irving.]        ORE    DEPOSITS    OF    THE    NORTHERN    BLACK    HILLS.  135 
are  live  in  number,  and  have  been  severally  designated  Bald  Mountain 
area,  Yellow  Creek  area,  Lead  area,  Garden  area,  and  Squaw  Creek 
area.  The  last  named  was  at  the  time  of  survey  little  more  than 
a  prospect,  but  it  has  since  become  an  important  producer.  The  Bald 
Mountain  area  is  the  most  extensive  and  important.  It  is  a  northwest- 
southeast  belt,  about  1  mile  in  width  and  1£  miles  in  length,  the 
width  being  limited  by  the  annular  exposure  of  Cambrian  rocks 
that  surrounds  the  Algonkian  nucleus  of  the  region.  The  ore- 
bearing  strata  dip  to  the  southwest  and  pass  beneath  the  Silurian 
and  Carboniferous  limestones,  while,  except  in  a  very  few  instances, 
they  have  been  eroded  from  the  Algonkian  hills  to  the  northeast. 
Hence,  on  the  north,  the  ore  bodies  are  exposed  at  the  surface,  but  to 
the  south  shafts  are  necessary  to  reach  them.  At  the  southeast  end 
this  area  is  cut  off  from  the  Yellow  Creek  area  by  Whitewood  Creek. 
At  the  northern  end  the  Cambrian  rocks  are  present  in  nearly  their 
full  thickness.  With  relation  to  the  ore  bodies,  the  area  may  be 
divided  into  two  portions,  the  Ruby  Basin  district  and  the  Portland 
district.  In  the  former  the  shoots  are  larger  in  the  lower  ore-bearing 
beds;  in  the  latter,  larger  in  the  upper. 
The  Garden  area  is  situated  at  the  head  of  Blacktail  and  Sheep- 
tail  gulches  and  an  east  tributary  of  False  Bottom  Creek.     It  is  located 
;on  the  northern,  as  the  Bald  Mountain  area  is  on  the  southern,  rim  of 
the  Cambrian  outcrop.  The  beds  dip  to  the  northeast  and  the  shoots 
so  far  mined  have  been  on  the  lower  contact.     A  rhyolite  cap  of  great 
,  thickness  and  extent  covers  the  country  to  the  north  and  the  Cambrian 
beds  pass  beneath  it.  The  average  trend  of  the  ore  bodies  here  is 
about  N.  55°  E.,  much  more  nearly  east- west  than  in  any  of  the  other 
areas. 
i  The  Lead  area  is  located  on  one  of  the  Cambrian  outliers  that 
caps  the  hill  north  of  Deadwood,  and  the  ore  bodies  extend  over  the 
gold  lode  of  the  Homestake  mine.  A  heavy  sill  of  line-grained  rhyo- 
lite lies  above  the  Cambrian  on  the  tops  of  the  hills.  The  ore  bodies 
are  exposed  at  the  surface  on  the  westernmost  edge  of  this  area,  but  lie 
beneath  the  shales  to  the  east.     The  ore  from  this  district  is  richer 
j  than  that  elsewhere  mined,  and  contains  great  quantities  of  barite, 
wolframite,  and  in  several  instances  large  amounts  of  free  gold.     The 
.  Hidden  Fortune  mine  is  an  instance  of  this  kind. 
The  Yellow  Creek  area  is  situated  a  little  more  than  2  miles  slightly 
east  of  south  from  the  city  of  Lead.     The  ore  shoots  are  in  a  thin 
,  capping  of  Cambrian  strata  on  the  divide  between  Whitewood  Creek  on 
i  the  west  and  Yellow  Creek  on  the  east.  The  shoots  lie  on  the  basal 
quartzite  about  15  to  26  feet  above  the  Algonkian.  Much  wolframite 
and  barite  are  also  found  in  the  ore  from  this  area. 
The  Squaw  Creek  area  lies  near  the  mouth  of  Squaw  Creek.     Work- 
ings have  been  run  upon  some  ore-bearing  beds  which  pass  rapidly 
