An ancient volcano is exposed on the foreshore immediately south of Blinking Billy Point, Sandy Bay. It formed during the period 60-40 Mya (early Tertiary), when Tasmania began to be ripped apart from Antarctica. The site was visited by Charles Darwin in 1836 and he noted two distinct eruption phases evident in the rocks.
The younger volcanic eruption sequence is composed of two rock types: a thick sequence of black lava (basalt) exposed at the southern end of Long Beach, and a thick sequence of pale volcanic tuff, exposed further south on Little Sandy Bay beach).
An older volcanic sequence is exposed at the southern end of Little Beach (shown within the orange circle in the map below).
The geology of the site is detailed in -Alan Spry's study of "Tertiary Volcanic Rocks of Lower Sandy Bay.
Darwin also travelled a couple of miles south from here, to the rocky shore platform at the bottom of Porter Hill (see separate text-Fossil Platform).
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