METALLIFEROUS    ORES.  15 
Advance1  notices  of  most  of  the  above  reports  have  already  appeared  in  previous  num- 
bers of  the  Economic  Bulletin  in  the  form  either  of  abstracts  or  of  preliminary  reports  on 
the  results  of  the  field  work.  Where  this  has  not  been  done,  or  where  the  final  publica- 
tion of  the  report  has  been  long  delayed,  there  has  been  some  good  reason  therefor  which 
may  not  alwa}^s  be  apparent  to  the  public. 
The  survey  of  the  Park  City  mining  district  has  disclosed  unexpected  structural  com- 
plications in  the  geology  which  promise  to  have  an  important  influence  on  the  mining 
development  of  the  region  and  demand  a  correspondingly  great  amount  of  care  and  del  ail 
in  their  working  out.  Other  duties  to  which  he  has  from  time  to  time  been  assigned  have, 
furthermore,  taken  a  certain  amount  of  Mr.  Boutwell's  time  from  this  work.  That  he 
might  push  it  to  completion  with  the  shortest  possible  delay,  Mr.  Boutwell  undertook  no 
field  work  whatever  during  the  past  year,  but  spent  the  entire  summer  in  office  work  on 
this  report,  which  it  is  expected  will  be  completed  before  the  opening  of  another  field 
season. 
For  a  number  of  years  past  there  has  been  in  preparation  a  detailed  study  of  the  com- 
plicated vein  systems  of  the  copper  district  of  Butte,  which  will  constitute  the  most  impor- 
tant record  yet  made  of  the  manner  of  formation  of  copper  in  veins  in  granite,  their  sub- 
sequent faulting  by  a  new  system  of  secondary  veins,  and  the  sulphide  enrichment  of 
both  systems  by  descending  waters.  This  record  is  of  relatively  small  importance  to  the 
immediate  development  of  the  district,  its  greatest  value  being  to  the  mining  world  in 
general  as  an  illustration  of  the  typical  development  of  this  important  class  of  copper 
deposits.  Completeness  of  the  record  has,  therefore,  been  of  more  importance  than  early 
publication,  especially  as,  pending  the  settlement  of  the  many  lawsuits  in  regard  to  prop- 
erty rights  in  the  district,  the  Survey  report  might  exercise  an  unfavorable  influence  on 
one  side  or  another  on  the  questions  at  issue;  hence  Mr.  Weed's  work  on  this  report  has 
been  put  aside  from  time  to  time  to  admit  of  his  carrying  on  other  investigations  whose 
publication  seems  of  more  immediate  importance  to  the  mining  public.  In  view  of  the 
recent  important  underground  discoveries  at  Butte,  this  delay  has  proved  to  be  most 
wise,  since  it  will  have  rendered  the  record  far  more  complete  than  it  could  otherwise  have 
been.  It  is  intended,  however,  that  the  report  shall  now  be  prepared  for  the  earliest 
possible  publication. 
In  the  case  of  the  resurvey  of  the  Leadville  district,  whose  long  delay  has  not  unnaturally 
been  the  cause  of  some  unfavorable  comment,  the  conditions  governing  its  publication  are 
more  difficult  to  explain,  especially  to  those  who  are  not  practically  familiar  with  the  actual 
mining  work  and  manner  of  occurrence  of  ore  in  the  district  and  with  the  peculiar  methods 
which  consequently  have  to  be  pursued  in  making  a  geological  map  there.  The  ordinary 
method  of  making  a  geological  map  of  a  given  area  is  to  carefully  examine  its  surface  and 
enter  on  the  map  the  outlines  of  the  different  rock  formations,  with  their  dips  and  strikes, 
supplementing  this  with  what  data  may  be  obtained  from  the  underground  workings  of  the 
mines  or  their  artificial  excavations.  Thus,  in  order  to  depict  the  underground  structure, 
the  surface  outcrops  are,  so  to  speak,  projected  downward.  In  the  Leadville  district, 
however,  practically  no  information  is  derived  from  the  surface,  and  the  geological  outlines 
represented  on  the  surface  map  must  be  made  by  projecting  upward  to  the  surface  the 
information  obtained  in  studying  the  underground  workings  of  the  mines.  This,  although 
more  laborious,  is  a  very  practicable  method,  provided  only  that  the  underground  workings 
extend  nearly  continuously  over  the  whole  area.  This  is  unfortunately  not  the  case  at 
Leadville,  for  although  in  certain  portions,  where  the  ore  bodies  are  concentrated,  mine 
drifts  honeycomb  the  rocks  in  all  directions,  there  are  considerable  areas  where  ore  has 
not  been  found  or  which  are  practically  unexplored  underground.  Even  in  the  explored 
areas  there  are  gaps  in  possible  information  where  extensive  mines  have  been  abandoned 
and  their  drifts  have  become  inaccessible,  with  regard  to  which  no  accurate  geological  data 
can,  therefore,  be  obtained.  With  each  new  mining  development  portions  of  these  gaps 
are  filled  up,  and  when  the  mines  are  visited  while  still  open  and  accessible  the  information 
gathered  adds  to  that  already  obtained  with  regard  to  the  actual  underground  structure 
