GEOLOGY. 293 



and it is naturally a plastic mass, -which, even when the grains of quartz 

 are large, can be worked by the wheel or hand, or moulded with ease. 

 Vessels can be formed of it so thin that the grains of quartz in their 

 size limit the thickness only. This porcelain earth differs from all the 

 varieties of pipe-clay, in containing its silicate of alumina in the form 

 of scales, imbued with silicate of potash and soda in minute quantity, 

 which causes solidification by heat, with only slight contraction of 

 the mass. Pipe-clays, besides silicate of alumina, contain hydrate 

 of alumina, and never solidify without great contraction, and do not 

 afford solid masses, unless largely mixed with sand or previously 

 baked clay. These essential differences are seen in the porcelain 

 wares and common queen's ware. The clay washed out from the 

 quartz of the granite fire-clay forms excellent porcelain paste or 

 fine crucible ware. An average obtained from several hundred pounds 

 of the clay afforded 52 parts quartz, 48 kaolin, in 100 parts. An- 

 other sample, 55 quartz, 45 kaolin. The quartz grains are singu- 

 larly roughened by cavities and irregularities, so that the kaolin 

 embraces them with great cementing power. The moist mass resem- 

 bles solid granite ; when dry, it becomes a crumbling earth, having 

 specific gravity of 2.602. 100 parts of the mass dried in the air lost, 

 after exposure to a violent heat, only 3.6-10 parts. No indications of 

 fusion took place at the melting point of iron, and, in small samples, 

 platina melted without fusing the clay. Its color becomes nearly white 

 by heat, indicating that the iron sand does not burn. 



A comparison with the best known and most highly esteemed fire- 

 clays in the world is here given. 



Granite Clay. Stourbridge. Strasburg. 



Silica, 63.00 ' . . 63.70 . . 66.70 



Alumina, 29.00 . . 20.70 . . 18.20 



Potash, &c., 1.20 . .60 



Water, 6.00 . . 10.00 . . 12.00 



Ox. Iron, &c., .52 . . 4.50 . . 1.50 



It will be thus seen that the granite fire-clay contains, for its plastic 

 material, a true apyrous or fire-resisting clay. The quartz with which 

 it is mixed naturally, represents so much more silica, which is infusible 

 in any furnace-fire ; and, considering such a mixture as composed of 50 

 dry kaolin and 55 quartz, we have a composition of 83.50 silica, and 

 15.40 alumina, as the essential constituents of the fire-bricks. Excel- 

 lent crucibles for blast furnaces, it is well known, are made^ from, 

 silecious sandstone, presenting nearly the same amount^ of silica in 100 

 parts. As these stones resist the corroding action of iron oxides and 

 slags, it is a reasonable conclusion that the granite fire-clay will have 

 greater power of endurance, when exposed in the same way. It may, 

 when moist, be applied to hot surfaces, where it adheres, and for 

 repairs and linings to heated parts it is well adapted. 



ON THE MEERSCHAUM FORMATION OF ASIA MINOR. 



THE following is an abstract of remarks made before the American 

 Association, Albany, by Dr. J. Lawrence Smith, late Geologist to the 



25* 



