542  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,  1904.         [bull.  260. 
Mount  Jackson  and  New  Market. — Numerous  exposures  of  the 
argillaceous  limestone  may  be  seen  in  the  foothills  of  Short  Mountain, 
several  miles  east  of  Mount  Jackson,  and  also  in  the  immediate 
vicinity  of  New  Market.  Practically  the  same  thickness  of  rock  as 
that  shown  at  Woodstock  and  vicinity  is  shown  here,  while  the 
analysis  of  the  rocks  at  both  of  these  places  indicates  that  in  chemical 
composition  at  least  they  are  quite  similar  to  the  best  Lehigh  rock. 
Analysis  of  Trenton  limestone,  near  Mount  Jackson,  Va. 
Silica   (Si02) 18.20 
Alumina  (A1203)  and  iron  oxide  (Fe203) 8.00 
Lime  carbonate  (CaC03) 70.00 
Magnesium  carbonate   (MgCOa) 2.00 
Water  (H20) 3.00 
Western  edge  of  valley,  north  of  Staunton. — The  outcrops  of  the 
Trenton  limestone  along  the  western  edge  of  this  part  of  the  valley 
are  in  general  so  remote  from  railroads  that,  in  spite  of  the  excellent 
rock  shown  at  a  few  places,  exploitation  of  this  region  is  at  present 
useless.  Furthermore,  throughout  a  considerable  portion  of  this 
region  the  argillaceous  limestones  are  cut  out  by  overthrust  faulting, 
the  magnesian  limestone  resting  upon  the  shales  of  still  higher  for- 
mations. But  a  single  area  can  be  mentioned  in  which  the  cement 
rocks  are  exposed  within  a  reasonable  distance  of  a  railroad.  Several 
miles  north  of  Stokesville,  the  terminus  of  the  Chesapeake  and  West- 
ern Railroad,  and  a  few  miles  south  of  Little  North  Mountain,  good 
outcrops  of  the  rock  are  encountered.  The  quantity  and  quality  of 
these  limestones  are  such  that,  with  the  railroad  facilities  so  near  at 
hand,  the  rock  will  undoubtedly  prove  of  economic  importance. 
Shales  are  at  hand  for  mixture  with  the  cement  rock  when  its  per- 
centage of  lime  is  too  high,  while  pure  limestones,  to  increase  the 
percentage  when  necessary,  are  found  in  sufficient  quantity  in  the 
valley  just  to  the  east.  Indeed,  even  with  the  present  facilities,  this 
is  one  of  the  most  promising  cement  localities  in  the  valley. 
The  composition  of  an  average  sample  of  the  rock  is  shown  by  the 
f olloAving  analysis : 
Analysis   of  Trenton   limestone   from    an    exposure   several    utiles   north    of 
Stokesville,  Va. 
Silica    (Si02) 14.34 
Alumina  (A1203)  and  iron  oxide  (Fe203) 6.49 
Lime  carbonate  (CaC03) 73.  14 
Magnesium  carbonate   (MgCOs) 2.90 
Water  (H20) 4.00 
Mount  Sterling  and  vicinity. — From  Staunton  to  Mount  Sterling 
and  thence  for  several  miles  northeast  the  Valley  Branch  of  the  Bal- 
timore and  Ohio  Railroad  either  closely  parallels  or  cuts  through 
