334  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   1903.  [bull. 225. 
composition  and  thickness.  In  fact,  they  appear  to  be  variable  in 
both  characteristics,  but  generally  they  consist  of  soft  material,  the 
outcrop  of  which  is  often  obscured  by  blocks  of  sandstone  from  the 
overturned  lower  member,  and  they  seem  to  range  in  thickness  from 
150  to  300  feet.  Economically  they  are  the  most  important  beds  of 
the  basins,  since  they  carry  most  of  the  coals  that  are  of  workable 
thickness.  In  places  beds  of  coal  of  considerable  size  appear  within 
15  to  20  feet  of  the  top  of  the  sandstone,  but  occasionally  the  most 
at  tractive  beds  seem  to  belong  from  200  to  300  feet  above  the  same 
horizon.  It  seems  probable  that  the  interval  is  made  up  of  a  number 
of  coal  beds  of  different  sizes  separated  by  dark  shales,  and  probably 
some  thin  sandstone  layers. 
The  next  succeeding  formation  is  a  bright-red  shale,  which  is  one  of 
the  most  conspicuous  beds  of  the  region.  Unless  it  is  deeply  covered 
by  debris  from  some  adjacent  sandstone  ridge,  its  outcrop  is  almost 
always  apparent  from  the  color  of  the  soil.  Its  exact  thickness  could 
not  be  determined,  but  presumably  it  ranges  from  350  to  400  feet. 
The  rocks  above  the  red  shale  just  mentioned  are  but  little  known, 
and  the  present  investigation  was  not  extended  enough  to  determine 
definitely  the  sequence  and  thickness  of  the  superjacent  beds,  but  at 
the  north  end  of  Third  Hill  Mountain,  which  here  occupies  nearly  the 
center  of  the  syncline,  the  red  shales  are  clearly  overlain  by  a  bed  of 
massive  sandstone  at  least  20  feet  in  thickness.  Above  the  sandstone 
is  dark  shale,  in  which  a  small  bed  of  coal  has  been  discovered,  and  in 
the  shales  associated  with  this  coal  occurs  a  Mississippian  type  of 
Lepidodendron,  which  shows  clearly  that  the  entire  series  exposed  in 
the  basin  is  of  Pocono  age. 
Geologic  structure. — The  structure  of  the  Meadow  Branch  field  is 
comparatively  simple,  consisting  in  a  general  way  of  an  open,  syn- 
clinal fold,  but  this  is  complicated  by  one  or  two  minor  flexures  and 
by  the  slight  overturning  of  the  southeastern  limb,  so  that  its  true 
structure  is  not  readily  apparent. 
The  beds  forming  the  northwestern  limb  of  the  syncline  dip  to  the 
southeast  at  angles  which  vary  from  20°  to  60°.  The  massive  sand- 
stone underlying  the  coal-bearing  member  of  the  formation  has  so 
resisted  erosion  that  it  forms  the  summit  of  Sleepy  Creek  Mountain, 
which  extends  in  an  unbroken  line  from  the  northern  to  the  southern 
extremity  of  the  field.  In  the  eastern  limb  the  rocks  stand  either 
vertical,  or  are  overturned  so  as  to  give  southeastern  dips  which  vary 
from  G0°  to  90°.  In  this  position  the  heavy  sandstone  beds  are  easily 
eroded,  and  consequently  the  outer  rim  of  the  syncline  has  been 
breached  in  many  places  by  small  streams  flowing  to  the  east.  The 
rim  of  the  syncline,  especially  near  the  north  end,  is  not  continuous 
and  topographically  is  not  so  conspicuous  as  Third  Hill  Mountain, 
