LIMESTONES. 363 



Monocacey, of which the* columns in the Hall of Represen- 

 tatives at Washington. 



Porphyry conglomerates, basaltic conglomerates, pumiceous 

 conglomerates, consist respectively of pebbles or fragments of 

 porphyry, basalt, pumice. 



Tufa is a sandrock consisting of volcanic material, either 

 cinders or the comminuted lavas. Pozzuolana is a kind of 

 tufa found in the vicinity of Rome, Italy. It consists of 

 silica 34'5, alumina 15, lime 8*8, magnesia 4*7, potash 1*4, 

 soda 4*1, oxyds of iron and titanium 12, water 9*2. Pepe- 

 rino is a coarse sandrock, made up of volcanic cinders or 

 fine fragments of scoria, partially agglutinated. 



LIMESTONES. 



Limestones consist essentially of carbonate of lime, and 

 belong to the species calcite, (p. 115,) or of the carbonates of 

 lime and magnesia. They are distinguished by being easily 

 scratched with a knife, and by effervescing with an acid. 

 They are either compact or granular in texture : the com- 

 pact break with a smooth surface, often conchoidal ; the 

 granular have a crystalline granular surface, and the fine 

 varieties resemble loaf sugar. 



Granular limestone. The finest and purest white crystal 

 line limestones are used for statuary and the best carving, 

 and are called statuary marble. A variety less fine in texture 

 is employed as a building material. Its colors are white, and 

 clouded of various shades. It often contains scales of mica 

 disseminated, and occasionally other impurities, from which 

 the cloudings arise. 



The finest statuary marble comes from the Italian quarry 

 at Carrara ; from the Island of Paros, whence the name 

 Parian ; from Athens, Greece ; from Ornofrio, Corsica, of 

 a quality equal to that of Carrara. The Medicean Venus 

 and most of the fine Grecian statues are made of the Parian 

 marble. These quarries, and also those of the Islands of Scio, 

 Samos and Lesbos, afforded marble for the ancient temples of 

 Greece and Rome. The Parthenon at Athens was con- 

 structed of marble from Pentelicus. 



Statuary marble has been obtained in the United Sates, 

 but not of a quality equal to the foreign. Good building 

 material is abundant along the Western part of Vermont, 

 and south through Massachusetts to Western Connecticut 

 and Eastern New York. In Berkshire county, Mass., mar* 



