Sandstone and ash

A holiday today for the long weekend but it is damp and blustery, so an inside blip today. This is a rock from my collection, a sandstone from southern Greenland. It's Pre-Cambrian (about 3000 million years old) and you can clearly see the different layers of bedding as the sand grains were deposited. The darker red colouring indicates more oxidised layers of iron-rich sand that was perhaps longer exposed to the atmosphere. What I really like about this rock is the thin dark crust at the top - which is a layer of welded volcanic ash that has fallen on the cold surface of the Earth (the sandstone) and cooled to solid rock. If you look carefully you will see a thin dark-and-orange line separating the sandstone from the ash - this is where the sandstone was partially melted as it was buried by the very hot ash.