spencer.]  THE    JUNEAU    GOLD    BELT,   ALASKA.  33 
indications  which  have  warranted  considerable  prospecting  each  year. 
The  rocks  are  in  part  lithologically  similar  to  the  slates  of  the  Juneau 
belt,  and  the  island  is  separated  from  Douglas  Island  by  a  channel  in 
places  less  than  2  miles  wide.  The  distance  between  known  areas  of 
mineralization  on  the  two.  islands  is  much  less  than  the  width  of  the 
Juneau  belt,  and  it  seems  that,  though  practically  separate,  the  island 
and  mainland  belts  are  two  parts  of  a  wide  zone  of  mineralization, 
divided  longitudinally  by  Stephens  Passage. 
The  Admiralty  belt  has  not  been  studied  with  care,  but  many  of  its 
features  conform  with  those  of  the  Juneau  belt.  In  both  belts  many  of 
the  veins  and  composite  lode  systems  follow  the  strike  of  the  country 
rocks,  frequently  holding  to  the  vicinity  of  contacts  between  beds  of 
different  character,  such  as  slate  and  greenstone.  Composite  lode  sys- 
tems, such  as  Becker  has  called  stringer  leads,  are  perhaps  a  charac- 
teristic type  for  the  region  at  large,  but  in  the  Juneau  belt  there  are 
many  crosscutting  veins  which  are  sometimes  well  defined  for  long 
distances  when  contained  in  massive  rocks,  such  as  diorite,  or  green- 
stone which  has  not  received  schistose  structure.  In  the  slates  cross- 
cutting  veins  are  seldom  found,  because  these  rocks  are  too  flexible  to 
break  with  extensive  continuous  fractures. 
Toward  the  northwest  both  the  Admiralty  and  the  Juneau  belts 
should  appear  on  the  west  shore  of  Lynn  Canal,  the  course  of  which 
is  slightly  diagonal  to  the  strike  of  the  formations.  Reports  of  the 
comparatively  small  amount  of  prospecting  which  has  been  done  in 
this  region  suggest  that  the  veins  occurring  in  the  vicinity  of  James 
Bay  and  Endicott  River  correspond  in  a  general  way  with  the  Admi- 
ralty belt,  while  mineralization  existing  on  Sullivan  Island  lies  directly 
in  line  with  an  extension  of  the  Juneau  belt  beyond  the  Berners  Bay 
district.  Measured  across  the  strike  of  the  rocks  the  distance  between 
the  known  deposits  of  the  two  belts  is  practically  the  same  as  that 
already  noted  between  deposits  on  Douglas  and  Admiralty  islands,  and 
it  is  believed  that  future  work  in  the  region  west  of  Lynn  Canal  along 
the  shores  of  Chilkat  Inlet  will  demonstrate  intervening  mineralization. 
The  data  collected  during  the  season  have  been  sufficient  to  bear  out 
the  previously  suggested  existence  of  a  main-lode  system,  which  is  now 
known  to  follow  a  definite  geologic  horizon  for  a  long  distance  on  the 
mainland.  The  observed  facts  do  not  warrant  the  further  suggestion 
that  there  are  other  narrow  bands  conforming  to  divisions  in  the  bed- 
rock formations,  in  which  profitable  mineralization  is  to  be  expected 
throughout  great  distances  along  the  strike.  It  seems,  on  the  other 
hand,  that  outside  of  the  main-lode  system  mineralization  has  been 
widely  and  irregularly  distributed.  Gold  veins  or  vein  complexes 
may  follow  or  recur  along  certain  beds  for  several  miles,  but  no  zones 
of  limited  width  can  be  designated  as  specially  suited  for  their  occur- 
rence and,  therefore,  as  eminently  favorable  for  prospecting.  At  the 
Bull.  225—04 3 
