CONTRIBUTIONS  TO  ECONOMIC  GEOLOGY, 
1905. 
S.  F.  Emmons,  E.  C.  Eckel,  Geologists  in  Charge. 
INTRODUCTION. 
By  C  W.  Hayes,  Geologist  in  Charge  of  Geology. 
This  bulletin  is  the  fourth  of  a  series,  including  Bulletins  Nos.  213,  225,  and  260,  Con- 
tributions to  Economic  Geology  for  1902,  1903,  and  1904,  respectively.  These  bulletins 
are  prepared  primarily  with  a  view  to  securing  prompt  publication  of  the  economic  results 
of  investigations  mad1  by  the  United  States  Geological  Survey.  They  are  designed  to 
meet  the  wants  of  the  busy  man,  and  are  so  condensed  that  he  will  bo  able  to  obtain  results 
and  conclusions  with  a  minimum  expenditure  of  time  and  energy.  They  also  afford  a 
better  idea  of  the  work  which  the  Survey  as  an  organization  is  carrying  on  for  the  direct 
advancement  of  mining  interests  throughout  the  country  than  can  readily  be  obtained  from 
the  more  voluminous  reports. 
In  the  first  two  bulletins  of  this  series  were  included  numerous  papers  relating  to  the 
economic  geology  of  Alaska.  In  view  of  the  rapid  increase  of  economic  work  both  in 
Alaska  and  in  the  States  and  the  organization  of  a  division  of  Alaskan  mineral  resources, 
distinct  from  the  division  of  geology,  it  was  last  year  considered  advisable  to  exclude  all 
papers  relating  to  Alaska.  These  were  brought  together  in  a  separate  volume  entitled 
"Report  of  Progress  of  Investigations  of  Mineral  Resources  of  Alaska  in  1904,"  Bulletin 
No.  259.     A  similar  segregation  of  papers  relating  to  Alaska  has  been  made  this  year. 
In  the  preparation  of  the  present  volume  promptness  of  publication  has  been  made 
secondary  only  to  the  economic  utility  of  the  material  presented.  The  papers  included  are 
such  only  as  have  a  direct  economic  bearing,  all  questions  of  purely  scientific  interest 
being  excluded. 
The  papers  are  of  two  classes:  (1)  Preliminary  discussions  of  the  results  of  extended 
economic  investigations,  which  will  later  be  published  by  the  Survey  in  more  detailed  form; 
(2)  comparatively  detailed  descriptions  of  occurrences  of  economic  interest,  noted  by  geolo- 
gists of  the  Survey  in  the  course  of  their  field  work,  but  not  of  sufficient  importance  to  nec<  s- 
sitate  a  later  and  more  extended  description.  A  third  class  of  papers  was  included  in  the 
bulletin  for  1902—  name  ly,  abstracts  of  certain  economic  papers  which  had  appeared  in 
Survey  publications  during  the  year,  chiefly  such  as  gave  a  general  account  of  the  distribu- 
tion and  mode  of  occurrence  of  particular  mineral  deposits  throughout  the  United  States. 
Most  of  the  publications  on  economic  geology  which  have  appeared  during  the  past  year 
were  abstracted  for  advance  publication  in  Bulletin  260,  and  it  has  therefore  been  unneces- 
sary to  abstract  them  in  this  volume. 
The  papers  have  been  grouped  according  to  the  subjects  treated.  At  the  end  of  each 
section  is  given  a  list  of  previous  publications  on  that  subject  by  this  Survey.  These  lists 
will  be  serviceable  to  those  who  wish  to  ascertain  what  has  been  accomplished  by  the 
Survey  in  the  investigation  of  any  particular  group  of  mineral  products.     They  are  generally 
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