!L.] 
1'ENNSYLVANMA. 
289 
[uarries usually show rock carrying from 70 to 80 per cent of lime 
larbonate. The mills in this vicinity, therefore, require practically 
10 pure limestone, as the quarry rock itself is sufficiently high in lime 
arbonate for the purpose. Indeed, it is at times necessary for these 
lants to add clay or slate instead of limestone to their cement rock 
n order to reduce its content of lime carbonate to the required figure. 
I general, however, it may be said that Lehigh practice is to mix a 
ow-carbonate cement rock with a relatively small amount of pure 
imestone, and analyses of both these materials, as used at various 
lants in the district, are given below. 
Analyse* of materials used in the Lehigh district. 
iliea (Si0 2 ) ■ 
|(imina (A1 2 3 ) 
•on oxide (Feo0 3 ) ... 
me carbonate 
(CaC0 3 ) 
agncsium carbonate 
(MgCOa) 
Cement rock. 
i .">.().". 19.06 
9.02 1.11 
1.14 
1.27 
70.10 
3.96 
69. 24 
4.21 
19. 08 
7.92 
67.07 
4.06 
7.24 
.92 
63.45 
4.56 
13. 80 
6.08 
76. 08 
4.51 
9. 52 
4.72 
80.71 
4. 92 
19. 62 
5.68 
69. 78 
4.90 
14.20 
6.11 
74.30 
3.24 
Pure limestone. 
2. 14 
1.46 
94. 35 
2.18 
3.02 1.98 
I.'.mi .70 
92.05 95.19 
:;. (il , 2.03 
CHARACTER AND COMPOSITION OF TIIK CEMENT ROCK. 
The cement rock is a dark-gray to black slaty limestone, breaking 
7ith an even fracture into flat pieces, which usually have smooth, 
listening surfaces. As the percentage of lime carbonate in the rock 
acreases — i. e., as the lower beds of the formation are reached — the 
olor becomes a somewhat lighter gray, and the surfaces of the frag- 
ments lose their slaty appearance. 
The range in composition of the cement rock as used at various 
lants is well shown in the first eight columns of the above table, 
^he nearer the material from any given quarry or part of a quarry 
pproaches the proper Portland-cement composition (say 75 to 77 per 
ent lime carbonate) the less addition of pure limestone will be neces- 
ary. In by far the greater part of the district, as above noted, the 
ement rock is apt to run about 65 to 70 per cent of lime carbonate, 
herefore requiring the addition of a proportionate amount of lime- 
tone. Most of the quarries near Bath and Nazareth, however, have 
ieen opened on beds of cement rock running considerably higher in 
ime carbonate, and occasionally running so high (80 per cent, etc.) as 
o require the addition of shale or clay rather than of pure limestone. 
CHARACTER AND COMPOSITION OF THE PURE LIMESTONES. 
The pure limestones added to the cement rock are commonly gray, 
nd break into rather cubical fragments. The fracture surfaces show 
Bull. 243—05 19 
