[Silica]—an oxide of silicon (SiO₂).
[Siliceous]—containing or pertaining to [silica].
[Silt]—fine muddy [sediment] consisting of particles intermediate in size between clay particles and sand grains.
[Siltstone]—a very fine-grained [sedimentary rock] composed of [silt] grains, and intermediate between [shale] and [sandstone].
[Stratified rocks]—[sedimentary rocks]; those formed in beds, layers, or [strata].
[Stratum]—an individual layer of [rock formation]. (Plural, [strata].)
[Superposition], law of—in an undisturbed sequence of [rocks] younger beds overlie older beds.
[Syncline]—a trough-like fold in the [rocks], with the beds dipping inward on either side. See [Anticline].
[Talus]—a mass of [rock] debris commonly on slopes or at the base of a steep mountain or cliff.
[Topography]—the configuration of a land surface.