CLAYS    AND    SHALES    IN    CAMBKIA    COUNTY,  PA.  351 
{Analysis  of  flint  clay  from  the  Mercer  horizon  near  the  viaduct,   Cambria  County,  Pa.a 
Silica  (Si02) 45. 42 
Alumina  (A1203) 36.  80 
Ferric  oxide  (Fe203) 3.  88 
Manganese  oxide  (Mn02) 48 
Magnesia  (MgO) 45 
Lime  (CaO) 87 
Water  and  organic  matter 12.  65 
100. 00 
This  clay  is  smooth,  hard,  compact,  light  to  dark  gray  in  color,  and 
breaks  with  a  conchoidal  fracture.  It  burns  to  a  straw-yellow  color. 
The  analysis,  as  far  as  it  goes,  indicates  a  fairly  high-grade  material, 
with  perhaps  a  little  too  much  iron.  The  presence  or  absence  of 
[alkalies  was  unfortunately  not  determined. 
The  clay  mined  at  South  Fork  is  in  part  shipped  to  Johnstown  and 
in  part  mixed  with  plastic  clay  from  the  Lower  Kittanning  seam  and 
worked  up  at  the  local  brick  plant.  The  refractory  character  of  some 
of  the  products  of  this  flint  clay  has  been  tested  at  the  plant  of  the 
Cambria  Steel  Company  at  Johnstown  and  they  have  proved  highly 
satisfactory. 
Plastic  clay. — About  South  Fork  a  plastic  clay  has  been  observed 
at  some  places  near  the  top  of  the  Mahoning  sandstone.  Its  position 
corresponds  with  that  of  the  band  of  flint  clay  in  the  Johnstown  dis- 
trict. In  the  region  about  South  Fork  it  has  been  observed  at  but 
few  places  and  is  of  doubtful  value.  The  clay  below  the  Upper  Free- 
port  (Lemon)  coal  seam  is  fairly  thick  in  this  region,  but  is  not  worked 
at  present.  At  O.  M.  Stineman's  mine  No.  3,  2  feet  3  inches  of  clay 
were  measured  below  this  coal,  which  may  be  worked  at  some  future 
time  in  connection  with  the  coal.  This  clay  is  not  comparable  in 
thickness  with  that  directly  underlying  the  Miller  coal  seam,  which 
about  South  Fork,  as  near  Johnstown,  is  the  most  important  plastic 
clay  in  the  Allegheny  formation.  The  plastic  clay  associated  with 
the  Miller  coal  seam  is  usually  workable,  at  some  places  having  a 
thickness  of  6  to  8  feet,  though  averaging  about  3  to  4  feet  of  workable 
clay  of  good  grade.  A  brief  note  on  the  character  of  this  clay  will  be 
found  in  the  description  of  its  occurrence  in  the  Johnstown  district, 
where  analyses  also  are  given.  There  is  every  reason  to  suppose  that 
in  this  district  it  is  of  the  same  quality  as  the  clay  mined  about  Johns- 
town. Most  of  the  clay  product  of  the  mines  about  South  Fork  is 
mined  in  connection  with  the  coal  and  is  used  almost  entirely  at  the 
local  brick  plant. 
Shale. — So  far  as  known  the  shales  in  the  South  Fork  district  have 
not  been  utilized.  In  the  two  large  cuts  west  of  the  town  of  Wilmore, 
on  the  main  line  of  the  Pennsylvania  Railroad,  shale  beds  are  exposed 
a  Second  Geol.  Survey  Pennsylvania,  vol.  HH,  p.  147. 
