﻿354 
  Penfield 
  and 
  Ford 
  — 
  Siliceous 
  Calcites, 
  etc. 
  

  

  rare 
  pyramidal 
  form. 
  Fig. 
  3 
  represents 
  the 
  pyramid 
  8-8*16'3, 
  

   without 
  modification, 
  and 
  if 
  the 
  siliceous 
  calcites 
  were 
  origin- 
  

   ally 
  of 
  this 
  shape 
  it 
  is 
  evident 
  that 
  by 
  corrosion 
  and 
  weather- 
  

   ing 
  the 
  acute 
  * 
  terminations 
  would 
  rapidly 
  become 
  rounded, 
  

   while 
  by 
  a 
  little 
  wearing 
  away 
  of 
  the 
  horizontal 
  middle 
  edges 
  

   a 
  barrel-shaped 
  form 
  similar 
  to 
  fig. 
  2 
  would 
  result. 
  Fig. 
  4 
  

   represents 
  a 
  combination 
  of 
  the 
  pyramid 
  7, 
  8-8*16'3, 
  with 
  the 
  

   rhombohedron 
  r, 
  1011 
  and 
  the 
  base 
  c, 
  0001, 
  described 
  and 
  

   figured 
  by 
  Cesaro, 
  and 
  by 
  only 
  a 
  very 
  little 
  corrosion 
  and 
  

   weathering 
  of 
  such 
  a 
  combination 
  a 
  rounded 
  shape 
  like 
  fig. 
  2 
  

   would 
  result. 
  

  

  The 
  crystals 
  from 
  the 
  Bad 
  Lands 
  occur 
  at 
  times 
  singly, 
  but 
  

   more 
  often 
  grown 
  together 
  in 
  groups, 
  the 
  latter 
  at 
  times 
  of 
  

   considerable 
  size. 
  The 
  accompanying 
  half-tone 
  plate 
  will 
  give 
  

   some 
  idea 
  of 
  the 
  size 
  and 
  character 
  of 
  the 
  specimens. 
  The 
  

   crystals 
  have 
  evidently 
  formed 
  in 
  a 
  bank 
  or 
  deposit 
  of 
  strati- 
  

   fied 
  sand, 
  for, 
  as 
  shown 
  by 
  the 
  upper, 
  left 
  hand 
  crystal 
  and 
  the 
  

   central 
  group 
  in 
  the 
  plate, 
  the 
  original 
  bedding 
  of 
  the 
  deposit 
  

   may 
  be 
  detected 
  running 
  through 
  the 
  crystals 
  in 
  directions 
  

   which 
  have 
  no 
  relation 
  to 
  their 
  crystallographic 
  symmetry. 
  

   The 
  central 
  group 
  resembles 
  a 
  somewhat 
  weathered 
  clay-stone 
  

   concretion, 
  or 
  the 
  sculpture 
  forms 
  resulting 
  from 
  the 
  corrosion 
  

   of 
  some 
  stratified 
  sandstones; 
  it 
  has, 
  however, 
  the 
  crystalline 
  

   character 
  of 
  the 
  other 
  specimens, 
  although 
  the 
  shapes 
  of 
  the 
  

   crystals 
  have 
  *been 
  nearly 
  obliterated 
  by 
  excessive 
  weathering. 
  

   The 
  sand 
  in 
  the 
  specimens 
  is, 
  for 
  the 
  most 
  part, 
  of 
  a 
  nearly 
  

   uniform 
  grain, 
  the 
  grains 
  averaging 
  from 
  about 
  -J- 
  to 
  ^- 
  mm 
  in 
  

   diameter, 
  and 
  being 
  well 
  rounded. 
  Occasionally 
  there 
  occur, 
  

   imbedded 
  along 
  with 
  the 
  finer 
  sand, 
  large, 
  rounded 
  grains, 
  true 
  

   quartz 
  pebbles, 
  measuring 
  as 
  much 
  as 
  a 
  centimeter 
  in 
  diameter. 
  

   One 
  specimen, 
  the 
  lower 
  right 
  hand 
  one 
  of 
  the 
  plate, 
  is 
  a 
  verit- 
  

   able 
  pudding 
  stone, 
  yet 
  in 
  spite 
  of 
  the 
  coarseness 
  of 
  grain 
  the 
  

   pyramidal 
  forms 
  are 
  well 
  developed. 
  The 
  crystals 
  have 
  a 
  gray 
  

   color 
  almost 
  exactly 
  like 
  that 
  of 
  the 
  Fontainebleau 
  specimens, 
  

  

  Sheffield 
  Laboratory 
  of 
  Mineralogy 
  and 
  Petrography, 
  

   Yale 
  University, 
  New 
  Haven, 
  April, 
  1900. 
  

  

  