It's somewhere between Einstein's Dreams and Lem's The Cyberiad - there are stories told using the early times of the Universe, of the world, of dinosaurs, molloscs and the "time" before the Big Bang. The storyteller is not a God, but clearly a more than human entity that remembers being different beings, but it's unclear how much he remembers from one story to the next, or if the stories all happen in the same world.

Despite being about the early days of the world, there are cheerfully anachronistic touches. One character, on seeing that his child does not recognize that he is a dinosaur, ends by walking far away and finally catching a train. Another story has him losing his sister when the Earth solidifies, only to find her later in 1912 married to a rail station manager.

There is no conclusion or deeper story involved, but it's almost more alien in the familiar concepts -- for example, what does it mean to be an "immigrant" before there is any such thing as time and space? Calvino doesn't shy away from the inherent absurdity in the stories he's telling, which ironically makes them stronger.