310  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   L906,   PART    I. 
FIRE  CLAYS. 
(LAVS    AT    CHELTENHAM. 
The  area  from  which  fire  clays  arc  derived  has  its  center  in  a  section 
of  the  city  knowii  as  Cheltenham,  lying  south  of  Forest  Park.  It 
extends  about  4  miles  southeastward,  in  a  tongue  about  2  miles  wide, 
and  westward  to  a  line  running  south  from  Clayton.  An  exami- 
nation of  the  geological  map  (fig.  11)  will  show  that  this  area  is  an 
extension  or  peninsula  of  the  Pennsylvanian  coal  measures.  The 
clay  is  mined  very  much  after  the  manner  of  coal  mining,  both  shafts 
and  slopes  being  used.  The  depth  below  the  surface  is  generally 
between  60  and  100  feet. 
STRUCTURE   AND    DISTRIBUTION. 
The  geologic  feature  to  which  the  presence  of  the  fire  clay  within 
the  area  named  is  mainly  due  i.^  a  faint  synclinal  basin,  whose  center  is 
not  far  from  the  sontheast  corner  of  Foresl  Park.  North  and  east  of 
this  point  there  are  no  mines.  Certain  small  variations  from  the 
genera]  structure  here  described  are  probably  due1  to  minor  folds, 
which  are  too  small  to  he  reduced  to  system  with  any  data  now 
obtainable.  The  lowest  level  from  which  the  clay  is  mined  is  lot  feet 
above  sea  level,  this  being  within  the  bend  of  the  \)os  Peres  River, 
near  the  southeast  corner  of  Forest  Park.  From  this  point  the  eleva- 
tion of  the  bed  increases  both  t<>  the  west  and  to  the  south.  The 
highest  kix.wn  level  of  the  clay  is  494  feet,  in  the  Van  Cleave  mine, 
ahout  1  mile  northwest  of  the  insane  asylum,  near  the  intersection  of 
the  old  Manchester  and  Watson  roads.  West  of  that  point  the  strata 
are  affected  by  a  gentle  anticline,  oxer  which  the  Des  Peres  River 
flows  southwest  ward ,  the  combined  effects  of  the  folding  and  erosion 
being  t<>  erode  the  clays  from  this  area.  Similar  conditions  on  the 
east  and  south  of  the  productive  area  have  caused  the  complete 
erosion  of  the  day-hearing  series. 
in  so  far  as  system  is  discernible  in  the  gentle  folding,  all  axes 
-(cm  Jo  have  a  northwest-southeast  direction.  The  product ive  area 
south  <>f  <  Jlayton  lies  in  a  gent  le  syncline  parallel  to  the  one  above  men- 
t  ionedj  t  he  t  wo  axes  being  1  or  5  miles  apart . 
STRATIGRAPHY. 
Within    the    area    named,    the    Pennsylvanian    coal     measures   lie 
uncon fori ii ably  on  1  he  St .  Louis  limestone  of  the  lower  Carboniferous* 
These  coal  measures  are  generally  less  than  100  feet  thick.  It  is  not 
probable  that  the  beds  here  present  represent  the  base  of  the  system. 
They  consist  mainly  of  shales  and  clays,  but  comprise  subordinate 
beds  of  limestone.  At  the  base  is  a  thin  though  persistent  sandstone 
forming  the  floor  of  the  fire  clay  mines,  all  of  which  arc  in  the  very 
persistent  overlying  bed  of  fire  clay  known  as  the  "Cheltenham 
seam," 
