12()  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   L906,   PART    1. 
rathei   than  with  the  enstatite.     Clarke's  analyses"  of  the  rock  and 
of  the  olivine  arc  as  follows: 
Analyses  of  peridotite  and  olivint  from  Nickel  Mountain,  Oregon. 
Loss  on  ignition. 
Sio- 
AI263 
Cr203 
F02O:< 
FeO 
Rock. 
<  MiviiH'. 
4.41 
41.43 
.04 
.76 
6.  25 
0.57 
42.  81 
.79 
2.61 
7.  21) 
NiO. 
MnO 
Ca< ) . 
MgO. 
Rock. 
0.  in 
.55 
43.74 
<  Uivine. 
0.26 
45.  12 
The  lock  analyzed  was  more4  than  two-thirds  olivine.  The  olivine 
analyzed  was  not  entirely  free  from  chromite  and  enstatite.  Yon 
Foullon  analyzed  the  olivine  of  a  peridotite  from  this  region  and  found 
it  to  contain  0.32  per  cent  of  nickel  oxide;  aboui  80  per  cent  of  his 
rock  was  olivine.  His  analysis  of  the  rhombic  pyroxene  of  the 
peridotite  gave  only  0.05  per  cent  of  nickel  oxide. 
Analyses  of  the  serpentines  which  have  keen  derived  from  the1  peri- 
dotite also  show  the  presence  of  nickel.  For  example,  Von  Foullod 
states''  that  a  specimen  of  serpentine  taken  near  the  border  of  the 
peridotite  area  contained  0.45  per  cent  of  nickel  oxide.  A  specimen 
taken  by  J.  S.  Diller  from  Iron  Mountain,  in  the  Port  Orford  quad] 
rangle,  more  than  25  miles  west  of  Nickel  Mountain,  yielded  0.13  pel 
cent  of  nickel  oxide.'  A  specimen  obtained  by  the  writer  from  a 
large  serpentine  area  northeast  of  Nickel  Mountain  and  analyzed  by 
George  Steiger  showed  0.26  per  cent  of  nickel,  equivalent  to  0.33  pel 
cent  of  nickel  oxide.  Indeed,  when  we  consider  that  the  rocks  con- 
taining  nickel  in  small  quantities  are  so  widespread  in  this  region,  it 
is  surprising  thai  t  he  deposits  of  nicked  silicate  appear  so  scanty.  The 
writer  has  no  definite  evidence  to  account  for  the  fact  that  the  serf 
pentines  derived  from  the  peridotite  on  the  southern  slope  of  Nickel 
Mountain  are  further  decomposed  into  nickel  silicate,  silica. and  iron 
oxide,  whereas  elsewhere  they  show  no  such  alteration.  It  may  he 
that  the  rocks  in  the  vicinity  of  the  deposits  contained  many  more 
minute  fractures  and  fissures  than  the  rocks  in  other-  places.  If  sol 
weathering  action  must  have  keen  more  effective  and  the  decompo- 
sition of  the  rocks  more  complete  near  these  deposits  than  where  the 
fractures  were  fewer. 
The  field  study  of  the  nickel  deposits  and  their  associations  reveals 
the  various  stages  from  the  fresh  peridotite  to  the  final  products  of 
decomposition.  The  peridotite,  under  the  ordinary  atmospheric 
weathering  processes,  has  keen  decomposed  into  serpentine,  which  in 
turn  was  further  decomposed,  the  resulting  products  being  hydrous 
oClarke,  I'.  W.,  Ajm.  Jour.  Sci.,  3d  ser.,  vol.  35, 1888,  p.  485. 
b  Jahxbuch  K.  k.geol.  Eteichsanstalt,  vol.  42,  1892,  p. 
«  Geologic  Atlas  U.  S.,  folio  89,  U.  S.  Geol.  Survr\  .  L903,  p.  4. 
