CLAYS    AND    SHALES    IN    CAMBRIA    COUNTY,  PA.  347 
the  top  of  the  Mahoning  sandstone.  Northwest  of  Johnstown,  in  the 
valley  of  Laurel  Run,  a  short  distance  east  of  the  old  coke  yard,  from 
which  the  Upper  Freeport  coal  gets  its  local  name,  this  flint  clay  is 
exposed,  indicating  a  possible  continuity  of  the  bed  as  far  west  as 
this  point.  Northwest  of  Johnstown,  on  the  road  ascending  Pleasant 
Hill  from  the  valley  of  the  Conemaugh  River,  a  flint  clay  occurs  about 
110  feet  above  the  Upper  Freeport  coal  and  10  feet  below  a  smaller 
seam  of  coal.  This  latter  coal  may  possibly  be  higher  than  the  seam 
70  feet  above  the  Upper  Freeport  at  the  Baltimore  and  Ohio  tunnel. 
If  so,  this  flint  clay  of  Pleasant  Hill  is  higher  than  that  previously 
described. 
On  the  headwaters  of  Mill  Creek  and  Dalton  Run  and  near  the  south 
edge  of  the  area  west  of  Stony  Creek,  a  fairly  persistent  flint  clay  was 
observed  well  toward  the  base  of  the  Conemaugh  formation.  These 
occurrences  are  too  far  from  lines  of  transportation  to  be  of  great 
economic  importance  at  the  present  time. 
It  should  be  added  that  the  occurrences  noted  above  are  largely 
roadside  outcrops  at  which  it  is  impossible  to  determine  the  exact 
thickness  and  nature  of  the  clays.  Only  careful  prospecting  can  deter- 
mine these  points,  but  the  fact  that  one  of  the  flint  clays  is  being 
successfully  used  at  one  point  is  significant. 
Plastic  clay. — The  flint  clay  above  the  Mahoning  sandstone  assumes 
a  plastic  phase  at  places  in  the  Johnstown  district.  Most  of  the  valu- 
able plastic  clay  in  this  region,  however,  occurs  in  the  Lower  Pro- 
ductive Measures  or  Allegheny  formation.  At  a  few  places  a  clay  bed 
of  workable  thickness  lies  below  the  Upper  Freeport  coal,  in  connec- 
tion with  which  it  might  be  mined.  At  the  Cyrus  Shepard  mine, 
leased  by  L.  J.  Mitchell,  east  of  Franklin,  2  feet  \\  inches  of  fire  clay 
were  measured,  but  the  bed  may  not  be  persistent.  A  clay  bed 
which  promises  to  be  of  some  importance  underlies  the  limestone 
below  the  Upper  Kittanning  or  UC"  coal  seam.  This  clay  has  been 
developed  to  some  extent,  though  so  far  as  the  writers  are  aware  it  is 
not  now  worked.  According  to  T.  T.  Morrell  a  it  has  the  following- 
composition: 
Analysis  of  clay  near  Johnstown,  Pa. 
Silica  (SiOa) 71.  98 
Alumina  (A1203) 26.  29 
Ferric  oxide  (Fe203) 2.21 
Magnesia  (MgO) 44 
Manganese  dioxide  (Mn02) 32 
101. 34 
a  Second  Geol.  Survey  Pennsylvania,  Rept.  H2,  p.  148. 
