 
  is 
  not 
  more 
  than 
  

   half 
  its 
  average 
  thickness 
  in 
  other 
  portions 
  of 
  the 
  State, 
  where 
  it 
  

   has 
  not 
  been 
  subjected 
  to 
  erosion. 
  The 
  outcrops 
  only 
  show 
  the 
  

   presence 
  of 
  from 
  25 
  to 
  75 
  feet 
  of 
  the 
  lower 
  part 
  of 
  the 
  formation, 
  

   the 
  remainder, 
  with 
  the 
  overlying 
  Upper 
  Silurian 
  strata 
  which 
  were 
  

   probably 
  deposited 
  over 
  this 
  portion 
  of 
  the 
  State, 
  have 
  been 
  removed 
  

   by 
  tin' 
  long-continued 
  eroding 
  agencies 
  which 
  immediately 
  preceded 
  

   the 
  Upper 
  Carboniferous 
  era. 
  

  

  The 
  Trenton 
  limestone 
  affords 
  some 
  good 
  building 
  stone, 
  and 
  aome 
  

   of 
  the 
  layers 
  take 
  a 
  good 
  polish, 
  and 
  make 
  a 
  handsome 
  marble. 
  

   Usually 
  it 
  has 
  too 
  large 
  a 
  per 
  cent, 
  of 
  alumina 
  and 
  magnesia 
  to 
  

   make 
  a 
  good 
  material 
  for 
  the 
  lime-kiln. 
  

  

  (lays 
  suitable 
  for 
  brick, 
  pottery 
  ami 
  drain 
  tile 
  are 
  abundant, 
  and 
  

  

  some 
  of 
  the 
  lire-clays 
  of 
  the 
  lower 
  Coal 
  Measures 
  seem 
  to 
  he 
  adapted 
  

  

  to 
  the 
  manufacture 
  of 
  fire-brick. 
  

  

  Coal 
  LS 
  by 
  far 
  the 
  most 
  important 
  and 
  valuable 
  mineral 
  product 
  

   "I 
  LaSalle 
  county, 
  ami 
  its 
  Favorable 
  position 
  On 
  the 
  extreme 
  north- 
  

   ern 
  border 
  of 
  tho 
  productive 
  coal 
  field 
  enhances 
  the 
  value 
  of 
  this 
  

   product, 
  both 
  for 
  consumption 
  in 
  manufacturing 
  establishments 
  at 
  

  

  