The beach has other natural history interest for example fossils of organisms that once grew on reefs such as corals, bivalve shells, and crinoid ossicles. These can be found in the limestone revetments placed on the toe of the promenade. Fossils can also be found in the small beach boulders particularly at Old Colwyn where fossilised corals can sometimes be seen.
Amongst the boulders that strew parts of the Old Colwyn beach Scottish and Lake District granites can be distinguished from the more locally derived limestone and mudstone boulders. On occasion it is possible to find the distinctive black and white granite derived from the island of Ailsa Craig where they are quarried today to make the famous curling stones.
Glacially transported rocks such as these described here are known as erratics having been transported by south flowing glaciers during the last ice age.