22  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   1903.  [bull. 225. 
blende  altered  to  carbonate  and  silicate  near  the  surface,  occur  in 
brecciated  zones  in  the  limestone  of  which  they  form  a  part  of  the 
cementing  material. 
CALIFORNIA. 
Economic  Geology  of  the  Redding  Quadrangle,  by  J.  S.  Diller. 
In  the  course  of  his  areal  mapping  of  the  Redding"  quadrangle  in 
northern  California,  which  he  completed  last  summer,  Mr.  Diller  gath- 
ered data  on  its  general  economic  resources,  which  will  appear  as  part 
of  the  text  of  the  folio.  An  abstract  of  this  report  is  given  elsewhere 
in  this  volume.  The  data  on  copper  ore  was  given  in  less  complete 
form  in  Bulletin  No.  213. 
COLORADO. 
The  only  economic  work  in  Colorado  during  the  past  season  has  been 
the  resurvey  of  the  Cripple  Creek  district,  which  has  been  undertaken 
in  cooperation  with  the  State  authorities,  half  the  expense  being  paid 
by  Colorado. 
The  original  field  work  in  this  district  was  completed  ten  years  ago, 
and  in  the  time  that  has  elapsed  mining  developments  have  been  car- 
ried on  most  actively  to  a  depth,  in  many  places,  of  over  1,000  feet. 
The  district  is  the  largest  gold  producer  in  the  United  States,  and  the 
mine  owners  are  naturally  desirous  of  knowing  whether  the  geolog- 
ical conditions  of  the  district  shown  by  the  present  developments  indi- 
cate any  probable  falling  off  of  the  ores  with  depth.  The  extent  of 
ground  to  be  studied  was  so  great,  and  the  problems  to  be  solved  so 
delicate,  that  it  was  deemed  wise  to  employ  two  of  our  best  geologists 
to  do  this  piece  of  work.  Messrs.  Lindgren  and  Ransome  were  thus 
assigned  to  it.  it  being  arranged  that,  while  they  divided  [the  field 
between  them,  each  should  be  cognizant  of  and  verify  all  important 
conclusions  arrived  at  by  the  other.  They  were  assisted  in  the  field 
by  Messrs.  Graton  and  Rock.  Mr.  Ransome  carried  on  his  fie*d  work 
continuously  during  the  summer.  Mr.  Lindgren  was  called  out  of 
the  country  by  private  business  at  the  end  of  July,  but  returned  in 
January,  and  will  complete  his  part  of  the  field  work  in  April,  1904. 
The  present  condition  of  the  work  is  as  follows: 
The  revision  of  the  areal  or  surface  geology  is  completed  and  over 
half  of  the  underground  work  is  done.  Under  these  conditions  it  is 
not  practicable  to  present  any  preliminaiy  report.  It  can  only  be  said 
that  evidence  of  secondary  enrichment  has  not  been  found  in  the  ore 
bodies  thus  far  studied,  and  this,  as  far  as  it  goes,  is  in  favor  of  the 
permanence  of  the  rich  ores  in  depth.  The  work  will  be  pushed  to 
completion  as  rapidly  as  its  delicate  nature  and  the  Survey  facilities 
for  carrying  it  on  will  permit. 
