Secondary Strata. An extensive series of the stratified rocks which compose the crust of the globe, with certain characters in common, which distinguish them from another series below them called primary, and from a third series above them called tertiary.
Secular Refrigeration. The periodical cooling and consolidation of the globe from a supposed original state of fluidity from heat. Sæculum, age or period.
Sedimentary Rocks are those which have been formed by their materials having been thrown down 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 much magnesian 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 color, like the skin of some serpents.
Shale. A provincial term, adopted by geologists, to express an indurated slaty clay. Etym., German schalen, to peel, 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 geologists have applied it as a generic name for all minerals composed entirely of that earth, of which there are many of different external forms.