82  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   1906,  PART    I. 
was  full.  The  claim  farthest  upstream  that  was  examined  was  the! 
Golden  Treasure,  about  25  miles  above  the  dam.  The  bulk  of  the 
work  was  done  in  the  neighborhood  of  the  old  placers  in  order  to  deter- 
mine the  value  of  the  ground  that  was  formerly  considered  profitable. 
U  was  found  that  the  values  were  very  irregularly  distributed  and  in 
but  few  places  equal  to  the  claims  made  by  those  interested  in  the 
land.  The  prospecting  was  accomplished  by  means  of  test  pits,  pan- 
ning, and  sampling,  the  samples  taken  being  shipped  to  Portland, 
Oreg.,  where  they  wen4  treated  and  assayed  by  the  Survey  in  connec- 
tion with  the  black-sand  investigation.  The  information  gained  by 
the  field  tests  and  the  assay  of  samples  is  not  such  as  to  place1  a  specific 
valuation  on  any  particular  claim;  hut  the  results  derived  give  the 
average  values  carried  by  the  ground  over  which  the  pits  were  dis- 
tributed. Comparative  values  for  the  various  samples  were  deter- 
mined in  a  preliminary  way,  merely  for  comparative  purposes,  on  the 
ground  by  the  count  of  the  gold  colors,  and  thus  ready  knowledge 
\\a^  had  as  to  the  location  and  extent  of  the  mineral-bearing  material. 
It  was  found  that  in  general  the  values  were  concentrated  in  the  bot- 
tom of  the  loam  and  the  upper  portion  of  the  underlying  gravels. 
The  surface  soil  or  sandy  loam  is  common  and  ranges  in  thickness 
from  2  to  L2  feet  or  more.  The  gold  was  everywhere  of  the  finest 
flourlike  particles,  a  large  percentage  of  which  would  pass  through 
a  150-mesh  screen.  The  rocks  are  in  general  much  smaller  than  a 
man's  head,  although  in  a  few  places  rocks  large  enough  to  interfere 
with  dredging  or  other  mining  operations  were  encountered. 
After  the  sampling  and  assaying  were  completed  the  remainder  of 
the  " undersize u  was  mixed  and  run  over  a  Wilfiey  concentrating 
table  to  determine  the  minerals  present  and  to  see  whether  or  not  the 
gold  could  be  saved  by  that  type  of  machine.  The  results  obtained 
were  excellent  on  both,  tic  loam  and  the  gravel.  A  charge  of  2,172 
pounds  of  loam  assaying  lo  cents  per  ton  was  U^\  to  the  table,  and  a 
concentrate  weighing  6  pounds  1  1  ounces  was  obtained,  which  assayed 
$33.28  per  ton.  The  assay  of  the  middlings  (30  pounds)  and  of  the 
tailings  (5  assay  tons  being  used  in  the  huge  crucibles)  showed  only  a 
trace  of  gold.  The  gravel  gave  equally  satisfactory  results;  3,850 
pound-  assaying  8  cents  per  ton  yielded  8  pounds  10J  ounces  of  con- 
centrates assaying  $34.01  per  ton.  The  middlings  (52J  pounds)  and 
tailings  contained  only  a  trace. 
No  other  minerals  of  any  commercial  importance  were  found.  No 
platinum  or  monazite  was  observed  and  only  a  trace  of  zircon.  The 
richest  sample  contained  only  4  pounds  of  magnetite  per  ton.  These 
results  indicate  that  the  percussion  type  of  machine  can  be  used 
advantageously  in  separating  the  Snake  River  fine  gold  from  the 
loam  and  gravels,  especially  after  preliminary  concentration  in  ordi- 
nary sluice  boxes  and  shunting  the  concentrates  onto  the  tables  by 
