CHAPTER XXVIII. 

 EXCAVATING THE RAW MATERIALS. 



THE excavation of the raw materials is the first step toward the 

 actual manufacture of Portland cement, and the one concerning which 

 least has been published. Local conditions enter into this preliminary 

 phase to such an extent that few general statements can be made con- 

 cerning it. To a large extent, each separate deposit of raw material 

 is an individual proposition to be handled best in a way peculiar to 

 itself. The natural raw materials which are at present used in the 

 American Portland-cement industry are worked by one of three gen- 

 eral methods. These are: (1) quarrying or digging from open pits; 

 (2) mining from underground workings, and (3) dredging from deposits 

 covered by water. Occasionally the cement manufacturer will have 

 an opportunity to choose his general method of working the deposit, 

 in which case his choice will depend partly on the physical characters 

 of the material to be excavated and partly on the topographic and 

 geologic conditions. Usually, however, he will have no opportunity 

 to choose a method, for in any given case one of the methods will be 

 so evidently the only possible mode of handling the material as to leave 

 no room for other considerations. 



The three different general methods of excavation will first be briefly 

 considered, after which the cost of excavating various raw materials 

 will be discussed in some detail. 



Quarrying. 



In the following pages the term " quarrying" will be used to cover 

 all methods of obtaining raw materials from open excavations quarries, 

 cuts, or pits whether the material excavated be a limestone, a shale, 

 or a clay. Quarrying is the most natural and common method of 

 excavating 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 are obtained by quarry- 



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