A chunk of rock in a box at The Old Courthouse Museum, Batemans Bay, has special interest for geologist Stewart Needham.
Mr Needham said the 450 million-year-old banded grey shale from the Bilgola plateau, just north of Tomakin, originates from a deep ocean trench formed by continental collision during the Ordovician Period.
“Back then, our eastern seafront was about 2,000 kilometers further east, out into the Tasman sea,” Mr Needham said.
Mr Needham said although most sediment on the Eurobodalla coast was carbonaceous shales, grey and black, and sandstone, there were many interesting sites.
“At Bingie, the rocks demonstrate how two different magmas mix before they solidify – it is a significant teaching spot for university students,” Mr Needham said.
He noted good examples of melange rock formations at Observation Point and Bronte Headland.
“These sites show where the layering of rock is buggered up,” Mr Needham said.
“We call that melange – one rock type mixed with another.
“Sometimes there are potato-like lumps of more resistant rock.
“There are plenty of melanges around the world but it is not a common rock type. The story these rocks represent are a large piece of the global geological jigsaw puzzle,” he said.
Mr Needham’s chunk of shale will be soon displayed in the museum’s developing geological room.
Curator Myf Thompson said a collection of local rocks with local, regional and national significance would be displayed.
“Our rocks will have a series of information posters,” Ms Thompson said.
“Each poster will have a cue code, which people can use to access website information at high-school and university level.
“People can chose their own level of engagement.”
“There is a lot of interest locally in the geology of the region,” she said.
To help satisfy that interest, Mr Needham runs an introductory geology course for U3A Batemans Bay. U3A runs activities for those aged over 50 years. The 2016 geology course was oversubscribe and will run again in the first term of 2017.
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