16  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1905. 
of  the  district.  Thus,  since  starting  the  review  of  the  Leadviile  work  in  1890,  the  writer 
has  made  visits  to  the  region  every  year  or  two  to  gather  such  new  data,  but  causes  beyond 
his  control  have  rendered  it  impossible  for  him  to  have  compiled  at  any  given  period  the 
material  already  gathered  in  form  for  publication.  These  recent  studies  have  shown  that 
the  broad  outlines  of  geological  structure,  as  given  on  the  original  maps  of  the  region,  are 
substantially  correct.  The  modifications  of  them  that  the  new  data  will  necessitate  are 
such  as  no  human  foresight  could  have  predicated,  consisting  mainly  of  faults  and  intrusive 
sheets  of  which  no  indication  could  be  seen  at  the  surface  or  in  the  underground  workings 
then  accessible.  On  these  early  maps  much  of  the  underground  structure  shown  was 
necessarily  inference  and  some  pure  surmise.  On  the  new  maps  it  is  desired  to  restrict 
the  area  of  inference  and  surmise  as  much  as  possible.  [nasmu<  h  as  the  manner  of  occur- 
rence of  the  ore  is  thoroughly  understood  by  Leadviile  miners,  the  principal  value  of  the 
present  review  will  be  to  afford  a  picture  of  the  ground  already  opened  and  ii  can  not  be 
expected  to  show  very  much  that  is  new  with  regard  to  ground  that  has  not  been  opened; 
hence,  while  the  work  has  not  been  intentionally  delayed,  the  delay  that  has  occurred 
has  added  greatly  to  its  value.  It  can,  in  the  nature  of  things,  be  of  little  use  in  determining 
the  position  of  undiscovered  ore  bodies,  but  it  may  afford  means  of  estimating  more  nearly 
the  area  of  possible  extension  of  ore-bearing  horizons  in  some  parts  of  the  region,  such  as 
those  that  are  buried  beneath  several  hundred  feel  of  wash.  It  is  the  present  intention 
of  the  writer  to  publish  smaller  preliminary  maps  of  such  areas  as  <  an  be  prepared  without 
waiting  till  the  accumulated  data  are  sufficient  for  the  accurate  reconstruction  of  the  map 
of  the  entire  district. 
ECONOMIC   WORK   IN   PROGRESS   DURING  THE  YEAR. 
GENERAL    DISCUSSION. 
An  important  step  has  been  taken  during  the  year  toward  rendering  the  economic  work 
of  (he  Survey  more  comprehensive  and  efficient  by  instituting  a  closer  cooperation  between 
the  section  of  metalliferous  ores  and  the  division  of  mineral  statistics.  To  this  end,  early 
in  the  year,  the  supervision  of  the  collection  of  statistics  of  the  precious  metals  was  placed 
in  charge  of  Mr.  Waldemar  Lindgren,  of  the  former  section,  who  thus  assumed,  besides 
his  regular  work,  a  xciy  considerable  addition  of  labor  in  reorganizing  and  improving 
the  method  of  collection  hitherto  pursued.  Some  of  the  shortcomings  in  the  previous 
method  have  been  pointed  out  in  a  former  number  of  this  bulletin.  The  amelioration 
that  can  be  expected  from  the  supervision  of  the  work  by  a  man  like  Mr.  Lindgren,  who 
combines  long  experience  in  all  the  details  of  the  precious-metal  industry  with  a  profound 
knowledge  of  the  geological  relations  of  their  deposits,  will  be  important,  even  more  than 
in  furnishing  accurate  statistics  of  the  total  production  of  the  country,  for  segregating 
the  proportions  of  that  production,  not  only  among  States  and  counties  but  among  dis- 
tricts, and  in  furnishing  at  the  same  time  sufficient  geological  data  with  regard  to  the  less 
known  districts  to  render  possible  an  annual  discussion  of  the  precious-metal  industry 
with  reference  to  its  geological  distribution.  But  of  more  immediate  importance  to  those 
actively  interested  in  mining  will  be  the  fact  that  with  regard  to  individual  mining  dis- 
tricts, especially  those  that  are  new  or  little  known,  the  investor  in  mines  can  feel  sure 
that  the  information  furnished  is  given  by  men  who  are  not  only  competent  to  speak  with 
authority  from  a  technical  point  of  view  but  that  what  they  say  is  wholly  unbiased  and 
free  from  even  the  suspicion  of  any  personal  interest  that  might  make  them  consciously 
or  unconsciously  regard  the  future  in  too  favorable  a  light. 
The  beneficial  results  of  this  change  in  method  can  not  be  fully  appreciated  until  the 
mineral  statistics  for  the  year  1905  shall  have  been  published,  but  an  improvement  is 
already  noticeable  in  those  for  the  year  1904,  in  which,  jilt  hough  the  actual  figures  had 
been  collected  before  he  took  charge,  Mr.  Lindgren  was  enabled  to  introduce  decided 
improvements  in  the  methods  of  presentation  of  facts  and  their  discussion. 
