hiving.]  OURAY    DISTRICT,   COLORADO.  69 
ing  away  of  the  outer  portions  of  the  rock.  Here,  and  for  a  long 
distance  into  the  side  of  the  hill,  it  consisted  of  a  brownish  iron- 
stained  material  resembling  limonite  and  containing  free  gold,  either 
too  fine  for  observation  or  in  the  form  of  wire  gold.  It  did  not 
entirely  fill  the  cavities,  but  was  concentrated  in  the  lower  portions  of 
the  open  spaces.  The  gold  was  crystalline  and  was  almost  invariably 
richer  at  the  bottom  of  the  mass.  The  present  foreman  reports  only 
wire  gold,  but  it  is  stated  that  large  nuggets  were  found,  some  of  them 
of  great  size.  The  brown  material  is  undoubtedly  limonite  in  great 
part,  but  in  all  probability  further  examination  will  show  that  it  con- 
tains a  large  percentage  of  ferric  sulphate.  Mixed  with  the  oxidized 
ore  are  found  siderite,  barite,  kaolin,  and  sulphur. 
Often  a  lining  of  honeycombed  quartz  is  observable,  as  much  as  -t  or  5 
inches  in  thickness,  either  lining  the  cavity  or  completely  filling  it. 
The  cell-like  spaces  in  this  quartz  are  sometimes  irregular,  but  often 
have  the  form  of  pyrite  crystals,  showing  clearly  that  they  are  caused 
by  the  oxidation  and  removal  of  former  masses  and  crystals  of  iron 
sulphide.  Much  of  the  oxidized  ore  was  shoveled  directly  from  the 
cavities  into  ore  sacks  and  shipped  without  further  soiling.  Mor< 
careful  sorting  is  now  necessary. 
On  penetrating  farther  into  the  hill  the  ore  gradually  changes  to 
pyrite.  This  is  either  massive,  with  occasional  cavities  into  which 
complete  crystals  of  pyrite  project,  or  is  composed  of  crystalline 
grains  of  pyrite  embedded  in  a  matrix  of  gray  and  white  secondary 
quartz.  Large  admixtures  of  chalcopyrite  and  galena  and  other 
sulphides  are  found,  among  which  are  sphalerite,  telluride  of  gold  and 
silver  (perhaps  hessite,  found  usually  in  the  Jonathan  mine),  molyb- 
denite, and  gray  copper  (probably  argentiferous  tetrahedrite) . 
Barite  is  also  of  very  frequent  occurrence  in  the  sulphide  ore, 
and  fibrous  bands  of  gypsum  were  seen  between  the  ore  and  the  over- 
lying black  shales. 
The  sulphide  ore  is  more  common  directly  beneath  the  black  shales, 
as  are  also  the  more  extensive  ore  bodies. 
The  contact  between  the  ore  and  the  quartzite  is  usually  very  sharp 
and  shows  the  irregular  and  undulating  surface  so  often  seen  in 
replacement  deposits.    . 
From  these  facts  it  is  not  difficult  to  form  a  connected  history  of 
the  mine. 
First  occurred  the  intrusion  of  the  porphyry,  producing  the  dikes 
and  sheets.  After  this  rock  had  cooled  a  shattering  took  place,  which 
produced  fissures  in  the  massive  quartzite — fissures  which  were 
usually  lost  in  the  fissile  black  shales  above,  but  in  some  instances 
extended  into  the  porphyry  itself. 
Hot  waters,  presumably  alkaline,  charged  with  metallic  sulphides, 
|   then  ascended  through  the  fissures  until  their  upward  progress  was 
