142  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.         [bull.  260. 
the  volcanic  belt,  have  taken  up  old  claims,  and  have  made  new 
discoveries.  The  most  widely  heralded  of  these  new  finds  is  that  at 
Bullfrog,  about  60  miles  southeast  of  Goldfield,  in  the  Amargosa 
Desert.  This  has  not  yet  been  visited  by  the  writer.  Ores  are  also 
reported  in  the  Kawich  Range,  about  50  miles  east  of  Tonopah  andi 
Goldfield. 
PROGRESS  OF  GEOLOGIC  KNOWLEDGE. 
The  prediction  made  in  last  year's  report  that  new  veins  belonging 
to  the  productive  period  of  the  earlier  andesite  would  probably  be 
discovered  underneath  the  later  overlying  lavas  has  been  fulfilled | 
during  the  past  year  by  the  discovery  of  several  such  veins.     In  the 
Montana -Tonopah,  north  of  the  first  large  vein  discovered  (the  Mon- 
tana  vein),   another  large  east-west  vein  has  been   discovered   and 
developed.     This  vein  contains  large  quantities  of  rich  sulphide  ore.' 
and  has  been  called  the  "  Macdonald  vein."     West  of  the  Montana-. 
Tonopah  mine  the  Tonopah  Extension  shaft  has  cut  a  similar  riehl 
and  large  vein  in  the  earlier  andesite,  in  a-  portion  of  the  district  I 
which,  while  on  the  borders  of  the  formerly  known  productive  region,! 
had  not  been  shown  to  contain  any  valuable  ores.     This  vein,  encoun- 
tered beneath  the  overlying  later  andesite,  is  as  strong  as  any  of  the 
other  first-class  veins  yet  developed,  and  may,  indeed,  be  the  exten- 
sion of  some  of  the  earlier-known  lodes.     Besides  these  important' 
discoveries,  fragments  of  similar  veins  broken  by  intrusion  or  fault  j 
ing,  so  as  not  to  have  at  present  as  great  economic  value  as  the  un 
broken  veins,  and  similar  veins  of  smaller  size  have  been  encounteret  j 
in  other  mines,  such  as  the  North  Star,  the  Midway,  and  the  Tonopal 
and  California. 
COMPOSITION    OF    ORES. 
A  preliminary  account  of  the  early  andesite  ores  was  given  in  thi 
last  report,  in  which  it  was  shown  that  the  primary  ore  was  essenn 
tially  a  rich  silver  sulphide,  black  in  color  and  often  antimonia] 
Since  that  time  Dr.  W.  F.  Hillebrand,  of  the  Geological  Survey,  ha 
made  a  prolonged  chemical  investigation  of  the  ores,  which  is  o 
great  interest,  as  it  touches  their  origin  and  their  commercial  treat 
ment.  The  primary  sulphide  ore  taken  from  the  Montana  Tonopa] 
(Montana  vein)  has  the  folloAving  composition: 
: 
