diller.]  BEDDING    QUADRANGLE,    CALIFORNIA.  177 
The  limestone  near  Kennett  is  the  only  one  extensively  quarried, 
and  has  furnished  the  material  from  which  18,500  barrels  of  lime  were 
burned  in  1902  at  Kennett,  besides  3,500  tons  of  rock  shipped  chiefly 
to  the  Keswick  smelter.  As  the  demand  increases  with  development 
the  output  was  probably  greater  in  1903. 
The  general  scarcity  in  northern  California  of  hydraulic  limestone 
or  cement  rock,  suitable  for  the  manufacture  of  hydraulic  cement, 
creates  a  demand  for  the  small  quantities  of  such  rock  that  exists  and 
of  other  material  which  may  be  used  for  the  purpose.  The  only  beds 
of  promise  in  the  Redding  quadrangle  are  in  the  lower  half  of  the 
Hosselkus  limestone  of  Brock  Mountain  and  elsewhere,  which  is  much 
thinner  bedded  than  the  upper  portion,  and  in  places  is  somewhat 
darker  gray,  with  an  earthy  odor  as  if  containing  somewhat  more  clay 
than  the  general  mass. 
It  is  well  known  that  hydraulic  cement  of  good  quality  may  be  made 
by  mixing  ordinary  lime  with  some  siliceous  substance  in  such  pro- 
portions that  the  interaction  of  the  two  forms  silicate  of  lime  and  sets 
or  hardens  the  cement.  In  Italy,  tuffaceous  volcanic  material,  there 
known  as  "pozzuolana,"  is  extensively  used  for  the  purpose,  and  in 
parts  of  Germany  a  volcanic  tuff  called  trass  is  largely  employed  in 
the  same  way.  The  Tuscan  tuff,  bordering  the  northern  end  of  the 
Sacramento  Valley,  is  very  like  the  trass  of  the  Rhine  Valley.  This 
is  especially  true  of  that  on  Stillwater,  near  the  Copper  City  road,  or 
east  of  Millville,  and  at  a  number  of  points  on  the  western  side  of  the 
Sacramento  Valley.  The  limestone  and  the  tuff  are  at  several  places 
within  a  few  miles  of  each  other,  and  there  is  reason  to  believe  that  a 
good  quantity  of  hydraulic  cement  may  be  made  from  them  within 
convenient  reach  of  the  railroad.  This  matter  is  of  importance  in  the 
construction  of  large  dams  for  irrigation  or  water  power  in  the 
Redding  region. 
CHROMITE. 
Chromite  is  mined  on  Shot  Gun  Creek,  but  the  serpentine  in  which 
it  occurs  reaches  as  far  south  as  Slate  Creek,  and  it  is  not  improbable, 
from  the  trend  of  the  chromite  bodies,  that  some  may  }^et  be  discovered 
within  the  northwest  portion  of  the  Redding  quadrangle.  At  the 
forks  of  Shot  Gun  Creek,  about  a  mile  from  the  Southern  Pacific 
Railroad,  a  series  of  lenticular  chromite  bodies  occur  in  a  somewhat 
indefinite  shear  zone,  which  is  vertical,  and  courses  S.  40°  W.  through 
the  serpentine.  Five  bodies,  ranging  from  200  to  1,500  tons  each, 
connected  by  more  or  less  distinct  vein -like  leaders,  have  been  mined 
within  a  distance  of  250  yards.  The  ore  masses  have  nothing  in  them 
resembling  vein  structure,  except  some  of  the  connecting  leaders. 
Generally,  the  ore  separates  easily  from  the  serpentine,  but  in  other 
cases  it  is  "frozen"  firmly  to  it.  Other  parallel  zones,  but  as  yet  less 
Bull.  225—04 12 
