76  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   1903.  [bull. 225. 
In  the  southwestern  part  of  the  field,  in  the  neighborhood  of  the 
Asses  Ears,  is  an  elevated  area  of  white  crystalline  limestone  rest- 
ing on  or,  as  is  much  more  probable,  intruded  by  masses  of  very 
coarsely  crystalline  granites,  one  of  which  forms  the  "Ears."  At  the 
eastern  border  of  the  field  the  schists  are  interrupted  by  a  great  mass 
of  eruptives,  with  a  central  core  of  granites  and  diorites  flanked  by 
andesites  and  lavas.  The  andesites  are  more  widely  developed  than 
the  granites  and  surround  them  on  all  sides,  so  that  in  approaching  the 
higher  elevations  of  the  divide  one  meets  first  the  cellular  lavas,  then 
andesites,  and  finally  the  granites,  extremely  coarse  and  in  places  with 
little  or  no  quartz. 
A  characteristic  feature  of  these  mountains  is  the  terraced  appear- 
ance which  they  present  when  viewed  from  a  distance,  produced  by 
the  benches  of  broken  blocks  of  the  country  rock. 
GOLD    OCCURRENCES. 
For  convenience  in  description  the  principal  streams  where  gold  has 
been  produced  may  be  divided  into  two  main  districts — the  Inmachuk 
River  drainage  area  and  the  Candle  Creek  area,  belonging  in  the 
Kiwalik  River  drainage  system.  Of  these  two  districts,  viewed  from 
the  standpoint  of  production  in  the  past,  Candle  Creek  is  by  far  the 
more  important. 
Inmachuk  River. — The  Inmachuk  River  is  between  25  and  30  miles 
in  length.  It  rises  in  the  limestone  area  of  the  western  part  of  the 
field,  flows  toward  the  northeast  to  the  flats  bordering  Kotzebue 
Sound,  and  then  meanders  slowly  in  the  same  general  direction  to  the 
sound.  At  Record  City  the  eastern  fork,  known  as  Pinnell  River, 
joins  the  main  stream  from  the  south. 
The  most  productive  portion  of  the  Inmachuk  begins  near  the  mouth 
of  Pinnell  River  and  extends  down  the  stream  for  a  number  of  miles. 
The  valley  is  much  broader  than  those  of  the  tributaries,  and  in  this 
portion  is  occupied  by  a  series  of  broad  flats,  having  in  places  a  width 
of  more  than  a  quarter  of  a  mile. 
The  gravels  occasionally  reach  a  thickness  of  0  to  8  feet.  They  are 
invariably  frozen,  except  in  the  channel  of  the  river,  and  are  often 
covered  by  an  ice  bed.  The  bench  and  creek  claims  on  the  Inmachuk 
have  been  more  extensively  prospected  than  on  the  other  streams,  with 
the  result  that  in  a  number  of  places  a  well-defined  pay  streak  is 
known.  At  two  localities  lines  of  holes,  extending  across  the  valley, 
have  been  thawed  down  to  bed  rock,  and  at  a  number  of  places  lines 
of  holes  have  been  sunk  part  way  across.  This  work  is  carried  on 
with  the  aid  of  thawers,  the  boilers  ordinarily  furnishing  steam  to 
4-foot  points  set  twice  each  day.  The  consumption  of  fuel  in  work  of 
this  kind  is  large,  and  greatly  increases  the  cost  of  mining. 
