272 ON THE FORMATION OF ROCKS. (Jancr 



X. Sand beds, consisting of small particles of rocks round- 

 ed by friction or Attrition. 



2. Gravel beds, consisting of large particles of rocks, 

 ' rounded by friction or attrition. 



3. Clay beds, sediments by water, including Marie, and 



all sediments in impalpable powder. 



4. Sea- Salt, with all its attendants of ArgileTy G3rpsum, 



&c. 



5. Sandstone, particles of sand rotmded by friction, and 



cemented by calcareous or other infiltration into a 

 hard adhe'sive rock. 



6. Puddingstone, particles of gravel rounded by attrition, 



and cemented by the infiltrations of siliceous, calca- 

 reous, ferruginous, and other aqueous depositions,, 

 &c. 



7. Braunkohle Turf, or other bituminous or vegetable 



substances included in the beds of the above alluvial 

 rocks. 



8. Bog Iron Ore, Pyrites, 8s;c. included in the above al- 



luvial. 



9. Calcareous Tujfa, a coarse-grained deposition from a 



chemical dissolution in warm springs, &c. &c. from 

 a rapid and sudden precipitation. 



10. Calcareous deposition, chilled Travertina at Rome, from 

 a slower precipitation, by evaporation of water, per- 

 mitting it to take a compact and solid form. 



11. Silex from siliceous precipitations: slowly as in pe- 

 trified wood and other organic matter, w hich are solid 

 and compact, or suddenly as from the hot springs of 

 Iceland, where it is cellular and rather coarse-grained. 



The above-mentioned rocks are stratified horizontally, 

 following the inequality of the surface on w^hich they rest; 



