PART II. LIMES. 



CHAPTER VI. 



COMPOSITION, ORIGIN, AND GENERAL CHARACTERS OF 



LIMESTONES. 



LIMESTONE is the raw material on which is based the manufacture 

 of lime, and it is also the most important ingredient, in one form or 

 another, in a Portland-cement mixture. Further, impure limestones 

 of certain types are employed in the manufacture of hydraulic limes 

 and natural cements. It will thus be seen that limestone plays a very 

 important part in the manufacture of nearly all the cementing materials 

 discussed in this volume, only the plasters (Chapters I-V) being manu- 

 factured without its use. 



For this reason it has seemed desirable to discuss in the present 

 chapter the origin, composition, varieties, and chemical and physical 

 characters of limestone in general. This has been done in considerable 

 detail. The present chapter will therefore serve as an introduction 

 not only to the limes but to the hydraulic limes and the natural and 

 Portland cements. More detailed statements concerning the special 

 kinds of limestone required in the different industries will be found in 

 the sections on those industries, particularly in Chapters XXIII-XXV of 

 the section on Portland cement. 



Origin of limestones.* Limestones have been formed largely by 

 the accumulation at the sea-bottom of the calcareous remains of such 

 organisms as the foraminifera, corals, and moljusks. Many of the thick 

 and extensive limestone deposits of the United States were probably 

 deep-sea deposits formed in this way. Some of these limestones still 

 show the fossils of which they were formed, but in others all trace of 



* For a more detailed discussion of this subject the reader will do well to 

 consult Chapter VIII of Prof. J. F. Kemp's "Handbook of Rocks". 



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