GLASS-SAND    INDUSTRY    OF    INDIANA,  KENTUCKY,   AND    OHIO.       365 
which  lie  18  to  24  inches  of  surface  clay.  Owing  to  the  scarcity  of 
outcrops  and  the  thinness  of  the  beds  the  sandstone  of  the  Niagara 
formation  can  hardly  be  regarded  at  present  as  a  very  valuable 
source  of  glass  sand  in  this  region. 
Devonian. — Rocks  of  Devonian  age,  like  those  of  Silurian  age,  are 
covered  by  thick  drift  where  they  occur  in  the  northern  part  of  Indiana, 
but  farther  south  are  more  favorably  situated.  In  the  vicinity  of 
Pendleton,  28  miles  northeast  of  Indianapolis,  there  is  a  massive,  soft, 
white  sandstone,  varying  in  thickness  from  7  to  15  feet.  This  sand- 
stone is  sufficiently  pure  for  use  as  a  glass  sand  and  has  been  quarried 
as  such  at  Pendleton,  but  in  general  has  not  proved  thick  enough 
for  successful  exploitation. 
Carboniferous. — Sandstone  and  shale  of  Pennsylvanian  age  con- 
stitute the  country  rock  of  the  southwest  part  of  Indiana  from  Ohio 
River  northward  to  Benton  County,  for  a  distance  of  200  miles,  in 
which  they  outcrop  to  a  width  varying  from  2  to  3  miles  at  the  north 
and  reaching  75  miles  at  the  south.  These  rocks  dip  westward,  or 
a  little  south  of  west,  so  gently  that  locally  they  are  nearly  horizontal. 
Active  quarries  at  Wolcott,  White  County;  Loogootee,  Martin 
County,  and  Coxville,  Parke  County,  are  in  Pennsylvanian  rocks,  the 
first  two  being  in  the  Mansfield  sandstone. 
The  Mansfield  sandstone,  or  "  Millstone  grit,"  the  basal  conglom- 
eratic sandstone  of  the  Pennsylvanian  series,  doubtless  is  more 
important  to  the  glass-sand  industry  than  any  other  formation  in  the 
State.  It  varies  greatly  in  texture,  color,  and  thickness.  Locally 
it  is  a  coarse  conglomerate,  which  grades  into  a  coarse  sandstone,  and 
in  places  it  consists  of  alternating  sandy  and  pebbly  strata.  The 
sandstone  may  be  massive  or  thin  bedded,  and  at  many  places  it 
shows  cross-bedding.  The  rock  is  mostly  rather  friable,  but  along 
bedding  planes,  in  places  where  it  is  cemented  by  ferric  oxide,  it 
becomes  very  hard.  It  comprises  hollow  nodular  masses  and  thin 
streaks  of  limonite  and  thin  streaks  of  carbonaceous  matter  in  all 
stages  of  alteration,  from  decomposed  woody  matter  to  bituminous 
coal,  and  these  are  accompanied  by  seams  of  fire  clay.  The  color  of 
the  rock,  where  freshly  broken,  ranges  from  white  and  light  gray, 
through  buff,  yellow,  and  brown,  to  red.  The  outcrop  area  of  the 
formation  is  about  12  miles  wide  from  west  to  east  in  Martin  County, 
where  the  rock  is  well  exposed  by  the  drainage  system  of  East  Fork 
of  White  River.  The  beds  strike  in  general  N.  12°  W.,  and  a  strip 
running  15  miles  wide  extends  in  Indiana  from  Ohio  River  at  Can- 
neltown,  Perry  County,  for  about  180  miles  north-northwest  into 
Benton  County,  where  it  becomes  hidden  by  consolidated  gravels, 
clays,  and  soils  of  Quaternary  age.  The  Mansfield  sandstone  occurs 
in  Benton,  Jasper,  Owen,  Monroe,  Greene,  Lawrence,  Martin,  Daviess, 
Orange.  Dubois,  Crawford,  Perry,  and  Spencer  counties.     Owing  to 
Bull.  315—07 24 
