KASSLKK.  i 
CEMENT    MATERIALS    OF    VALLEY    OF    VIRGINIA. 
535 
On  account  of  the  high  percentage  of  magnesia  these  limestones  are 
of  no  value  for  the  manufacture  of  Portland  cement,  but  their  com- 
position does  not  preclude  their  use  in  the  making  of  natural  cement. 
For  many  years  natural  cement  has  been  burned  from  the  magnesian 
limestones  of  the  lower  part  of  this  division  at  the  plant  at  Glasgow, 
Rockbridge  County.  The  product  from  this  plant  was  used  in 
building  the  locks  of  the  James  River  and  Kanawha  Canal.  The 
following  analyses  of  this  rock  show  its  usual  range  in  composition : 
[nali/sis  of  uidf/iirsidii  limestone.  Glasgoic,  Va. 
Silica  (SiO,)  _... 
Alumina  (A1203)  - 
Iron  oxide  (Fe2Os) 
Lime(CaO)-- 
Magnesia  (MgO) . 
17.21 
Tr. 
1.62 
24.85 
16.58 
Carbon  dioxide  (CO.,) 37. 95 
17.38 
[■      7.  SO 
34.  23 
9.  51 
30.40 
1.   C.  L.  Allen,  analyst.     The  Virginias,  vol.  3,  p.  88. 
'2.   E.   C.   Boynton,  analyst.     Gillmore  :   Limes,  Cements,  and  Mortars,  p.   125. 
Occasionally,  however,  strata  of  pure  limestone  will  be  found 
interbedded  with  the  more  typical  magnesian  rock,  and  it  is  in  this 
occurrence  that  the  formation  will  prove  of  value  in  the  manufacture 
of  Portland  cement.  Such  strata  have  been  observed  in  various 
parts  of  the  valley,  but  their  occurrence  is  more  or  less  sporadic. 
Because  of  this,  and  also  on  account  of  the  geologic  structure  of  the 
entire  formation  and  the  small  percentage  of  pure  limestones,  these 
nonmagnesian  strata  can  not  be  definitely  mapped  and  must  be 
determined  by  experiment  in  the  field.  In  New  Jersey  and  Pennsyl- 
vania the  same  arrangement  of  a  few  strata  of  nonmagnesian  lime- 
stones interbedded  with  a  great  series  of  highly  magnesian  limestones 
obtains,  and  the  former  is  the  source  of  part  of  the  limestone  used 
in  the  Lehigh  district  to  bring  the  cement  rock  up  to  the  required 
percentage  of  calcium  carbonate.  Near  Annville,  Pa.,  these  non- 
magnesian limestones  occur  in  greater  quantities  than  usual,  and 
much  is  quarried  for  shipment  to  cement  plants.  The  following 
analyses  of  this  rock  are  introduced  for  comparison  with  the  Vir- 
ginia pure  limestones : 
