If,  for  any  reason,  a  greater  thickness  than  specified  is  made  by  the
Contractor,  no  extra  allowance  for  such  additional  thickness  will  be
made.
THIRD  COURSE.
MATERIAL.
The  third  course  of  macadam  construction  is  to  consist  of  trap  rock
screenings  varying  in  size  from  dust  to  1-inch  pieces.  Other  material
than  trap  rock  screenings  may  be  used  if  approved  by  the  Engrineer.
SPREADING.
After  the  second  course  of  No.  2  stone  has  been  rolled  and  completed
as  above  described,  the  screenings  are  to  be  spread,  but  in  no  case  are
screenings  to  be  used  until  the  second  course  has  been  thoroughly  rolled
and  compacted.  The  screenings  are  to  be  spread  dry  with  shovels  from
piles  alongside  the  road,  or  from  dumping  boards,  but  in  no  case  are  the*
screenings  to  be  dumped  directly  on  the  second  course.  The  quantity
of  screenings  used  is  to  be  such  as  will  just  cover  the  second  course.
WATERING   AND   ROLLING.
After  the  screenings  are  spread  they  are  to  be  sprinkled  with  water
from  a  properly  constructed  sprinkling  cart,  and  then  rolled  with  a
steam-roller  weighing  not  less  than  ten  tons.  The  amount  of  water
necessary  is  to  be  determined  by  the  Engineer.  The  rolling  is  to  begin  at
the  sides  and  to  continue  until  the  surface  is  hard  and  smooth  and  shows
no  perceptible  tracks  from  vehicles  passing  over  it.
If,  after  rolling  the  screenings,  the  No.  2  stone  appears  at  the  surface,
additional  screenings  shall  be  used  in  such  places.
The  rolling  and  watering  shall  continue  until  the  water  flushes  to  the
surface.  The  rolling  is  to  extend  over  the  whole  width  of  the  road  includ-
ing the  shoulders.
212  THIRD   REPORT    ON    THE    HIGHWAYS   OF   MARYULND


UNEVENNESS    AND    DEPRESSIONS.
