144 



DOMAIN II. SILICEOUS. 



of sand, which covers a great part of the 

 globe, either alone or mixed with clay, that 

 late chemists infer that such sand arises not 

 only from the decomposition of rocks, but 

 is often a disturbed or hasty crystallisation 

 of silica*. This is further confirmed by the 

 circumstance that many primitive moun- 

 tains consist of granular quartz, of an arena- 

 ceous appearance, like agglutinated sand. 



The stones now called siliceous, were 

 formerly denominated verifiable; because, 

 with an alkali, they may be melted into 

 glass; and the finest Venetian glass was 

 fabricated from quartz, by the Italians 

 called tarso-f. Silica, like the other sim- 

 ple earths, is a fine white powder; but the 

 particles have a harsh feel, like minute 

 sand. Alone it is scarcely fusible; but 

 when newly precipitated, is soluble in 1000 

 parts of water. 



* The purity of this term may be doubted. Alumina is ridicu- 

 lous, being the plural of alumen. In the fabrication of new words 

 grammatical precision ought always to be studied. 



f In the Phil. Trans. 1683, Dr. Lister says tar so is the quartzose 

 sand of which the fine Venetian glass was made. The same inge- 

 nious author there proposes, p. 739, Mineral Maps of Counties, as 

 he calls them. 



