There’s no shortage of sandstone in the Sydney area, almost the entire extent of Garigal National Park sits on what’s known as the Hawkesbury Sandstone. The Sydney 1:100 000 Geological Sheet classifies it as “Medium to course-grained quartz sandstone, very minor shale and laminite lenses” I wanted to highlight two sandstone formations, both of which are a bit of a mystery as to how they form. I came across these formations on a trail run on a section of single track in Belrose that runs from the end of Ralston Ave down to the Bare Creek trail next to Bare Creek. The first formation is called tessellated pavement.

This is a collection of unusual structures on the underside of a small sandstone overhang. It’s made of different material than the surrounding sandstone, it’s a hard to the touch with no visible sand grains. Most of the surface is made of tiny nodules that almost look like condensation on a cold surface. In the center is a more prominent raised area that looks like a cast of an animal burrow.