138  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1903.  [toll.  225. 
size  and  are  of  less  importance  than  those  which  occur  in  other  forma- 
tions. Two  districts,  the  Ragged  Top  and  the  Carbonate,  have  been 
important  producers. 
The  Ragged  Top  district  comprises  the  country  which  lies  to  the 
northwest  of  the  large  mountain  of  phonolite,  known  as  Ragged  Top. 
There  is  here  a  series  of  seven  nearly  equally  spaced  vertical  fissures 
or  veins,  which  have  been  termed  the  Ragged  Top  "  verticals."  These 
fractures  or  crevices  in  the  heavy,  massive  limestone  show  at  the 
surface  a  maximum  width  of  about  10  feet,  and  narrow,  as  they  pass 
downward,  to  extremely  minute  crevices.  In  the  lower  portions  where 
the  surface  alteration  has  not  been  extensive  the  ore  can  be  observed  to 
pass  laterally  into  the  limestone  walls  without  disturbance  of  the  struc- 
ture of  the  latter  rock.  The  ore  is  of  a  light,  uniform,  buff  tint,  which  is 
so  nearly  the  color  of  the  surrounding  limestone  that  it  is  difficult  to 
distinguish  it  from  the  unmineralized  rock.  It  differs  in  its  superior 
hardness  and  slight  yellow  color.  Much  of  the  ore  is  composed  of 
angular,  brecciated  fragments  of  what  was  once  limestone  but  now  is 
completely  altered  to  silica.  Traces  of  tellurium  have  been  detected 
in  these  ores.  At  some  points  in  the  limestone  area  about  Ragged 
Top  Mountain  flat,  blanket-like  beds  of  ore  are  found.  These  are 
either  without  distinct  connection  with  the  verticals  or  seem  to  have 
spread  out  from  them.  Some  of  the  ore  from  these  verticals  was  very 
rich,  and  in  general  it  carried  higher  values  than  the  siliceous  ores 
found  in  the  Cambrian  rocks. 
These  Carboniferous  siliceous  ores  have  not  at  any  time  been  very 
heavy  producers,  but  have  yielded  small  amounts  of  ore  for  some  years. 
They  have  recently  been  successfully  treated  by  the  cyanide  process. 
Lead-silver  ores. — Lead-silver  ores  were  in  the  earlier  days  of  min- 
ing in  the  Black  Hills  a  very  important  factor  in  the  production  of 
precious  metals.  They  were  found  in  the  vicinity  of  the  town  of 
Carbonate,  which  was  in  1886  a  flourishing  camp,  producing  consid- 
erable silver  and  lead.  The  product  was  almost  exclusively  from  the 
Iron  Hill  mine,  but  other  mines  in  the  neighborhood  added  a  little  to 
the  total. 
The  country  rock  that  carries  the  ore  is  the  gray,  Carboniferous  lime- 
stone, in  which  sills,  dikes,  and  irregular  masses  of  porphyry  have 
been  intruded.  The  ore  bodies  are  of  two  kinds — large,  irregular 
bodies  of  lead  carbonate,  which  pass  in  places  into  more  or  less 
unaltered  galena,  and  generally  lie  in  close  contact  with  porphyry 
masses,  and  partially  filled  crevices  which  resemble  in  a  general  way 
the  verticals  of  Ragged  Top. 
The  first  type  of  deposit  is  that  which  has  formed  the  chief  source 
of  silver  in  the  district,  and  this,  as  shown  above,  was  largely  obtained 
from  the  Iron  Hill  mine.  In  this  mine  the  ore  was  a  large  mass  of 
argentiferous  lead  carbonate  extending  down  300  feet  on  the  east  side 
