24  CONTEIBUTIONS    TO    ECONOMIC    GEOLOGY,   1903.^  [bull. 225. 
energy  of  the  American  miner  will  probably  find  means  to  overcome 
these  difficulties,  and  from  the  future  development  of  the  mines  it  is 
hoped  that  valuable  information  may  be  obtained  with   regard  to  the 
characteristics  of  this  rather  unusual  class  of  ore  deposits. 
Notes  on  the  Geology  of  the  Gbldfields  District,  Nevada,  by  J.  E.  Spurr. 
The  Goldfields  district  lies  about  23  miles  southeast  of  Tonopah. 
It  was  briefly  examined  by  Mr.  Spurr  during  the  past  summer,  and 
the  above-named  paper,  which  is  printed  in  a  subsequent  part  of  this 
volume,  contains  his  notes  on  the  geology  of  the  region.  The  ore 
deposits  themselves  were  as  yet  too  little  developed  to  permit  any 
judgment  to  be  formed  as  to  their  probable  value. 
SOUTH    DAKOTA. 
Ore  Deposits  of  the  Northern  Black  Hills,  by  J.  P.  Irving. 
This  paper,  which  appears  in  a  subsequent  part  of  this  volume,  is  an 
abstract  of  the  report  on  the  mineral  resources  (mainly  gold)  of  the 
northern  Black  Hills,  now  in  process  of  publication. 
UTAH. 
Park  City  Mining  District,  by  J.  M.  Boutwell. 
The  study  of  the  geology  and  ore  deposits  of  the  Park  City  mining 
district  has  been  continued  during  the  past  summer  try  Mr.  Boutwell 
and  his  assistants.  This  district  is  situated  in  the  most  complicated 
part  of  the  great  Wasatch  Range,  which  itself  is  remarkable  for  its 
complex  geological  history,  and  it  has  been  of  the  utmost  importance 
to  decipher  the  geological  structure  of  the  region,  for  this  affords  the 
only  sure  guide  for  the  miner  in  following  his  ore  bodies. 
The  working  out  of  this  structure  has  been  rendered  especially  diffi- 
cult by  the  peculiar  local  conditions,  and  it  was  not  until  autumn  that 
Mr.  Boutwell  was  able  to  consider  this  portion  of  his  labors  completed 
and  undertake  the  detailed  examination  of  the  mine  workings  in  the 
light  of  the  knowledge  thus  acquired.  As  a  consequence  of  this  delay 
the  underground  work  is  not  yet  completed.  In  the  latter  part  of  this 
volume  Mr.  Boutwell  gives  a  sketch  of  the  general  results  achieved 
since  the  publication  of  his  preliminary  notes  in  Bulletin  213.  He 
also  gives  the  result  of  an  examination  of  iron  deposits  in  the  Uinta 
Mountains,  farther  eastward,  which  are  especially  interesting  because 
of  the  general  absence  of  the  deposits  of  the  useful  metals  in  that 
