I didn't quite get it at Denham Anglican Church when they said the church was made out of shells. I looked at the large brick blocks that the church was constructed form and yes there were little shells in it. I thought that they must have somehow been compressed from shells.
But no. Shells had been compacted together over a long period of time. The church blocks were quarried from this material. We saw the quarry on the way to the Stromatalite area.
This beach and one near it called Shell Beach - had no sand. The whole beach was Shells. Amazing.