Geology hub
Sedimentary
Layers, grains, fossils, and environments—how surface processes become rock and how to read the record.
Subtopics
Sandstone
Grain size, sorting, and cement tell you about rivers, deserts, and shorelines.
Limestone & carbonates
How shells, reefs, and chemical precipitation build carbonate rocks—and why acid reaction matters.
Fossils in context
What fossils can (and can’t) tell you about age, environment, and correlation.
Bedding & structures
Cross-beds, ripples, mud cracks, and graded beds—small structures with big environmental meaning.