BLACK    SANDS    FROM    PLACER    MINES.  151 
In  the  spring  of  1905  Congress  directed  that  the  report  on  the  Mineral  Resources  of  the 
United  States  should  include  an  investigation  into  the  useful  values  contained  in  the  black 
sands  of  the  Pacific  slope. 
PLAN  OF  PRESENT  INVESTIGATION. 
EXAMINATION    OF    SAMPLES. 
As  the  initial  step  in  this  investigation  the  Geological  Survey  sent  a  circular  letter  to  the 
placer  miners  of  the  United  States,  requesting  them  to  send  by  mail  samples,  weighing  1 
pounds  or  less,  of  the  heavy-sand  residues  left  in  their  sluice  boxes  in  placer  mining.  This 
met  with  hearty  response  and  a  large  amount  of  material  for  a  preliminary  examination  was 
rapidly  accumulated.  In  all,  over  2,000  samples  have  been  sent  in  from  34  States  and  Ter- 
ritories, and  from  British  Columbia,  Mexico,  and  South  America.  The  following  table 
shows  the  chief  mineral  constituents  contained  in  these  sands: 
