46 
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 passed 
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 or 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 p^jrites, or marcasites, and 
are formed by the intimate union of sulphur with some of the metals. 
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. 
The other chemical substances, which I shall have occasion to 
speak of, as performing a considerable part in some of those extra- 
ordinary transmutations which will come under our observation, I 
shall strive to treat of, in the places where they occur, with that 
