﻿352 
  Pen 
  field 
  and 
  Ford 
  — 
  Siliceous 
  Calottes 
  from 
  the 
  

  

  Akt. 
  XXXIII. 
  — 
  Siliceous 
  Calcites 
  from 
  the 
  Bad 
  Lands, 
  Wash- 
  

   ington 
  County, 
  South 
  Dakota/ 
  by 
  S. 
  L. 
  Penfield 
  and 
  

   W. 
  E. 
  Ford. 
  With 
  Plate 
  Y. 
  

  

  The 
  siliceous 
  calcites 
  from 
  Fontainebleau, 
  sometimes 
  called 
  

   Fontainebleau 
  limestone, 
  are 
  well 
  known 
  objects 
  to 
  the 
  min- 
  

   eralogist, 
  and 
  specimens 
  are 
  to 
  be 
  found 
  in 
  many 
  cabinets. 
  

   They 
  consist 
  of 
  calcite 
  enclosing 
  from 
  fifty 
  to 
  sixty 
  per 
  cent 
  

   of 
  sand, 
  and 
  were 
  early 
  described 
  by 
  Lassone* 
  and 
  Haiiy.f 
  

   Specimens 
  of 
  almost 
  the 
  same 
  character 
  as 
  those 
  from 
  Fon- 
  

   tainebleau 
  have 
  recently 
  been 
  found 
  in 
  the 
  Bad 
  Lands 
  of 
  

   South 
  Dakota, 
  and 
  have 
  been 
  sent 
  to 
  New 
  Haven 
  for 
  exami- 
  

   nation 
  by 
  L. 
  W. 
  Stilwell 
  of 
  Deadwood, 
  South 
  Dakota, 
  and 
  Mr. 
  

   Geo. 
  L. 
  English 
  of 
  ISTew 
  York. 
  Our 
  attention 
  has 
  also 
  been 
  

   called 
  to 
  the 
  occurrence 
  by 
  Prof. 
  E. 
  H. 
  Barbour 
  of 
  Lincoln, 
  

   Nebraska, 
  and, 
  as 
  he 
  has 
  expressed 
  his 
  intention 
  to 
  visit 
  the 
  

   locality, 
  he 
  will 
  doubtless 
  be 
  able 
  to 
  furnish 
  interesting 
  infor- 
  

   mation 
  concerning 
  the 
  mode 
  of 
  occurrence 
  of 
  the 
  crystals. 
  

   The 
  specimens 
  sent 
  by 
  Mr. 
  English 
  consist 
  of 
  a 
  representative 
  

   suite 
  of 
  handsome 
  cabinet 
  specimens 
  for 
  the 
  Brush 
  Collection, 
  

   together 
  with 
  abundant 
  material 
  for 
  study, 
  and 
  thanks 
  are 
  due 
  

   to 
  him 
  for 
  his 
  generosity. 
  A 
  quantitative 
  examination 
  of 
  a 
  

   typical 
  specimen 
  was 
  made, 
  and 
  indicated 
  that 
  the 
  material 
  

   consists 
  of 
  about 
  forty 
  per 
  cent 
  of 
  calcite 
  enclosing 
  sixty 
  per 
  

   cent 
  of 
  quartz 
  sand. 
  In 
  the 
  region 
  of 
  the 
  Bad 
  Lands 
  of 
  

   Dakota, 
  whence 
  the 
  crystals 
  come, 
  the 
  White 
  Piver 
  sandstone 
  

   is 
  a 
  very 
  abundant 
  rock 
  and 
  consists 
  of 
  sand 
  grains 
  cemented 
  

   together 
  by 
  calcareous 
  material. 
  Evidently 
  the 
  crystals 
  in 
  

   question 
  represent 
  a 
  phase 
  of 
  sand 
  cementation 
  in 
  which 
  the 
  

   crystalline 
  form 
  of 
  the 
  calcite 
  is 
  preserved. 
  This 
  kind 
  of 
  

   cementation 
  might 
  take 
  place, 
  for 
  example, 
  in 
  a 
  sand 
  deposit 
  

   wet 
  with 
  water 
  carrying 
  calcium 
  carbonate 
  in 
  solution. 
  The 
  

   calcite 
  crystallization 
  may 
  be 
  conceived 
  to 
  go 
  on, 
  until 
  crystals 
  

   of 
  a 
  certain 
  size 
  have 
  been 
  produced, 
  the 
  calcite 
  material 
  grow- 
  

   ing 
  about 
  and 
  enclosing 
  the 
  sand 
  grains, 
  and 
  then 
  it 
  seems 
  

   necessary 
  to 
  consider 
  that 
  the 
  crystallization 
  ceased, 
  owing 
  to 
  

   changed 
  conditions, 
  for 
  otherwise 
  an 
  ordinary 
  solid 
  sandstone 
  

   with 
  calcareous 
  cement 
  would 
  result. 
  The 
  partial 
  wearing 
  

   away 
  -of 
  such 
  a 
  sand 
  deposit 
  in 
  which 
  crystallization 
  had 
  taken 
  

   place 
  would 
  then 
  expose 
  the 
  crystals. 
  

  

  An 
  interesting 
  feature 
  of 
  the 
  siliceous 
  calcites 
  from 
  the 
  new 
  

   locality 
  is 
  the 
  peculiar 
  shape 
  of 
  the 
  crystals. 
  The 
  crystals 
  

   from 
  Fontainebleau 
  have 
  the 
  shape 
  of 
  the 
  rhombohedron, 
  

   f, 
  0221, 
  —2, 
  fig. 
  5, 
  p. 
  263 
  of 
  Dana's 
  Mineralogy, 
  which 
  is 
  a 
  

  

  *Mem. 
  d. 
  l'acad. 
  royal. 
  Paris, 
  1775, 
  p. 
  65. 
  

   f 
  Traite 
  de 
  Mineralogie, 
  vol. 
  i, 
  p. 
  424, 
  1822. 
  

  

  