Among  the  various  later  Paleozoic  formations  there  are  four  which
develop  well  marked  sandstone  series.  These  are  the  Pottsville,  the
Pocono,  the  Monterey  and  the  Tuscarora.  None  of  these  have  been
worked  to  any  considerable  extent  as  building  stones,  because  of  the
lack  of  demand  and  transportation  facilities.
The  Pottsville  Formation. — The  Pottsville  is  the  lowest  division
of  the  coal  measures  and  forms  the  mountain  ridges  which  border  the
coal  basins.  It  consists  of  sandstone  and  conglomerates  interstrati-
fied  with  sandy  shales  in  which  thin  beds  of  coal  are  locally  developed.
The  sandstones  are  usually  coarse-grained  and  conglomeritic,  with
marked  evidences  of  cross-bedding  which  are  irregular  in  extent  and
distribution.  The  individual  pebbles,  frequently  very  small,  are  held
together  by  a  siliceous  cement,  which  indicates  great  durability  for  the
rock.  Unfortunately  such  a  cement  renders  the  working  of  the  stone
both  difficult  and  expensive.  It  is  probable  that  this  material  will
never  become  of  economic  importance  except  in  the  supply  of  local
demands  for  foundations,  steps  and  occasional  door  sills.
The  Pocono  Formation. — The  Pocono  formation  is  very  similar
to  the  Pottsville  and  consists  mainly  of  hard,  thin-bedded  flaggy  sand-
stones which  occasionally  become  sufficiently  conglomeritic  to  produce
confusion  between  the  two  formations.  The  sandstones  of  the  former
have  received  but  little  attention  and  have  been  used  only  occasion-
ally as  a  supply  for  flagging.  It  seems  quite  probable  that  as  the
demand  for  building  stones  increases  the  flags,  which  are  well  devel-
oped in  places,  may  come  to  be  of  some  importance.
The  Monterey  and  Tuscarora  Formations. — These  two  forma-
tions have  a  considerable  development  in  Allegany  and  Washington


MARYLAND  GEOLOGICAL  SURVEY.
VOLUME  II,  PLATE  XXIX.
Fig.  l.-MONOCAGY  AQUEDUCT,  WHITE  QUARTZITE  FROM  BELT'S  QUARRY.
Fig.  2.-SANDSTOXE  QUARRY,  POINT  OF  ROCKS,  FREDERICK  COUNTY.
