CLAYS    OF    BIRMINGHAM    DISTRICT,  ALABAMA.  293 
The  highest  bed  of  shale  used  for  brick  is  that  above  the  Mary 
Lee  coal  group  in  the  Warrior  basin.  This  is  generally  a  blue  clay 
shale,  weathering  yellow,  about  200  feet  thick.  It  is  a  persistent 
stratum,  extending  throughout  the  Warrior  basin  in  this  area  where 
not  removed  by  erosion.  It  is  very  uniform  in  appearance,  though, 
as  stated  below,  considerable  variation  in  composition  may  occur  at 
different  points  or  at  different  levels.  The  vertical  continuity  of 
the  shale  is  broken  here  and  there  by  a  layer  of  sandstone  up  to  10 
feet  thick  or  possibly  more  at  some  points. 
Shale  from  the  bottom  of  this  mass  is  extensively  used  for  brick  by 
the  Graves  Shale  Paving  Brick  Company,  at  Graves. 
Below  is  a  section  of  the  shale  quarry  at  this  place: 
Section  of  shale  beds  at  Graves. 
Feet. 
Yellow  shale 6 
Gray  shale 10 
Blue  shale 28 
44 
The  shale  dips  from  10°  to  15°  W.,  into  the  hill.  According  to 
Ries,a  the  yellow  shale  is  somewhat  sandy  and  has  a  large  content  of 
ferric  oxide.  It  vitrifies  at  2,250°  F.  and  fuses  at  2,500°,  yielding  a 
brick  that  has  a  tensile  strength  of  40  pounds  per  square  inch.  The 
gray  shale  is  less  sandy  and  ferruginous.  It  vitrifies  at  2,200°  F. 
and  fuses  at  2,500°,  yielding  a  brick  of  good  red  color,  with  an  average 
tensile  strength  of  105  pounds  per  square  inch.  The  brick  are 
burned  for  nine  days  in  round  down -draft  kilns.  Paving  brick  and 
chemical  brick  are  made.  The  latter  are  used  principally  for  pack- 
ing acid  chambers  in  making  sulphuric  acid,  a  use  for  which  they  are 
well  adapted,  since,  on  account  of  their  density,  they  absorb  almost  no 
water.  The  daily  capacity  is  50,000  brick  and  the  actual  output  is 
reported  to  be  28,000  to  38,000  daily. 
At  Coaldale  shale  from  two  horizons  is  used.  The  upper  horizon 
is  that  of  the  Jefferson  coal  seam  and  the  lower  is  on  an  average  about 
150  feet  below  the  Black  Creek  coal  seam. 
Shale  from  the  upper  horizon  is  utilized  by  the  Southern  Clay 
Manufacturing  Company  for  vitrified  paving  brick. 
The  section  at  this  company's  quarry  is  as  follows: 
Section  at  Southern  Clay  Manufacturing  Company's  quarry,  Coaldale. 
Feet. 
Reddish,  somewhat  sandy  shale 20 
Dark  clay  shale  with  mica 15 
Coal 1 
Stiff  gray,  somewhat  sandy  shale .°>0 
Coal 1 
a  Ries,  Heinrich,  Bull.  Alabama  Geol.  Survey  No.  6,  1900,  p.  185. 
