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forms; for instance, the various kinds of 

 marble and chalk are carbonates of lime. 

 The composition of marble and chalk is 

 exactly the same as that of limestone. The 

 difference is chiefly one of molecular 

 rather than chemical structure. Marble 

 is what chemists would call an allotropic 

 or changed form of limestone; and, as be- 

 fore stated, the difference seems to consist 

 in the fact that the marble assumes a crys- 

 talline arrangement of its atoms and will 

 therefore take a high polish, which is not true 

 of ordinary limestone. Marble varies greatly 

 in coloring and texture, all of which differ- 

 ences are explainable under the one head of 

 molecular arrangement. Nearly pure carbon 

 exists in three distinct forms the diamond, 

 graphite, and charcoal. As is the case with 

 marble, these differences in the different forms 

 of carbon are not chemical, but molecular 

 differences. The substances are the same, but 

 their infinitesimal particles are differently ar- 

 ranged. 



Carbonate of lime as it exists in its vari- 

 ous forms, as limestone, from which lime and 

 cement are made, and marble, which is such 

 an important element in the arts is a sub- 

 stance of great importance to man. We have 

 already noted some of the processes that nature 

 uses in gathering up these substances from the 

 ocean by the employment of various forms of 



