CLAYS    OF    OHIO    VALLEY    IN    PENNSYLVANIA. 
473 
in  thickness  from  2  to  10  feet,  although  in  places  it  may  be  replaced 
by  limestone  and  iron  ore  as  at  Adams.rt 
No  analysis  of  the  Upper  Freeport   clay  from  Beaver  County  is 
available,  but  analyses  from  other  places  follow: 
Analyses  of  Upper  Freeport  clay. 
1. 
2. 
3. 
Si02 
Per  cent. 
57.80 
25.  50 
Per  cent. 
56.78 
26.89 
Per  cent. 
63.81 
A1203 
26.  39 
Ti02 
FeO 
2.51 
.25 
.61 
2.69 
8.35 
2.25 
.322 
.369 
.987 
3.92 
|    &8.38 
a  1.23 
CaO 
Tr. 
MgO  .  1 
Tr. 
Alkalies 
H20  combined 
H20  uncombined 
&9.12 
100.  00 
100.  548 
100.  55 
«  As  Fe203.  b  Loss  by  ignition. 
1.  East  Palestine,  Ohio.  Paving-brick  clay,  Upper  Freeport.  Lord,  analyst.  Geol. 
Surv.  Ohio,  Vol.  VII,  p.  137. 
2.  Furnace  clay  on  Jacobs  Creek,  2  miles  southeast  of  Jacobs  Creek  Station. 
McCreath,  analyst.     Second  Geol.  Surv.  Pennsylvania,  Rept.  L,  p.  112. 
3.  Bolivar,  Pa.  From  King  mine  of  Reese,  Hammond  &  Co.  Hopkins,  Clay  and 
clay  industries  of  western  Pennsylvania,  p.  81. 
The  Upper  Freeport  clay  in  Beaver  County,  lying  immediately 
under  the  Upper  Freeport  coal,  is  not  at  the  horizon  of  the  famous 
Bolivar  clay.  The  horizon  of  the  latter  is,  in  fact,  beneath  the  lime- 
stone which  usually  occurs  just  under  the  Upper  Freeport  clay,  but, 
so  far  as  observed,  it  seems  replaced  on  Ohio  and  Beaver  rivers  by  a 
less  refractory  shale.  When  the  limestone  is  absent,  however,  both 
clays  may  lie  together,  as  at  Salina,  Westmoreland  County,  without 
distinct  line  of  demarcation. 
The  infrequent  clay  beds  of  the  Conemaugh  formation  will  be,  with 
shales,  discussed  in  the  following  chapter. 
CARBONIFEROUS    SHALES. 
Allegheny  group. — As  has  already  been  stated,  shale  is  merely  con- 
solidated clay  of  character  similar  to  the  unconsolidated  material.  It 
has  been  found  that  a  mixture  of  the  two  gives  a  stronger  brick,  when 
great  strength  and  abrasive  qualities  are  desired,  as  in  paving  brick, 
a  Prof.  Paper  U.  S.  Geol.  Survey  No.  11,  1903,  p.  230. 
