460  CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   1903.  [bull. 225. 
the  relatively  high  ratio  of  silica  to  iron  and  alumina,  which  would 
tend  to  increase  the  refractory  character  of  the  clinker  and  reduce  the 
output,  is  offset  by  the  extremely  finely  divided  condition  and  intimate 
mixing  of  the  material  as  naturally  developed.  It  is  noted  that  one  of 
these  beds  closely  approaches  in  composition  the  celebrated  French 
hydraulic  lime. 
Near  Indian  Rock  on  the  James  River  division  of  the  Chesapeake 
and  Ohio  Railroad  there  is  one  of  the  largest  pure  limestone  deposits 
in  Virginia.  The  topographic  conditions,  however,  are  very  unfavor- 
able, and  there  are  no  known  deposits  of  shales  or  clay  readily 
accessible. 
At  Eagle  Mountain,  on  the  James  River  division  of  the  Chesapeake 
and  Ohio  Railroad,  is  a  large,  but  localized,  deposit  of  good  limestone. 
The  black  shales  of  the  Devonian,  which  have  been  shown  to  be 
suitable  for  such  purposes,  and  which  are  well  developed  just  through 
the  gap  at  the  mouth  of  Craig  Creek,  could  be  utilized  in  combination. 
A  most  admirable  site  could  be  gotten  at  Bessemer,  which  is  at  the 
end  of  the  Craig  Valley  Branch. 
The  only  Portland  cement  manufactory  of  note  which  has  been  well 
established  in  the  State  is  the  plant  of  the  Virginia  Portland  Cement 
Company,  located  at  Craigsville,  a  description  of  which  by  F.  H. 
Lewis  will  be  found  in  "The  Cement  Industry."  The  conditions  there1 
are  typical  of  a  number  of  places  either  on  or  near  the  Chesapeake 
and  Ohio  Railroad.  These  conditions  do  not  seem  to  be  duplicated 
farther  south  on  the  line  of  the  Norfolk  and  Western.  The  beds 
which  go  to  make  up  No.  6  Rodgers,  the  lower  Helderberg  limestone, 
are  well  developed  there  in  the  following  order  measured  from  below: 
Section  near  Oraigsville. 
Feet. 
1.  Layer  heavy  fossiliferous  limestone  passing  into  sandstone. 
2.  Very  dark  slaty  siliceous  limestone 10 
3.  Gray  fossiliferous  limestone 10 
4.  Dark,  irregular  siliceous  magnesian  limestone 2  to  20 
5.  Gray,  soft,  highly  fossiliferous  limestone 30  to  50 
6.  Dark,  close-grained  limestone  of  varying  thickness  and  carrying  varying 
quantities  of  flint. 
The  most  important  beds  of  this  series  and  the  ones  which  would  be 
used  in  the  manufacture  of  Portland  cement  are  (3)  and  (5).  The 
principal  facts  to  be  determined  are  the  extent  and  decomposition  of 
the  superimposed  layers,  and  therefore  the  ease  and  cheapness  with 
which  (3)  and  (5)  can  be  secured.  The  black  slates  of  the  Devonian 
everywhere  fill  the  valleys  in  this  section  and  afford  very  excellent 
material  to  combine  with  the  limestone.  The  following  analyses  are  I 
of  the  limestones  and  slates  taken  from  the  property  adjoining  that  of 
the  Virginia  Portland  Cement  Company: 
