226* DOMAIN II. SILICEOUS-. 



also been found in micaceous schistus, and at a 

 vast depth in many mines, may be well regarded 

 as belonging to this formation ; for it is well 

 known, that if the crystallisation be much dis- 

 turbed, the substance will descend in small irre- 

 gular particles. 



Siliceous sand-stones are far more uncommon 

 than the calcareous or argillaceous. The limits 

 of the chalk country in England are singularly 

 marked by large masses of siliceous sand-stone, 

 irregularly dispersed. Those of Stonehenge af- 

 ford remarkable examples of the size and nature 

 of those fragments, but the original rock has not 

 been discovered. Trap or basaltin often reposes 

 on siliceous sand-stone. 



STRUCTURE I. LARGELY GRANULATED. 



This division of course includes siliceous bricias 



and pudding-stones. The most eminent and sin- 



Bricia of gular of these occur in Egypt, in the celebrated 



Egypt. & 



universal bricia of the Valley of Cosseir, and in 

 the siliceous bricia of the same chain, in which 

 are imbedded those curious pebbles known by the 

 name of Egyptian jasper ; and which also some- 

 times contains agates. This last, from its colour * 

 .and decomposition, might perhaps be more pro- 

 perly classed among the Siderous Intrites; but 



