﻿ECONOMIC 
  GEOLOGY 
  205 
  

  

  the 
  same 
  composition 
  as 
  augite 
  which 
  occurs 
  in 
  trap; 
  and 
  a 
  horn- 
  

   blende 
  granite 
  should 
  be 
  a 
  very 
  good 
  road 
  metal. 
  Where 
  horn- 
  

   blende 
  is 
  absent 
  one 
  would 
  expect 
  to 
  find 
  less 
  binding 
  power. 
  

  

  Granite 
  is 
  harder 
  than 
  trap 
  and 
  therefore 
  should 
  resist 
  wear 
  

   better, 
  but 
  this 
  quality 
  is 
  offset 
  by 
  its 
  usually 
  smaller 
  binding 
  

   power 
  so 
  that 
  trap 
  should 
  be 
  preferred 
  as 
  a 
  rule. 
  

  

  Granite 
  is 
  found 
  in 
  the 
  Adirondack 
  region 
  and 
  in 
  the 
  Highlands 
  

   of 
  the 
  Hudson, 
  also 
  in 
  Westchester 
  county. 
  The 
  commercial 
  term 
  

   granite 
  includes 
  various 
  kinds 
  of 
  gneiss. 
  

  

  Magnesian 
  limestone 
  has 
  great 
  binding 
  power 
  but 
  is 
  quite 
  soft 
  

   and 
  therefore 
  not 
  very 
  durable 
  for 
  heavy 
  traffic. 
  Chemically, 
  this 
  

   rock 
  is' 
  a 
  carbonate 
  of 
  lime, 
  containing 
  also 
  magnesia, 
  alumina 
  

   and 
  silica. 
  It 
  has 
  been 
  suggested 
  that 
  it 
  might 
  be 
  used 
  profitably 
  

   as 
  a 
  binder 
  with 
  stone 
  of 
  less 
  binding 
  power. 
  

  

  Sandstone 
  has 
  usually 
  no 
  lime, 
  magnesia 
  or 
  alumina 
  and 
  there- 
  

   fore 
  has 
  no 
  binding 
  properties 
  and 
  never 
  makes 
  a 
  first 
  rate 
  road, 
  

   as 
  the 
  fragments 
  continually 
  break 
  loose. 
  

  

  Limestone 
  is 
  found 
  chiefly 
  in 
  areas 
  parallel 
  to 
  and 
  near 
  the 
  

   main 
  line 
  of 
  the 
  New 
  York 
  Central 
  railroad 
  and 
  in 
  a 
  zone 
  around 
  

   the 
  Adirondacks. 
  

  

  In 
  New 
  York 
  the 
  best 
  road 
  materials 
  occur 
  in 
  certain 
  limited 
  

   areas, 
  and 
  at 
  points 
  distant 
  from 
  these 
  the 
  cost 
  of 
  transportation 
  

   is 
  the 
  controlling 
  feature. 
  

  

  For 
  high 
  class 
  road 
  building, 
  trap 
  and 
  granite 
  will 
  be 
  preferred 
  

   and 
  used 
  in 
  all 
  places 
  w^here 
  their 
  cost 
  is 
  not 
  prohibitory. 
  Ex- 
  

   perience 
  shows, 
  however, 
  that 
  unless 
  these 
  materials 
  are 
  used 
  

   under 
  the 
  direction 
  of 
  experienced 
  road 
  engineers, 
  they 
  are 
  less 
  

   satisfactory 
  than 
  limestone, 
  and 
  when 
  it 
  is 
  proposed 
  to 
  mac- 
  

   adamize 
  a 
  road 
  by 
  simply 
  covering 
  it 
  with 
  broken 
  stone, 
  the 
  

   latter 
  though 
  less 
  durable, 
  will 
  be 
  more 
  satisfactory. 
  

  

  When 
  granite 
  and 
  trap 
  are 
  properly 
  laid, 
  on 
  a 
  well 
  prepared 
  

   bed 
  and 
  rolled 
  with 
  a 
  heavy 
  steam 
  roller 
  to 
  the 
  proper 
  standard 
  

   of 
  firmness, 
  nothing 
  can 
  be 
  better, 
  but 
  where 
  nO' 
  steam 
  roller 
  is 
  

   available 
  and 
  the 
  subgrade 
  is 
  not 
  properly 
  prepared, 
  the 
  trap 
  and 
  

   granite 
  are 
  liable 
  to 
  afford 
  only 
  an 
  unpleasant 
  and 
  uneven 
  surface 
  

   of 
  hard 
  angular 
  fragments 
  which 
  ceaselessly 
  roll 
  about 
  on 
  the 
  

  

  