Looking like giant alien eggs, the Moeraki Boulders scatter across the Otago coast of New Zealand. They can be up to 10 ft (3 meters) across, are generally hollow & roughly spherical, with calcite exteriors broken by 'septaria' or cracks. What strange bird lays such eggs? (📷: Karsten Sperling)

roc

I saw one being born.

Obviously, a roc.

Eggs of the Bigassaurus, of course!!

They're made of mud, silt bound with calcite, likely formed in the Paleocene, 50-60 MYA. The actual structures represent 5 million years of accretion, likely where the sea receded & fresh groundwater rich in calcium bubbled into the seabed substrata. (📷: William M. Connolley)

Giant ammonite fossils!

Wow... We went to see them on our wedding day in feb 1996.

My camera died when I was there in 2009 (with geologists, who btw were inconclusive on how these concretions form). Fortunately, it revived for penguins nearby:

I got a few words into this, read what I thought was "the Moeraki Brothers," and was very confused for seven or eight seconds.

What do they look like inside? 🤔