Someone posted a picture of the ladybird invasion of '76 here:- Harrison Drive Ladybird Swarm
This is looking back east towards Harrison Drive and the junction with the King's Parade wall. Were the dark bumpy rocks you mention the old anti-invasion defences from WWII?
Maybe you walked as far as Leasowe Bay, which was unprotected by concrete and the sand dunes (the yellow sandstone you mention?) were eroding away.
Forget civilisation, I'd have kept walking the other way