a:  is  wold.]         COAL    IN    BURGETTSTOWN     QUADRANGLE,    PA.  403 
wood  limestone  and  the  Uniontown  coal.  The  limestone  mentioned  is 
i  solid  brown  rock  a  foot  or  two  in  thickness,  breaking  with  uneven 
fracture  and  showing  a  number  of  small  crystals  of  calcite.  This  bed 
is  underlain  persistently  by  green  shale,  and  it  is  at. a  constant  dis- 
tance of  about  150  feet  above  the  Pittsburg  coal. 
The  Uniontown  coal  is  about  1  foot  in  thickness.  It  is  of  no  com- 
mercial importance  in  the  Burgettstown  quadrangle,  but  it  is  gen- 
erally present,  and  is  valuable  as  a  geologic  marker.  It  is  only  a  few 
feet  above  the  upper  ledge  of  the  Benwood  limestone,  and,  owing  to 
this  fact,  it  can  be  readily  identified.  It  is  200  feet  above  the  Pitts- 
burg bed.  This  interval  was  found  to  be  very  constant  throughout 
the  quadrangle. 
The  depth  of  the  Pittsburg  coal  below  other  beds,  such  as  the 
Waynesburg  coal,  Washington  coal,  and  Washington  limestone,  was 
determined,  but,  as  these  strata  are  farther  away  from  the  coal,  not 
30'  many  good  comparisons  could  be  obtained.  Whenever  possible 
he  limestone  beds  and  Uniontown  coal  Avere  used  in  determining  the 
position  of  the  Pittsburg  seam  where  the  latter  lies  below  the  surface 
md  is  inaccessible. 
If  the  intervals  between  the  different  strata  are  well  determined, 
he  mapping  of  an  underground  seam,  such  as  the  Pittsburg  coal,  is 
rery  simple.  The  distance  from  a  particular  outcropping  stratum 
o  the  coal  is  subtracted  from  the  elevation  of  the  outcrop  and  the 
•emaincler  is  the  elevation  of  the  Pittsburg  coal  at  that  point.  When 
his  method  was  applied  to  all  known  outcrops  occurring  in  the 
egion  where  the  Pittsburg  coal  is  not  exposed,  the  altitude  of  the 
oal  was  known  at  a  great  many  points,  and  by  connecting  the 
>oints  of  equal  altitude  by  lines  the  accompanying  contour  map 
f  the  coal  seam  (PL  III)  was  formed. 
GENERAL    DESCRIPTION. 
Location  of  the  quadrangle. — The  territory  represented  by  this 
lap  is  rectangular  and  has  a  width  of  about  13  miles  from  east  to 
est  and  a  length  of  17  miles  from  north  to  south.  It  lies  in  south- 
estern  Pennsylvania,  south  of  Ohio  River,  and  includes  parts  of 
eaver,  Allegheny,  and  Washington  counties.-  Burgettstown  is  sit- 
ated  on  the  Pennsylvania  Railroad,  27  miles  west  of  Pittsburg, 
pproximately  in  the  center  of  the  area,  and  from  this  village  the 
uadrangle  takes  its  name. 
Tocography. — There  are  no  striking  topographic  features.  The 
pgion  is  made  up  of  hills  and  valleys  without  definite  arrangement, 
s:cept  that  the  principal  valleys  coincide  with  the  major  streams, 
he  topography  is  typical  of  that  of  much  of  western  Pennsylvania, 
rest  Virginia,  and  southeastern  Ohio.    The  altitude  of  the  surface 
