About 10 years ago I excavated a 5'x5' square hole in my back yard 6.5' deep.
To place a concrete anchor block that supports a free standing antenna tower.
My soil below the topsoil layer is clay infused sand.
First few feet down were riven with constuction debris from when the houses in the area were built
And the soil excavated for basements was spread out.
Broken bricks, steel bands that once held brick bundles together etc.
Then about 5' down I came across a layer of limestones, edges smoothed from eons of lapping of water.
A shingle beach is what we call this sort of arrangement.
On the top of the stones a black carbon layer was present.
I am in south Sauga, about 6km north of present day Lake Ontario.
At some time on the distant past this lake was a lot bigger.
And this spot was once a lake edge when a forest fire burned through to leave this carbon deposit layer.