44 
forms the common jimt, and horn-stone ; the more pure chalcedony / 
and the still purer quartz, or rock crystal ; the variously-figured 
agate ; the arborised mochoa ; the beautifully-marbled jasper ; the 
sportive Egyptian pehhle ; and the finely-veined wood-stone, still 
retaining the mark of every fibre, which regulated its pristine struc- 
ture. Combined with a certain portion of alumine, it forms the 
chief constituent of the amethyst, topaz, and various other stones, 
which, from their brilliancy, hardness, and colour, are estimated as 
gems. This earth, also, chiefly helps to constitute the granite, of 
which the primitive mountains are formed. This stone frequently 
displays, in a most beautiful and distinct manner, the three sub- 
stances of which it is composed. The feldspar, the constituents of 
which are silica, alumine, and magnesia, will be seen, generally, in 
oblong, curd-like masses, of various sizes. The mica, composed of 
the same constituents, but in different proportions, will appear gene- 
rally in grains about the size of a pin’s head, of different colours, but, 
most commonly, black j and sometimes in white flakes of a metallic 
lustre. The quartz will be found interposed between these generally 
of a greyish colour ; and appearing to be the medium by which the 
other two substances are agglutinated together. 
Lime is the earth which, united with carbonic acid, chiefly 
forms the various lime-stones, which are placed, in different layers, 
beneath the beds of clay and sand. This earth is rendered to- 
lerably pure, when, by intense heat, it is made into quick- lime. It 
fuses, when combined with flint and clay ; and readily combines 
with acids. It is soluble in 700 times its weight of water, forming 
the liquid called lime-water. From its caustic qualities, and its 
solubility in water, it is now generally considered as an alkaline 
substance. 
From the combination of lime with carbonic acid ; the acid which 
is formed by the union of carbon, the chief matter of charcoal and 
