GLOSSARY. 
Seams. " Thin layers which separate strata of greater mag- 
nitude." 
Secondary Strata. "An extensive series of the stratified 
rocks, which compose the crust of the globe, with certain char- 
acters in common, which distinguish them from another series 
below them, called primary, and another above them, called 
tertiary." 
Sedimentary Rocks are those which have been formed by 
their materials having been thrown down from a state of sus- 
pension or solution in water. 
Selenite. Crystallized gypsum. 
Septaria. Flattened balls of stone, which have been more or 
less cracked in different directions, and cemented together by 
mineral matter which fills the fissures. 
Serpentine. A rock composed principally of hydrated silicate 
of magnesia. It is generally an unstratified rock. 
Shale. An indurated slaty clay, which is very fissile. 
Shell Marl — Fresh-water Shell Marl. A deposite of fresh-water 
shells, which have disintegrated into a gray or white pulveru- 
lent mass. ^ 
Shingle. The loose, water-worn gravel and pebbles on shores 
and coasts. 
Silex. The name of one of the pure earths which is the base 
of flint, quartz, and most sands and sandstones. 
Silt. " The more comminuted sand, clay, and earth which 
is transported by running water." 
Simple Minerals are composed of a single mineral substance. 
Rocks are generally aggregates of several simple minerals ce- 
mented together. 
Slate. A rock dividing into thin layers. 
Stalactite. Concreted carbonate of lime, hanging from the 
roofs of caves, and like icicles in form. 
Stalagmites. Crusts and irregular- shaped masses of concreted 
carbonate of lime, formed on the floors of caves by deposites 
fi'om the dripping of water. 
Stratification. An arrangement of rocks in strata. 
Strata. Layers of rock parallel to each other. 
Stratum. A layer of rocks ; one of the strata. 
Strike. The direction in which the edges of strata crop out. 
It is synonymous with line of bearing. 
Syenite and Sienite. A granite rock, in which hornblende re- 
places the mica, or forms an ingredient. 
Synclinal line and Synclinal axis. When the strata dip down- 
ward in opposite directions, hke the sides of a gutter. 
T. 
Talvs. In geology, a sloping heap of broken rocks and stones 
at the foot of many cliffs. 
