91av

I took these photos at Shelly Beach in Queensland. Can any reader explain how these almost symmetrical shapes were formed? (Continued)

• I believe the previous answer identifying the structures as mud mounds is incorrect. From the photos, the features appear to be developed in rock. Furthermore, shows Shelly Beach has areas of rock and sandy beaches, but no areas of mud.

The rock is likely homogeneous sandstone, and the features can be grouped within the term , which covers a range of “solution pits”, mounds, and various other types and patterns of seashore weathering of rock. They frequently occur in clusters that can transform a rock formation. They can be found in a variety of climates, but particularly in areas covered at high tide and exposed at low tide.

Alan Tait, Ivanhoe, Victoria, Australia