eckel.] QUARRYING AND MINING. 41 
METHODS AND COST OF EXCAVATING RAW MATERIALS. 
The natural raw materials used in Portland-cement manufacture are 
obtained by one of three methods: (1) Quarrying, (2) mining, and (3) 
dredging. The method will depend partly on the physical character 
of the material and partly on the topographic and geologic conditions. 
Usually, however, there is no opportunity for choice, as one of the 
methods will offer the only possible mode of handling the material. 
The three different methods of excavation will first be briefly con- 
sidered, after which the cost of raw materials at the mill will be 
discussed. 
Quarrying. — In the following pages the term "quarrying" will 
include all methods of obtaining raw materials from open excavations — 
quarries, cuts, or pits — whether the material be a limestone, a shale, 
or a clay. Quarrying is the most natural and common method of exca- 
vating the raw materials for cement manufacture. If marl, which is 
usually worked by dredging, be excluded from consideration, it is 
probably within safe limits to say that 95 per cent of the raw mate- 
rials used at American Portland-cement plants is obtained by < (Har- 
rying. If marls be included, the percentages excavated by the 
different methods would probably be about as follows: Quarrying, 88 
per cent; dredging, 10 per cent; mining, 2 per cent. 
In the majority of limestone quarries the material is blasted out and 
loaded by hand onto cars or carts. In a few limestone quarries a 
team shovel is employed to do the loading, and in shale quarries the use 
bf steam shovels is more frequent. In certain clay and shale pits, 
where the materials are of suitable character, the steam shovel does 
ill the work, both excavating and loading the raw materials. 
The rock is usuall} 7 shipped to the mill as quarried, without any treat- 
ment except sledging it to convenient size for loading. At a few 
juarries, however, a crushing plant is installed, and the rock is sent 
jis crushed stone to the mill. At a few quarries driers have been 
nstalled, and the stone is dried before being shipped to the mill. 
Except the saving of mill space thus attained, this practice seems to 
(lave little to commend it. 
'Mining. — The term "mining" will be used, in distinction from 
quariwing," to include methods of obtaining any kind of raw mate- 
rial by underground workings, through shafts or tunnels. Mining is, 
)f course, rarely employed in excavating substances of such low value 
3er ton as the raw materials for Portland-cement manufacture. Occa- 
sionally, however, a thin bed of limestone or shale will be overlain by 
such a thickness of other strata that mining will be cheaper than strip- 
ping and quarrying. 
Mining is considerably more expensive than quarrying, but it has a 
few advantages that serve to counterbalance partly the greater cost per 
