Chemistry. [Lecture 80. 



earth is soluble in water, and deposited in the 

 bodies of other substances. The quantity of 

 earth, however, contained in the water is very 

 small, and for that reason the petrifactions are 

 formed very slowly. 



4. The shells of all crustaceous animals, from 

 the coarsest to the pearl which lines the shell of 

 an oyster, are all composed of carbonate or phos- 

 phate of lime, and perhaps a small quantity of 

 gelatine or animal glue, a viscid fluid, which at first 

 issues from the body of the animal, and at last ac- 

 quires great hardness. Egg-shells are nearly of the 

 same nature, as well as those marine bodies which, 

 from their hardness and vegetable appearance, 

 are called stony plants : such, indeed, are all the 

 species of coral, which are the work of small ani- 

 mals of the polypus kind. 



5. Marls, which are generally divided into 

 three kinds: 1. The shell marl; 2. Clay marl; 

 3. Stone marl. The first is found in beds of 

 considerable extent, and consists of the remains 

 of sea and land shells : that which consists of sea 

 shells is generally found in the greatest quantity. 

 Of this kind is that of Paris, mentioned by M. 

 Reaumur, which is about ten feet deep, and of 

 great extent, consisting of oyster and other sea 

 shells. The relics of land shells are those of 

 snails: they have probably been carried off by 

 the current of some water, which being drained 

 off, the shells remain behind. Beds of fresh water 

 shells are also found. Clay marl is a calcareous 



