'290 ON THE FORMATION OF ROCKS, [Juivy 



aggregate of sand and calcareous matter, regembling 

 the calcareous tuffa of the first order of Neptunian 

 rocks, or a kind of indurated marie, not much different 

 in some places from chalk. 



15. ChalJc formation is analogous in structure 

 and component parts to the disposition and precipita- 

 tions of Nos. 3 and 9 of the ^^st order of Neptunian 

 rocks ; it contains calcareous and siliceous petrifactions 

 of organic matter, with pyrites, as in Nos. 8 and 11, so 

 that it unites most of the different modes of precipita* 

 tion, and deposition, we have observed to be followed 

 by nature in the formation of rocks of the first order ; 

 except the aggregates of particles rounded by attri- 

 tion. 



Its situation is generally in flat or level countries, 

 seldom or never found in mountainous, occupies in ge- 

 neral extensive fields, as from the east part of Cham- 

 paigne in France, to near Bath in England ; and from 

 Flanders to the vicinity of Orleans ; with some inter- 

 ruptions common to most formations. It is seldom or 

 never found alternating with compact limestone, or 

 with coal, or sea salts. Iron seems as yet the only 

 metal it contains, and it is seldom or never found al- 

 ternating with any kind of shist, or having any dis- 

 tinct or uniform stratification. 



16. Compact Limestone resembles in structure 

 and component parts No. 10 of the first order : it con- 

 tains shells and organic remains of animals found at pre- 

 sent to exist only in water, and of course it is by direct 

 analogy of Neptunian origin. 



