On the home front (II)

The floor of our house was once the floor of a sea. The shells of creatures that lived and died in the sea are still there:

This is cool, yes. But the floor of a sea is a soft silty place, which doesn't change much even millions of years later after it's turned into stone. So if a child were running around on the stone and happened to knock over something heavy, something like this for example:

... then you'd get five powdery holes in your new floor. Something like this in fact: