NICKEL    DEPOSITS    OF    NICKEL    MOUNTAIN,  OREGON.  127 
Ickel-magnesium  silicate,  silica,  and  iron  oxides.  Thehydrous  nickel- 
lagnesinm  silicate  and  silica  were  dissolved,  carried  out,  and  rede- 
osited  in  the  cracks  and  crevices  so  abundant  in  the  peridotite. 
he  iron  oxide,  unless  transported  mechanically,  remained  behind  in 
le  spaces  formerly  composed  of  peridotite  or  serpentine.  It  is 
robable  that  much  of  the  material  now  found  in  the  veins  and  vein- 
its  in  the  peridotite  has  been  leached  from  deposits  formed  higher 
p,  carried  down,  and  redeposited.  Some  material  has  probably  been 
irried  down  mechanically. 
This  theory  of  origin  is  in  accord  with  that  advanced  by  Von  Foul- 
in  a  after  a  careful  study  of  the  deposits.  A  similar  view  has  recently 
een  presented  by  Glasser  b  in  explanation  of  the  nickel-silicate 
eposits  of  New  Caledonia. 
If  this  theory  is  correct,  the  downward  extension  of  the  main 
eposits  will  be  limited  to  the  depth  of  decomposition  of  the  peridotite. 
'n  the  other  hand,  if  the  theory  of  deposition  by  ascending  thermal 
aters,  as  advanced  by  Austin,  is  correct,  the  deposits  may  extend 
pally  to  greater  depths,  but  of  this  there  is  no  favoring  evidence  on 
re  surface.  The  depth  of  the. deposit  appears,  from  present  evi- 
ence,  to  be  comparatively  shallow. 
a  Jahrbueh  K.  k.geol.  Reichsanstalt,  vol.  42,  1892,  pp.  224-233. 
b  Annales  des  Mines,  10th  scr.,  vol.  4,  1904,  pp.  448-464. 
