12  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,    1903.  [bull.  225. 
abstracts  of  certain  economic  papers  which  had  appeared  in  Survey 
publications  during  the  year,  chiefly  such  as  gave  a  general  account  of 
the  distribution  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  in 
Bulletin  213,  and  it  has  therefore  been  unnecessary  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  found  serviceable  by 
those  who  wish  to  ascertain  what  has  been  accomplished  by  the  Sur- 
vey in  the  investigation  of  any  particular  group  of  mineral  products. 
They  are  generally  confined  to  Survey  publications,  though  a  few 
titles  of  important  papers  published  elsewhere  by  members  of  the 
Survey  are  included. 
The  preparation  of  this  bulletin,  as  well  as  of  the  corresponding 
bulletin,  published  last  year,  has  been  chiefly  the  work  of  Mr.  E.  C. 
Eckel,  to  whom  is  due  in  large  measure  the  credit  for  planning  the 
work  and  carrying  it  to  a  successful  issue. 
The  results  of  the  Survey  work  in  economic  geology  have  been 
published  in  a  number  of  different  forms,  which  are  here  briefly 
described: 
1.  Papers  and  reports  accompanying  the  Annual  Report  of  the 
Director,  United  States  Geological  Survey. — Prior  to  1902  many  eco- 
nomic reports  were  published  in  the  royal  octavo  cloth-bound  volumes 
which  accompanied  the  Annual  Report  of  the  Director.  This  form  of 
publication  for  scientific  papers  has  been  discontinued  and  a  new  series, 
termed  Professional  Papers,  substituted. 
2.  Bulletins  of  'the  United  States  Geological  Survey. — The  bulletins 
of  the  Survey  comprise  a  series  of  paper-covered  octavo  volumes,  each 
in  general  containing  a  single  report  or  paper.  These  bulletins,  for- 
merly sold  at  nominal  prices,  are  now  distributed  free  of  charge  to 
those  interested  in  the  special  subject  discussed  in  any  particular 
bulletin.  This  form  of  publication  facilitates  promptness  of  issue  for 
economic  results,  and  most  economic  reports  are  therefore  published 
as  bulletins.  Their  small  size,  however,  precludes  the  use  of  large 
maps  or  plates,  and  reports  containing  large  illustrations  are  therefore 
issued  in  the  series  of  Professional  Papers. 
3.  Professional  Papers  of  the  United  States  Geological  Survey. — 
This  series,  paper  covered,  but  quarto  in  size,  is  intended  to  include 
such  papers  as  contain  maps  or  other  illustrations  requiring  the  use  of 
a  large  page.  The  publication  of  the  series  was  commenced  in  1902, 
and  the  papers  are  distributed  in  the  same  manner  as  bulletins. 
4.  Monographs  of  the  United  States  Geological  Survey.—  This  series 
consists  of  cloth-bound  quarto  volumes,  and  is  designed  to  include 
