MAGNESITE    DEPOSITS    OF    CALIFORNIA.  387 
x>rous  as  the  result  of  its  decomposition  by  percolating  surface  waters.     The  rock  shrinks 
hrough  the  gradual  removal  of  its  components  and  the  magnesite  fills  the  enlarging  spaces 
H'tween  the  fragments.     The  magnesite  formed  through  the  decomposition  of  serpentine 
xcupies  about  four-fifths  of  the  space  of  the  original  rock,  so  that  a  magnesite  vein  maybe 
md  probably  is  formed  very  largely  from  the  serpentine  which  formerly  occupied  the  space 
illed  by  the  vein,  the  remainder  coming  from  the  rock  in  a  comparatively  narrow  zone  on 
;ach  side.     The  large  width  of  some  of  the  veins  is  thus  easily  explained  by  supposing  I  hat 
hey  occupy  spaces  made  by  the  disintegrating  serpentine  almost  as  fast  as  they  are  left 
rather  than  natural  fissures  or  cracks  in  the  rocks.     The  veins  are  thus,  in  a  sense,  partly 
residual  from  the  serpentine.     Such  belts  of  disintegration  are  naturally  along  the  channel-; 
with  greatest  circulation  of  water,  generally  coincident  with  the  larger  faults.     Every  crack 
and  joint  along  the  line  makes  a  feeder  for  the  trunk  channels.     Among  these  reticulations 
the  same  process  of  deposition  is  going  on,  and  in  places  sudden  enlargements  of  the  veins 
occur,  making  so-called  "  bowlders  "  of  magnesite,  which  may  be  2  or  3  feet  in  diameter  and 
nearly  equidimensional.     This  lack  of  linear  extension  in  small  deposits,  together  with  the 
number  of  faults  known  to  cross  the  Coast  Range  serpentines  in  every  direction,  makes  the 
following  of  veins  by  widely  separated  outcrops  very  uncertain,  for  there  is  no  reason  to 
believe  that  sudden  terminations  do  not  occur  in  the  large  deposits  as  in  the  smaller  ones. 
Little  is  known  of  the  depth  to  which  the  veins  extend.  If  it  is  considered  that  they  are 
formed  through  the  influence  of  percolating  surface  water,  it  seems  fair  to  assume  that  the 
deposits  may  extend  down  to  the  limit  of  circulation  of  these  waters,  their  size  being  modified 
by  the  time  through  which  such  circulation  has  existed,  any  difference  in  the  hardness  or  com- 
position of  the  rock,  etc.;  and  faulting  is  as  likely  to  cut  the  veins  off  in  depth  as  in  length. 
Cinnabar  and  chromite  are  frequently  found  accompanying  the  serpentines  in  the  neigh- 
borhood of  the  magnesite  deposits. 
LIVERMORE    DEPOSITS. 
Near  Livermore,  a  town  48  miles  southeast  of  San  Francisco,  are  a  number  of  magnesite 
deposits,  of  which  the  only  one  being  worked  is  located  32  miles  southeast  of  Livermore  and 
belongs  to  the  American  Magnesite  Company. 
An  excellent  road  follows  up  Arroyo  Mocho,  crossing  into  and  running  down  Arroyo  Colo- 
rado. The  maximum  grade  for  the  haul  from  the  mine  is  said  to  be  3  per  cent.  At  the 
mines  the  company  has  erected  good  buildings  and  roads,  and  an  aerial  tram  2,500 feet  long, 
with  a  capacity  of  100  tons  per  ten-hour  day,  delivers  the  magnesite  to  bunkers,  from  which  it 
is  loaded  into  iron  wagons  for  hauling  to  Livermore.  The  wagons  carry  17^  tons  each,  and 
two  are  hauled  by  an  oil-burning  traction  engine.  The  magnesite  is  shipped  to  Oakland, 
where  the  company's  factories  for  brick,  carbon  dioxide,  and  other  products  are  situated. 
The  mine  offices  and  other  buildings  are  located  near  springs  that  give  sufficient  water  for  the 
needs  of  the  engines,  the  mine,  and  other  purposes. 
The  magnesite  veins  stand  out  prominently  in  the  bright  sunshine  of  the  valley  and  are 
almost  dazzlingly  white,  so  that  they  can  be  seen  from  the  higher  hills,  miles  away.  One  of 
the  veins,  called  the  "  Mammoth,"  stands  fully  10  feet  above  the  hillside.  Many  of  the  veins, 
however,  are  largely  covered  by  debris.  The  magnesite  shows  many  peculiarities  in  weath- 
ering. Some  of  the  surfaces  weather  into  a  pattern  that  looks  like  sun  cracks  in  mud.  with 
flatly  oval  surfaces  from  one-eighth  to  three-fourths  of  an  inch  wide  between  the  cracks.  In 
places  there  are  fluted  surfaces  such  as  occur  on  exposed  limestones,  but  in  narrower  lines, 
and  at  times  the  weathered  surface  is  thickly  studded  with  sharp  points.  At  this  place  sur- 
faces frequently  are  covered  with  a  white  powder  which  has  been  supposed  to  be  magnesium 
oxide  or  hydromagnesite,  but  which  has  been  determined  by  W.  T.  Schaller,  of  the  chemical 
laboratory  of  the  United  States  Geological  Survey,  to  be  another  form  of  the  magnesite. 
Underground,  nodules  or  portions  of  veins  of  magnesite  will  turn  to  this  almost  impalpable 
powder,  leaving  a  core  of  solid  material.  Mr.  C.  PI.  Spinks,  the  superintendent  of  the  mines, 
told  the  writer  that  certain  other  veins  belonging  to  the  company,  a  few  miles  dist  ant,  carried 
several  feet  of  this  powder.     Why  it  should  take  this  form,  breaking  down  from  the  solid 
