Rock, one grain at a time.
STRATUM is a sedimentary basin caught mid-formation. Sand, silt and clay settle into graded beds, storms cut erosional surfaces, and every so often a fault throws the whole section. The layers never stop arriving.
Three things happen to sediment. You can watch each one.
A stratigraphic column is a book read bottom to top — oldest at the base, this morning at the surface. Sediment arrives, gets cut away, and is sometimes shoved out of line. The log on the right names each bed as it is written.
Beds accrete
Grains rain out of still water and pile into layers — coarse sand where the current is strong, fine mud where it slows. A graded bed fines upward; the contact between two is a moment of quiet.
Storms scour
A flood or a storm strips the top clean, gouging an uneven surface into beds it took millennia to lay. What's missing is called an unconformity — time you can measure by its absence.
A fault throws it
Stress builds until the crust snaps and slides. The beds on one side drop against the other, offsetting every layer at once — the whole history bent by a single afternoon of movement.
Left to itself, this basin lays down less than a millimetre a century — slower than a fingernail grows, for longer than there have been trees. To keep the outcrop in frame it also subsides: the floor sinks as fast as it fills, so the surface stays put while a kilometre of rock quietly stacks beneath it. What you're watching is compressed a hundred million times. Come back later; it will have written a different page.