78  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1906,  PART    I. 
per  cubic  yard.  Pay  streaks  that  run  $2  to  $3  per  cubic  yard  are  ver 
thin  and  rare.  The  average  run  of  the  gravels,  all  the  pa}r  streaks, 
and  the  comparatively  barren  gravels  being  considered  together,  is 
between  7  and  10  cents  per  cubic  yard.  Only  one  piece  of  coarse 
gold  has  thus  far  been  found  at  this  place.  The  nugget  was  said  to 
be  about  half  the  size  of  a  tenpenny  nail. 
During  the  last  year  several  hundred  dollars  worth  of  gold  was 
taken  from  this  area.  In  Mineral  Resources  of  the  United  Stated 
for  1905,  page  341,  the  following  statement  is  made  under  the  heading 
of  Uinta  County,  Wyo.:  "A  little  placer  gold  is  reported  from  Jack- 
son Hole  near  the  western  boundary  line  of  t  he  State." 
Four  samples  of  black-sand  concentrates  were   taken   from  Davis 
diggings  and  David  T.  Day  in  his  report  on  these  samples  makes  th 
following  statement: 
: 
These  samples  consist  largely  of  magnetite,  No.  1.  apparently  qoI  much  cone* 
trated,  containing  1  ounce  of  magnetite  to  1'.  ounces  of  the  original  material.  They 
are  all  rich  in  gold  bul  contain  no  platinum.  The  percentage  of  gold  was  not  deter- 
mined, but  they  will  all  range  from  $30  to  $100  per  ton  and  probably  more.  This  gdm 
could  easily  be  ext  racted  by  menus  of  shaking  tables  of  the  Pinder,  Wilfley,  Woodburj 
or  Deistertype,  bu1  ii  is  doubtful  whether  \  ery  much  can  be  taken  out  by  other  means, 
certainly  not  by  sluice  boxes,  as  you  have  probably  already  found. 
Doctor  Day  in  his  work  on  the  investigation  of  black  sands  from 
placer  niinesa  found  that  the  effective  operation  of  these  concentrate 
tables  is  comparatively  independenl  of  the  fineness  of  the  gold.  In 
many  sands,  gold  as  tine  as  200  mesh  is  readily  saved  on  the  table* 
frequently  from  95  to  98  per  cenl  of  the  total  assayed  value.  A  brief  I 
description  of  these  tables  and  additional  data  on  the  black  sands  of! 
the  Pacific  slope  by  David  T.  Day  and  R.  II.  Richards  maybe  found 
in  Mineral  Resource.^  of  the  United  States  for  1905,  pp.  1175-1258. 
PINE  BAR  DIGGINGS. 
The  terrace  at  the  mouth  of  Pine  Creek,  on  the  south  side  of  Snal 
River,  has  been  worked  during  the  last  two  years  by  Ivan  L.  Hoffc 
and  L.  M.  Rosencrans.  The  methods  employed  are  much  the  same* 
as  those  above  described  for  the  Davis  diggings.  The  water  for 
hydraulicking  is  broughl  from  a  point  some  distance  up  Pine  ('reek 
in  a  ditch  across  the  bench  and  used  wherever  it  may  he  desired. 
The  terrace  or  old  bar  at  tins  point  is  1  mile  long  and  one-twelfth  tc 
one-eighth  mile  wide.  Th:  terrace  for  the  most  part  is  from  40  to  5C 
feet  above  the  water  level  in  Snake  River, 
Mr.  Hoffer  informed  the  writer  that  on  this  bar  there  is  about  8  feet! 
of  overlying  gravel  that  contains  about  15  very  fine  colors  per  cubic 
foot,  followed  by  32  feet  of  gold-bearing  gravel  to  water  level  withoil 
striking  bed  rock.     So  far  only  the  upper  12  feet  of  this  gravel,  wind- 
is  supposed  to  be  better  than  that  lower  down,  has  been  worked. 
a  Bull.  No.  285,  U.  S.  Gcol.  Survey,  1906,  p.  L64. 
