32  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   1903.  [bull.  225 
British  Columbia  and  the  State  of  Washington.  The  intrusive  rocks 
of  this  zone  have  been  grouped  by  Dawson  under  the  name  of  Coast 
Range  granite,  and  they  have  been  described  in  general  terms  as 
hornblende-granites.  With  our  present  knowledge  this  designation 
can  not  be  followed  consistently,  because  in  the  portion  of  the  belt 
which  has  been  examined  with  more  or  less  care  by  the  geologists  of 
the  Survey,  dioritic  rocks  are  the  rule  and  granites  the  exception. 
In  the  Juneau  district  the  diorites  show  a  considerable  variation  not 
only  in  the  main  mass  which  bounds  the  sedimentary  rocks,  but  also  in 
the  outlying  arms  and  stocks  which  are  intrusive  in  the  schists  and 
black  slates.  Some  of  the  masses  are  normal  hornblende-diorites  or 
quartz-diorites,  others  are  granodiorites,  while  an  extreme  variet}^  is 
the  albite-syenite,  occurring  in  the  Treadwell  mines.  In  general,  the 
rocks  are  closely  related  and  similar  in  appearance  to  the  granular 
intrusives  of  the  Sierra  Nevada. 
The  diorite  masses  generally  follow  the  stratification  of  the  older 
rocks.  Locally  there  is  a  certain  amount  of  crosscutting,  and  in  the 
case  of  the  main  contact  the  amount  of  transection  is  measured  by  the 
varying  width  of  the  schist  band,  which  is  noted  above. 
The  main  mineralization  of  the  Juneau  belt  occurred  subsequent  to 
the  intrusion  of  the  diorite,  in  which  respect  the  deposits  correspond 
in  general  with  those  of  the  gold  belt  of  California. 
THE  GOLD  VEINS. 
The  principal  geologic  features  of  the  Juneau  region  have  been 
described  in  the  foregoing  paragraphs.  It  seems  appropriate  to 
speak  of  the  mainland  strip  which  is  accessible  from  the  waters  of  the 
inland  passage  as  the  Juneau  gold  belt,  for  the  reason  that  gold  is 
found  very  generally  distributed  throughout  the  area  in  which  the 
crystalline  schists  and  the  slate-greenstone  series  outcrop.  In  the 
former  band,  however,  and  in  the  main  diorite  of  the  mountains  back 
of  the  coast,  but  little  promise  has  been  found  of  valuable  mineraliza- 
tion, such  veins  as  exist  being  mostly  mere  stringers,  showing  little 
tendency  toward  segregation  into  workable  lode  S3rstems. 
All  of  the  promising  prospects,  working  lode  mines,  and  placers 
of  the  Juneau  belt  occur  in  the  outer  part  of  the  mainland  strip  or  on 
Douglas  Island  adjacent,  either  in  the  slate-greenstone  band  or  in 
intrusive  masses  of  diorite  which  lie  outside  of  the  main  core  of  the 
Coast  Range.  In  the  aggregate  gold-bearing  quartz  veins  or  other 
forms  of  mineralization  are  distributed  throughout  the  whole  exposed 
width  of  this  band  between  its  inner  boundary  next  to  the  crystalline 
schists  and  the  channels  which  separate  the  mainland  from  the  adja- 
cent islands.  Although  only  their  large  geologic  features  are  known,  ( 
many  of  these  islands  contain  mineral  veins,  and  Admiralty  Island, 
which  parallels  the  coast  for  70  miles  opposite  the  Juneau  belt,  affords 
