20  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.         [bull.  260. 
Bulletins: 
No.  246.  Zinc  and  Lead  Deposits  of  Northwestern  Illinois,  H.  F.  Bain. 
No.  254.  Resurvey  of  the  Cripple  Creek  District,  by  W.  Lindgren  and  F.  L. 
Ransome. 
No.  255.  Fluorspar  of  Southern  Illinois,  by  H.  F.  Bain. 
Folios: 
No.  111.  Globe  District,  Arizona. 
No.  112.  Bisbee  District,  Arizona. 
The  title  of  the  first  work  on  the  list,  "A  Treatise  on  Metamorph- 
ism,"  does  not  at  first  suggest  reading  that  would  be  of  interest  to  the 
man  engaged  in  practical  mining,  but  if  one  has  the  desire  to  get  at 
the  root  of  his  subject  he  may  reflect  that  metamorphism,  which  is  the 
general  term  used  to  express  the  changes  that  rocks  have  undergone 
since  their  formation,  must  necessarily  have  to  do  with  ore  deposits, 
since  the  most  of  those  worked  to-day  are  the  result  of  changes  and 
transfers  of  material  within  the  rock  masses  that  make  up  the  earth's 
crust.  If  he  will  consult  this  monumental  volume,  which  is  the  final 
result  of  the  profound  studies  carried  on  by  the  author  for  many 
years,  largely  in  the  great  iron-ore  regions  of  the  Northwest,  he  will 
find  that  the  last  240  pages  are  devoted  to  an  elucidation  of  the  prin- 
ciples which  control  ore  deposition,  and  that  a  careful  study  of  these 
pages  will  greatly  aid  in  giving  him  a  clearer  idea  of  the  manner  in 
which  the  ores  he  is  mining  have  reached  their  present  form,  and  hy 
inverse  reasoning  he  will  be  better  fitted  to  trace  out  the  probable 
direction  in  which  they  are  liable  to  extend  in  the  parts  of  his  mine 
that  are  as  yet  unexplored. 
Abstracts  of  all  the  other  publications  have  already  appeared  in 
previous  economic  bulletins  (Bulls.  213  and  225),  with  the  exception 
of  the  preliminary  report  on  the  "  Resurvey  of  the  Cripple  Creek 
district,'1  an  abstract  of  which  is  published  in  this  volume.  This 
publication  has  been  pushed  in  advance  of  all  other  Survey  reports 
for  the  reason  that  half  of  the  cost  of  the  work  was  paid  by  the 
citizens  of  the  State  of  Colorado,  and  it  was  considered,  therefore, 
that  they  had  the  right  to  know,  at  the  earliest  possible  moment, 
such  of  its  results  as  may  have  immediate  commercial  value.  It  is 
probable  that  some  of  these  citizens  will  be  disappointed  because 
the  report  does  not  speak  more  freely  with  regard  to  the  future  of 
the  district.  Such  persons  do  not  fully  understand  the  limitations 
of  geological  investigation  and  the  caution  which  the  careful  stu- 
dent must  necessarily  observe  in  speaking  of  the  results  of  his 
survey  before  the  facts  which  he  has  gathered  have  been  worked 
over  with  scientific  thoroughness  in  all  their  multiple  bearings.  The 
members  of  the  Survey  would  be  pleased  to  satisfy  everyone  if  it 
were  possible — those  who  wish  results  published  as  rapidly  as  news- 
paper notices,  as  well  as  those  who  desire  that  they  should  have  the 
