For Kids · The land and the sky · The ground under you

The ground under Marseille

Provence-Alpes-Côte d'Azur · Mediterranean Europe · shale country

Fall · October 7, 2026

Marseille, Provence-Alpes-Côte d'Azur

Try it

Dig down under Marseille

Drag the spade down, or tap Dig deeper, through the leaves, the living topsoil and the subsoil, all the way to the bedrock that is really down there.

About 0 cm down

The grass

the top of the ground

Under the grass is a whole hidden world. Drag the spade down — or press Dig deeper — to find out what is down there.

Layer 0 of 5

It takes hundreds of years to make one centimetre of topsoil. The depths are typical — every place is different — and the ruler is squashed at the bottom so the rock fits on the screen.

Say it like this

Age 2“Dig, dig, dig! Who lives down there? A wiggly worm!”
Age 4“Leaves, dark soil, lighter soil, broken rock, solid rock. Can you count the layers? Five!”
Age 6“Topsoil is made of rotted leaves and tiny bits of broken rock. Why do you think it takes hundreds of years to make?”

Go outside: Dig a small hole in the garden and count how many worms live in one shovelful — then put them all back and fill it in.

The river right now

Water near Marseille is running very high

330%

of the ten-year median for this date · 1.1 m³/s against 0.3 normally

very high

drynormal for the dateflood

Well above normal. The river is moving gravel and wood, the banks are undercut and unreliable, and this is the state in which people drown. Watch it from the bank. It is rising — about 79% more water by the end of the week.

Under your feet

Marseille sits on shale

About 56 million years old — after the dinosaurs, as mammals and grasslands spread.

All the kinds of rock, and how each one forms →

At the surface56 million years oldNeither way
Shale
transgressive deposit · Eocene
What it is
Compressed clay and silt, laid down where the water was too quiet to move anything larger. The particles are flat and settle flat, which is why shale splits into sheets.
How it wears
Into chips, then into clay. It is weak, so it forms valleys and slumping banks rather than hills, and road cuts through it keep sliding.
What it means above ground
Heavy clay soil that holds water and drains badly. Shale is impermeable, so water runs off it rather than into it, and streams on shale rise and fall fast after rain.
Below, layer 256 million years oldSweetens the soil
Limestone
conglomerate [5.0%..50.0%]; impure Carbonate [5.0%..50.0%]; limestone [50.0%..95.0%]; sandstone [5.0%..50.0%] · Eocene
What it is
Mostly calcium carbonate, most of it the shells and skeletons of animals that lived in warm shallow water where this place now sits. Break a fresh face and you can often see them.
How it wears
It dissolves rather than crumbles. Rain is faintly acid and limestone is the one common rock that reacts with it, so the ground develops fissures, sinkholes, caves and springs, and rivers can vanish underground and come out somewhere else.
What it means above ground
Thin, sweet, fast-draining soil over flat pavements of rock, with plants rooted straight into the cracks. Water that has run through it comes out hard and full of dissolved calcium, which is why limestone country grows so much fish food.
Below, layer 3201 million years oldNeither way
Sedimentary rock
Mesozoic sedimentary rocks · Jurassic
What it is
The family that covers about three quarters of the land surface, in a thin skin over everything else. Some geological maps say only this much, which still tells you it will be layered and may hold fossils.
How it wears
Along its bedding planes, layer by layer, at a rate set by whatever the layers are made of — which is why sedimentary country weathers into steps.
What it means above ground
Layered country with flat-topped hills and stepped valley sides. What grows on it depends entirely on whether the beds are limey or sandy, which is the question worth asking next.

Bedrock and soil figures are modelled from national geological surveys and global soil mapping, at a resolution of a few hundred metres — right for the shape of a district, not for a particular garden. River discharge is modelled, not gauged. For anything that matters, dig a hole and look.

The field note for Marseille, every week

One email, Sunday evening. Unsubscribe anytime.

The ground under Marseille

Provence-Alpes-Côte d'Azur · Mediterranean Europe · shale country

Try it

Dig down under Marseille

Drag the spade down, or tap Dig deeper, through the leaves, the living topsoil and the subsoil, all the way to the bedrock that is really down there.

About 0 cm down

The grass

the top of the ground

Under the grass is a whole hidden world. Drag the spade down — or press Dig deeper — to find out what is down there.

