Two to 12 million years ago, the Hornsby plateau was
uplifted to between 150 and 250 metres above sea leve. As
rivers flowed across this plateau, they gradually cut deep
V-shaped valleys into it, leaving narrow sandstone ridges
behind. Then, during the past million years, rising sea
levels flooded the lower valleys. The sea cut off some of
the plateau peaks, forming islands like Scotland Island.
Source:
Ku-ring-gai Chase NP,
NSW National Parks & Wildlife Service
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