80 
GLOSSARY 
materials having been thrown clown from a state of suspension 
or solution in water. 
Selenite. Crystallized gypsum, or sulphate of lime — a simple 
mineral. 
Septaria. Flattened balls of stone, generally a kind of iron-stone, 
which, on being split, are seen to be separated in their interior 
into irregular masses. Etym., septa, inclosures. 
Serpentine. A rock usually containing muchmagnesian earth, for 
the most part unstratified, but sometimes appearing to be an 
altered or metamorphic stratified rock. Its name is derived 
from frequently presenting contrasts of colour, like the skin of 
some serpents. 
Shale. A provincial term, adopted in geological science, to express 
an indurated slaty clay. Etym., German schalen, to peal, to 
split. 
Shell Marl. A deposit of clay, peat, and other substances mixed 
with shells, which collects at the bottom of lakes. 
Shingle. The loose and completely water-worn gravel on the sea- 
shore. 
Silex. The name of one of the pure earths, being the Latin word 
for flint, which is wholly composed of that earth. French geo- 
logists have applied it as a generic name for all minerals com- 
posed entirely of that earth, of which there are many of different 
external forms. 
Silica. One of the pure earths. Etym,, silex, flint, because found 
in that mineral. 
Silicate. A chemical compound of silica and another substance, 
such as silicate of iron. Consult elementary works on che- 
mistry. 
Siliceous. Of or belonging to the earth of flint. Etym., silex, which 
see. A siliceous rock is one mainly composed of silex. 
Silicified. Any substance that is petrified or mineralized by sili- 
ceous earth. 
Silt. The more comminuted sand, clay, and earth, which is trans- 
ported by running water. It is often accumulated by currents 
in banks. Thus we speak of the mouth of a river being silted 
up when its entrance into the sea is impeded by such accumula- 
tion of loose materials. 
Simple Mineral. Individual mineral substances, as distinguished 
from rocks, which last are usually an aggregation of simple mine- 
rals. They are not simple in regard to their nature, for when 
subjected to chemical analysis, they are found to consist of a 
variety of different substances. Pyrites is a simple mineral in 
