348  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   L906,   PART    I. 
lit  < 
The  most  valuable  plastic  clay  in  the  Allegheny  formation  is  thai 
underlying  the  Miller  coal  seam.  Many  of  the  mines  operating  thl 
coal  about  Johnstown  produce,  as  well,  considerable  amounts  o 
this  clay.  This  clay  bed  in  this  district  generally  ranges  from  3  to 
feet  in  thickness,  but  may  possibly  be  thicker  locally.  It  nsm 
underlies  the  lower  bench  of  the  Miller  seam,  from  which  it  is  sepi 
rated  by  a  few  inches  of  shale  or,  in  the  absence  of  this  lower  bench, 
it  occurs  below  the  main  coal  itself,  being  separated  from  it  by  3  to  4 
inches  of  bone  or  shale.  It  is  a  light-drab  clay,  not  very  bard,  of 
irregular  fracture,  greasy  to  the  touch,  and  slakes  on  exposure  to  the 
weather.      [ts  composition  is  indicated  by  the  following  analyses: 
Analyses  of  clay  n  >,<i<  rh/i n<i  tin   Miller  seam. 
Silica    3i0  
Mumi 
Ferric  oxidi 
Lime    i     0  

Titanium  oxide     I 
on  ignitioD 
a  1.60 
..a 
1.20 
66   K) 
19.80 
.61 
.10 
1. 00 
53.10 
.tin 
.  IS 
1.20 
10  20 
100.26 
" 
(>N  82 
2.  79 
.'23 
.S2 
Mi.o,  .<;6 
:..S3 
i  Hi.OO 
:,:l  iron  calculate  I 
1.  Citizens' Coal  i  i  ITill  mine,  J  *       ullivan,  analyst- 
ean    e  stone  bridge,  Johnstown,  Pa.;  E.  C.  Sullivan,  analysj 
i  Coal  Company's  mine,  Seward,  \v-  ■  I  (  oiu  i\    Pa.;  I-'..  C  Sullivan,  analyst. 
■i.  Clay  underlyu  n;  T.  T.  Morrell,  analyst,  Second  Geol.  Survey  ivim- 
sylvania,  Ri  1 18. 
This  clay  is  worked  aboul  Johnstown  by  W.  J.  Williams  at  Kernl 
ville;  by  the  <  itizens'  Coal  Company  at  Green  Hill;  by  A.  J.  Haws  & 
Sons  Limited  }  both  at  ( loopersdale  ami  near  \\w  famous  stone  bridge! 
and  by  Robertson  &  Griffin  on  St.  Clairs  Run;  at  each  place  in  conl 
aection  with  the  overlying  coal.  Though  not  always  worked,  thil 
clay  i-  present    at  many  places  in  this  district  in  workable  thickness. 
Nearly  all  t  he  product  of  the  Johnstown  mines  is  used  at  local  brick 
plants  where  it  i>  mixed  with  flint  clay  from  the  Mercer  horizon] 
shipped  from  South  Fork  and  from  other  points.  When  thus  mixed 
in  proper  amount  it  forms  a  suitable  bond  in  a  clay  that  is  used  in 
the  manufacture  of  high-grade  refractory  products  and  bricks,  for 
blast  furnace  and  open-hearth  work,  and  in  making  sleeves,  nozzles] 
tuyeres,  and  other  articles  that  are  exposed  to  high  temperatures. 
The  lowest  plastic  day  in  the  Johnstown  district  is  associated  with 
the  Mercer  coal,  hut  is  not  exposed  in  the  immediate  vicinity  of  the 
city.  In  the  hills  lying  east  of  Stony  Creek,  south  of  Kring,  on  the. 
Baltimore  and  Ohio  Railroad,  this  horizon  has  been  prospected  and 
some  clay  and  shales  have  been  found,  but  they  have  never  been 
worked.     Flint  clay  was  not  seen  at  any  of  the  old  prospect  pits. 
