﻿GEOLOGY. 
  225 
  

  

  other 
  beds 
  of 
  limestone, 
  of 
  equal 
  value 
  for 
  building 
  pur- 
  

   poses, 
  will 
  doubtless 
  be 
  found 
  in 
  other 
  quarters. 
  

  

  Limestone 
  of 
  a 
  different 
  character, 
  known 
  commonly 
  

   as 
  the 
  white, 
  or 
  rotten 
  limestone, 
  exists 
  in 
  immense 
  de- 
  

   posits, 
  particularly 
  in 
  what 
  is 
  termed 
  the 
  prairie 
  lands, 
  

   in 
  which 
  it 
  is 
  met 
  with 
  frequently 
  cropping 
  out 
  on 
  the 
  

   surface, 
  but, 
  from 
  the 
  deficiency 
  of 
  hardness, 
  and 
  an 
  

   aptitude 
  to 
  decompose 
  and 
  fall 
  to 
  powder, 
  by 
  exposure 
  

   to 
  the 
  atmosphere, 
  is 
  rather 
  to 
  be 
  classed 
  as 
  an 
  indurated 
  

   marl, 
  than 
  a 
  consolidated 
  rock. 
  

  

  Experiments 
  in 
  building 
  have 
  been 
  made 
  with 
  some 
  

   of 
  the 
  most 
  compact 
  and 
  harder 
  descriptions 
  of 
  this 
  rock, 
  

   which 
  although 
  readily 
  cut 
  into 
  blocks 
  in 
  the 
  moist 
  state 
  

   in 
  the 
  quarry 
  by 
  the 
  ordinary 
  cross-cut 
  saw, 
  was 
  found 
  

   to 
  harden 
  when 
  properly 
  dried, 
  and 
  some 
  very 
  imposing 
  

   and 
  extensive 
  edifices 
  were 
  erected 
  of 
  it 
  in 
  St. 
  Stephens, 
  

   in 
  Alabama, 
  about 
  the 
  year 
  1818. 
  It 
  was 
  found, 
  how- 
  

   ever, 
  very 
  liable 
  to 
  exfoliate 
  and 
  crumble 
  from 
  the 
  effects 
  

   of 
  damp 
  and 
  frost. 
  

  

  Whether 
  this 
  can 
  be 
  prevented, 
  and 
  if 
  an 
  exterior 
  

   coating 
  of 
  hydraulic 
  cement 
  will 
  remedy 
  this 
  defect, 
  is 
  

   perhaps, 
  worthy 
  of 
  experiment. 
  

  

  Less 
  widely 
  and 
  more 
  sparingly 
  distributed, 
  we 
  find 
  

   calcareous 
  tufa, 
  claystones, 
  or 
  concretions, 
  deposited 
  by 
  

   the 
  calcareous, 
  or 
  hard 
  water 
  of 
  some 
  of 
  our 
  springs 
  

   percolating 
  through 
  the 
  marly 
  soil. 
  

  

  Of 
  the 
  latter 
  character, 
  in 
  nodular 
  or 
  cylindrical 
  forms, 
  

   it 
  is 
  associated 
  with 
  all 
  of 
  our 
  newer 
  marls. 
  

  

  Lime, 
  in 
  the 
  form 
  of 
  a 
  sulphate 
  or 
  selenite, 
  has 
  been 
  

   revealed 
  in 
  the 
  cut 
  of 
  the 
  railroad 
  near 
  Clinton, 
  in 
  Hinds 
  

   Count}^, 
  occurring 
  in 
  flattened 
  crystals 
  with 
  pointed 
  ends, 
  

   sometimes 
  several 
  inches 
  in 
  diameter, 
  and 
  in 
  vertical 
  

   plates 
  seaming 
  the 
  gypseous 
  marl 
  of 
  the 
  locality. 
  

  

  Crystals 
  of 
  selenite 
  have 
  also 
  been 
  found 
  ten 
  or 
  fifteen 
  

   15 
  

  

  