﻿186 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  oxides; 
  some 
  of 
  the 
  rich 
  purple 
  tints 
  are 
  said 
  to 
  be 
  due 
  to 
  oxide 
  

   of 
  manganese. 
  

  

  The 
  gray 
  and 
  blue 
  tints 
  are 
  produced 
  by 
  iron 
  in 
  the 
  form 
  of 
  

   ferrous 
  silicate 
  or 
  carbonate. 
  By 
  an 
  irregular 
  association 
  of 
  

   masses 
  of 
  different 
  colors 
  a 
  variegated 
  surface 
  is 
  produced, 
  or 
  by 
  

   an 
  alternation 
  of 
  white 
  and 
  variously-colored 
  laminae 
  a 
  striped 
  

   appearance 
  is 
  given 
  to 
  the 
  mass. 
  

  

  Sandstones 
  occur 
  stratified 
  and 
  in 
  beds 
  of 
  greater 
  or 
  less 
  thick- 
  

   ness, 
  and 
  they 
  are 
  said 
  to 
  be 
  thick-bedded 
  or 
  thin-bedded. 
  In 
  

   some 
  cases 
  the 
  beds 
  are 
  so 
  thick, 
  and 
  the 
  stone 
  of 
  such 
  a 
  uniform 
  

   texture, 
  that 
  the 
  stone 
  can 
  be 
  worked 
  equally 
  well 
  in 
  all 
  direc- 
  

   tions, 
  and 
  is 
  known 
  as 
  freestone. 
  A 
  laminated 
  structure 
  is 
  com- 
  

   mon, 
  especially 
  in 
  the 
  thin 
  strata, 
  or 
  when 
  the 
  stone 
  is 
  micaceous. 
  

   When 
  the 
  beds 
  can 
  be 
  split 
  into 
  thin 
  slabs 
  along 
  planes 
  parallel 
  

   to 
  the 
  bedding, 
  it 
  is 
  called 
  a 
  flagstone. 
  A 
  less 
  common 
  structure 
  

   is 
  what 
  is 
  termed 
  lenticular 
  or 
  wedge-shaped, 
  in 
  which 
  the 
  upper 
  

   and 
  under 
  surfaces 
  lack 
  parallelism, 
  and 
  the 
  beds 
  wedge 
  out. 
  It 
  

   makes 
  the 
  quarrying 
  more 
  difficult, 
  and 
  produces 
  more 
  waste 
  

   material. 
  

  

  The 
  variations 
  in 
  the 
  nature 
  of 
  the 
  component 
  grains, 
  and 
  

   binding 
  material, 
  in 
  their 
  arrangement, 
  and 
  in 
  the 
  forms 
  of 
  bed- 
  

   ding, 
  produce 
  a 
  great 
  variety 
  of 
  stone, 
  and 
  the 
  gradations 
  from 
  

   one 
  to 
  another 
  are 
  slight. 
  The 
  hardness, 
  strength, 
  beauty 
  and 
  

   durability 
  are 
  determined 
  by 
  these 
  varying 
  elements 
  of 
  constitu- 
  

   tion. 
  The 
  stone 
  best 
  resisting 
  the 
  action 
  of 
  the 
  atmospheric 
  

   agencies 
  is 
  that 
  in 
  which 
  the 
  quartz 
  grains 
  are 
  cemented 
  by 
  a 
  

   silicious 
  paste, 
  or 
  in 
  which 
  the 
  close-grained 
  mass 
  approachee 
  

   in 
  texture 
  a 
  quartzite. 
  

  

  The 
  presence 
  of 
  mineral 
  liable 
  to 
  decomposition, 
  as 
  feldspar 
  

   highly 
  kaolinized, 
  of 
  mica, 
  marcasite, 
  and 
  pyrite, 
  of 
  calcite 
  in 
  

   quantity, 
  and 
  clays, 
  affects 
  the 
  durability 
  and 
  tends 
  to 
  its 
  de- 
  

   struction. 
  

  

  Sandstones 
  are 
  classified 
  according 
  to 
  their 
  geologic 
  age 
  also. 
  

   They 
  are 
  found 
  occurring 
  in 
  all 
  the 
  series, 
  from 
  the 
  oldest 
  to 
  the 
  

   most 
  recent 
  formations. 
  Those 
  of 
  a 
  given 
  age 
  are 
  generally 
  

  

  