The Barnard Islands and coastal ranges from Double Point to about Bramston Beach make up the Barnard Metamorphics. The coastal ranges in the Barnard Metamorphics include the Moresby Range between Mourilyan Harbour and Flying Fish Point, and Seymour range from Flying Fish Point to Bramston Beach. They were formed in the Neoproterozoic – Cambrian age and are tightly folded along an axis with a north-west or north-north-west regional trend.
These coastal ranges represent narrow uplifted horsts between the down-faulted blocks of the Mulgrave River Corridor (the coastal plain) and the continental shelf. They separate the coastal plain from the ocean.
The Barnard metamorphics comprise mainly muscovite-chlorite and biotite-muscovite schist, quartzite, meta-arenite, phyllite, ‘greenstone’, minor biotite gneiss, (garnet) amphibolite, talc-rich rock and ultramafic rocks.
At the listed coordinates near the southern end of Etty Bay beach, you will see a section of now-vertical schist rock. It most likely moved from horizontal to vertical during the uplift of the horst and subsequent folding that formed these coastal ranges. This vertical schist runs from south east to north west and if you cast your eye northwards you will see it is in line with an outcrop of rocks on the beach. This outcrop is part of the same section of schist.
To claim a find on this earthcache you must first answer the following questions and email your answers to me:
- The width of the vertical section of schist at this point spans from the water’s edge to rocks at the edge of the rainforest. Estimate the distance of this span (in metres).
- There is a change in the rock surface across this section of schist. Describe this change.
- How far (in metres) from the sea side edge of the section does the change occur?
- According to the information above, what type of geological feature does the Moresby Range represent?
Source: F de Keyser (1963/79) Explanatory notes on the Innisfail 1:250,000 Geological Sheet S.E. 55-6 [Dept National Development, Bureau of Mineral Resources, Geology and Geophysics, Canberra].