180 
woolsey.]  CLAYS    OF    OHIO    VALLEY    IN    PENNSYLVANIA.  467 
exposed  at  Homewood  as  the  "Homewood  sandstone."  In  the  locali- 
ties where  it  is  exposed  this  formation  carries  several  beds  of  lire  clay, 
but  being  scarcely  exposed  in  the  region  considered,  very  little  can  be 
said  of  its  contents.  As  to  facilities  for  exploitation,  however,  the 
Pottsville  here  is  at  a  great  disadvantage  as  compared  with  the  Alle- 
gheny formation  above  it. 
Allegheny  formation. — Resting  on  the  Pottsville  sandstone  and 
reaching  to  the  top  of  the  Upper  Freeport  coal,  this  formation  shows 
in  outcrop  as  a  narrow  belt  bordering  the  river  hills  with  its  base  just 
below  river  level.  The  average  thickness  of  the  Allegheny  formation 
is  about  300  feet.  The  following  generalized  section,  presented  in 
natural  order  from  the  top  downward,  shows  its  character  and  indicates 
the  position  of  fire-clay  beds: 
Section  of  Allegheny  formation. 
Feet. 
1.  Upper  Freeport  coal;  "  Four-foot"  or  "Hookstown  vein" 0  to    4 
2.  Fire  clay 2  to    4 
3.  Limestone - 1  to    4 
4.  Shale  and\  Kn  .    ^n 
5.  Sandstone/ " 50  to  '° 
6.  Lower  Freeport  coal  (usually  absent) 0  to    2 
7.  Fire  clay 0  to    5 
8.  Limestone  (sometimes  present) 
9.  Sandstone  or  sandstone  and  shale 70  to  90 
10.  Darlington  coal ;  ' '  Block  vein  "at  Smiths  Ferry 1  to    2 
11.  Fire  clay 4 
12.  Black  slate  with  iron  nodules 20  to  30 
13.  Lower  Kittanning  coal ;  ' '  Sulphur  vein  " 2  to    3 
14.  Fire  clay 6  to  10 
15.  Sandstone!  ACi 
16.  Shale        / ; w 
17.  Limestone,  ferriferous,  "  Vanport  limestone" 1  to  20 
Black  shale 15 
(Fire  clay      1 
18. 1  Sandy  shale  [ 20 
[Fire  clay      J 
19.  Clarion  coal * 1: 
20.  Fire  clay 4  to    6 
21.  Sandstone 23 
22.  Shale 25 
23.  Brookville  coal 6 
24.  Fire  clay 4 
This  is  by  far  the  richest  group  of  rocks  along  the  upper  Ohio  River, 
containing  as  it  does  most  of  the  workable  clays,  coals,  limestones, 
and  sandstones  of  central  western  Pennsylvania. 
Brookville  clay. — This  deposit  of  clay,  underlying  the  Brookville 
coal,  first  comes  to  the  surface  under  the  Pittsburg  and  Lake  Erie 
Railroad  bridge  across  the  mouth  of  Bradys  Run,  then  rises  gently 
up  Beaver  River,  but  in  most  places  it  is  covered  by  river  deposits. 
So  far  as  known  it  has  not  been  exploited  for  clay  in  this  county.  No 
analysis  of  clay  from  this  vicinity  is  available,  but  here  are  appended 
analyses  of  clay  from  nearby  localities. 
100 
