352  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1906,  PART    T. 
that  vary  in  position  from  400  to  675  feet  above  the  Upper  Freepo_ 
coal.  These  beds  contain  many  promising. shales,  which  arc  found  in 
the  surrounding  hills,  conveniently  situated  with  respect  to  transpor- 
tation. Their  appearance  indicates  that  they  may  be  adapted  to  thj 
manufacture  of  paving  brick  and  other  materials  that  require  only  an 
inferior  grade  of  clay  or  shale.  To  determine  their  fitness  for  any 
purpose,  however,  practical  tests  must  be  made.  In  a  recent  cud 
opposite  Ehrenfeld  station,  along  the  new  county  road,  a  bed  of  shale] 
50  to  60  feet  thick,  lying  60  feel  above  the  Upper  Freeport  coal,  also] 
appears  to  be  promising. 
BLACKLICK    CREEK    DISTRICT. 
The  South  Fork  of  Blacklick  Creek  flows  along  the  northern  vd^e 
of  the  Johnstown  quadrangle.  It  is  joined  by  the  North  Fork  a  short 
distance  west  of  Yintondale  and  then  flows  westward  beyond  the 
limits  of  the  area.  Deposits  <>f  Hint  and  plastic  clay  are  found  in  the 
adjacent  hills  along  the  creek,  and  although  many  of  these  are  con- 
veniently situated  with  respect  to  lines  of  transportation,  the  demanl 
has  not  yet  been  sufficient  to  justify  their  exploitation. 
Flint  clay.  The  Hint  clay  in  the  Blacklick  Creek  district  occurs  at 
two  horizons.  The  higher  (lint  clay  is  found  in  the  lower  part  o\'  the 
Conemaugh  formation  above  what  is  thought  to  be  the  equivalent  of 
the  Mahoning  sandstone  and  a  few  feet  below  a  small  coal  bed,  pos- 
sibly the  Gallitzin  coal.  This  (lint  clay  has  been  observed  in  many 
place-  north,  west,  and  south  of  Wehrum,  but  the  rise  of  the  beds 
toward  the  east  causes  a  gradual  increase  in  its  distance  from  the  val- 
ley and  from  transportation  facilities  and  finally  its  complete  absence 
from  the  hills.  West  of  Wehrum.  however,  both  north  and  south  of 
Blacklick  Creek,  it  occurs  at  many  points,  having  the  unusual  thick- 
ness of  7  to  s  feet  in  places.  It  is  a  typical  flint  clay  in  appearance, 
though  it-  content  of  iron  oxide  is  apparently  very  high.  A  sample 
collected  from  a  roadside  exposure  west  of  Dilltown  gave  the  following 
analysis: 
Hal  analysis  of  flint  clay  from  a  natural  t  tposurt  west  of  Dilltown. 
[E.  c.  Sullivan,  analyst.] 
Silica    SiO      50.3 
Alumina    Al_.<>    21.3 
Ferric  oxide    IV. <  )3)  a 10.4 
Magnesia    MgO) 0.61 
Lime  (CaO) 0.  39 
Soda    Na_0) 0. 18 
Potash  (K20) lit 
Titanium  oxide  (Ti02) 0.90 
Loss  on  ignition 12.  00 
97-  22 
o  Total  iron  calculated  as  Fe20a. 
