basslek:]         CEMENT    MATERIALS    OF    VALLEY    OF    VIRGINIA.  539 
indications  of  these  marls  arc  usually  so  meager  that  no  estimate  of 
their  quantity  or  extent  can  l>e  determined  from  these  alone. 
GENERAL   DISTRIBUTION    OF    ARGILLACEOUS    TRENTON    LIMESTONE. 
On  account  of  the  geologic  structure  of  the  valley  the  argillaceous 
limestones  are  found  in  three  well-defined  belts.  Two  of  these  belts 
are  formed  by  the  outcropping  edges  of  the  syncline  forming  Mas- 
sanutten  Mountain,  while  the  third  follows  the  western  edge  of  the 
valley.  P^xposures  of  the  easternmost  belt  are  found  at  numerous 
places  along  a  northeast-southwest  line  from  a  point  about  5  miles 
east  of  Woodstock  to  Fisherville.  The  next  belt  to  the.  west  parallels 
this  and  shows  many  outcrops  along  a  similar  line  from  Woodstock 
to  Staunton.  At  several  places  along  these  lines  of  outcrop  the 
argillaceous  limestone  is  missing.  The  most  pronounced  areas  where 
this  has  been  observed  are  (1)  the  region  just  south  of  Massanutten 
Mountain,  with  McGaheysville  on  the  eastern  edge,  and  (2)  the  area 
south  of  Staunton,  bounded  by  Staunton,  Barter  Brook,  and  Fisher- 
ville. 
The  third  belt  occurs  along  the  western  edge  of  the  valley  and 
parallels  the  other  two.  Here,  however,  these  limestones  are  often 
cut  out  by  the  great  overthrust  fault  of  this  portion  of  the  valley. 
In  this  section  the  best  exposures  of  these  rocks  are  found  along  the 
eastern  edge  of  Little  North  Mountain,  especially  in  the  vicinity  of 
Dry  River,  north  of  Stokesville.  The  valley  proper,  as  has  been 
remarked  before,  is  usually  occupied  by  the  dolomitic  limestones,  but 
occasionally  synclines  exposing  the  argillaceous  limestones  and  shales 
are  found.  The  most  important  of  these  from  an  economic  stand- 
point occurs  just  west  of  Harrisonburg.  In  the  vicinity  of  Lexington 
and  Natural  Bridge  the  Trenton  limestones  have  been  compressed  into 
close  folds  and  occupy  considerably  wider  areas  than  farther  north. 
The  most  important  of  these  areas  is  that  in  which  Lexington  is 
located,  the  rest,  as  a  glance  at  the  map  will  show,  being  too  far  away 
from  railroad  facilities. 
DETAILS  OF  LOCALITIES. 
Below  are  briefly  discussed  the  more  favorable  localities,  showing 
good  exposures  of  the  argillaceous  limestone,  from  Woodstock,  in 
the  northernmost  part  of  the  valley  visited,  to  the  vicinity  of  Natural 
Bridge.  In  indicating  advantageous  sites  for  cement  plants,  the 
writer  means  simply  to  imply  that  the  cement  rock  and  pure  lime- 
stone deposits  occur  at  the  places  mentioned,  and  that  the  transporta- 
tion and  other  necessary  facilities  are  at  hand.  Whether  a  good 
cement  can  be  made  from  the  raw  materials  found  at  these  places  is 
a  matter  which  can  be  determined  only  by  experimentation  on  a 
