Maria has some very interesting geology. Here are some of the cliffs of the NE shore:

The hills are largely granite, but in the cliffs you can see banded sandstones and just to my left is, very surprisingly, a limestone quarry with an amazing fossil bed:

There are bands of limestone here that are almost entirely fossils, as you can see. But there are also some anomalous stones:

These are quite fascinating. The interpretation is that they are ‘dropstones’. This limestone was laid down in a cold shallow sea when Australia was much further south (it is currently moving north at about 10cm per year). These stones arose from the action of ice on much older adjacent rocks, and were carried out to sea on seasonal ice floes. In summer the ice melted and the stones it was carrying dropped onto the shellfish beds on the sea floor beneath, with the whole lot subsequently becoming fossilised. At other times sandstone and mudstone was laid down as sea levels changed. The whole cycle was repeated many times over a very long period giving rise to the bands visible in the cliffs today.

But there is more to these beds than this. Firstly, look at some of the shells:

This particular one is Deltopecten, and as you can see it is almost indistinguishable from a modern scallop, Pecten,  despite the fact that it is well over 200 million years old!  The reason for this seems to be that they have hit upon a successful design, ideally suited for their lifestyle. The ecological niche they occupy stays remarkably stable over very long periods of time; there is no need to evolve a new body shape or style of life – so they don’t! Amazing.

But that’s not all. Some of this fossil bed lies right on the Triassic-Jurassic boundary (now dated  with extraordinary accuracy to 201 million years ago) when over a period of certainly less than 10 000 years about half of all species then alive globally went extinct – which freed up ecological niches allowing the subsequent rise of the dinosaurs. The probable cause was volcanic rather than meteoric. And this site is part of the evidence. Amazing again.