Layer 0 of 5

It takes hundreds of years to make one centimetre of topsoil. The depths are typical — every place is different — and the ruler is squashed at the bottom so the rock fits on the screen.

Say it like this

Age 2“Dig, dig, dig! Who lives down there? A wiggly worm!”
Age 4“Leaves, dark soil, lighter soil, broken rock, solid rock. Can you count the layers? Five!”
Age 6“Topsoil is made of rotted leaves and tiny bits of broken rock. Why do you think it takes hundreds of years to make?”

Go outside: Dig a small hole in the garden and count how many worms live in one shovelful — then put them all back and fill it in.

Try it

Dig down under Marseille

Drag the spade down, or tap Dig deeper, through the leaves, the living topsoil and the subsoil, all the way to the bedrock that is really down there.

About 0 cm down

The grass

the top of the ground

Under the grass is a whole hidden world. Drag the spade down — or press Dig deeper — to find out what is down there.

Layer 0 of 5

It takes hundreds of years to make one centimetre of topsoil. The depths are typical — every place is different — and the ruler is squashed at the bottom so the rock fits on the screen.

Say it like this

Age 2“Dig, dig, dig! Who lives down there? A wiggly worm!”
Age 4“Leaves, dark soil, lighter soil, broken rock, solid rock. Can you count the layers? Five!”
Age 6“Topsoil is made of rotted leaves and tiny bits of broken rock. Why do you think it takes hundreds of years to make?”

Go outside: Dig a small hole in the garden and count how many worms live in one shovelful — then put them all back and fill it in.

The river right now

Water near Marseille is running very high

330%

of the ten-year median for this date · 1.1 m³/s against 0.3 normally

very high

drynormal for the dateflood

Under your feet

Marseille sits on shale

About 56 million years old — after the dinosaurs, as mammals and grasslands spread.

All the kinds of rock, and how each one forms →

At the surface56 million years oldNeither way
Shale
transgressive deposit · Eocene
What it is
Compressed clay and silt, laid down where the water was too quiet to move anything larger. The particles are flat and settle flat, which is why shale splits into sheets.
How it wears
Into chips, then into clay. It is weak, so it forms valleys and slumping banks rather than hills, and road cuts through it keep sliding.
What it means above ground
Heavy clay soil that holds water and drains badly. Shale is impermeable, so water runs off it rather than into it, and streams on shale rise and fall fast after rain.
Below, layer 256 million years oldSweetens the soil
Limestone
conglomerate [5.0%..50.0%]; impure Carbonate [5.0%..50.0%]; limestone [50.0%..95.0%]; sandstone [5.0%..50.0%] · Eocene
What it is
Mostly calcium carbonate, most of it the shells and skeletons of animals that lived in warm shallow water where this place now sits. Break a fresh face and you can often see them.
How it wears
It dissolves rather than crumbles. Rain is faintly acid and limestone is the one common rock that reacts with it, so the ground develops fissures, sinkholes, caves and springs, and rivers can vanish underground and come out somewhere else.
What it means above ground
Thin, sweet, fast-draining soil over flat pavements of rock, with plants rooted straight into the cracks. Water that has run through it comes out hard and full of dissolved calcium, which is why limestone country grows so much fish food.
Below, layer 3201 million years oldNeither way
Sedimentary rock
Mesozoic sedimentary rocks · Jurassic
What it is
The family that covers about three quarters of the land surface, in a thin skin over everything else. Some geological maps say only this much, which still tells you it will be layered and may hold fossils.
How it wears
Along its bedding planes, layer by layer, at a rate set by whatever the layers are made of — which is why sedimentary country weathers into steps.
What it means above ground
Layered country with flat-topped hills and stepped valley sides. What grows on it depends entirely on whether the beds are limey or sandy, which is the question worth asking next.

The field note for Marseille, every week

One email, Sunday evening. Unsubscribe anytime.

The ground under Marseille

Dig down under Marseille

Water near Marseille is running very high

Marseille sits on shale

Shale

Limestone

Sedimentary rock

The field note for Marseille, every week

The ground under Marseille

Dig down under Marseille

Dig down under Marseille

Water near Marseille is running very high

Marseille sits on shale

Shale

Limestone

Sedimentary rock

The field note for Marseille, every week

Dig down under Marseille