DOMAIN n. SILICEOUS. 



" This sand-stone effervesces with aquafortis 5 

 very weakly; but the effervescence may be in- 

 creased, if the acid in which it is put is heated ; 

 but which does not deprive it either of its co- 

 herence or its hardness, for it strikes fire, even 

 after this proof. The grains of fine sand and mi- 

 ca, of which this sand-stone is composed, must 

 then be united by a quartzy or argillaceous glu- 

 ten, and the calcareous particles which produce 

 the slight effervescence that was observed, be in- 

 filtrated, and deposed as a foreign body in its ex- 

 ternal pores. 



" I have seen in Italy antique works, which 

 were said to be basalt, but which appeared to me 

 of a kind of rock very similar to this, and conse- 

 quently very different from real volcanic basalts. 

 A statue of a child, that is shown in the gallery 

 of Florence under the name of Britannicus, and 

 which is said to be of basalt, is most likely of this 

 same kind of rock. I have had a piece of this 

 sand-stone worked ; and the kind of polish which 

 it has taken, perfectly resembles that of this sta- 

 tue."* 



sembles the green bricia of Egypt, as I am informed by an ingenious 

 French traveller. 

 * Sauss. 493. 



