30  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   1903.  [bull. 225. 
opened  on  a  large  scale.  The  product  of  these  mines  for  the  year  is 
estimated  at  $2,400,000,  while  the  total  output  of  the  belt  to  the  end 
of  1903  has  been  more  than  $20,000,000. 
Several  properties  which  were  formerly  worked  are  not  now  pro- 
ducing bullion,  either  because  they  have  been  worked  out  or  because 
the  conditions  of  further  development  would  involve  too  great  an 
increase  in  mining  costs. 
The  examinations  which  have  been  made  indicate  that  the  known 
prospects  in  the  belt  tributary  to  Juneau  are  of  sufficient  promise  to 
warrant  all  the  work  now  in  progress  and  the  expenditure  of  still 
more  capital  in  development  work.  There  is  still  room  in  this  field 
for  development  companies  with  adequate  capital  for  acquiring  con- 
trol of  promising  properties  to  be  explored  and  sold  to  operators.when 
their  value  has  been  proved.  The  participation  of  new  interests, 
which  seems  about  to  begin,  will  undoubtedly  bring  about  a  rapid 
quickening  of  the  mining  industry,  but  the  development  of  the  field 
has  reached  a  critical  stage,  and  owners  of  unproved  or  partially 
explored  claims  should  remember  that,  though  experienced  operators 
are  willing  to  pay  good  prices  for  properties  of  determined  value,  it 
can  not  be  expected  that  the}T  will  make  the  heav}r  cash  payments  often 
demanded  for  the  privilege  of  risking  larger  sums  in  developing  mere 
prospects.  It  is  commonly  reported  that  overreaching  in  this  direc- 
tion has  already  done  much  to  retard  the  progress  of  mining  operations 
in  the  Juneau  belt. 
GEOLOGY. 
The  observations  of  the  summer  were  confined  almost  entirely  to 
the  mainland  opposite  Stephens  Passage  and  Lynn  Canal,  where  a  belt 
nearly  200  miles  in  length  was  examined  with  sufficient  care  for  the 
determination  of  its  main  geologic  features.  The  results  of  this  work 
will  be  published  in  a  report  dealing  with  the  geology  and  mineral 
deposits  of  the  district,  which  will  contain  a  topographic  and  geologic 
map  of  the  mainland  from  Windham  Bay  to  the  head  of  Lynn  Canal 
and  the  Porcupine  district. 
Structure. — In  the  mainland  belt  northward  from  Windham  Bay  the 
bedded  or  sedimentary  formations  all  strike  northwest  and  southeast, 
and  dip,  almost  without  exception,  toward  the  northeast  into  the 
mountains.  The  igneous  rocks  closely  follow  the  structure  of  the 
sediments,  as  a  rule,  so  that  viewed  either  in  detail  or  in  their  general 
relations  the  rocks  are  found  to  occur  in  bands  parallel  with  the 
general  trend  of  the  coast. 
Division  of  the  rocks. — The  rocks  may  be  grouped  into  three  series, 
which  are  named  in  the  order  of  their  occurrence  from  southwest  to 
northeast:  (1)  Black  slates  and  black  limestones  alternating  with  green- 
