i 
254  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   L906,   PART    I. 
116  foot  of  dolomite  gave  silica  ranging  from  0.96  to  7.28  per  cen| 
with  an  average  of  3.26  per  cent.     This  shows  a  still  greater  increa 
in  silica  content  to  the  northeast.     The  writer  suspects  that   in  th 
latter  case  the  samples  were  obtained  at   a  horizon  above  the  tru 
chert -free  dolomite,  which  north  of  Doleito  is  apparently  confined  to 
the  flat  land  along  the  valley  and  does  not  show  in  outcrop  to  any 
extent. 
On  account  of  the  fact  that  the  dolomite  outcrops  along  the  valle; 
bottoms  but  little  above  drainage  the  conditions  for  quarrying  an 
not  very  favorable,  inasmuch  as  it  is  necessary  to  keep  the  quarrie 
dry  by  constant  pumping  and  the  rock  has  to  be  raised  from  consider 
able  depth.  It  is  especially  difficult  to  keep  the  quarries  dry  in  heav 
and  prolonged  rains,  and  at  times  work  has  to  be  suspended  o 
account   of  Hooding. 
The  mosl  favorable  conditions  for  quarrying  exisl  in  Murphree  Val 
ley  between  Remlap  and  Chepultepec,  where  the  dolomite  outcrops 
well  up  on  the  east  side  of  Gravelly  Ridge,  and  though  the  rock  dips 
to  the  west  at  a  considerable  angle  large  bodies  could  be  quarried  in 
such  a  way  as  to  be  self-draining:  moreover,  the  expense  involved  i: 
raising  the  rock  from  a  deep  quarry  on  level  ground  would  be  entirely 
avoided. 
The  suitability  of  this  dolomite  for  flux  has  been  amply  demon- 
strated by  its  use  in  the  furnaces  of  the  region  for  the  last  ten  years, 
and  no  comments  on  that  phase  of  the  matter  need  be  made  here. 
The  results  obtained  in  actual  use  throughout  this  period  prove  that 
the  dolomite  is  in  every  respect  equal  to  the  best  limestone  to  be  had 
in  t  he  region  for  fluxing  purposes.  (  me  company  reports  its  exclusive 
use  in  smelting  iron  for  the  manufacture  of  steel  by  the  basic  process] 
The  abundance  of  the  rock  in  proximity  to  the  furnaces  is  another 
condition  fa\  oring  its  use. 
CONASAUGA   LIMESTONE. 
The  Conasauga  limestone  is  a  thin-bedded  bluish  to  gray  rock, 
immediately  underlying  the  Knox  dolomite.  It  is  the  lowest  and 
oldest  rock  format  ion  exposed  in  the  region  under  consideral  ion.  The 
limestone  is  interbedded  with  more  or  less  shale.  It  is  known  in  the 
region  as  the  Platwoods  formation,  because  it  underlies  the  flat,  badly 
drained  lands  of  the  valleys.  Thus  it  underlies  Opossum  Valley,  as  at 
North  Birmingham,  for  two-thirds  of  its  width;  and  east  of  Cemetery 
Ridge  it  has  an  outcrop  more  than  a  mile  in  width  in  the  central  part 
of  the  city  of  Birmingham,  where  its  ledges  can  be  seen  here  and  there 
in  the  streets.  Most  of  the  limestone  seen  outcropping  in  Opossum 
Valley  between  Village  Creek  and  the  Louisville  and  Nashville  Rail- 
road is  Conasauga.  This  outcrop  wedges  out  a  mile  south  of  Wylam, 
and  to  the  north  it  gradually  tapers  to  a  point  and  disappears  beneath 
