(If you have difficulty reading the information from the photograph of the sign I have retyped it below.)

Information next to the pie chart:  

About four million years ago faulting caused the Hallett Cove area to sink beneath the sea. This warm shallow sea lapped against the foot of the Mount Lofty Rangers.

Typing next to the sign's photograph:  

These white blocks which have fallen from the thin overhanging ledge are remnants of a sea floor. Look carefully at the rocks and you will see the fossilised shells and imprints of the marine creatures which flourished in the warm, shallow sea four million years ago.

The sea brought with it sand, coral, coiled marine snails, oysters and scallops. As these creatures died their shells fell to the sea floor where they were mixed with sand, and later cemented to form this hard layer of sandstone.

Underlying the sandstone are soft glacial sands and silts deposited in a lake during an ice age about 280 millions years ago. The surface between the soft sediments and the white sandstone represents a break in time of about 276 million years.  This is the second major unconformity at Hallett Cove.

The features described were not visible from the path, as may be seen by the following photograph.

As we were about to leave the area we found a large rock nearer the path that clearly showed a variety of marine fossils.