MODE III. CLAY ROCK. 



MODE III. CLAY ROCK. 



Texture, of a fine earthy grain. Characters. 



Hardness, marmoric, sometimes gypsic. Frac- 

 ture, generally even, sometimes flatly conchoidal. 

 If slaty, it approaches to clay slate. Fragments, 

 amorphous, rather blunt. 



Weight, granitose. 



Lustre, dull. Opake. 



This is the thonstein of Werner, which forms 

 large rocks, and is the base of his clay por- 

 phyry, which will be described among the Ar- 

 gillaceous Intrites. 



In some countries, such as the Salses of Mo- 

 dena, in the Crimea, and near Girgenti in Sicily, 

 hills and masses of indurated clay are produced 

 by a singular cause, the eruption of what are 

 called muddy volcanoes. Dolomieu has mi- 

 nutely described that of Macaluba, near Gir- Macaluba, 

 genti. A circular mountain, about 150 feet in 

 height, is terminated by a plain somewhat con* 

 vex, and about half a mile in circumference, 

 which is surmounted by a great number of trun- 

 cated cones, with little craters like funnels. 

 The soil on which they rest is a grey dry floor, 

 which covers a wide and immense gulf of mud. 



