﻿Geology 
  and 
  Mineralogy. 
  73 
  

  

  Potrero 
  San 
  Francisco; 
  by 
  Chas. 
  Palache. 
  — 
  This 
  presents 
  the 
  re- 
  

   sults 
  of 
  a 
  study 
  of 
  this 
  rock 
  both 
  in 
  the 
  field 
  and 
  in 
  the 
  laboratory. 
  

   The 
  facts 
  obtained 
  show 
  that 
  it 
  is 
  the 
  result 
  of 
  alteration 
  of 
  a 
  very 
  

   basic 
  igneous 
  rock 
  intruded 
  into 
  the 
  San 
  Francisco 
  sandstone. 
  

  

  Xo. 
  6. 
  On 
  a 
  rock 
  from 
  the 
  vicinity 
  of 
  San 
  Francisco 
  contain- 
  

   ing 
  a 
  new 
  Soda-Amphibole 
  ; 
  by 
  the 
  same 
  author. 
  — 
  The 
  rock 
  con- 
  

   sists 
  of 
  fine 
  grains 
  of 
  albite. 
  Through 
  this 
  is 
  thickly 
  sprinkled 
  the 
  

   amphibole 
  in 
  small 
  acicular 
  crystals, 
  in 
  simple 
  forms. 
  The 
  optical 
  

   relations 
  determined 
  in 
  thin 
  section 
  are 
  b=h, 
  c:a 
  = 
  11° 
  — 
  13° 
  in 
  

   front 
  : 
  Pleochroism 
  strong 
  : 
  a=sky-blue 
  to 
  dark 
  blue, 
  b=violet, 
  

   c=yellowish 
  brown 
  to 
  greenish 
  yellow. 
  Absorption 
  q 
  ^ 
  6> 
  c. 
  Is 
  

   often 
  zonally 
  built. 
  A 
  chemical 
  analysis 
  gave 
  the 
  following 
  results 
  : 
  

  

  SiOo 
  Alo0 
  3 
  Fe 
  2 
  3 
  FeO 
  MnO 
  MgO 
  CaO 
  Na 
  2 
  K 
  2 
  H 
  2 
  Sum. 
  

   ■5502 
  4 
  75 
  10-91 
  9-46 
  tr. 
  9'30 
  2'3S 
  7-62 
  0'27 
  ? 
  = 
  9970 
  

  

  A 
  consideration 
  of 
  the 
  molecular 
  ratios 
  of 
  the 
  oxides 
  from 
  this 
  

   analysis 
  shows 
  them 
  to 
  be 
  

  

  Si0 
  2 
  

  

  •918 
  

  

  FeO 
  

  

  •131 
  

  

  A1 
  2 
  3 
  

  

  •046 
  ) 
  -114 
  

  

  MgO 
  

  

  •233 
  

  

  Fe 
  2 
  3 
  

  

  •0(58 
  J 
  

  

  CaO 
  

  

  •043 
  

  

  :J5h» 
  

  

  K 
  2 
  

  

  whence 
  (Na, 
  K) 
  2 
  : 
  E 
  2 
  O 
  s 
  : 
  Si0 
  2 
  : 
  : 
  .126: 
  -114: 
  480:: 
  1-05: 
  0-95: 
  4 
  

   and 
  RO: 
  Si0 
  2 
  : 
  : 
  '407 
  : 
  -437 
  : 
  : 
  1 
  : 
  1. 
  

  

  From 
  which 
  it 
  appears 
  that 
  the 
  mineral 
  is 
  a 
  mixture 
  of 
  the 
  

  

  actinolite 
  (Ca, 
  Mg, 
  Fe)SiO 
  , 
  the 
  glaucophane 
  KaAl(SiO 
  ) 
  and 
  

  

  in 
  

   the 
  riebeckite 
  NaFe(Si0 
  3 
  ) 
  2 
  molecules. 
  The 
  author 
  proposes 
  for 
  it 
  

   the 
  name 
  crossite 
  after 
  Mr. 
  Whitman 
  Cross 
  of 
  Washington. 
  

  

  The 
  propriety 
  of 
  giving 
  new 
  names 
  to 
  indefinite 
  mixtures 
  of 
  

   isomorphous 
  molecules 
  is 
  at 
  best 
  a 
  very 
  doubtful 
  one, 
  unless 
  from 
  

   constancy 
  and 
  frequence 
  of 
  occurrence 
  there 
  is 
  a 
  positive 
  demand 
  

   for 
  such 
  a 
  term. 
  By 
  far 
  the 
  larger 
  part 
  of 
  the 
  work 
  of 
  chemical 
  

   mineralogy 
  in 
  the 
  last 
  few 
  decades 
  has 
  been 
  ridding 
  the 
  termi- 
  

   nology 
  of 
  just 
  such 
  synonyms; 
  and 
  one 
  needs 
  only 
  to 
  glance 
  at 
  

   the 
  index 
  to 
  the 
  recent 
  edition 
  of 
  Dana's 
  Mineralogy 
  to 
  become 
  

   convinced 
  of 
  this 
  fact. 
  The 
  best 
  usage 
  seems 
  to 
  require 
  that 
  

   definite 
  mineral 
  molecules 
  once 
  established 
  should 
  receive 
  definite 
  

   names, 
  arid 
  isomorphous 
  mixtures 
  should 
  be 
  classed 
  under 
  the 
  one 
  

   prevailing. 
  

  

  No. 
  7. 
  Geology 
  of 
  Angel 
  Island 
  ; 
  by 
  F. 
  L 
  Ransome. 
  — 
  This 
  

   is 
  a 
  very 
  careful 
  and 
  excellent 
  study 
  of 
  the 
  geology 
  and 
  petrog- 
  

   raphy 
  of 
  a 
  small 
  island 
  in 
  San 
  Francisco 
  bay. 
  The 
  island 
  con- 
  

   sists 
  in 
  the 
  main 
  of 
  the 
  San 
  Francisco 
  sandstone 
  which 
  is 
  folded, 
  

   and 
  intruded 
  with 
  serpentine 
  and 
  a 
  "basic 
  igneous 
  rock 
  classed 
  by 
  

   the 
  author 
  under 
  fourchite. 
  It 
  is 
  accompanied 
  by 
  a 
  detailed 
  

   geological 
  map 
  and 
  plates, 
  and 
  Dr. 
  G. 
  H. 
  Hinde 
  adds 
  a 
  chapter 
  

   on 
  the 
  idiolarian 
  chert 
  found 
  on 
  the 
  island. 
  l. 
  v. 
  p. 
  

  

  7. 
  Mineral 
  Resources 
  of 
  the 
  United 
  States. 
  Vol. 
  IX. 
  Calen- 
  

   dar 
  Year, 
  1892, 
  850 
  pp. 
  'Washington, 
  1893. 
  Vol. 
  X. 
  Calendar 
  

   Year, 
  1893, 
  810 
  pp. 
  Washington, 
  1894. 
  David 
  T. 
  Day, 
  Chief 
  

   of 
  Division 
  of 
  Mining 
  Statistics 
  and 
  Technology 
  (U. 
  S. 
  Geol. 
  

  

  