﻿Bad 
  Lands, 
  Washington 
  County, 
  South 
  Dakota. 
  353 
  

  

  common 
  and 
  typical 
  development 
  for 
  calcite. 
  Those 
  from 
  the 
  

   Bad 
  Lands, 
  however, 
  are 
  steep 
  hexagonal 
  pyramids, 
  somewhat 
  

   barrel-shaped 
  and 
  with 
  rounded 
  ends. 
  Fig. 
  1, 
  from 
  a 
  photo- 
  

   graph, 
  represents 
  a 
  complete 
  crystal, 
  natural 
  size, 
  and 
  gives 
  a 
  

   good 
  idea 
  of 
  the 
  general 
  shape 
  of 
  the 
  specimen 
  and 
  the 
  char- 
  

   acter 
  of 
  the 
  grain. 
  As 
  usual 
  with 
  photographic 
  representa- 
  

   tions 
  of 
  crystals, 
  however, 
  the 
  edges 
  are 
  not 
  very 
  well 
  defined, 
  

   and 
  the 
  pen 
  and 
  ink 
  sketch, 
  fig. 
  2, 
  has 
  been 
  introduced 
  to 
  

   bring 
  out 
  with 
  greater 
  distinctness 
  the 
  hexagonal 
  character. 
  

   In 
  a 
  rhombohedral 
  species 
  a 
  hexagonal 
  pyramid 
  must 
  be 
  a 
  

   pyramid 
  of 
  the 
  second 
  order, 
  and 
  that 
  the 
  crystals 
  from 
  the 
  

   Bad 
  Lands 
  are 
  of 
  this 
  character 
  may 
  readily 
  be 
  told 
  by 
  exam- 
  

  

  S3 
  : 
  

  

  •'1 
  

  

  

  - 
  n 
  

  

  

  yp', 
  

  

  

  

  ^-;; 
  -; 
  

  

  ■ 
  4?%? 
  

  

  

  M 
  : 
  s 
  

  

  

  tt 
  

  

  

  I 
  

  

  Hi 
  

  

  w 
  

   w 
  

  

  ining 
  their 
  ends 
  before 
  a 
  strong 
  light, 
  when, 
  on 
  turning 
  the 
  

   crystals, 
  it 
  will 
  be 
  found 
  that 
  the 
  flash 
  or 
  reflection 
  from 
  the 
  

   rhombohedral 
  cleavage 
  of 
  the 
  calcite 
  is 
  only 
  caught 
  when 
  the 
  

   alternate 
  edges 
  of 
  the 
  pyramid 
  are 
  toward 
  the 
  light. 
  With 
  the 
  

   aid 
  of 
  a 
  1 
  lens 
  no 
  difficulty 
  is 
  experienced 
  in 
  observing 
  the 
  cal- 
  

   cite, 
  filling 
  the 
  interstices 
  between 
  the 
  quartz 
  grains, 
  and 
  in 
  

   detecting 
  its 
  cleavage. 
  Pyramids 
  of 
  the 
  second 
  order 
  are 
  

   seldom 
  observed 
  in 
  calcite, 
  even 
  as 
  small 
  faces 
  in 
  complex 
  com- 
  

   binations, 
  while 
  crystals 
  showing 
  the 
  hexagonal 
  pyramid 
  alone, 
  

   or 
  with 
  but 
  slight 
  modifications 
  are 
  exceedingly 
  rare. 
  Cajcite 
  

   crystals 
  from 
  Ehisnes, 
  Belgium, 
  having 
  the 
  pyramid 
  7, 
  8*8'lG-3, 
  

   as 
  the 
  prevailing 
  type 
  and 
  only 
  slightly 
  modified 
  by 
  other 
  

   forms 
  have 
  been 
  described 
  by 
  Cesaro,* 
  and 
  the 
  crystals 
  from 
  the 
  

   Bad 
  Lands 
  are 
  undoubtedly 
  rounded 
  modifications 
  of 
  this 
  same 
  

  

  * 
  Mem. 
  de 
  l'acad. 
  roy. 
  d. 
  Belgique, 
  xxxviii, 
  p. 
  1, 
  1886. 
  

  

  