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statuary it is, of course, of special value. The name " marble "" 

 may be given to any limestone which is sufficiently close in texture 

 to admit of being polished. The beautiful lustre of statuary 

 marble is due to the way it reflects light. This is able to penetrate 

 a short distance into the stone, since the individual calcium car- 

 bonate crystals are transparent, and it suffers reflection at the sur- 

 faces of crystals lying at a deeper level. Amongst the most cele- 

 brated marbles are the following : — Pentelic marble was the 

 material in which the ancient Greek sculptors, Phidias and 

 Praxiteles, worked. The Elgin Marbles now in the British 

 Museum may be taken as examples. Parian marble from the Isle 

 of Paros was also used by the Greeks. Carrara marble from the 

 Apuan Alps, an offshoot of the Appenines, was used by Michael 

 Angelo and is a favourite of present day sculptors. Veined and 

 mottled marbles, although unsuited for statuary, are much valued 

 for architectural purposes. The markings may be due to the pre- 

 sence of fossils or to the infiltration of water charged with colour- 

 ing matters, such as compounds of iron and manganese. Black 

 marbles owe their colour to the presence of bituminous matter or 

 other carbonaceous substances. Some stones technically known as 

 marbles are stalagmitic in origin. The Algerian onyx-marble is 

 one of the most beautiful of these. It was used centuries ago both 

 in Rome and in Carthage, but the secret of its source was long 

 lost; the quarries were, however, rediscovered in 1849. Marbles 

 of similar character are found in Mexico and California. It was 

 probably to marble of this kind, essentially calcium carbonate 

 deposited from solution, that the name Alabaster was originally 

 applied. The word now stands for certain valuable kinds of 

 calcium sulphate, chemically a quite different substance. While 

 speaking of marbles it may be well to refer to the ancient game 

 known by that name. The little spheres now used for the purpose 

 are made of clay or glass, but in the 18th century they were, some- 

 times at least, actually made of marble, chips of that materia! 

 being rounded in a special kind of mill. Some were made in 

 Derbyshire and other parts of England, but Nuremberg was the 

 centre of the industry. The name " ally " or " alley " applied to 

 marbles of superior quality as distinguished from the cheaper 

 " commonies " is said to be a diminutive of alabaster. Readers 

 of Dickens will remember the reference to " Alley-tors " in the 

 Pickwick Papers. 



So far we have only considered uses of native calcium car- 

 bonates which have undergone no preparation save that of cutting, 

 sawing, or otherwise shaping ; let us now go one stage further and 

 consider means for separating from chalk the impurities it con- 

 tains while not interfering with its chemical composition. Al- 

 though chalk is mainly composed of calcium carbonate it usually 

 contains a certain amount of what, for our purpose, may be 

 described as grit. If the chalk be ground with water and the milky 

 liquid poured off into another vessel, the grit will be left in the first 

 vessel, the finer particles remain in suspension somewhat longer 



