46 



With the phosphoric acid, an acid originating, perhaps, in the 

 animal kingdom, lime also frequently combines, to form phosphate 

 of lime. By this combination, is also formed phosphorite* a stone 

 found in large masses, chiefly in Spain and in German} 7 . 



Lime has been supposed by those of high authority, to have been 

 entirely of animal origin. This, however, cannot be admitted; al- 

 though it is indubitable, that a considerable portion of it has pass- 

 ed through the animal kingdom : vast masses existing of animal re- 

 mains, resolved into this earth, which still retain sufficient of their 

 previous structure, to point out the form they had originally 

 borne. 



MAGNESIA is a very light substance, and soluble in about 2000 

 times its weight of water. The various stones, in which magnesia 

 predominates, almost always show its presence, by a smooth and 

 unctuous feel ; this is particularly, the case with the various steatites, 

 or soap-stones. They also sometimes manifest a flaky structure, as 

 is the case with common talc. Sometimes they display a striated 

 texture, with a lustre of the silky kind, as in the amianthus, and in 

 the asbestos; the stone, from which may be made incombustible 

 cloth. Serpentine, a stone which, from the disposition of its colours, 

 is supposed somewhat to resemble the skin of a serpent ; and which 

 has rather a soft, and somewhat of a greasy feel, with a silky lustre, 

 is composed of this earth, with a certain quantity of silica, and a 

 very small portion of iron. 



SULPHURETS OF METALS, and particularly that of iron, found at 

 various depths, and frequently entering into the composition of se- 

 condary fossils, demand a few words. These are the substances 

 more commonly known by the name of pyrites, or marcasites, and 

 are formed by the intimate union of sulphur with some of the rne- 

 tals. They, in general, shine with a brilliant metallic lustre : and 

 when they do not, they frequently suffer decomposition, on exposure 

 to the action of the air. 



