Stratified Rocks. 1 3 



rocks the particles are partly cemented by oxides of iron, 

 in others by carbonate of lime. Minor beds of limestone 

 are often formed on land from calcareous springs. Marine 

 strata, formed of limestone, in the Adriatic, were found 

 by Marsilli to be consolidated a foot beneath the surface. 

 A great many rocks contain more or less carbonate of 

 lime, and .along with this, or alone, many others 

 contain silicates of soda or potash. These are soluble 

 in carbonic acid, and entering into new combinations 

 the whole becomes petrified. During these processes 

 shells, echini, corals, bones, teeth, and scales of fish and 

 of marine mammals, &c., are imbedded and cased in 

 stone, and in a less degree terrestrial plants and animals 

 are floated into lakes and estuaries, and occasionally 

 out to sea, where those parts that escape decay and pre- 

 daceous fish may become fossilised. 



If we examine the stratified rocks that form the 

 land, we very soon discover that a large proportion of 

 them are arranged in thin layers or thicker bands or 

 beds of shale, sandstone, conglomerate, and limestone, 

 more or less pure ; for shales are sometimes sandy, sand- 

 stones sometimes shaly, and most conglomerates have a 

 sandy and sometimes a shaly or marly base in which the 

 FIG. i. 



pebbles are embedded, while limestones occur of every 

 degree of impurity. These must have been formed in 

 a manner analogous to that which I have just described, 

 proving that such beds have been deposited as sedi- 

 ments from water. Take, for instance, a possible cliff 



