TAB. XXXIX. and XL. 



S I L E X arenacea. 

 Siliceous Sandstone. 



Class 2, Earths. Ord. 3. Aggregated, 

 Gen. 6. Silex. Spec. 2. Grains of Silex more or less agglutinated,, 



Div. 3. Amorphous. 



Spec. Char. Fracture granular. 



Syn. Siliceous sandstones. Kiriv. v. 1. 364. 



Cos friabilis. Linn. Syst. v. 3. p. 63. 9» 



— coagmentata. Linn. Syst. v. 3. p. 63. 10. 



Quartz arenacee agglutinee, ou Gres. Haiiy, v. 4. 

 , 464. 



Sandstones may be said to be composed chiefly of quartz 

 in smaller or larger particles, which, according to Kirwan, 

 should not exceed one third of an inch in diameter. In the 

 representation of such as are not primitive sandstones, it is 

 thought of much utility to put those which have impres- 

 sions on their surfaces of plants, shells, or other things for- 

 merly organized, that while we acquire a common idea of 

 the substance, it may help geological purposes, which will 

 be found extremely essential in mineralogy, as it leads to the 

 sera of formation of different strata, distinguishing by such 

 helps the more recent from the most remote. 



