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WARNING

I am speaking with a completely amateur voice, and everything I say may be totally wrong!

 

I visited Shelly Beach some time ago with my friend who sings with magpies. At the weekend J and I returned, this time in search of Cambrian-Ordovician rocks, laid down in deep water under the ocean somewhere between 460 and 500 million years ago. Our guide was an information sheet produced by four geologists, who are taking a group (including us) to five local sites in November. As a mature age learner I can't bear to arrive in a state of total ignorance, and this reconnoitre was to puzzle over the site and become a bit familiar with it, not least how to get there.

Yet again J leaves me trailing. He's spent a chilly week reading Winchester's The map that changed the world and envying the clarity of English geology; and perusing Mary White's Reading the rocks to get a handle on the big picture of Australian geology, which is apparently much messier and much less clearly laid out.

What we were seeing at Shelly Beach was our first taste of sedimentary rock, originally created from deposits of fine sand and silt. The typical layering of sedimentary rock was visible (I think): but this layering has been interfered with by the weight of overlaying sediment and by the heat and pressure generated by the action of plate tectonics, which has also uplifted and deformed the sedimentary beds. We could actually see some of the resulting folds quite clearly, although my capacity to think in 3D is limited. By the end of the morning we were discussing buying plasticine so J could demonstrate his explanations by slicing layers with a very sharp knife.

 

Folding: two lines of rock angling away from each other, most noticeable in the last photo of this series

 

Clear lines of sedimentation?

 

By the time we left this very beautiful array of rocks (I'm preparing a post that concentrates on aesthetics!) I had a few understandings and a number of questions.

 

Exploring the mysteries of rocks

Are these lines of sediment pressured or heated out of shape?

Why the inverted ledge?

Why are these rocks flaking? What is the story behind the honeycombing?

 

And finally we came across something I could understand without cogitation, and smile at rather than frown over.