452 
CONTRIBUTIONS    TO    ECONOMIC    GEOLOGY,   1903. 
[BULL.  225. 
noted,  Jill  of  the  "  cement  rock"  is  derived  from  the  middle  part  of  the 
Trenton  formation,  where  the  beds  will  run  from  60  to  70  per  cent  of 
lime  carbonate.  The  pure  limestone  which  is  required  to  bring*  this 
material  up  to  the  necessary  percentage  of  lime  carbonate  (75  per  cent 
or  so)  is  obtained  either  from  the  lower  portion  of  the  Trenton  itself  ■ 
or  from  certain  low-magnesian  beds  occurring  in  the  Kittatinny 
formation. 
In  the  plants  located  near  Bath  and  Nazareth,  however,  the  practice 
has  been  slightly  different.  In  this  particular  area  the  cement-rock 
quarries  usually  show  rock  carrying  from  70  to  80  per  cent  of  lime 
carbonate.  The  mills  in  this  vicinity,  therefore,  require  practically  noj 
pure  limestone,  as  the  quarry  rock  itself  is  sufficiently  high  in  lime 
carbonate  for  the  purpose.  Indeed,  it  is  at  times  necessary  for  these] 
plants  to  add  clay  or  slate,  instead  of  limestone,  to  their  cement  rock, 
in  order  to  reduce  its  content  of  lime  carbonate  to  the  required  figure.; 
In  general,  however,  it  may  be  said  that  Lehigh  practice  is  to  mix  a| 
low-carbonate  cement  rock  with  a  relatively  small  amount  of  purei 
limestone,  and  analyses  of  both  these  materials,  as  used  at  various 
plants  in  the  district,  are  given  below. 
Analyses  of  materials  used  in  the  Lehigh  district. 
Silica  (Si02) 
Alumina  (AL03) 
Iron  oxide  (Fe203)  . . . 
Lime     carbonate 
(CaC03) 
Magnesium  carbonate 
(MgC03) 
Cement  rock. 
Per  ct. 
15.05 
9.02 
1.27 
70.10 
Per  ct. 
19.06 
4.44 
1.14 
69.24 
Per  ct 
19.08 
67.07 
4.06 
Per  ct. 
22.22 
)  7.24 
I     .92 
63.45 
4.56 
Per  ct, 
18.80 
6.08 
Per  ct. 
9.52 
4.72 
76.08  |  80.71 
4.51  !     4.92 
Per  ct. 
19.62 
5.68 
69. 78 
4.90 
Per  ct. 
14.20 
6.14 
74. 30 
3.24 
Pure  limestone. 
Per  ct. 
2.14 
1.46 
94.35 
2.18 
Per  ct. 
3.02 
1.90 
92. 05 
3.04 
Pi  ret. 
198 
.70, 
95. 11 
2.03 
Character  and  composition  of  the  cement  rock. — The  cement  rock  is  a  | 
dark-gray  to  black,  slaty  limestone,  breaking  with  an  even  fracture  I 
into  flat  pieces,  which  usually  have  smooth,  glistening  surfaces.  Asl 
the  percentage  of  lime  carbonate  in  the  rock  increases — i.  e.,  as  the! 
lower  beds  of  the  formation  are  reached — the  color  becomes  a  some-i 
what  lighter  gray,  and  the  surfaces  of  the  fragments  lose  their  slatjj 
appearance. 
The  range  in  composition  of  the  cement  rock  as  used  at  various- 
plants  is  well  shown  in  the  first  eight  columns  of  the  above  table! 
The  nearer  the  material  from  any  given  quarry  or  part  of  a  quarry 
approaches  the  proper  Portland-cement  composition  (say  75  to  77  per' 
cent  lime  carbonate)  the  less  addition  of  pure  limestone  will  be  neces- 
sary. In  by  far  the  greater  part  of  the  district,  as  above  noted,  the 
cement  rock  is  apt  to  run  about  65  to  70  per  cent  of  lime  carbonate, 
therefore  requiring  the  addition  of  a  proportionate  amount  of  lime- 
stone.    Most  of  the  quarries  near  Bath  and  Nazareth,  however,  have] 
